Development And Application Of Wearable Sensor Based On Multifunctional Hydrogels

With the rise of smartphones and the Internet of Things(IoT),convenient,affordable and easy-to-use wearable sensors are showing great potential for applications in health monitoring,clinical diagnostics and personalized medicine.Particularly,wearable biosensors based on electrochemical,colorimetric and fluorescence sensing technologies are capable of non-invasive,real-time dynamic monitoring of various biochemical markers contained in biological fluids,which have attracted wide attention.However,these wearable devices often suffer from unsatisfactory flexibility,poor biocompatibility,single function or delamination of electronic fillers and substrates in practical applications.Besides,the high mechanical strength of the material substrate may affect wearing comfort.resulting in a poor user experience.Among various materials for the construction of wearable sensors,hydrogels with excellent mechanical properties and biocompatibility are one of the most suitable and potential candidates.In addition,hydrogels can achieve unique properties and diversified functions to fulfill different needs of applications by changing conductive fillers,cross-linking methods or functional additives.So far,various hydrogel-based wearable sensors have been developed to monitor human movements and tiny physiological signals in real-time.In this thesis,a series of multifunctional hydrogel-based wearable sensors were developed to fulfill the practical application requirements by taking biofluid as the monitoring object and utilizing the adjustable network structure,mechanical properties and multifunctional characteristics of hydrogel itself,further broadening the application of hydrogel in the wearable field.The specific research content is as follows:1.The wearable strain sensor based on superabsorbent hydrogel realized the reliable detection of sweat volume.The superabsorbent hydrogel which was thermally crosslinked by sodium polyacrylate and polyvinyl alcohol,was prepared and embedded with a strain sensing fabric in it to form a complete wearable strain sensor.Taking advantage of its rapid water absorption and swelling properties,the hydrogels directly absorbed sweat from the skin surface to cause swelling,which triggered the resistance response of the strain sensing fabric.This sensor successfully converted sweat volume into an intuitive change in electrical resistance,achieving real-time detection of sweat volume(0.15～700 μL).Moreover,this strain sensor was not disturbed by motion or light and showed good reliability,repeatability and stability in the physiological range(pH 4 to 9,NaCl 0 to 100 mM).Such sensor combing swellable hydrogels with strain sensing fabrics provided a novel measurement method of wearable devices for sweat volume monitoring.2.The adhesive and self-healing wearable hydrogel colorimetric patch enabled the on-demand detection of sweat biomarkers.The hydrogen bonding between polyvinyl alcohol and sucrose gave the hydrogel excellent self-healing ability and adhesion,and colorimetric detection ability was introduced into hydrogels by a simple solvent substitution method.Thanks to these excellent properties,the users could choose the colorimetric hydrogel patch with the appropriate target for their needs according to their own needs to directly attach to human skin for in situ sweat sampling and analysis,without any complex preparation steps.As a demonstration of concept,such wearable hydrogel patch integrated with a smartphone showed excellent accuracy,reliability and stability in measuring pH(4～9),glucose(0～2 mM),Cl-(0～100 mM)and Ca2+(0-16 mM)in human sweat.The analysis and detection of multiple sweat biomarkers of 15 healthy volunteers have been successfully realized by effectively converting the analyte concentration into RGB digital signals through the wearable hydrogel patch.Such a user-friendly wearable hydrogel patch with flexible,self-healable,adhesive properties successfully achieved on-demand in situ sweat colorimetric detection,holding great potential in point-of-care devices.3.A hydrogel-elastomer based electrochemical device achieved comfortable wearable sweat monitoring.We used a thin thermoplastic polyurethane film as an intermediate layer to bridge stretchable hydrogels and conductive ink,thus maintaining excellent electrical conductivity without compromising mechanical flexibility.The prepared electrochemical device had a Young’s modulus(0.37 MPa)similar to that of the skin,thereby greatly improving the conformality with the curved surface of the skin and the wearing comfort during exercise.The device could achieve monitoring pH,Na+ and K+in sweat with high sensitivity(58.14 mV/pH for pH,58.89 mV/decade for Na+,and 59.11 mV/decade for K+),high specificity and high reproducibility.Importantly,the device maintained such excellent electrochemical performance even at 30%tensile strain without the need for any complicated external structural design.Such a hydrogel-elastomer based electrochemical device with excellent wearing comfort and mechanical deformability provided the considerable potential for wearable biofluid monitoring in personalized health applications.4.Multifunctional hydrogel with antibacterial,hemostatic and adhesive properties as a wound dressing realized intelligent wound monitoring.In the whole intelligent wound monitoring process,the hydrogel wound dressing customized by wound recognition could accurately match the wound contour for precise treatment.The multifunctional hydrogel dressing not only effectively promoted wound healing,but also introduced pH colorimetric capability through a solvent replacement procedure to enable real-time monitoring of wound infection status.In addition,a personalized wound management model based on a convolutional neural network machine learning algorithm could analyze and assess wound healing and infection status through colorimetric signals from hydrogel dressings with an accuracy rate of 94.47%.This multifunctional hydrogel wound dressing,which integrated precise treatment,real-time monitoring and personalized management for intelligent wound monitoring,provided an advanced solution to accelerate wound healing and reduce bacterial infections and played an inestimable step for future intelligent wound management.