Human Mesenchymal Stem Cells Cultured on Silk Hydrogels with Variable Stiffness and Growth Factor Differentiate into Mature Smooth Muscle Cell Phenotype

Cell-matrix and cell-biomolecule interactions play a critical role in a diversity of biological events including cell adhesion, growth, differentiation, and apoptosis. Evidence suggests that a concise crosstalk of these environmental factors may be required to direct stem cell differentiation toward desired cell type and function. However, the culmination of these complex interactions to direct stem cells into highly specific phenotypes in vitro as well as the underlying mechanisms governing these events is still widely unknown. In this study, we utilized tunable hydrogels based on a simple high pressure CO2 method and silk fibroin (SF) the structural protein of Bombyx Mori silk fibers. Modification of SF protein concentration results in hydrogels of variable stiffness whilst retaining key structural parameters such as matrix pore size and β-sheet crystallinity. To further resolve the complex crosstalk of chemical signals with matrix properties, we chose to investigate the role of substrate elasticity and growth factor (TGF- β1) on SF matrices, with the aim of correlating the effects on the vascular commitment of human mesenchymal stem cells (hMSCs). Our data revealed the potential to upregulate mature vascular smooth muscle cell (vSMC) phenotype of hMSCs cultured with appropriate matrix stiffness and growth factor within 72 h. Overall, our observations suggest that chemical and physical stimuli within the cellular microenvironment are tightly coupled systems involved in the fate decisions of hMSCs. The production of tunable scaffold materials that are biocompatible and further specialized to mimic tissue-specific niche environments will be of considerable value to the research community and future tissue engineering platforms.