Increased poly(dimethylsiloxane) stiffness improves viability and morphology of mouse fibroblast cells

We monitored the viability and morphology of mouse fibroblast cells cultured on PDMS substrates with different degrees of polymer stiffness. The stiffness was controlled by varying the ratio between base and crosslinker agent during mixing. Although the standard PDMS mixing ratio is 10: 1 (base to crosslinker; Young's modulus, E=580 kPa), we found that a PDMS substrate with a high stiffness (mixing ratio of 5: 1, E=1,000 kPa) was more favorable as a substrate for fibroblast cell growth. It is important to note that an extracellular matrix coating was not applied to the PDMS so that the effect of stiffness on cell growth could be studied in isolation. A stiffness reduction of 40% (from a mixing ratio of 5: 1 to 10: 1) produced a significant reduction in survival rate (viability was reduced by 15%), and viability worsened (was reduced by 45%) for a substrate stiffness of 280 kPa (a mixing ratio of 20: 1). The rate of spreading for the cells was measured to show that stiffer materials promoted more prolific fibroblast growth. These results provide PDMS stiffness guidelines for cell culture substrates.