Research On The Fabrication And Applications Of The Soft And Stretchable Bioelectrode

Neurophysiological activity recording has become a vital research method in current life science and medical research field because of its important role in human-computer interaction,disease diagnosis and treatment.When monitoring neural potential signal,the flexibility and stretchability of the soft electrode array allow them to overcome the mechanical and geometrical mismatches between the arrays and tissues existing in traditional rigid bioelectrodes to form conformal contact and maintain the high quality of the collected signal.Therefore,the soft bioelectrode is not only a representative flexible sensor device,but also has great application values to life science and medical research.Different from the resistive bioelectrode where the conductor part is in direct contact with the biological tissue,the capacitive bioelectrode records signal by forming capacitive coupling through the dielectric layer,which can separate the conductor part and the biological tissue to avoid the hidden danger of leakage current and the risk of allergic reactions.To fabricate soft bioelectrodes,especially those with great stretchability,polymer materials with low-modulus?like silicone rubber?are widely used to keep the flexibility of device.However,there is a major drawback of such kind of materials,of which the permittivity is relatively low,meaning it is hard for the capacitive bioelectrode to collect signal with high quality when used for dielectric layer due to the low equivalent capacitance value.Therefore,how to promote the permittivity of the used material for dielectric layer is one of the problems to be solved to prepare high-performance stretchable capacitive bioelectrode for neurophysiological activity recording.To overcome the above problems,a stretchable capacitive bioelectrode is presented in this thesis by using BaTiO₃/PDMS composite to serve as dielectric layer,which is prepared by doping barium titanate?BaTiO3?nanoparticles into polydimethylsiloxane?PDMS?.The performance of the bioelectrode has been verified by using it for ECoG signal acquisition.Firstly,The BaTiO₃/PDMS composite was obtained successfully by improving the doping process and tested by XRD,Raman spectroscopy and EDS to prove its stability.Then,the capacitive electrode was fabricated by lift-off,transfer-printing,dry-etch and other technology.The electrical properties of the electrode were characterized by leakage measurement and electrochemical impedance spectroscopy,while the mechanical reliability was analyzed by finite element model.As for the biological experiments,the ECoG signals and steady-state visual evoked potential?SSVEP?signals of rats were collected by using the as-prepared capacitive electrode array.The signal acquisition capability of capacitive electrode array got evaluated by comparing the signal acquisition results come from screw electrode,capacitive electrode array and resistive electrode array.Meanwhile,the relationship between the weight fraction of BaTiO₃ in the composite and the signal quality was also systematically discussed with the consideration of the permittivity,wettability and stiffness of the composite and the electrode array.The results of the study show that the designed and fabricated stretchable capacitive bioelectrode has excellent electrical and fluidic isolation performance while ensuring high quality of the collected ECoG signals.The average Pearson correlation coefficient of the collected ECoG signals between the stretchable capacitive bioelectrode array and screw electrode reachs to 83.32%,which means a relatively high signal quality.Meanwhile,the signal noise ratio?SNR?of SSVEP signals collected by capacitive bioelectrode represents a higher level than which of screw electrode.The analysis of the test characterization results shows that the weight fraction of BaTiO₃ in the composite has a significant influence on the permittivity and hydrophilicity of BaTiO₃/PDMS composites,which exist relationship with the device performance.Therefore,choosing an appropriate BaTiO₃ weight fraction is very important for the preparation of stretchable capacitive bioelectrodes based on BaTiO₃/PDMS composites.