Histological sections taken from the unsilicified plain silk controls (A, E, I), and the GSSR5 composites with low (B, F, J), medium (C, G, K) and high (D, H, L) loadings of the R5 peptide after 6-week culture of hMSCs in osteogenic medium. H&E staining (A, B, C, D), von Kossa staining (E, F, G, H) and Sirius red staining (I, J, K, L). Schematic representation of cell differentiation along the GSSR5 composites (M). Scale bar, 50 μm (A–D); 200 μm (E–L). Unsilicified plain silk composites served as controls. Arrows indicate calcification; asterisks indicate composites. O, osteoblast-like cells; C, collagen-like bundles; F, fibroblast-like cells.