Multifunctional double network cellulose-acrylamide based hydrogel sensor reinforced by liquid metal for human motion detection and dual-mode handwriting recognition by transfer learning algorithm

Abstract

Conductive hydrogels have received extensive attention as a candidate material for flexible strain sensors. Especially, cellulose hydrogel has good flexibility, biocompatibility and environmental degradability, which can be widely applied in wearable electronics, human-machine interfaces and soft robotics. However, the typical single network cellulose hydrogel sensor reveals low mechanical loadings, greatly limiting practical applications. It is still a great challenging to develop a cellulose conductive hydrogel sensor with excellent mechanical properties and ideal conductivity. Herein, a novel multifunctional conductive hydrogel based on cellulose, acrylamide and liquid metal (LM) was prepared via one-pot synthesis strategy. The acrylamide monomers combined with N,N'-methylenebisacrylamide (MBA) to form a robust three-dimensional polyacrylamide network. Meanwhile, acrylamide is physically cross-linked with cellulose. LM as conductive fillers embeded into the network of the hydrogel, can not only enhanced the stability of the network structure, but also improved conductive ability. This resulted in high tensile properties (963%), superior strain responses (with a gauge factor of 21.7), fast response time of 240 ms and a 90% retention of performance after 600 cycles. Moreover, as-prepared hydrogel sensor can continuously monitor human motion and measure the contraction of muscles in different parts including biceps, triceps and pectoralis major. By integrating the transfer learning algorithm (Resnet50), an intelligent dual-mode handwriting recognition system was developed for sensing finger touch signals (compressive-contact mode) and finger wiggle signals (finger strain mode), with both high accuracy (100%) and fast recognition time (<1s) when recognizing arabic numbers. This study showed that the multifunctional cellulose hydrogels will have broad application prospects in constructing intelligent human-machine interfaces, virtual reality interactions, and future bioelectronics.