Polyacrylamide Gels for Cell Substrates

Polyacrylamide gels (PAA) of different stiffness were prepared by cross-linking 40% poly-acrylamide and 2% bis-acrylamide solution, as described.19 (link) Protocols for substrate preparation and modulus values were adopted from a published work.20 Briefly, the gels were prepared between two glass coverslips, one coated with 3-APTMS (Sigma) and the other with octadecyl-trichlorosilane (Sigma-Aldrich). After gelation, the non-adherent plate was removed. The gel was coated with type I collagen (50 μg ml^–1) (Advanced Biomatrix) using sulfo-SANPAH based conjugation at 4 °C overnight.5 (link) The control glass coverslips were also coated with Type 1 collagen. Throughout our experiments, the gel thickness was controlled by controlling the volume of gel solution placed between the coverslips. Before cell seeding, any excess collagen was washed off and the gel was equilibrated with media for one hour.