Materials Science

Cell Versus Gel

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Science  08 Jun 2012:
Vol. 336, Issue 6086, pp. 1213
DOI: 10.1126/science.336.6086.1213-b

The physical properties of a substrate are known to affect the fate of stem cells by influencing whether they spread out and remain potent, or whether they undergo differentiation. In vivo, for example, human epidermal stem cells can adhere to the extracellular matrix (ECM), which regulates the differentiation depending on which signaling molecules are present. Trappmann et al. show that this picture needs to be expanded to include not just the substrate stiffness but the way in which the cells interact with and alter the underlying material. They prepared polydimethylsiloxane (PDMS) substrates with varying stiffness to which collagen-I was directly coupled to avoid issues of ECM remodeling. For both epidermal cells and human mesenchymal cells, the stiffness did not affect the cell spreading or differentiation. However, this was not the case for cells seeded on collagen-I attached to polyacrylamide (PAAm) hydrogels. For very soft gels, cells could not form stable focal adhesions, leading to differentiation. The authors noted that for the PAAm hydrogels, changes in stiffness correlated with changes in porosity, which in turn affected the density of the attached collagen-I. By varying either the strength of the collagen-I attachment at a fixed density, or the density with a fixed underlying substrate stiffness, they confirmed that the level of feedback between the gel properties and the adhered cells strongly affected cell fate.

Nat. Mater. 11, 10.1038/NMAT3339 (2012).

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