Characterization and optimization of RGD-containing silk blends to support osteoblastic differentiation

The effect of blending two silk proteins, regenerated Bombyx mori fibroin and synthetic spidroin containing RGD, on silk film material structure (β-sheet content) and properties (solubility), as well as on biological response (osteoblast adhesion, proliferation and differentiation) was investigated. Although the elasticity and strength of silks make them attractive candidates for bone, ligament, and cartilage tissue engineering applications, silk proteins generally lack bioactive peptides for enhancing cell functions. Thus, a synthetic spider silk, spidroin, containing two RGD cell adhesive sequences (RGD-spidroin) was engineered. RGD-spidroin was blended with different ratios of fibroin and spun coat into films on glass coverslips. β-Sheet formation, contact angle, surface topography and RGD surface presentation were characterized and correlated with cell behavior. We found that the amount of β-sheet formation was directly related to the RGD-spidroin content of the blends after annealing, with the pure RGD-spidroin demonstrating the highest amount of β-sheet content. The increased β-sheet content improved film stability under culture conditions. A new visualization technique demonstrated that the RGD presentation on the film surface was affected by both the RGD-spidroin content and annealing conditions. It was determined that 10 mass% RGD-spidroin was necessary to improve film stability and to achieve osteoblast attachment and differentiation.