Continuous fabrication of Janus liquid crystal elastomer fibers with programmable actuation

Domain: neuroscience
Published: 2026-02-02
Editorial outcome: major_revision

Abstract
Smart fibers, particularly liquid crystal elastomer (LCE) fibers, are pivotal in soft robotics and adaptive textiles. However, existing fabrication methods are limited to simple monolithic structures, hindering the realization of complex actuation behaviors. To overcome this limitation, we develop a continuous extrusion platform for producing Janus LCE fibers that emulate asymmetric biological structures, such as plant tendrils, thereby enabling sophisticated actuation. This approach seamlessly integrates an LCE network with a dynamic covalent polymer network, allowing programmable on-demand liquid crystal orientation for actuation via dynamic bond exchange. The resulting Janus fibers exhibit enhanced mechanical properties and multifunctional capabilities, including adaptive object manipulation, stimuli-responsive directional motion, and scalable integration into smart fabrics for thermal management. By unifying material intelligence with structural programmability, this work advances the development of bioinspired soft robotic systems with enhanced environmental adaptability.

Introduction
Fibrous artificial muscles 1–6 are crucial for a wide range of applications, including prosthetic limbs 6, adaptive textiles 7–10, and miniature actuators 5, 11–14. Among polymer-based smart fibers (e.g., responsive gels 15, 16, shape-memory polymers 17, 18, dielectric elastomers 19, and thermally expandable polymers), liquid crystal elastomers (LCEs) stand out due to their high reversible strain and rapid response 20. Their actuation behavior is determined by two key factors: geometric structure and liquid crystal orientation, where the former dictates their application scenarios and the latter governs their ability to undergo reversible deformation under external stimuli. Building on the seminal study that established the basic principle for producing LCE fibers via mechanical stretching followed by photopolymerization to achieve mesogen alignment 21, several advanced fabrication techniques have emerged. These include melt drawing 22, direct ink writing 23, 24, and electrospinning 25, 26, all proven effective in fabricating LCE fibers with strong actuation properties. Their structures, however, are typically constrained to simple and monolithic forms, which limits the potential for achieving complex actuation behaviors.

In nature, plants like tendrils exhibit sophisticated deformations through asymmetric fiber lignification, forming helical structures that are capable of multimodal bending and coiling, thereby adapting to the environment 27. Mimicking such mechanisms in artificial muscles requires replicating intrinsic structural complexity, yet existing approaches struggle to achieve this. Pioneering work demonstrating “self-winding” LCE utilized a mold-fabricated helical precursor. Locking the orientation during secondary stretching enabled controllable shape transformations, including bending, twisting, coiling, and contraction, within a monolithic fibrous architecture 28. An elegant approach involves leveraging the shear gradient differential between the core and sheath during direct ink writing to program varying liquid crystal orientations in LCE fibers, enabling complex actuation modalities 29. This approach primarily modulates orientation distributions while remaining constrained in terms of hierarchical structural design.

Janus architectures, integrating two distinct materials with different functionalities within a compact structure, offer an innovative paradigm for sophisticated structural and functional design 30–32. Fabricating Janus architectures beyond nanoparticles or thin membranes remains challenging, primarily due to the difficulty in achieving uniform anisotropic construction throughout three-dimensional fibrous structures. Although millimeter-scale Janus hydrogel fibers have been produced via wet spinning 33, these methodologies prove fundamentally incompatible with LCE. This arises from LCEs’ stringent requirements for both liquid crystal phase preservation and precise liquid crystal orientation, a criterion that current hydrogel-based fabrication techniques cannot meet due to inherent chemical constraints. Furthermore, these existing approaches are restricted to producing large-diameter fibers, limiting their applicability. We envision whether we can fabricate a Janus fiber that combines asymmetric structural design with multifunctional performance. The selection of material composition is critical: one component should provide actuation capabilities, while the other serves as a structural support with programmable orientation control. Here, dynamic covalent polymers 34–36, usually copolymerized with LCE, are particularly well-suited for this purpose, as their bond exchange reactions permit the on-demand programming of liquid crystal orientation. Beyond that, dynamic covalent polymers like polyurethane enhance mechanical robustness significantly when incorporated into LCE to form interpenetrating networks, enabling ultrastrong actuation-mechanics properties and representing a milestone in high-performance LCE development 37.

Therefore, we present in this work a continuous asymmetric extrusion platform for the seamless integration of an LCE network (for actuation) with a dynamic covalent polymer network (for programming). The selection of compatible chemistries is critical, as the two polymer precursors must exhibit matched extrusion viscosities, identical curing conditions, and synchronized curing kinetics. Through precise chemical design, we employ UV-curable LCE and the dynamic covalent polymer to enable continuous Janus fiber production. The resulting Janus fibers exhibit adaptive object manipulation, directional motion under thermal/infrared laser stimuli, and navigation capabilities in complex environments. This work merges material intelligence with structural programmability, paving the way for multifunctional soft robots with bioinspired environmental adaptability.

Results
Bioinspired continuous fabrication of Janus fibers
As Fig. 1a illustrates, plant tendrils usually induce anisotropic contraction through asymmetric lignification of gelatinous fiber (g-fiber) cells, which finally leads to helical coiling to adapt to the environment 27. Such tendrils can be considered as natural Janus structures capable of switching between “on” and “off” states through the modulation of intrinsic curvature 38. This characteristic enables them to be sufficiently compliant for interaction with the environment while remaining mechanically robust enough to perform functional tasks (Fig. 1b). Inspired by this, we design a continuous asymmetric spinning platform to fabricate Janus fibers (Fig. 1c and Movie S1). This platform co-extrudes two precursors through a conical Janus nozzle, followed by an in situ ultraviolet (UV) light curing. These two precursors are composed of LCE and polyurethane (PU) precursors, respectively (Fig. 1d). Specifically, the LCE precursor is synthesized via the thiol-Michael addition reaction among 1,4-bis[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (RM82), 3,6-dioxa-1,8-octanedithiol (DODT), and pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). The PU precursor is prepared in accordance with the procedure described in the literature 33. The chemical structures of both precursors are characterized by nuclear magnetic resonance, as shown in Fig. S1. Janus fibers that contained these two materials are then partially cured through the photoinitiated free radical polymerization of (meth)acrylate from two precursors.

To further induce mesogens alignment in LCE, the fibers are mechanically drawn using a differential-speed winding system, followed by a secondary UV curing process, which allows the materials to be fully cured to lock the strain-induced orientation. This dual-step curing process separates geometric structure formation from functional orientation fixing, enabling programmable on-demand actuation of LCE. Subsequent thermal annealing facilitates the ordered reorganization of hydrogen bonds through dynamic bond exchange within the PU segments, ultimately strengthening the mechanical integrity of the fibers 35.

The experimental details of the whole process can be found in the Supplementary Information. All processing steps can be conducted under ambient conditions without the need for oxygen degassing. This facilitates greater accessibility and scalability of the process, while ensuring the maintenance of chemical fidelity. Consequently, the Janus fiber obtained through this method exhibit a well-defined biphasic morphology in cross-section at the microscopic level (Fig. 1e) and possess the potential for scalable production at the macroscopic level (Fig. 1f). Compared with conventional LCE fibers reported in the literature 5, 29, 39–52, it demonstrates not only a higher elastic modulus but also greater breaking strength, which can be attributed to the mechanical reinforcement provided by the PU component (Fig. 1g).

The successful continuous fabrication of Janus fibers relies on achieving precise compatibility in both rheological behavior and polymerization kinetics between the LCE and dynamic covalent PU network. Gel permeation chromatography results reveal that they possess the molecular weight of 1.1 × 10^5 and 4.4 × 10^4 g/mol, respectively (Fig. S2). The stable co-extrusion capability can be attributed to the high viscosity (5500 and 2200 Pa·s) and the shear-thinning behavior of both precursors (Fig. 2a and Fig. S3). In contrast, viscosity mismatch or excessively low viscosities disrupt interfacial stability, leading to distorted Janus interfaces or droplet-like co-extrusion morphologies, underscoring the necessity of maintaining an appropriately matched rheological window for continuous fiber formation (Figs. S4 and S5). More importantly, the photopolymerization kinetics of the two precursors exhibit remarkable synchronization. Upon exposure to 365 nm UV light, the LCE precursor undergoes rapid photopolymerization, as evidenced by time-resolved infrared spectroscopy and the corresponding increase in acrylate conversion (Fig. 2b and Fig. S6). According to Flory’s gelation theory, the LCE precursor reaches the gel point after 2 s of exposure (calculations provided in the Supporting Information). Similarly, the PU precursor displays comparably fast crosslinking kinetics, with the gel fraction exceeding >21% within 2 s (Fig. 2c). These rapid curing dynamics enable the concurrent formation of both networks, thereby ensuring fiber solidification during the initial stages of UV curing.

Properties regulation of Janus fibers
The composition and morphology of Janus fibers can be further regulated by adjusting the extrusion speed. As shown in Fig. 2d, when the extrusion speeds of LCE and PU precursor solutions are identical, the diameter of the Janus fibers decreases with increasing extrusion speed. Conversely, when the extrusion speeds differ, the component with the slower extrusion speed exhibits a higher content (Fig. 2e). Hereafter, we use the same extrusion speed of 5 m·min^−1. Longitudinal SEM images confirm the clear two-phase interface along the fiber axis. SEM images of knotted fibers show that the Janus architecture remains intact under complex deformation, demonstrating structural robustness (Fig. S7). Moreover, two materials in Janus fibers remain unchanged when subjected to different imposed twist levels (Fig. S8), confirming interfacial stability under torsion.

The two-step UV curing strategy enables precise control over the crosslinking density to fix the mesogen orientation during fiber stretching (Fig. S9). To evaluate the mesogen alignment in fully UV-cured LCE, polarized optical microscopy (POM) is used to characterize the orientational order of the LCE phase in Janus fibers. When the fiber axis (i.e., mesogen alignment direction) is parallel to the polarizer, the fiber appears dark. When rotated to 45° relative to the polarizer, one half of the fiber became bright, indicating well-aligned LCE mesogens (Fig. 2f). The degree of fiber orientation is determined by the speed ratio of V3 to V2, as illustrated in Fig. 1c. As shown in Fig. S10, a higher speed ratio corresponds to more pronounced birefringence effects. Two-dimensional wide-angle X-ray scattering (2D-WAXS) shows effective mesogen alignment (Fig. 2g), because the initially isotropic diffraction ring becomes anisotropic arcs perpendicular to the alignment direction. Increasing the stretching speed ratio from 1 to 1.8 induces a rise in the orientational order parameter from 0 to 0.61, as calculated from Fig. S11.

Dynamic mechanical analysis (DMA) identifies two distinct thermal transitions in the Janus fiber. The first corresponds to the glass transition temperature (Tg) of ~17°C, originating from the soft-segment matrix of the LCE network, while the second represents the nematic-to-isotropic transition temperature (TNI) of around 67°C, characteristic of the mesogenic domains within the LCE (Fig. 2h). The PU network exhibits stress relaxation behavior above 55°C, with a faster relaxation rate observed at higher temperatures. This results in an activation energy of ~54.9 kJ·mol^−1, confirming the efficient dynamic exchange of hydrogen bonds in the PU network (Fig. 2i). Beyond that, the resulting Janus fibers demonstrate excellent mechanical performance. As shown in Fig. S12, the fibers exhibit a tensile strain of 156%, a tensile strength of 40.4 MPa, a Young’s modulus of 12.7 MPa, and a toughness of 17.1 MJ·m^−3. Comparison with pure LCE and PU fibers reveals that the Janus architecture significantly enhances breaking strength, effectively overcoming the mechanical limitations of conventional single-network LCE systems (Fig. 2j). This improvement arises from the synergistic integration of the aligned LCE phase and dynamic covalent PU network. A visual demonstration shows that a single Janus fiber (diameter ~200 μm) is capable of supporting a hanging load exceeding 160,000 times its own weight over a vertical distance of ~20 cm during externally driven motion (Fig. S13 and Movie S2), highlighting the exceptional strength and robustness of this hybrid design. To better understand the factors governing mechanical performance, we examined the effect of extrusion speed. Higher extrusion speeds produce thinner fibers, which exhibit increased Young’s modulus and enhanced toughness, revealing a clear dependence of mechanical properties on fiber diameter that can be systematically tuned through the extrusion parameters (Fig. S14). In addition to their improved mechanical robustness, the continuously extruded Janus fibers also display excellent thermal actuation performance. Upon heating, the fibers undergo a transition from a linear to a helical configuration; therefore, the reported actuation strain corresponds to a length-change ratio rather than a conventional uniaxial contraction strain. The effective fiber length in the helical state was measured as illustrated in Fig. S15, and the detailed calculation formula for the actuation strain is provided in the Supporting Information. At 80°C, the fibers exhibit an actuation strain of ~85%, defined here as the length-change ratio, together with a high actuation strain rate of 193%·s^−1, and generate an energy density approaching 50 kJ·m^−3 under a load of 200 kPa (Figs. S15 and S16). Collectively, these mechanical and actuation characteristics indicate the potential applicability of Janus fibers in scalable artificial-muscle systems (see Table S3 for quantitative comparison).

Programmable and reprogrammable actuation of Janus fibers
The inherent soft elasticity of LCE 53 and the dynamic bond exchange in PU enable various programming strategies for shaping and actuating Janus fibers. The first strategy involves direct mechanical stretching (Fig. 3a i). At room temperature, LCE exhibits soft elasticity and retains its stretched shape after the force is removed (Fig. S17). In contrast, PU shows entropic elasticity and returns to its original shape once the force is released. As a result, the Janus fiber can coil due to the asymmetric contraction of the two materials after mechanical programming. Further heating would remove the soft elasticity of LCE, causing the coiling to disappear. Representative images of the process are shown in Fig. S18. The applied strain affects the helical structure of the fiber, with higher strain leading to tighter and denser helices (Fig. 3a ii). The helical density, therefore, increases nonlinearly, approaching ~5 cm^−1 at 100% prestrain, while the coil diameter decreases and plateaus near 0.1 cm at higher strains (Fig. 3a iii). The pitch likewise decreases with strain, stabilizing at ~0.2 cm (Fig. S19).

Another approach is precisely the opposite. At elevated temperatures (90°C), LCE is capable of recovering its original shape after the removal of an external force, whereas PU, due to stress relaxation resulting from dynamic bond exchange, undergoes plastic deformation and fails to recover (Fig. S20). Fibers are stretched to 60% strain and subsequently annealed at 90°C for varying durations (Fig. 3b i). The annealing time affects the helical structure of the fibers, with longer annealing durations leading to tighter and denser helices (Fig. 3b ii). The helical density, therefore, increases nonlinearly with annealing time, approaching ~6.5 cm^−1 after prolonged annealing, while the coil diameter decreases and plateaus near 0.08 cm (Fig. 3b iii). The pitch likewise decreases with annealing time, stabilizing at ~0.15 cm (Fig. S21). In this case, when the fibers cool to room temperature, the reversible actuations occur due to the orientation of LCE, which will be discussed in detail later.

To further quantify this asymmetry, we introduced a geometric model:
L2 - L1 = N · H · (sqrt(π^2 · D^2 + p^2) - sqrt(π^2 · (D - 2d)^2 + p^2)) (1)
Here, L1 and L2 represent the lengths of the PU and LCE domains, respectively; N is the helical density; H is the axial length of the helix; D is the outer diameter of the helix; d is the diameter of the fiber; and p is the helical pitch (Fig. S22). Substituting experimentally measured parameters into the analytical model revealed distinct trends in the domain length differentials. Under direct mechanical stretching, L2 - L1 was positive and increased with applied strain, reaching a maximum at 100% strain. In contrast, thermal annealing yielded a negative L2 - L1, with the absolute value reaching a maximum after 10 min of annealing, which is in good agreement with experimental results. These observations confirm the effectiveness of the analytical framework in capturing the asymmetric strain-induced coiling behavior of Janus LCE fibers.

Further implementation of spatial programming strategies enables heterogeneous actuation within a single Janus fiber (Fig. 3c). Near-infrared (NIR) laser irradiation (808 nm, 2000 mW·cm^−2, 5 min) is selected to achieve this activation. The fiber is first uniformly stretched to 50% strain under controlled external stress and then selectively irradiated. During programming, even when NIR irradiation raises temperatures above the LCE phase transition, contraction-induced stresses in LCE are insufficient to overcome external stretching, while PU undergoes stress relaxation. Upon release of the applied strain, two distinct regions emerged, exhibiting opposite spiral orientations and differing pitches. Importantly, when heated to 70°C, the irradiated regions transformed into helical structures with varying pitches, while the previously unirradiated region returned to a linear configuration. These results showcase the ability of Janus fibers to achieve programmable, on-demand heterogeneity within a structurally continuous architecture.

Dynamic bonds enable efficient reprogramming of liquid crystal mesogen orientation, allowing the desired actuation (Fig. 4a). Unlike conventional methods that incorporate dynamic bonds into the LCE network through copolymerization 29, 54–56, our Janus design retains efficient reorientation while preserving the strong mechanical properties of dynamic covalent polymers. After programming, the loosely coiled helical configurations are capable of reversibly switching between loose and tight helices and exhibit excellent stability during two hundred heating and cooling cycles (Movie S3), and this reversible actuation is maintained even when small external loads are applied (Fig. S23). Finite element analysis (FEA) is utilized to predict this actuation, and the numerical simulations show close agreement with the experimental results (Fig. 4b). More importantly, these structures can be reprogrammed into diverse helical architectures through dynamic bond exchange (Fig. 4c and Movie S4). Cyclic testing demonstrates that the fibers exhibit no signs of actuation fatigue within 200 cycles (Fig. S24). After 200 actuation cycles, the interfaces of Janus fiber remained intact, demonstrating that fibers produced via our fabrication method exhibit excellent structural stability (Fig. S25). Additional FEA simulations of all three helical structures are conducted (Fig. S26), showing excellent agreement with the experimental results. This characteristic enables the potential application of Janus fibers as soft robots.

Multimodal actuation and functional demonstrations of Janus fiber robots
Inspired by the adaptive grasping mechanism of climbing tendrils, our Janus fibers demonstrate the ability to autonomously coil for object manipulation. Upon approaching a heated wire at 90°C, localized heating induces Janus LCE fiber curling, thereby enabling firm grasping and lifting of the wire (Fig. 5a and Movie S5). Despite a cross-sectional diameter of approximately 170 μm, the fibers are capable of lifting loads up to 0.5 g, corresponding to a load-bearing capacity exceeding 20 N/cm^2. Subsequent cooling allows for the controlled release of the wire. This localized heating can also be achieved through NIR laser irradiation, enabling on-demand light-guided locomotion, with the actuation magnitude precisely tunable via the irradiation intensity (Fig. S27). We therefore design a “water strider”, in which four of its legs are composed of Janus fibers coated with carbon nanotubes. NIR laser irradiation (808 nm, 5000 mW·cm^−2, 0.5 s) of the left-side legs causes the fibers to bend. Removing the light triggers shape recovery, reversing the bending for movement in the opposite direction (Fig. 5b and Movie S6). This “water strider” can achieve an initial average speed of 4.7 mm/s (Fig. S28a). In contrast, NIR laser irradiation (808 nm, 5000 mW·cm^−2, 0.5 s) on the right legs can generate a rotational torque, achieving a controllable clockwise rotation of ~14°/s and reaching an angular displacement of 125° within 9 s (Fig. 5c and Fig. S28b). These results demonstrate that multimodal locomotion can be achieved through the integration of Janus LCE fibers with different actuation directions by leveraging localized NIR laser stimuli. Control experiments employing non-actuating PU fibers as locomotive elements exclude thermally induced Marangoni effects. These results confirm that motion originates from programmed NIR-triggered bending of Janus fibers. The asymmetric leg configuration, in which the left legs have opposite LCE-facing orientations while the right legs share the same orientation, allows selective illumination to generate either a net propulsive force for translation or an unbalanced torque for rotation, enabling the robot to switch between straight-line motion and controlled rotation in a programmable manner.

Heterogeneous structural design of Janus LCE fibers can also enable directional locomotion. To achieve this, we design a spring fiber with gradient helical architectures (Fig. S29). Upon insertion into narrow glass tubes and heating to 100°C, asymmetric contraction along the fiber generates axial movement. During the cooling phase to 40°C, shape recovery further enhances the overall movement. Through repeated thermal cycling, an inchworm-like locomotion is achieved (Fig. 5d and Movie S7), with each cycle resulting in ~0.2 mm of forward progression (Fig. S30).

The continuously fabricated fibers can be incorporated into smart fabrics through conventional textile manufacturing techniques. During the weaving process, Janus LCE fibers are integrated as weft threads in a plain weave structure, enabling active functional control while maintaining mechanical integrity. The resulting textiles display a uniform weave free of defects, confirming the fibers’ robustness under the shear and tensile stresses experienced during the weaving process (Fig. 5e). When stretched, the mechanical stretching induces a structural transformation in the Janus LCE fibers, generating coiled architectures that increase fabric porosity and loft density. This geometric reconfiguration significantly enhances thermal insulation performance, as demonstrated in Fig. 5f and Fig. S31. And the mechanically induced thermal insulation enhancement is reversible, as mild heating initiates structural recovery to the original compact form. The highly tunable insulation properties render the material exceptionally suitable for wearable and adaptive thermal management applications.

Methods
Materials
1,4-Bis [4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (RM82) was procured from Daken Chemical Company. 3,6-Dioxa-1,8-octanedithiol (DODT, 97%), Tolylene-2,4-diisocyanate (95%) and 2-(tert-butylamino)ethyl methacrylate (98%) was obtained from TCI. Pentaerythritol tetrakis (3-mercaptopropionate) (PETMP, 95%), triethylamine (TEA, 99%), dimethylolbutanoic acid (DMBA, 98%), ditin butyl dilaurate (DBTDL, 95%), and Phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (Irgacure 819, 97%) were obtained from Aladdin. Poly(tetrahydrofuran)diol (Mn=1000) was purchased from B&D and vacuum-dried at 100°C before being used. All chemicals were used as received unless otherwise noted.

Synthesis of LC oligomer
RM82 (10.00 g), DODT (2.024 g), TEA (2% of the monomers), and toluene (10.00 g) were added into a 50 mL flask and stirred at 70°C for 24 h. After the reaction, toluene was evaporated at 70°C to yield a white viscous liquid, which was further dried in a 70°C vacuum oven for 24 h. The molecular structure was characterized by 1H-NMR and FTIR analysis (Figs. S1a and S4).

Synthesis of PU precursor
The PU precursor containing dynamic hindered urea bonds and pendant carboxylic acid groups was synthesized via three steps. First, poly(tetrahydrofuran)diol (0.05 mol) and tolylene-2,4-diisocyanate (0.1 mol) were added to a three-necked flask equipped with a mechanical stirrer, followed by the addition of the catalyst DBTDL (0.1 wt% of poly(tetrahydrofuran)diol), and stirred at 50°C for 4 h. Subsequently, dimethylolbutanoic acid (0.033 mol) was added and reacted for 4 h. Finally, 2-(tert-butylamino)ethyl methacrylate (0.033 mol) was introduced and reacted for an additional 4 h using ethylene glycol diacetate as the solvent to control viscosity. The molar ratio of dimethylolbutanoic acid to 2-(tert-butylamino)ethyl methacrylate was maintained at 1:1 to ensure equimolar content of hindered urea bonds and carboxylic acid groups. The chemical structure of the resulting PU precursor was confirmed by 1H NMR analysis (Fig. S1b).

Preparation of LCE precursor
Combine LC oligomer (1.00 g), RM82 (0.50 g), DODT (65.20 mg), PETMP (187.30 mg), and Irgacure 819 (10 mg) in toluene (500 μL) with a magnetic stirrer. Stir the solution at room temperature for 30 min to dissolve. The final precursor was collected as a viscous liquid after evaporating the toluene under vacuum. The precursor was ready for use.

Preparation of PU precursor
The PU precursor was mixed with ethylene glycol diacetate for viscosity control, using a maximum solvent content of 40 wt%, followed by the addition of the Irgacure 819 (3 wt%). The resulting mixture was stored in the dark prior to use.

Fabrication system
Janus fibers were fabricated using a custom-built high-speed extrusion-spinning setup comprising a coaxial fiber extrusion module and a synchronized fiber collection unit. The extrusion module employed a modified direct ink writing printhead from a commercial bioprinter (Regenovo, Bio-Printer SR, China) to simultaneously extrude LCE and PU precursors through a custom-designed Janus nozzle under in situ UV irradiation (365 nm, 9000 mW·cm^−2), thereby forming a single biphasic filament. The extrusion and collection speeds were precisely matched to ensure uniform fiber formation. The fiber diameter and the interfacial ratio between the LCE and PU domains were tuned by adjusting the applied air pressure, nozzle diameter, and roller speed. A differential speed between the two rollers (defined by the ratio of V3 to V2) enabled uniaxial stretching of the extruded fiber and was followed by secondary UV curing (365 nm, 9000 mW·cm^−2, 10 min) to achieve further crosslinking of the Janus architecture and to lock in the aligned mesogen orientation within the LCE domain. Unless otherwise specified, the subsequent Janus fibers were fabricated under optimized conditions with an extrusion speed of 5 m·min^−1 and roller speeds set to V1=V2=2 r·min^−1 and V3=V4=3.6 r·min^−1. The Janus nozzle was independently designed and fabricated via DLP 3D printing with a nozzle diameter of 0.4 mm.

Characterization
NIR laser (808 nm) was generated by a laser source (MDL-H-808-5W, Changchun New Industries Optoelectronics Technology Co., Ltd.). Supporting Information Videos were recorded by a digital camera (Sony, Alpha 7). Surface morphology was characterized by scanning electron microscopy (SEM, Hitachi S-4800). The 1H nuclear magnetic resonance (1H-NMR) spectra were collected on a Bruker Avance III spectrometer operating at 500 MHz. FTIR spectra were recorded using a VERTEX 70 FTIR spectrometer. Gel permeation chromatography (Waters) was performed using tetrahydrofuran as the mobile phase with a flow rate of 1 mL·min^−1. Rheological measurements were conducted with a rotational rheometer (DHR-2, TA Instruments). The alignment and Janus structure of fibers was observed using polarized optical microscopy (POM, ECLIPSE E600W POL) with crossed polarizers. Two-dimensional wide-angle X-ray scattering (2D-WAXS) patterns and data were gathered utilizing an X-ray diffractometer (XENOCS) at room temperature. Mechanical tensile tests of Janus fibers were carried out on a universal testing machine (Instron 5966) at a stretching rate of 20 mm·min^−1. Dynamic mechanical analysis (DMA) was conducted using a TA Q800 analyzer.

Programming strategy 1: direct mechanical stretching
Janus fibers were programmed by subjecting them to tensile strains ranging from 20 to 100% at a temperature of 25°C, followed by the release of the applied strain. The deformed shape was retained due to the soft elasticity exhibited by LCE. The degree of coiling (N) was quantified as the number of coils per unit fiber length (N=n/H), where “H” denotes the original length of the unprogrammed fiber and “n” is the number of visible coils formed after programming. In addition, the coil diameter and helix pitch was measured to assess the morphological response of the fibers under different programming strains.

Programming strategy 2: thermal annealing
Janus fibers were programmed by applying a tensile strain of 60% at 90°C and subsequently annealed for varying durations (1-10 min) under the same temperature, followed by immediate strain release. The resulting deformed shape was attributed to stress relaxation caused by dynamic bond exchange in PU. The resulting coiled configurations were then evaluated as a function of annealing time, and the coil density (N), coil diameter, and helical pitch were further quantified and compared across different annealing times.

Programming strategy 3: spatial programming
Janus fibers were first stretched to 50% strain at 25°C. Near-infrared (808 nm) laser irradiation (2000 mW·cm^−2, 5 min) was then applied in a spatially selective manner to predefined regions along the fiber. The laser was scanned longitudinally along the fiber axis at a controlled speed to locally activate dynamic covalent bond exchange. No observable contraction was detected during programming, indicating that the non-oriented LCE domains and applied external stress prevented deformation gradients, preserving the programming of the PU phase. Upon releasing the applied strain, the laser-irradiated regions—designated as Programming 2—retained their elongated shape, while the non-irradiated regions (Programming 1) spontaneously relaxed into helical coils. This spatially patterned programming yielded a single fiber comprising both linear and helical segments. When heated to 70°C, the fiber exhibited thermally induced bimodal switching: the initially linear segments (Programming 2) transformed into helices, while the preformed helical segments (Programming 1) relaxed into linear configurations. This dual-mode integration highlights a programmable and reversible strategy for spatially encoded multimodal actuation within a single Janus fiber.

Shape reconfiguration of coiling and reversible actuation performance of Janus fibers
Fibers were twisted to a twist density of 6 turns·cm^−1 and heated to ~90°C to activate dynamic bond exchange while introducing internal stress, followed by cooling to ~25°C under constant tension and subsequent release of the applied stress. The resulting fibers were then immersed in oil baths maintained at ~90°C to induce thermally triggered coiling. Simultaneously, further dynamic bond exchange reconfigured and fixed the transient helical shape into a stable geometry. Notably, by varying the inserted twist densities (e.g., 5, 8, and 10 turns·cm^−1), three additional reconfigured helical architectures were generated, each exhibiting distinct geometries and actuation behaviors. These reconfigured fibers were subsequently subjected to 50 heating-cooling cycles between 70 and 25°C to assess their reversible actuation performance. During each cycle, changes in the axial length of the helix were recorded to quantify actuation strain and evaluate fatigue resistance.

Data availability
The authors declare that the data supporting the findings of this study are provided within the article and its Supplementary Information file. Additional data were available upon request from the corresponding author. Source data are provided with this paper.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "There are two highlights of this work: 1. The fabrication of Janus-structured fibrous artificial muscles by bicomponent extrusion spinning; the combination of polyurethane (PU) and liquid crystal elastomer (LCE) improves the mechanical properties of the LCE. 2. Leveraging the soft elasticity of liquid crystal elastomers and the dynamic bond exchange of polyurethane (PU), multi-modal shape programming of Janus fibers has been achieved. However, as a fibrous artificial muscle, shape change is only one aspect; the actuation properties (strain, stress, energy density, etc.) are even more crucial. The following revisions are suggested:\n1. For straight Janus LCE/PU fibers prepared by a continuous extrusion platform, please provide their actuation strain, actuation strain rate, actuation stress, as well as energy density, these metrics are important to evaluate actuation properties for shape-changing materials used as artificial muscles.\n2. For spring-like Janus fiber actuators, how about their loading capabilities? Can these spring-like soft actuators load external load and cyclically lift the load like a soft spring upon thermal actuation?\n3. What factors influence the order parameter? What is the range of the order parameter for processed fiber?\n4. For continuous extrusion-stretching process，Fig. 1c is a schematic diagram of processing device and fiber processing. Is there a video actually shot to show the processing device and the processing process?\n5. For the swimming robot shown in Fig. 5b, the authors need to rule out the possibility of the thermal-induced Marangoni effect. This effect can also propel a floating object on the water surface to move.", "reviewer_2": "Recommendation:\nRecommend for publication after minor revisions.\nOverall Comments:\nThis manuscript presents a novel approach for the fabrication of Janus Fibers. The authors create continuously extruded Janus fibers created from Liquid Crystalline Elastomer (LCE) and polyurethane (PU). The authors demonstrate improved properties of these Janus fibers through mechanical testing. The authors also demonstrate the creation of several functional examples of Janus fiber including tendril actuation, and programmable coiling behavior. The work is well written, well executed, and has complete and thorough supporting information for claims. The method has potential for improving existing methodologies for Janus fiber production and advances the usefulness of LCE fibers by improving their properties.\nTherefore, the reviewer believes it will be of interest to the community of Nature Communications and offers the following\nminor comments.\nItems to be addressed:\n1) The authors claim “synchronization” in photopolymerization kinetics, suggesting that there is a coupling between the\nphotocuring behavior of the two materials. Could the authors explain this coupling or simply state that the two materials\npolymerize on similar time scales?\n2) The authors claim a single Janus fiber can lift 160,000 times its own weight. This is supported by a photo in the SI, but the\ndimensions of the fiber are not given or shown, and there is no information on how far the fiber lifted the weight, making it\ndifficult to reproduce or use as a benchmark. Could the authors add information about fiber dimensions and the distance the\nweight was lifted?\n3) Figure 4 does not distinguish between LCE and PU as BLUE and RED respectively. It can be inferred from other figures,\nbut explicit references are preferred.\n4) The authors state that a 0.61 orientation order parameter is demonstrated from 2D-WAXS images without further\nexplanation. Could the authors elaborate in the SI how this order was determined from the images?\n5) The work is missing citations and discussion for key pioneering works in the area of LCE fibers including:\na. Seminal work introducing preparation of LCE fibers: https://pubs.acs.org/doi/abs/10.1021/acsami.9b04401\nb. Initial work showing polyurethane/polyacrylate for ultrasong mechanical properties, like breaking strength (your Fig. 2j):\nhttps://pubs.acs.org/doi/10.1021/jacs.9b06757\nc. Initial work showing “self-winding”: Zhiming Hu, Yunlong Li, Tonghui Zhao, Jiu-an Lv, Self-winding liquid crystal\nelastomer fiber actuators with high degree of freedom and tunable actuation, Applied Materials Today, 2022", "reviewer_3": "The manuscript describes a continuous extrusion method for fabricating Janus LCE fibers. The integration of dynamic\ncovalent bonds with programmable molecular alignment to create asymmetric, biomimetic fibers is a compelling approach,\nand the work constitutes a meaningful contribution to the field. Applications in soft robotics and adaptive textiles effectively\ndemonstrate the potential of this methodology.\nThat said, the study would benefit from more comprehensive quantitative data to firmly substantiate its main conclusions.\nSeveral claims currently rely on qualitative demonstrations rather than systematic experimental validation. Mechanistic\nexplanations, particularly those concerning material interactions and actuation control, need further development to be fully\nconvincing.\nI recommend major revision to address the following points:\n1.The proposed reinforcement mechanism involving the PU network requires more direct evidence at the molecular level. A\ndeeper analysis of the LCE-PU interface and how dynamic covalent bonding specifically enhances mechanical properties\nwould strengthen this section.\n2.Although the material shows promising reversibility over 50 cycles, extended cycling tests (e.g., several hundred cycles)\nare necessary to properly evaluate its long-term durability and fatigue resistance.\n3.The influence of extrusion parameters on mechanical performance needs quantitative support. Data establishing clear\ncorrelations between extrusion speed and tensile properties, with statistical validation, should be included.\n4.The shape recovery behavior under different temperature gradients requires further systematic quantification. Recovery\nrates and positional accuracy across a range of controlled thermal conditions would help clarify performance limits.\n5.The control of various motion modes via light-thermal stimuli needs clearer characterization. Quantitative relationships\nbetween stimulus parameters (e.g., intensity, wavelength, duration) and the resulting actuation behavior should be\nestablished.\n6.The motion mechanism of the quadruped robot needs clarification. Please explain the functional differences between the\ntwo side feet and how each contributes to the distinct locomotion modes.\n7.There is an inconsistency in light source labeling between the main text (NIR, 808 nm) and Figure 5 (IR). The figure should\nbe corrected for accuracy and consistency.", "reviewer_4": "This manuscript presents a strategy for the continuous fabrication of Janus LCE fibers that integrate a stimuli-responsive\nLCE network with a dynamically reconfigurable PU network. The authors demonstrate programmable and reprogrammable\nactuation, bioinspired design, and scalable integration into functional textiles, representing a notable advance in the field of\nsoft robotics and adaptive materials.\n1.The success of co-extrusion relies on the viscosity matching between the two precursors. Could the authors provide\nquantitative data or discussion on how small viscosity deviations affect the interface stability and fiber morphology?\n2.The PU component exhibits dynamic covalent bond exchange above 55 °C, while the Tₙᵢ of the LCE is around 67 °C.\nFigure 2i indicates that the PU network undergoes relatively fast stress relaxation upon heating. Could the authors elaborate\non how the rate of dynamic bond exchange affects the long-term actuation stability, as well as potential creep and fatigue\nbehaviors under repeated thermal cycling?\n3.Regarding the fabrication process of the Janus fibers, I have several technical questions: (1) The process involves a two-\nstep UV curing. How is the crosslinking degree controlled during the first UV exposure to ensure that further alignment and\nsecondary curing can proceed effectively? (2) During the first UV curing, does the partial polymerization already fix the\nshear-induced orientation of the LCE domains, or is the alignment mainly achieved during the subsequent stretching step?\n(3) Upon the final thermal treatment, will the pre-aligned LCE phase experience slight shrinkage that may influence the\nmorphology of the adjacent PU domain, even if the temperature does not reach Tₙᵢ? (4) Could the authors further elaborate\non the detailed mechanism by which heating promotes hydrogen-bond formation within the PU network?\n4.What is the interfacial adhesion strength between the LCE and PU domains? Are these two materials prone to\ndelamination under mechanical deformation? For long-term use, could a mismatch in strain or modulus between the LCE\nand PU layers lead to interfacial instability or fatigue?\n5.In Figure 3c, what is the surface temperature reached during NIR laser irradiation? Is the temperature distribution across\nthe irradiated region uniform? Typically, the central zone tends to be hotter than the edges—how do the authors ensure\ncontrolled and uniform photothermal processing?\n6.Upon localized heating by NIR light, does the LCE layer experience partial thermal transition or contraction that might\nintroduce internal stresses or deformation gradients within the Janus structure?\n7.Does the PU network contain any catalyst that facilitates the dynamic covalent exchange reaction? If not, how can the\nurethane bond exchange proceed efficiently at such a relatively low temperature and with a low apparent activation energy?\nIt is suggested that the authors provide more detailed synthetic procedures of the polymer precursors to minimize confusion.\n8.How did the authors regulate the viscosities of the LCE and PU precursors during co-extrusion? Were any solvents used\nin the precursor formulations? If solvents were employed, could their evaporation affect the fiber morphology, phase\ninterface, or mechanical performance during fabrication?", "reviewer_5": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "We sincerely thank the reviewers for their insightful and constructive feedback on our\nmanuscript. We have extensively revised the manuscript with all the changes highlighted in\nred in the main text and supporting information. We believe the revision pushes the work to\na much higher level. Below are the point-by-point responses to the review comments with\nour responses highlighted.\nReviewer #1:\nThere are two highlights of this work: 1. The fabrication of Janus-structured fibrous artificial\nmuscles by bicomponent extrusion spinning; the combination of polyurethane (PU) and liquid\ncrystal elastomer (LCE) improves the mechanical properties of the LCE. 2. Leveraging the soft\nelasticity of liquid crystal elastomers and the dynamic bond exchange of polyurethane (PU), multi-\nmodal shape programming of Janus fibers has been achieved. However, as a fibrous artificial\nmuscle, shape change is only one aspect; the actuation properties (strain, stress, energy density,\netc.) are even more crucial. The following revisions are suggested:\nResponse: We gratefully acknowledge the reviewer’s recognition of our innovation in Janus fiber\ncontinuous fabrication and multimodal shape programming. We also sincerely appreciate the\nthoughtful comments and valuable suggestions regarding the actuation properties, which are\ncrucial for advancing our work to a higher standard. In response to the reviewer’s\nrecommendations, we have carefully addressed each point and implemented appropriate revisions\nto enhance the clarity of our manuscript.\n1. For straight Janus LCE/PU fibers prepared by a continuous extrusion platform, please provide\ntheir actuation strain, actuation strain rate, actuation stress, as well as energy density, these metrics\nare important to evaluate actuation properties for shape-changing materials used as artificial\nmuscles.\nResponse: We thank the reviewer for the insightful suggestion. To comprehensively evaluate the\nactuation performance of the straight Janus LCE/PU fibers fabricated via our continuous extrusion\nplatform, we quantified their thermally induced actuation under well-controlled conditions. At an\nactuation temperature of 80 °C, the straight Janus fibers (diameter≈120 µm, prepared at V /V =1.8)\n3 2\n1\nundergo thermally driven coiling, enabling us to calculate the actuation strain using the equivalent\nhelical deformation. The fibers exhibit a large actuation strain of 85.3  2.4% (Fig. S15), together\nwith a high actuation strain rate of 192.9  8.3%·s-1. When lifting a load of 0.228 g, the fibers\ngenerate an actuation stress of 197.7 kPa, corresponding to an energy density of 49.0  2.7 kJ·m-3\n(Fig. S16). These quantitative metrics collectively demonstrate that the continuously extruded\nJanus fibers achieve high-amplitude, rapid, and energy-efficient actuation, underscoring their\npotential for artificial-muscle applications. For clarity, the corresponding descriptions and\ncalculations are provided in main text and supporting information shown below:\nRevisions in the manuscript are on Page 10, Line 20:\n“In addition to their improved mechanical robustness, the continuously extruded Janus fibers also\ndisplay excellent thermal actuation performance. At 80 °C, the fibers achieve a large actuation\nstrain of ~85% (Fig. S15) with rapid actuation kinetics, generating an energy density approaching\n50 kJ·m-3 (Fig. S16). These combined mechanical and actuation attributes underscore the strong\npotential of Janus fibers for scalable artificial-muscle applications.”\nRevisions in the supporting information are on Page 12-13 and Page 27, Line 10:\n“Fig. S15. Temperature-dependent actuation strain of Janus fibers. (a) Actuation strain of Janus\nfibers measured at different temperatures. (b) Fiber morphology under different thermal\nconditions and the measurement of minimum length 𝑥 at maximum contraction. The initial\n𝑚𝑖𝑛\nfiber length 𝑥 was 1.5 cm.”\n𝑟𝑒𝑠𝑡\n2\n“Fig. S16. Work capacities of straight Janus fibers under different loads.”\n“2. Calculation of actuation properties\nThe actuation strain of a Janus fiber was calculated as:\n(𝑥 −𝑥 )\n = 𝑟𝑒𝑠𝑡 𝑚𝑖𝑛 ×100%\n𝑎𝑐𝑡\n𝑥\n𝑟𝑒𝑠𝑡\nwhere 𝑥 is the initial fiber length and 𝑥 is the minimum length at maximum contraction.\n𝑟𝑒𝑠𝑡 𝑚𝑖𝑛\nDue to thermal-induced coiling of the fiber, the actuation strain was expressed using the equivalent\nhelical diameter.\nThe average actuation strain rate was determined as:\n\n̇ = 𝑎𝑐𝑡\n𝑎𝑣𝑔 𝑡\nwhere 𝑡 is the actuation time.\nThe actuation stress was calculated from the measured force as:\n𝑚𝑔\n =\n𝑎𝑐𝑡\n𝐴\n𝑓𝑖𝑏𝑒𝑟\nwhere 𝑚 is the lifted mass, 𝑔 is the gravitational acceleration, and 𝐴 is the fiber cross-\n𝑓𝑖𝑏𝑒𝑟\nsectional area.\nThe energy density (Work Capacity) or work capacity of the fiber was calculated as:\n𝑚𝑔·𝐿\n𝑊𝑜𝑟𝑘 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 =\n𝑉\n𝑓𝑖𝑏𝑒𝑟\nwhere 𝛥𝐿 is the displacement along the force direction, 𝑚 is the lifted mass, 𝑔 is the gravitational\nacceleration, and 𝑉 is the fiber volume.”\n𝑓𝑖𝑏𝑒𝑟\n3\n2. For spring-like Janus fiber actuators, how about their loading capabilities? Can these spring-like\nsoft actuators load external load and cyclically lift the load like a soft spring upon thermal actuation?\nResponse: We thank the reviewer for this thoughtful question regarding the loading capability of\nthe spring-like Janus fiber actuators. For Janus fibers in a straight structure, a large external force\ncan be applied as shown in Fig. S13. However, for a spring-like Janus fiber, if a large external\nforce is applied, its spring structure will disappear and transform into a straight structure. To\npreserve the spring structure during deformation, only a small external force can be applied.\nTo directly evaluate actuation performance in spring structure under external loads, we conducted\nlifting experiments with spring-like Janus fibers subjected to suspended masses of 3, 4, and 5 mg\n(newly added Fig. S23). The fibers were able to reproducibly lift these small loads and the\nmaximum is 5 mg. It also shows excellent cyclic stability during two hundred heating and cooling\ncycles (Supplementary Movie 3). While the load is relatively small, it still proves critically\nvaluable for micro robots and smart fabric.\nRevisions in the manuscript are on Page 14, Line 5:\n“After programming, the loosely coiled helical configurations are capable of reversibly switching\nbetween loose and tight helices and exhibit excellent stability during two hundred heating and\ncooling cycles (Supplementary Movie 3), and this reversible actuation is maintained even when\nsmall external loads are applied (Fig. S23).”\nRevisions in the supporting information are on Page 16:\n“Fig. S23. Thermal actuation of spring-like Janus fiber actuators under external loading. (a)\nActuation behavior under a 3 mg load. (b) Actuation behavior under a 4 mg load. (c) Actuation\nbehavior under a 5 mg load.”\n4\n3. What factors influence the order parameter? What is the range of the order parameter for\nprocessed fiber?\nResponse: We thank the reviewer for these important questions. The order parameter is\npredominantly governed by the stretching rate. As documented in Ref. Adv. Mater. 2023, 2211800,\nthe order parameters increase from 0.22 up to 0.76 during LCE fiber stretching. In this work,\nunstretched fibers exhibit near-zero order parameters, evidenced by the isotropic 2D WAXS\npattern in Fig. 2g. Controlled stretching via V /V speed modulation elevates the order parameter,\n3 2\nreaching 0.61 at V /V =1.8. Further speed increases risk fiber fracture, thereby constraining\n3 2\nachievable order parameters within the 0-0.61 range. We have made it clear in the manuscript.\nRevisions in the manuscript are on Page 8, Line19:\n“Increasing the stretching speed ration from 1 to 1.8 induces a rise in the orientational order\nparameter from 0 to 0.61, as calculated from Fig. S11.”\n4. For continuous extrusion-stretching process, Fig. 1c is a schematic diagram of processing device\nand fiber processing. Is there a video actually shot to show the processing device and the\nprocessing process?\nResponse: The video (Supplementary Movie 1) is now added accordingly.\n5. For the swimming robot shown in Fig. 5b, the authors need to rule out the possibility of the\nthermal-induced Marangoni effect. This effect can also propel a floating object on the water\nsurface to move.\nResponse: We have added a controlled experiment in revised Supplementary Movie 6. It is a robot\nconstructed using four carbon nanotubes (CNTs)-coated PU fibers instead of Janus LCE/PU fibers\nto rigorously distinguish photothermal actuation from thermally induced interfacial phenomena.\nThese CNT-coated PU fibers exhibit comparable optical absorption and heating properties but do\nnot experience photothermal deformation. Under the same NIR irradiation, the control robot\ndemonstrated no leg bending and showed neither translational nor rotational movement, remaining\nentirely stationary on the water surface. This result conclusively eliminates the possibility of\nthermal-induced Marangoni flow contributing to the locomotion observed in the Janus fiber robot.\nRevisions in the manuscript are on Page 16, Line 15:\n5\n“Control experiments employing non-actuating PU fibers as locomotive elements exclude\nthermally induced Marangoni effects. These results confirm that motion originates from\nprogrammed NIR-triggered bending of Janus fibers”\nRecommendation:\nRecommend for publication after minor revisions.\nOverall Comments:\nThis manuscript presents a novel approach for the fabrication of Janus Fibers. The authors create\ncontinuously extruded Janus fibers created from Liquid Crystalline Elastomer (LCE) and\npolyurethane (PU). The authors demonstrate improved properties of these Janus fibers through\nmechanical testing. The authors also demonstrate the creation of several functional examples of\nJanus fiber including tendril actuation, and programmable coiling behavior. The work is well\nwritten, well executed, and has complete and thorough supporting information for claims. The\nmethod has potential for improving existing methodologies for Janus fiber production and\nadvances the usefulness of LCE fibers by improving their properties. Therefore, the reviewer\nbelieves it will be of interest to the community of Nature Communications and offers the following\nminor comments.\nResponse: We sincerely appreciate the reviewer’s positive assessment. In response, we have\nconducted additional experiments and thoroughly reviewed relevant literature to fully address the\nraised concerns. These improvements have significantly enhanced the significance and clarity of\nour manuscript.\nItems to be addressed:\n1. The authors claim “synchronization” in photopolymerization kinetics, suggesting that there is a\ncoupling between the photocuring behavior of the two materials. Could the authors explain this\ncoupling or simply state that the two materials polymerize on similar time scales?\nResponse: We appreciate the reviewer’s query regarding synchronization in photopolymerization\nkinetics. This term specifically denotes the comparable curing timescales between PU and LCE\ncomponents under identical UV exposure. Both the LCE and PU precursors undergo gelation after\n2 s of UV exposure, indicating that their photopolymerization kinetics are well synchronized.\nSpecifically, at 2 s exposure, the double-bond conversion of the LCE precursor reaches 62%,\nconsistent with the Flory gel-point criterion (Fig. 2b), while the PU resin exhibits a gel content of\n21% (Fig. 2c). The matching photopolymerization kinetics ensures the formation of the LCE/PU\n7\nfiber network. To more clearly elucidate the dynamic compatibility between the two systems, we\nhave revised the manuscript accordingly.\nRevisions in the manuscript are on Page 7, Line 10:\n“More importantly, the photopolymerization kinetics of the two precursors exhibit remarkable\nsynchronization. Upon exposure to 365 nm UV light, the LCE precursor undergoes rapid\nphotopolymerization, as evidenced by time-resolved infrared spectroscopy and the corresponding\nincrease in acrylate conversion (Fig. 2b and Fig. S6). According to Flory’s gelation theory, the\nLCE precursor reaches the gel point after 2 s of exposure (calculations provided in the Supporting\nInformation). Similarly, the PU precursor displays comparably fast crosslinking kinetics, with the\ngel fraction exceeding >21% within 2 s (Fig. 2c). These rapid curing dynamics enable the\nconcurrent formation of both networks, thereby ensuring fiber solidification during the initial\nstages of UV curing.”\n2. The authors claim a single Janus fiber can lift 160,000 times its own weight. This is supported\nby a photo in the SI, but the dimensions of the fiber are not given or shown, and there is no\ninformation on how far the fiber lifted the weight, making it difficult to reproduce or use as a\nbenchmark. Could the authors add information about fiber dimensions and the distance the weight\nwas lifted?\nResponse: We thank the reviewer for this constructive suggestion. We have now clarified the\nexperimental details for the reported 160,000 self-weight lifting capacity of a single Janus fiber.\nThe fiber used in the lifting experiment has a diameter of 200 µm. As demonstrated in\nSupplementary Movie 2, the fiber successfully lifts the mass through a vertical displacement of\n~20 cm.\nRevisions in the manuscript are on Page 10, Line 12:\n“Visual demonstration shows a single Janus fiber (diameter ~200 µm) could lift an object over\n160,000 times its own weight and raised it over a distance of ~20 cm (Fig. S13 and Supplementary\nMovie 2), highlighting the exceptional strength and robustness of this hybrid design.”\nRevisions in the supporting information are on Page 11:\n8\n“Fig. S13. Lifting demonstration of a Janus fiber. Photograph showing a 0.5 mg Janus fiber\nlifting a weight of 80 g over a distance of ~20 cm.”\n3. Fig. 4 does not distinguish between LCE and PU as BLUE and RED respectively. It can be\ninferred from other figures, but explicit references are preferred.\nResponse: We sincerely apologize for the confusion. An explanation of the color scheme has now\nbeen added to the caption of Fig. 4.\nRevisions in the manuscript are on Page 15:\n“In all the schematic diagrams, blue color represents LCE and red color represents PU.”\n4. The authors state that a 0.61 orientation order parameter is demonstrated from 2D-WAXS\nimages without further explanation. Could the authors elaborate in the SI how this order was\ndetermined from the images?\nResponse: We appreciate the reviewer’s valuable suggestion. The orientational order parameter\n(S) was determined using the half-width method, derived from the azimuthal intensity distribution\nof the 2D wide-angle scattering pattern.\nRevisions in the manuscript are on Page 8, Line 19:\n“Increasing the stretching speed ration from 1 to 1.8 induces a rise in the orientational order\nparameter from 0 to 0.61, as calculated from Fig. S11.”\n“\nFig. S11. The correlation between azimuthal angle and scattering intensity.”\n“Order parameter calculation: The two-dimensional wide-angle X-ray scattering (2D WAXS)\npatterns were analyzed with the FIT2D software to extract the azimuthal intensity distribution, as\nillustrated in Fig. S11. The order parameter S was then calculated according to the following\nequation [2]:\n∆ 𝜑\n1\n𝑆 = 1− 2\n180°\nwhere ∆ 𝜑 denotes the angular difference between the position of the maximum intensity and the\n1\n2\nangle corresponding to half of this maximum, and S represents the order parameter.”\n5. The work is missing citations and discussion for key pioneering works in the area of LCE\nfibers including:\na. Seminal work introducing preparation of LCE fibers:\nhttps://pubs.acs.org/doi/abs/10.1021/acsami.9b04401\nb. Initial work showing polyurethane/polyacrylate for ultrasong mechanical properties, like\nbreaking strength (your Fig. 2j): https://pubs.acs.org/doi/10.1021/jacs.9b06757\nc. Initial work showing “self-winding”: Zhiming Hu, Yunlong Li, Tonghui Zhao, Jiu-an Lv, Self-\nwinding liquid crystal elastomer fiber actuators with high degree of freedom and tunable\nactuation, Applied Materials Today, 2022\nResponse: We thank the reviewer for highlighting these important pioneering works in the field\nof LCE fibers. We have carefully evaluated the recommended references and incorporated them\nto better contextualize our study in the revised manuscript.\nThe recommended references have been cited as Ref. 24, Ref.28 and Ref. 37:\n“24. Wang, Y., Li, Q., Liu, Q. et al. Preparation of liquid crystal elastomer fibers with\nprogrammable actuation. ACS Appl. Mater. Interfaces 11, 20405–20414 (2019).”\n“28. Hu, Z., Li, Y., Zhao, T. & Lv, J. Self-winding liquid crystal elastomer fiber actuators with high\ndegree of freedom and tunable actuation. Appl. Mater. Today 28, 101507 (2022).”\n“37. Li, C., Shi, K., Zhang, S. et al. Polyurethane/polyacrylate hybrid networks with ultrahigh\nmechanical strength. J. Am. Chem. Soc. 141, 19956–19963 (2019).”\nThe manuscript describes a continuous extrusion method for fabricating Janus LCE fibers. The\nintegration of dynamic covalent bonds with programmable molecular alignment to create\nasymmetric, biomimetic fibers is a compelling approach, and the work constitutes a meaningful\ncontribution to the field. Applications in soft robotics and adaptive textiles effectively demonstrate\nthe potential of this methodology.\nThat said, the study would benefit from more comprehensive quantitative data to firmly\nsubstantiate its main conclusions. Several claims currently rely on qualitative demonstrations\nrather than systematic experimental validation. Mechanistic explanations, particularly those\nconcerning material interactions and actuation control, need further development to be fully\nconvincing.\nI recommend major revision to address the following points:\nResponse: We sincerely thank the reviewer for recognizing our work as a compelling approach to\nthe development of biomimetic Janus fibers and for their positive assessment of its meaningful\ncontribution to the field. We also appreciate the reviewer’s feedback regarding the need for\nadditional quantitative data. We are grateful for the opportunity to address these comments in detail\nand welcome further discussion to clarify aspects of our study. Below, we provide point-by-point\nresponses to the reviewer’s specific concerns. We reiterate our deep appreciation for the time and\nexpertise the reviewer has dedicated to this thorough evaluation.\n1. The proposed reinforcement mechanism involving the PU network requires more direct\nevidence at the molecular level. A deeper analysis of the LCE-PU interface and how dynamic\ncovalent bonding specifically enhances mechanical properties would strengthen this section.\nResponse: We sincerely thank the reviewer for highlighting these critical interfacial and\nmechanical concerns. The PU used in this work was adapted from Ref. Nature 2024, 631, 783–\n788. In this reference, the formation of hydrogen bonds between amide linkages during heating\nhas been clearly demonstrated by temperature-dependent FTIR spectra as presented below.\nRef. Nature 2024, 631, 783–788)\nIn this work, thermal annealing facilitates dynamic bond reorganization, promoting hydrogen bond\nformation that enhances the mechanical robustness of the fibers. Besides, the interface between\nLCE and PU might be another contribution to the superior mechanical properties. LCE and PU\nprecursors contain photopolymerizable acrylate groups with comparable polymerization kinetics\n(Figs. 2b, 2c), and upon extrusion they undergo simultaneous interfacial contact and co-\npolymerization under UV irradiation, forming a seamless junction. Fig. 1e shows that the interface\nis microscopically homogeneous without defects, indicating robust molecular-level adhesion.\nGiven that the fiber dimensions of approximately 200 μm preclude the use of conventional peeling\ntests to distinguish the mechanical properties, we employed torsional deformation assays to assess\ninterfacial integrity. These mechanical assessments revealed no delamination tendencies under\ntorsional stresses, confirming stable bonding under operational strains, as shown in Fig. S9. In\naddition, we have included 200 consecutive actuation cycles and there are no apparent signs of\nactuation fatigue or creep. Microscopic image of the Janus fiber after 200 actuation cycles revealed\nno detectable interfacial damage (Fig. S24). We have incorporated in-depth discussions about\nreinforcement mechanism in the manuscript.\nRevisions in the manuscript are on Page 5, Line 20 and Page 14, Line 14:\n“Subsequent thermal annealing facilitates the ordered reorganization of hydrogen bonds through\ndynamic bond exchange within the PU segments, ultimately strengthening the mechanical integrity\nof the fibers35.”\n13\n“After 200 actuation cycles, the interfaces of Janus fiber remained intact, demonstrating that\nfibers produced via our fabrication method exhibit excellent structural stability (Fig. S25).”\nRevisions in the supporting information are on Page 17:\n“Fig. S25. Microscopic image of a helical Janus fiber after 200 actuation cycles.”\n2. Although the material shows promising reversibility over 50 cycles, extended cycling tests (e.g.,\nseveral hundred cycles) are necessary to properly evaluate its long-term durability and fatigue\nresistance.\nResponse: We thank the reviewer for this valuable suggestion. In response, we conducted\nextended cycling tests to more thoroughly evaluate the long-term durability and fatigue resistance\nof the Janus fibers as shown in Supplementary Movie 3. The helical structure displayed stable and\nreliable performance during extended operation, without observable fatigue throughout the 200-\ncycle test. The corresponding data have been added to the revised manuscript.\nRevisions in the manuscript are on Page 14, Line 13:\n“Cyclic testing demonstrates that the fibers exhibit no signs of actuation fatigue within 200 cycles\n(Fig. S24).”\nRevisions in the supporting information are on Page 17:\n14\n“Fig. S24. Actuation cycles of reprogrammed Janus fibers over 200 cycles.”\n3. The influence of extrusion parameters on mechanical performance needs quantitative support.\nData establishing clear correlations between extrusion speed and tensile properties, with statistical\nvalidation, should be included.\nResponse: We thank the reviewer for this valuable comment. Extrusion speed critically determines\nJanus fiber morphology and must be synergistically optimized with complementary parameters,\nsuch as UV irradiation intensity and collecting speed. By modulating extrusion pressure while\noptimizing ancillary processing conditions, we fabricated Janus fibers with controlled diameter of\n140 m, 210 m and 350m. Quantitative analysis confirms that increased extrusion pressure\nreduces fiber diameter, and crucially, tensile testing demonstrates enhanced Young’s modulus and\ntoughness in thinner fibers, establishing direct correlations between extrusion parameters and\nmechanical performance. The corresponding data and plots have been added to the revised\nmanuscript (Fig. S14), providing quantitative support for the effect of extrusion parameters on\nfiber mechanics.\nRevisions in the manuscript are on Page 10, Line 15:\n“To better understand the factors governing mechanical performance, we examined the effect of\nextrusion speed. Higher extrusion speeds produce thinner fibers, which exhibit increased Young’s\nmodulus and enhanced toughness, revealing a clear dependence of mechanical properties on fiber\ndiameter that can be systematically tuned through the extrusion parameters (Fig. S14).”\nRevisions in the supporting information are on Page 12:\n15\n“Fig. S14. Influence of fiber diameter on mechanical performance.”\n4. The shape recovery behavior under different temperature gradients requires further systematic\nquantification. Recovery rates and positional accuracy across a range of controlled thermal\nconditions would help clarify performance limits.\nResponse: We thank the reviewer for this insightful comment. To systematically evaluate the\nshape recovery behavior of Janus fibers under different thermal conditions, we measured the\nactuation strain at controlled temperatures and expressed it as an equivalent deformation.\nSpecifically, due to the curling of the fibers upon heating, the effective fiber length was calculated\nfrom the helical diameter. The calculation details of actuation properties can be found in supporting\ninformation on Page 27. Our results show that the actuation strain increases sharply within 60-\n70 °C, which corresponds closely to the nematic-isotropic phase transition temperature (T ~67 °C)\nNI\nof the LCE domain. The actuation strain continues to increase with temperature, reaching a\nmaximum of 91% at 90 °C. These measurements demonstrate the excellent thermally driven\nactuation performance of the Janus fibers and quantitatively clarify their shape recovery limits\nacross a range of controlled thermal conditions. To further assess positional accuracy and long-\nterm recovery fidelity, we conducted 200 consecutive actuation cycles under repeated heating and\ncooling. The helical geometry exhibited minimal drift in pitch and diameter throughout cycling,\ndemonstrating excellent durability, positional stability, and fatigue resistance. These results\ncollectively confirm that the Janus fibers maintain reliable and accurate shape recovery across a\nwide thermal range as well as long-term cyclic operation.\nRevisions in the manuscript are on Page 10, Line 20 and Page 14, Line 13:\n“In addition to their improved mechanical robustness, the continuously extruded Janus fibers also\ndisplay excellent thermal actuation performance. At 80 °C, the fibers achieve a large actuation\n16\nstrain of ~85% (Fig. S15) with rapid actuation kinetics, generating an energy density approaching\n50 kJ·m-3 (Fig. S16). These combined mechanical and actuation attributes underscore the strong\npotential of Janus fibers for scalable artificial-muscle applications.”\n“Cyclic testing demonstrates that the fibers exhibit no signs of actuation fatigue within 200 cycles\n(Fig. S24).”\nRevisions in the supporting information are on Page 12:\n“Fig. S15. Temperature-dependent actuation strain of Janus fibers. (a) Actuation strain of Janus\nfibers measured at different temperatures. (b) Fiber morphology under different thermal\nconditions and the measurement of minimum length 𝑥 at maximum contraction. The initial\nfiber length 𝑥 was 1.5 cm.”\n𝑟𝑒𝑠𝑡\n5. The control of various motion modes via light-thermal stimuli needs clearer characterization.\nQuantitative relationships between stimulus parameters (e.g., intensity, wavelength, duration)\nand the resulting actuation behavior should be established.\nResponse: We sincerely appreciate this valuable suggestion. Establishing quantitative correlations\nbetween photothermal stimuli parameters and actuation behavior is essential for mechanistic\nunderstanding and precise motion control. In the revised manuscript, we have systematically\nmeasured the actuation strain of Janus fibers under varying laser intensities. Because the fibers\nundergo coiling during heating, the effective fiber length was calculated based on the measured\nhelical diameter. Although direct infrared thermography was infeasible due to microscale fiber\ndiameters (~200 μm), the photothermal response closely follows the trends of direct thermal\nactivation as shown in Fig. S15. It shows an abrupt strain increase within 1140-1520 mW·cm-2,\nwhich indicates the nematic-isotropic transition, and reaches a maximum strain of 89% at 1960\n17\nmW·cm-2. These quantitative relationships demonstrate exceptional photothermal controllability\nfor precise regulation of soft robotic motion modes. We have made it clear in the manuscript.\nRevisions in the manuscript are on Page 16, Line 3:\n“This localized heating can also be achieved through NIR laser irradiation, enabling on-demand\nlight-guided locomotion, with the actuation magnitude precisely tunable via the irradiation\nintensity (Fig. S27).”\nRevisions in the supporting information are on Page 18:\n“Fig. S27. Laser-intensity-dependent actuation strain of Janus fibers. (a) Actuation strain of\nJanus fibers measured under different laser intensities. (b) Fiber morphology observed at varying\nlaser intensities, together with the measurement of the minimum length 𝑥 at maximum\nmin\ncontraction. The initial fiber length 𝑥 was 0.8 cm.”\nrest\n6. The motion mechanism of the quadruped robot needs clarification. Please explain the functional\ndifferences between the two side feet and how each contributes to the distinct locomotion modes.\nResponse: We thank the reviewer for the insightful comment. As shown in Fig. R2, the robot’s\nfour legs are constructed from Janus LCE fibers with intentionally designed opposite orientations\non the left side and identical orientations on the right side. This structural asymmetry leads to\ndifferent mechanical outputs under localized NIR illumination.\nblue representing the LCE phase and red representing the PU phase.\nLeft-side legs: generation of net translational thrust.\nWhen the left legs are illuminated, each Janus fiber bends toward its LCE side; however, because\nthe two fibers have opposite LCE-facing orientations, their bending directions differ. In the\nillumination phase, these opposite bending directions generate a small backward pull along the left\nmargin. When the light is turned off, the elastic recovery produces a stronger forward reactive\nforce. The asymmetry between the bending and recovery phases yields a net thrust directed toward\nthe right, enabling linear translation of the robot.\nRight-side legs: generation of rotational torque.\nIn contrast, the right legs share the same LCE-facing orientation. Upon illumination, both fibers\nbend in the same direction, creating a unilateral deformation relative to the robot’s center of mass.\nThis produces a non-zero torque rather than a net translational force, driving controlled clockwise\nrotation. Under continuous illumination, the robot achieves an angular velocity of ~14° s-1 and a\ncumulative rotation of ~125° within 9 s.\nWe have enhanced the manuscript with detailed mechanistic explanations of the differential\nfunctions between bilateral feet and their contributions to distinct quadrupedal locomotion modes.\nAdditionally, we incorporated a schematic diagram of the water strider-inspired robot design in\nSupplementary Movie 6 to facilitate comprehension.\nRevisions in the manuscript are on Page 16, Line 18:\n“The asymmetric leg configuration, in which the left legs have opposite LCE-facing orientations\nwhile the right legs share the same orientation, allows selective illumination to generate either a\nnet propulsive force for translation or an unbalanced torque for rotation, enabling the robot to\nswitch between straight-line motion and controlled rotation in a programmable manner.”\n7. There is an inconsistency in light source labeling between the main text (NIR, 808 nm) and Fig.\n5 (IR). The figure should be corrected for accuracy and consistency.\nResponse: Thank you for pointing out this inconsistency. We have revised Fig. 5 accordingly, and\nthe light source is now labeled as “NIR” to ensure accuracy and consistency with the main text.\nThis manuscript presents a strategy for the continuous fabrication of Janus LCE fibers that\nintegrate a stimuli-responsive LCE network with a dynamically reconfigurable PU network. The\nauthors demonstrate programmable and reprogrammable actuation, bioinspired design, and\nscalable integration into functional textiles, representing a notable advance in the field of soft\nrobotics and adaptive materials.\nResponse: We sincerely appreciate the reviewer’s recognition of our work as “a notable advance\nin soft robotics and adaptive materials,” particularly regarding the continuous fabrication strategy\nintegrating stimuli-responsive LCE with dynamically reconfigurable PU networks. We are grateful\nfor the constructive technical suggestions, which have been comprehensively addressed through\nadditional experiments and textual refinements.\n1. The success of co-extrusion relies on the viscosity matching between the two precursors. Could\nthe authors provide quantitative data or discussion on how small viscosity deviations affect the\ninterface stability and fiber morphology?\nResponse: We appreciate the reviewer’s insightful comment regarding viscosity matching in the\nco-extrusion process. To address this issue, we have supplemented quantitative viscosity data and\ncorresponding morphological results for three representative LCE/PU precursor pairs. Our\nfindings indicate that the successful formation of a continuous Janus interface necessitates the\nviscosities of the two components to be within an appropriate matching range.\nWhen both precursors exhibit high and comparable viscosities within the optimal rheological\nwindow (LCE: 1400-5100 Pa·s; PU: 1200-5200 Pa·s), the two streams undergo synchronous\nextensional thinning during drawing, followed by rapid UV-induced solidification, yielding well-\ndefined Janus filaments (Figs. S4, S5a). In contrast, when one precursor falls below the rheological\nwindow while the other remains within it, a significant viscosity mismatch arises (e.g., LCE:\ncore, resulting in distorted interfaces and spiral morphologies (Fig. S5b). Furthermore, when the\nviscosities of both precursors are insufficiently low (LCE: 15 Pa·s; PU: 20 Pa·s), Rayleigh-Plateau\ninstabilities dominate, leading to droplet-like emission rather than continuous filament formation\n(Fig. S5c). These observations demonstrate that maintaining viscosities within a well-defined\nmatching window is essential to achieve stable, continuous Janus fibers.\n“In contrast, viscosity mismatch or excessively low viscosities disrupt interfacial stability, leading\nto distorted Janus interfaces or droplet-like co-extrusion morphologies, underscoring the necessity\nof maintaining an appropriately matched rheological window for continuous fiber formation\n(Figs.S4, S5).”\nRevisions in the supporting information are on Page 6-7:\n“Fig. S4. Stable formation of continuous Janus interfaces requires LCE and PU precursors to\nexhibit well-matched viscosities within an appropriate rheological window. (a) Viscosity range\nof LCE precursors (1400-5100 Pa·s). (b) Viscosity range of PU precursors (1200-5200 Pa·s).”\n21\n“Fig. S5. Viscosity-dependent co-extrusion behaviors of representative LCE/PU precursor pairs.\n(a) Stable Janus interface formed when both LCE (3400 Pa·s) and PU (2900 Pa·s) exhibit high,\nwell-matched viscosities within the rheological window. (b) Distorted interface and helical\nmorphology observed due to viscosity mismatch, with LCE below and PU within the rheological\nwindow (LCE: 890 Pa·s; PU: 1200 Pa·s). (c) Droplet-like morphology induced by Rayleigh-\nPlateau instability when viscosities of both precursors are too low (LCE: 15 Pa·s; PU: 20 Pa·s).”\n2. The PU component exhibits dynamic covalent bond exchange above 55 °C, while the Tₙᵢ of the\nLCE is around 67 °C. Fig. 2i indicates that the PU network undergoes relatively fast stress\nrelaxation upon heating. Could the authors elaborate on how the rate of dynamic bond exchange\n22\naffects the long-term actuation stability, as well as potential creep and fatigue behaviors under\nrepeated thermal cycling?\nResponse: We thank the reviewer for this insightful comment. Potential creep and fatigue\nbehaviors mediated by dynamic bond exchange are governed by temperature, heating time and\nstress. During thermal programming, the Janus fiber was subjected to external stress to reach\nvarying high strains at 90 °C for 10 minutes, enabling complete dynamic bond exchange and stress\nrelaxation. In contrast, the helical actuation only involves transient exposure to the near T\nNI\ntemperature without sustained mechanical loading. Therefore, the dynamic bond exchange does\nnot noticeably affect the long-term actuation stability of the Janus fibers. We have included 200\nconsecutive actuation cycles and there are no apparent signs of actuation fatigue or creep. We have\nmade it clear in the manuscript.\nRevisions in the manuscript are on Page 14, Line 13:\n“Cyclic testing demonstrates that the fibers exhibit no signs of actuation fatigue within 200 cycles\n(Fig. S24).”\nRevisions in the supporting information are on Page 17:\n“Fig. S24. Actuation cycles of reprogrammed Janus fibers over 200 cycles.”\n3. Regarding the fabrication process of the Janus fibers, I have several technical questions: (1) The\nprocess involves a two-step UV curing. How is the crosslinking degree controlled during the first\nUV exposure to ensure that further alignment and secondary curing can proceed effectively? (2)\nDuring the first UV curing, does the partial polymerization already fix the shear-induced\norientation of the LCE domains, or is the alignment mainly achieved during the subsequent\n23\nstretching step? (3) Upon the final thermal treatment, will the pre-aligned LCE phase experience\nslight shrinkage that may influence the morphology of the adjacent PU domain, even if the\ntemperature does not reach Tₙᵢ? (4) Could the authors further elaborate on the detailed mechanism\nby which heating promotes hydrogen-bond formation within the PU network?\nResponse: We thank the reviewer for raising these important comments about the fabrication of\nJanus fibers. Please find our point-by-point response as below:\n(1) The two-step UV curing method has been well validated as an effective method for fabricating\nLCE fibers with fixed mesogen orientation during stretching as shown in Ref. Adv. Mater. 2023,\n2211800 and Adv. Funct. Mater. 2025, e15319. The crosslinking degree increases along with the\nUV exposure as shown in Fig. 2b. We have measured the gel content after the first curing to be\n~46%, which was effective for the primary fiber forming. During the stretching, the secondary\ncuring increased gel content to 87%, locking the mesogen orientation at the same time. We have\nmade it clear in the manuscript.\nRevisions in the manuscript are on Page 8, Line 8:\n“The two-step UV curing strategy enables precise control over the crosslinking density to fix the\nmesogen orientation during fiber stretching (Fig. S9).”\nRevisions in the supporting information are on Page 9:\n“Fig. S9. Gel fraction of Janus fibers measured before initial and after secondary UV curing.\nError bars correspond to s.d. (n=3).”\n(2) The first curing actually doesn’t fix the shear-induced orientation. As without further stretching,\nthe 2D WAXS patterns in Fig. 2g indicates no observable orientation. Instead, the majority of the\ndomain alignment is achieved during the subsequent stretching and secondary curing step, where\nthe remaining reactive sites allow effective reorganization and orientation of the mesogens. This\n24\ntwo-step strategy ensures both fiber formability and controlled molecular alignment, which are\ncritical for achieving the desired actuation performance.\n(3) The thermal annealing process is conducted under external stress (Fig. 1c). In the absence of a\nchemical mechanism for thermal stress relaxation within the LCE layer, the PU phase morphology\nremains unaffected.\n(4) The molecular design of PU used in this work was from Ref. Nature 2024, 631, 783-788, in\nwhich hydrogen bonds form between amide linkages during heating have been well emonstrated\nby temperature-dependent FTIR spectra.\nFig. R1. Temperature-dependent FTIR spectra. v (N–H), the N–H vibration. (Reproduced from\nRef. Nature 2024, 631, 783–788)\nIn brief, hydrogen bonds arise from amide linkages between polymer chain segments. During\nthermal annealing under applied tension, the polymer chains adopt a more ordered configuration.\nMeanwhile, hydrogen-bond exchange occurs, enhancing the directional alignment and order of the\nhydrogen-bond network. We have updated the description, just as follow:\nRevisions in the manuscript are on Page 5, Line 20:\n“Subsequent thermal annealing facilitates the ordered reorganization of hydrogen bonds through\ndynamic bond exchange within the PU segments, ultimately strengthening the mechanical integrity\nof the fibers35.”\n4. What is the interfacial adhesion strength between the LCE and PU domains? Are these two\nmaterials prone to delamination under mechanical deformation? For long-term use, could a\n25\nmismatch in strain or modulus between the LCE and PU layers lead to interfacial instability or\nfatigue?\nResponse: We sincerely appreciate the reviewer for raising these critical interfacial and\nmechanical concerns. The LCE and PU precursors both incorporate photopolymerizable acrylate\ngroups exhibiting comparable polymerization kinetics, as quantitatively demonstrated in Figures\n2b and 2c. Upon exiting the spinneret, these precursors undergo simultaneous interfacial contact\nand co-polymerization under UV irradiation, forming a seamless junction. Fig. 1e confirms the\nresulting interface displays microscale homogeneity without any observable defects, indicating\nrobust molecular-level adhesion. Given the ~200 μm fiber dimensions preclude conventional peel\ntesting, we employed torsional deformation assays to assess interfacial integrity. These mechanical\nassessments revealed no delamination tendencies under torsional stresses, confirming stable\nbonding under operational strains, as shown in Fig. S8. In addition, we have included 200\nconsecutive actuation cycles and there are no apparent signs of actuation fatigue or creep.\nMicroscopic image of the Janus fiber after 200 actuation cycles revealed no detectable interfacial\ndamage (Fig. S25).\nRevisions in the manuscript are on Page 5, Line 20 and Page 14, Line 14:\n“Subsequent thermal annealing facilitates the ordered reorganization of hydrogen bonds through\ndynamic bond exchange within the PU segments, ultimately strengthening the mechanical integrity\nof the fibers35.”\n“After 200 actuation cycles, the interfaces of Janus fiber remained intact, demonstrating that\nfibers produced via our fabrication method exhibit excellent structural stability (Fig. S25).”\nRevisions in the supporting information are on Page 17:\n“Fig. S25. Microscopic image of a helical Janus fiber after 200 actuation cycles.”\n5. In Fig. 3c, what is the surface temperature reached during NIR laser irradiation? Is the\ntemperature distribution across the irradiated region uniform? Typically, the central zone tends to\n26\nbe hotter than the edges—how do the authors ensure controlled and uniform photothermal\nprocessing?\nResponse: We thank the reviewer for raising this important point. Due to the small diameter of\nJanus fibers (~200 μm), direct infrared thermography measurement was infeasible. Instead, we\nprojected the laser beam onto a black cardstock substrate to accurately characterize the beam\nprofile. To quantify processing temperatures, we measured surface temperature under 808 nm NIR\nirradiation at 2000 mW·cm-2 for 5 seconds. Infrared thermal imaging confirmed a maximum\ntemperature of ~110 °C at the beam center, significantly exceeding the hindered urea bond\nactivation temperature (~90°C). Despite lower peripheral temperatures, the high temperature core\narea ensures the entire fiber resides within a thermal field sufficient to trigger bond exchange\nduring irradiation. In this work, to mitigate photothermal inhomogeneity, we implemented\nlongitudinal laser scanning along the fiber axis at controlled speed. This dynamic irradiation\neliminates thermal gradients and guarantees spatially uniform heating. We have made it clear in the\nSupporting Information.\nRevisions in the supporting information are on Page 25, Line 17:\n“Janus fibers were first stretched to 50% strain at 25 °C. Near-infrared (808 nm) laser irradiation\n(2000 mW·cm-2, 5 min) was then applied in a spatially selective manner to predefined regions\nalong the fiber. The laser was scanned longitudinally along the fiber axis at a controlled speed to\nlocally activate dynamic covalent bond exchange.”\nFig. R3. Infrared thermal image of the NIR laser spot projected onto a black cardstock.\n27\n6. Upon localized heating by NIR light, does the LCE layer experience partial thermal transition\nor contraction that might introduce internal stresses or deformation gradients within the Janus\nstructure?\nResponse: We sincerely appreciate the reviewer’s insightful inquiry regarding NIR-induced\nthermal effects during programming. The spatially selective programming was performed on Janus\nfibers featuring non-oriented LCE domains under 150% fixed-length stretching with controlled\nexternal stress. Crucially, even when NIR irradiation elevates temperatures beyond the LCE phase\ntransition threshold, contraction-induced stresses in LCE remain insufficient to counteract\ndeformation imposed by external forces, while concurrent stress relaxation occurs in the PU phase.\nUpon force release, the LCE domain exhibits soft elasticity that retains its extended conformation,\nwhereas the PU phase demonstrates entropic elasticity, recovering its original configuration except\nin stress-relaxed regions. This differential recovery behavior enables spatially programmed\narchitectures. Subsequent heating above T induces the contraction LCE to its original length. As\nNI\na result of the PU stress relaxation, spatially selective spring structures appear in the NIR\nirradiation regions. We have made it clear in the Manuscript.\nRevisions in the manuscript are on Page 12, Line 9:\n“The fiber is first uniformly stretched to 50% strain under controlled external stress and then\nselectively irradiated. During programming, even when NIR irradiation raises temperatures above\nthe LCE phase transition, contraction-induced stresses in LCE are insufficient to overcome\nexternal stretching, while PU undergoes stress relaxation.”\n7. Does the PU network contain any catalyst that facilitates the dynamic covalent exchange\nreaction? If not, how can the urethane bond exchange proceed efficiently at such a relatively low\ntemperature and with a low apparent activation energy? It is suggested that the authors provide\nmore detailed synthetic procedures of the polymer precursors to minimize confusion.\nResponse: We thank the reviewer for raising this question. The PU network (adapted from Nature\n2024, 631, 783-788) contain dibutyltin dilaurate (DBTDL) catalyst, which was introduced during\nprecursor synthesis. Consequently, the dynamic urethane/urea bond exchange proceeds efficiently\nat 90°C with low activation energy. We have provided a more detailed synthetic procedure in the\nSupporting Information.\nRevisions in the supporting information are on Page 22, Line 17:\n28\n“Synthesis of PU precursor: The PU precursor containing dynamic hindered urea bonds and\npendant carboxylic acid groups was synthesized via three steps. First, poly(tetrahydrofuran)diol\n(0.05 mol) and tolylene-2,4-diisocyanate (0.1 mol) were added to a three-necked flask equipped\nwith a mechanical stirrer, followed by the addition of the catalyst ditin butyl dilaurate (DBTDL,\n0.1 wt% of poly(tetrahydrofuran)diol), and stirred at 50 °C for 4 h. Subsequently,\ndimethylolbutanoic acid (0.033 mol) was added and reacted for 4 h. Finally, 2-(tert-\nbutylamino)ethyl methacrylate (0.033 mol) was introduced and reacted for an additional 4 h using\nethylene glycol diacetate as the solvent to control viscosity. The molar ratio of dimethylolbutanoic\nacid to 2-(tert-butylamino)ethyl methacrylate was maintained at 1:1 to ensure equimolar content\nof hindered urea bonds and carboxylic acid groups. The chemical structure of the resulting PU\nprecursor was confirmed by ¹H NMR analysis (Fig. S1b).”\n8. How did the authors regulate the viscosities of the LCE and PU precursors during co-extrusion?\nWere any solvents used in the precursor formulations? If solvents were employed, could their\nevaporation affect the fiber morphology, phase interface, or mechanical performance during\nfabrication?\nResponse: We thank the reviewer for the insightful question regarding viscosity regulation and\nsolvent use. To achieve the optimal rheological window (1200-5200 Pa·s) for stable co-extrusion,\nthe PU precursor was formulated with ethylene glycol diacetate as solvent (< 40%) for viscosity\ntailoring. Conversely, the LCE precursor was used essentially solvent-free. Complete solvent\nvolatilization occurred during Janus fiber spinning and thermal annealing. As all morphological\nand mechanical characterizations were performed on solvent-free fibers, potential structural or\nperformance impacts of solvent are negligible. We have made it clear in the Supporting\nInformation.\nRevisions in the supporting information are on Page 23, Line 6:\n“Preparation of PU Precursor: The PU precursor was mixed with ethylene glycol diacetate for\nviscosity control, using a maximum solvent content of 40 wt%, followed by the addition of the\nphoto-initiator Irgacure 819 (3 wt%). The resulting mixture was stored in the dark prior to use.”\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is\npart of the Nature Communications initiative to facilitate training in peer review and to provide\nappropriate recognition for Early Career Researchers who co-review manuscripts.\nResponse: We sincerely acknowledge Reviewer 5 for participating as a co-reviewer under the\nNature Communications Early Career Researcher training initiative. Although no formal critiques\nwere provided in the official report, the co-reviewer’s involvement in the peer review process\noffered insightful perspectives that enriched the overall evaluation of the manuscript. This program\nreflects the journal’s dedication to supporting the professional growth of early career researchers,\nand we appreciate the opportunity to contribute to this meaningful initiative.\nWe sincerely thank the reviewers for their insightful and constructive feedback on our\nmanuscript. We have extensively revised the manuscript with all the changes highlighted in\nred in the main text and supporting information. We believe the revision pushes the work to\na much higher level. Below are the point-by-point responses to the review comments with\nour responses highlighted.\nReviewer #1:\n1. Since the fiber underwent a transition from a curved shape to a helical shape, the “strain”\ncalculated by the authors, which is shown in Figure S15, should be the length-change ratio, rather\nthan referring to the actuation strain generated during the uniaxial contraction of a fiber, usually\nemployed.\nResponse: We thank the reviewer for pointing out that the actuation strain in our Janus fibers\nshould be interpreted as a length-change ratio, distinct from conventional uniaxial contraction\nstrain. In the revised manuscript, we clarify that upon heating, the fibers transition from a linear to\na helical configuration, and the reported actuation strain (~85% at 80 C) reflects this length-\nchange ratio. The effective fiber length in the helical state and the calculation method are provided\nin Fig. S15 and the Supporting Information.\nRevisions in the manuscript are on Page 10, Line 20:\n“In addition to their improved mechanical robustness, the continuously extruded Janus fibers also\ndisplay excellent thermal actuation performance. Upon heating, the fibers undergo a transition\nfrom a linear to a helical configuration; therefore, the reported actuation strain corresponds to a\nlength-change ratio rather than a conventional uniaxial contraction strain. The effective fiber\nlength in the helical state was measured as illustrated in Fig. S15, and the detailed calculation\nformula for the actuation strain is provided in the Supporting Information. At 80 C, the fibers\nexhibit an actuation strain of ~85%, defined here as the length-change ratio, together with a high\nactuation strain rate of 193 %·s-1, and generate an energy density approaching 50 kJ·m-3 under a\nload of 200 kPa (Figs. S15 and S16).”\n1\n2. The authors need to compare the fiber’s performance metrics (length change ratio, deformation\nrate, and load) with previous reported helical fiber actuators, which can support their statement\n“These quantitative metrics collectively demonstrate that the continuously extruded Janus fibers\nachieve high-amplitude, rapid, and energy-efficient actuation, underscoring their potential for\nartificial-muscle applications.” Currently, this statement lacks metrics-comparison support.\nResponse: We thank the reviewer for stressing the need for quantitative benchmarking. In\nresponse, we have systematically compared the actuation performance of the continuously\nextruded Janus fibers with previously reported helical fiber actuators in terms of length-change\nratio, deformation rate, and load, as summarized in Table S2. As shown, the Janus fibers combine\nlarge actuation amplitude with rapid response, achieving performance comparable to\nrepresentative helical fiber systems. This quantitative comparison directly supports our statement\nthat the Janus fibers enable high-amplitude, fast, and energy-efficient actuation, underscoring their\npotential for artificial-muscle applications.\nWe note that the load capacity of the Janus fibers is relatively modest, which primarily arises\nfrom the intrinsically low modulus of the LCE and PU materials employed, in contrast to stiffer\nsystems such as PE fiber, PI fibers, nylon fibers and CNT-reinforced composites. Importantly, the\npresent work focuses on programmable heterogeneity and reconfigurable actuation within a single\nfibrous architecture rather than maximizing load output, and this distinction is now explicitly\nclarified in the revised discussion.\nRevisions in the manuscript are on Page 10, Line 30:\n“Collectively, these mechanical and actuation characteristics indicate the potential applicability\nof Janus fibers in scalable artificial-muscle systems (see Table S2 for quantitative comparison).”\nRevisions in the supporting information are on Page 21:\nTable S2. Comparison of actuation performance of reported helical fiber actuators and the\nJanus LCE fibers in this study.\nlength change deformation\nMaterial system load Reference\nratio (%) rate (%·s-1)\n25 a\nJanus LCE-PU fiber 193 200 kPa This work\n85 b\nTwisted LCE/CNT fiber 56.9 a 189.7 0.84 MPa ACS Nano. 2023, 17, 12809-12819\n19.8 a\nHelical PE/AgNW yarn - 24 kPa ACS Nano. 2018, 12, 3898-3907\n37 b\nArchimedean spiral\n~100 a 28 0.013 N Adv. Funct. Mater. 2025, e19002\nNylon/PI fiber\nHigh-spring-index PEC\n20.7 a - 0.5 MPa Science. 2025, 387, 1101-1108\nfiber\nTwisted LCE fibers 60 a 15 0.3 g Adv. Mater. 2024, 36, 2401140\n12 a\nCOCe-PE bimorph fiber - 1 g Science. 2019, 365, 145-150\n50 b\nCNT-wrapped nylon 6,6\n21 a 7.9 22 MPa Science. 2014, 343, 868-872\nmonofilament fiber\nPEO-SO3@CNT muscles 15 a 5.5 33 MPa Science. 2019, 365, 150-155\nSelf-winding LCE fiber 150 a 258 21.5 mg Appl. Mater. Today 2022, 27, 101449\nCoiled CNT@nylon yarn 26.4 a 15.8 4.18 MPa ACS Nano 2024, 18, 9500−9510\naUnder applied load; bWithout applied load.\n“Discussion: The relatively modest load capacity of the Janus fiber mainly reflects the intrinsically\nlow modulus of the LCE and PU materials used in this work, compared with stiffer fiber systems\n(e.g., PE fiber, PI fibers, nylon fibers and CNT-reinforced composites). This study emphasizes\nspatially programmable heterogeneity and reconfigurable, multimodal actuation within a single\nfibrous architecture, and Table S2 is provided to contextualize actuation performance under this\ndesign consideration rather than to benchmark maximum load output.”\nRecommendation:\nRecommend after minor revisions.\nOverall Comments:\nThe authors have addressed most reviewer comments, however, there remain key comments that\nmust be addressed before full recommendation for publication.\nResponse: We sincerely appreciate the reviewer’s recommendation and rigorous evaluation of the\nrevised manuscript. In this updated version, we have addressed all remaining comments in detail\nand made corresponding revisions to enhance the clarity and robustness of the manuscript.\nItems to be addressed:\n1. In reference to the reviewer’s initial comment: “The work is missing citations and discussion\nfor key pioneering works in the area of LCE fibers including:\na. Seminal work introducing preparation of long LCE fibers:\nhttps://pubs.acs.org/doi/abs/10.1021/acsami.9b04401IF: 8.2 Q1\nb. Initial work showing polyurethane/polyacrylate for ultrasong mechanical properties, like\nbreaking strength (your Fig. 2j): https://pubs.acs.org/doi/10.1021/jacs.9b06757IF: 15.6 Q1\nc. Initial work showing “self-winding”: Zhiming Hu, Yunlong Li, Tonghui Zhao, Jiu-an Lv, Self-\nwinding liquid crystal elastomer fiber actuators with high degree of freedom and tunable actuation,\nApplied Materials Today, 2022\nThe authors seem to have used AI-generated citations as the cited works do not match the\nreferenced works. The reviewer recommends reviewing all citations for accuracy.\nFurthermore, the referenced citations are not discussed in sufficient detail. Each of these are\nseminal works in the field. Please include a short description of the cited works and their impact\non the field and their relations to the current work.\nResponse: We sincerely apologize for the citation mistake in the revised manuscript. We also\nthank the reviewer for drawing our attention to these seminal works in the field of LCE fibers.\nIn this revision, we have corrected all citation errors through a comprehensive reference verification.\nThe three recommended pioneering studies works have now been cited as Refs. 21, 28, and 37,\nand their relevance and impact are substantially discussed in the appropriate sections of the\nmanuscript.\n“Building on the seminal study that established the basic principle for producing LCE fibers via\nmechanical stretching followed by photopolymerization to achieve mesogen alignment21, several\nadvanced fabrication techniques have emerged. These include melt drawing22, direct ink writing23,\n24, and electrospinning25, 26, all proven effective in fabricating LCE fibers with superior actuation\nproperties.”\n“Pioneering work demonstrating “self-winding” LCE utilized a mold-fabricated helical precursor.\nLocking the orientation during secondary stretching enabled controllable shape transformations,\nincluding bending, twisting, coiling, and contraction, within a monolithic fibrous architecture28.”\n“Beyond that, dynamic covalent polymers like polyurethane enhance mechanical robustness\nsignificantly when incorporated into LCE to form interpenetrating networks, enabling ultrastrong\nactuation-mechanics properties and representing a milestone in high-performance LCE\ndevelopment37.”\nThe recommended references have been cited as Ref. 21, Ref.28 and Ref. 37:\n“21. Roach, D. J. et al. Long liquid crystal elastomer fibers with large reversible actuation strains\nfor smart textiles and artificial muscles. ACS Appl. Mater. Interfaces 11, 19514–19521\n(2019).”\n“28. Hu, Z., Li, Y., Zhao, T. & Lv, J. Self-winding liquid crystal elastomer fiber actuators with high\ndegree of freedom and tunable actuation. Appl. Mater. Today 27, 101449 (2022).”\n“37. Lu, H.-F., Wang, M., Chen, X.-M., Lin, B.-P. & Yang, H. Interpenetrating liquid-crystal\npolyurethane/polyacrylate elastomer with ultrastrong mechanical property. J. Am. Chem. Soc.\n141, 14364–14369 (2019).”\nIt should be noted that the comparation of elastic modulus and tensile strength values in Fig. 2g\nare specific to the realm of LCE fibers. Therefore, the recommended reference (J. Am. Chem. Soc.\n2019, 141, 14364–14369) was not included. These additions strengthen the context of our work,\nclarify its relationship to prior advances in LCE fiber fabrication, mechanical reinforcement, and\nself-winding techniques, and emphasize how our Janus LCE/PU fiber design extends these\napproaches through spatially programmable, multimodal actuation.\n2. In response to: “The authors claim a single Janus fiber can lift 160,000 times its own weight.\nThis is supported by a photo in the SI, but the dimensions of the fiber are not given or shown, and\n5\nthere is no information on how far the fiber lifted the weight, making it difficult to reproduce or\nuse as a benchmark. Could the authors add information about fiber dimensions and the distance the\nweight was lifted?”\nIt is now understood that the Janus fiber can simply support loads during human-driven lifting\nmotions. The reviewer believes that the use of the terminology “lifting capacity” or “lifting” is\nhighly misleading. The terminology throughout the manuscript and SI video should be revised as\nthe actuation properties of the LCE are not performing work, such as lifting, however, are simply\nsupporting loads during human-driven lifting.\nCurrently, the lifting of weight using the fiber is a highly qualitative measure of the fiber’s strength\nand robustness. The reviewer recommends performing breaking strength experiments to\ndemonstrate the mechanical strength of the fibers.\nResponse: We thank the reviewer for this important clarification regarding the interpretation of\nthe load demonstration. We agree that the previous use of the terms “lifting capacity” and “lifting”\ncould be misleading, as the Janus fibers do not autonomously perform mechanical work to lift\nloads, but instead support loads during externally driven motions. Accordingly, in the revised\nmanuscript and Supporting Information (including the SI video), we have revised the terminology\nthroughout, replacing “lifting” with “hanging” or “load-supporting” to more accurately reflect the\nexperimental conditions and avoid overinterpretation of the actuation behavior.\nWe also agree that qualitative load-hanging demonstrations alone are insufficient as\nquantitative benchmarks of mechanical performance. The mechanical robustness of the Janus\nfibers has been evaluated through systematic tensile testing, as presented and discussed in the\nmanuscript (Page 10, Line 6). “As shown in Fig. S12, the fibers exhibit a tensile strain of 156%, a\ntensile strength of 40.4 MPa, a Young’s modulus of 12.7 MPa, and a toughness of 17.1 MJ·m-3.”\nThese quantitative breaking-strength metrics provide a rigorous and reproducible assessment of\nfiber strength and substantiate the load-bearing capability illustrated in the hanging demonstrations.\nRevisions in the manuscript are on Page 10, Line 12:\n“A visual demonstration shows that a single Janus fiber (diameter ~200 µm) is capable of\nsupporting a hanging load exceeding 160,000 times its own weight over a vertical distance of ~20\ncm during externally driven motion (Fig. S13 and Supplementary Movie 2), highlighting the\nexceptional strength and robustness of this hybrid design.”\nRevisions in the supporting information are on Page 10:\n6\n“Fig. S13. Load-supporting demonstration of a Janus fiber. Photograph showing a 0.5 mg Janus\nfiber supporting and hanging a load of 80 g over a vertical distance of ~20 cm.”\nFollowing a careful evaluation of the revised manuscript, I find that the authors have thoroughly\nand effectively addressed all previous comments. The revisions have substantially improved the\nclarity, rigor, and overall presentation of the work.\nThe manuscript now demonstrates a high level of scientific quality. The experimental design is\nsound, the analysis is comprehensive, and the conclusions are well supported by the presented data.\nImportantly, the authors have clarified key mechanistic aspects and strengthened the logical\nstructure of the manuscript, significantly enhancing its readability and impact.\nIn its current form, the study represents a strong and meaningful contribution to the field. I\nrecommend acceptance without further revision.\nResponse: We sincerely appreciate the reviewer’s recommendation and constructive suggestions,\nwhich have significantly strengthened the quality and impact of our manuscript.\nThe authors’ response has adequately addressed my concerns, and I have no further questions on\nthis point.\nResponse: We are delighted that our response has adequately addressed the reviewer’s concerns\nand sincerely appreciate their constructive guidance and support.\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is\npart of the Nature Communications initiative to facilitate training in peer review and to provide\nappropriate recognition for Early Career Researchers who co-review manuscripts.\nResponse: We sincerely appreciate the reviewer’s time and effort in evaluating our manuscript.\n10"}]

Decision letter