Human mesenchymal stem cells (hMSC) are promising candidates for promoting bone growth on biodegradable polymer scaffolds however little is known about early hMSC-polymer interactions. Adhesion is highly dynamic and during adhesive reinforcement, numerous proteins form adhesion plaques linking the cell's cytoskeleton with the extracellular environment. These proteins are known to affect cellular function but their role in hMSC differentiation is less clear. Adhesion plaques are associated with adhesive force, still a detachment force of hMSC on polycaprolactone (PCL), polylactide-co-glycolide (PLGA) or alginate has never been described or shown to affect downstream function.

We demonstrate that hMSC attached to PCL, PLGA and alginate exhibit different adhesion strengths (τ₅₀) as determined by both fluid shear and spinning disk systems, with PLGA demonstrating the greatest T50. Elastic modulus and hydrophobicity were characterized for these surfaces and correlated positively with τ₅₀ to an optimum. Attachment studies of hMSC showed that adhesion plateau timespans were independent of cell line and surface but both morphology and focal adhesion expression varied by polymer type. Differentiation studies of hMSC on PLGA and PCL showed a strong association between markers of differentiation (alkaline phosphatase activity and mineral content) and τ₅₀ within polymer groups, but a poor relationship was found between τ₅₀ and differentiation across polymer groups, suggesting that other polymer properties may be important for differentiation.

Subsequently, we examined the role of focal adhesion kinase (FAK) and Rho-GTPase (RhoA) on hMSC adhesion and differentiation when plated onto PLGA. hMSC were retrovirally transduced with mutant constructs of FAK and RhoA cDNA. Alternatively, hMSC were treated with Rho-kinase inhibitor, Y27632. Both cells transduced with mutant RhoA or FAK constructs, or those treated with Y27632 displayed aberrant cell morphology and changes in focal adhesion number. Differentiation studies demonstrated that both constitutively active RhoA and mutants of FAK increase osteoblastic activity, while both dominant negative RhoA cells and hMSC treated with Y27632 exhibited a decrease in osteoblastic markers. Manipulating FAK or RhoA in hMSC resulted in greater modulations in osteogenesis on PLGA previously demonstrating maximal τ₅₀. This suggests that hMSC differentiation on polymers exhibiting high adhesion strength depends on FAK and RhoA signaling.