The Design, Fabrication and Structural Modeling of Biomimetic Soft Materials for Robotic Applications

The prospects of endowing soft actuators with biomimetic functions are promoting the development of intelligent robotics. Harnessing the energy from the ambient environmental conditions, various stimuli-responsive soft robots have been fabricated and applied in artificial muscles, human-machine interfaces and smart wearable devices. For example, a humidity-responsive actuator based on a mono-layered [1], and a multi-stimuli-responsive actuator based on a double-layered conducting polymer thin film have been fabricated [2], which demonstrated an outstanding actuation force and sensitive responses to their respective stimuli. The actuation behavior of soft actuators largely relies on their energy conversion and the underlying structural reconfiguration ability of stimuli-responsive materials. More importantly, these two processes are also essential for the reorganization of their intrinsic structural network, which is the key to self-healing ability of the material. Despite the tremendous advances in stimuli-responsive soft actuators, it is still a challenge to incorporate multiple-stimuli sensitivity and self-healing ability into a single material system. To solve this problem, great efforts have been devoted to develop structural-reconfigurable materials based on dynamic non-covalent crosslinking. For sample, a cellulose-based packaging paper have been fabricated, of which the humidity-responsiveness and hydration-induced self-healing ability depends on reversible hydrogen crosslinking of cellulose [3]. In another case, two stimuli-responsive and structural-reconfigurable layers with complimentary thermal expansion and compatible mechanical properties are combined as a bi-layered actuator <i>via</i> hierarchical assembly. The actuator is self-healing through a sequential treatment of heating and humidifying as each of the bi-layer is healable with the aid of either of these two energy inputs. Moreover, by combining various analytical techniques, we introduced the models for structural reconfiguration of these stimuli-responsive materials at multiple length scales, which could be used as the design platform for more biomimetic materials. Based on these achievements, we anticipate that these actuators hold great promise in a plethora of fields wherever programmable structural reconfigurations are needed, such as applications in space explorations and intelligent robotics.<br/><br/><b>References</b><br/>[1] Q. Chen, X. Yan, H. Lu, N. Zhang, M. Ma, Programmable Polymer Actuators Perform Continuous Helical Motions Driven by Moisture. ACS Appl. Mater. Interfaces 2019, 11, 22, 20473-20481<br/>[2] X. Yan*, Q. Chen*, Z. Huo, N. Zhang, M. Ma. Programmable Multistimuli-Responsive and Multimodal Polymer Actuator Based on a Designed Energy Transduction Network. ACS Appl. Mater. Interfaces 2022, 14, 11, 13768-13777 (* equal contribution)<br/>[3] Q. Chen, B. Sochor, A. Chumakov, M. Betker, N. M. Ulrich, M. E. Toimil-Molares, K. Gordeyeva, L. D. Söderberg, S. V. Roth, Cellulose-Reinforced Programmable and Stretch-Healable Actuators for Smart Packaging. Adv. Funct. Mater.2022, 32, 2208074