Fabrication And Performance Investigation Of Microstructural Flexible Pressure Sensors

Along with the tide of the Internet of Things(Io T),artificial intelligence,big data,and cloud computing,global information technology presents the following characteristics:interconnection of all things and intelligence of all things.Wearable medical electronics serve as data source in Io T space to continuously track human physiological or behavioral characteristics,which are expected to change the traditional disease-centered healthcare service system into a personalized healthcare mode focusing on disease prevention and health promotion.Piezoresistive pressure sensors have merits of low energy consumption,high sensitivity,simple structure,cost effective fabrication,large-scale manufacturing,and easy signal collection,are the most attractive frontier for the next-generation wearable biomedical service in personalized real-time health monitoring and point-of-care diagnosis.As the advant development of pressure-sensing technology,the pressure-sensing mechanisms with different microstructures are stilled unsettled,unstable contact between devices and skin,trade-off between sensitivity and linear detection range,and applications in monitoring complex physiological information are constantly promoted.In this dissertation,systematically studied the pressure-sensing mechanism with different microstructure,designed novel flexible materials,constructed diverse microstructures,optimized the structure and performance of the piezoresistive pressure sensors.Moreover,the monitoring various physiological signals have been carried out.Details are as follows:(1)3 dimension(3D)conductive and elastic topological nanofiber films were utilized to fabricate ultrasensitive piezoresistive pressure sensors.This film was prepared through surface modification of the electrospun polyvinylidene fluoride(PVDF)nanofibers backbone by the polydopamine(PDA)layer,following the uniform deposition of PPy particles in self-polymer.The PDA was added to strengthen interfacial adhesion between PPy and PVDF nanofiber,which are beneficial to homogeneously deposit PPy particles on the nanofiber surface.Because of the unique structure of this coaxial nanofiber network,the obtained sensor showed excellent sensitivity(139.9 k Pa^-1),rapid response(22 ms),low limit of detection(LOD,0.9 Pa),and good cycling stability for over 10,000 cycles.The excellent sensing performance enabled the pressure sensor to monitor human physiological signal and show potential applications in disease monitoring,speech recognition,and so on.(2)The ever-increasing demand for real-time health monitoring and point-of-care diagnosis are driving interest in fabrication of high-performance and flexible piezoresistive sensors by introducing structures in piezoresistive sensor.However,fabrication of various structures mainly involves complicated and time-consuming chemical treatment,even toxic chemicals,it is urgent to develop ecologically-benign,cost-effective and facile approach to fabricating structured piezoresistive sensors.Here,the biocompatible and biodegradable MXene/cellulose fibrous structured films were fabricated by coating MXene on the cellulose fibers through drip-coating method,where inherent fibrous structured cotton cellulose as the skeleton,and MXene as conductive material was strongly adhered to surface of cellulose fibers,and form a 3D conductive network elastomer.The MXene/cellulose film provides a porous fibrous structure,resulting in good sensitivity(17.73 k Pa^-1)in a wide pressure range(100 Pa to 30 k Pa),subtle pressure detection of limit(2 Pa),fast response/recovery time(80/40 ms),good cycle stability(over 10,000 cycles),and excellent ability in detection of finger and muscle motion,human pulse,swallow,as well as speak.(3)Electronic textiles are changing our way of living in fundamental and meaningful ways.However,the inability to effectively recycle them creates a considerable burden on the environment.In this study,the cotton fiber based piezoresistive textiles(CF p-textiles)were developed,which are biocompatible,biodegradable,and environmentally friendly.Using a scalable dip-coating method,strong hydrogen bonding enables an intimate adhesion of conductive MXene flakes onto the hierarchically porous cotton cellulose fibers,which are employed as the building blocks to construct soft electronic textiles for wearable biomonitoring.This cotton-fiber system provides a good sensitivity of 17.73k Pa^-1 in a wide pressure range(100 Pa to 30 k Pa),subtle pressure detection of limit(2Pa),fast response/recovery time(80/40 ms),and good cycle stability(over 5,000 cycles).With compelling sensing performance,the CF e-textile is applied in detecting various human biomechanical activities,including pulsation,muscle movement,and swallowing,along with excellent wearing comfort.Moreover,the cotton cellulose is decomposed into low-molecular cellulose or glucose as a result of the 1,4-glycosidic bond breakage in the process of acid or natural degradation,which allows the electronic textile to be biodegradable.This work offers an ecologically-benign,cost-effective and facile approach to fabricating high-performance wearable bioelectronics.(4)To solve the problems of environmental pollution caused by electronic waste,and meet the need for implantable physiological monitoring,a piezoresistive pressure sensor based on HCSs/silk fibroin were prepared by using hollow carbon nanospheres as conductive fillers,silk fibroin as flexible,and degradable substrates.The red rose petals as a template to fabricate HCSs/silk fibroin flexible conductive pressure-sensitive films with convex micro-hemisphere structure through two-steps template method,following assembled into HCSs/silk fibroin piezoresistive flexible pressure sensor in a cross-linking and interlocking manner.The flexible piezoresistive sensors show relatively high sensitivity of 5.63 k Pa^-1 in a narrow pressure range(0-0.5 k Pa)and low sensitivity of 2.62k Pa^-1 in a wide pressure range(0.5 k Pa-10 k Pa);fast response time(147 ms);and stable cyclability(over 1,5000 cycles).To satisty the conformal contact between devices and human skin,Ca Cl₂ is added to adjust the flexibility of the pressure-sensing film(HCSs/silk fibroin).This sensor can be attached to different positions of the body to monitor diverse physiological activities such as finger bending,muscle movement,and facial expressions.