Preparation Of Functionalized Chitosan-based Ion-conductive Hydrogels And Their Application In Flexible Sensors

With the rapid development of flexible wearable electronic devices,flexible wearable devices have shown great market prospects in the fields of human motion monitoring,medical health,artificial intelligence,energy storage devices and so on.And the sensors as the core components of wearable devices have also received more attention.The flexible wearable sensors that have been put into application are generally based on elastomer or polymer films,but their low stretchability,poor biocompatibility and lack of functionality hinder their further development as wearable sensors.As a soft material with good biocompatibility and multifunctionality,hydrogel has been used to develop into various flexible wearable sensors.However,with the development of flexible devices,single-function hydrogels have gradually failed to meet the practical needs,and there is an urgent need to develop a variety of hydrogels with different functions to meet their needs as flexible wearable sensors.In this paper,a series of hydrogels with different functionalities are designed and prepared using natural polymer chitosan with good biocompatibility as a substrate,and assembled into flexible wearable sensors for application.The details are as follows:1.A double-network ionic conductive hydrogel was prepared by free radical polymerization using chitosan（CS）as a substrate,acrylamide（AM）and acrylic acid（AA）as monomers,the addition of trisodium citrate salt（Na₃Cit）give the hydrogel excellent electrical conductivity.This ion-conductive hydrogel exhibits ultra-high tensile properties and stable sensing performance.It can rapidly recover（after 20 min）to the original length after high stretching（5000%）.Also,it can recover its own performance in time after repeated multiple deformations,keeping the gauge factor（GF）of the sensor basically unchanged,demonstrating its stability as a sensor.In addition,the flexible strain sensor based on this hydrogel can accurately monitor the movement of some joints in the human body.2.Based on the first part of the work,an antifreeze and moisturizing component-glycerol was introduced into it,and the hydrogels with antifreeze and moisturizing properties were prepared using water/glycerol as a binary solvent.This hydrogel can maintain its properties at a low temperature of-40°C and remain flexible at room temperature for a long time（about 3 months）.The hydrogel also has high sensitivity（GF=4.93）,fast response（100 ms）,and good cycling stability.When assembled into a flexible strain sensor,it can monitor some micro-expressions of the human body,such as smiles and frowns.3.With chitosan as the substrate and acrylamide as the monomer,Fe Cl₃ and tannic acid（TA）were introduced into the system.The ultrafast polymerization of the hydrogel was achieved by using the redox reaction between TA and Fe³⁺,and the hydrogel could be successfully prepared within one minute at 60°C.Moreover,the hydrogel has excellent self-adhesive properties and can adhere to the surface of a variety of substrates.Also,the ionic coordination in the system gives the hydrogel self-healing properties and prolongs the service life of the hydrogel.When assembled into a flexible strain sensor,it can directly adhere to human skin without any side effects,and can monitor joint movements with large deformation as well as movements with small deformation（e.g.pronunciation and drinking）.