Breakthrough Assembly of a Silk Fibroin Composite for Application in Resistive Pressure Sensing

Driven by the dictates of sustainability, we have designed, realized, and optimized a method for easy development of biocompatible, highly porous, and electrically conductive 3D structures from the combination of natural and synthetic polymers for pressure sensing applications. In particular, a foaming method followed by a fast freezing step, both performed on blends made of silk fibroin (SF) aqueous solution, PEDOT:PSS electrically conductive polymer, and water-soluble PVA, has allowed the fabrication of conductive electrosponges, intrinsically integrating the structural and electrical counterparts of a resistive pressure sensor in a single “green” material. An exhaustive analysis of their structural (with FTIR), morphological (with μ-CT), and mechanical (by means of stress–strain measurements) properties has been performed, of which the latter was coupled with the electrical characterization of the electrosponges while undergoing compression–decompression cycles. PVA addition has been recognized as crucial for conferring to the material the right compromise among elasticity, recovery attitude, and resilience/durability to the proposed constructs. The fabricated electrosponges show a promising combination of mechanical and electrical properties, with the former induced by both the highly porous structure of the foamed/frozen compound and the elasticity enhancement induced by PVA, whose concentration influences the electrosponge resilience and recovery attitude. Based on the results from the material characterization, the composite with 1% v/v PVA content has shown the best compromise among elasticity, resilience, and shape recovery. The related sensor shows a sensitivity comparable to other hybrid SF composites (10^–3 kPa/mA vs 10^–3–10^–2 kPa/decade), an applied stress magnitude-dependent swiftness (from hundreds of milliseconds to few seconds), and an exhaustive current recovery on numerous repeated compression–decompression cycles in wet conditions.