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

Abstract

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) two-dimensional 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 × 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.

Designing of a Multifunctional 3D-Printed Biomimetic Theragenerative Aerogel Scaffold via Mussel-Inspired Chemistry: Bioactive Glass Nanofiber-Incorporated Self-Assembled Silk Fibroin with Antibacterial, Antiosteosarcoma, and Osteoinductive Properties

“…Upon adding Fe(III) ions to a blend of SFO, TA, and BGNF-PDA at defined mass ratios of SFO/TA of 20:2 and controlled pH (pH = 9), a cross-linking reaction occurs, resulting in a six-coordinated octahedral complex. Our prior research indicates the sensitivity of this complex formation to reaction parameters like pH, SF oxidation degree, and metal ion concentration …”

“…44 Since the SF backbone contains many tyrosine residues, they were oxidized through the tyrosinase enzyme to obtain 3,4dihydroxyphenylalanine (DOPA) groups in the SF chain to make SFO. BGNFA-PDA and TA were then easily cross-linked with SFO via mussel-inspired coordination chemistry 39 by adding Fe(III) ions at a basic pH to form an octahedral sixcoordinated complex compound. The process is based on the natural biological adhesive properties seen in marine mussels, which resulted in the formation of shear-thinning 3D printable hydrogel materials.…”

Flexible resistive tactile pressure sensors

“…This material exhibits both high adhesiveness and high stretchability (∼600%) and can be employed in flexible resistive tactile sensors. 83 Additionally, following the principles of biomimicry, we can integrate biomimetic sensing molecules or cell-mimicking materials into sensors to create biomimetic sensing materials. This approach allows for selective sensing of specific stimuli.…”

Recent developments in stretchable and flexible tactile sensors towards piezoresistive systems: A review

“…148,202 These all are π-conjugated polymer chains in highly aggregated morphologies that make up conductive polymers and give these materials their stiffness and brittleness as well as their ability to trans- Hydrogels can be classified as synthetic hydrogels such as polyacrylamide (PAAm or PAM), 239 and PVA, 240 and biopolymers. 241,242 Biopolymers can be further classified as polysaccharides (chitosan, 243 silk fibroin, 244 and cellulose, 245 ) and proteins (gelatin 246 and collagen 247 ).…”

“…Hydrogels can be classified as synthetic hydrogels such as polyacrylamide (PAAm or PAM), 239 and PVA, 240 and biopolymers 241,242 . Biopolymers can be further classified as polysaccharides (chitosan, 243 silk fibroin, 244 and cellulose, 245 ) and proteins (gelatin 246 and collagen 247 ). Arif et al 248 have discussed in detail about environment‐friendly and biodegradable biopolymers, which are gaining popularity, whether natural or synthetic.…”