Fabrication And Performation Evaluation Of PPY/Cotton Textile Electrode For ECG Signal Monitoring

In recent decades, ECG fabric electrodes used for long-term electrocardiogramsignals monitoring have attracted more and more attentions aound the world. On onehand, the long-term ECG signals monitoring for potential heart disease patients canprevent and treat heart diseases in time. As a result, many scholars have made theirefforts to develop wearable monitoring equipments for the long-term ECG signalmonitoring. On the other hand, ECG fabric electrodes of soft quality can not only fitwell with the skin, but can also overcome some shortcomings of the clinical usedAg/AgCl gel electrodes, such as skin allergies caused by the conductive gel andinaccurate test signal caused by the drying of the conductive gel as time goes on.Therefore, a lot of researchers have been exploring the process of fabricating ECGfabric electrodes to replace the traditional electrodes.At present, there are three methods of fabricating ECG fabric electrodes. One isto weave fabric electrode by yarns made of conductive fibers or the fibers withconductive particles. The other one is to sew the conductive yarns into the fabrics.The last one is to deposite the conductive metals or conductive polymers on the fabricsurface. Comparing the three methods, it is found that the third method can keep thefabric of good physical and mechanical properties and the fabrication process issimple and very promising. As a kind of conductive polymers, polypyrrole has manybenefits such as excellent stability, light weight, non-toxic, low cost and so on. In thisstudy, polypyrrole was selected as the conductive polymer composited on the fabric tofabricate fabric electrodes. In addition, the performance of the fabric electrodes indetecting ECG signal were discussed to choose the optimum scheme, including theeffects of the dopant concentration on the efficiency of fabric electrodes in detectingECG signal and the influnence of the interface between skin and the electrode on thedetecting result.Focusing on these aspects, this study concentrats on the following contents:(1) The polypyrrole/cotton ECG fabric electrode was fabricated. Chemicaloxidation method was used as the fabrication method. The woven cotton fabric as thebase cloth was immersed in an aqueous solution containing pyrrole monomer anddopant. Then, the oxidizing agent was added into the solution in oder to make thepyrrole polymerized on the surface of cotton fabric. The appearance characteristics and conductive properties of the conductive fabric were tested. Actualelectrocardiogram signals were recorded by the fabric electrodes.(2) The influence of dopant NDSA concentrations on the properties of the fabricelectrodes was discussed. The woven cotton fabrics were immersed in the aqueoussolutions with five different dopant concentrations to prepare fabric electrodes bychemincal oxidation method. According to the ECG signal measurement standard, theimpedance value of the electrode materials, defibrillation recovery and DC clearoffset voltage were typical parameters in characterizing the performance of theelectrodes. Some electrochemical workstation testing methods, such as theelectrochemical impedance spectroscopy, cyclic voltammetry curve test and opencircuit potential, were used to test the polypyrrole/cotton fabric electrodes in order toobtain the relative optimum dopant concentration.(3) The equivalent circuit model of polypyrrole/cotton electrodes for ECGmeasurement was built. Fabric electrodes detecting ECG signal by collecting the bodysurface potential. The signal collecting proess can be divided into two parts. One isthe electrochemical reaction between the electrod and the skin surface, in which theorganisms ion stream was turned into the electron stream for collection device. Theother is the movement of the electrons in the electrode material. By using aelectrochemical workstation, the two parts of the equivalent circuit of the electrodematerials were built and the circuit elements values were caculated. Additionaly, theinfluence of the fabrication parameters for electrode materials on its performance wasanalyzed.The polypyrrole/cotton ECG textile electrodes fabricated by chemical oxidationmethod can record, completely and clearly, the ECG special wave signals. After thepolymerization, the square resistance of polypyrrole/cotton conductive fabric was995Ω and the rate of the weight gained was16.4%, which showed the fabric wasdeposited by pyrrole polymerization and became conductive after the process of theoxidation reaction. Besides, the electrochemical impedance spectroscopy resultsshowed that the impedance of the fabric electrode gradually declined when the dopantconcentrations increased. But when the NDSA concentration increased to0.0045mol/L, a further increase of the dopant concentration caused litte change of theelectrode impedance. The characteristics of the cyclic voltammetry curves showedthat the increase of the dopant concentration in the rang of0~0.0045mol/L willimprove the oxidation and reduction performance of the fabric electrodes which isbeneficial for the defibrillation recovery of the electrodes. The open circuit voltage testing results showed that the signal tested by the electrode had good stability. Theequivalent circuit model of the electrode-skin interface consisted of a charge transferresistance and a double-layer capacitance in parallel, and then connected in serieswith a solution resistance. The equivalent circuit of fabric electrode material is theresistance and capacitance connected in parallel.