Direct Writing of Conductive Microstructures inside a Thermoresponsive Hydrogel

The integration of soft electronic devices with biological systems has garnered increasing attention for applications such as bioinspired soft robotics and wearable health monitors. These devices are designed to interface with biological surfaces or tissues, mimicking the transmission of electrical signals through neural tissues while ensuring high biocompatibility and flexibility. Conductive polymer hydrogels, combining conductive polymers and hydrogels, have emerged as promising materials owing to their flexibility, stretchability, and biocompatibility. In the realization of advanced soft electronic devices, it is key to employ materials with high flexibility and biocompatibility and, moreover, develop techniques for the fabrication of precise and localized conductive structures inside hydrogels. In this study, we demonstrated the spatially selective polymerization of conductive polymers inside a thermoresponsive hydrogel. A poly(N-isopropylacrylamide) (PNIPAM) hydrogel was immersed in a precursor solution of polyaniline (PANI), and polymerization was induced by femtosecond laser pulse irradiation. Conductive polymer microstructures were successfully fabricated inside the hydrogel. Furthermore, using the thermal responsiveness of the PNIPAM hydrogel, we demonstrated that the electrical resistance of the PANI structures changed in response to temperature. The present method provides a strategy for the precise and localized fabrication of conductive structures inside hydrogels, offering an approach to the fabrication of soft electronic devices.