Fig. 3

Characterization of 3T3 cell spreading on collagen I-coated gels. a Cartoon representing the three ways to conjugate collagen I to viscoelastic PAA gels. Adhesion proteins are crosslinked to the elastic part of the gel by adding NHS during the polymerization of the PAA network. Collagen I is crosslinked to both forms of PAA in the gel by sulfoSANPAH treatment. Collagen I is conjugated to the viscous part of the gel by adding NHS during the polymerization of the linear PAA. b Bright field images of 3T3 cells after 24 h of spreading on gels with G’ = 5 kPa and variable G”, coated with 50 µg/ml collagen I. Scale bar = 50 µm. c Average projected cell area of 3T3 fibroblasts after 24 h (right) on gels functionalized with collagen I on the elastic part of the gel (left) or on the elastic and the viscous part of the gel (right). Sample size: NHS gels 0 Pa n = 179 cells, 200 Pa n = 185 cells, 500 Pa n = 187 cells; sulfoSANPAH gels: 0 Pa n = 314 cells, 200 Pa n = 314 cells, 500 Pa n = 315 cells. ***Statistically significant difference with a p-value of <0.01, as calculated by non-parametric Tukey's tests; “ns” indicates no statistical difference