Nanoscale control of silica particle formation via silk-silica fusion proteins for bone regeneration

The biomimetic design of silk/silica fusion proteins was carried out, combining the self-assembling domains of spider dragline silk (Nephila clavipes) and the silaffin-derived R5 peptide of Cylindrotheca fusiformis that is responsible for silica mineralization. Genetic engineering was used to generate the protein-based biomaterials, incorporating the physical properties of both components. With genetic control over the nanodomain sizes and chemistry, as well as modification of synthetic conditions for silica formation, controlled mineralized silk films with different silica morphologies and distributions were successfully generated as three-dimensional (3D) porous networks, clustered silica nanoparticles (SNPs), or single SNPs. Silk serves as the organic scaffolding to control the material stability, and multiprocessing makes silk/silica biomaterials suitable for different tissue regenerative applications. The influence of these new silk-silica composite systems on osteogenesis was evaluated with human mesenchymal stem cells (hMSCs) subjected to osteogenic differentiation. hMSCs adhered, proliferated, and differentiated toward osteogenic lineages on the silk/silica films. The presence of the silica in the silk films influenced osteogenic gene expression, with the upregulation of alkaline phosphatase (ALP), bone sialoprotein (BSP), and collagen type 1 (Col I) markers. Evidence for early bone formation as calcium containing deposits was observed on silk films with silica. These results indicate the potential utility of these new silk/silica systems toward bone regeneration. © 2010 American Chemical Society.