Stretchable, adhesive and low impedance hydrogel prepared by one-pot method used as ECG electrodes

Flexible, self-adhesive and conductive hydrogel has attracted a deal of interest in ECG biosensors. However, the balance between mechanical properties and ionic conductivity of hydrogels is challenging, and there are tremendous difficulties in preparing a multifunctionally integrated hydrogel. Herein, we designed a multi-network conductive hydrogel, the poly(vinylalcohol)/carboxymethylcellulose sodium-poly([2-(methacryloyloxy) ethyl] dimethyl-(3-sulfo-propyl) ammonium hydroxide-co-acrylamide) (PVA/CMC-Na-P(SBMA-co-AM), PVA/CMC-SAM) hydrogel was obtained by thermal initiation and freeze-thaw cycles. Because of the existence of three-dimensional porous structure, its ionic conductivity reaches 0.91 S/m. The elastic modulus is 0.17 MPa, the fracture strain is 105%, and the tensile strength is 0.21 MPa. At the same time, hydrogels can be bound to different surfaces with the adhesion properties, leading to the low contact impedance on human skin surface. Due to the dynamic cross-linking of hydrogen bonds, hydrogels also exhibit obvious self-healing properties. The resistance of hydrogel is sensitive to strain and can accurately monitor subtle physical movements like finger bending, while continuously, steadily and clearly collecting ECG signals. Therefore, the multifunctionally integrated hydrogel can display promising applications in ECG biosensors.