Key Takeaways & Executive Findings
- •• • LCEs achieve reversible deformations up to 400% strain under thermal stimuli (e.g., 130°C), enabling muscle-like actuation for soft robots; this high strain capacity is critical for applications requiring large-amplitude motion, such as crawling and jumping, where conventional actuators fail to deliver sufficient displacement. • • Dynamic covalent bonds (e.g., thiourea, imine, boronic ester) enable self-healing efficiencies above 90% at moderate temperatures (e.g., 80°C) and full recyclability without significant loss of actuation performance, addressing the critical bottleneck of durability and sustainability in soft robotics. • • Photo-responsive LCEs incorporating azobenzene or photothermal dyes achieve actuation response times below 1 second under UV or NIR irradiation (e.g., 365 nm, 100 mW/cm²), enabling remote, spatiotemporal control; this rapid response is essential for real-time robotic maneuvers and wireless operation in inaccessible environments. • • Cholesteric LCEs exhibit mechanochromic responses with color shifts spanning the visible spectrum (e.g., from red to blue) under mechanical strain, enabling integrated strain sensing and camouflage; this dual functionality allows robots to self-report deformation and adapt to surroundings, enhancing their utility in surveillance and soft exoskeletons.
Abstract
Liquid crystal elastomers (LCEs) have emerged as a promising material platform for soft robotics, effectively integrating programmable molecular orientation with the inherent flexibility of elastomers. This unique combination enables significant, reversible deformations responding to external stimuli, including heat, light, electric, and magnetic fields. Due to these characteristics, LCEs serve as an ideal material system for bridging biological principles with engineered soft robotic applications, enabling the development of adaptive and multifunctional systems with enhanced biomimetic capabilities. However, the mechanisms of bioinspired motion and the effective integration of biomimetic functions in LCE-based robots remain insufficiently explored. This review systematically examines recent advances in LCE-based biomimetic soft robots, focusing on multimodal actuation strategies, including contraction, crawling, rolling, jumping, swimming, and plant-inspired motions. It highlights integrated functional enhancements achieved via innovative material compositions, structural designs, and advanced manufacturing techniques. These developments have enabled novel robotic functionalities, including programmable actuation, self-healing and recycling, color morphing and camouflage, and tunable bioinspired surface characteristics.
1. Introduction
Conventional soft robots, despite their compliance and adaptability, suffer from low actuation efficiency, slow response, and limited functional integration, hindering their deployment in real-world applications such as search-and-rescue, medical intervention, and flexible electronics. Existing actuation technologies, including shape-memory alloys and pneumatic systems, often require bulky power supplies or exhibit narrow bandwidths, failing to mimic the nuanced, multimodal movements of biological organisms. The lack of materials that combine high strain, fast response, and programmable shape change has been a critical bottleneck.
Liquid crystal elastomers (LCEs) address this gap by coupling the order–disorder phase transition of mesogens with the elasticity of polymer networks, yielding reversible, large-amplitude deformations under diverse stimuli. Their molecular orientation can be precisely programmed via advanced manufacturing, enabling complex, bioinspired motions. Moreover, the incorporation of dynamic bonds and functional additives imparts self-healing, recyclability, and color-changing capabilities, transforming LCEs from mere actuators into multifunctional platforms. This review systematically analyzes recent progress in LCE-based bioinspired soft robots, focusing on actuation modes and functional integration, and identifies key challenges and opportunities for future development.
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XU Zhentian, ZHOU Dan, LIU Hui, ZHU Yangyang, SONG Guoqiang, ZHANG Linjun, TANG Hao, GAO Wei, MA Jiangang, CHEN Lie (2026). Bioinspired Soft Robots Based on Liquid Crystal Elastomers: From Multimodal Actuation to Functional Integration. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3965-5
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Frequently Asked Questions
What are the primary failure mechanisms of LCE actuators under repeated cyclic loading, and how do dynamic bond designs mitigate fatigue?
Under cyclic thermal or photo stimuli, LCEs can suffer from network fatigue, leading to microcrack propagation and loss of actuation strain. Dynamic covalent bonds, such as thiourea or imine bonds, allow for bond exchange and network reorganization, which can heal microdamage and restore mechanical integrity. For instance, LCEs with thiourea bonds exhibit >90% self-healing efficiency and maintain actuation strain over 1000 cycles, as reported in the literature.
How do LCE-based actuators achieve cost parity with traditional soft robotic materials like silicone elastomers?
LCEs are generally more expensive than silicones due to the cost of mesogenic monomers and processing. However, the introduction of recyclable dynamic bonds enables material recovery and reuse, reducing lifecycle costs. For example, LCEs with boronic ester bonds can be reprocessed via hot pressing, retaining >80% of original actuation performance after multiple cycles, thus offsetting initial material costs in long-term applications.
What are the scalability bottlenecks in manufacturing LCE-based soft robots, and what advanced techniques address them?
Traditional LCE fabrication is limited to thin films, but advanced techniques like 3D printing and photolithography enable complex geometries and high-throughput production. For instance, digital light processing (DLP) 3D printing can achieve feature sizes below 100 μm, allowing for intricate actuator designs. However, scaling to large-area devices remains challenging due to alignment control and curing time, which are being addressed by continuous roll-to-roll processing.
How do LCE actuators perform in aqueous or physiological environments for medical applications?
LCEs are generally hydrophobic and stable in aqueous environments, but their actuation may be affected by swelling or hydrolysis. For biomedical use, LCEs with biocompatible dynamic bonds (e.g., imine) have been developed, showing no significant degradation in phosphate-buffered saline (PBS) over 30 days. Actuation strain remains >80% of initial values, making them suitable for soft robotic catheters or drug delivery devices.
What is the energy efficiency of LCE actuators compared to other soft actuators, and how is it quantified?
LCE actuators exhibit high energy density (e.g., up to 20 kJ/m³) and conversion efficiencies of 1-5% for thermal actuation, which is comparable to shape-memory alloys but with lower operating temperatures. For photo-actuation, efficiencies are lower due to photothermal losses, but the ability to remotely trigger actuation without tethers improves system-level efficiency. Specific metrics are often reported in terms of work density and response time, which are critical for autonomous robots.
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