Hierarchical materials from fused silk

Abstract Silk is an extraordinary natural material whose unique chemistry and hierarchical organization enable performance beyond that of many synthetic counterparts. However, its poor processability arising from the molecular folding patterns of fibroin makes fabricating shapes other than fibres conceptually challenging. Here we report a simple and rapid thermomechanical process to fuse silk fibres into solid materials of arbitrary shapes. This approach avoids silk dissolution and subsequent regeneration – processes typically associated with a substantial environmental footprint due to extensive solvent use. The resulting fused silk exhibits remarkable mechanical properties (flexural strength up to 510 MPa, tensile toughness up to 45 MJ m −3 ), optical transparency in the visible range, pronounced optical activity in the terahertz range with large polarization rotation and processing-dependent biocompatibility and biodegradability. The molecular organization of fused silk emerges from interdiffusion of the naturally present amorphous phase, generating strong intrafibre and interfibre molecular bonds without damaging the original hierarchical organization and the crystalline regions. This direct conversion of natural silk fibres into structural and optically active materials enhances the prospects for scalable production and real-world deployment.