Patterning conductive tracks within hydrogel matrices for soft bioelectronics devices

Hydrogels are biocompatible polymer-based materials widely used in biomedicine thanks to their mechanical affinity with soft tissues. Besides their characteristics make them ideal candidates to substitute metals and semiconductor devices for bioelectronics applications, the lack of electrical conductivity represents a huge drawback limiting the possibility of functionalizing hydrogels. In this thesis, we introduce a method to exploit electrical conductivity in hydrogels through direct laser writing. Through the two-photon absorption process, we are able to achieve the photoreduction of silver ions into silver nanoparticles and obtain highly localized conductive structures embedded inside the gel matrix. We demonstrate the conductor-like behavior of the written structures and the stability of the silver particles stored into a wet environment, defining the writing parameters to obtain a reproducible and reliable process. In this way we can avoid further processing of the substrates after the direct laser writing and ensure electrical conductivity without compromising the mechanical properties of the hydrogel.