Interface Effects Of Flexible Electronics And Its Application In Wound Healing

With the development of new materials and new processes,flexible electronics have been vigorously developed in academia and industry in recent years.Considering the application scenarios of flexible electronics involving biological surface / internal devices,the basic mechanical mismatch between flexible electronics and biological interfaces is an urgent scientific problem to be solved,and it is one of the key technologies for the development of next-generation flexible electronic devices.Flexible electrical stimulation devices,as one of the applications of flexible electronics in the medical field,have great medical significance.Since the electrodes of flexible electrical stimulation devices need to be directly connected to the organism,the scientific problem involved is how to overcome the mismatch of mechanical properties at the interface between electronic devices and soft biological tissues,so as to maximize the effect of electrical stimulation.Considering this scientific problem,this work mainly explores the following aspects:(1)improving the stability of the connection between electrodes and other rigid components and organs,(2)exploring the conversion mechanism of electrical stimulation,(3)selecting the optimal electrical stimulation signal and realize it in a flexible electrical stimulation device.Firstly,the characteristics of liquid metal EGa In(eutectic gallium-indium)as a rigid-flexible connection interface and the internal interconnection of flexible circuits are explored,and EGa In is compared with conductive silver paste,a commonly used soldering material,about the failure mechanism,proving the superiority of EGa In as an interface and interconnection material;through finite element analysis,rat skin electrical modeling,etc.,the conversion mechanism of electrical stimulation acting on the electrode-skin interface under different conditions is discussed,and an optimal window of electrical stimulation parameters is proposed;based on the above theoretical research,a flexible electrical stimulation chitosan dressing with an optimized structure is designed,which can be applied to skin wounds with different sizes.Then its practicability and effectiveness is verified through animal experiments.The main contents and results of this research are as follows:(1)A variety of failure analysis methods(tensile,bending,torsion,high-frequency vibration,temperature change)are utilized to analyze the reliability of the external interface and the internal interconnection of flexible electronics;the interface/interconnect properties of the commonly used interface/interconnect material conductive silver paste and liquid metal EGa In are compared.The spot-welded interface structure and the injection-type internal interconnection structure are designed,and the failure analysis of these two application scenarios is carried out respectively.Strains generated by single and multiple stretching,bending,torsion,and highfrequency vibration as well as the thermal strain caused by temperature change are obtained respectively,so as to explore the electrical properties of the interface/interconnection.Through these experiments,we verify the excellent characteristics of the liquid metal EGa In as an interface/interconnection of flexible electronic devices.(2)In the research of flexible electronic-skin interface,the impedance spectrum of each layer is obtained through a layered test of rat skin,where inductive characteristics are discovered,and the equivalent circuit of each layer is proposed by EIS fitting.Based on the EIS fitting,a more accurate RCL(resistance-capacitance-inductance)threeelement skin circuit equivalent model is developed,and the potential distribution in different skin layer under various electrical stimulation signals is simulated.Through the detailed analysis of the pulsed electrical signal applied to the skin,combined with the electrochemical and bioelectric theory,the electron-ion conversion mechanism at the electrode-skin interface is analyzed.Firstly,the main ion transport characteristics around the electrode-skin interface are analyzed based on the electric field distribution,and then the p H changes were obtained.According to the characteristics of p H change and the relationship between wound repair and p H change,a wide-ranging charge theory,which is applicable to DC,AC,constant voltage,and pulsed electricity,is proposed.This charge theory considered the total amount of charge injected and the DC component are the key factors for optimizing the electrical stimulation parameters.An optimal window of electrical stimulation parameters is then established,which provides a theoretical basis for the parameter selection of electrical stimulation to repair skin wounds.(3)Based on the optimal window of electrical stimulation parameters,this work conducts animal experiments on the back wound of diabetic rats with various electrical stimulations,including constant-voltage DC(CVDC),single-phase high-voltage(HVSP),single-phase low-voltage(LVSP),biphasic high-voltage(HVBP)and biphasic low-voltage(LVBP)pulsed stimulation.The analysis of the repair process and the secretion of vascular endothelial growth factor(VEGF)leads to the conclusion that the effect of HVSP electrical stimulation is the best.Based on the results of the electrical stimulation experiment,this work developed a dressing by flexible circuit design which realizes single-phase pulse electrical stimulation with adjustable voltage,frequency and duty cycle.By utilizing a meandering structure,this dressing is adaptive to wounds with various sizes.Then this work combines the flexible electronic dressing with chitosan,and find that this can greatly promote the repair of the wound under the combined effect of chitosan treatment and electrical stimulation adjuvant treatment.