Wearable textile-based phototherapy platform with customized NIR OLEDs toward non-invasive hair loss treatment

Domain: chemistry
Published: 2026-01-10
Editorial outcome: major_revision

Abstract
Hair loss presents a widespread clinical and psychological challenge, yet conventional pharmacological treatments often incur systemic side effects such as hormonal imbalance and mood disturbances. To provide a non-pharmacological alternative, a wearable textile-integrated near-infrared (NIR) organic light-emitting diode (OLED) platform was developed with emission closely aligned with the action spectrum of human dermal papilla cells (hDPCs). By employing a top-emitting microcavity structure, we tuned the emission peak of the NIR OLEDs (around 730–740 nm) to align with the hDPC activation spectrum, thereby enhancing photon delivery to the follicle niche and enabling irradiation at wavelengths that promote hDPC photoactivation. This non‑invasive, skin‑conformable textile‑based device exhibits mechanical resilience to repeated bending at a radius of 2 mm, low heat generation to prevent skin burns, and waterproof performance under water immersion. In vitro, NIR irradiation from the customized microcavity‑tuned OLED device significantly reduced senescence-associated β-galactosidase activity by 91.6% and increased hDPC migration, with greater effects than those observed for red light and broad full‑width at half-maximum (FWHM) NIR irradiation groups. These findings suggest that microcavity-tuned textile-based NIR OLEDs can serve as scalable, biocompatible platforms for non-invasive wearable phototherapy aimed at hair-follicle modulation and future hair-loss management.

Introduction
Hair loss, or alopecia, represents a widespread disease with significant psychological and social implications, affecting millions of people worldwide. Moreover, people suffered from hair loss is expected to rise due to aging and lifestyle-induced stress1. Conventional hair loss treatments primarily include pharmaceutical interventions, such as minoxidil and finasteride, and procedural approaches like hair transplants2,3. While these treatments have demonstrated adequate efficacy in hair growth, they are often accompanied by many drawbacks. Specifically, pharmaceutical treatments require prolonged use of medications and can cause side effects like irritation and hormonal imbalances, while hair transplants are invasive and costly4–6. In light of these potential risks, photobiomodulation (PBM) has emerged as a promising non-pharmacological and non-invasive alternative for hair regrowth, by stimulating cellular activity without experiencing side effects associated with pharmaceutical treatments7,8.

PBM offers considerable therapeutic potential across a range of biomedical applications, including hair-loss treatment. However, conventional PBM devices primarily utilize LED or laser-based platforms, each of which presents critical limitations for wearable use. LED-based systems often exhibit non-uniform light dispersion, leading to inconsistent dosimetry across the target area. Laser-based systems, while offering improved directionality, are typically rigid and bulky, which significantly restricts mobility and user comfort.

A notable class of commercial PBM systems for hair-loss treatment adopts helmet- or hairband-type configurations incorporating arrays of LEDs and lasers9–11. This device is characterized by a mechanically robust helmet-typedesign that can be securely fixed to the head. However, the platforms are restricted to use in indoor home environments rather than during daily outdoor activities, and the reliance on numerous point‑like LED and laser emitters, each illuminating only a small area, necessitates large emitter counts to cover the scalp, which can increase the overall device weight.

To address these limitations, wearable PBM platforms are required that deliver spatially uniform light stimulation without compromising user mobility. Recent studies have explored alternative light‑source–based wearables, including micro‑LED patches and OLED‑based cage devices. Micro‑LED patches offer a more flexible form factor than rigid helmet or home‑use phototherapy systems and can improve conformity to skin. However, limitations arise from the patch properties and the micro‑scale emitting area of individual sources. Because attachment typically relies on skin adhesives, patches can inadvertently induce hair traction during application and removal, which is a non‑trivial concern for patients with weakened hair follicle anchorage12. In addition, the pixelated point‑source nature of micro‑LEDs complicates scaling to large treatment areas and tends to produce non‑uniform irradiance with local hotspots, thereby limiting dose homogeneity across the scalp. Motivated by these constraints, OLED‑based phototherapy device has been suggested. Unlike conventional light sources for phototherapy device, such as LEDs and lasers, OLEDs offer a combination of ultra-thin, flexible form factors and uniform light emission. An OLED-based platform provides large, homogeneous emission and have been reported to induce PBM relevant to hair‑loss treatment13. However, barriers to day‑to‑day wearability persist. The platform has been designed for helmet-type configurations, and as a result, core OLED attributes such as thin profiles and mechanical flexibility remain underutilized.

Furthermore, the light irradiation should be capable of stimulating cellular activation. The PBM effect depends on the target cell type and wavelength band. Recent studies indicate that human dermal papilla cells (hDPCs), which play a crucial role in hair regeneration14, exhibit enhanced proliferation after exposure to near-infrared (NIR) irradiation compared with red light at the same dose, providing the importance of selecting an optimal wavelength for effective treatment15,16.

NIR light (700–900 nm) exhibits superior tissue penetration because strong absorption by melanin and water is avoided and scattering is reduced, enabling a range of biomedical applications7,17,18. These optical characteristics make NIR light particularly suitable for non-invasive phototherapy, allowing efficient delivery of therapeutic light to subdermal target19.

An NIR OLED, in which the PBM advantages of NIR light are coupled with the flexibility of OLEDs, is a promising light source for wearable phototherapy systems. Despite these promising characteristics, the practical implementation of wearable NIR OLEDs remains relatively unexplored. While some studies have demonstrated the fabrication of NIR OLEDs on flexible plastic substrates for wrist-worn sensor applications, the broader utilization of this technology beyond sensing remains uncommon20,21. One of the major limitations is the mechanical fragility of traditional NIR OLEDs, which have generally based on indium tin oxide (ITO) electrodes. Due to the brittle nature of ITO, these devices lack the mechanical resilience required for repeated bending and deformation, which is essential for true wearable applications.

Most NIR OLEDs reported to date adopt a bottom‑emitting structure, in which light exits through the substrate. An optical characteristic of the NIR OLEDs are highly dependent on substrate transmittance, which inherently restricts the range of applicable substrate materials15,22. These factors have hindered the adoption of NIR OLEDs in wearable biomedical applications, emphasizing the need for alternative device structures to enhance versatility in such applications.

In this study, we report a wearable textile-based NIR OLEDs that employ a microcavity structure to optimize light characteristics for enhanced human dermal papilla cell (hDPCs) activation for hair-loss treatment. The device consisted of around 240 µm-thick polyester-based textile platform and a top-emitting NIR OLED combined with a flexible encapsulation layer to protect the OLED from oxygen and water, with a total thickness of less than 1 µm. The textile substrate provides a user-friendly, flexible platform suitable for integration into wearable items such as hats or clothing23–25.

To achieve wavelength-optimized operation of NIR OLEDs intended for hDPC-targeted phototherapy, a microcavity structure was implemented. This architecture enables spectral tuning without changing the emitter material, because PBM responses are dependent on wavelength. In this configuration, the conventional ITO electrode was replaced with a thin silver layer, forming a top-emitting microcavity device with improved optical characteristics and mechanical flexibility, which in turn enables controlled spectral tuning and use as a wearable device. By adjusting the organic thickness of the OLED, the emission peak can be precisely tuned in 10 nm increments within the NIR spectral range (700–800 nm) with sufficient light intensity for phototherapy, enabling the NIR OLED characteristics to be tailored specifically to match the actions spectrum peak for optimal activation of hDPCs7.

The NIR OLED was integrated into a textile platform and demonstrated its feasibility as a skin-contact wearable device. The flexibility of the textile-based top-emitting OLEDs were validated through repeated bending tests, confirming stable radiance output and mechanical robustness without delamination even after 10,000 bending cycles at a bending radius of 2 mm, corresponding to 2.1% tensile strain. The device exhibited water resistance, retaining over 90% of its initial performance after 50 h of water immersion. Additionally, continuous operation of the devices for 20 min resulted in a surface temperature below 30 °C on the emitting side (the skin-contact area), demonstrating the device’s thermal safety against skin burns.

To validate the biological responses of the NIR OLED system, in vitro studies were conducted using hDPCs, focusing on cellular migration and senescence. As a result, improved migration activity was observed in hDPCs exposed to NIR OLED irradiation compared with non-irradiated controls. Furthermore, greater suppression of senescence-associated β-galactosidase activity and senescence markers was observed under irradiation with the NIR device than under red OLED and conventional NIR OLED conditions with a full-width at half-maximum (FWHM) greater than 100 nm. A 91.6% reduction in senescence-associated markers was demonstrated following exposure to the microcavity NIR OLED relative to the non-irradiated control group.

Results
Wearable NIR OLEDs for phototherapy
A device is designed for targeted photic activation of hDPCs using NIR illumination (Fig. 1a). The wearable textile-based NIR OLED is used as a non-invasive photobiomodulation (PBM) device for hair-loss treatment. Near-infrared emission from the textile device is transmitted through the skin to the dermal papilla, where human dermal papilla cells are activated.

The fabrication process of textile-based device entails the sequential deposition of functional layers onto an uncoated, pristine polyester textile substrate. Textile consists of bundles of fibrous filaments, ensuring flexibility and mechanical strength (Supplementary Fig. 1). In addition, the polyester-based textile, commonly used in clothing, offers excellent flexibility, making it highly suitable as a wearable platform (Supplementary Fig. 2a).

However, the regular textile weave introduces substantial surface roughness, which can compromise the performance of OLEDs fabricated by thermal deposition. Given the intrinsic roughness associated with a ~170 µm weave, planarization was applied to enable NIR OLED fabrication and to ensure stable driving. To achieve a uniform surface, a 3 µm parylene-C layer was deposited via chemical vapor deposition (CVD) and mechanically bonded to the textile substrate using a 19 µm adhesive layer26. This process significantly reduced surface roughness, ensuring uniform deposition of materials in giving stable NIR OLED operation (Fig. 1b).

To shield the OLED devices from moisture and oxygen, a bottom thin-film encapsulation (TFE) layer composed of Al2O3/TiO2 nanolaminates (30 nm) was deposited via atomic layer deposition (ALD) at 40 °C. This method preserved the mechanical integrity of the polyester textile27. Subsequently, both OLED electrodes and organic layers were fabricated using physical vapor deposition (PVD) to establish a top-emitting structure, where light can be propagated in the direction opposite to the textile-based platform.

The polyester exhibited a poor transmittance of only 21% in the visible-to-NIR range (Supplementary Fig. 2b). Given that sufficient light intensity is essential for effective phototherapy, a top-emitting NIR OLED structure was specifically designed to ensure photon delivery independent of the inherent limitations of polyester. The detailed designs and optical considerations for this approach are discussed in the following section.

To provide additional protection, an identical nanolaminate TFE layer (30 nm) was deposited via ALD on the top of OLED structure. Finally, a 500 nm parylene-C layer was applied via CVD as an outermost encapsulation layer to prevent direct skin contact, ensuring enhanced durability and user safety (Fig. 1c).

The top-emitting OLED architecture introduces a significant refractive index contrast at the device-to-air interface, resulting in considerable optical confinement due to total internal reflection. This hybrid encapsulation, consisting of the upper TFE and outermost parylene-C layer, not only provides needed mechanical protection but also enhances light extraction efficiency (Fig. 3). Details on the light-extraction enhancement by the hybrid capping are provided in a subsequent section.

The final device architecture was confirmed using scanning electron microscopy (SEM) and cryo-focused ion beam (cryo-FIB) cross-sectional imaging. Milling at room temperature poses a risk of damaging the polyester-based textile substrate due to its low thermal tolerance, potentially leading to mechanical distortion. Hence, cryo-FIB-SEM was employed to minimize thermal effects while enabling precise structural analysis. This method facilitated high-resolution imaging, clearly resolving the textile substrate, adhesive and planarization layers, and parylene-C encapsulation of all OLED components without compromising structural integrity (Fig. 1d).

To evaluate the practical applicability of the textile-based NIR OLEDs in wearable phototherapy systems, a prototype NIR OLED-based wearable device was implemented and its integration into various commercially available hat forms was demonstrated. The textile OLEDs were embedded onto representative hat platforms, including bucket hats and baseball caps, to show flexibility and operational reliability under realistic usage conditions.

Operation of the OLED array on a commercial hat/cap platform, while maintaining the flexibility required for a wearable device, was demonstrated by mounting the array on the textile and interfacing it with a flexible printed circuit board (FPCB) that provided array driving and section‑wise switching for scalp‑specific operation. The array comprised NIR OLEDs with emission areas of 69 mm² and 1000 mm², each wired to an independent FPCB channel to enable individual on/off control of each scalp section. An image of the textile‑based NIR OLED device integrated into a commercial bucket hat during operation shows stable performance and uniform emission across the fabric surface (Fig. 1e). The integrated devices exhibited stable on/off switching and maintained consistent electroluminescence under repeated bending (Supplementary Movie 1). Furthermore, a photographic comparison of a mannequin head fitted with the textile NIR OLED device in the off and on states illustrates the contrast in NIR emission (Fig. 1f). In both hat types, the textile OLEDs remained operational under realistic wearing conditions (Supplementary Movies 2, 3).

Furthermore, a wireless phototherapy device composed entirely of flexible components was fabricated to validate portable operation. The system comprised a FPCB for switch-based on/off control and battery-driven OLED operation, the NIR OLED, and a flexible battery (Supplementary Fig. 3a, b). The individual component thicknesses were ~90 µm (FPCB), ~230 µm (textile), and ~450 µm (battery), and the maximum local stack thickness within the hat form factor was ~2.0 mm (Supplementary Fig. 3c–f). Switch-controlled on/off operation of the textile-based OLED stripe integrating fully flexible components was demonstrated without the use of a benchtop power supply (Supplementary Movie 4). For a cap-type platform integrating multiple OLED stripes, continuous emission was maintained during donning and doffing (Supplementary Movie 5).

Clinically validated light-therapy systems for hair loss, such as a helmet- and headband-type devices, have demonstrated therapeutic effects but rely on rigid platforms that are primarily suited for indoor use. In this study, the textile-based NIR OLED was implemented in a hat-type platform to propose a phototherapy device design that can be used in both indoor and outdoor settings. Compared with conventional rigid systems, this textile-integrated design offers mechanical flexibility and conformal contact with the scalp and employs an OLED-based NIR area source rather than point-like emitters such as red LEDs or lasers, enabling more uniform illumination over the treatment region (Table 1).

Characterization of Top-emitting NIR OLED
The microcavity-based top-emitting NIR OLEDs are designed to harness optical interference effects for enhanced emission efficiency and spectral control. The device structure comprises a fully reflective anode, serving as a bottom mirror, and a semi-transparent cathode with a reflectance of approx. 70–80% (Fig. 2a). Hence, the light is emitted through the semi-transparent cathode, which is positioned on the opposite side of the textile-based substrate. This configuration induces an interference of light called micro-cavity effect, where light generated within the emissive layer (EML) undergoes multiple reflections between the highly reflective anode and the semi-transparent cathode, modulating the spectral output. The micro-cavity effect is defined as a function of the reflectance and transmittance of each electrode, as well as the distance between the electrodes, referred to as the cavity length.

The micro-cavity effect was examined under varied conditions with ITO (150 nm) and Ag (30 nm) as the top electrode materials (Fig. 2b). This micro-cavity term, derived from Fabry-Pérot resonance and two-beam interference, was calculated using a 2 × 2 transfer matrix simulation28. The results indicate that when the cathode is ITO (dashed line), the micro-cavity term remains relatively constant, exhibiting minimal wavelength-dependent variations. In contrast, the Ag cathode (solid line) significantly enhances the micro-cavity effect within specific wavelength bands, amplifying light emission at the targeted spectral regions.

Figure 2c presents the power dissipation spectra at λ = 730 nm for top-emitting OLEDs, highlighting the effects of different cathode materials and cavity length tuning strategies. The dissipation profiles show that when ITO is employed as the top electrode (non-cavity), the proportion of the air mode is lowered in comparison with cavity OLEDs (i.e., OLEDs with micro-cavity effect) utilizing an Ag cathode. In addition, to investigate which organic layer more effectively enhances the air mode portion, mode distributions were analysed by adjusting the thicknesses of the HTL and ETL, respectively. To compare the two tuning strategies, the optical cavity length was maintained constant by applying an identical thickness increment to either the HTL or ETL. In the HTL‑tuned OLED, the NPB layer was increased by 37 nm relative to the conventional recipe, which adjusted the optical path and positioned the main EL peak at 730 nm. Using this optimized condition as a reference, the ETL‑tuned OLED was fabricated by extending the TPBi layer by the same 37 nm, thereby preserving an equivalent cavity length across both configurations. The microcavity top-emitting OLED, in which the cavity length was tuned via HTL thickness, exhibited an air mode proportion of 38.9%. In contrast, tuning via ETL thickness yielded an air mode proportion of 24.2%, while the non-cavity OLED with an ITO top electrode exhibited an air mode proportion of 18.4%. Such adjustment effectively suppressed the surface plasmon polariton (SPP) mode, thereby enhancing light extraction through the air mode. This improvement shows that the photon extraction can be facilitated by increasing the air mode ratio of cavity structure, thereby improving overall light outcoupling efficiency. In fact, in cavity OLEDs, cavity length modulation through HTL thickness resulted in a maximum external quantum efficiency (EQEmax) of 7.8%, whereas tuning cavity length via ETL thickness yielded a EQEmax of 3.6%. This indicates that HTL-tuning led to approximately a 2.1-fold increase in EQEmax compared to ETL-based tuning strategy (Supplementary Fig. 4a). The observed enhancement is attributed not only to the increased air-mode ratio but also to better carrier transportation arising from layer thickness adjustments. Because hole transport in NPB exceeds electron transport in TPBi, adjustment of the NPB thickness, in part owing to the carrier mobility imbalance29, positioned the recombination zone more effectively within the emissive layer, to reduce the proportion of non-radiative interfacial exciplex. In fact, the HTL-tuned OLED exhibited slightly improved operational lifetime compared with the ETL-tuned device (Supplementary Fig. 4b).

As shown in Supplementary Fig. 5, there existed a red shifting as the cavity length increased. More specifically, a 10 nm variation in cavity length corresponded to a 15 nm shift in the EL spectral peak. This result demonstrates that the optical characteristics of the NIR OLED, especially the peak position, can be tuned through microcavity modulation without modifying the emitter. The recorded max. radiances varied with wavelength, ranging from approximately 40 to 60 W m⁻² sr⁻¹, validating the tunability and high radiance (Fig. 2d). EL spectrum shown in Fig. 2e illustrates tunable emission band over the 720–750 nm region with NIR emitter [Pt(fprpz)2] that underwent spontaneous self-assembly during thin film formation30,31, allowing fine spectral tuning in 10 nm increments. Furthermore, NIR band centered at ∼800 nm can be also fabricated by increasing the cavity length (Supplementary Fig. 6a). The device exhibited low leakage current levels and radiance exceeding 10 W m⁻² sr⁻¹ (Supplementary Fig. 6b).

In top-emitting OLEDs, a capping layer is required to facilitate light extraction, owing to the large refractive index mismatch between air (nair = 1) and the emitting medium (nemitter = 1.96), which causes internal light trapping. A capping layer was designed to enhance outcoupling efficiency and was subsequently incorporated into the device architecture (Fig. 3a). It not only improves OLED efficiency but also ensures good device flexibility and operational reliability through a hybrid structure comprising inorganic and organic materials. The inorganic layer, consisting of Al2O3/TiO2 nanolaminate, protects the device from both moisture and oxygen, while the parylene-C organic layer enhances the biocompatibility, which is particularly crucial for applications involving direct contact with human skin.

The refractive index of the Al2O3/TiO2 nanolaminate is 1.87, and that of parylene-C is 1.6 in the NIR region. The thickness of the organic layer was optimized to maximize light outcoupling from the OLED, revealing that 500 nm resulted in the most efficient light extraction (Supplementary Fig. 7). By depositing this capping layer over the cathode, reduced the fraction of light trapped by total internal reflection, thereby facilitating more efficient photon extraction. Furthermore, the capping layer enhanced the Fabry-Pérot contribution in the NIR spectral region, leading to an increased NIR emission intensity (Supplementary Fig. 8). Next, the transmittance was measured for both the nanolaminate inorganic layer (30 nm) and hybrid structure comprising the same inorganic layer and an additional 500 nm-thick organic parylene-C film (Fig. 3b). A glass substrate was used as the baseline. c J–V–R characteristics for devices with and without the capping layer (closed symbols, with capping; open symbols, without capping). d Electroluminescence spectra measured at a current density of 21 mA cm⁻². e, f External quantum efficiency and power density as functions of current density, showing the effect of the hybrid capping layer on device performance.

Stability of wearable NIR OLEDs
The mechanical and deformational stability of textile-based NIR OLEDs was evaluated to establish their feasibility for wearable applications. To implement the developed NIR OLED structure on a wearable configuration, only the substrate material was changed, while the fabrication process remained identical. Despite the change in substrate, the corresponding EL characteristic of NIR OLED was preserved, as shown in Supplementary Fig. 10a. In addition, device stability was maintained without any detectable leakage paths, and the emitted light intensity exceed 10 W m-2 sr-1 at approximately 12 V and a current density of 31.5 mA cm-2 for the textile device, the minimum level required for phototherapy (Supplementary Fig. 10b)7. Continuous operation was demonstrated under bending, wrinkling, and submersion owing to the inherent flexibility of the NIR OLEDs and the textile platform, without immediate degradation observed (Fig. 4a, b).

Flexibility of the textile-based device was assessed by cyclic bending at a radius of 2 mm, corresponding to an applied tensile strain of 2.1%. Finite element analysis indicated that, for the textile platform with a woven warp and weft architecture, this condition represented the maximum point at which the applied strain could be defined24. The J–V–R characteristics remained stable after 5000 and 10,000 bending cycles, with no evidence of electrical leakage, mechanical delamination, or degradation in radiance output (Fig. 4c), indicating robust structural reliability.

Submersion stability of OLEDs was assessed by evaluating their water resistance through immersion testing. Various encapsulation strategies were systematically investigated for their ability to preserve device integrity under submerged conditions (Fig. 4d). Devices encapsulated solely with an inorganic barrier layer showed significant degradation within 10 min of immersion. In contrast, OLEDs protected with a 30 µm-thick PET layer applied retained operational stability for up to 1 h before deterioration was observed. Notably, OLEDs encapsulated with a 500 nm-thick parylene-C layer developed in this study exhibited water resistance, maintaining over 90% of their initial radiance after 50 h of continuous submersion. Performance degradation became pronounced only after prolonged exposure, with radiance falling below 50% following 80 h of immersion.

To validate the risk of skin burns upon contact, the temperature of the device was monitored. This was analysed for a continuous operation under various radiation levels during 20 minutes (Fig. 4e). Regardless of applied current density, their temperature levelled shortly after initiation. The devices reached 28.0 °C at 3 mW cm⁻², 34.0 °C at 4 mW cm⁻², and 41.0 °C at 7 mW cm⁻², respectively. The polyester-based textile platform used in this study possesses a relatively low thermal conductivity (0.3–0.4 W/m·K), significantly lower than that of glass (~1 W/m·K). Such thermal accumulation leads to heat retention in the active layer during prolonged operation, thereby accelerating device degradation. Reducing heat accumulation and suppress OLED degradation caused by heat, a heat sink tape was attached to the textile devices. As a result, their temperatures were further reduced to 27.5 °C, 28.0 °C, and 32.0 °C, ensuring safe operation against possible skin burns. Additionally, to assess long-term device reliability, operational lifetime was evaluated on different substrates. OLEDs exhibited comparable LT50% performance regardless of whether glass or textile substrates were used (Supplementary Fig. 11a, b). Furthermore, the incorporation of a heat sink extended the lifetime for both configurations. Notably, the enhancement was more pronounced in textile-based OLEDs. Devices with a heat sink demonstrated up to a two-fold increase in LT50% compared to those without it. This improvement is attributed to the effective dissipation of heat generated during operation, which reduces thermal degradation on the OLED stack.

Penetration of NIR irradiation
Non-invasive phototherapy requires sufficient light penetration into the skin to stimulate biological targets without surgical intervention. Since human hair follicles are typically located approximately 3 mm beneath the skin surface, achieving light transmission to this depth is critical for effective light delivery to dermal papilla cells within the follicle niche. To assess whether the NIR OLED devices meet this requirement, pig skin was employed as a tissue model due to its structural and optical resemblance to human skin, enabling analysis of in vivo light propagation.

As shown in Fig. 5a, the pig skin sample is shown together with its front view and thickness. The experimental setup used to evaluate light transmission through pig skin, with the OLED positioned behind the sample, is shown in Fig. 5b. To enable accurate measurement of transmitted light intensity, the OLED emitting area was fully covered by the skin sample. Because OLEDs exhibit a broad angular emission unlike narrow beam lasers or LEDs and scattered light arising from melanin and other tissue components in pig skin also needed to be captured. Consequently, the pig skin area (324 mm2; 18 mm × 18 mm) was set to approximately five times the OLED emitting area (69 mm2; 8.3 mm × 8.3 mm), thereby ensuring full coverage for reliable measurement.

To assess the effects of OLED emission wavelength and angular distribution for non-invasive phototherapy, transdermal transmission was analyzed using four OLED device types, including a cavity red OLED with a peak at 640 nm, a non-cavity and a cavity NIR OLED with peak at around 730-740 nm, and a cavity NIR OLED with peak at 800 nm (Supplementary Fig. 12). Angular emission profiles of the cavity and non-cavity NIR OLEDs were compared to a Lambertian reference distribution (Fig. 5c). The non-cavity OLED exhibited a super-Lambertian emission pattern, while the cavity OLED showed an angular profile closely matching that of a Lambertian emitter. Although cavity OLEDs typically demonstrate sub-Lambertian behavior due to their optical interference effects, the cavity OLED developed in this study exhibited near-Lambertian characteristics. This deviation is attributed to prior optimization of the ETL thickness in the non-cavity OLED structure30,32, which may have increased lateral scattering toward oblique angles (i.e., viewing angles exceeding 10°). In contrast, the cavity structure enhanced forward emission, achieving an angular distribution closer to a Lambertian profile. A blue shift of the EL spectrum with increasing viewing angle was observed in cavity NIR OLEDs, attributable to microcavity resonance that shifts the cavity mode toward shorter wavelengths with increased viewing angles (Supplementary Fig. 13).

The cavity red and the cavity NIR (800 nm) OLEDs exhibited sub-Lambertian and super-Lambertian angular distributions, respectively, as shown in Supplementary Fig. 14. The 800 nm device, which was red-shifted by approximately 60 nm from the emitter’s photoluminescence peak (730–740 nm) due to microcavity effect with increased optical path, exhibited increasing intensity at oblique angles compared to the normal direction. This super-Lambertian profile shows that when the spectral peak shifts significantly from the intrinsic PL peak, a relatively higher portion of emitted light is directed toward off-normal angles compared to the forward direction.

The EL spectra obtained under equal radiance revealed a narrowing of the spectral bandwidth upon cavity integration. The FWHM decreased from 130 nm in the non-cavity device to 45 nm in the cavity OLED. At the same time, emission intensity in the 730–740 nm region was enhanced by the cavity configuration. At normal emission, the band‑integrated photon radiance within the region was approximately 2.4 times greater for the cavity NIR OLED than for the non‑cavity device. This tuning can provide to greater photon delivery at the hDPCs activation peak near 730 nm, compared with the non-cavity device, thereby enhancing photostimulation under equivalent dose condition, as shown in Fig. 5d. An analysis relating hDPCs activation to the OLEDs’ optical properties is provided in the in vitro section.

Transdermal light propagation under realistic operation was assessed by placing the emitting surface of each OLED in direct contact with epidermis of pig skin (Fig. 5e). Transmittance was defined as the ratio of the radiance measured at the dermal exit plane along the normal direction to the radiant output of the OLED. As shown in Fig. 5f, the cavity NIR OLED achieved the highest transdermal transmission efficiency at 12%, surpassing the cavity red OLED (8%), the non-cavity NIR OLED (6%) and the NIR OLED with an 800 nm peak (5%). The transmission of the cavity NIR OLED shows the improved tissue penetrability of longer wavelength NIR emissions (700–800 nm) compared to shorter wavelength red emissions (600–700 nm). Furthermore, the enhanced transmission observed in the cavity NIR OLED compared to its non-cavity counterpart suggests the role of forward-directed emission for non-invasive light therapy.

To validate transmittance of the NIR OLED light in real skin, Monte Carlo simulations were performed to measure photon delivery from a skin conformal wearable near infrared OLED to the hair follicle region. In this model, the epidermis, dermis, and subcutaneous fat layers were defined with layer-specific refractive indices scattering coefficients (µs), and anisotropy factors (g), all set as wavelength-dependent values from the literature33. The emission source was set an 8.3 × 8.3 mm² square that was placed in direct contact with the epidermis surface (Supplementary Fig. 15a). Planar receivers were positioned normal to the surface at depths from 1.0 mm to 5.0 mm. The ratio of receiving surface irradiance to power density of emitting surface was 4.3% at 3.0 mm, 1.4% at 4.0 mm, and 0.5% at 5.0 mm (Supplementary Fig. 15b).

Simulated transmission was lower than the measured value in porcine skin. The difference was attributed to two features of the experimental setup. The skin was dried before measurement, which reduced absorption by water. In addition, the samples consisted only of epidermis and dermis, whereas the model included epidermis, dermis, and subcutaneous fat. However, the receiving ratio at depths of 3 to 4 mm was similar to that in our in vitro setup, which showed a PBM effect under OLED irradiation as described in the below section.

In vitro PBM induced by OLED irradiation
To validate the phototherapy effects of NIR OLEDs on hDPCs and their potential for hair regeneration applications, this study conducts an in vitro tests. hDPCs are specialized mesenchymal cells situated within the dermal papilla at the base of hair follicles. They play a central role in hair follicle regulation by secreting critical growth factors, including fibroblast growth factor-7 (FGF-7) and insulin-like growth factor-1 (IGF-1), which directly influence follicular growth and cycling34–37. Promoting the migration of hDPCs is crucial for effective cell-cell communication and follicular regeneration, particularly during an anagen phase. Moreover, preventing or delaying cellular senescence—an irreversible state of growth arrest—is vital for maintaining follicular health and mitigating age-related hair loss37. Enhanced migratory capacity and anti-aging properties of hDPCs represent significant factors for hair loss therapy.

Effects of light exposure on cell migration and cellular senescence of hDPCs were examined. To validate the influence of light treatment on biological responses, a cell migration assay and a cellular senescence assay were performed. For the migration assay, a scratch was made at the center of a cell culture to create an empty space. NIR emission was then irradiated onto the scratched region, and the extent of cell movement into the gap was observed over time to evaluate the migration. For the senescence assay, senescent cells were stained with blue color using a standard β-galactosidase staining method, and changes in the number of stained cells were monitored following NIR OLED irradiation to investigate its potential to suppress cellular aging (Fig. 6a).

Three OLED types were employed to assess the effect of optical properties on cell activation, including the cavity NIR OLED fabricated in this study and two devices used in the transdermal section, a cavity red OLED and a non-cavity NIR OLED. Device characteristics including peak wavelength and full width at half maximum were summarized in Table 2.

The OLEDs were positioned 15 mm above the well plate to mitigate thermal effects on cells (Supplementary Fig. 16a). For each OLED, the emitting‑surface radiance was set to around 10 W m-2 sr-1 for continuous irradiation during 20 min. Analysis of cell activation was limited to an orthogonally aligned square region, where the emitting surface measured 8.3 × 8.3 mm² and the area matched the beam size of OLED (Supplementary Fig. 16b).

To verify the light dose delivered to the cell medium, a Monte Carlo simulation that reproduced the in vitro configuration was performed. Because dose delivery to a way from emitting surface depends on the OLED angular emission profile, the receiving surface was defined as the full well with a diameter of 35 mm. The simulation indicated an energy spread for the non-cavity NIR OLED, with an effective illuminated diameter of approximately 6.0 mm as shown in Supplementary Fig. 16c. The cavity NIR OLED exhibited an effective illuminated diameter of approximately 4.5 mm (Supplementary Fig. 16d). This observation is consistent with the more diffuse super Lambertian emission of the non-cavity device. However, to ensure that in vitro outcomes were obtained from cells exposed to light, the analysis area was fixed to match the beam size and aligned orthogonally to the OLED.

Under these conditions the effective irradiance at the cell medium was 0.06 mW cm⁻², which is approximately 2% of the emitting surface power density of 3 mW cm⁻², and this corresponded to a delivered irradiance of 0.072 J cm⁻² during 20 min of continuous exposure. This configuration allowed to compare cellular responses under same dose to red versus NIR emission and to evaluate the impact of NIR spectral bandwidth.

Cell activation after OLED exposure was examined by optical microscopy of hDPC cultures. For the migration assay, optical microscopy (OM) images were acquired immediately after scratch formation and 16 h after OLED irradiation, and greater closure of the scratched area was observed in both red- and NIR-irradiated groups compared with the non-irradiated control (Fig. 6b). Cellular senescence was evaluated by SA-β-gal staining at two passages. Passage-3 and passage-13 cells were used as references. The experimental group was composed of passage-13 hDPCs. Based on SA-β-gal staining, the lowest fraction of positive cells was observed in passage-3 hDPCs despite the absence of light exposure, consistent with their younger passage. Across all experimental groups, the proportion of stained cells decreased relative to the control. However, a greater reduction was achieved with NIR irradiation than with red, and the cavity-tuned NIR OLED was associated with the most pronounced decrease (Fig. 6c).

Cell migration during the 16 to 22 h period after OLED irradiation was quantified as the filled‑area ratio relative to the initial scratch area (Fig. 6d). Interval observations at 2 h increments from 16 to 22 h were performed, and progressive filling of the scratched region by migrated cells was observed (Supplementary Fig. 17). At 16 h, the control filled 30.7% of the scratched area, whereas closure reached 60.9% in the cavity NIR OLED group, 73.5% in the non‑cavity NIR OLED group, and 56.8% in the red OLED group. Over time, the gap continued to close and the migration rate reached saturation. At 22 h, closure reached 97.1% in the cavity NIR OLED group, 93.8% in the non‑cavity NIR OLED group, and 92.3% in the red OLED group, exceeding the 80.5% observed in the control (Table 2).

Cellular senescence was defined as the proportion of SA-β-gal-positive cells and was calculated by dividing the number of stained cells by the total cell count. Results are presented in Fig. 6e and Table 3. With identical culture duration, SA-β-gal positivity in passage-3 hDPCs was 0.18%, and few blue-stained cells were observed in OM images (Supplementary Fig. 18a). Without light exposure, SA-β-gal positivity in passage-13 hDPCs was 38.2% (Supplementary Fig. 18b). The difference between untreated passage-3 and passage-13 cultures is attributable to passage effects and is consistent with lower baseline senescence at younger passages. Under cavity red OLED irradiation, SA-β-gal positivity was 36.5% (Supplementary Fig. 18c). Under NIR exposure, SA-β-gal positivity was lower than under red exposure, at 3.2% in the cavity-tuned NIR group and 23% in the non-cavity NIR group (Supplementary Fig. 18d, e). These findings are consistent with the hDPCs activation profile in Fig. 5d. Compared with red exposure, lower senescence fractions were obtained under NIR exposure, with the lowest value observed for the cavity-tuned NIR OLED, which is characterized by higher photon amount in the 730–740 nm band.

Methods
NIR OLEDs fabrication
NIR OLEDs were fabricated by thermal evaporation (base pressure, 2 × 10⁻⁶ Torr). Organic and electrode layers were sequentially deposited on the substrate under this vacuum. The Al anode (100 nm) and Ag cathode (30 nm) were deposited at 2 Å s⁻¹. A Pt(II) complex–based NIR emitter was used as the emissive layer30 (EML, 20 nm) and was deposited at 0.2 Å s⁻¹. The carrier‑blocking layer, N,N′‑dicarbazolyl‑3,5‑benzene (mCP, 15 nm), the hole‑transport layer, N,N′‑di(1‑naphthyl)‑N,N′‑diphenyl‑(1,1′‑biphenyl)‑4,4′‑diamine (NPB, 87 nm), and the electron‑transport layer, 1,3,5‑tris(N‑phenylbenzimidazole‑2‑yl)benzene (TPBi, 60 nm) were deposited at rates of 0.5–1 Å s⁻¹. The NPB thickness (87 nm) was selected to tune the optical microcavity to a peak emission near 730 nm. The hole‑injection layer, molybdenum(VI) oxide (MoO₃, 10 nm), and the electron‑injection layer, 8‑quinolinolato lithium (Liq, 2 nm), were deposited at 0.5 Å s⁻¹ and 0.1 Å s⁻¹, respectively.

Encapsulation was formed with an inorganic/organic nanolaminate. An Al₂O₃/TiO₂ inorganic layer (30 nm total) was deposited by thermal atomic layer deposition (ALD) at 40 °C using trimethylaluminum (TMA) and tetrakis(dimethylamino)titanium (TDMAT) as metal precursors. An organic parylene‑C layer (500 nm) was subsequently deposited by chemical vapor deposition.

Textile-based NIR OLED fabrication
The textile platform was prepared according to previous research26. Prior to OLED deposition, a 30 nm Al2O3/TiO2 nanolaminate barrier layer was deposited on the textile by ALD. NIR OLED was subsequently fabricated on the textile platform using the same fabrication sequence and recipe described NIR OLED fabrication section.

OLED characterization
OLEDs were driven under constant bias using a Keithley 2400 benchtop source meter. Electrical operating conditions were controlled and logged via computer. Optical measurements were performed using a CS-2000 spectroradiometer (Konica Minolta) and a Blue-Wave spectrometer (StellarNet). Angular emission data were acquired by rotating the light source about the spectrometer normal in fixed increments. Flexibility was assessed using a bending tester from Sciencetown Inc.

Hat-type prototype
To demonstrate operation of the OLED array on a commercial hat/cap platform, the array was mounted on the textile and interfaced to a flexible printed circuit board (FPCB) that provided array driving and section‑wise switching for scalp‑specific operation. The array comprised OLED emitters with emission areas of 69 mm2 and 1,000 mm2, each wired to an independent FPCB channel for individual on/off control. For array‑level characterization, the source was operated in constant‑current mode using a benchtop source meter (Keithley 2636B). The operation is shown in Supplementary Movies 1–3.

A wireless prototype was assembled to evaluate portability. The architecture integrated a flexible battery for portable operation, a flexible printed circuit board providing on/off control, battery power delivery, and OLED interconnection, and the NIR OLED. A 3 V flexible Renata thin-film battery (CP042350) was employed, and 3 or 4 cells were connected in series to achieve the required minimum level of light intensity for phototherapy. All components were integrated on the polyester-based textile to form a single portable module, and operation was performed from the flexible battery without benchtop supply (Supplementary Movies 4, 5).

Pig-skin transdermal propagation
Porcine skin membranes comprising the epidermis and dermis (micropig Franz Cell Membrane, APURES) were used. Membranes were thawed at room temperature for approximately 1 h before use. Each membrane was placed on an OLED with the epidermal surface facing the emission area to measure transdermal propagation. Red OLEDs were fabricated following the protocol described in previous research45. Non-cavity NIR OLEDs were fabricated according to the procedure reported in previous research15. The OLEDs were operated under each condition to achieve same power density, and light transmitted through the skin was measured on the opposite side.

Monte Carlo simulation
Monte Carlo simulations were performed using LightToolsTM. For the in vitro configuration, the geometry of each well and each OLED was reproduced to match the experimental setup. The angular emission profile and the emitting area of each OLED were defined from measured data. For the real skin model, literature-reported optical parameters were used to construct a multilayer skin geometry comprising the epidermis, dermis, and subcutaneous tissue33,46, and scattering was represented by the Henyey–Greenstein scattering phase function. To mimic non-invasive phototherapy, the emitting surface of the OLED was placed in direct contact with the epidermal surface in the model.

In vitro setup
During all irradiations, the distance from the OLED emitting surface to the cell culture plate was set to ~15 mm. A transparent plate lid was placed over the wells to minimize particulate contamination. Each well was filled with cell culture medium such that the vertical optical path length from the inner surface of the lid to the medium surface was ~15 mm. The well plate was placed within the OLED driving equipment, which shielded the wells from ambient light so that only the OLED emission reached the medium. A 6-well plate was used, with one OLED assigned to each well, and cell activation was validated in each well.

Cell culture
hDPCs at passage 5 to passage 13 were obtained (c-12071; PromoCell) and cultured in Follicle DPC Growth Medium (c-26501; PromoCell) with 0.1% Gibco™ antibiotic-antimycotic (Thermo Fisher Scientific, Waltham, MA, USA). Cells were maintained in a humidified incubator at 37 °C under 5% CO2.

Cell migration assay
hDPCs (passage 3) were seeded in a 6-well plate at a concentration of 2.5 × 105 cells/well and incubated until reaching 80% confluence. The cell cultures were scratched with a sterile 1000 µL pipette tip. Detached cells were washed away with PBS (21-030-CVR; Corning). Subsequently, 2 mL of DPC growth medium was added. Horizontal reference lines were drawn on the bottom of the plate with an ultrafine tip marker to create a grid for alignment during image acquisition. The plate was then placed in the illumination device, and light irradiation was applied under controlled conditions. Following irradiation, the plate was placed under a microscope aligned using the reference marks. Selected regions of interest were imaged every 2 h from 16 h to 24 h post-scratch using a microscope (Nikon, ECLIPSE Ts2) with a 4× objective. Scratch area, wound coverage, and average wound width were quantified using the ImageJ plugin Wound Healing Size Tool.

Cellular senescence assay
hDPCs (passage 13) were seeded in a 6-well plate at a concentration of 1 × 105 cells/well and incubated for 24 h. After light exposure, the cells were cultured for 2 days, placed into a new 6-well plate at half density, and cultured for an additional 4 days. SA-β-gal activity was assessed using a histological staining kit according to the manufacturer’s instructions (#9860S, Cell Signaling).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript “Wearable textile based phototherapy with customized near infrared OLEDs for superior hair loss treatment” by Cho et al. presents an integrated phototherapeutic platform that couples wavelength-tuned, top-emitting NIR OLEDs with a textile substrate for non-invasive, ergonomic hair loss treatment. The authors engineered a microcavity OLED architecture to precisely match the NIR emission spectrum (700–800 nm) to the activation profile of human dermal papilla cells (hDPCs), the key cell type involved in follicular regeneration. The resulting devices exhibit mechanical robustness (tolerating 10,000 bending cycles), water resistance (over 90% radiance retention after 50 h submersion), and thermal safety (<30 °C skin-contact temperature under continuous use), all while preserving high optical output and directional emission.\nFrom a technical perspective, the work is well-executed in some aspect. The use of Ag-based reflective electrodes, HTL/ETL thickness modulation for spectral tuning, and parylene-C encapsulation are appropriate choices for realizing narrowband top-emitting OLEDs. The optical tuning to the cytochrome c oxidase absorption window is biologically relevant and represents thoughtful device-biology integration.\nHowever, the degree of novelty and scope of biological validation should have significant room for improvement, which makes us concerned that the current work does not match the level of Nature Communications.\nMajor comments:\nAlthough we have some concerns above, I recognize the authors demonstrate commendable effort in showing a solid command of microsystem assembly. Additionally, the manuscript presents a promising attempt to address meaningful medical needs, the superior hair loss treatment. It is one promising and attractive research direction. Here are some detailed concerns on the current manuscript.\n1.The scope of biological validation is limited to in vitro studies. While the scratch assay and β-galactosidase staining on hDPCs demonstrate promising cellular outcomes, no systematic in vivo validation is provided. This weakens the therapeutic relevance of the claims. The authors should consider adding systematic in vivo studies to assess light penetration, dose delivery, and its overall effectiveness.\n2.The significance of this paper can be modified to state more clearly. It can be improved while benchmarking against clinical or FDA-cleared phototherapy systems. Without sufficient comparison to red-light helmets or laser-based PBM devices, it is unclear whether the proposed OLED system offers a distinctive, meaningful clinical advantage. The authors could consider adding irradiance, power density, and angular emission data to support their claims of improved therapeutic delivery.\n3.The innovation presented in this work appears to lie primarily in the thoughtful integration of several established device technologies into a wearable phototherapy platform. Microcavity-tuned OLEDs, reflective Ag electrodes, textile substrates, and parylene encapsulation are all well-documented in prior OLED and wearable electronics literature. While the combination here is executed effectively and tailored to a biologically relevant spectral window, the manuscript would benefit from a clearer articulation of how this integration offers concrete advances over previously reported wearable PBM systems. For instance, prior studies on cage-type OLEDs and micro-LED arrays have also addressed flexibility and form factor, albeit with different approaches and trade-offs.", "reviewer_2": "This paper presents the development and validation of a novel, fully wearable phototherapy system that integrates microcavity-tuned, top-emitting near-infrared (NIR) OLEDs into textiles, precisely engineered to match the activation spectrum of human dermal papilla cells (hDPCs) for non-invasive, effective hair regeneration via photobiomodulation (PBM), while addressing the limitations of conventional pharmacological and light-based therapies for alopecia. Overall, this is an interesting work and can be recommended for publication in Nature Communications after major revision. The following are some comments that might be helpful for further improvement of their manuscript to publish in future publications.\n1. The paper claims tuning to match the action spectrum of hDPCs via CCO activation. However, CCO’s absorption range is broad and varies across mitochondrial states. What is the justification for targeting 730 nm and 800 nm specifically, and how do these correspond to CCO isoforms or ROS generation thresholds in vivo?\n2. All validation was performed using 2D hDPC monolayers. However, in vivo hair follicles reside within a 3D dermal environment and are exposed to vasculature, hormones, and other cell types. How do you account for the translational gap between 2D in vitro data and actual follicular behavior?\n3. The authors claim the cavity NIR OLED is superior, yet the non-cavity NIR showed greater hDPC migration after 16 hours. How do they reconcile this observation with their main claim of improved performance via cavity tuning? Could this be related to angular distribution or unintended dose differences?\n4. With such spatial and angular variations in emission, how do you control for accurate irradiance delivery over curved, irregular scalp surfaces? Are there active or passive dosimetry mechanisms built into the textile?\n5. The study attributes effects to CCO activation and ROS signaling, but presents no direct biochemical validation (e.g., ROS quantification, antioxidant gene expression, or ATP production levels). Why was no such mechanistic validation performed?\n6. The pigskin model is useful, but did the authors perform Monte Carlo simulations or tissue-mimicking phantoms to more precisely model photon distribution to the follicle base (~3 mm)? 12% transmission is relative—how much actual photon energy reaches target biological chromophores?\n7. Has the team quantified how the refractive index mismatch between parylene-C and human skin affects photon loss via internal reflection or scattering? Could this be mitigated with intermediate index-matching layers?\n8. Your microcavity devices show ~40 nm FWHM. Some studies suggest broader bandwidths (~100 nm) can stimulate a wider range of cellular photoreceptors. Could overly narrow spectral targeting reduce holistic tissue activation?\n9. While HTL-tuned microcavity devices show higher EQE than ETL-tuned ones, did you quantify trade-offs in carrier balance, recombination zone position, or angular intensity losses at oblique angles? How does the angular spectral stability compare under real-world usage conditions?\n10. The manuscript claims 'markedly superior efficacy' of the textile-integrated NIR OLED system compared to conventional phototherapy methods. However, there is no quantitative benchmarking against existing commercial or clinically validated devices (e.g., LLLT helmets like iRestore, HairMax, or LG Pra.L Medi Hair). Can the authors provide a controlled, side-by-side comparison of their device’s therapeutic outcomes — such as hDPC migration rates, senescence reduction, and transdermal photon flux — relative to these established devices under matched irradiance and exposure conditions?\nWithout such benchmarking, how can superiority over current clinical standards be substantiated?\"\n11. OLEDs are known to suffer from current spreading issues and voltage gradients on large substrates. How do you ensure homogeneity of brightness across a large, curved textile interface?\n12. How consistent are key performance metrics such as luminance, EQE, FWHM, and turn-on voltage across batches? What is the coefficient of variation in performance across 10+ fabricated devices?\n13. Given that EQE roll-off is a critical issue in NIR OLEDs due to triplet-triplet annihilation and thermal quenching, what is the trade-off between brightness and stability? Have you characterized thermal degradation and emission roll-off in that regime?\n14. In this work, the merit and demerit of the textile‑integrated near‑infrared OLED system should be discussed when applied to biocompatible platforms for non‑invasive wearable phototherapy.", "reviewer_3": "The authors did solid OLED engineering work, showing how the proposed device optimization leads to better biological response compared to others (not optimized or similar to commercially available products). The methodology is sound, and the work could be of significance in the field of wearable electronics if adjustments to the manuscripts are properly made.\nThe major point I have is about wearability and usability of the presented device in real life scenarios.\nThe general idea of this work presupposes the existence of a supporting circuitry that ideally fits into the hat, and is removable when washing is necessary (Of course, more creative solutions could be implemented to realize portability, this was just an example).\nIn this regard, I failed to find information about the driving scheme used to realize the videos proposed as demonstrations.\nFor this reason, at the present time, there is the need to add data about this aspect to fully comply with the message of portability proposed in the manuscript, and also to show that this device is indeed compatible with the notion of wearable electronic platforms. In other words, the OLED per se is wearable, but the phototherapy (quoting the title that the authors chose) probably still relies on benchtop power supplies. Therefore, I suggest that the authors come up with a circuitry that allows the OLED to be driven in a truly portable fashion, demonstrating that with the application requirements, the power supply (maybe a battery) can be sufficient to drive the OLED for a substantial amount of time (or equivalently, enough therapeutic sessions). This should be documented in the method section and shown in a Figure.\nI have some minor comments referring to the different sections of the manuscripts.\nROW 102: “Additionally, most NIR OLEDs have been designed a bottom-emitting architecture” probably contains an error.\nROWS 115-116: Typically, bottom emitting OLEDs provide different advantages over top-emitting ones. While it is clear that bottom emitting devices based on ITO are susceptible to mechanical damage under certain stress, the author here exclude the whole category of bottom-emitting OLEDs without addressing the general motivation. Could they elaborate more on this design choice?\nROW 128: Why are the authors using this specific tensile strain (2.1%)? What are the ranges of expected strains during use and during washing of the “hat”? It is suspected that this object will face grater deformations for the intended wearable application. What would be the number of bending tests that the OLED would tolerate for a strain in the range conform to the application needs?\nROW 183: I think the authors should reference figures 3 and 5 here.\nROWS 246—248: It is useful for the reader to directly access the information about the ETL and HTL thickness from this line. Could the authors explicitly state the thicknesses in the non-optimized VS. optimized case and provide an explanation for their claim on the better carrier transport in the optimized configuration?\nROW 307: What are the requirements in terms of optical power density (or equivalently energy density) that are required to exhert relevant beneficial effects with this type of therapy? This information is difficult to retrieve without accessing to reference 7. I think it would be of service to explicitly mention this in the text. It is also important to state at what voltages and currents the OLEDs presented in this work reach this range.\nROW 320: See the comment related to the choice of a 2.1% strain.\nROW 341: I think the content of ROWS 355-361 should be moved here for better readability.\nROW 495: It would be appropriate to show a plot with the superposition of hDPC activation spectrum (or peak if not available) and the different OLEDs EL spectra. Most probably the authors can add the hDPC missing information directly into figure 2E."}, "author_response": "Manuscript Number: NCOMMS-25-35152B\nTitle: \"Wearable textile‑based phototherapy with customized near‑infrared OLEDs for\nsuperior hair loss treatment\"\nCorrespondence Author: Eun Hae Cho, Jingi An, Yun Chi and Kyung Cheol Choi.\nResponses to the reviewer’s comments\nNovember 6, 2025\nDear Reviewers,\nLet us open by thanking the reviewers for their insightful comments. The reviewers gave us\nclear guidance and some positive critiques. Following the reviewers’ suggestion, we spent more\ntime reading and came to the revision process better prepared. We enjoyed the process and\nthink that the reviewers’ comments have tremendously improved the revised draft. The\nreviewers should now clearly see the difference they made to the revised manuscript. In the\nfollowing lines, we detail the responses and changes that were made in line with the reviewers’\ncomments. The reviewers’ comments are highlighted in bold type. In the manuscript, the\nrevisions addressing the reviewers’ comments are highlighted in red, and the voluntary\nmodifications are highlighted in blue.\nReviewer #1: The manuscript “Wearable textile-based phototherapy with customized\nnear infrared OLEDs for superior hair loss treatment” by Cho et al. presents an\nintegrated phototherapeutic platform that couples wavelength-tuned, top-emitting NIR\nOLEDs with a textile substrate for non-invasive, ergonomic hair loss treatment. The\nauthors engineered a microcavity OLED architecture to precisely match the NIR\nemission spectrum (700–800 nm) to the activation profile of human dermal papilla cells\n(hDPCs), the key cell type involved in follicular regeneration. The resulting devices\nexhibit mechanical robustness (tolerating 10,000 bending cycles), water resistance (over\n90% radiance retention after 50 h submersion), and thermal safety (<30 °C skin-contact\ntemperature under continuous use), all while preserving high optical output and\ndirectional emission. From a technical perspective, the work is well-executed in some\naspect. The use of Ag-based reflective electrodes, HTL/ETL thickness modulation for\nspectral tuning, and parylene-C encapsulation are appropriate choices for realizing\nnarrowband top-emitting OLEDs. The optical tuning to the cytochrome c oxidase\nabsorption window is biologically relevant and represents thoughtful device-biology\nintegration. However, the degree of novelty and scope of biological validation should have\nsignificant room for improvement, which makes us concerned that the current work does\nnot match the level of Nature Communications.\nRESPONSE\nWe thank the reviewer for the insightful comments and for their interest in our research. The\nfollowing are our responses to the individual comments.\nReviewer’s comment 1) The scope of biological validation is limited to in vitro studies.\nWhile the scratch assay and β-galactosidase staining on hDPCs demonstrate promising\ncellular outcomes, no systematic in vivo validation is provided. This weakens the\ntherapeutic relevance of the claims. The authors should consider adding systematic in\nvivo studies to assess light penetration, dose delivery, and its overall effectiveness.\nRESPONSE\nWe appreciate the reviewer’s comment regarding the limited scope of biological validation. In\nfact, subsequent in vivo study is underway. We provide a brief overview of our ongoing in vivo\nwork using textile‑based OLED devices.\n◼ Follow up research about in vivo test using the textile-based OLEDs\nAs part of an ongoing, follow‑up study to evaluate PBM in vivo, the textile‑based NIR\nOLED was applied to C57BL/6 mouse model to validate PBM effect for hair-loss treatment.\nA dorsal skin was trimmed to ~1 mm using an electric razor, with careful control to avoid\nwounding, as skin injury itself can artificially induce hair regrowth (FigR.1a). Light irradiation\n2\nwas performed under respiratory anesthesia at 730 nm (± 5 nm), 3 mW cm-2, for 20 minutes\nper day, which were the same conditions as those used for the in vitro test in this study. The\nsame dorsal region was targeted at a fixed time each day (FigR.1b).\nBased on the experiments described above, we are currently setting the experimental\nconditions by optimizing both the animal model and the OLED irradiation parameters.\nFigR.1 | In vivo validation of phototherapy. a, Mouse after dorsal hair removal (shaved). b,\nPhotograph of irradiation during wearable phototherapy with the textile-based NIR OLED.\n3\n◼ Light penetration after penetration of mice skin\nFigR.1 | Light transmission of the textile-based OLED. a, Photograph of shaved and depilated mouse\nskin prepared for in vivo phototherapy. b, Emission image of the textile-based OLED placed beneath\nthe mouse skin.\nThis experiment was designed to examine whether residual fine hair attenuated light energy\nand to verify whether OLED irradiation delivered sufficient optical power to the hair follicles.\nAs shown in FigR.2a, both shaved skin and fully depilated skin were excised from mice to\nprepare skin tissue samples. These tissues were placed directly on the OLED emission surface,\nand the transmitted light intensity was measured (FigR.2b). Even though with residual hair,\napproximately 26% of the emitted light penetrated through the skin, while fully depilated skin\ntransmitted about 52% (FigR.3).\nAlthough some attenuation was caused by hair, these values indicate that a considerable\nportion of the OLED emission was still transmitted, and the resulting irradiance was well above\nthe effective dose established in our in vitro assays (please refer to our response to Reviewer\n2, Comment 3).\n4\nw/o\nskin\nw/\nshaved\nskin\nw/\ndepilated\nskin\nFigR.3 | Light intensity measured after transmission through each mouse skin condition.\n◼ Conclusion\nThe NIR OLED constitute a non‑invasive light‑delivery modality capable of activating DP\ncells within the skin. However, in vivo validation of hair growth, unlike in vitro assays, cannot\nrely solely on cellular activation, as outcomes are strongly influenced by signaling dynamics\ngoverned by the murine hair‑cycle stage. Accordingly, optimization of the animal model and\nPBM irradiation parameters (irradiance and treated period) is in progress for the in vivo\nexperiments.\n5\n)%(\necnaidar\nevitaleR\n1 0\n8\n6\n4\n2\n0\n0\n0\n0\n0\nclearly. It can be improved while benchmarking against clinical or FDA-cleared\nphototherapy systems. Without sufficient comparison to red-light helmets or laser-based\nPBM devices, it is unclear whether the proposed OLED system offers a distinctive,\nmeaningful clinical advantage. The authors could consider adding irradiance, power\ndensity, and angular emission data to support their claims of improved therapeutic\ndelivery.\nRESPONSE\nWe appreciate the reviewer’s suggestion to benchmark our OLED system against clinical or\nFDA-cleared phototherapy systems to better highlight its distinctive advantages. To more\nclearly delineate the advantages of our device relative to existing systems, additional datasets\nand simulations were included to revised manuscript.\n1. Quantifying NIR OLED power density and on-cell irradiance\nTo validate clearly our NIR OLEDs light effect to cell medium, we design our in-vitro set\nup for monte carlo simulation and simulated it to define a light effect. In vitro irradiation was\nexecuted at a source power density of 3 mW·cm⁻² for 20 minutes, selected to remain within\nthe commonly reported PBM therapeutic window while ensuring safe exposure for cultured\ndermal papilla cells. Under our culture geometry, the on-cell irradiance was estimated at\napproximately 2% of the source value, yielding ~ 0.06 mW·cm⁻². This corresponds to a fluence\nof 0.72 J·cm⁻². Despite the low dose, the NIR OLED condition yielded a reduction in cellular\nsenescence markers relative to the red-light control in the same assay by about 90% under\notherwise matched exposure. This difference was attributed to spectral matching of the\ncustomized NIR OLED to the dermal papilla cell action spectrum rather than to an increase in\ntotal dose. Details are provided in the Response to Reviewer 2, Comment 3.\n2. Simulation for real skin model relevant skin model\nTo translate source emission into depth‑resolved dose under anatomically relevant\nconditions, three‑dimensional Monte Carlo simulations were performed using a layered\nhuman‑skin model. The simulations quantified post‑penetration irradiance customized NIR\n(this study) OLEDs. The results indicated sufficient delivery of optical energy to dermal depths\nof approximately 3–5 mm in the NIR range, supporting the relevance of our wearable system,\nwhich could be close to scalp, emission for effective PBM. Details are provided in the Response\nto Reviewer 2, Comment 6.\n6\n3. Angular profile of NIR OLEDs\nTypically, OLED emission is not confined to the forward direction; rather, its intrinsic\nangular distribution illuminates a broad tissue area, increasing the spatial coverage of optical\nstimulation. However, our NIR OLEDs exhibit angle‑dependent spectral characteristics due to\ntheir microcavity effect (Supplementary Fig. 13, the figure is added for revised manuscript).\nOn curved scalp geometries, such angular dispersion can introduce modest spectral shifts that\nalter the wavelength composition reaching the tissue. The angle‑dependent blueshift of cavity\nOLEDs is a potential limitation for PBM applications targeting a band near 730 nm for hair‑loss\ntreatment.\nNevertheless, this limitation could be mitigated by incorporating scattering outcoupling\nlayers, which stabilize the spectral peak across viewing angles and help maintain the designed\nNIR emission near 730 nm. We recognize this potential weakness but note that the inherent\nspectral shift of cavity OLEDs can be effectively alleviated using scattering layers or additional\nsurface engineering (related with Response to Reviewer 2, Comment 4).\nSupplementary Fig. 13| Emission spectra of cavity NIR OLEDs as a function of viewing\nangle.\n7\n).u.a(\nytisnetni\nevitaleR\n1\n0\n0\n0\n0\n0\n.0\n.8\n.6\n.4\n.2\n.05\n0 0 5\n0\n1\n2\n3\n4\n5\n6\n7\n8\n5\n00000000\n0 6 0 0\nW a\n6\nv\n5\ne\n0\nle n g\n7\nth\n0 0\n( n m\n7\n)\n5 0 8 0 0 8 5 0\nModifications to the revised manuscript in lines 427–430 of the Result section for\nproviding the angular profile data.\nIn contrast, the cavity structure enhanced forward emission, achieving an angular distribution\ncloser to a Lambertian profile. A blue shift of the EL spectrum with increasing viewing angle\nwas observed in cavity NIR OLEDs, attributable to microcavity resonance that shifts the cavity\nmode toward shorter wavelengths with increased viewing angles (Supplementary Fig. 13).\n4. Comparison with commercial phototherapy devices\nPublicly available information on commercial devices (e.g., red‑light helmets and\nlaser‑based PBM systems) rarely includes beam width, angular distribution, or\nwavelength‑resolved irradiance at the tissue interface, which limits direct benchmarking.\nHowever, as elaborated in our responses to Reviewer 2 (Comments 10 and 14), compared\nwith commercially available devices and previously reported platforms, our textile-based NIR\nOLEDs systematically leverages both the PBM advantages and the platform‑level benefits for\nhair‑loss treatment.\nFurthermore, beyond validating optical delivery and demonstrating PBM efficacy, the\nprincipal qualitative advantage of the textile‑based system is its compatibility with a familiar\ndaily platform—a hat. Low‑level laser devices are commonly implemented as helmet‑type or\notherwise bulky systems that constrain where and how they can be used. By contrast, the\napproach proposed here can be applied to conventional caps and integrated into the hat\narchitecture. In addition, to demonstrate portability in a wearable textile‑based phototherapy\ndevice, we fabricated a prototype composed entirely of flexible components—a flexible\nbattery, an FPCB with an on/off switch and drive capability, and OLEDs—as shown in our\nResponse to Reviewer 3, Comment 1 (Supplementary Videos 4, 5).\nthe thoughtful integration of several established device technologies into a wearable\nphototherapy platform. Microcavity-tuned OLEDs, reflective Ag electrodes, textile\nsubstrates, and parylene encapsulation are all well-documented in prior OLED and\nwearable electronics literature. While the combination here is executed effectively and\ntailored to a biologically relevant spectral window, the manuscript would benefit from a\nclearer articulation of how this integration offers concrete advances over previously\nreported wearable PBM systems. For instance, prior studies on cage-type OLEDs and\nmicro-LED arrays have also addressed flexibility and form factor, albeit with different\napproaches and trade-offs.\nRESPONSE\nWe appreciate the reviewer’s comment and agree that the manuscript will benefit from a clearer\narticulation of how the proposed platform offers concrete advances over previously reported\nwearable PBM systems.\nPrior studies on micro-LED arrays and cage-type OLEDs have indeed addressed flexibility\nand form factor, but they remain limited by certain trade-offs. Micro-LED arrays have been\ndemonstrated on flexible platforms, but their fabrication process is complex, and the small light\nsources make them unsuitable for large-area uniform irradiation.1 Cage-type OLEDs have\nprimarily been used to validate the therapeutic effects of red OLEDs on alopecia, which is\nvaluable for demonstrating efficacy.2 However, they offer limited significance in terms of new\nplatform development, as the rigid platform restricts comfort and conformability, making them\nunsuitable for wearable devices (TableR.1).\nTableR.1 | Comparison of phototherapy devices reported in previous studies.\napplications, specifically across three key aspects: the light source, the wavelength, and the\nplatform.\n1. Advantages of OLEDs\nCompared with LEDs and lasers, OLEDs offer superior irradiance uniformity and design\nscalability. Because OLEDs are fabricated by mask-based vacuum deposition of organic layers,\nthe emission area and shape can be freely patterned (FigR.4). This allows fabrication of\ncustomized devices tailored to the geometry of alopecic scalp regions.\nFigR.4 | Textile-based NIR OLEDs with each scale.\n2. Advantages of NIR light (especially around 730 nm)\nNIR light is well recognized for its ability to penetrate deeply into skin without significant\nenergy loss. More importantly, PBM relies on wavelength-specific activation of cellular\nprocesses. From the perspective of alopecia treatment, NIR light, and specifically 730 nm, has\nbeen shown to outperform the red spectral range. Our previous work demonstrated that 730 nm\nlight stimulates dermal papilla cell proliferation.3 We further show that it effectively suppresses\ncellular senescence, thereby offering therapeutic advantages over conventional red-light PBM\napproaches in this study.\nOLEDs.\n3. Advantages of textile platform\nIntegration into a textile substrate enables use in hat-type devices, in contrast to adhesive\npatch systems. This form factor allows safe coverage over residual hair without direct adhesion\nto skin, enhancing both safety and user comfort. The device is lightweight, flexible, and can\nconform closely to the scalp. While textile-based phototherapy devices have been minimally\nexplored (with few exceptions such as neonatal jaundice or PPG monitoring),4,5 PBM\napplications have not yet been reported. Our work therefore introduces a new concept of textile-\nintegrated OLEDs for phototherapy, expanding the scope of wearable biomedical applications.\nOverall, these advances—uniform and customizable OLED emission, the biological\nadvantages of NIR light at 730 nm, and a textile-based platform optimized for practical,\ncomfortable wear—distinguish our system from previously reported wearable PBM devices.\nThe above content has been added to the revised manuscript.\nReferences\n[R1] Lee, H.E., Lee, S.H., Jeong, M., Shin, J.H., Ahn, Y., Kim, D., Oh, S.H., Yun, S.H. & Lee,\nK.J. ACS Nano, 12, 9587-9595 (2018).\n[R2] Sun, S.-Q., Shen, J.-J., Wang, Y.-F., Jiang, Y.-T., Chen, L.-F., Xin, H., Wang, J.-N., Shi,\nX.-B., Zhu, X.-Z., Sun, Q., Liao, L.-S., Chen, Q., Fung, M.-K. & Lee, S.-T. Nano Research,\n11\n16, 7164-7170 (2023).\n[R3] Cho, E. H., Choi, H.-R., Park, Y., Jeong, S. Y., Song, Y. J., Hwang, Y. H., Lee, J., Chi, Y.,\nWang, S.-F., Jeon, Y., Huh, C.-H. & Choi, K. C. ACS Appl. Mater. Interfaces 15, 57415–57426\n(2023).\n[R4] Choi, S., Jeon, Y., Kwon, J. H., Ihm, C., Kim, S. Y. & Choi, K. C. Adv. Sci. 9, 2204622\n(2022).\n[R5] Lee, H. S., Kong, S. U., Kwon, S., Cho, H.-E., Noh, B., Hwang, Y. H., Choi, S., Kim, D.,\nHan, J. H., Lee, T.-W., Jeon, Y. & Choi, K. C. ACS Nano 18, 20363–20379 (2024).\nModifications to the revised manuscript in lines 64–87 of the Introduction section\nMicro‑LED patches offer a more flexible form factor than rigid helmet or home‑use\nphototherapy systems and can improve conformity to skin. However, limitations arise from the\npatch architecture and the micro‑scale emitting area of individual sources. Because attachment\ntypically relies on skin adhesives, patches can inadvertently induce hair traction during\napplication and removal, which is a non‑trivial concern for patients with weakened hair follicle\nanchorage.10 Moreover, the pixelated point‑source nature of micro‑LEDs complicates scaling\nto large treatment areas and tends to produce non‑uniform irradiance with local hot spots,\nthereby limiting dose homogeneity across the scalp. Motivated by these constraints,\nOLED‑based phototherapy device has been suggested. Unlike conventional light sources for\nphototherapy device, such as LEDs and lasers, OLEDs offer a combination of ultra-thin,\nflexible form factors and uniform light emission. A OLED-based platform provides large,\nhomogeneous emission and have been reported to induce PBM relevant to hair‑loss\ntreatment.11 However, barriers to day‑to‑day wearability persist. The platform has been\ndesigned for helmet‑type configurations, paralleling commercial systems such as iRestore and\nLG Pra.L Medi Hair, and therefore do not fully exploit core OLED attributes—low mass, thin\nprofiles, and mechanical flexibility.\neffect depends on the target cell type and wavelength band. Recent studies indicate that human\ndermal papilla cells (hDPCs), which play a crucial role in hair regeneration,12 exhibit enhanced\nproliferation after exposure to near-infrared (NIR) irradiation compared with red light at the\nsame dose, providing the importance of selecting an optimal wavelength for effective\ntreatment.13,14\nReviewer #2: This paper presents the development and validation of a novel, fully wearable\nphototherapy system that integrates microcavity-tuned, top-emitting near-infrared (NIR)\nOLEDs into textiles, precisely engineered to match the activation spectrum of human dermal\npapilla cells (hDPCs) for non-invasive, effective hair regeneration via photobiomodulation\n(PBM), while addressing the limitations of conventional pharmacological and light-based\ntherapies for alopecia. Overall, this is an interesting work and can be recommended for\npublication in Nature Communications after major revision. The following are some\ncomments that might be helpful for further improvement of their manuscript to publish in\nfuture publications.\nRESPONSE\nWe are grateful for the reviewer’s careful assessment and insightful suggestions. These\ncomments provided a valuable opportunity to enhance the manuscript. Our responses to each\ncomment follow.\nReviewer’s comment 1) The paper claims tuning to match the action spectrum of hDPCs\nvia CCO activation. However, CCO’s absorption range is broad and varies across\nmitochondrial states. What is the justification for targeting 730 nm and 800 nm\nspecifically, and how do these correspond to CCO isoforms or ROS generation thresholds\nin vivo?\nRESPONSE\nWe appreciate the reviewer’s insightful comment regarding the broad absorption spectrum of\ncytochrome c oxidase (CCO). Indeed, CCO exhibits multiple absorption peaks, and the overall\nabsorption profile is influenced by the chromophores present in mitochondria, which vary\nbetween different cell types. As a result, the wavelength-dependent activation profile of cells\ndiffers according to cell type. Recognizing this, we tuned the emission of our textile-based\nOLEDs based on experimental data from Cho, Eun Hae, et al. ACS Applied Materials &\nInterfaces 15, 57415–57426 (2023), which had previously been obtained by our group.\n◼ Justification for selecting 730 nm\nTo make clear the reason for designing our NIR OLED at 730 nm, we have now included in\nFig.5d. This figure presents a direct comparison between the wavelength-dependent activation\nprofile of dermal papilla cells, as verified in our earlier studies, and the emission spectra of our\ncustomized and non-customized OLEDs. Both OLEDs were normalized to the same radiance\nfor this comparison.\ndependent penetration comparisons, an additional device with a main emission peak at\napproximately 800 nm was fabricated by adjusting the optical cavity. The 800 nm device was\nfabricated to demonstrate spectral tunability and to support penetration analysis, but it was not\nused in the in vitro assays focused on hDPC activation near 730–740 nm.\nThe in vitro experiments targeted dermal papilla cell activation, whose action spectrum\npeaks at 730–740 nm; therefore, under equivalent dose conditions, the 730–740 nm device\nprovides the most appropriate stimulus. In view of this spectrum, the 800 nm device is less\naligned with the activation peak than the 730–740 nm device. You can see the advantage of the\ncustomized NIR OLED in response to your Comment 8.\n1.0\n) %\nN\nu\nos\nn\nt\n-\no\ncm\nus\niz\nto\ne\nm\nd\ni\nN\nze\nIR\nd N\nO\nI\nL\nR\nE\nO\nD\nLED\n0.8\n) .u\n.a\n(\nle 140\n(\ny\nve\ntis\nl\nn o 130 0.6\nn\netn\nita i\nL\nv E\nitc 120 0.4\ne\na v\nlle ita\nC 110 le\n0.2 R\n100\n0.0\n450 500 550 600 650 700 750 800\nWavelength (nm)\nModified Fig. 5d | Overlap between the human dermal papilla cell action spectrum for\nproliferation13 and the EL spectra of the cavity NIR OLED and non-cavity NIR OLED under\nsame radiance\n◼ Correspondence to CCO Isoforms and ROS Generation Thresholds\nIn terms of ROS thresholds, PBM enhances mitochondrial output through the transient\nproduction of ROS as signaling molecules. This response follows a hormetic paradigm: low-\nto-moderate increases in ROS act as beneficial messengers, whereas excessive ROS can be\ndetrimental. The key is that PBM is delivered within safe irradiance and fluence ranges,\nensuring that ROS remain in a range that upregulates antioxidant defenses, growth factors, and\n15\nproliferative signals without exceeding cytotoxic thresholds1\nFigR.6 | hDPC proliferation versus illumination wavelength and exposure time (10–30\nmin), normalized to the non-irradiated control.2\nIn our previous research,2 we evaluated dermal papilla cell proliferation as a function of\nwavelength and exposure time. Under illumination at 730–740 nm, a 20 min exposure\nproduced a greater increase in proliferation than both 10 min and 30 min exposures,\ndemonstrating a biphasic dose–response (FigR.6). These findings were used to optimize the\nOLED emission wavelength and dose conditions.\nIn the present study, using the optimized regimen (730–740 nm for 20 min), we performed\nin vitro assays of cell migration and cellular senescence. In the senescence assay, the\ncustomized NIR OLED provided the lowest levels of senescence‑associated readouts among\nthe tested conditions.\nOur in vitro assays were performed under dose-matched conditions, with the irradiance\ndelivered to the cell medium standardized across OLED groups (see our response to your\nComment 3 for details). The experiments quantified wavelength-dependent changes in cellular\nactivation and highlighted the importance of wavelength tuning.\nConsistent with the reviewer’s point, tissue penetration in noninvasive phototherapy varies\nwith wavelength. Therefore, in vivo comparisons conducted under identical fluence constraints\nwould require wavelength-specific adjustment of OLED power density to achieve matched\n16\n)%(\nnoitarefilorp\nlleC\n1\n1\n1\n1\n1\n8\n6\n4\n2\n0\n8\n6\n0\n0\n0\n0\n0\n0\n1 0\n2 0\n3 0\ntr o\nm in\nm in\nm in\nl. 7 0\n*\n0\n* *\nn\n* *\nm\n* *\n7\n*\n3\n*\n0\n* *\nn\n*\nm\n*\n7\n*\n5\n* * *\n0 n\n* *\nm\n* *\n7 9\n*\n0\n* *\nn\n* *\nm\n* tissue-delivered dose. However, PBM is influenced by irradiation wavelength. Thus, the 730–\n740 nm device, which is aligned with the hDPC activation peak, could lead to greater cellular\nactivation than the 800 nm device under dose-matched conditions.\nReferences\n[R1] Chen, A. C.-H., Huang, Y.-Y., Sharma, S. K. & Hamblin, M. R. Photomed. Laser Surg.\n29, 383–389 (2011).\n[R2] Cho, E. H., Choi, H.-R., Park, Y., Jeong, S. Y., Song, Y. J., Hwang, Y. H., Lee, J., Chi, Y.,\nWang, S.-F., Jeon, Y., Huh, C.-H. & Choi, K. C. ACS Appl. Mater. Interfaces 15, 57415–57426\n(2023).\nModifications to the revised manuscript in lines 413–417 of the Result section to show\nwhy we used 800 nm device, clearly.\nTo assess the effects of OLED emission wavelength and angular distribution for non-invasive\nphototherapy, transdermal transmission was analyzed using four OLED device types, including\na cavity red OLED with a peak at 640 nm, a non-cavity and a cavity NIR OLED with peak at\naround 730-740 nm, and a cavity NIR OLED with peak at 800 nm (Supplementary Fig. 12).\nModifications to the revised manuscript in lines 439–446 of the Result section to describe\nbenefits of tuned OLED.\nAt normal emission, the band-integrated photon radiance within the region was approximately\n2.4 times greater for the cavity NIR OLED than for the non-cavity device. This tuning can\nprovide to greater photon delivery at the hDPCs activation peak near 730 nm, compared with\nthe non-cavity device, thereby enhancing photostimulation under equivalent dose condition, as\nshown in Figure 5d. An analysis relating hDPCs activation to the OLEDs’ optical properties\nis provided in the in vitro section.\nHowever, in vivo hair follicles reside within a 3D dermal environment and are exposed to\nvasculature, hormones, and other cell types. How do you account for the translational\ngap between 2D in vitro data and actual follicular behavior?\nRESPONSE\nWe thank the reviewer for raising the important issue of the translational gap between 2D in\nvitro assays and the complex in vivo follicular environment.\nIn this work, we employed in vitro assays to demonstrate that irradiation from our\ncustomized NIR OLED significantly reduced premature senescence in dermal papilla (DP)\ncells and maximized their anti-aging response. These assays offered a controlled setting in\nwhich OLED light directly interacted with DP cells without the influence of intervening tissue\nlayers. We fully recognize that the in vivo follicular niche is a three-dimensional system in\nwhich multiple intrinsic and extrinsic factors—including melanin, water content, vasculature,\nendocrine cues, and diverse neighboring cell types—modulate both light propagation and\nfollicular responses. We also note that DP cells naturally adopt a 3D spheroidal organization in\nvivo. Interventions that enhance DP cell activity in 2D culture, such as PBM, are expected to\nfurther potentiate follicle-inductive capacity when applied in more physiologically relevant 3D\nspheroid or organoid models, consistent with prior reports that three-dimensional\nreprogramming restores hair-inductive properties in human dermal papilla cells.1\nThus, although structural and microenvironmental differences exist between culture\nsystems, the beneficial effects observed in vitro are consistent with those obtained in more\nphysiologically relevant 3D or tissue-based models.\nTo further, we agree that translating in vitro effects to real skin is critical. However, previous\nresearches have provided bridging evidence to address the gap between in vitro and in vivo\ncontexts. For instance, in ex vivo human follicle culture, 650 nm red light enhanced follicle\nproliferation and delayed catagen progression, and clinically, LLLT devices significantly\nimproved scalp hair growth in androgenetic alopecia.2 These concordant findings suggest that\nmechanisms observed in vitro can translate to real follicles when adequate energy delivery is\nachieved. Furthermore, bridging studies show that improving DP cell health in vitro correlates\nwith better follicle performance in vivo: rejuvenating aged DP cells with exosomes reduced\nsenescence markers and restored inductive genes in vitro, and those treated cells enhanced hair-\nfollicle regeneration in patch assays,3 which are in vivo experiments performed in nude mice\n18\nto assess whether transplanted cells retain or regain their hair-inductive capacity.\nWe believe that such evidence reinforces that the anti-senescence activity of customized NIR\nOLED irradiation demonstrated in vitro has translational relevance in vivo.\nReferences\n[R1] Higgins, C.A., Chen, J.C., Cerise, J.E., Jahoda, C.A.B., & Christiano, A.M. PNAS, 110,\n19679–19688 (2013).\n[R2] Yang, K., Tang, Y., Ma, Y., Liu, Q., Huang, Y., Zhang, Y., Shi, X., Zhang, L., Zhang, Y.,\nWang, J., Zhu, Y., Liu, W., Tan, Y., Lin, J. & Wu, W. Annals of Dermatology, 33, 553–561\n(2021).\n[R3] Liu, F., Liu, S., Luo, X., Fan, Z., Huang, S., Deng, F., Liu, H., & Shi, G. Experimental\nDermatology, 32, 1646–1657 (2023).\ncavity NIR showed greater hDPC migration after 16 hours. How do they reconcile this\nobservation with their main claim of improved performance via cavity tuning? Could this\nbe related to angular distribution or unintended dose differences?\nRESPONSE\nWe appreciate the reviewer’s insightful comment. To address the possibility that the greater\nhDPC migration observed for the non‑cavity NIR OLED after 16 h might be attributable to\nangular emission or unintended dose differences, the in‑vitro irradiation geometry was\nreproduced identically in a Monte Carlo model and the energy delivered to the cell medium at\nthe receiving surface was quantified.\n◼ Monte Carlo Replication of the In Vitro Irradiation Geometry\nFigR.7 | Schematic of the in vitro experimental setup. a, Top view of the set-up. b, Cross-\nsectional side view of the setup.\nTo mimic the in vitro configuration, the irradiation geometry was reproduced in a Monte\nCarlo model, identical to our in vitro environment. In this model the OLED-to-cell plate\ndistance was approximately 15 mm, a transparent lid acted as an additional optical interface to\nprevent particulate contamination, and the well was filled with cell medium corresponding to\n~15 mm vertical distance from the lid to the medium surface. (FigR.7a, b)\nvitro test., b. Monte-Carlo simulation for in vitro test.\n◼ Angular-Resolved Dose Comparison Between Cavity and Non-Cavity OLEDs\nTo analyze the dose delivered to the cell medium at the receiving surface, the angular\nemission profiles of cavity and non‑cavity OLEDs were incorporated into the Monte Carlo\nframework (FigR.8). When the receiving surface was defined as the full well (diameter 35\nmm), contour mapping indicated a broader energy spread for the non‑cavity device (effective\nilluminated diameter ~6.0 mm, as shown in FigR.9a) relative to the cavity device (~4.5 mm,\nas shown in FigR.9b), consistent with the non‑cavity’s more diffuse, super‑Lambertian\nemission.\nHowever, the biological readout was restricted to an orthogonally aligned cell area. The\nemitting surface measured 8.3 × 8.3 mm², and the analyzed area of cell medium was same. In\nthis study, the analysis of cell activation following OLED irradiation was confined to cells\nlocated within this predefined orthogonal region. Under these conditions, the effective\nirradiance at the cell layer was 0.06 mW cm-2 (2% of the emitting‑surface radiant intensity,\n3mW cm-2), corresponding to a delivered energy of 0.052 J during 20 min of continuous\nirradiation (0.072 J cm-2).\nAs a result, the normal‑direction component of each OLED—whose emission wavelength\nwas customized by the microcavity—was dominantly delivered to the cells. The configuration\nshowed dose equivalence within the orthogonal region across device types.\nOLED source. b, Microcavity-tuned NIR OLED source.\n◼ Conclusion\nThe observed differences are therefore not attributed to unintended angular dose\ncontributions but are more likely due to short-term cellular responses that do not fully reflect\nthe advantages of cavity tuning. It is speculated that migration assays might be involved\nvariability, as scratches are produced manually, potentially introducing differences in wound\nwidth and uniformity.\nNevertheless, a substantial enhancement in migration was observed in the irradiated OLED\ngroups compared with the non-irradiated control group, indicating that light exposure exerted\na strong pro-activating effect under the stated conditions. Also, the cavity OLED was designed\nto enhance spectral alignment with the CCO absorption band and to deliver higher irradiance\nat the therapeutic wavelength. These benefits become more apparent in senescence\nsuppression. We have clarified this reason in the revised manuscript to avoid misinterpretation.\nFor each OLED, the emitting-surface radiance was set to around 10 W m-2 sr-1 for\ncontinuous irradiation during 20 minutes. Analysis of cell activation was limited to an\northogonally aligned square region, where the emitting surface measured 8.3 × 8.3 mm² and\nthe area matched the beam size of OLED (Supplementary Fig. 17b).\nTo verify the light dose delivered to the cell medium, a Monte Carlo simulation that\nreproduced the in vitro configuration was performed. Because dose delivery to away from\nemitting surface depends on the OLED angular emission profile, the receiving surface was\ndefined as the full well with a diameter of 35 mm. The simulation indicated an energy spread\nfor the non-cavity NIR OLED, with an effective illuminated diameter of approximately 6.0\nmm as shown in Supplementary Figure 17c. The cavity NIR OLED exhibited an effective\nilluminated diameter of approximately 4.5 mm (Supplementary Fig. 17d). This observation\nis consistent with the more diffuse super Lambertian emission of the non-cavity device.\nHowever, to ensure that in vitro outcomes were obtained from cells exposed to light, the\nanalysis area was fixed to match the beam size and aligned orthogonally to the OLED.\nUnder these conditions the effective irradiance at the cell medium was 0.06 mW cm⁻²,\nwhich is approximately 2% of the emitting surface power density of 3 mW cm⁻², and this\ncorresponded to a delivered irradiance of 0.072 J cm⁻² during 20 min of continuous exposure.\nThis configuration allowed to compare cellular responses under same dose to red versus NIR\nemission and to evaluate the impact of NIR spectral bandwidth.\ncontrol for accurate irradiance delivery over curved, irregular scalp surfaces? Are there\nactive or passive dosimetry mechanisms built into the textile?\nRESPONSE\nWe appreciate the reviewer’s thoughtful comment on the potential role of passive dosimetry\nmechanisms. Such functionality would indeed be highly valuable for wearable systems;\nhowever, the current textile OLED platform does not incorporate embedded passive dosimetry\nfeatures.\nAs you know, cavity OLEDs inherently exhibit angle-dependent emission characteristics.\nWhen applied to curved scalp surfaces, this angular dispersion may lead to minor spectral shifts\nsuch that slightly different wavelength components reach the tissue depending on local\ngeometry. We believe that the wearable textile design itself provides a mitigating factor, as the\ndevice is highly flexible and enables closing to the scalp via a hat platform without the need\nfor adhesive materials, thereby reducing air gaps and maintaining close contact with the tissue.\nThis intimate skin conformity was a central aspect of our design strategy for textile-based\nphotonic devices.\nWe acknowledge that angular-dependent spectral variation remains a limitation of\nmicrocavity OLEDs (Supplementary Fig. 12). Since our study identified 730 nm as the most\neffective wavelength for follicular activation, maintaining this peak across all emission angles\nis essential. In the field of phototherapy, cellular activation strongly depends on wavelength;\ntherefore, ensuring spectral stability is particularly important. However, we believe that the\nlimitation of cavity OLEDs could be addressed by integrating a scattering layer (SL) in\nfollowing research.\n24\n1.0\n0.8\n0.6\n0.4\n0.2\n0.0\n500 550 600 650 700 750 800 850\nSupplementary Fig. 13| Emission spectra of cavity NIR OLEDs as a function of viewing\nangle.\nShin et al. had shown that introducing SL can reduce angle-dependent spectral shift. Shin et\nal. reported that an OLED without the SL exhibited a spectral shift of more than 30 nm between\n0° and 60°, whereas the SL-equipped OLED reduced this shift to below ~10 nm.1 In addition,\nKeum et al. showed that applying RIE treatment to the upper Parylene-C layer can increase\nscattering without damaging a OLEDs, effectively preventing the blue shift of the emission\npeak with viewing angle.2\nThus, incorporation of scattering technology into our wearable phototherapy device could\nenable angle-independent emission centered at 730 nm, thereby ensuring consistent delivery\nof the most effective therapeutic wavelength to hair follicles. To date, such studies have\nprimarily been conducted in the visible spectral range; however, applying the same concept to\nNIR OLEDs is expected to similarly suppress angular-dependent spectral shifts, ensuring stable\nemission at therapeutic wavelengths.\nReferences\n[R1] Shin, J.-W., Cho, D.-H., Moon, J., Joo, C. W., Lee, J., Huh, J. W., Park, S. K., Han, J.-H.,\nCho, N. S., Hwang, J., Chu, H. Y., Lee J.-I. Opt. Lett. 39, 3527–3530 (2014).\n[R2] Keum, C., Murawski, C., Archer, E., Kwon, S., Mischok, A., Gather, M. C. Nat. Commun.\n11, 6250 (2020).\n25\n).u.a(\nytisnetni\nevitaleR\n0\n10\n20\n30\n40\n50\n60\n70\nReviewer’s comment 5) The study attributes effects to CCO activation and ROS\nsignaling, but presents no direct biochemical validation (e.g., ROS quantification,\nantioxidant gene expression, or ATP production levels). Why was no such mechanistic\nvalidation performed?\nRESPONSE\nWe acknowledge the reviewer’s concern regarding the absence of direct biochemical validation\nfor the proposed CCO/ROS mechanism. The study was designed to prioritize phenotypic\noutcomes of customized OLED exposure on cellular senescence, interpreting the results within\nestablished photobiological frameworks rather than performing direct ROS or ATP assays.\n◼ ROS hormesis and attenuation of senescence via CCO activation\nA “Goldilocks” range of ROS—neither too low nor excessive—has been shown to activate\nadaptive stress‑response pathways (mitohormesis).1 In this context, CCO stimulation by the\ncustomized OLED is posited to generate moderate ROS that function as signaling mediators to\nupregulate protective programs. Contemporary models of aging indicate that mild ROS\nelevations induce antioxidant defenses and other pro‑survival pathways, thereby limiting\nsenescence and supporting cellular fitness. Consistent with this view, beneficial ROS signaling\nis understood to engage redox‑sensitive regulators (e.g., Nrf2 and related factors), augmenting\nDNA repair capacity, antioxidant enzyme expression, and mitochondrial quality control, with\nnet delay of cellular aging.2\n◼ Custom OLED spectrum, CCO activation, and non‑damaging ROS signaling\nThe OLED emission spectrum was tuned to coincide with known CCO absorption features,\nthereby enhancing enzymatic activity. Prior PBM studies reported that specific red/NIR\nwavelengths are absorbed by CCO chromophores, elevating electron‑transport activity and,\nconsequently, mitochondrial ROS production as a signaling cue.3\nWe agree that additional biochemical assays would further refine the mechanism. However,\ngiven the established link between cellular activation and ROS production, emphasis was\nplaced on the resultant senescence phenotype rather than intermediate measurements.\nReferences\n[R1] Shields, H. J., Traa, A., & Van Raamsdonk, J. M. Frontiers in cell and developmental\nbiology, 9, 628157 (2021).\n[R2] Heo, J. C., Park, J. A., Kim, D. K., & Lee, J. H. Scientific reports, 9, 10114 (2019).\n26\n[R3] Cardoso, F. D. S., Barrett, D. W., Wade, Z., Gomes da Silva, S., & Gonzalez-Lima, F.\nFrontiers in neuroscience, 16, 818005 (2022).\nReviewer’s comment 6) The pigskin model is useful, but did the authors perform Monte\nCarlo simulations or tissue-mimicking phantoms to more precisely model photon\ndistribution to the follicle base (~3 mm)? 12% transmission is relative—how much actual\nphoton energy reaches target biological chromophores?\nRESPONSE\nWe sincerely appreciate the reviewer’s insightful comment. To complement the pigskin\ntransmission measurements with a more evaluation, Monte Carlo simulations were performed\nto approximate photon distribution within skin and to assess energy delivery toward the follicle\nbase (3 mm ~).\n◼ Monte-carlo simulation of photon transport in a skin model\nSupplementary Fig. 14 | Monte Carlo simulation of photon transport and depth-dependent power\ndensity distribution. a, Monte Carlo simulation setup. An OLED (8.3 × 8.3 mm²) was placed on the\nskin surface. b, Depth-dependent relative intensity. Grey indicates the maximum power density within\nthe receiver plane, and red indicates the area-averaged power density.\nIn this model, the epidermis, dermis, and subcutaneous fat layers were defined with layer-\nspecific refractive indices scattering coefficients (µ ), and anisotropy factors (g), all set as\ns\nwavelength-dependent values from the literature.1 The OLED emission source was defined as\nan 8.3 × 8.3 mm² square emitter, placed in direct contact with the epidermal surface. To avoid\nedge artefacts, the simulated skin area was chosen to be larger than the emitting area\n27\n(Supplementary Fig. 14a). Planar receivers were placed orthogonally beneath the epidermal\nsurface at depths of 1–5 mm at 0.5 mm intervals (8.3 × 8.3 mm², same with emitting area). At\neach plane, the irradiance was tallied and normalized to the input, enabling relative intensity\nanalysis across depths. The ratio of receiving‑surface irradiance to the emitting‑surface\nirradiance was quantified as 4.3% at 3.0 mm, 1.4% at 4.0 mm, and 0.5% at 5.0 mm, indicating\nthat sufficient photon energy can still be delivered to the follicular niche (~3 mm) to support\ncellular activation despite strong attenuation (Supplementary Fig. 14b). In addition, contour\nmaps revealed progressive lateral broadening with increasing depth due to multiple scattering;\nnevertheless, dose delivery remained predominantly concentrated along the axis orthogonal to\nthe OLED emitting area (Fig R. 10).\nFig R. 10 | Contour maps of irradiance at receiver planes located 1.0–5.0 mm beneath the\nepidermal surface\n◼ Explaining the discrepancy between pigskin transmission and the simulation\nTwo experimental factors are considered to account for the higher transmission observed in\npigskin (~12%) relative to the simulation (~4.3%). First, the pigskin samples were desiccated\nprior to measurement, which reduced water-mediated absorption. Second, only the epidermis–\ndermis slab was used (i.e., no subcutaneous fat layer), eliminating an additional refractive-\nindex boundary and a layer that would otherwise contribute to internal reflection and multiple\nscattering. These differences show the reason of high measured transmission level relative to\nthe multilayer Monte Carlo simulation based on real skin model.\n◼ Conclusion\nNotably, our in vitro measurements showed an emission‑to‑reception power ratio of\napproximately 2%. Despite the modest dose (0.052 J, corresponding to 0.043 mW for 20 min),\nwe observed clear enhancements in dermal papilla cell migration and anti‑senescence\nresponses (see our response to your Comment 3). Consistent with these data, the simulations\nindicate that a NIR OLED in direct skin contact can deliver sufficient photon energy to the\nfollicular niche to stimulate dermal papilla cell activation.\n[R1] Shimojo, Y., Nishimura, T., Hazama, H., Ozawa, T., & Awazu, K. Journal of biomedical\noptics, 25, 045002-045002 (2020).\nModifications to the revised manuscript in lines 463–479 of the Result section for\nincluding simulation results.\nTo validate transmittance of the NIR OLED light in real skin, Monte Carlo simulations\nwere performed to measure photon delivery from a skin conformal wearable near infrared\nOLED to the hair follicle region. In this model, the epidermis, dermis, and subcutaneous fat\nlayers were defined with layer-specific refractive indices scattering coefficients (µ ), and\ns\nanisotropy factors (g), all set as wavelength-dependent values from the literature.32 The\nemission source was set an 8.3 × 8.3 mm² square that was placed in direct contact with the\nepidermal surface (Supplementary Fig.15a). Planar receivers were positioned normal to the\nsurface at depths from 1.0 mm to 5.0 mm. The ratio of receiving surface irradiance to power\ndensity of emitting surface was 4.3% at 3.0 mm, 1.4% at 4.0 mm, and 0.5% at 5.0 mm\n(Supplementary Fig.15b).\nSimulated transmission was lower than the measured value in porcine skin. The difference\nwas attributed to two features of the experimental setup. The skin was dried before\nmeasurement, which reduced absorption by water. In addition, the samples consisted only of\nepidermis and dermis, whereas the model included epidermis, dermis, and subcutaneous fat.\nHowever, the receiving ratio at depths of 3 to 4 mm was similar to that in our in vitro setup,\nwhich showed a PBM effect under OLED irradiation as described in the below section.\nbetween parylene-C and human skin affects photon loss via internal reflection or\nscattering? Could this be mitigated with intermediate index-matching layers?\nRESPONSE\nWe appreciate the reviewer’s insightful comment regarding refractive index mismatch at the\ndevice–tissue interface. Indeed, differences in refractive index can introduce photon loss\nthrough reflection and scattering, and this is an important factor to consider in wearable\nphotonic systems. Accordingly, the magnitude of photon loss arising from the refractive-index\nmismatch was quantified using the Fresnel reflection equation.\n◼ Fresnel analysis of refractive index mismatch and photon loss\nAt the air–skin interface, photon loss can be estimated using the Fresnel reflection formula:\nwhere n and n are the refractive indices of the two adjacent media. For air (n=1) in contact\n1 2\nwith epidermis of skin (n≈1.44), the reflection at normal incidence is:\n1.00−1.44\nR = ( )2 ≈ 0.033,(3.3 %)\n𝑎𝑖𝑟−𝑠𝑘𝑖𝑛 1.00+1.44\nConsidering the refractive-index mismatch at the air–skin boundary, Fresnel reflection is\nexpected to contribute only a modest loss at normal incidence. In the NIR region, taking the\nskin refractive index as n≈1.44,1 the normal‑incidence Fresnel reflection at the air–skin\ninterface is 3.3%. This represents a modest reduction, and the effect is considered relatively\nminor in the context of overall light delivery to the tissue. Consequently, while an air gap does\nintroduce inevitable reflection loss, its contribution to the overall transmission is relatively\nsmall and does not significantly compromise photon delivery to the follicular region.\n◼ Potential role and limitations of index-matching layers\nIntroducing an intermediate layer with a refractive index close to skin (n≈1.4–1.5) between\nparylene-C and tissue could reduce internal reflection within the OLED stack and improve light\noutcoupling.\nCase 1 — w/o index-matching layer: parylene-C (1.65) ~ air (1.00) ~ skin (1.44)\n1.65−1\nR = ( )2 ≈ 0.0602,(6.02 %)\n𝑝𝑎𝑟𝑦𝑙𝑒𝑛𝑒−𝐶~𝑎𝑖𝑟 1.65+1\n30\n1.00−1.44\nR = ( )2 ≈ 0.033,(3.3 %)\n𝑎𝑖𝑟~𝑠𝑘𝑖𝑛 1.00+1.44\nUnder the assumption that multiple reflections in the intermediate region are incoherent, the\ntotal reflectance (R ) can be computed using the following expressions:\ntotal\n0.033\nR = (0.0602)2 + (1−0.0602)2 ≈ 0.089,(8.9 %)\ntotal 1−0.0602×0.033\nCase 2 — with an index‑matching layer: parylene‑C (n = 1.65) ~ index‑matching polymer\n(n ≈ 1.5) ~ skin (n = 1.44)\n1.65−1.5\nR = ( )2 ≈ 0.0023,(0.23 %)\n𝑝𝑎𝑟𝑦𝑙𝑒𝑛𝑒−𝐶~𝑖𝑛𝑑𝑒𝑥−𝑚𝑎𝑡𝑐ℎ𝑖𝑛𝑔 1.65+1.5\n1.5−1.44\nR = ( )2 ≈ 0.0042,(0.042 %)\n𝑎𝑖𝑟~𝑠𝑘𝑖𝑛 1.5+1.44\nSo, R is:\ntotal\n0.0042\nR = (0.0023)2 + (1−0.0023)2 ≈ 0.004,(0.4 %)\ntotal 1−0.0023×0.0042\nIf a fully adhesive, index‑matching layer were applied to eliminate any air gap between the\ndevice and skin—so that the interface transitions as parylene-C (n≈1.65) → intermediate layer\n(n≈1.5) → skin (n≈1.44)—the interfacial Fresnel loss would fall to <0.5%, yielding highly\nefficient photon delivery. Nevertheless, this design brings a trade‑off: such adhesive layers may\npull or damage residual hair upon device removal, limiting practicality in wearable applications.\nIn summary, an air gap at the device–skin interface introduces photon loss. Nevertheless,\nFresnel analysis indicates that, at normal incidence, this loss is limited to approximately 3–4%\nand is therefore minor. Although additional index‑matching interlayers could further reduce\nthe loss, the risk of residual hair damage imposes significant constraints for users. Accordingly,\nour device is expected to enable non‑invasive delivery of photons to the follicular region with\nminimal interfacial losses.\n[R1] Ding, H., Lu, J. Q., Wooden, W. A., Kragel, P. J., & Hu, X. H. Physics in Medicine &\nBiology, 51, 1479 (2006).\nReviewer’s comment 8) Your microcavity devices show ~40 nm FWHM. Some studies\nsuggest broader bandwidths (~100 nm) can stimulate a wider range of cellular\nphotoreceptors. Could overly narrow spectral targeting reduce holistic tissue activation?\nRESPONSE\nWe appreciate the reviewer’s insightful question. Our view is that, for PBM in which\nmitochondrial CCO dominates the response, spectral precision that concentrates photons\nwithin the CCO‑effective window is advantageous over broadband emission that spreads\npower across less responsive wavelengths.\n◼ PBM effect follows cell activation spectrum\nPBM efficacy depends on how many photons are absorbed by relevant chromophores, not\non total radiant power alone. In practical terms, the relevant figure of merit is the spectral\nphoton flux density delivered to tissue and its overlap with the cellular action spectrum.\nThe cellular action spectrum is wavelength‑dependent, so concentrating photons near its\npeak increases the biological response. Under same irradiance and dose conditions, a spectrum\nthat places more photons where absorption is highest yields a larger cellular response. A ~100\nnm broadband source distributes the same total power over a wider span, reducing photon\ndensity in the optimal wavelength region (around 730 nm). By contrast, a customized OLED\nwith a ~40 nm FWHM spectrum centered in the CCO‑mediated cellular action‑spectrum region\nincreases photon density at the wavelengths most relevant for mitochondrial activation while\nkeeping the total dose unchanged (FigR.11a). Notably, the non‑customized and customized\nOLEDs had nearly identical peak wavelengths at ~730 nm, but the spectral peak intensity\n(photon density) at 730 nm was ~2.5× higher for the customized microcavity device.\naction spectrum for proliferation with the EL spectra of the cavity OLED (red and NIR) non-cavity\nOLED (NIR) under same radiance. b, Cellular senescence after irradiation with each OLED at same\ndose.\nIn fact, our in vitro data support 730 nm targeting. In our assays, DP cells exhibited the\nstrongest activation after irradiation with the cavity NIR OLED, with the most pronounced\nanti‑senescence effects, when compared to the red and non‑customized OLED spectra under\nmatched total irradiance and dose (FigR.11b). Moreover, PBM efficacy followed the order Red\n< non‑cavity NIR < cavity NIR, in agreement with the cell‑activation profile. Thus, the greater\nphoton flux delivered at the CCO‑effective peak explains the amplified cellular response in the\ncustomized condition.\n◼ Influence of narrow spectral bandwidth to cell activation\nPBM is associated with CCO activation. CCO contains metalloprotein centers (CuA, heme\na, heme b) with distinct activation wavelengths. Comprehensive activation of CCO therefore\nrequires stimulation that encompasses the entire complex.2,3 A narrow‑band spectrum may\nselectively excite only certain components and thus may be insufficient to induce overall CCO\nactivation, potentially reducing PBM effects.\nPBM efficacy has not been researched by narrowing FWHM while maintaining an identical\npeak wavelength. Thus, we think additional investigation is required to evaluate this parameter.\n[R1] Ding, H., Lu, J. Q., Wooden, W. A., Kragel, P. J., & Hu, X. H. Physics in Medicine &\nBiology, 51, 1479 (2006).\n[R2] Karu, T. I., & Kolyakov, S. F. Photomedicine and Laser Therapy, 23, 355-361 (2005).\n[R3] Hamza, I., & Gitlin, J. D. Journal of bioenergetics and biomembranes,34, 381-388 (2002).\nModifications to the revised manuscript in lines 443–450 of the Results section.\nAt normal emission, the band-integrated photon radiance within the region was approximately\n2.4 times greater for the cavity NIR OLED than for the non-cavity device. This tuning can\nprovide to greater photon delivery at the hDPCs activation peak near 730 nm, compared with\nthe non-cavity device, thereby enhancing photostimulation under equivalent dose condition, as\nshown in Figure 5d. An analysis relating hDPCs activation to the OLEDs’ optical properties\nis provided in the in vitro section.\nETL-tuned ones, did you quantify trade-offs in carrier balance, recombination zone\nposition, or angular intensity losses at oblique angles? How does the angular spectral\nstability compare under real-world usage conditions?\nRESPONSE\nWe appreciate the reviewer’s interest in our work. As noted by the reviewer, carrier balance,\nrecombination‑zone (RZ) position, and angular intensity are important parameters in OLED\ndevelopment. Trade‑offs were quantified by comparing operational lifetime and the\nangle‑resolved intensity profile. Two device sets with an identical optical cavity length were\nfabricated; only the distribution of the organic thickness was varied to realize HTL‑tuned and\nETL‑tuned stacks (FigR.12a).\n◼ Trade-offs in each parameter of OLEDs\nTo assess carrier balance and RZ position, operational lifetime was measured under\ncontinuous constant‑current drive with matched initial radiance across all devices. A faster\nradiance decay was observed for ETL‑tuned devices than for HTL‑tuned devices (FigR.12b).\nThis trend is consistent with carrier imbalance and an RZ pinned near the EML/ETL interface\nin the ETL‑tuned case, which can increase interfacial non‑radiative loss. Considering the\nmobility asymmetry—hole transport in typical HTLs exceeding electron transport in ETLs—\nplacing the additional thickness on the HTL side rebalanced the carrier fluxes,1 broadened and\ncentered the RZ within the EML, and was associated with improved operational stability under\nidentical optical loading.\nFigR.12 | Comparison of HTL-tuned and ETL-tuned microcavity OLEDs at identical cavity\nlength. a, Schematic of the architecture in which the total optical cavity length is held constant while\nthe organic thickness is allocated on the HTL-tuned or the ETL side. b, Operational lifetime measured\nunder continuous, constant-current drive at a matched initial radiant intensity. c, Angle-resolved radiant-\nintensity profiles.\nsteeper decrease in intensity at oblique angles was observed for ETL‑tuned microcavities,\nparticularly beyond ~40–50° (FigR.12c). When the RZ is located closer to the EML/ETL\ninterface, the effective optical path to the output mirror (thin Ag cathode) is increased and the\nangle‑dependent cavity phase is strengthened, owing to the cavity phase being proportional to\nthe distance between the output electrode and the RZ. These effects are consistent with\nmicrocavity interference theory and are accounted for the larger decrease in intensity at oblique\nangles. Additionally, a longer optical path results in greater absorption, thereby reducing the\nlight intensity.\nTherefore, in HTL‑tuned devices, an RZ located closer to the output mirror mitigates these\neffects, thereby reducing internal optical losses and enabling stronger light emission.\n◼ Angular spectral stability under real-world usage conditions\nCustomized NIR OLED (HTL-tuned) in this study were observed to exhibit a decrease in\nintensity with viewing angle; however, the angular distribution remained close to Lambertian.\nIn contrast to laser emission, which occurs predominantly along the surface normal, the near-\nLambertian emission of OLEDs is advantageous for non-invasive phototherapy in the\nfollowing respects.\n① Dose uniformity under misalignment and motion\nA broadly distributed angular profile tends to support more uniform fluence on curved tissue\nwhen the emitter is tilted or laterally displaced. Sensitivity to pointing error is reduced relative\nto directional sources, which can improve repeatability across sessions in wearable use.\n② Mitigation of hot spots and thermal load\nThe absence of narrow angular lobes lowers the likelihood of localized over-irradiance and\nassociated surface heating, facilitating compliance with exposure limits at a given average\ndose.\n③ Robustness to air-gap and standoff variations\nFor near-Lambertian fields, attenuation of dose with increasing emitter–tissue distance is\ngradual, maintaining useful fluence across 0–5 mm air gaps that are typical of textile wearables,\nwhereas narrow-beam sources often show a steeper on-axis decrease at small tilts.\nTo compare the two tuning strategies, the optical cavity length was maintained constant by\napplying an identical thickness increment to either the HTL or ETL. In the HTL-tuned OLED,\nthe NPB layer was increased by 37 nm relative to the conventional recipe, which adjusted the\noptical path and positioned the main EL peak at 730 nm. Using this optimized condition as a\nreference, the ETL-tuned OLED was fabricated by extending the TPBi layer by the same\n37 nm, thereby preserving an equivalent cavity length across both configurations.\nModifications to the revised manuscript in lines 280–285 of the Results section.\nBecause hole transport in NPB exceeds electron transport in TPBi, adjustment of the NPB\nthickness, in part owing to the carrier mobility imbalance,27 positioned the recombination zone\nmore effectively within the emissive layer, to reduce the proportion of non-radiative interfacial\nexciplex. In fact, the HTL-tuned OLED exhibited slightly improved operational lifetime\ncompared with the ETL-tuned device (Supplementary Fig. 4b).\nReference\n[R1] Rhee, S. H., Nam, K.b., Kim, C. S., Song, M., Cho, W., Jin, S. H., & Ryu, S. Y. ECS Solid\nState Letters, 3, R19 (2014).\ntextile-integrated NIR OLED system compared to conventional phototherapy methods.\nHowever, there is no quantitative benchmarking against existing commercial or clinically\nvalidated devices (e.g., LLLT helmets like iRestore, HairMax, or LG Pra.L Medi Hair).\nCan the authors provide a controlled, side-by-side comparison of their device’s\ntherapeutic outcomes — such as hDPC migration rates, senescence reduction, and\ntransdermal photon flux — relative to these established devices under matched\nirradiance and exposure conditions? Without such benchmarking, how can superiority\nover current clinical standards be substantiated?\"\nRESPONSE\nWe thank the reviewer for the insightful comment. A head‑to‑head clinical comparison against\nspecific commercial systems was difficult to perform in this study because key device‑level\nspecifications are not publicly disclosed, operating conditions differ across products, and PBM\nefficacy evaluation models differ across studies, making precise comparative analysis difficult.\n◼ PBM advantages\nHowever, to demonstrate the superior PBM efficiency of the customized NIR OLED in this\nstudy, experiments were conducted with the same type of light source, the same distance\nbetween the cell culture and each OLED, the same emitting‑area size, the same exposure time,\nthe same surface irradiance on the cell medium, and the same total dose; the independent\nvariables were limited to (i) the central wavelength and (ii) the full width at half maximum\n(FWHM). Within this framework, a red band representative of commercial LLLT devices such\nas iRestore, HairMax, and LG Pra.L Medi Hair was compared with near‑infrared emissions,\nincluding a cavity‑tuned spectrum centered at 730–740 nm and broader non‑cavity NIR bands.\nUnder matched irradiance, human dermal papilla cells (hDPCs) exhibited photostimulation\nacross the red–NIR range, and the cavity‑tuned 730–740 nm spectrum yielded the greatest\nactivation at the same dose, consistent with alignment with the hDPC activation spectrum.\n◼ Wearable design advantages\nAs summarized in the TableR.2, commercial low‑level light therapy devices such as\niRestore, HairMax, and LG Pra.L Medi Hair adopt rigid helmet or hair‑band form factors\npopulated with discrete LEDs/lasers whose emitting areas are typically reported at the device\nlevel but not at the source level (often in the tens of micrometres for individual laser apertures).\nThese architectures concentrate light into sparse beam spots across the scalp and require a hard\nshell to maintain source positioning, which constrains comfort, conformability, and uniformity\nduring use. In contrast, the presented textile‑based NIR OLED integrates a contiguous,\n38\nmillimetre‑scale emitting area directly onto a flexible polyester textile and is demonstrated in\na hat‑type platform. This configuration enables continuous, areal emission that conforms to\nscalp curvature, reduces local hot‑spotting, and improves irradiance uniformity across targeted\nregions.\nTableR.2 | Comparison of commercial phototherapy devices for hair loss treatment.\nFurthermore, from a wearable‑use perspective, the textile form factor offers additional\ndesign advantages. First, flexibility of the emissive substrate and interconnects allows natural\ndeformation during donning, doffing, and head movement without disrupting optical\nalignment. Second, the platform is not restricted to a rigid shell; integration in hat‑type\ngarments permit unobtrusive, day‑to‑day wear and supports use beyond home settings. Finally,\nthe areal‑emission modality of the OLED could be supported scalable coverage by tiling pixels\nover large regions. These suggest that the textile‑integrated NIR OLED platform can be offered\nwearable‑design advantages over commercial devices.\n[R1] Kim, H., Choi, J. W., Kim, J. Y., Shin, J. W., Lee, S. J. & Huh, C. H. Dermatol. Surg. 39,\n1177–1183 (2013).\n[R2] Leavitt, M., Charles, G., Heyman, E. & Michaels, D. Clin. Drug Investig. 29, 283–292\n(2009).\n[R3] Kim, J. W., Kwon, Y. S., Chang, Y. Y., Hong, S. H., Shin, J. W., Na, J. I. & Huh, C. H.\nMedical Lasers: Engineering, Basic Research, and Clinical Application 9, 150–158 (2020).\nModifications to the revised manuscript in lines 64–87 of the Introduction section\nMicro‑LED patches offer a more flexible form factor than rigid helmet or home‑use\nphototherapy systems and can improve conformity to skin. However, limitations arise from the\npatch architecture and the micro‑scale emitting area of individual sources. Because attachment\ntypically relies on skin adhesives, patches can inadvertently induce hair traction during\napplication and removal, which is a non‑trivial concern for patients with weakened hair follicle\nanchorage.10 Moreover, the pixelated point‑source nature of micro‑LEDs complicates scaling\nto large treatment areas and tends to produce non‑uniform irradiance with local hot spots,\nthereby limiting dose homogeneity across the scalp. Motivated by these constraints,\nOLED‑based phototherapy device has been suggested. Unlike conventional light sources for\nphototherapy device, such as LEDs and lasers, OLEDs offer a combination of ultra-thin,\nflexible form factors and uniform light emission. A OLED-based platform provides large,\nhomogeneous emission and have been reported to induce PBM relevant to hair‑loss\ntreatment.11 However, barriers to day‑to‑day wearability persist. The platform has been\ndesigned for helmet‑type configurations, paralleling commercial systems such as iRestore and\nLG Pra.L Medi Hair, and therefore do not fully exploit core OLED attributes—low mass, thin\nprofiles, and mechanical flexibility.\neffect depends on the target cell type and wavelength band. Recent studies indicate that human\ndermal papilla cells (hDPCs), which play a crucial role in hair regeneration,12 exhibit enhanced\nproliferation after exposure to near-infrared (NIR) irradiation compared with red light at the\nsame dose, providing the importance of selecting an optimal wavelength for effective\ntreatment.13,14\nvoltage gradients on large substrates. How do you ensure homogeneity of brightness\nacross a large, curved textile interface?\nRESPONSE\nThank you for the insightful comment. For phototherapy OLEDs, device-level luminance\nuniformity is critical because dosing requires consistent irradiance at the specific therapeutic\nwavelength. We achieve uniformity on the textile platform by (i) applying a CVD-deposited\nplanarization layer formed on glass and transferred to the textile, and (ii) avoiding a single large\nlight source in favor of around 10 mm beam, which consider a balance between skin-\npenetration depth and OLED stability.\n◼ Overcoming a roughness of textile through additional planarization layer.\nA planarization film based on parylene-C was deposited by CVD onto a glass carrier and\nthen transferred onto the textile. Owing to the high step coverage of CVD, the planarization\nfilm replicated the smoothness of the glass rather than the weave‑induced height variations of\nthe textile.1 In the absence of a planarization layer, OLED deposition followed the inherent\nroughness of the textile (FigR.13a, b), and the resulting devices could not be electrically\ndriven. After introducing the planarization layer, the textile roughness was significantly\nmitigated, and the subsequently deposited OLED no longer conformed to the underlying\ntexture (FigR.13c, d).\nFigR.13| Parylene-C planarization to compensate textile roughness. a, Optical microscopy (OM)\nimage of the textile surface before planarization. b, OM image of an OLED deposited on a non-\nplanarized textile. c, Surface image of the textile after parylene-C planarization. d, OM image of an\n◼ Avoiding large‑area gradients of OLED based on trade-off between beam width\nand OLEDs stability.\nLuminance uniformity issues—often arising from organic-layer deposition non‑uniformity\nand, in cavity OLEDs, from resonance‑wavelength shifts with electrode and organic‑layer\nthickness—are intrinsic to large‑area OLEDs, even on rigid glass. This issue is not specific to\ntextile platforms. In addition, excessively large emitting areas exacerbate lateral voltage drop\nand thermal stress, thereby accelerating OLED degradation. However, in our application, this\ndoes not impose a practical limitation.\nTypically, penetration depth is primarily related to the light wavelength, but it is also\ninfluenced by the beam size. For non‑invasive phototherapy devices, skin penetration of light\nwas observed to saturate when the beam width exceeded ~10 mm, and this saturation effect\npersisted up to approximately 40 mm, so further increases in beam size provide no additional\nbenefit.2 Accordingly, we fabricated and evaluated a single‑pixel OLED with an emitting\naperture of 8.3 mm × 8.3 mm (beam size ~10 mm). Sample‑to‑sample spectral variation was\nminimal (main peak within ~5 nm), indicating negligible organic‑layer thickness differences\nand consistent electro‑optical behavior.\nOn this basis, if a textile device were to array these pixels, it would preserve optical\nuniformity and maintain non‑invasive skin penetration, enabling efficient phototherapy.\nFurthermore, by limiting the emitting area to such pixel dimensions, localized degradation\narising from thermal stress in large‑area OLEDs can be mitigated, thereby preventing lifetime\nreduction.\nReferences\n[R1] Cho, H. E., Kim, M. J., Chang, J., An, J., Na, Y., Choi, S., Jeong, S. Y., & Choi, K. C. npj\nflexible electronics, 9, 36 (2025).\n[R2] Ash, C., Dubec, M., Donne, K., & Bashford, T. Lasers in medical science, 32, 1909-1918\n(2017).\nEQE, FWHM, and turn-on voltage across batches? What is the coefficient of variation in\nperformance across 10+ fabricated devices?\nRESPONSE\nWe appreciate the reviewer’s comment regarding the reliability of our dataset. To evaluate the\nvariation of each OLEDs depending on the capping layer, device-to-device variability was\nquantified by fabricating and characterizing 10 OLEDs.\nThe variation was computed for electrical metrics (EQE and radiance) and for optical metrics\n(EL peak wavelength and FWHM). Because visual sensitivity is minimal in the NIR, luminance\nwas not adopted as a primary figure of merit; radiance was analyzed instead (FigR.14). As\nshown in Figure 3 of the main text, the performance enhancement induced by deposition of\nthe capping (encapsulation) layer—comprising inorganic and organic sublayers—was verified\nthrough batch-to-batch comparison.\nFigR.14 | Batch-to-batch performance metrics of the NIR OLEDs a, Schematic of the emitting-side\n(top-emitting) device stack. b, EL spectra of individual devices driven at a same voltage. c, Current-\ndensity–voltage–radiance (J–V–R) characteristics. d, External quantum efficiency (EQE) as a function\nof current density. For b–d, all devices (n = 10) were measured under identical conditions across\nbatches. (closed symbol: w/ encap, open symbol: w/o encap)\n44\n◼ Optical characteristics\nAn average EL main peak of 752.4 nm for devices without encapsulation and 755.6 nm for\ndevices with encapsulation was observed, yielding an approximately 3 nm red shift (TableR.3).\nTableR. 3 | EL peak wavelength of individual devices and batch mean (n = 10).\nThe FWHM increased from approximately 39 nm (without encapsulation) to 46.2 nm (with\nencapsulation), corresponding to an increase of about 7 nm (TableR.4).\nTableR.4 | FWHM of individual devices and batch mean (n = 10).\n◼ Electrical characteristics\nJ–V characteristics were overall maintained between devices without encapsulation and with\nencapsulation. However, near the maximum operating voltage, more stable operation was\nobserved for encapsulated devices. Under stress (higher current density), devices without\nencapsulation exhibited degradation, whereas encapsulated devices did not. The maximum\nEQE increased from an average of 3.7% to 11.4% after encapsulation (TableR.5).\nThe maximum radiance increased from 44.8 W m−2 sr−1 to 78.7 W m−2 sr−1 after\nencapsulation (TableR.6)\nTable.6 | Maximum radiance of individual devices and batch means (n = 10).\nAdditional data were included to reinforce Figure 3 in the manuscript. The revised\nmanuscript was improved with statistical analysis based on inter-sample variation and mean\nvalues.\nModifications to the revised manuscript in lines 323–330 of the Results section.\nTo investigate the influence of the capping layer on device performance, the optoelectronic\ncharacteristics of OLEDs were compared with and without the added layer through 10 devices.\nIntegration of the capping layer did not alter the electrical characteristics, as evidenced by\nunchanged input bias characteristics, whereas an enhancement in radiance was observed (Fig.\n3c). After encapsulation, the maximum radiance increased from 44.8 W m⁻² sr⁻¹ to 78.7 W m⁻²\n46\nsr⁻¹, accompanied by a 3 nm redshift of the main peak and a 7 nm broadening of the FWHM\n(Supplementary Fig. 9a, b).\nModifications to the revised manuscript in lines 331–334 of the Results section.\nSimilar trend was observed in devices without encapsulation, indicating that the low level of\nroll-off, as shown in Supplementary Figure 9c. The maximum power density, calculated from\nthe angular distribution of each device, increased from 19 mW cm⁻² to 33 mW cm⁻² (Fig. 3f).\nSupplementary Fig. 9| Batch-to-batch performance metrics of the NIR OLEDs. a,\nCurrent-density–voltage–radiance characteristics. b, EL spectra of individual devices driven at\na same voltage. c, External quantum efficiency as a function of current density. For a–c, all\ndevices (n = 10) were measured under identical conditions across batches. (closed symbol: w/\nencap, open symbol: w/o encap)\nReviewer’s comment 13) Given that EQE roll-off is a critical issue in NIR OLEDs due to\ntriplet-triplet annihilation and thermal quenching, what is the trade-off between\nbrightness and stability? Have you characterized thermal degradation and emission roll-\noff in that regime?\nRESPONSE\nWe appreciate the reviewer’s interest in our study. In response, the brightness–stability\ntrade‑off was evaluated by measuring operational lifetime under continuous operation across\nmultiple radiant intensities, with explicit quantification of EQE roll‑off and thermal\ndegradation.\nAt power densities of 4, 5, and 9 mW cm−2, EQEs were 11.14%, 11.10%, and 10.83%, and\nLT values were 17, 9, and 4 h, respectively. Across 4–9 mW cm−2, the absolute decrease in\nwhereas LT decreased sharply with increasing radiant intensity. This trend was independent\n50\n47\nof substrate type and was not attributable to the textile platform (FigR.15a, b).\nFigR.15 | Brightness–stability correlation of NIR OLEDs. a, Operational lifetime (LT ) of\n50\nglass-based NIR OLEDs under continuous operation as a function of radiant intensity. b,\nOperational lifetime of textile-based NIR OLEDs under continuous operation as a function of\nradiant intensity. c, Operating temperature of the textile-based NIR OLED under continuous\noperation as a function of radiant intensity. closed symbol: w/o heat sink, open symbol: w/ heat\nsink.\nThese results show that EQE roll‑off reflects the instantaneous efficiency–current\nrelationship, whereas LT represents cumulative chemical and interfacial degradation under\n50\nsustained operation at elevated temperature. In fact, measurements showed that when the\nradiant intensity was increased from 3 to 7 mW cm−2, the OLED surface temperature rose by\napproximately 10 °C (FigR.15c). Consequently, higher radiant intensity required increased\ndriving voltage and current, which elevated device temperature.\nConsidering the results indicate that while low roll‑off remains across the tested operating\nrange for reached to radiant intensity with sufficient to PBM applications, device stability is\ndegraded at higher radiance due to thermal degradation induced by elevated driving conditions.\nWe acknowledge that the current NIR OLEDs exhibit limited operational stability for\nlong‑term PBM applications, which is primarily attributed to the laboratory‑synthesized\nemissive material rather than commercialized product. Nevertheless, our devices demonstrated\nsufficient optical output for effective PBM irradiation and for validation as wearable\nprototypes.\nWe emphasize that the primary aim of this work was to demonstrate the feasibility of a\ntextile‑integrated OLED platform for wearable PBM, rather than to optimize material lifetime.\nWe believe that further development of high‑stability emissive materials, combined with\nreductions in driving voltage and current and enhancements in out‑coupling efficiency, will\n48\nultimately enable OLEDs to meet the long‑term reliability required for continuous PBM\noperation.\nReviewer’s comment 14) In this work, the merit and demerit of the textile‑integrated\nnear‑infrared OLED system should be discussed when applied to biocompatible\nplatforms for non‑invasive wearable phototherapy.\nRESPONSE\nWe thank the reviewer for requesting a balanced appraisal of the textile‑integrated NIR OLED\nin biocompatible, non‑invasive wearable phototherapy. In the revised manuscript, a dedicated\nsubsection has been added in the Discussion.\n◼ Merits\n1. Spectral control and therapeutic irradiance. A top-emitting microcavity architecture\nwas engineered to place the main peak within the therapeutic NIR window and to deliver the\nrequired irradiance at practical drive conditions. Additionally, the OLED's structure was\ntailored to the activation requirements of DP cells to treat hair-loss.\n2. Biocompatible device interface on textile. Parylene-C–based planarization layer was\napplied to the textile substrate, and the outermost capping and encapsulation layer of the OLED\nwas also formed with parylene-C. The resulting stack is composed of a biocompatible polymer\nthat provides conformal coverage over textile surface morphology. As known as, parylene‑C\nis a one of the biocompatible polymer which was approved by FDA, is widely employed as a\ncoating for biomedical devices.\n3. Coverage and scalp-specific customization. Leveraging the OLED light source,\nwhich provides large‑area emission with a microcavity‑tuned spectrum, the emitting areas can\nbe engineered to deliver light selectively to clinically relevant scalp zones with low irradiance\nnonuniformity.\n4. Wearable form factor and daily usability. A hat-type platform is a one of the user-\nfriendly platform, it could be improved wearability and supports treatment during routine\nactivities.\n◼ Limitations\n1. Angular spectral shift intrinsic to microcavities. As the emission angle increases, the\npeak wavelength shifts to the blue. DP‑cell activation occurs near 730 nm within the NIR band.\ndisadvantageous by reducing spectral overlap with the cell‑responsive band.\n2. Operational stability under continuous drive. Despite small EQE roll-off at the\nintended irradiance window, lifetime remains a constraint for prolonged continuous use.\n3. Portable power and runtime. Sufficient energy density is required to drive an OLED\narray in a fully flexible, battery‑driven system (flexible battery, FPCB, and OLED). A trade‑off\nexists between capacity and mechanical compliance. Generally, greater capacity reduces\nflexibility.\nThe revised manuscript describes the merits and demerits of the textile‑based NIR OLED\nplatform.\nModifications to the revised manuscript in lines 615–635 of the Discussion section.\nThe textile‑integrated NIR OLED system offers advantages as a biocompatible platform for\nnon‑invasive phototherapy. The microcavity structure enables precise spectral control within\nthe therapeutic range, effectively matching the activation spectrum of dermal papilla cells.\nUsing parylene‑C, which is FDA‑approved material, as both a planarization and encapsulation\nlayer for textile‑based OLEDs ensures biocompatibility at the skin interface.22,24 This material\nselection strategy enables safe, non‑invasive wearable phototherapy in close contact with the\nskin. In addition, textile‑based OLEDs, composed entirely of flexible materials including\ntextile substrate and OLED light source, could be close to the scalp surface and provide uniform\nillumination of targeted regions with minimal irradiance variation. Furthermore, we have\ndemonstrated a prototype in which embedding the device in a hat‑type form factor facilitates\nnatural wearability and comfort, allowing users to receive phototherapy during routine daily\nactivities without the need for benchtop instrumentation, showing its potential as a wearable\ndevice.\nDespite these advances, several constraints for translation remain. Microcavity OLEDs\nare characterized by view‑angle–dependent spectral shifts, which reduce overlap with cellular\n50\naction spectra at oblique incidence. Furthermore, portable operation and device flexibility are\nlimited by trade‑offs among deliverable energy density, total device thickness, and capacity of\nthe power‑supply components required for OLED driving.\nReviewer #3: The authors did solid OLED engineering work, showing how the proposed\ndevice optimization leads to better biological response compared to others (not optimized or\nsimilar to commercially available products). The methodology is sound, and the work could\nbe of significance in the field of wearable electronics if adjustments to the manuscripts are\nproperly made.\nRESPONSE\nWe thank the reviewer for the thoughtful and constructive feedback. We believe that this\nguidance has raised the quality of the manuscript. Detailed point by point responses are\nprovided below.\nReviewer’s comment 1) The major point I have is about wearability and usability of the\npresented device in real life scenarios. The general idea of this work presupposes the\nexistence of a supporting circuitry that ideally fits into the hat, and is removable when\nwashing is necessary (Of course, more creative solutions could be implemented to realize\nportability, this was just an example). In this regard, I failed to find information about\nthe driving scheme used to realize the videos proposed as demonstrations. For this reason,\nat the present time, there is the need to add data about this aspect to fully comply with\nthe message of portability proposed in the manuscript, and also to show that this device\nis indeed compatible with the notion of wearable electronic platforms. In other words, the\nOLED per se is wearable, but the phototherapy (quoting the title that the authors chose)\nprobably still relies on benchtop power supplies. Therefore, I suggest that the authors\ncome up with a circuitry that allows the OLED to be driven in a truly portable fashion,\ndemonstrating that with the application requirements, the power supply (maybe a\nbattery) can be sufficient to drive the OLED for a substantial amount of time (or\nequivalently, enough therapeutic sessions). This should be documented in the method\nsection and shown in a Figure.\nRESPONSE\nWe thank the reviewer for considering real‑life scenarios and for noting the lack of information\non how the hat‑type device is driven. Consistent with your comment, our goal is to demonstrate\nan integrated phototherapy device based entirely on flexible components, including a\ntextile‑based OLED, a battery, and a circuit board. We agree that demonstrating device\n52\nportability better substantiates the manuscript’s daily‑use treatment claim. Accordingly, a fully\nportable, integrated driving system was demonstrated, and the driving scheme is described in\nthe revised manuscript.\nDevice portability was demonstrated using a hat-type device based on an all-flexible\narchitecture that integrates a flexible battery for portable operation, a flexible printed-circuit\nboard (FPCB) providing on/off control and battery power delivery, and an OLED.\n◼ Portable device composed of flexible components\nA wireless prototype composed entirely of flexible components was fabricated (FigR.16).\nThe system comprised an FPCB, a textile‑based single‑pixel NIR OLED, and a flexible battery.\nOn/off operation was verified, stable emission was maintained under bending, and the total\nstack thickness was approximately 2mm. A demonstration video documenting operation\nwithout benchtop power supply has been provided (Supplementary Video 4, 5). Switch-\ndriven on–off operation of the OLED stripe array is shown in Supplementary Video 4, and\nstable operation of a wireless cap-type platform integrating multiple OLED stripes during\nrepeated donning and doffing is shown in Supplementary Video 5.\nFigR.16 | Portable phototherapy hat based on an all-flexible system.\nFigure R16 shows the integrated, all‑flexible platform used to demonstrate portability. The\nFPCB provides on/off control and battery connection for portable drive (FigR.17a). The\n53\nflexible battery enables wireless operation (FigR.17b). The polyester textile hosts the device\nstack (FigR.17c). The thicknesses of the FPCB (~90 µm), the flexible battery (~450 µm), and\nthe textile (~230 µm) are reported (FigR.17d–f), and the maximum local thickness of the\nassembled stack is approximately 2 mm (FigR.17g). Together, these components constitute a\nfully integrated hat‑type module in which power delivery and control are embedded, enabling\nportable phototherapy without benchtop instrumentation.\nFigR.17 | Fully flexible, integrated system. a, FPCB incorporating an on/off power button\nand battery connection pads for portable driving. b, Flexible battery used for wireless\noperation. c, Polyester-based textile substrate. d–f, Thickness of the FPCB, flexible battery,\nand textile, respectively. g, Most thick part of the fully flexible integrated stack (around 2 mm).\nA wireless hat‑type phototherapy prototype intended for portable, daily use was\ndemonstrated. However, we suggest two points for improvement toward a commercial product.\nFirst, the present prototype employed 3V battery cells due to lack of flexible battery with\nsufficient voltage. This voltage was insufficient to drive the NIR OLED at the target operating\npoint that provides sufficient irradiance for phototherapy. Therefore, the batteries were\nconnected in series to realize the demonstration. Development of flexible batteries with\nadequate voltage and power capacity is required for a commercial product. Second, the overall\nthickness could be reduced by relocating the FPCB and the battery to alternative regions within\nthe hat to distribute the stack and decrease local thickness.\n◼ Driving the device for phototherapy\nwe assembled a flexible power stack using four 3 V thin‑film cells (Renata CP042350, 25–28\nmAh each) in series to provide ~12 V at the pack level.\nFor an emission area of 69 mm² with current density around 31.5mA cm-2, the device was\ndriven at approximately I ≈ 7.3 mA to maintain the therapeutic power density. With a series-\nconnected pack capacity of C = 25–28 mAh, the theoretical continuous runtime is:\n𝐶 25~28 𝑚𝐴ℎ\n𝑇𝑖𝑚𝑒 = = = 3.4~3.8 ℎ𝑜𝑢𝑟𝑠\n𝑖𝑑𝑒𝑎𝑙 𝐼 7.3𝑚𝐴\nIntegrated with the FPCB driver and our flexible OLED module, this configuration delivered\nstable operation at the target current over the 69 mm² aperture and sustained the required radiant\noutput, demonstrating feasibility for portable phototherapy. Given that phototherapy is\ntypically administered in 2–30 minutes, the calculated runtime theoretically confirms that this\nportable battery configuration provides sufficient operating time.\nHowever, the attainable performance is governed by the battery system and design of\ncircuit board. The choice of rechargeable operation and the addition of a charging function on\nthe FPCB can increase device thickness and reduce mechanical flexibility. Thus, to enable\nreal world use, follow up work is needed to joint design of the FPCB and the battery and the\nmechanical layout required to preserve flexibility while meeting the electrical and optical\ntargets for phototherapy.\n◼ Washing compatibility\nTo reflect real‑world use, both washability and mechanical flexibility are being addressed.\nFor a phototherapy device to be washable, waterproof characteristics are required at the device\nlevel and at the interfaces among the battery,1,2 PCB, and OLED.3 Washable OLED\nencapsulation strategies have been reported, and multiple groups are actively investigating\nwashable flexible batteries and washable OLEDs. Additionally, research on waterproofing\napproaches for PCB and FPCB components is in progress. Although full washability was not\nimplemented in the present prototype, component‑level washability is being pursued for each\nsubsystem. Based on these ongoing efforts, we believe that the remaining challenges are\nexpected to be resolved, enabling a washable, integrated device.\n[R1] He, J., Lu, C., Jiang, H., Han, F., Shi, X., Wu, J., Wang, L., Chen, T., Wang, J., Zhang, Y.,\nYang, H., Zhang, G., Sun, X., Wang, B., Chen, P., Wang, Y., Xia, Y. & Peng, H. Nature 597,\n57–63 (2021).\n[R2] Khudiyev, T., Grena, B., Loke, G., Hou, C., Jang, H., Lee, J., Noel, G. H., Alain, J.,\nJoannopoulos, J., Xu, K., Li, J., Fink, Y. & Lee, J. T. Materials Today 52, 80–89 (2022).\n[R3] Jeong, E. G., Jeon, Y., Cho, S. H. & Choi, K. C. Energy Environ. Sci. 12, 1878–1889\n(2019).\nModifications to the revised manuscript in lines 206–212 of the Results section for\nproviding information of prototype device\nOperation of the OLED array on a commercial hat/cap platform, while maintaining the\nflexibility required for a wearable device, was demonstrated by mounting the array on the\ntextile and interfacing it with a flexible printed circuit board (FPCB) that provided array driving\nand section‑wise switching for scalp‑specific operation. The array comprised NIR OLEDs\nwith emission areas of 69 mm² and 1,000 mm², each wired to an independent FPCB channel to\nenable individual on/off control of each scalp section.\nModifications to the revised manuscript in lines 221–231 of the Results section.\nFurthermore, a wireless phototherapy device composed entirely of flexible components\nwas fabricated to validate portable operation. The system comprised a FPCB for switch-based\non/off control and battery-driven OLED operation, the NIR OLED, and a flexible battery\n(Supplementary Fig. 3a, b). The individual component thicknesses were ~90 μm (FPCB),\n~230 μm (textile), and ~450 μm (battery), and the maximum local stack thickness within the\nhat form factor was ~2.0 mm (Supplementary Fig. 3c–f). Switch-controlled on/off operation\nof the textile-based OLED stripe integrating fully flexible components was demonstrated\nwithout the use of a benchtop power supply (Supplementary Video 4). For a cap-type platform\nintegrating multiple OLED stripes, continuous emission was maintained during donning and\ndoffing (Supplementary Video 5).\nTo reach real-world applicability, further technological refinement is required. The\ndevelopment of flexible batteries with sufficient voltage and power capacity is essential for\ncommercial deployment. Reducing overall thickness through redistribution of the FPCB and\nbattery across alternative hat regions would improve user comfort and decrease localized bulk.\nIn addition, practical use demands that washability and mechanical flexibility be achieved\nsimultaneously. Attaining washability requires comprehensive waterproofing at the device\nlevel and reliable sealing of interfaces among the battery, FPCB, and OLED. Although full\nwashability has not yet been implemented in the current prototype, component-level studies on\nwaterproof OLED encapsulation,38 flexible batteries,39,40 and circuit boards are ongoing. These\nefforts are expected to fabricate a fully washable and stable system capable of sustained\noperation in daily use, thereby advancing the textile-integrated NIR OLED platform toward\npractical, commercially viable wearable phototherapy.\nModifications to the revised manuscript in lines 684–701 of the Method section.\nHat-type prototype\nTo demonstrate operation of the OLED array on a commercial hat/cap platform, the array was\nmounted on the textile and interfaced to a flexible printed circuit board (FPCB) that provided\narray driving and section‑wise switching for scalp‑specific operation. The array comprised\nOLED emitters with emission areas of 69 mm2 and 1,000 mm2, each wired to an independent\nFPCB channel for individual on/off control. For array‑level characterization, the source was\noperated in constant‑current mode using a benchtop sourcemeter (Keithley 2636B). The\noperation is shown in Supplementary Videos 1–3.\nA wireless prototype was assembled to evaluate portability. The architecture integrated a\nflexible battery for portable operation, a flexible printed circuit board providing on/off control,\n57\nbattery power delivery, and OLED interconnection, and the NIR OLED. A 3V flexible Renata\nthin-film battery (CP042350) was employed, and 4 cells were connected in series to achieve\nthe required minimum level of light intensity for phototherapy. All components were integrated\non the polyester-based textile to form a single portable module, and operation was performed\nfrom the flexible battery without benchtop supply (Supplementary Videos 4, 5).\nof the manuscripts.\nRESPONSE\nWe greatly appreciate the opportunity to improve the manuscript based on your detailed\ncomments.\nReviewer’s comment 2-1) ROW 102: “Additionally, most NIR OLEDs have been\ndesigned a bottom-emitting architecture” probably contains an error.\nRESPONSE\nMost NIR OLEDs reported to date have been implemented as bottom‑emitting devices, owing\nto a prevailing focus on the synthesis of novel NIR emitters rather than on application‑oriented\ndevice design. As noted by the reviewer, the original sentence could lead to misunderstanding;\ntherefore, the wording has been revised to clarify our intent.\nModifications to the revised manuscript in lines 103–106 of the Introduction section.\nMost NIR OLEDs reported to date adopt a bottom‑emitting structure, in which light exits\nthrough the substrate. An optical characteristic of the NIR OLEDs are highly dependent on\nsubstrate transmittance, which inherently restricts the range of applicable substrate\nmaterials.13,20\nReviewer’s comment 2-2) ROWS 115-116: Typically, bottom emitting OLEDs provide\ndifferent advantages over top-emitting ones. While it is clear that bottom emitting\ndevices based on ITO are susceptible to mechanical damage under certain stress, the\nauthor here exclude the whole category of bottom-emitting OLEDs without addressing\nthe general motivation. Could they elaborate more on this design choice?\nRESPONSE\nTo address the reviewer’s question regarding our structural choices, the reason is summarized\nbelow.\n◼ Reason for employing a top‑emitting architecture\n1. The textile platform exhibits low transmittance in the near‑infrared (NIR) range\n(≈20%). Thus, emission through the substrate is inefficient. A top‑emitting\n59\nconfiguration was therefore selected to extract light away from the textile and to ensure\nefficient optical delivery to the target tissue.\n◼ Reason for employing a silver electrode instead of ITO\n1. Mechanical compliance for wearability: Ag‑based thin electrodes provide lower sheet\nresistance at comparable or lower thickness than ITO and remain operational at higher\nbending strains, which supports the flexibility required for wearable electronics.\n2. Spectral control for PBM: In a cavity‑tuned, top‑emitting stack, the Ag\nsemi‑transparent electrode (together with the reflective bottom mirror and capping\nlayers) enables precise control of the optical resonance. This allows tuning of the peak\nwavelength and linewidth without changing the emitter, which is critical for PBM\nwhere efficacy is strongly wavelength dependent.\nModifications to the revised manuscript in lines 116–119 of the Introduction section.\nTo improve the phototherapeutic efficacy of wearable, textile-integrated NIR OLEDs for hair-\nloss treatment, a microcavity structure was used. This architecture enables spectral tuning\nwithout changing the emitter material, as PBM outcomes are strongly wavelength dependent.\nReviewer’s comment 2-3) ROW 128: Why are the authors using this specific tensile strain\n(2.1%)? What are the ranges of expected strains during use and during washing of the\n“hat”? It is suspected that this object will face grater deformations for the intended\nwearable application. What would be the number of bending tests that the OLED would\ntolerate for a strain in the range conform to the application needs?\nRESPONSE\nThank you for the comment. Responses to each question are provided below.\n◼ Reason for choosing the specific strain (2.1%)\nFirst of all, a strain of 2.1% corresponds to a bending radius of 2 mm for the textile platform.\nFor planar substrates, the bending strain of OLEDs is approximated by t/2R; however, because\nthe textile substrate consists of a woven warp and weft architecture, this planar approximation\nis not applicable. Therefore, the bending strain in the textile platform was determined by finite\nelement analysis.1 The analysis indicated that the highest strain that can be quantified reliably\n60\noccurs at 2.1% when the bending radius is 2 mm. Beyond this point, an accurate definition of\nstrain becomes ambiguous. Accordingly, a nominal strain of 2.1% was applied to the textile\nOLED for the bending tests.\nAdditionally, previous studies have reported that textile-based red OLEDs maintained stable\nperformance even after 1,000 bending cycles at a bending radius of 1.25 mm.2 Although the\nexact strain applied to the textile cannot be precisely defined, this observation demonstrates\nthat the flexibility of textile OLEDs can be preserved even under more severe bending\nconditions.\n◼ Strain in real-world use\nThe typical curvature radius of an adult head is approximately 90 mm.3 This value indicates\na much gentler curvature than R = 2 mm, under which the textile-based OLED remained stable\nfor up to 10,000 bending cycles.\n◼ Considerations for hat washing\nBecause the hat is flexible, machine washing can fold the device (effective R ≈ 0), imposing\nlarge strain under which the OLED may be damaged. This issue could be addressed by\nmechanically optimizing the device architecture so that the neutral axis coincides with the\nOLED, thereby minimizing bending‑induced strain. As a temporary expedient, hand washing\nrather than machine washing is recommended to mitigate strain and maintain the mechanical\nstability of the textile OLED device.\nTo clarify the textile bending condition, the bending radius value was included in\nIntroduction section.\nModifications to the revised manuscript in lines 128–131 of the Introduction section.\nThe flexibility of the textile-based top-emitting OLEDs were validated through repeated\nbending tests, confirming stable radiance output and mechanical robustness without\ndelamination even after 10,000 bending cycles at a bending radius of 2 mm, corresponding to\n2.1% tensile strain.\n[R1] Lee, J., Gu, C. Y., Chang, J., Cho, E. H., Kim, T. S., & Choi, K. C. npj Flexible Electronics,\n8, 73 (2024).\n[R2] Cho, H. E., Kim, M. J., Chang, J., An, J., Na, Y., Choi, S., Jeong, S. Y., & Choi, K. C. npj\nflexible electronics, 9, 36 (2025).\n[R3] Borghi, A., Heutinck, P., Rodriguez-Florez, N., Koudstaal, M., Ruggiero, F., Ajami, S.,\nSchievano, S., Jeelani, N.U.O. & Dunaway, D. The Cleft Palate Craniofacial Journal, 60,\n1591-1599 (2023).\nReviewer’s comment 2-4) ROW 183: I think the authors should reference figures 3 and\n5 here.\nRESPONSE\nThank you for your consideration. To improve reader comprehension, Fig. 3 has been cited\nearlier in the encapsulation content.\nModifications to the revised manuscript in lines 188–191 of the Results section.\nThis hybrid encapsulation, consisting of the upper TFE and outermost parylene-C layer, not\nonly provides needed mechanical protection but also enhances light extraction efficiency (Fig.\n3). Details on the light-extraction enhancement by the hybrid capping are provided in a\nsubsequent section.\nthe information about the ETL and HTL thickness from this line. Could the authors\nexplicitly state the thicknesses in the non-optimized VS. optimized case and provide an\nexplanation for their claim on the better carrier transport in the optimized configuration?\nRESPONSE\nThank you for the helpful suggestion. The ETL and HTL thicknesses for the non‑optimized\nand optimized devices have been included in the revised manuscript.\nTo keep the optical cavity length identical across cases, the same increment was applied. In\nthe HTL‑tuned device, increasing the NPB layer (HTL) by 37 nm aligned the main EL peak at\n730 nm. Based on this result, to maintain the cavity length for each case, the ETL‑tuned device\nwas fabricated by increasing the TPBi layer (ETL) by 37 nm. As detailed in our response to\nReviewer 2, Comment 9, additional validations were performed at matched radiance for both\nthe HTL‑tuned and ETL‑tuned OLEDs, including operational lifetime and angle‑resolved\nemission intensity. The advantages associated with the recombination zone position in each\nconfiguration, including benefits in light extraction and carrier transport, were included in the\nrevised manuscript.\nModifications to the revised manuscript in lines 259–265 of the Results section.\nTo compare the two tuning strategies, the optical cavity length was maintained constant by\napplying an identical thickness increment to either the HTL or ETL. In the HTL‑tuned\nOLED, the NPB layer was increased by 37 nm relative to the conventional recipe, which\nadjusted the optical path and positioned the main EL peak at 730 nm. Using this optimized\ncondition as a reference, the ETL‑tuned OLED was fabricated by extending the TPBi layer\nby the same 37 nm, thereby preserving an equivalent cavity length across both configurations.\nModifications to the revised manuscript in lines 280–285 of the Results section.\nBecause hole transport in NPB exceeds electron transport in TPBi, adjustment of the NPB\nthickness, in part owing to the carrier mobility imbalance,27 positioned the recombination zone\nmore effectively within the emissive layer, to reduce the proportion of non-radiative interfacial\n63\nexciplex. In fact, the HTL-tuned OLED exhibited slightly improved operational lifetime\ncompared with the ETL-tuned device (Supplementary Fig. 4b).\nReviewer’s comment 2-6) ROW 307: What are the requirements in terms of optical power\ndensity (or equivalently energy density) that are required to exhert relevant beneficial\neffects with this type of therapy? This information is difficult to retrieve without accessing\nto reference 7. I think it would be of service to explicitly mention this in the text. It is also\nimportant to state at what voltages and currents the OLEDs presented in this work reach\nthis range.\nRESPONSE\nThank you for the comments. The revised manuscript was included the minimum specific\nintensity required for phototherapy. In addition, the input power of the textile device required\nto reach sufficient light intensity for a phototherapeutic effect has been specified.\nModifications to the revised manuscript in lines 349–352 of the Results section.\nIn addition, device stability was maintained without any detectable leakage paths, and the\nemitted light intensity exceed 10 W m-2 sr-1 at approximately 12 V and a current density of 31.5\nmA cm-2 for the textile device, the minimum level required for phototherapy (Supplementary\nFig. 10b).7\nReviewer’s comment 2-7) ROW 320: See the comment related to the choice of a 2.1%\nstrain.\nRESPONSE\nThank you for the comment. The description of the strain defined by finite element analysis of\nthe textile’s woven warp and weft architecture has been added to the revised manuscript.\nModifications to the revised manuscript in lines 356–360 of the Results section.\nFlexibility of the textile-based device was assessed by cyclic bending at a radius of 2 mm,\ncorresponding to an applied tensile strain of 2.1%. Finite element analysis indicated that, for\nthe textile platform with a woven warp and weft architecture, this condition represented the\nmaximum point at which the applied strain could be defined.22\nmoved here for better readability.\nRESPONSE\nThank you for the helpful suggestion on readability. We agree and have revised the manuscript\naccordingly to enhance clarity and flow.\nModifications to the revised manuscript in lines 378–384 of the Results section.\nRegardless of applied current density, their temperature levelled shortly after initiation. The\ndevices reached 28.0 °C at 3 mW cm⁻², 34.0 °C at 4 mW cm⁻², and 41.0 °C at 7 mW cm⁻²,\nrespectively. The polyester-based textile platform used in this study possesses a relatively low\nthermal conductivity (0.3–0.4 W/m·K), significantly lower than that of glass (~1 W/m·K).\nSuch thermal accumulation leads to heat retention in the active layer during prolonged\noperation, thereby accelerating device degradation. Reducing heat accumulation and suppress\nOLED degradation caused by heat, a heat sink tape was attached to the textile devices.\nsuperposition of hDPC activation spectrum (or peak if not available) and the different\nOLEDs EL spectra. Most probably the authors can add the hDPC missing information\ndirectly into figure 2E.\nRESPONSE\nWe appreciate the reviewer’s recommendation. We agree that plotting the overlap between the\nOLED EL spectra and the cell activation spectrum significantly improves reader\ncomprehension and supports our main argument. Accordingly, the activation spectrum was\nincorporated into modified Figure 5d, comparing the customized and non‑customized OLEDs.\nThe revised manuscript has been updated to reflect this change. Thank you for the valuable\nsuggestion.\nCustomized NIR OLED 150\nNon-customized NIR OLED\n140\n130\n120\n110\n100\n450 500 550 600 650 700 750 800\nWavelength (nm)\nModified Fig. 5d | Overlap between the human dermal papilla cell action spectrum for\nproliferation13 and the EL spectra of the cavity NIR OLED and non-cavity NIR OLED under\nsame radiance\n66\n)%(\nlevel\nnoitavitca\nlleC\n1.0\n0.8\n0.6\n0.4\n0.2\n0.0\n).u.a(\nytisnetni\nLE\nevitaleR\nVoluntary modification\nBeyond the point‑by‑point responses for reviewers, several voluntary revisions were made to\nenhance clarity and reproducibility of the work.\n1. Edits for improving readability. The manuscript text was improved by providing\ndetailed description.\n2. Figures improved. We refined and, where helpful, expanded the main figures and\nsupplementary materials to present key results more clearly.\n3. Methods expanded. We added procedural details to support replication.\n4. Source data provided. We supply complete source data files in this study.\nWe believe that these updates could be assisted readers and reviewers by improving\nreadability and enabling precise reproduction of the experiments and analyses.\nAgain, we would like to express our appreciation for the reviewers’ thoughtful suggestions.\nWe have been able to revise and improve the paper because of the reviewers’ valuable feedback.\nWe look forward to your positive response.\nThank you very much for your time and attention.\nSincerely yours,\nKyung Cheol Choi\nProfessor\nSchool of Electrical Engineering, KAIST\nDaejeon 305-701, Korea\nPhone: +82-42-350-3482\nFax: +82-42-350-8082\nE-mail: kyungcc@kaist.ac.kr\nReviewer #1: The authors have substantially revised the manuscript “Wearable textile-\nbased phototherapy with customized near-infrared OLEDs for superior hair loss\ntreatment” in response to the first-round reviews. In particular, they added (1) pilot in\nvivo experiments using a mouse model together with ex vivo skin-penetration\nmeasurements, (2) quantitative analysis of power density and on-cell irradiance\nsupported by Monte Carlo simulations in a layered skin model, and (3) a clearer\npositioning of their textile NIR OLED platform relative to commercial PBM devices and\npreviously reported cage-OLED / micro-LED systems. I thank the authors for their\ndetailed and constructive revision. The additions to the manuscript and response letter\nclearly show substantial effort. The new data and analysis improve the rigour of the\noptical characterization and strengthen the positioning of the textile-integrated NIR\nOLED platform. My major concerns about optical dose characterization and\nbenchmarking (previous Comments 2 and 3) are now largely addressed. The remaining\nweakness is that in vivo validation of therapeutic efficacy is still preliminary: the new\ndata mainly document light delivery through murine skin and ongoing animal studies,\nbut do not yet demonstrate hair-growth outcomes or dose–response relationships. The\nauthors have, however, clarified these limitations and softened their claims. Given the\ndevice-centric nature of the work and the strengthened quantitative analysis of light\ndelivery, I believe the manuscript is now much closer to the bar of Nature\nCommunications. I would be comfortable with publication after minor revision, mainly\nto ensure that the limited status of the in vivo data is clearly conveyed in the main text.\nRESPONSE\nWe sincerely appreciate the reviewer’s insightful comments and the interest to our work. Our\npoint-by-point responses are provided below.\nReviewer’s comment 1) Regarding previous comments on the scope of biological\nvalidation / in vivo relevance: These additions partially address my original concern. In\nparticular: (1) The skin-penetration measurements are useful and directly relevant to the\nquestion of whether sufficient NIR power can reach the follicular region in a realistic\nsetting. (2) The explicit acknowledgment that full in vivo hair-growth validation is\nongoing and non-trivial makes the biological scope of the current work more honest and\ntransparent. However, the in vivo component remains exploratory rather than\nsystematic. The material presented in Fig. R1 mainly documents the experimental setup\nrather than quantitative biological outcomes (e.g., hair-density maps, histology, or\nlongitudinal regrowth curves). I understand that performing a comprehensive preclinical\nefficacy study may be beyond the scope of this device-focused paper; in that case, the\nmain text should clearly avoid overstating therapeutic claims. Therefore, in the revised\nmanuscript, please ensure that statements about “superior hair-loss treatment” or\n“therapeutic efficacy” are toned down and framed as potential or anticipated benefits\nsupported by cellular assays and realistic light-delivery analysis, rather than as fully\ndemonstrated in vivo outcomes. It would also be helpful to summarize the key\nquantitative numbers from the skin-penetration experiment (relative radiance with\n1\nshaved vs. depilated skin) in the main text or a main-figure panel, not just in the response.\nRESPONSE\nWe appreciate the reviewer’s comments on the scope of biological validation and the need to\ntone down therapeutic claims. To avoid over-interpretation of the present experimental results\nand to more clearly delineate the scope and significance of this work, we have revised the\nwording throughout the manuscript. In particular, statements regarding the effects of the NIR\nOLED system are now framed as potential or anticipated benefits supported by in vitro cellular\nassays and realistic light-delivery analysis, rather than as fully demonstrated in vivo therapeutic\noutcomes.\nModifications to the revised manuscript in lines 16–32 of the Abstract section\nTo provide a non-pharmacological alternative, a wearable textile-integrated near-infrared\n(NIR) organic light-emitting diode (OLED) platform was developed with emission closely\naligned with the action spectrum of human dermal papilla cells (hDPCs). By employing a top-\nemitting microcavity structure, we tuned the emission peak of the NIR OLEDs (around 730–\n740 nm) to align with the hDPC activation spectrum, thereby enhancing photon delivery to the\nfollicle niche and enabling irradiation at wavelengths that promote hDPC photoactivation. This\nnon‑invasive, skin‑conformable textile‑based device exhibits mechanical resilience to repeated\nbending at a radius of 2 mm, low heat generation to prevent skin burns, and waterproof\nperformance under water immersion. In vitro, NIR irradiation from the customized\nmicrocavity‑tuned OLED device significantly reduced senescence-associated β-galactosidase\nactivity by 91.6% and increased hDPC migration, with greater effects than those observed for\nred light and broad full‑width at half‑maximum (FWHM) NIR irradiation groups. These\nfindings suggest that microcavity-tuned textile-based NIR OLEDs can serve as scalable,\nbiocompatible platforms for non-invasive wearable phototherapy aimed at hair-follicle\nmodulation and future hair-loss management.\nSince human hair follicles are typically located approximately 3 mm beneath the skin surface,\nachieving light transmission to this depth is critical for effective light delivery to dermal papilla\ncells within the follicle niche.\nModifications to the revised manuscript in lines 638–646 of the Discussion section\nIn addition, hair-loss pathology involves multiscale interactions that extend beyond hDPC\nresponses, including crosstalk with epithelial stem cells, immune system, the vasculature and\nsystemic endocrine signals. Therefore, the results obtained from our in vitro tests should be\ninterpreted as evidence of photobiological modulation at the cellular level rather than as direct\nproof of hair-loss treatment. To establish whether wavelength-optimized textile-integrated NIR\nOLEDs can ultimately provide clinically meaningful benefits, future studies will need to\ninclude controlled in vivo models and, eventually, clinical trials to evaluate changes in hair\ndensity, hair-shaft thickness and hair length.\nrevisions substantially strengthen the manuscript. The combination of measured\nirradiance, modelled dose in tissue, and angular emission data now provides a\nquantitative and mechanistic basis for discussing light delivery, rather than relying on\nqualitative statements alone. The benchmarking against commercial devices is\nnecessarily limited by the sparse publicly available specifications, but the discussion is\nreasonable and helps to contextualize the work. Moreover, I suggest ensuring that typical\nranges of fluence and irradiance used in clinical PBM protocols are cited and that your\noperating regime is clearly positioned within those ranges. This will help readers outside\nthe PBM community interpret the numbers. Consider summarizing the key\nbenchmarking parameters (e.g., wavelength, approximate irradiance at the scalp, form\nfactor) in a compact comparison table in the main text, even if the underlying details\nremain in the Supplementary materials.\nRESPONSE\nWe agree with the reviewer that clearly positioning our operating regime with respect to typical\nfluence and irradiance ranges used in clinical PBM protocols is important. We have compiled\nvalues from relevant literature and added a compact comparison table to the manuscript that\nsummarizes key benchmarking parameters (such as wavelength, form factor, and light source)\nfor our textile device and representative helmet-type devices.\nModifications to the revised manuscript in lines 57–64 of the Introduction section\nA notable class of commercial PBM systems for hair-loss treatment adopts helmet- or\nhairband-type configurations incorporating arrays of LEDs and lasers.9–11 This device is\ncharacterized by a mechanically robust helmet-type design that can be securely fixed to the\nhead. However, the platforms are restricted to use in indoor home environments rather than\nduring daily outdoor activities, and the reliance on numerous point‑like LED and laser emitters,\neach illuminating only a small area, necessitates large emitter counts to cover the scalp, which\ncan increase the overall device weight.\nModifications to the revised manuscript in lines 234–242 of the Results section\nClinically validated light-therapy systems for hair loss, such as helmet- and headband-\ntype devices, have demonstrated therapeutic effects but rely on rigid platforms that are\nprimarily suited for indoor use. In this study, the textile-based NIR OLED was implemented in\n4\na hat-type platform to propose a phototherapy device design that can be used in both indoor\nand outdoor settings. Compared with conventional rigid systems, this textile-integrated design\noffers mechanical flexibility and conformal contact with the scalp and employs an OLED-\nbased NIR area source rather than point-like emitters such as red LEDs or lasers, enabling more\nuniform illumination over the treatment region (Table 1).\nCharacteristics of phototherapy devices for hair-loss treatment\nDevices\nCharacteristics\nRef. 9 Ref. 10 Ref. 11 This work\nLight source Laser LED + Laser LED + Laser OLED\nRed Red\nRed NIR\nWavelength\n(630 ± 20, 655 ± 5 (630, 650 and\n(655 ± 33 nm) (730 ± 10 nm)\nand 660 ± 7 nm) 660 nm)\nPower density - 3.04 mW cm-2 92.15 mW cm-2 3 mW cm-2\nPlatform Hairband Helmet Helmet Hat\nFlexibility Rigid Rigid Rigid Flexible\nHome use Home use Home use Unrestricted\nUsage\n(indoor and\nenvironment\n(indoor) (indoor) (indoor) outdoor)\nStudy type Clinical Clinical Clinical In vitro\nTable 1. Key characteristics of phototherapy platforms for hair-loss treatment\nexplanations that could be interpreted as complete therapeutic validation; instead,\nemphasize that these are pilot studies demonstrating the feasibility of light delivery and\nsetup for future efficacy experiments.\nRESPONSE\nWe appreciate this constructive suggestion and agree that the in vivo mouse experiments should\nnot be interpreted as complete therapeutic validation. In the revised manuscript, the in vivo\ndata are explicitly described as pilot studies demonstrating the feasibility of light delivery and\nexperimental setup for future efficacy experiments, and we will keep this important distinction\nin mind when designing and reporting future work.\nReviewer’s comment 4) I suggest some careful edits to remove any remaining instances\nof over-strong claims, such as “superior hair loss treatment” in contexts where in vivo\nhair regrowth is not yet shown, which would improve the overall balance of the\nmanuscript.\nRESPONSE\nWe appreciate the reviewer’s suggestion to remove remaining instances of over-strong claims\nand fully agree that such wording could be misleading in the absence of in vivo hair-regrowth\ndata. Accordingly, the wording has been carefully revised throughout the manuscript to avoid\nimplying demonstrated therapeutic superiority. In particular, the expression “superior hair loss\ntreatment” has been removed from the title and main text, and all descriptions of therapeutic\neffects have been reframed as potential or anticipated benefits supported by in vitro assays and\nrealistic light-delivery analysis.\nModified Title: Wearable textile-based phototherapy with customized near-infrared OLEDs\ntoward hair-loss treatment\nReviewer #2: The authors well-replied and address the concerned sections. Therefore, I\nsuggested that the current revised manuscript can be accepted by Nature Communications.\nRESPONSE\nWe sincerely appreciate the reviewer’s positive assessment and recommendation for\nacceptance. We believe that the incorporation and refinement of the Monte Carlo light-transport\nsimulations, as suggested, has substantially strengthened the mechanistic foundation of this\nstudy and its relevance under realistic conditions. This revision process has been a valuable\nexperience for us.\nResponses to the reviewer 3’s comments\nReviewer #3: Amazing work.\nRESPONSE\nWe sincerely appreciate the reviewer’s positive comment. Developing the NIR OLED devices\nand textile-based prototypes has been a highly rewarding experience for us, and we are grateful\nthat the reviewer found value in this work.\n7"}]

Decision letter