Silk and Wool Protein Microparticle-Reinforced Crystalline Polylactic Acid Biocomposites with Improved Cell Interaction for Targeted Biomedical Applications

Silk fibroin and wool keratin are easily available biocompatible structural protein fibers with cell adhesion properties. Bottom-up approaches to convert silk and wool fibers to biomaterials of different forms require harsh chemicals and result in materials with poor mechanical properties. In this work, microparticles were prepared from wool and three types of silk fibers by a top-down approach, which is scalable and requires less processing as compared to other bottom up approaches. The fabricated microparticles (5 wt %) were added during melt extrusion of poly(lactic acid) [PLA] to create hybrid biocomposites. Thermal stability of these protein particles in retaining the native structure present in fibers, particularly in silk varieties containing poly-alanine [poly(Ala)] domains, allowed their inclusion in melt-based processing without thermal degradation. The influence of protein microparticles of different amino acid compositions of silk and wool on molecular weight, crystal growth, microstructure, and mechanical, thermal, hydrophilic, and cell compatibility of PLA was investigated. Crystal density of PLA was increased up to 4.5 times and % crystallinity was increased up to 2 times on the addition of the particle fillers. Silk-containing amino acid repeats of poly(Ala) domains were found to be more effective fillers and had good interfacial adhesion with PLA, while the interaction between PLA and wool was poor. Silk fillers produced more hydrophilic biocomposites and supported higher activity of UMR 106 cells in comparison to neat PLA. PLA is gaining increasing attention from the research community and the biomedical industries as a potential alternate to metal implants in bone fixation devices. The study demonstrates that silk particles, particularly those with a poly(Ala) sequence, amplify the acceptability of PLA biocomposites as advanced biodegradable composites for targeted biomedical applications such as bone-fixation devices.