A tactile gripper on an optical fiber for perception and actuation

Domain: physics
Published: 2025-12-13
Editorial outcome: minor_revision

Abstract
Optical fibers with integrated robotic microstructures are promising for cutting-edge applications. However, the development of microbots on a fiber system for synergistic sensing and actuation is challenging. Herein, inspired from natural Bobbit worm, we report a tactile gripper-on-a-fiber system that integrates wave spring, planar reflector with a scattering cone and a smart gripper on a single-mode fiber. The wave spring fabricated via two-photon polymerization of SU-8 can convert the applied micro-force into detectable stretching or compression, serving as a Fabry-Perot interferences sensor. Additionally, a pH responsive gripper with SU-8 frames and bovine serum albumin muscles is integrated with the wave spring, forming the tactile gripper-on-a-fiber system. As a proof-of-concept, the tactile gripper-on-a-fiber system was employed for micro-object sorting, flexible micro-block assembly, synergistic prey detection/capture, the measurement of Young’s modulus of zebrafish zygotes, and in-situ fetal movement monitoring, revealing great potential in biomedicine, precision manufacturing, minimally invasive and robotics surgery.

Introduction
Microbots are miniature intelligent microsystems that consist of integrated sensing, actuation and control units1,2, holding great promise for cutting-edge applications in biomedicine3, precision manufacturing, minimally invasive and robotic surgery4. Unlike, conventional micro-electromechanical systems (MEMS) based on silicon, microbots can be designed and fabricated using smart soft materials, revealing improved flexibility and biocompatibility3,4. At present, the development of microbots mainly resorts to advanced micro/nano manufacturing technologies and the development of smart materials, the former usually refers to self-assembly, 3D/4D printing, two-photon polymerization (TPP)5; and the latter relays on stimuli-responsive materials that can undergo reversible reconfiguration under external stimuli6. Based on this design principle, microbots with different functionalities have been successfully developed by combining advanced manufacturing protocols with various smart materials7. Correspondingly, microbots can be manipulated via different driving strategies including both physical signals such as light/magnetic/electric fields8–20, and chemical stimuli such as moisture21, pH value4,7,22, different solvents23,24. For example, Xiong et al. presented a 4D-printed artificial heart composed of N-isopropylacrylamide (NIPAM)-doped single-walled carbon nanotubes (SWNTs) hydrogel, which emulates the cardiac pulsation by programmable periodic light manipulation of the contractile-diastolic behavior of the structure9. To realize the magnetic manipulation of microbots, Xu et al. developed a poly(ethylene glycol) diacrylate (PEGDA) hydrogel doped with magnetic nanoparticles (MNP)3. The resultant micro-mechanical claw produced via TPP enables grasping and cell transfer with the help of magnetic field. Florea et al. reported the TPP fabrication of 4D microstructures based on a phenyl-boronic acid copolymer, which can be controlled by modulating sugar concentration23. In contrast to other chemical reagents, the use of sugar as a driving source may reduce the harm to organisms.

Previously, we have developed an artificial musculoskeletal system based on bovine serum albumin (BSA) and SU-8 composite structures, demonstrating pH-responsive actuation capabilities7. The resulting microgripper exhibited exceptional dexterity in performing various manipulation tasks, including precise object grasping and controlled release operations. Nevertheless, despite the fact that soft microbots enable programmable shape morphing, their practical applications are fundamentally constrained by the lack of force feedback ability, which becomes critical for developing intelligent robotic systems2,3,25. The implementation of real-time force detection systems could yield multiple operational benefits, including enhanced dexterity in manipulating microscopic objects, minimized mechanical trauma to delicate biological structures13, more precise force regulation17, and adaptive responsiveness to dynamic environments4. These advancements collectively suggest that force feedback integration is essential for soft microrobots development. However, significant challenges remain in achieving high-density sensor integration with miniature soft robots while maintaining their inherent deformability.

Considering the limitations with respect to dimension and loading capacity, microbots with integrated perception and actuation capabilities cannot be developed by directly assembling sensing and actuating components together. Consequently, the manipulation, signal perception and feedback functions of microbots have to rely on their working platforms3,6. As a representative example, optical fibers that feature anti-electromagnetic interference26, small size, and biocompatibility, have emerged as a versatile working platform for microbots27–32. In the past decade, individual functional devices including sensors, actuators and imaging components have been successfully integrated with optical fibers, enabling signal perception33, mechanical operation34,35 and imaging36,37. For instance, the integration of sensitive microstructures on optical fibers makes it possible to detect multi-signals such as temperature38, pressure39,40, minuscule force41, humidness42 and pH value43. Unfortunately, these sophisticated sensors are incapable of mechanical manipulation. On the other hand, with the help of micro/nanofabrication technologies, squeezing and hydraulically driven mechanical microstructures have also been manufactured on fibers34,35, enabling on-demand actuation. Nevertheless, these fiber-based actuators lack the perception abilities for dynamic signal feedback and on-time adjustment. To date, the development of fiber microbots that permit both sensitive perception and robotic actuation remains a big challenge, because it requires an innovative combination of smart materials and their manufacturing technologies32.

Herein, inspired from natural Bobbit worm, we developed a tactile gripper-on-a-fiber (TGoF) system that enables both perception and actuation through multiple on-tip TPP fabrication process. The Bobbit worm, characterized by its elongated fibrous morphology, is a sophisticated marine ambush predator despite lacking eyes and the brain. It employs five cephalic antennae to detect the mechanical and biochemical cues. When triggered by prey movement, the organism executes explosive strikes from its sedimentary burrow, ensnaring targets with scissor-like maxillae44,45. The TGoF system that mimics Bobbit worm enables synergistic optical sensing and chemical actuation. Typically, it mainly consists of a wave spring, a planar reflector with a scattering cone and a smart gripper, as well as a single-mode fiber (SMF). The multi-layer wave spring on the tip of the SMF can converts the applied micro-force into detectable stretching or compression deformation, serving as a Fabry-Perot (F-P) interferences sensor. To prevent the influence from environmental light and the interference signals, a finely tuned scattering cone has been incorporated onto the upper plane. In addition to sensitive perception, a smart gripper with a pair of SU-8 frames and in-situ integrated BSA muscle is fabricated on top of the wave spring, forming the TGoF system. With the help of a coupled microfluidic chamber, the smart gripper can be manipulated via pH change, by which the expansion/shrinking of BSA muscle can trigger the grab/release operation. As a proof-of-concept, the TGoF system was employed for synergistic micro-objects manipulation and microforce sensing, for instance, the measurement of Young’s modulus of zebrafish zygotes and in-situ fetal movement. The TGoG system may hold great promise for future applications in biomedicine, precision manufacturing, minimally invasive and robotic surgery.

Results
Design, working mechanism and fabrication of TGoF system
Inspired by natural Bobbit worm, a TGoF system that enables both perception and actuation is designed and fabricated. Figure 1a shows the basic design principle of the TGoF system, in which a circular base, a wave spring for minuscule force detection, a planar reflector with scattering cone for eliminating the interference of stary light (Supplementary Fig. 1-3, Supplementary Note 1), and a pH responsive gripper for on-demand manipulation are integrated on the tip of a SMF. With the flexible processing capabilities of the femtosecond laser46–54, such a precise and complex 3D microstructure composed of different materials is produced by multiple and in-situ TPP fabrication (insets of Fig. 1a). To achieve micro force measurement, a multi-layer wave spring with a planar reflector is designed and fabricated based on SU-8, serving as a F-P sensor. Unlike conventional helical springs, the wave spring may have significantly enhanced mechanical stability and shock resistance. It can convert small stress into detectable stretching or compression, giving rise to the variation in cavity length (Fig. 1b). In this way, the applied micro force can be calculated through an intuitive spectral representation (Supplementary Fig. 4, Supplementary Note 2). More importantly, with the help of a smart gripper, our micro force sensor is workable in both stretching and compression states.

The smart gripper is manufactured using SU-8 as frameworks and BSA as pH responsive muscles, respectively. The SU-8 framework can guarantee the mechanical stability in different environments, and the BSA muscles can be dynamically actuated (swelling and shrinking) upon pH change. The cooperation of the musculoskeletal structure enables controllable gripping and release performance. The essential driving mechanism is schematically illustrated in Fig. 1c. Briefly, the BSA hydrogels mainly consists of amino acids, and the electrostatic repulsion of these functional groups dominates their volume. It is well known that the isoelectric point of BSA is about 4.77. In this condition, the electrostatic repulsion is the smallest, demonstrating a shrinking state. When the pH value decreases or increases, the BSA structure would possess positive or negative charges, respectively, leading to significant swelling due to the electrostatic repulsion. The reversible actuation of the BSA muscles make it possible to manipulate the gripper in a highly controlled fashion.

The in-situ fabrication of sensing and actuating structures on the tip of a SMF is realized through multiple TPP processes. To achieve the in-situ integration of the SU-8 structure, the SMF was fixed on a cover glass, where a microfluidic chamber was equipped (Fig. 1d). Consequently, the in-situ TPP fabrication and developing processes can be implemented on the stage. The first TPP fabrication was performed to manufacture SU-8 microstructures including the circular base, the wave spring and the reflector, as well as the gripper framework. To make the gripper smart, BSA muscles was integrated with the SU-8 framework by performing the secondary TPP fabrication. In this way, a robotic SMF equipped with a tactile gripper (TGoF) is developed.

Mechanical simulation of the wave springs
The sensing properties of the TGoF system primarily rely on the mechanical deformation of the wave springs. Consequently, the sensing performance can be optimized through reasonable modulation of the wave spring parameters. Figure 2a shows the design model of the wave spring, which consists of multi-layers of circular wave belts that stack together in a staggered manner. Detailed description of the correlation between the outer diameter (D1), the inner diameter (D2), the band height (h), the band thickness (t), the band number (N), and mechanical properties of the wave spring is provided in equation (S6) (supplementary information). To give a clear depiction of the TGoF system, a partially transparent model is shown in Fig. 2b, demonstrating the 3D configuration of the wave spring utilized in the mechanical simulation. To simplify the simulation process, we neglected the influence of the scattering cone and gripper on the mechanical properties of the spring. Since the sensitivity depends on the deformation of the wave spring under an equivalent load, we set a monitored point at the center of the planar reflector (underneath the scattering cone) to record the displacement.

In the finite element simulation, both stretching and compression states with different loads are measured, respectively. As shown in Fig. 2c, a comprehensive analysis on stretching and compression deformation of the wave spring are conducted under applied forces of 0.2 µN, 0.6 µN, and 1 µN, respectively. Notably, the displacement of each part of the wave spring can be well identified from the color distribution. The corresponding data diagram indicates that the displacement remains consistent under both stretching and compression states when subjected to the same load (Fig. 2d). According to equation (S6), varying the wave belt thickness (t) can tune the mechanical properties of the wave spring directly. In the following simulation, we tuned thickness (t) from 0.5 µm to 2 µm, while kept the applied loads for both stretching and compression at 1 µN (Fig. 2e). The dependence of displacement on load for wave springs of different belt thickness is shown in Fig. 2f. The decrease of belt thickness leads to a significant increase in displacement. In this regard, a relatively small thickness may give rise to much higher sensitivity. Nevertheless, considering the mechanical strength and the stability, when t is less than 1 µm, the resultant wave spring lacks sufficient structural strength to support the grippers. In this work, the bandwidth and thickness of the wave spring are set to be 5 µm and 1 µm, respectively (Supplementary Fig. 5, Supplementary Note 3). In addition, the influence of number of layers on the mechanical properties and the deformation under torsional force were also explored (Supplementary Fig. 6 and 7, Supplementary Note 4).

Microforce sensing
In the microforce sensing measurements, three wave springs with belt thicknesses of 1 µm (WS-1), 1.5 µm (WS-2), and 2 µm (WS-3) were fabricated and tested for comparison. To quantify the micro force applied to the sensor, a homemade system was constructed. Since commercial optical fibers feature standardized properties with known dimensions and Young’s modulus, we developed a custom micro force generator based on fiber optics for micro force calibration41. As shown in Fig. 3a, with the assistance of the precision measurement platform, the wave spring sensor can gradually approach the cantilever fiber. When the wave spring sensor pressed against the end of the cantilever fiber, the as-generated micro force can be fed back to the wave spring, leading to the compression. According to the length of cantilever fiber (Lfiber) and the displacement of the contact point (Δd), the load received by the sensor can be precisely calculated (equation S7), while the spectra shift of the F-P sensor can be recorded for calibration.

Figure 3b–g show the evolution of the interference spectra and the micro force sensitivity of the three wave spring sensors. Generally, with the increase of the compression load, the cavity length decreases, and the interference spectra are blue shifted. In the case of WS-1, the interference spectrum shifted from 1547.6 to 1534.6 nm when the compression load increased from 0 to 42 µN (Fig. 3b). Linear regression analysis of the load and interference wavelength suggests a high correlation coefficient of 0.999 and a slope of −0.32, indicating a high sensitivity of −0.32 nm/µN (Fig. 3c). In sensing experiments of the other two wave springs, similar blue-shift effects are also observed (Fig. 3d, f). The micro force sensitivities with respect to WS-2 and WS-3 are −0.10 nm/µN and −0.03 nm/µN, respectively (Figs. 3e, g). By comparison, the micro force sensitivity decreases with the increase of belt thickness. Therefore, the mechanical characteristics of the wave spring can be precisely modulated to meet diverse requirements by tuning these structural parameters. Despite slender springs can lead to relatively higher sensitivities, large deformation may result in structural instability in practical force detection. Simultaneously, a substantial change in cavity length can induce a pronounced drift in the spectra, which hampers sensitivity demodulation. Considering the sensitivity, measuring range and stability, we chose WS-1 for the following experiments. Meanwhile, an exploration experiment is conducted on the relationship between the laser power and the sensitivities of the wave springs (Supplementary Fig. 8, Supplementary Note 5). In addition to compression, the sensitivity of stretching process is also evaluated (Supplementary Fig. 9 and 10). Moreover, the micro force sensitivity of the F-P sensor is closely related to the refractive index of the environment. To meet the requirement in practical applications, the sensitivity in aqueous solutions of different pH value is also characterized (Supplementary Fig. 11, 12). Additionally, to assess the cyclic durability of the wave spring, we performed 200 loading cycles, which indicated reasonable stabilities of the TGoF system (Supplementary Fig. 13, Supplementary Note 5). It is worth pointing out that both the wave spring and the gripper fabricated via TPP may suffer from relatively high variability. To minimize such experimental differences, the laser processing parameters and developing conditions should be strictly consistent. Because the deformation of the wave spring is very small within a moderate load range, we employed a more flexible coil spring to visualize the stretching and compression process (Supplementary Fig. 14). When the coil spring (equipped with a disc) was compressed and stretched, its length change can be clearly identified. At the same time, the corresponding interference spectra show obvious blue or red shift (Supplementary Video 1). To evaluate the mechanical stability against bending torque, we investigated the deformation behavior of the wave spring theoretically and experimentally by applying a perpendicular force to the axis. Additionally, to verify the excellent stability of the wave spring, we designed and fabricated a helical spring array, and made a comprehensive comparison against bending torque (Supplementary Fig. 15–20, Supplementary Table 1, Supplementary Note 6).

Actuation of grippers
Soft microbots that feature flexible body yet controllable deformation are promising for developing fiber manipulators6,7. To endow the wave spring sensor with robotic actuation, we further fabricated a smart gripper based on a stiff/soft synergistic dual material system, in which the relatively stiffer SU-8 is used as supporting frameworks and pH responsive BSA is employed as muscle for gripper actuation. As shown in Fig. 4a, the expansion of the BSA in basic condition (e.g., pH=13) can drive the gripping behavior, whereas the shrinking near isoelectric point (pH=5) can lead to the release of the gripper. In TPP fabrication, the 3D model is first converted into point cloud data, where the scanning step length (SL) specifically denotes the spatial interval between two adjacent voxels within this dataset. critical parameters governing the power density received by photopolymer include laser power, single-point exposure duration, and scanning SL, which collectively determine the photopolymerization efficacy and final structural fidelity. When laser power and exposure time are fixed, the voxel dimensions remain constant. By adjusting SL to modulate the degree of voxel overlap, the density of the polymer network can be precisely controlled. To optimize the pH responsive property of BSA, we fabricated three BSA blocks by varying the SL from 200 nm to 100 nm, and investigated their volume change in aqueous solutions of three typical pH values (pH=1, 5, and 13, Fig. 4b). Generally, the BSA microstructure fabricated using larger SL may have a much looser BSA network, demonstrating a relatively greater length swelling ratio (LpH=13/LpH=5, LpH=1/LpH=5). Additionally, for the structure fabricated using the same SL, the length swelling ratio between pH=13 and pH=5 is much larger than that between pH=1 and pH=5. However, it is worthy pointing out that a larger swelling ratio cannot guarantee larger driving effect, since both the Poisson ratio and Young’s modulus are different. Therefore, the BSA muscles fabricated based on different SL are integrated with the SU-8 frameworks for further comparison. The resultant grippers and their responsiveness under different pH values are demonstrated in Fig. 4c. In acid condition (pH=1), the BSA structure of 100 nm SL can drive the gripper clamping, whereas in basic condition (pH=13), both grippers fabricated using 100 nm and 150 nm SL are workable. In the following experiments, we fixed the scanning SL of BSA at 150 nm for the gripper manipulation.

By integrating the pH responsive gripper and the wave spring sensor with a SMF, the TGoF system formed. Figure 4f–h show the open/close manipulation of the gripper in aqueous solutions. To get better control over the environmental pH values, a tri-channel microfluidic chip was employed as the working platform (Supplementary Fig. 21, Supplementary Note 7), where the pH can be freely switched. Interestingly, when the initial pH value was ~5, and the gripper was fully open. By switching the environment to alkalinous solution (pH=13), the gripper was closed (Fig. 4f, Supplementary Video 2). According to the quantitative responsiveness experiments, both the response and recovery time for the gripper is evaluated to be ~1.4 s (Supplementary Fig. 22 and Note 7). Additionally, to assess the cyclic durability of the pH-responsive gripper, we performed 200 actuation cycles, which confirmed the durability of the TGoF system (Supplementary Fig. 23, Supplementary Note 7). To explore the gripping force, a Y-shape structure with an original included angle of 36° was positioned at the center of the gripper (Fig. 4g). After switching the pH value to 13, the gripper clamped and pressed Y-shape structure. Consequently, the included angle decreased to 16° in 2.8 s (Fig. 4g, Supplementary Video 2). To represent the as-generated forces, a displacement-stress simulation of the Y-shaped structure was built (Supplementary Fig. 24, Supplementary Note 8), and the clamping forces is simulated to be ~1.5 µN (Supplementary Fig. 25). Additionally, in a passive process, the Y-shape structure was pulled through the closed gripper when the environmental pH was kept at 13 (Fig. 4h, Supplementary Video 2). Notably, due to the confinement of the gripper, the Y-shape structure deformed and propped open the gripper until passed through it.

Operation of TGoF system
At present, precise assembly of microstructures in a highly controlled fashion remains a challenging task, because it requires miniature yet complex sensing and actuation components that permit aiming, flexible gripping, installation, release, and the real-time perception of these processes55,56. To demonstrate the sensing and actuation capabilities of our TGoF system, we performed several operations including micro-objects sorting, flexible assembly of micro-building blocks, and perceivable hunting that mimics Bobbit worm. First, micro-objects of circular, triangular, and the square shapes are designed and fabricated for corresponding sorting (Fig. 5a). With the help of the piezoelectric platform, the tactile gripper successfully picked up these micro-objects and released them into the corresponding containers (Fig. 5b, Supplementary Video 3). In addition to flexible manipulation, non-invasive and sensitive interaction with the micro-objects is imperative55. Interestingly, the wave spring sensor also enable real-time microforce detection and feedback. In the assembly of micro-building blocks (Fig. 5c), the roof of the micro-castle anchored to the substrate was picked up by breaking the connecting wire, and the real-time stress change during this process was recorded by the TGoF sensor (Supplementary Video 4). As shown in Fig. 5d, with the increase of pulling displacement, obvious red-shift of the interference spectra can be observed. The dependence of the as-generated micro forces on the pulling displacement shows that the breaking point appears at ~20 µm, and the breaking force of the connecting wire is ~127.7 µN. Additionally, by mimicking natural Bobbit worm, the TGoF system also enables synergistic prey detection and capture by coupling an automatic pH switching system. Figure 5g shows the schematic illustration of the working mechanism, in which the threshold of micro force for the pH switch is set to be 80 µN. When the fish model gradually press the TGoF system, the as-generated force can be well recorded and calculated simultaneously. When the micro force exceeded the threshold (80 µN), the pH switch can be triggered and the gripper clamped the prey at once. Moreover, in the subsequent grasping process, the pulling tension can be also detected until the connecting wire anchored the fish model was broken (Supplementary Video 5). The evolution of the interference spectra in the prey detection and grasping processes, as well as the micro force change on relative displacement are shown in Fig. 5i–k, respectively.

Proof-of-concept applications of the TGoF system
The sensing and actuation abilities of the TGoF system hold great promise for cutting edge applications, for instance, the minimally invasive surgical intervention and endoscopic operation57–59. Nevertheless, the actuation process that usually involves acid or alkali solutions has imposed limitations on their practical applications in biomedical applications7. To address this issue, the gripper structure was re-designed, in which a replaceable gripper-based microprobe is proposed (Fig. 6a). The sensing microprobe can work in conventional physiological environment (pH=7), and the probe tip can be replaced with other ones in alkali solutions. As shown in Fig. 6a, a series of microprobes of different sizes can be designed and fabricated for complex stress measurement. For instance, the microprobe equipped TGoF system can be employed for measuring the Young’s modulus of the zebrafish zygotes (Fig. 6b). In the practical operation, we demonstrated the installation of a microprobe of ~35 µm in length and 6 µm in diameter (Fig. 6c, Supplementary Video 6). According to the classical Hertzian contact model, the Young’s modulus of the cell can be measured by fitting the probe size, the indentation depth, and the corresponding micro force (Supplementary Fig. 26, Supplementary Note 9). When the SMF fixed on a high-precision stepper motor gradually approached and pressed the zebrafish fertilized zygotes, the displacement of the microprobe and the corresponding indentation of the zygote can be clearly observed (Fig. 6d, Supplementary Video 6). Meanwhile, obvious blue-shift of the interference spectra can be recorded (Fig. 6e). With the increase the relative displacement, the pressure on the wave spring increased, and the interference spectra regularly shifted to short wavelength. According to the sensitivity of the wave spring, the micro force subjected to the fertilized zygote can be deduced backwards. In this way, a model of indentation depth and micro force is constructed (Fig. 6g). By nonlinear fitting of indentation depth and micro force in equation (S9), the Young’s modulus of the fertilized zygote in the present case was measured to be ~0.103 MPa. In addition, the TGoF probe can also detect the fetal movement of an active embryo of Oryzias latipes (Fig. 6h). Notably, the heart beating and the seedling rotating of the embryo can be observed from the microscopic images. In the stationary state, the interference spectrum kept stable without fluctuation. When fetal movement occurred, the interference spectrum showed obvious red-shift (Fig. 6i, Supplementary Video 7). In terms of biological properties, previous results have confirmed that both BSA hydrogels and SU-8 photoresist demonstrate low immunogenicity and cytotoxicity, making them suitable for biomedical device fabrication60,61. These proof-of-concept applications suggest that the TGoF system holds great promise for future applications in the fields of micromanipulation, biomedicine, and surgical robotics.

Methods
Preparation of pH-responsive BSA photoresist
BSA (Sigma-Aldrich, A7638) and methylene blue (MB, Sigma-Aldrich, M9140) were used as monomers and photoinitiators, respectively. 600 mg of BSA was added to 800 µL of MB solution (0.6 mg/mL). Then the mixture was incubated at 5°C for 48 h to ensure complete dissolution of BSA. The pH solutions involved in the BSA actuation experiments are pH=1 (0.2 mol/L HCL+0.2 mol/L KCL), pH=5 (0.1 mol/L NaOH + 0.2 mol/L potassium hydrogen phthalate), and pH=13 (1.0 mol/L NaOH).

Fabrication of the SU-8 and BSA structures on a SMF
The fiber optic stripper (CFS-3) and the fiber cleaver (FC-6T) were employed to precisely remove a portion of the SMF coating and neatly sever the tip. After being cleaned with alcohol and acetone, the SMF was horizontally positioned on a pristine cover-glass and securely affixed using UV curing adhesive. An appropriate volume of SU-8 (2075, NANO, MicroChem) photoresist was dispensed onto the tip of the SMF, followed by placing the entire assembly in a light-free constant temperature chamber at 95°C for 1 h. The TPP processing system consists of a Fs laser source (Ti: the sapphire femtosecond laser oscillator with a central wavelength of 800 nm, a pulse width of 120 fs, and a repetition rate of 80 MHz), an oil-immersed objective lens (Olympus, ×60, numerical aperture: 1.4), a piezo stage (Physik Instrument), and a galvo scanning system (Sunny Technology). According to the pre-designed model, the laser spot was moved in the SU-8 photoresist in a strategy of the point-by-point and layer-by-layer polymerization to finally outline the complete structure. The laser power and SL are 12 mw and 200 nm, respectively. The processed SU-8 structure was subjected to a 30-minute curing process at 90°C, followed by immersion in a developer for 20 min to facilitate the development.

In the secondary TPP process, the BSA photoresist was added to the SU-8 structure. Prior to the TPP processing of the BSA, the piezo stage was adjusted in order to ensure precise deployment of laser focus at a predetermined position. Subsequently, the same laser scanning strategy was employed to seamlessly integrate the BSA unit within its corresponding SU-8 frame. The SL for BSA was set as 100 nm, 150 nm, and 200 nm for different experiments, while the laser power is 18 mW. After completing the composite processing, the whole structure was immersed in distilled water for 5 h to remove the uncured BSA photoresist.

Simulation
The finite element simulation was performed in Comsol Multiphysics 6.0. In simulation models, the Young’s modulus, density and Poisson’s ratio of SU-8 were set to 4.8 GPa, 1200 kg m−3 and 0.26, respectively. Detailed modeling methods and parameter settings were reported in corresponding chapters and supplementary information.

Cells experiment
Zebrafish fertilized zygotes: One day after fertilization, the cells are fixated in a paraformaldehyde solution and stored at 11°C in the dark.

Characterization
The detailed characteristics of samples were obtained using a field emission electron microscope (SEM, JSM-7500F, JEOL), with the current intensity and gold spray time set to 20 mA and 75 s, respectively. Meanwhile, the optical images were characterized by an inverted biological microscope (NIB410, with a 20 MP Sony Exmor CMOS Sensor). The optical fiber spectrum demodulator (GC-97001C-06-04, 1525–1568 nm) was self-built, and the scanning frequency is twice per second.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors describe an innovating method to fabricate a complex mechanical system (including multi-material actuators and optical sensors), on the tip of an optical fibre. The gripper is controlled by change in pH in a microfluidic chip changing the volume of a BSA gel. They present a computational study of the mechanical property of their system and performances of their sensors. The authors finally conclude with the description of a series of test to demonstrate the use of the system with practical application such as micromanipulation and microprobing.\nThis work is demonstrating that complex multimaterial microrobot with multiple functions can be fabricated using 2PP and used in complex micromanipulation task and even interaction with living and moving specimens.\nThe authors supplement their paper with a large number of complementary materials ranging from complementary simulation to further description of the system.\nThis paper bring new light on the possibility of 2PP fabrication using SU-8 and more specialised materials. This paper is also putting together a lot of the methods and devices published previously in the field of microrobotics and thus proving that complex system are feasible. The large emphasis in application and\nThe high quality of the writing, schematics and figures make this paper worth publishing in Nature Communication.\nBefore publishing, please consider the following suggestions.\nThe microfluidic chip is currently one of the main elements for inducing a change of pH and thus actuating the microgripper. This makes it a fundamental part of the robotic system presented here. The schematic presented in supplementary note 6 should be present in the main paper even if in a smaller picture version. Additionally, a picture of the experimental setup should be added to the final manuscript or supplementary material.\n2PP Microrobotics system often suffer from high variability during experiments in between devices and within a single device repeated experiments due to changes on the condition of the polymers and its mechanical property. This paper does not discuss any of those issues or show any repeated experiments. Please address this point by experiments or discussion.\nSimilarly, change of properties of those material with time and repetition is a concern. Data showing the behaviour of the gripper and spring during many repeated cycles would be improving the understanding of the capability of such system.\nThe discussion part of this paper consists only of a conclusion and summarize. Please extend this to discuss limitation of such system, future possible improvement and discussion of the obtain results and applications. Comparison to state-of-the-art silicon-based MEMS devices would be a valuable addition to this paper.\nL74 replace “tiny” by scientifically significant word. Please review the article for similar instance of non-descriptive word.\nL262, please define the parameter “scanning step length”. A link to the power density received by the material or the partial polymerisation state of the material would be ideal.\nL398 “Generally, optical fibers can server as a versatile”\nCongratulation for the great job.\nDr Florent Seichepine\nIMPERIAL, Bioengineering Department", "reviewer_2": "This paper proposes a bio-inspired smart microgripper that is manufactured at the tip of an optical fiber. While the system is well-designed, the paper lacks sufficient contribution and requires substantial improvement before it can be considered for submission as a journal article.\nIntroduction :\n1.The introduction highlights the potential impact of microbots in a wide range of applications in the future. With the help of TPP and smart materials, building microbots that can be manipulated on demand by external physical stimuli became possible. The authors stated that much of the reported research focused on actuators, with less emphasis on perception-capable actuators. The reviewer understands that the main contribution of this research is the manufacturing of a microgripper on an optical fiber, enabling high-sensitivity force perception. While the authors successfully elaborated on microbots, they failed to emphasize the importance of force feedback and discuss the challenges in previous research related to force sensing (e.g., comparison with Ref. 46).\n2.The authors mentioned that the system is bio-inspired by the natural Bobbit worm but did not discuss in detail how the two are similar. All living creatures have sensing abilities as well as manipulation capabilities, i.e., sensor and actuator functions. In the introduction, the authors should include details on how Bobbit worms hunt their prey based on perceived forces.\n3.In line 69, references 33–38 are irrelevant to the context and should be reconsidered.\n4.The microgripper with BSA as the artificial muscle discussed in the article exhibits similarities to the system presented in “Ma, ZC., Zhang, YL., Han, B. et al. Femtosecond laser programmed artificial musculoskeletal systems. Nat Commun 11, 4536 (2020).” The authors must emphasize the contribution of the sensing structure in the introduction section to distinguish their work.\nResult:\n1.In the results section, the authors mentioned that the wave spring may significantly enhance mechanical stability and shock resistance (line 111). To support this statement, stability against torsional force is provided in the supplementary notes, but no information is given about bending torque. If the contribution of the sensor lies in its structural design, the authors should observe the response to bending torque when an external force is applied perpendicularly to the axis of the wave spring. Additionally, stability was explained in terms of minimal deformation in the structure based on mechanical simulation. However, will the optical response also remain insensitive? The authors should analyze and present experimental results of the sensor’s performance under both torsional force and bending torque.\n2.There is no clear explanation of why the optical fiber is used as the cantilever during sensor calibration instead of a beam structure with a known modulus.\n3.Could the authors explain in detail the purpose of the experiment shown in Fig. 3(h, i)? Tensile or compressive forces with numerical measurements would be adequate for readers to perceive the force. What is the purpose of visualizing the response using another softer spring?\n4.The overall text including the figures should be rechecked. There were several misspelled words, supplementary notes were not mentioned (line 207), some words had different text size, and the figure 4b had wrong legend.", "reviewer_3": "This manuscript presents an innovative tactile gripper-on-a-fiber (TGoF) system inspired by the natural Bobbit worm, integrating advanced design principles and manufacturing techniques. The system demonstrates high sensitivity and functionality in micro-force sensing and gripping applications. While the work shows some novelty, there are still issues with certain details. Therefore, the reviewer recommends that the authors address the following points before the manuscript can be considered for publication.\n1. The authors used wave springs for microforce sensing and investigated the impact of band thickness and height on mechanical sensing performance. However, the effect of the spring's configuration on performance was not discussed, nor was the cyclic stability of its mechanical sensing evaluated.\n2. The responsive performance of the pH-responsive BSA muscle will directly influence the flexibility of the TGoF system. How quickly does it respond? Is there a stress relaxation effect? And how stable is it over long-term use?\n3. Are the planar reflector and scattering cone also made of SU-8? What is the wavelength and power of the initial light emitted from the SMF? What is the reflectivity of this structure?\n4. Whether stretching or compression, these are longitudinal deformation modes. However, in practical applications, wave springs may also experience lateral bending. The authors should consider the force response in this context as well.\n5. A more detailed description of the microfluidic chip should be given in Supplementary Fig 11, including design, channel size and functionality, etc.\n6. Given the potential biologically relevant applications of this microsystem, the authors should assess its biological properties, such as cytotoxicity.\n7. The authors do not provide a specific comparison of the TGoF system with existing tactile sensors or micro-robots. Could the authors discuss how their system improves upon or differs from existing technologies in terms of functionality, sensitivity, stability, cost, etc.?"}, "author_response": "Response to reviewers’ comments\nWe thank all reviewers and their valuable comments. Their comments help us\nto improve the quality of our work. We have revised our manuscript with care\naccording to the comments. Changes have been highlighted in red. A point-by-\npoint response has been listed as follow.\nReviewer: 1\nComments: The authors describe an innovating method to fabricate a complex\nmechanical system (including multi-material actuators and optical sensors), on\nthe tip of an optical fibre. The gripper is controlled by change in pH in a\nmicrofluidic chip changing the volume of a BSA gel. They present a\ncomputational study of the mechanical property of their system and\nperformances of their sensors. The authors finally conclude with the\ndescription of a series of test to demonstrate the use of the system with practical\napplication such as micromanipulation and microprobing.\nThis work is demonstrating that complex multimaterial microrobot with\nmultiple functions can be fabricated using 2PP and used in complex\nmicromanipulation task and even interaction with living and moving specimens.\nThe authors supplement their paper with a large number of complementary\nmaterials ranging from complementary simulation to further description of the\nsystem.\nThis paper bring new light on the possibility of 2PP fabrication using SU-8 and\nmore specialised materials. This paper is also putting together a lot of the\nmethods and devices published previously in the field of microrobotics and thus\nproving that complex system are feasible. The large emphasis in application and.\nThe high quality of the writing, schematics and figures make this paper worth\npublishing in Nature Communication.\nBefore publishing, please consider the following suggestions.\nResponse: Thank you very much for your positive and encouraging feedback. We\nare grateful for your recognition of the innovation in our study and the potential\nimpact of our work. We also appreciate your constructive suggestions, and we are\ncommitted to carefully addressing the issues raised in order to improve the\nmanuscript.\nComment 1: The microfluidic chip is currently one of the main elements for\ninducing a change of pH and thus actuating the microgripper. This makes it a\nfundamental part of the robotic system presented here. The schematic\npresented in supplementary note 6 should be present in the main paper even if\nin a smaller picture version. Additionally, a picture of the experimental setup\nshould be added to the final manuscript or supplementary material.\nResponse: Thank you for your valuable comments. The schematic diagram of the\nmicrofluidic system (original supplementary note 6) and the photograph of the real\nmicrofluidic chip have been added to the revised manuscript (Fig. 4d and 4e).\nAdditionally, the schematic diagram of the entire experimental platform is provided\nin supplementary information (see new supplementary note 7).\nFig. 4| d Schematic diagram of the microfluidic system for manipulating the gripper.\ne Photograph of the real microfluidic chip for the TGoF system.\nPage 22, Line 338, the caption of Fig. 4d and 4e: “d Schematic diagram of the\nmicrofluidic system for manipulating the gripper. e Photograph of the real\nmicrofluidic chip for the TGoF system.”\nSupplementary Note 7\nA schematic diagram of the experimental setup shows a tri-channel\nmicrofluidic chip for the TGoF system\nSupplementary Fig. 21| Schematic diagram of the entire experimental platform\nfor pH switching and the manipulation of the TGoF system.\nAs illustrated in Supplementary Fig. 21, a microfluidic chip was developed to\nprecisely control the pH of the solution. Acid and alkaline solutions can be injected\ninto the microfluidic chip via two inlets, and the pH of the resultant solution can be\nprecisely controlled in the chamber using a syringe pump. The operation process can\nbe monitored by a microscope.\nComment 2: 2PP Microrobotics system often suffer from high variability\nduring experiments in between devices and within a single device repeated\nexperiments due to changes on the condition of the polymers and its mechanical\nproperty. This paper does not discuss any of those issues or show any repeated\nexperiments. Please address this point by experiments or discussion.\nResponse: Thank you for your insightful comments. Indeed, as compared with\nsilicon-based MEMS, the polymeric microrobots fabricated via TPP may suffer from\nrelatively high variability, which can be attributed to the slight fluctuation of laser\nprocessing conditions and the intrinsic material properties of photopolymers. To\nminimize such experimental differences, the laser processing parameters (e.g., laser\nintensity, exposure duration, scanning path, and spatial interval between two\nadjacent voxels) and heating/developing conditions should be strictly consistent. In\nthe revised manuscript, we emphasized the precautions against experimental\nvariability. Additionally, to verify the stability of a single device during repeated use,\nwe investigated the of the actuation performance of the gripper and the deformation\nproperty of the wave spring in 200 cycles, respectively. The experimental results\nconfirmed the reasonable stabilities of both the gripper and the wave spring. These\nresults have been added in Supplementary Information. For details, see the response\nto Comments 3.\nPage 15, Line 253: “It is worthy pointing out that both the wave spring and the\ngripper fabricated via TPP may suffer from relatively high variability. To minimize\nsuch experimental differences, the laser processing parameters and developing\nconditions should be strictly consistent.”\nComment 3: Similarly, change of properties of those material with time and\nrepetition is a concern. Data showing the behaviour of the gripper and spring\nduring many repeated cycles would be improving the understanding of the\ncapability of such system.\nResponse: Thank you for your valuable suggestion. To assess the cyclic durability\nof the pH-responsive micro-gripper, we performed 200 actuation cycles by switching\npH values between 5 and 13 while monitoring gripper kinematics. As depicted in\nSupplementary Fig. 23 (Supplementary Note 7), tip displacement is almost constant\nbetween pH=5 and pH=13, indicating the stable gripping behavior.\nSupplementary Fig. 23| The change of tip distance by switching the pH values\nbetween 5 and 13 in 200 cycles. Error bars denote the standard deviation of the\nmeasurements.\nAdditionally, to evaluate the mechanical durability of the wave spring, we\nconducted 200 cyclic loading tests with forces alternating between 0 µN and 42 µN.\nThe wave spring (WS-1) exhibited consistent deformation characteristics throughout\nthe testing regime, as evidenced by the stable wavelength patterns in interference\nspectra (Supplementary Fig. 13). This spectral stability under repeated mechanical\nstress demonstrates reliable elastic recovery performance, confirming the structural\nintegrity of the spring through multiple operational cycles.\nSupplementary Fig. 13| The change of wavelength in interference spectra\nduring 200 loading (42 µN)/unloading (0 µN) cycles.\nPage 15, Line 251: “Additionally, to assess the cyclic durability of the wave spring,\nwe performed 200 loading cycles, which indicated reasonable stabilities of the TGoF\nsystem (Supplementary Fig. 13, Supplementary Note 5).”\nComment 4: The discussion part of this paper consists only of a conclusion and\nsummarize. Please extend this to discuss limitation of such system, future\npossible improvement and discussion of the obtain results and applications. Comparison to state-of-the-art silicon-based MEMS devices would be a\nvaluable addition to this paper.\nResponse: Thank you for your valuable suggestion. In the revised manuscript, more\ndiscussion with respect to the limitation, the future improvement, the applications of\nthis system had been added. Additionally, we have made a comprehensive\ncomparison of our actuator with the state-of-the-art of Si-MEMS in the discussion\nsection, and the relevant literatures are suitably cited. Changes have been highlighted\nin red as follow:\nPage 34, Line 489: “While demonstrating notable advantages, the TGoF system\nexhibits discernible limitations compared to established silicon-based MEMS\ntechnologies [62-69]. Although TPP enables multi-material 3D microfabrication, its\nproduction efficiency remains suboptimal relative to conventional MEMS\nmanufacturing processes. Critical challenges in mass production, reproducibility,\nstandardization, and cost-effectiveness present primary barriers to practical\nimplementation. Furthermore, polymeric architectures display substantially inferior\nmechanical strength and durability compared to silicon-based counterparts,\npotentially limiting their reliability in high-stress operational environments.\nNevertheless, the relatively low Young's modulus and enhanced yield strength of\nphotopolymers versus silicon [62] confer distinct advantages for biomedical\napplications, particularly in minimizing risks of tissue trauma and inflammatory\nresponses. Notably, recent advancements in processable materials and femtosecond\nlaser processing systems suggest these limitations may be mitigated through high-\nthroughput parallel manufacturing approaches. This technological evolution\npositions TPP as a promising candidate for advanced additive manufacturing\napplications, including but not limited to 3D micro-robotic systems, compliant\nsensory arrays, 3D microfluidic networks, and biointegrated implants. We anticipate\nthat TPP-enabled miniaturized devices will emerge as complementary technologies\nto conventional silicon-MEMS platforms, particularly in emerging applications\nrequiring complex 3D architectures and biocompatible interfaces, holding\nsignificant potential for advancing next-generation intelligent microsystems across\nmultidisciplinary domains.”\nComment 5: L74 replace “tiny” by scientifically significant word. Please review\nthe article for similar instance of non-descriptive word.\nResponse: Thank you for your helpful comment. The \"tiny\" in the original text has\nbeen modified appropriately depending on the different description. The\nmodification contents are as follows.\nOriginal: “Microbots are tiny intelligent microsystems that consist of integrated\nsensing,”\nRevised: “Microbots are miniature intelligent microsystems that consist of\nintegrated sensing,”\nOriginal: “For instance, the integration of sensitive microstructures on optical fibers\nmakes it possible to detect multi-signals such as temperature [50], pressure [51,52],\ntiny force [53], humidness [54] and pH value [55].”\nRevised: “For instance, the integration of sensitive microstructures on optical fibers\nmakes it possible to detect multi-signals such as temperature [38], pressure [39,40],\nminuscule force [41], humidness [42] and pH value [43].”\nOriginal: “Fig. 1a shows the basic design principle of the TGoF system, in which a\ncircular base, a wave spring for tiny force detection,”\nRevised: “Fig. 1a shows the basic design principle of the TGoF system, in which a\ncircular base, a wave spring for minuscule force detection,”\nOriginal: “because it requires tiny yet complex sensing and actuation components\nthat permit aiming,”\nRevised: “because it requires miniature yet complex sensing and actuation\ncomponents that permit aiming,”\nComment 6: L262, please define the parameter “scanning step length”. A link\nto the power density received by the material or the partial polymerisation state\nof the material would be ideal.\nResponse: Thank you for your valuable comments. In the context of TPP fabrication,\nthe 3D model (STL format) must first be discretized into point cloud data for\nsubsequent point-by-point scanning. The parameter \"scanning step length\"\nspecifically denotes the spatial interval between two adjacent voxels within this\ndataset. During TPP processing, critical parameters governing the power density\nreceived by photopolymer include laser power, single-point exposure duration, and\nscanning step length, which collectively determine the photopolymerization efficacy\nand final structural fidelity. In the revised manuscript, we have formally defined the\n\"scanning step length\" parameter and systematically elucidated its relationship with\nthe photopolymerization dynamics.\nPage 19, Line 286: “In TPP fabrication, the 3D model is first converted into point\ncloud data, where the scanning step length (SL) specifically denotes the spatial\ninterval between two adjacent voxels within this dataset. critical parameters\ngoverning the power density received by photopolymer include laser power, single-\npoint exposure duration, and scanning SL, which collectively determine the\nphotopolymerization efficacy and final structural fidelity. When laser power and\nexposure time are fixed, the voxel dimensions remain constant. By adjusting SL to\nmodulate the degree of voxel overlap, the density of the polymer network can be\nprecisely controlled.”\nComment 7: L398 “Generally, optical fibers can server as a versatile”.\nResponse: Thank you for your comments. In the revised manuscript, inappropriate\nwords had been replaced.\nOriginal: “Generally, optical fibers can server as a versatile platform for microbot\nmanipulation and perception, revealing great potential for developing robot-on-a-\nfiber (RoF) systems”\nRevised: “Generally, optical fibers can server as a multifunctional platform for\nmicrobots manipulation and perception, revealing great potential for developing\nrobot-on-a-fiber (RoF) systems”\nReviewer: 2\nComments: This paper proposes a bio-inspired smart microgripper that is\nmanufactured at the tip of an optical fiber. While the system is well-designed,\nthe paper lacks sufficient contribution and requires substantial improvement\nbefore it can be considered for submission as a journal article.\nResponse: Thanks a lot for your comments. We have carefully revised our\nmanuscript, in which all of the comments have been suitably addressed. Changes\nhave been highlighted in red; a point-by-point response has been listed as follow.\nIntroduction:\nComment 1: The introduction highlights the potential impact of microbots in a\nwide range of applications in the future. With the help of TPP and smart\nmaterials, building microbots that can be manipulated on demand by external\nphysical stimuli became possible. The authors stated that much of the reported\nresearch focused on actuators, with less emphasis on perception-capable\nactuators. The reviewer understands that the main contribution of this research\nis the manufacturing of a microgripper on an optical fiber, enabling high-\nsensitivity force perception. While the authors successfully elaborated on\nmicrobots, they failed to emphasize the importance of force feedback and\ndiscuss the challenges in previous research related to force sensing (e.g.,\ncomparison with Ref. 46).\nResponse: Thank you for your valuable feedback. The importance of force feedback\nhas been emphasized, and the associated challenges has been incorporated into the\nrevised manuscript.\nPage 4, Line 61: “Nevertheless, despite the fact that soft microbots enable\nprogrammable shape morphing, their practical applications are fundamentally\nconstrained by the lack of force feedback ability, which becomes critical for\ndeveloping intelligent robotic systems [2,3,25]. The implementation of real-time\nforce detection systems could yield multiple operational benefits, including\nenhanced dexterity in manipulating microscopic objects, minimized mechanical\ntrauma to delicate biological structures [13], more precise force regulation [17], and\nadaptive responsiveness to dynamic environments [4]. These advancements\ncollectively suggest that force feedback integration is essential for soft microrobots\ndevelopment. However, significant challenges remain in achieving high-density\nsensor integration with miniature soft robots while maintaining their inherent\ndeformability.”\nPage 5, Line 84: “On the other hand, with the help of micro/nano fabrication\ntechnologies, squeezing and hydraulically driven mechanical microstructures have\nalso been manufactured on fibers [34,35], enabling on-demand actuation.\nNevertheless, these fiber-based actuators lack the perception abilities for dynamic\nsignal feedback and on-time adjustment.”\nComment 2: The authors mentioned that the system is bio-inspired by the\nnatural Bobbit worm but did not discuss in detail how the two are similar. All\nliving creatures have sensing abilities as well as manipulation capabilities, i.e.,\nsensor and actuator functions. In the introduction, the authors should include\ndetails on how Bobbit worms hunt their prey based on perceived forces.\nResponse: Thanks a lot for the comments. Details of how Bobbit worms perceive\nand capture prey have been added to the revised manuscript.\nPage 5, Line 93: “The Bobbit worm, characterized by its elongated fibrous\nmorphology, is a sophisticated marine ambush predator despite lacking eyes and the\nbrain. It employs five cephalic antennae to detect the mechanical and biochemical\ncues. When triggered by prey movement, the organism executes explosive strikes\nfrom its sedimentary burrow, ensnaring targets with scissor-like maxillae [44,45].”\nComment 3: In line 69, references 33–38 are irrelevant to the context and should\nbe reconsidered.\nResponse: Thank you for your valuable comments. References to relevant literature\nhave been revised.\nOriginal: “As a representative example, optical fibers that feature anti-\nelectromagnetic interference, small size, and biocompatibility, have emerged as a\nversatile working platform for microbots [33-44].”\nRevised: “As a representative example, optical fibers that feature anti-\nelectromagnetic interference [26], small size, and biocompatibility, have emerged as\na versatile working platform for microbots [27-32].”\nComment 4: The microgripper with BSA as the artificial muscle discussed in\nthe article exhibits similarities to the system presented in “Ma, ZC., Zhang, YL.,\nHan, B. et al. Femtosecond laser programmed artificial musculoskeletal\nsystems. Nat Commun 11, 4536 (2020).” The authors must emphasize the\ncontribution of the sensing structure in the introduction section to distinguish\ntheir work.\nResponse: Thank you for your valuable comments. In the revised manuscript, we\nhave introduced our previous work (Nat. Commun. 11, 4536, 2020) and emphasize\nthe contribution of the sensing structure in the introduction section. Changes have\nbeen highlighted in red as follows.\nPage 4, Line 56: “Previously, we have developed an artificial musculoskeletal\nsystem based on bovine serum albumin (BSA) and SU-8 composite structures,\ndemonstrating pH-responsive actuation capabilities [7]. The resulting microgripper\nexhibited exceptional dexterity in performing various manipulation tasks, including\nprecise object grasping and controlled release operations. Nevertheless, despite the\nfact that soft microbots enable programmable shape morphing, their practical\napplications are fundamentally constrained by the lack of force feedback ability,\nwhich becomes critical for developing intelligent robotic systems [2,3,25].”\nResult:\nComment 1: In the results section, the authors mentioned that the wave spring\nmay significantly enhance mechanical stability and shock resistance (line 111).\nTo support this statement, stability against torsional force is provided in the\nsupplementary notes, but no information is given about bending torque. If the\ncontribution of the sensor lies in its structural design, the authors should\nobserve the response to bending torque when an external force is applied\nperpendicularly to the axis of the wave spring. Additionally, stability was\nexplained in terms of minimal deformation in the structure based on\nmechanical simulation. However, will the optical response also remain\ninsensitive? The authors should analyze and present experimental results of the\nsensor’s performance under both torsional force and bending torque.\nResponse: Thank you for your valuable comments. To evaluate the mechanical\nstability against bending torque, we investigated the deformation behavior of the\nwave spring theoretically and experimentally by applying a perpendicular force to\nthe axis. The simulations of the bending deformation and relevant experimental\nresults are provided in new Supplementary Note 6 (including Supplementary Fig.\n15-17, 19-20), in which both mechanical deformation and the optical response under\nbending state have been discussed. Additionally, to verify the excellent stability of\nthe wave spring, we designed and fabricated a helical spring array, and made a\ncomprehensive comparison against bending torque (Supplementary Fig. 18-20,\nSupplementary Table 1).\nSupplementary Note 6\n1. The mechanical properties of wave springs against bending torque\nTo explore the mechanical property and the optical response of the wave spring\nagainst bending torque, we simulated the displacement of the wave spring by\napplying a perpendicular force to the axis. As shown in Supplementary Fig. 15,\nmicro-forces (perpendicular to z-axis) are applied along the x-axis and y-axis\ndirections, respectively. With the increase of the micro-force, the bending angle of\nthe wave spring gradually increased.\nSupplementary Fig. 15| Simulation of bending of wave spring under lateral load.\na Schematic diagram of the deformation when micro-force is applied along the x-\naxis direction. b Deformation of the wave spring under 0.2, 0.6 and 1 μN,\nrespectively. c Schematic diagram of deformation when micro-force is applied along\nthe y-axis direction. d Deformation of the wave spring under 0.2, 0.6 and 1 μN,\nrespectively.\nTo quantitatively analyze the displacement, we set the center of the upper cover\nas a monitoring point and recorded the displacements under different microforces\n(Supplementary Fig. 16b and 16d). With the increase of lateral force in the range of\n0.1-1 µN along the x-axis, the displacement of the monitoring point gradually\nincreased. When the lateral force is 1 µN, the displacement of the monitoring points\ncan reach 0.092 µm. Similarly, the displacement along the y-axis direction shows\ncomparable results.\nSupplementary Fig. 16| Displacement of the wave spring (monitoring point)\nunder lateral load. a Lateral force is applied along the x-axis direction. b\nDependence of the x-axis displacement of the monitoring point on different lateral\nforces within the range of 0.1-1 µN. c Lateral force is applied along the y-axis\ndirection. d Dependence of the y-axis displacement of the monitoring point on\ndifferent lateral forces within the range of 0.1-1 µN.\nIt is worth pointing out that the displacement of the monitoring point under\nlateral force does not represent the change in the length of the sensing cavity\n(Supplementary Fig. 17). When the external force is 0, the length of the F-P sensing\ncavity of the wave spring is L. Under lateral force, the wave spring bent, and the\nlength of the F-P sensing cavity is L’. Therefore, the change in the length of the F-P\nsensing cavity is ∆L (∆L=L’-L). According to the Pythagorean Theorem, ∆L can be\ncalculated to be 2.698×10-4 µm when the lateral force is 1 µN.\nSupplementary Fig. 17| Schematic diagram of the displacement of the wave\nspring under lateral force. a The structural deformation of the wave spring. b\nSchematic diagram of the length variation of the F-P sensing cavity.\n2. Comparison between wave spring and helical springs\nTo verify the excellent stability of the wave spring, a sensing structure with\nfour helical springs is designed for comparison. Supplementary Fig. 18 shows the\ndeformation simulation of a comparative sensing structure with four helical springs\nunder vertical and lateral load. To make the two structures comparable, the structural\nparameters of the helical springs are regulated to match the basic mechanical\nproperties of the wave spring. As shown in Supplementary Fig. 18b and c, the\ndisplacement of the upper cover structure is 0.077 µm under a vertical force of 1 µN,\nwhich is quite similar with that of the wave spring (0.074 µm) under the same force.\nNevertheless, when a lateral force is applied to the structure, more obvious bending\nbehavior can be observed Supplementary Fig. 18e and f. When lateral micro-force\nof 1 µN is applied, the displacement of the upper cover is 0.607 µm, corresponding\nto the change of the F-P sensing cavity length (ΔL) of 2.244×10-3 µm, which is one\norder of magnitude higher than that of the wave spring (Supplementary Table 1).\nThese simulation results confirm the superior mechanical stability of the wave spring\nagainst bending torque. When the sensing structure is subjected to the same vertical\nand lateral forces, the deformation in the vertical direction is dominant.\nSupplementary Fig. 18| Deformation simulation of a comparative sensing\nstructure with four helical springs under vertical and lateral load. a Schematic\ndiagram of the stretching model of the helical spring. b Deformation of the helical\nspring structure under 1 µN vertical micro-force. c Dependence of displacement on\nvertical microforce. d Schematic diagram of deformation when lateral micro-force\nis applied. e Bending deformation of the helical spring structure under lateral micro-\nforce (1 µN). f Dependence of displacement on lateral microforce.\nSupplementary Table 1. Comparison of deformation simulation results between\nwave spring and helical springs.\nwave spring helical spring\nChange of the F-P sensing cavity\nlength (ΔL) under 1 µN vertical 0.074 µm 0.077 µm\nforce\nChange of the F-P sensing cavity\nlength (ΔL) under 1 µN lateral 2.698×10-4 µm 2.244×10-3 µm\nforce\n3. Experimental comparison of the sensing properties between wave spring and\nhelical springs\nThe deformation and sensing properties of the wave spring and the helical\nsprings against bending torque were also investigated experimentally. We first\ncompared the deformation of the two springs under the same lateral force (~196 µN)\nvia microscopy. As shown in Supplementary Fig. 19, the wave spring bent slightly,\nwhereas the helical spring deformed significantly, indicating the superior\nmechanical stability of wave spring against bending torque.\nSupplementary Fig. 19| Deformation of wave spring and helical springs under\nlateral force (196 µN). a The microscopic image of the wave spring. b The\nmicroscopic image of the helical springs. The inset is the original shape of the helical\nsprings.\nIn addition to the mechanical deformation, the sensing properties were also\ncompared quantitatively (Supplementary Fig. 20). With the increase of the lateral\nforce, the interference spectra of both wave spring and helical springs undergo a\nuniform red-shift, indicating the increase of the sensing cavity length. By linearly\nfitting the characteristic wavelengths and micro-forces of the interference spectra,\nthe lateral force sensitivities of the wave spring and the helical spring are calculated\nto be 0.0131 nm/µN and 0.1156 nm/µN, respectively. Notably, the sensitivity of the\nhelical spring is much higher than that of the wave spring, confirming the anti-lateral\ninterference ability of the wave spring.\nSupplementary Fig. 20| Experimental sensing properties of the two springs\nunder lateral load. a The interference spectra of the wave spring sensor in the range\nof 0-295 µN. b Dips of the interference spectra and the linear fitted result. The\nmicroforce sensitivity is calculated to be 0.0131 nm/µN. c The interference spectra\nof the helical spring sensor in the range of 0-29.5 µN. d Dips of the interference\nspectra and the linear fitted result. The microforce sensitivity is 0.1156 nm/µN.\nComment 2: There is no clear explanation of why the optical fiber is used as the\ncantilever during sensor calibration instead of a beam structure with a known\nmodulus.\nResponse: Thank you for the comment. For microforce sensor calibration, applying\ncontinuously tunable microforces within a defined range is critical. Since\ncommercial calibration systems remain unavailable, we developed a custom\nmicroforce generator based on fiber optics following Ref. 53's methodology. As\nillustrated in Fig. 3a, the device employs a cantilevered optical fiber with one end\nfixed and the other deflected to produce precisely controlled microforces. These\nforces can be systematically calculated using Equation (S4). Since commercial\noptical fibers feature standardized properties with known dimensions and Young's\nmodulus, this method enables reliable microforce generation through predictable\nmechanical behavior. In the revised manuscript, we have briefly explained the reason\nfor utilizing optical fiber as a cantilever.\nPage 14, Line 217: “Since commercial optical fibers feature standardized properties\nwith known dimensions and Young's modulus, we developed a custom microforce\ngenerator based on fiber optics for microforce calibration [41]. As shown in Fig. 3a,\nwith the assistance of the precision measurement platform, the wave spring sensor\ncan gradually approach the cantilever fiber. When the wave spring sensor pressed\nagainst the end of the cantilever fiber, the as-generated microforce can be fed back\nto the wave spring, leading to the compression. According to the length of cantilever\nfiber (L ) and the displacement of the contact point (Δd), the load received by the\nfiber\nsensor can be precisely calculated (equation S7), while the spectra shift of the F-P\nsensor can be recorded for calibration.”\nComment 3: Could the authors explain in detail the purpose of the experiment\nshown in Fig. 3(h, i)? Tensile or compressive forces with numerical\nmeasurements would be adequate for readers to perceive the force. What is the\npurpose of visualizing the response using another softer spring?\nResponse: Thank you for your valuable comments. We have already included\nquantitative tensile/compressive force measurements in Fig. 3(b-g). However, for\nmicroforce detection, the deformation of the wave spring remains negligible and\nundetectable under microscopic observation. To better visualize the deformation\nprocess, we strategically employed a smaller spring with higher deformation\nsusceptibility. Given that both springs experience equivalent forces, the amplified\ndeformation observed in the smaller spring serves as an effective visual indicator of\nthe larger spring's force conditions. We appreciate this insightful comment and\nacknowledge that the original demonstration in Fig. 3 (h,i) could potentially cause\nreader confusion. Accordingly, these panels have been relocated to the Supporting\nInformation. A brief explanation of this experimental rationale has been added to the\nrevised manuscript.\nPage 15, Line 256: “Because the deformation of the wave spring is very small\nwithin a moderate load range, we employed a more flexible coil spring to visualize\nthe stretching and compression process (Supplementary Fig.14). When the coil\nspring (equipped with a disc) was compressed and stretched, its length change can\nbe clearly identified. At the same time, the corresponding interference spectra show\nobvious blue or red shift (Video 1).”\nComment 4: The overall text including the figures should be rechecked. There\nwere several misspelled words, supplementary notes were not mentioned (line\n207), some words had different text size, and the figure 4b had wrong legend.\nResponse: Thank you for your valuable comments.\nIn the revised manuscript, misspelled words and inappropriate words had been\nreplaced.\nIn line 84, “micronanofabrication” was modified to “micro/nano fabrication”.\nIn line 440, “microbot” was modified to “microbots”.\nIn line 442, “micronanostructures” was modified to “micro/nano structures”.\nIn the overall text, Fig. 6b and Supplementary Fig. 26, “egg” was modified to\n“zygote”.\nIn the revised manuscript, the unmentioned supplementary notes (in line 223) had\nbeen modified.\nOriginal: “According to the length of reference fiber (L ) and the displacement of\nfiber\nthe contact point (Δd), the load received by the sensor can be quantitatively\ndetermined, while the spectra shift of the F-P sensor can be recorded for calibration\n(supplementary information).”\nRevised: “According to the length of cantilever fiber (L ) and the displacement of\nfiber\nthe contact point (Δd), the load received by the sensor can be precisely calculated\n(equation S7), while the spectra shift of the F-P sensor can be recorded for\ncalibration.”\nIn the revised manuscript, the content with the wrong text size and font has been\ncorrected. The corrections include \"Preparation of pH-responsive BSA\nphotoresist\" in line 544, \"Fabrication of the SU-8 and BSA structures on a SMF\"\nin line 551, \"Simulation\" in line 576, \"Cells experiment\" in line 581,\n\"Characterization\" in line 584.\nAlso, include the “Supplementary Note 1-10” and captions of all figures in the\nsupporting text.\nIn the revised manuscript, the wrong legend of figure 4b has been corrected.\nOriginal: “Dependence of SL on the swelling ratio. The insets are microscopic\nimages of BSA blocks (SL=100 nm, SL=150 nm, SL=200 nm) at pH=1, pH=5 and\npH=13, respectively.”\nRevised: “Dependence of swelling ratio of BSA microstructures on SL. The insets\nare microscopic images of BSA blocks fabricated under different conditions and\nactuated under different pH values.”\nReviewer: 3\nComments: This manuscript presents an innovative tactile gripper-on-a-fiber\n(TGoF) system inspired by the natural Bobbit worm, integrating advanced\ndesign principles and manufacturing techniques. The system demonstrates high\nsensitivity and functionality in micro-force sensing and gripping applications.\nWhile the work shows some novelty, there are still issues with certain details.\nTherefore, the reviewer recommends that the authors address the following\npoints before the manuscript can be considered for publication.\nResponse: Thanks a lot for your comments. We have revised our manuscript with\ncare according to the comments. Changes have been highlighted in red. A point-by-\npoint response has been listed as follow.\nComment 1: The authors used wave springs for microforce sensing and\ninvestigated the impact of band thickness and height on mechanical sensing\nperformance. However, the effect of the spring's configuration on performance\nwas not discussed, nor was the cyclic stability of its mechanical sensing\nevaluated.\nResponse: Thank you for your valuable suggestion. To highlight the importance of\nthe wave spring configuration, a sensing structure with four helical springs is\ndesigned and fabricated for comparison. To make the two structures comparable, the\nstructural parameters of the helical springs are regulated to match the basic\nmechanical properties of the wave spring. The interference from lateral force on\nstructure deformation and sensing properties has been compared. Details of the\nsimulation and experimental results have been added in new Supplementary Note 6.\nIn addition, the cyclic stability of the wave spring sensor has been added in\nSupplementary Note 5. Changes have been highlighted in red as follow:\nSupplementary Note 6\n2. Comparison between wave spring and helical springs\nTo verify the excellent stability of the wave spring, a sensing structure with\nfour helical springs is designed for comparison. Supplementary Fig. 18 shows the\ndeformation simulation of a comparative sensing structure with four helical springs\nunder vertical and lateral load. To make the two structures comparable, the structural\nparameters of the helical springs are regulated to match the basic mechanical\nproperties of the wave spring. As shown in Supplementary Fig. 18b and c, the\ndisplacement of the upper cover structure is 0.077 µm under a vertical force of 1 µN,\nwhich is quite similar with that of the wave spring (0.074 µm) under the same force.\nNevertheless, when a lateral force is applied to the structure, more obvious bending\nbehavior can be observed Supplementary Fig. 18e and f. When lateral micro-force\nof 1 µN is applied, the displacement of the upper cover is 0.607 µm, corresponding\nto the change of the F-P sensing cavity length (ΔL) of 2.244×10-3 µm, which is one\norder of magnitude higher than that of the wave spring (Supplementary Table 1).\nThese simulation results confirm the superior mechanical stability of the wave spring\nagainst bending torque. When the sensing structure is subjected to the same vertical\nand lateral forces, the deformation in the vertical direction is dominant.\nSupplementary Fig. 18| Deformation simulation of a comparative sensing\nstructure with four helical springs under vertical and lateral load. a Schematic\ndiagram of the stretching model of the helical spring. b Deformation of the helical\nspring structure under 1 µN vertical micro-force. c Dependence of displacement on\nvertical microforce. d Schematic diagram of deformation when lateral micro-force\nis applied. e Bending deformation of the helical spring structure under lateral micro-\nforce (1 µN). f Dependence of displacement on lateral microforce.\nSupplementary Table 1. Comparison of deformation simulation results between\nwave spring and helical springs.\nwave spring helical spring\nChange of the F-P sensing cavity\nlength (ΔL) under 1 µN vertical 0.074 µm 0.077 µm\nforce\nChange of the F-P sensing cavity\nlength (ΔL) under 1 µN lateral 2.698×10-4 µm 2.244×10-3 µm\nforce\n3. Experimental comparison of the sensing properties between wave spring and\nhelical springs\nThe deformation and sensing properties of the wave spring and the helical\nsprings against bending torque were also investigated experimentally. We first\ncompared the deformation of the two springs under the same lateral force (~196 µN)\nvia microscopy. As shown in Supplementary Fig. 19, the wave spring bent slightly,\nwhereas the helical spring deformed significantly, indicating the superior\nmechanical stability of wave spring against bending torque.\nSupplementary Fig. 19| Deformation of wave spring and helical springs under\nlateral force (196 µN). a The microscopic image of the wave spring. b The\nmicroscopic image of the helical springs. The inset is the original shape of the helical\nsprings.\nIn addition to the mechanical deformation, the sensing properties were also\ncompared quantitatively (Supplementary Fig. 20). With the increase of the lateral\nforce, the interference spectra of both wave spring and helical springs undergo a\nuniform red-shift, indicating the increase of the sensing cavity length. By linearly\nfitting the characteristic wavelengths and micro-forces of the interference spectra,\nthe lateral force sensitivities of the wave spring and the helical spring are calculated\nto be 0.0131 nm/µN and 0.1156 nm/µN, respectively. Notably, the sensitivity of the\nhelical spring is much higher than that of the wave spring, confirming the anti-lateral\ninterference ability of the wave spring.\nSupplementary Fig. 20| Experimental sensing properties of the two springs\nunder lateral load. a The interference spectra of the wave spring sensor in the range\nof 0-295 µN. b Dips of the interference spectra and the linear fitted result. The\nmicroforce sensitivity is calculated to be 0.0131 nm/µN. c The interference spectra\nof the helical spring sensor in the range of 0-29.5 µN. d Dips of the interference\nspectra and the linear fitted result. The microforce sensitivity is 0.1156 nm/µN.\nSupplementary Note 5\nSupplementary Fig. 13| The change of wavelength in interference spectra\nduring 200 loading (42 µN)/unloading (0 µN) cycles.\nPage 15, Line 251: “Additionally, to assess the cyclic durability of the wave spring,\nwe performed 200 loading cycles, which indicated reasonable stabilities of the TGoF\nsystem (Supplementary Fig. 13, Supplementary Note 5).”\nComment 2: The responsive performance of the pH-responsive BSA muscle will\ndirectly influence the flexibility of the TGoF system. How quickly does it\nrespond? Is there a stress relaxation effect? And how stable is it over long-term\nuse?\nResponse: Thanks a lot for the comments. In the revised manuscript, the\nresponsiveness of the BSA muscle were quantitatively investigated (Supplementary\nFig. 22). As depicted in Supplementary Fig. 22 (Supplementary Note 7), the\nresponse time for the gripper is evaluated to be ~1.4s, and recovery time is also ~1.4s.\nTo investigate the stress relaxation effect, we performed 200 actuation cycles by\nswitching pH values between 5 and 13 while monitoring gripper kinematics. As\ndepicted in Supplementary Fig. 23 (Supplementary Note 8), tip displacement is\nalmost constant between pH=5 and pH=13, indicating the stable gripping behavior\nover long-term use.\nSupplementary Fig. 22| Dependence of the tip distance on response/recovery\ntime when switching the pH values between 5 and 13. The inset is the schematic\nillustration of the distance of tips.\nSupplementary Fig. 23| The change of tip distance by switching the pH values\nbetween 5 and 13 in 200 cycles. Error bars denote the standard deviation of the\nmeasurements.\nPage 20, Line 315: “According to the quantitative responsiveness experiments, both\nthe response and recovery time for the gripper is evaluated to be ~1.4s\n(Supplementary Fig. 22 and Note 7).”\nPage 20, Line 317: “Additionally, to assess the cyclic durability of the pH-\nresponsive gripper, we performed 200 actuation cycles, which confirmed the\ndurability of the TGoF system (Supplementary Fig. 23, Supplementary Note 7).”\nComment 3: Are the planar reflector and scattering cone also made of SU-8?\nWhat is the wavelength and power of the initial light emitted from the SMF?\nWhat is the reflectivity of this structure?\nResponse: Thank you for your insightful comments. Yes, the wave spring,\nmicrogripper, planar reflector and scattering cone are made of SU-8. The wavelength\nand power of the initial light emitted from the SMF have been provided in\nSupplementary Fig. 2. The reflectivity of the structure is simulated and calculated\nusing the finite element simulation method. The contents of the modification are\nadded to Supplementary Fig. 3. Changes have been highlighted in red as follow.\nSupplementary Fig. 2| Spectral characterization of initial light from the optical\nfiber spectrum demodulator.\nIn the sensing experiment, an optical fiber spectrum demodulator (OFSD) was\nused to record the sensing spectra, and both the light source and the signal receiving\nmodule were integrated in the OFSD. To demonstrate wavelength and power of the\ninitial light emitted from the SMF, the optical fiber patch cord was used to directly\nconnect the two ports of the OFSD. Port-1 acts as the light source, and port-2\nmonitors the optical signal. In order to show the characteristics of the original spectra\nmore directly, the initial light spectrum is characterized in Supplementary Fig. 2. For\ninterference spectra recorded by the OFSD, \"Amplitude\" is used to represent the\nintensity of the spectra.\nSupplementary Fig. 3| Schematic diagram of the light field simulation of the\noverall structure of planar reflector and scattering cone.\nIn order to explore the reflectivity of the overall structure of planar reflector\nand scattering cone, the emissivity was simulated and calculated using the finite\nelement simulation method. As shown in Supplementary Fig. 3, the lower surface is\nset as the incident port of the light and the upper surface is set as the exit port. The\nwavelength of the incident light is set to 1550 nm. According to relevant literature,\nthe refractive index of the SU-8 material at 1550 nm is 1.58, and the absorption loss\ncan be ignored [2]. Finally, the reflectivity of this structure was calculated to be\n7.1 %.\nComment 4: Whether stretching or compression, these are longitudinal\ndeformation modes. However, in practical applications, wave springs may also\nexperience lateral bending. The authors should consider the force response in\nthis context as well.\nResponse: Thank you for your valuable comment. To evaluate the effect of lateral\nbending, we investigated the deformation behavior of the wave spring theoretically\nand experimentally by applying a perpendicular force to the axis. The simulations of\nthe bending deformation and relevant experimental results are provided in new\nSupplementary Note 6 (including Supplementary Fig. 15-17, 19-20), in which both\nmechanical deformation and the optical response under bending state have been\ndiscussed. Additionally, to verify the stability against lateral bending, we designed\nand fabricated a helical spring array for comparison (Supplementary Fig. 18-20,\nSupplementary Table 1).\nSupplementary Note 6\n1. The mechanical properties of wave springs against bending torque\nTo explore the mechanical property and the optical response of the wave spring\nagainst bending torque, we simulated the displacement of the wave spring by\napplying a perpendicular force to the axis. As shown in Supplementary Fig. 15,\nmicro-forces (perpendicular to z-axis) are applied along the x-axis and y-axis\ndirections, respectively. With the increase of the micro-force, the bending angle of\nthe wave spring gradually increased.\nSupplementary Fig. 15| Simulation of bending of wave spring under lateral load.\na Schematic diagram of the deformation when micro-force is applied along the x-\naxis direction. b Deformation of the wave spring under 0.2, 0.6 and 1 μN,\nrespectively. c Schematic diagram of deformation when micro-force is applied along\nthe y-axis direction. d Deformation of the wave spring under 0.2, 0.6 and 1 μN,\nrespectively.\nTo quantitatively analyze the displacement, we set the center of the upper cover\nas a monitoring point and recorded the displacements under different microforces\n(Supplementary Fig. 16b and d). With the increase of lateral force in the range of\n0.1-1 µN along the x-axis, the displacement of the monitoring point gradually\nincreased. When the lateral force is 1 µN, the displacement of the monitoring points\ncan reach 0.092 µm. Similarly, the displacement along the y-axis direction shows\ncomparable results.\nSupplementary Fig. 16| Displacement of the wave spring (monitoring point)\nunder lateral load. a Lateral force is applied along the x-axis direction. b\nDependence of the x-axis displacement of the monitoring point on different lateral\nforces within the range of 0.1-1 µN. c Lateral force is applied along the y-axis\ndirection. d Dependence of the y-axis displacement of the monitoring point on\ndifferent lateral forces within the range of 0.1-1 µN.\nIt is worth pointing out that the displacement of the monitoring point under\nlateral force does not represent the change in the length of the sensing cavity\n(Supplementary Fig. 17). When the external force is 0, the length of the F-P sensing\ncavity of the wave spring is L. Under lateral force, the wave spring bent, and the\nlength of the F-P sensing cavity is L’. Therefore, the change in the length of the F-P\nsensing cavity is ∆L (∆L=L’-L). According to the Pythagorean Theorem, ∆L can be\ncalculated to be 2.698×10-4 µm when the lateral force is 1 µN.\nSupplementary Fig. 17| Schematic diagram of the displacement of the wave\nspring under lateral force. a The structural deformation of the wave spring. b\nSchematic diagram of the length variation of the F-P sensing cavity.\n2. Comparison between wave spring and helical springs\nTo verify the excellent stability of the wave spring, a sensing structure with\nfour helical springs is designed for comparison. Supplementary Fig. 18 shows the\ndeformation simulation of a comparative sensing structure with four helical springs\nunder vertical and lateral load. To make the two structures comparable, the structural\nparameters of the helical springs are regulated to match the basic mechanical\nproperties of the wave spring. As shown in Supplementary Fig. 18b and c, the\ndisplacement of the upper cover structure is 0.077 µm under a vertical force of 1 µN,\nwhich is quite similar with that of the wave spring (0.074 µm) under the same force.\nNevertheless, when a lateral force is applied to the structure, more obvious bending\nbehavior can be observed Supplementary Fig. 18e and f. When lateral micro-force\nof 1 µN is applied, the displacement of the upper cover is 0.607 µm, corresponding\nto the change of the F-P sensing cavity length (ΔL) of 2.244×10-3 µm, which is one\norder of magnitude higher than that of the wave spring (Supplementary Table 1).\nThese simulation results confirm the superior mechanical stability of the wave spring\nagainst bending torque. When the sensing structure is subjected to the same vertical\nand lateral forces, the deformation in the vertical direction is dominant.\nSupplementary Fig. 18| Deformation simulation of a comparative sensing\nstructure with four helical springs under vertical and lateral load. a Schematic\ndiagram of the stretching model of the helical spring. b Deformation of the helical\nspring structure under 1 µN vertical micro-force. c Dependence of displacement on\nvertical microforce. d Schematic diagram of deformation when lateral micro-force\nis applied. e Bending deformation of the helical spring structure under lateral micro-\nforce (1 µN). f Dependence of displacement on lateral microforce.\nSupplementary Table 1. Comparison of deformation simulation results between\nwave spring and helical springs.\nwave spring helical spring\nChange of the F-P sensing cavity\nlength (ΔL) under 1 µN vertical 0.074 µm 0.077 µm\nforce\nChange of the F-P sensing cavity\nlength (ΔL) under 1 µN lateral 2.698×10-4 µm 2.244×10-3 µm\nforce\n3. Experimental comparison of the sensing properties between wave spring and\nhelical springs\nThe deformation and sensing properties of the wave spring and the helical\nsprings against bending torque were also investigated experimentally. We first\ncompared the deformation of the two springs under the same lateral force (~196 µN)\nvia microscopy. As shown in Supplementary Fig. 19, the wave spring bent slightly,\nwhereas the helical spring deformed significantly, indicating the superior\nmechanical stability of wave spring against bending torque.\nSupplementary Fig. 19| Deformation of wave spring and helical springs under\nlateral force (196 µN). a The microscopic image of the wave spring. b The\nmicroscopic image of the helical springs. The inset is the original shape of the helical\nsprings.\nIn addition to the mechanical deformation, the sensing properties were also\ncompared quantitatively (Supplementary Fig. 20). With the increase of the lateral\nforce, the interference spectra of both wave spring and helical springs undergo a\nuniform red-shift, indicating the increase of the sensing cavity length. By linearly\nfitting the characteristic wavelengths and micro-forces of the interference spectra,\nthe lateral force sensitivities of the wave spring and the helical spring are calculated\nto be 0.0131 nm/µN and 0.1156 nm/µN, respectively. Notably, the sensitivity of the\nhelical spring is much higher than that of the wave spring, confirming the anti-lateral\ninterference ability of the wave spring.\nSupplementary Fig. 20| Experimental sensing properties of the two springs\nunder lateral load. a The interference spectra of the wave spring sensor in the range\nof 0-295 µN. b Dips of the interference spectra and the linear fitted result. The\nmicroforce sensitivity is calculated to be 0.0131 nm/µN. c The interference spectra\nof the helical spring sensor in the range of 0-29.5 µN. d Dips of the interference\nspectra and the linear fitted result. The microforce sensitivity is 0.1156 nm/µN.\nComment 5: A more detailed description of the microfluidic chip should be\ngiven in Supplementary Fig 11, including design, channel size and functionality,\netc.\nResponse: Thank you for your valuable comments. A more detailed description of\nthe microfluidic chip has been provided in the revised manuscript and the\nsupplementary information. The schematic diagram of the microfluidic system and\nthe photograph of the real microfluidic chip have been added to the revised\nmanuscript (Fig. 4d and 4e). Additionally, the schematic diagram of the entire\nexperimental platform is provided in supplementary information (see new\nsupplementary note 7).\nFig. 4| d Schematic diagram of the microfluidic system for manipulating the gripper.\ne Photograph of the real microfluidic chip for the TGoF system.\nPage 22, Line 338, the caption of Fig. 4e and 4e: “d Schematic diagram of the\nmicrofluidic system for manipulating the gripper. e Photograph of the real\nmicrofluidic chip for the TGoF system.”\n“Supplementary Note 7\nA schematic diagram of the experimental setup shows a tri-channel\nmicrofluidic chip for the TGoF system\nSupplementary Fig. 21| Schematic diagram of the entire experimental platform\nfor pH switching and the manipulation of the TGoF system.\nAs illustrated in Supplementary Fig. 21, a microfluidic chip was developed to\nprecisely control the pH of the solution. Acid and alkaline solutions can be injected\ninto the microfluidic chip via two inlets, and the pH of the resultant solution can be\nprecisely controlled in the chamber using a syringe pump. The operation process can\nbe monitored by a microscope.\nComment 6: Given the potential biologically relevant applications of this\nmicrosystem, the authors should assess its biological properties, such as\ncytotoxicity.\nResponse: Thank you for your valuable suggestion. Biocompatibility assessment is\ncritical for biomedical material safety and efficacy. In our prior study (Sun, Y. L. et\nal., Angew. Chem. Int. Ed. 2012, 15, 1558-1562), BSA hydrogels fabricated via TPP\ndemonstrated low biotoxicity through in vitro testing. Rabbit red blood cells\nsuspended in these hydrogels maintained structural integrity and viability during\n25°C/40°C incubation, with no cell adhesion observed microscopically.\nConcurrently, the hydrogels preserved unchanged morphology and dimensions\nthroughout cultivation, confirming the long-term biocompatibility and minimal\ncytotoxicity for biomedical applications. Additionally, the biocompatibility of cured\nSU-8 has also been well-documented. As reviewed by Chen et al.\n(Micromachines 2021, 12, 794), SU-8 photoresist demonstrates biomedical\nversatility in-vivo and in-vitro, serving in cell culture platforms, neural probes, and\nimplantable sensors. Its biocompatibility arises from minimal tissue interaction\nwithout inducing immune activation or cytotoxicity.\nIn view of the previous results, we briefly discuss the biological properties of\nboth BSA and SU-8 by citing suitable references. Changes have been highlighted in\nred as follow.\nPage 29, Line 419: “In terms of biological properties, previous results have\nconfirmed that both BSA hydrogels and SU-8 photoresist demonstrate low\nimmunogenicity and cytotoxicity, making them suitable for biomedical device\nfabrication [60,61].”\nComment 7: The authors do not provide a specific comparison of the TGoF\nsystem with existing tactile sensors or micro-robots. Could the authors discuss\nhow their system improves upon or differs from existing technologies in terms\nof functionality, sensitivity, stability, cost, etc.?\nResponse: Thank you for your comments. A comparative table highlighting the\nfunctional, sensitivity, and stability improvements of our TGoF system over existing\ntactile sensors and micro-robots has been included in the Supporting Information\n(Supplementary Table 2). In addition, the revised manuscript briefly discusses the\ntechnological novelty of this work based on this systematic comparison.\nPage 33, Line 477: “The TGoF system demonstrates significant advancements in\nintegrated sensing-actuation capabilities compared to state-of-the-art TPP-fabricated\ntactile sensors and microbots. As detailed in Supplementary Table 2 (Supplementary\nNote 10) comparing working platforms, materials, functionalities, sensitivity, and\nstability, current TPP-based microbots primarily employ glass substrates as the\nworking platform, which limits their sensing performance. While existing micro-\nsensors on optical fibers or microfluidic chips enable multiparametric detection\n(microforce, pH, temperature, and refractive index), they lack dynamic actuation\ncapacity. Our system innovatively integrates fiber-optic sensing structures with\nsmart grippers, achieving synergistic integration of microforce sensing and dynamic\nactuation. This dual-functional design not only enhances operational flexibility and\nsystem integration but also overcomes the inherent limitations of standalone sensors\nor actuators.”\nSupplementary Note 10 and the Supplementary Table 2 had been added.\nSupplementary Table 2. A summary of microrobots in function and composition.\nTypical Processing Working Function\nMaterials Ref.\ndevice method platform Actuation Sensing\nPEGDA- magnetic\nTPP cover glass - [4]\nUAO MNP field\nDPEPA\nTPP cover glass EMK pH - [5]\nAAc\nSU-8 &\nmulti-TPP cover glass pH - [10]\nBSA\nlight and\nNIPAM\nTPP cover glass magnetic - [11]\nAg NPs\nfields\nNIPAM\nTPP cover glass light - [12]\nAg NPs\nIP-Dip pneumatic\nTPP hollow fiber - [47]\nphotoresist actuation\nrefractive\nindex sensing\nTPP optical fiber SU-8 - [50]\n1385.819\nnm/RIU\nIGR-369\nand force sensing\nTPP optical fiber - [53]\nSR444, 1.51 nm/µN\nSR369\nPBMA magnetic\nFsLDBM cover glass - [59]\nγ-Fe2O3 field\nmillinewton-\nIP-S level force,\nTPP polymer - [62]\nCNT nonlinear\nresult\nmicrostereo indium tin photosensiti light\n- [68]\nlithography oxide glass -ve resins and heat\nin-situ SU-8 & force sensing This\noptical fiber pH\nmulti-TPP BSA 0.32 nm/µN work\nTPP: two-photon polymerization\nPEGDA: poly(ethylene glycol) diacrylate\nUAO: urethane acrylate oligomer\nMNP: superparamagnetic nanoparticles\nFs-DLW: femtosecond direct laser writing\nDDS: drug delivery system\nDPEPA: dipentaerythritol pentaacrylate\nEMK: 4,4′-bis-(diethylamino)benzophenone\nAAc: acrylic acid\nNIPAM: N-Isopropyl acylamide\nSR444: pentaerythritol triacrylate\nFsLDBM: femtosecond laser-directed bubble microprinting\nPBMA: poly(butyl methacrylate)\nCNT: carbon nanotubes"}, {"round": 2, "reviewer_comments": {"reviewer_2": "The authors responded exhaustively to all my comments and revised the paper accordingly. From my point of view, the\npaper can be published in the current form", "reviewer_3": "The authors have addressed all of my concerns in their revision. The manuscript has been significantly improved, and I find\nthe current version suitable for publication. I recommend acceptance in its present form without requiring further\nmodifications."}, "author_response": ""}]

Decision letter