Research On The Fabrication And Applications Of Flexible Bioelectrode Based On Functional Materials

Emerging flexible electronic devices can use a variety of functional materials to realize the device funtions in flexible and stretchable working circumstances,via the perfect combination of mechanics and electronics.Therefore,flexible electronic devices have been widely used in information,energy,medical and other fields.As an important developing area of flexible electronic devices,flexible bioelectrodes are widely investigated by researchers and medical workers in neurobiology,clinical medicine and other fields.At present,the research of flexible biological electrodes mainly includes resistive biological electrodes and capacitive biological electrodes.In the research of resistive bioelectrodes,researchershavedonealotofresearchwork.Various epidermal/implantable resistive bioelectrodes have been widely used in health monitoring,disease diagnosis and treatment,prosthetics,etc.However,direct contact of metallic electrodes with tissues can easily cause electrical safety,irritation,and allergic reactions.Therefore,long-term monitoring of human physical signals by using resistive bioelectrodes remains a challenge.In the research of capacitive bioelectrodes,researchers have made a lot of advances in recent years,which have made it possible for using capacitive bioelectrodes to effectively solve the problems currently faced by resistive bioelectrodes.However,almost all existing capacitive bioelectrodes can only be used to acquire signals from the human epidermis and require at least a few square centimeters of coupling area,which greatly limits the implantable applications of capacitive bioelectrodes,such as the electrocorticography（ECoG）signal acquisition.Thus,the use of functional materials to fabricate electrically safe and implantable capacitive bioelectrodes is of great significance for the development of flexible bioelectrodes.In order to solve the above problems,the thesis reports the design and fabrication of the capacitive bioelectrode arrays based on Ba TiO₃/PI nanocomposite,which has effectively reduced the coupling area of the electrodes by ultilizing the high dielectric constant of BaTiO₃/PI nanocompitite,and successfully monitered the ECoG of the rat.The first step in this research is to modify the barium titanate（BaTiO₃）nanoparticles with the 3-aminopropyltriethoxysilane（APTS）,and use the in-situ polymerization processto obtainhighperformancebariumtitanate/polyimide（BaTiO₃/PI）nanocomposites.Second,the thermal stability and high dielectric properties of the as-prepared BaTiO₃/PI nanocomposites were confirmed by thermogravimetric analysis（TGA）and dielectric constant measurements.Next,a variety of flexible bioelectrodes were fabricated using the transfer-printing technology,the lift-off technology and the biodegradable silk protein membranes,including implantable capacitive BaTiO₃/PI bioelectrode arrays,implantable capacitive pure PI bioelectrode arrays and implantable resistive bioelectrode arrays.Finally,the mechanical properties and electrical properties of the as-prepared flexible bioelectrodes based on functional materials were characterized and evaluated by three-dimensional finite element model（FEM）and electrochemical impedance spectroscopy（EIS）techniques,and the as-prepared functional material-based flexible bioelectrodes were used for the collection of ECoG signals and steady-state visual evoked potential（SSVEP）signals of rats.Three kinds of flexible bioelectrodes based on functional materials were compared and studied,including resistive electrode array,capacitive BaTiO₃/PI electrode array and capacitive pure PI electrode array.The results show that the flexible bielectrodes based on functional materials can be fabricated by using functional materials such as silk fibroin,Ba TiO₃/PI nanocomposites and so on.Compared with the resistive bioelectrodes,the as-prepared capacitive BaTiO₃/PI electrode arrays in this thesis are electrically safe;compared to the existing capacitive bioelectrodes,the as-prepared capacitive BaTiO₃/PI electrode arrays in this thesis have smaller coupling area thus are implantable and can achieve multi-channel ECoG signals and SSVEP signals.