The covalent attachment of adhesion molecules to silicone membranes for cell stretching applications

Strain devices with expandable polydimethylsiloxane (PDMS) culture membranes are frequently used to stretch cells in vitro, mimicking mechanically dynamic tissue environments. To immobilize cell-adhesive molecules to the otherwise non-adhesive PDMS substrate, hydrophobic, electrostatic and covalent surface coating procedures have been developed. The efficacy of different coating strategies to transmit stretches to cells however is poorly documented and has not been compared. We describe a novel and simple procedure to covalently bind extracellular matrix proteins to the surface of stretchable PDMS membranes. The method comprises PDMS oxygenation, silanization, and covalent protein cross-linking to the silane. We demonstrate improved attachment (∼2-fold), spreading (∼2.5-fold) and proliferation (∼1.2-fold) of fibroblasts to our new coating over established coating procedures. Further, we compared the efficiency of different PDMS coating techniques to transmit stretches. After 15% stretch, the number of maximally (15 ± 5%) stretched cells on our PDMS surface coating was ∼7-fold higher compared with alternative coating protocols. Hence, covalent linkage of adhesive molecules is superior to non-covalent methods in providing a coating that resists large deformations and that fully transmit this stretch to cultured cells.