3D printing conductive hydrogel with low modulus and anti-swelling for customized strain sensors

Developing antiswelling hydrogel that retains their low modulus and has three-dimensional (3D) printability to application in the biomedical field is a current critical issue. Here, we synthesized 3D printing ink consist of poly(acrylic acid-acrylamide-allyloxypolyethyleneglycol) (P(AA-Am-APEG)) and nanosilica (SiO 2 ) by free radical polymerization, immersed the hydrogel precursor printed by ink in ferric chloride solution to prepare a low modulus, antiswelling, and conductive hydrogel. In the physical cross-linking network, the coordination interaction and hydrogen bonds contributed to excellent mechanical properties and nSiO 2 regulated rheological behavior of ink. Especially, P(AA-Am-APEG) molecular chain was a structure containing of APEG branch chain, which could endow antiswelling (the equilibrium swelling rate was only 7% in deionized water) and low modulus (Young's modulus was less than 100 kPa) to hydrogel. The tensile stress could still maintain 90% of the original value after soaking for 24 h. In addition, the existence of iron and chloride ions provided high sensitive deformation-dependent conductivity to hydrogel. Therefore, the strategy of controlling the swelling and modulus by branch chains would expand the application of hydrogel in biosensors and other fields.