The interplay of peptide affinity and scaffold stiffness on neuronal differentiation of neural stem cells

Cells are sensitive to physical cues in their environment, such as the stiffness of the substrate, peptide density, and peptide affinity. Understanding how neural stem cells (NSCs) sense and respond to these matrix cues has the potential to improve disease outcome, particularly if a regenerative response can be exploited. While the material properties are known to influence other stem cells, little is known about how NSC differentiation is altered by this interplay of mechanical, or bulk properties, with peptide concentration and affinity, or microscale properties. We are interested in the combined effect of bulk and microscale features in an in vitro hydrogel model and therefore we investigated NSC differentiation by focusing on integrin interactions via RGD peptide affinity and concentration. Our studies demonstrated that the peptide concentration affected adhesion as there were more cells on scaffolds with 1 mM RGD than 2.5 mM RGD. The hydrogel stiffness affected neurite length in differentiating NSCs, as 0.1-0.8 kPa substrates promoted greater neurite extension than 4.2-7.9 kPa substrates. The NSCs differentiated towards β-ΙΙΙ tubulin positive cells on scaffolds with RGD after 7 days and those scaffolds containing 1 mM linear or cyclic RGD had longer neurite extensions than scaffolds containing 0.1 or 2.5 mM RGD. While peptide affinity had a lesser effect on the NSC response in our hydrogel system, blocking actin, myosin II, or integrin interactions resulted in changes to the cell morphology and focal adhesion assembly. Overall, these results demonstrated NSCs are more responsive to a change in tissue stiffness than peptide affinity in the range of gels tested, which may influence design of materials for neural tissue engineering.