(685g) Design of Polymer Hydrogels Used as Support Material for Compliance-Induced Differentiation of Stem Cells

In the past years, great effort has been put into investigations on how to direct stem cell differentiation towards specific fates. Specific stem cell differentiation may be induced by receptors binding to cues like ligands or growth factors, but also by changing the physical interactions between the cells and the culture substrate. Polymer hydrogels are ideal support materials for the culture of cells as they can be engineered to have Young's modulii similar to the native tissue the cell is derived from. The swelling behavior of hydrogels makes them very interesting for biomedical applications. In particular, recent studies have indicated that the mechanical compliance itself can alone determine the differentiation of stem cells [1].

In order to verify this claim, in the present work, polyacrylamide hydrogels were produced by copolymerization of acrylamide with low level of bisacrylamide crosslinker. In order to change the mechanical compliance of the substrate, different amounts of crosslinker were used. The hydrogels were characterized by analyzing their swelling behavior and measuring their mechanical compliance (Young's modulus). Compression testing revealed an increase in mechanical compliance with increased crosslinker concentration while swelling studies indicate greater swelling in the most compliant substrates. Human mesenchymal stem cells were then cultured on hydrogel substrates functionalized with fibronectin or the synthetic peptide sequence containing arganine-glycine-aspartic acid (RGD). Studies focusing on cell attachment and morphology were performed. It was found that the cell response was more pronounced with gels having a higher mechanical compliance: the cells attach better to stiffer gels and also start to spread earlier than on the softer hydrogel samples. Ligand choice also plays a role, where our findings show an increase in attachment and spreading on RGD functionalized substrates compared to fibronectin substrates. The effect of ligand choice and substrate compliance on differentiation is the focus of current investigations.

[1] A.J. Engler, S. Sen, H. Lee Sweeney and D.E. Discher, Cell, 126, 677-689 (2006)