Research On Construction And Application Of Packaged Hydrogel Strain Sensor

Hydrogels are extremely hydrophilic,three-dimensional networked materials that are chemically or physically cross-linked.In recent years,hydrogels have received increasing attention due to their special structure and tunable physicochemical properties.Flexible strain sensors based on conductive hydrogels have shown great potential for wearable devices,electronic skins and implantable bioelectronic devices.However,it is inevitable that hydrogels lose moisture and exhibit poor durability in long-term usage.In this thesis,an external packaging strategy was demonstrated for fabricating sandwichlike packaged hydrogel strain sensors(PHSSs)through the combination of conductive hydrogel injection and subsequent packaging via a photopolymerization procedure.Hydrogel-based strain sensors with electrical conductivity,transparency,conformal adhesion,durability,reusability and biocompatibility were obtained.The specific study was divided into two parts as follows:(1)Preparation and application of Alg-CNT hydrogel strain sensors.The carboxylated multi-walled carbon nanotubes(CNTs)were incorporated into a hydrogel matrix made of sodium alginate(Alg)derivatives to prepare nanocomposite Alg-CNT conductive hydrogels,followed by an injection process to obtain hydrogel conducting wires.The Alg-CNT conducting wires exhibited excellent linear sensing property and fast response to strain,and were then embedded into the hydrogel film as a sensing element through a facile photopolymerization process.The packaged hydrogel strain sensor could accurate monitoring of large and subtle movements of the human body.Compared to conventional naked hydrogel strain sensors(NHSS),the packaged hydrogel strain sensors exhibited a significantly longer lifespan due to the protective effect of the outer encapsulation layer on the embedded conductive hydrogel sensing elements.Even after severe dehydration,the swelling of the outer encapsulation layer endowed the sensor with the ability to recover its original size and shape as well as its sensing performance.This work provides a new route to the manufacture of longer-lived,reusable,flexible strain sensors.(2)Preparation and application of Ag NWs/Alg hydrogel strain sensors.Based on the research in the previous section,the properties and applications of encapsulated hydrogel strain sensors were further enriched and their potential as implantable and flexible sensors was further explored.In this work,an encapsulated hydrogel strain sensor was produced by using silver nanowires(Ag NWs)to produce a conductive gel,injecting it into conductive hydrogel wires and encapsulating a photopolymeric film on the outside.Thanks to the packaging strategy,multiple properties such as high sensitivity,linear sensing characteristics,good transparency,conformal adhesion were integrated into a single PHSS.C57/BL6 mice were chosen as a model,and by adhering the PHSS to the mouse heart surface and connecting it to an electrochemical workstation,ECG signal traces close to those of commercial Ag/Ag Cl electrodes could be obtained.This further demonstrates its ability to accurately detect not only human movement but also to monitor electrophysiological(EP)signals.