Stiffness-switchable hydrogel composite for transformable exo-suit

Abstract

Transformable exo-suits, which are soft and wearable under normal conditions and could increase stiffness dramatically on demand, are significant in personal protection and robotics and also a dream of science-fiction fans. Herein, an ideal candidate material based on a carbon fabric reinforced thermal-hardening hydrogel (CFRTH) composite is proposed for developing transformable exo-suits. The introduction of carbon fabric significantly enhances the mechanical performance of thermal-hardening hydrogel, and empowers the CFRTH composite with an active, rapid and repeatable stiffness switchability. At ambient temperature, the CFRTH composite developed is soft and wearable with excellent flexibility and shape adaptability, while the composite becomes hard and rigid instantaneously as temperature rises. The flexural modulus of the CFRTH composite increases from 2.3 MPa to 539.7 MPa (about 232 times) by applying an electro-thermal stimulus, which endows the composite with good energy absorption/dissipation performance. Compared with the untransformed CFRTH composite, the transformed CFRTH composite under the electro-thermal stimulus exhibits a giant improvement (200%) in the peak force attenuation ratio under dropping ball test and excellent puncture resistance under penetration test and knife stab. Finally, the transformable CFRTH composite demonstrates a high effectiveness in fragile product protection from the impact of steel ball. This study offers a novel and versatile strategy for developing transformable exo-suits which have wearable conformability under normal circumstances and exhibit enhanced stiffness and impact protection performance on-demand through an electro-thermal stimulus.