Preparation And Properties Of EGaIn-based All Flexible And Stretchable Bioelectrodes

Surface biopotentials such as electrocardiography（ECG）,electromyography（EMG）,and electroencephalography（EEG）collected from human skin contain important information about human physiology,and the rapid development of bioelectrodes has made it possible to diagnose and treat heart-,brain-,and muscle-related diseases by measuring surface biopotentials.In recent years,we have made great progress in the field of bioelectrodes,but how to meet the flexibility and stretchability of bioelectrodes while ensuring the conductivity of bioelectrodes is still a challenge.Liquid metals（especially eutectic gallium indium alloys,EGaIn）are suitable for flexible bioelectronics due to their high conductivity and deformability,but their high surface tension and poor wettability to most elastic substrates prevent them from forming high-resolution conductive patterns.EGaIn nanoparticles（EGaIn NPs）overcome this problem and have great potential applications in the field of flexible electronics.However,a sintering process is needed to destroy the oxide shell of EGaIn NPs to achieve the conductive path;moreover,due to the liquid nature of EGaIn,it must be encapsulated to avoid its leakage,which seriously hinders the application of EGaIn in the field of flexible electronics.Based on the above problems,the research contents of this paper are as follows:（1）For the first time,thermally sinterable EGaIn NPs inks were prepared by introducing thermally expanded microspheres（TEMs）into EGaIn NPs;（2）A new mechanical sintering method was proposed in which the printed EGaIn NPs form a conductive pathway by destroying the EGaIn NPs oxide layer by thermally expanded TEMs;（3）A highly conductive ionic elastomer was prepared by cross-copolymerizing acrylic acid and acrylic acid N-hydroxy succinimide esters in a deep eutectic solvent to prepare a highly conductive ionic elastomer with tunable mechanical properties,thus completing the encapsulation of the recording site portion of the electrode;（4）Characterization of the performance of bioelectrodes for the monitoring of human myoelectric signals.The results show that:（1）Mechanical sintering of TEMs can destroy the oxide layer of EGaIn NPs to form conductive particles（2）The conductive path prepared by using EGaIn as conductive material has good electrical stability:R/R₀ is only 1.47 at700%tensile strain,and R/R₀ after 1.5×10⁵ stretching-release cycles at 100%strain R₀ is only 1.237,even after 3 min of rotation at a high speed of 6000 rpm,the R/R₀ of the conductive path is only 1.369;（3）The interfacial adhesion strength of the prepared ionic elastomer encapsulating the bioelectrode recording site and the substrate material Ecoflex can reach 205 N/m,and the ionic elastomer has good conductive properties,under 100%strain R/R₀ is about 3.05,and its electrical properties remain stable even after 100 cycles of stretching at 100%strain;（4）Compared with the bare EGaIn electrode,the bioelectrode encapsulated with ionomer has a higher performance at 1k Hz than the bare EGaIn electrode.The electrochemical impedance is reduced from3094.64Ωto 389.32Ω,and has good electrochemical stability;（5）Applying the bioelectrode to human EMG signal monitoring,the signal-to-noise ratio of the bioelectrode is higher than that of commercial Ag/AgCl gel electrodes,and the electrode can be used to detect stable EMG signals under vigorous exercise（acceleration of 10 g）and high strain scenarios（under 100%static strain and 40%dynamic strain）,showing its potential for artificial intelligence,health monitoring,disease diagnosis and medical treatment.