Key Takeaways & Executive Findings
- •• • The LCP-PEG hydrogels achieve fracture strength of 11.2–14.7 MPa and fracture strain of 1600%–2100%, enabling robust actuation and load-bearing in soft robotics. • • Fracture energy reaches 1.7–2.8 MJ m−2, indicating high toughness essential for durable actuators in repeated deformation cycles. • • Young’s modulus ranges from 51.2 to 139.9 MPa, providing tunable stiffness for diverse mechanical requirements. • • The hydrogels exhibit multi-stimuli-responsive actuation (humidity, temperature, salty water) and multimodal locomotion (walking, somersaulting, object transfer), expanding operational versatility in soft robotics.
Abstract
Anisotropic hydrogels have attracted significant attention for applications in actuators, soft robotics, and artificial muscles due to their ability to undergo shape morphing and generate anisotropic responses under external stimuli. Here, we report a novel strategy for fabricating anisotropic hydrogels using liquid crystal polymers (LCPs). A series of liquid crystal polyester-polyethylene glycol (LCP-PEG) multiblock copolymers with varying PEG block molecular weights were synthesized via one-pot melt-polycondensation. Upon stretching, LCP-PEG forms a stable, oriented microphase-separated lamellar structure, which enables reversible shape changes driven by melting-induced contraction and crystallization-induced expansion of the oriented PEG crystals. This unique structure imparts anisotropic swelling behavior to the films when exposed to water or humidity. The oriented microphase-separated lamellar structure confers high fracture strength (11.2–14.7 MPa), fracture strain (1600%–2100%), fracture energy (1.7–2.8 MJ m−2), and Young’s modulus (51.2–139.9 MPa). Furthermore, the anisotropic LCP-PEG hydrogel actuators exhibit versatile locomotion modes, including object grabbing and transfer between water and air, object gripping in rainy conditions, walking and somersaulting on ratchet-patterned bases under humidity stimuli, and slope climbing through somersault locomotion under salty water stimuli. These results demonstrate the potential of LCP-based anisotropic hydrogels for advanced soft robotic applications.
1. Introduction
Conventional hydrogels suffer from isotropic mechanical properties and non-directional responses, limiting their utility in actuators and soft robotics where controlled shape morphing is critical. Existing fabrication methods for anisotropic hydrogels often rely on high-energy external fields (electric, magnetic) or specialized 3D printing, which are costly, complex, and difficult to scale. This bottleneck has hindered the translation of anisotropic hydrogels from laboratory curiosities to practical devices.
The present work addresses this by introducing a scalable one-pot melt-polycondensation synthesis of LCP-PEG multiblock copolymers. Stretching induces a stable, oriented microphase-separated lamellar structure, eliminating the need for external fields or complex equipment. This structural design not only imparts anisotropic swelling but also yields exceptional mechanical properties (fracture strength up to 14.7 MPa, fracture strain up to 2100%), directly tackling the performance and manufacturability challenges that have stalled commercial adoption.
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Yahui Wang, Shasha Li, Hongjing Yao, Rong Yang (2026). Anisotropic Liquid Crystalline Hydrogel Actuators with Multi-Stimuli-Responsive Actuation and Multimodal Locomotion. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3721-y
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Frequently Asked Questions
What is the maximum fracture strength and strain achieved, and how do these compare to conventional hydrogels?
The LCP-PEG hydrogels exhibit fracture strength of 11.2–14.7 MPa and fracture strain of 1600%–2100%, significantly outperforming conventional hydrogels which typically have strengths below 1 MPa and strains below 500%. This high strength and stretchability are attributed to the oriented microphase-separated lamellar structure, enabling robust actuation and load-bearing in soft robotic applications.
How does the anisotropic swelling behavior arise from the oriented lamellar structure?
The oriented microphase-separated lamellar structure, formed upon stretching, aligns PEG crystals in a specific direction. When exposed to water or humidity, the PEG domains swell anisotropically: swelling is restricted perpendicular to the lamellae but enhanced along the orientation direction. This directional swelling is the basis for the actuator's shape morphing and locomotion.
What are the specific locomotion modes demonstrated, and what stimuli trigger them?
The actuators demonstrate object grabbing and transfer between water and air, object gripping in rainy conditions, walking and somersaulting on ratchet-patterned bases under humidity stimuli, and slope climbing through somersault locomotion under salty water stimuli. These modes are driven by anisotropic swelling/deswelling in response to humidity or ionic strength changes.
What is the synthesis method and scalability potential of LCP-PEG copolymers?
The LCP-PEG multiblock copolymers are synthesized via one-pot melt-polycondensation, a solvent-free and industrially scalable method. This contrasts with complex fabrication techniques like 3D printing or external field alignment, making the production of anisotropic hydrogels more cost-effective and amenable to large-scale manufacturing.
How does the PEG molecular weight affect the properties of the hydrogels?
The study synthesized LCP-PEG copolymers with varying PEG molecular weights. This variation allows tuning of the microphase-separated structure and crystallinity, thereby modulating mechanical properties (e.g., Young's modulus from 51.2 to 139.9 MPa) and swelling behavior. This tunability is crucial for tailoring actuators to specific applications.
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