Engineering 3D-printed soft electronics: Roles of conducting polymers and conductive hydrogels in biosensor design

Three-dimensional (3D) printing has revolutionized the fabrication of advanced sensing platforms by integrating diverse materials into complex, functional architectures. This review presents a comprehensive comparison of two primary classes of printable conductive materials, conducting polymers (CPs) and conducting hydrogels (CHs), within the context of sensor and bioelectronic device fabrication. It details the roles of 3D printing technologies such as direct ink writing (DIW), digital light processing (DLP), and extrusion methods in tailoring the performance of soft, conductive structures, highlighting how CPs offer superior electrical conductivity and structural integrity, whereas CHs provide enhanced biocompatibility, flexibility, and adaptability to soft environments. The review discusses key material characteristics including conductivity, printability, mechanical robustness, and biocompatibility, alongside application-specific performance in wearable electronics, biosensing, and implantable systems. By critically assessing trade-offs and synergies of each material class, this work aims to guide future developments in soft and functional sensing devices via additive manufacturing.