(347f) Relative Influence of Scaffold Bioactivity Versus Modulus On Cell Behavior

To rationally select culture environments to evoke desired stem cell differentiation requires a deeper understanding of stem cell responses to specific stimuli than currently exists. A myriad of environmental signals are known to influence stem cell differentiation, including scaffold modulus and the concentration and identity of bioactivity presented to the cells. Although a range of studies have explored the separate impact of these two microenvironmental variables on stem cell behavior, few studies have evaluated the relative influence of these factors. This is significant, because, if one environmental signal proves dominant, then more attention can be focused on appropriately tuning this variable so as to elicit desired differentiation. The present study was designed to evaluate the influence of scaffold modulus relative to that of collagen I concentration (bioactivity) on mesenchymal progenitor cell differentiation. To isolate the influence of modulus from that of bioactivity, we employed hydrogels prepared from poly(ethylene glycol) (PEG). Collagen type I was incorporated into the PEG hydrogels at two separate post-swelling concentrations (0.1 mM and 0.5 mM). At each collagen concentration, three distinct scaffold moduli (70 kPa, 200 kPa, 500 kPa) were investigated by tuning the molecular weight and concentration of PEG. Mesenchymal progenitor cells encapsulated within the hydrogels were cultured for 21 days, with time points collected every 7 days. Differentiation was assessed by qRT-PCR and western blot for cell markers specific to various mesenchymal lineages. Over the time course of the study, collagen concentration appeared to dominate the observed differentiation, suggesting that bioactivity gradients may be more powerful in guiding mesenchymal progenitor cell differentiation than modulus gradients.