Preparation Of Ionic Liquid/Cellulose-Based Conductive Materials And Their Application On Electrocardiographic Sensors

ECG signal is one of the most important signals to reflect the health condition of human body.However,the traditional ECG signal monitoring equipment is large and costly,so it is especially important to develop portable ECG sensors.ECG monitoring electrodes are an important part of ECG sensors.Conventional commercial Ag/Ag Cl electrodes used on ECG sensors not only have the problem of easy sensitization,but also have the problem of drying out with extended use,which leads to a significant decrease in the quality of the monitored ECG signal and is not suitable for long-term use under practical conditions.In view of this,we propose to use cotton cellulose(CEL),which is widely available and inexpensive,and chitosan(CS),a biomass material,to prepare flexible ECG sensor electrodes that can be used for a long time with high sensitivity and good conformal contact with the skin.The green solvent 1-butyl-3-methylimidazolium chloride([Bmim]Cl)was firstly used to dissolve the cotton rags,and then the cellulose hydrogel was prepared by solvent replacement method,and then the dried cellulose membrane was prepared by heavy pressure,and the conductive electrode was prepared by palladium chloride activation and chemical silver plating to study its ECG signal monitoring performance.The electrical conductivity,microscopic morphology and chemical structure of the cellulose and Ag-cellulose membranes were analyzed by conductivity testing,field emission scanning electron microscopy(SEM),thermogravimetric testing(TG),X-ray diffraction spectroscopy(XPS),infrared spectroscopy(FTIR)and field emission spectroscopy(EDS).In addition,the ECG signal monitoring performance was compared with that of conventional commercial electrodes.The results show that the conductive electrode with Ag-cellulose film has low impedance and can be used for a long time.Thanks to the good conductivity of silver,the Ag-cellulose film shows a high conductivity(229 S/cm)at a concentration of 0.15 mol/L of silver nitrate and an impedance of about 8 kΩ/cm2 at 700 Hz, which is close to the impedance value of conventional commercial electrodes.In addition,the formation of dense structure after chemical plating makes the Ag-cellulose film have good hydrophobicity,which facilitates long-term preservation.To further meet the requirements of wearability,this topic was achieved by preparing self-adhesive and fatigue-resistant ionic gels with cellulose and polyacrylic acid as the backbone,combined with ionic liquids(ILs)to prepare a self-adhesive ECG sensor electrode with a threedimensional network.Its transmittance is 78% and has good fatigue resistance after 10 consecutive tensile cycles.In addition,this ionic gel has good tensile properties(strain at break of 226%),which can better adapt to the human skin at least 30% of the tensile performance requirements,and the ionic gel can still continuously and clearly monitor the human ECG signal after 90 days of storage.Therefore,the preparation of this iogel electrode provides a new idea for the design of wearable ECG sensors.After that,this project further enhances the toughness of the ionic gel by extending the polymer chain to improve its application performance in practical use.Copolymers of CS and acrylic acid(AA)and hydroxyethyl acrylate(HEMA)were used as the backbone,and ionic gels with three-dimensional network structure were prepared in combination with ionic liquids to prepare ionic gel ECG sensor electrodes with fatigue resistance(residual strain less than 0.313% after 10 tensile cycles),good toughness(17 MJ/m3),and clear signals even after 70 days of storage.The ionic gel electrode is self-adhesive and can form a good conformal contact with the skin,thus allowing it to monitor ECG signals under low-impedance conditions.Therefore,this ionic gel electrode can provide new ideas for the design of wearable ECG sensor monitoring devices with good toughness.