3D printed conductive hydrogel based on silk fibroin and tetramer-grafted-polyethylenimine micelle for body-motion monitoring

Abstract

Conductive hydrogels hold significant promise for applications in flexible wearable, soft robotics, implantable devices, and other fields, which offer distinct advantages due to their biomimetic structures, intrinsic properties, and biocompatibility. This study builds upon our previous research by fabricating a conductive hydrogel through the combination of 30 % Pluronic F127 and aniline tetramer-grafted-polyethyleneimine (AT-PEI) copolymers. To enhance the properties of hydrogels, we successfully engineered silk fibroin-based conductive hydrogels (SF-AD) by inducing the transition of silk fibroin from a random coil to a β-sheet structure using the F127 and AT-PEI/DNA complex (AD), endowing the hydrogels with dual ionic and electronic conductivity. The conductivity of all hydrogel exceeds 10⁻⁴ S/cm. Additionally, SEM was employed to characterize the pore size of the hydrogels, revealing a decrease with higher AD content. The swelling ratio ranged between 4.89 and 6.50, indicating the tunable nature of the hydrogels' structure. Utilizing 3D printing, we produced a 2 × 2 cm² mesh active conductive layer that ensures a more uniform stress distribution—maximum sensitivity with a grid width of 4 mm. Our assembled hydrogel sensor demonstrated long-term stability in cycling tests over 1000 cycles and proved capable of recognizing various human movements. The SF-AD hydrogel, characterized by its unique combination of properties and potential for customization, presents broad prospects for future applications in flexible electronics.