Abstract
The dependences of spreading and differentiation of stem cells plated on hydrogel and silicone gel substrates on the rigidity and porosity of the substrates have recently been a subject of some controversy. In experiments on human mesenchymal stem cells plated on soft, medium rigidity, and hard silicone gels we show that harder gels are more osteogenic, softer gels are more adipogenic, and cell spreading areas increase with the silicone gel substrate rigidity. The results of our study indicate that substrate rigidity induces some universal cellular responses independently of the porosity or topography of the substrate.
Highlights
The average areas of primary mouse keratinocytes and mouse embryonic fibroblasts (MEFs) cultured on the silicone gel substrates monotonically increased with the substrate elastic moduli, with differences in the cell areas between the three substrate rigidities being all significant for both cell types (Fig. S2A,B)
In agreement with the previous report[10], we found the phosphorylation level of focal adhesion kinase (FAK) to monotonically increase with the substrate rigidity for both keratinocytes and MEFs (Fig. S2C)
In all four types of assays, the dependence of the cellular functions on the substrate rigidity was qualitatively the same as for cells cultured on hydrogels and micropost arrays, suggesting that the effects of substrate rigidity on functions of plated cells are similar for all types of deformable substrates. These results demonstrate that substrate rigidity induces some universal cellular responses that are independent of porosity or topography of the substrate
Summary
The average areas of primary mouse keratinocytes and mouse embryonic fibroblasts (MEFs) cultured on the silicone gel substrates monotonically increased with the substrate elastic moduli, with differences in the cell areas between the three substrate rigidities being all significant for both cell types (Fig. S2A,B). The surfaces of silicone gel substrates used in our study have amino-reactive groups (Fig. S4), providing covalent binding of ECM proteins similar to the binding of ECM to the surfaces of hydrogels in refs 3 and 4 It is not completely clear, whether the ECM binding to the silicone gel surfaces used in refs 3 and 4 was covalent or passive, and as argued in both papers, cellular responses to the substrate rigidity are expected to depend on the details of binding of ECM to the substrate (see Supplementary Discussion)
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