Construction And Application Of Natural Material-based Gradient Hydrogel Flexible Strain Sensors

Hydrogel is an ideal material that can be used for bioelectronic devices.Due to its low modulus matching human skin,it can meet the needs of various applications.But making a single hydrogel sensor simultaneously self-adhesive,highly stretchable,highly linear,and with excellent sensing capabilities faces great challenges.Since hydrogels are inherently biocompatible,some natural materials are generally added to the hydrogel system to improve its performance without affecting its biocompatibility.Gradient structure is a common form of structure in biological systems,and this structure plays an important role in specific occasions,such as bone-chondral interface,gradient diffusion of intracellular substances,etc.In this work,a series of hydrogel strain sensors with gradient structures based on natural materials are designed.(1)A novel surface-confined gradient conductive network(SGN)strategy is designed to construct a conductive polymer hydrogel strain sensor(CHSS)with an ultra-high tensile capacity of 4000% strain,a transparency of over 90% at 600 nm,and a Young's modulus of 40 k Pa similar to that of skin.In the ultra-wide range(0%-4000%),the sensitivity can reach 3.0.And the CHSS also has a good linear sensing performance with a linear fit value of 0.994.With the help of SGN strategy,the CHSS is able to monitor human motions and activities at large and small scales.The SGN strategy opens a new avenue for the development of flexible strain sensors with excellent mechanical properties,transparency and sensing performance for the full range of human activity monitoring.(2)A novel gradient intersection strategy based on bifunctional montmorillonite nanoparticles was designed through the adsorption properties of montmorillonite(MMT).These nanoparticles can act as both cross-linkers and conductive fillers,intersecting the hydrogel and the conductive network and preventing relative slippage between them.In addition,the hydrogel sensor can detect human activities at large and small scales and achieve directional awareness.Importantly,the hydrogel sensor can be used to build a wireless sensor system to monitor human motion in real time.This work provides ideas for the design of next-generation flexible strain sensors,provides methods for the development of multifunctional montmorillonite materials,and expands the applications of montmorillonite materials and hydrogel sensors.