Silk Fibroin Gels Fabricated from Ajisawa Reagent with Mechanochromic Sensing Capability

Silk fibroin (SF) derived from Bombyx mori cocoons was employed to fabricate gels using Ajisawa reagent (AJ) as the extraction medium. The resulting regenerated SF solution was subsequently directly dialyzed against an ethanol–water mixture, inducing a gradual and controllable solution–gel transition. Obtained SF gels exhibit a pronounced increase in compressive strength aligned with rising initial fibroin concentration, along with excellent water stability. FESEM, FTIR, and synchrotron X-ray diffraction analyses reveal a homogeneous network structure, likely governed by uniformly distributed physical silk II crosslinks. SF gels containing Ca2+ ions predominantly retain the silk I conformation, consistent with optical transparency and higher ionic conductivity. Mechanochromic SF-based gel was further developed through a one-step process involving pentacosadiynoic acid (PCDA) infiltration, followed by UV-induced polymerization into polydiacetylene (PDA), yielding a blue-colored gel. Upon compression, the PDA-infused gel exhibits a clear color transition from blue to red, demonstrating avid mechanochromic behavior. This system represents a promising platform for Structural Health Monitoring (SHM), owing to its intrinsic self-reporting capability and direct visual detectability, enabling the effective sensing of stress-induced damage and crack formation.