Our results demonstrate that stretch-induced cell and SF alignment are highly dependent on the mechanical properties of the collagen matrix upon which cells are cultured. Cyclic stretch promoted alignment parallel to the direction of stretch in cells with attenuated contractility caused by adhesion to a soft collagen gel, as judged by the relatively few SFs relative to that in the same cell type on collagen-coated silicone rubber. This is consistent with previous studies performed with cells on fibronectin-coated silicone rubber showing that stretching promotes SF alignment parallel to the direction of stretch when cell contractility is attenuated with small molecule inhibitors of Rho-kinase or MLCK (Kaunas 2005, Lee 2010). This is in stark contrast to the perpendicular alignment observed when cell contractility is at normal levels for cells on silicone rubber coated with collagen or fibronectin (Kaunas 2005). In the case of a step stretch, cell and SF alignment was only observed on soft collagen gels, but not on silicone rubber coated with collagen. Our results provide evidence that the parallel alignment on soft gels is due to both anisotropic mechanical properties as well as a direct response by the cells to a stretch stimulus.
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