Conclusion

In this study, tether-free hair artificial muscles with extremely large tensile stroke and fast recovery were successfully made through twist insertion, coiling and steaming, without any chemical crosslinking. Coiling the twisted hair fiber with large diameters increases the muscles’ tensile stroke, and ethanol stimulation enables their fast recovery. The tensile stroke upon water actuation could be as large as 10000%, three times larger than the largest tensile stroke reported so far20. The fastest actuated muscle could fully recover in 10 to 20 seconds. Various applications such as long-distance climbing robots, weight pulling or lifting, and a smart water-sensitive switch were also demonstrated. This study provides a facile and green strategy to prepare advanced natural fiber-based artificial muscles, which have promising applications in soft robotics and biomedical fields.

Acknowledgement

This work was supported by the National Natural Science Foundation of China (grant no. 62002079, 62172114, 61772376, 62072129 and 62202112) and the National Key R&D Program of China (Grant no. 2019YFA0706401). The authors would like to thank Shiyanjia Lab (www.shiyanjia.com) for the support of DSC analysis.