Stretching Cells on PDMS Membranes

Once PDMS membranes were either directly coated with fibronectin or covalently attached to fibronectin-coated polyacrylamide/soft silicone gels, cells were seeded on the membrane and allowed to spread in the incubator for 0.5 h. Then, membranes were placed on the stretch system (Supplementary Fig. 1), consisting of a central loading post and an external ring. Vacuum was then applied through the space between the loading post and the external ring, thereby deforming and stretching the membrane. Cells spread on the membrane directly on top of the central loading post experienced an equibiaxial strain which depended on the vacuum pressure applied (Supplementary Fig. 1). The system was then mounted on the microscope stage. To modify osmolarity, cells were exposed to medium mixed with de-ionized water in which the concentrations of Ca²⁺ and Mg²⁺ had been corrected.