Biomimetic Flexible Electronic Materials from Silk Fibroin-MXene Composites Developed via Mussel-Inspired Chemistry as Wearable Pressure Sensors

Since humanity is rapidly moving toward the era of the Internet of Things (IoT) and artificial intelligence (AI) to achieve a higher level of comfort and connection, biocompatible, elastic, and self-healable soft electronic devices such as wearable sensors are needed to overcome the traditional silicon-based electronics rigidity. Inspired by catecholic amino acid (l-3,4-dihydroxyphenylalanine, DOPA) from the mussel foot plaque of marine organisms and Mytilus galloprovincialis mussels, which contribute significantly to the robust underwater adhesion of mussels to the surfaces, here, we report the synthesis and fabrication of a library of materials. These materials comprise adhesive, self-healable, and stretchable gum-like materials, hydrogels, and aerogels based on cross-linking of three components of the silk fibroin (SF) biopolymer, MXene (Ti3C2) twodimensional nanosheets, and tannic acid (TA). The synthesis relies on the coordination of oxidized SF (SF-DOPA), TA, and polydopamine (PDA)modified MXene nanosheets with ferric ions to fabricate materials with a mussel-inspired adhesiveness, mechanical flexibility (stretchability), electrical conductivity, and self-healing features. To control the type of the obtained materials as well as their resulting properties, namely, elasticity and electrical conductivity, the molar ratio of TA, MXene, and Fe(III) cross-linker as well as pH values was carefully varied to control the gelation kinetics and phase separation. The resulting optimized materials consist of highly flexible gum to 3D porous homogeneous hydrogels and subsequently aerogels after freeze-drying. The stretchability, electrical conductivity (6.5 x 10(-4 )S cm(-1)), human motion sensing performance, and significant strain sensitivity of the final gums confirmed their remarkable performance as intriguing next-generation materials for soft-electronic devices, such as electronic skins and piezoresistive wearable pressure sensors.