Fig. 2.

Stress relaxation tests with various materials commonly used for cell culture reveal that only fibrin and collagen gels exhibit strain-enhanced stress relaxation. (A) Stress relaxation tests at different strains for fibrin. (B) Isochronal display of elastic modulus for fibrin from stress relaxation tests of different strains. Data are shown as mean ± SD; n = 5. (C–E) Stress relaxation tests at different strains for polyacrylamide, agarose, and reconstituted basement membrane (rBM) matrix. Insets are all SEM images for each gel. (Scale bar: 1 µm.) (F) Normalized time constants of stress relaxation as a function of the normalized strain for the indicated materials. Strains were normalized by the strain at which the maximum of shear storage modulus (G′_max) is measured in amplitude sweep, and time is normalized by the time constant for stress relaxation at low strains imposed for each material (Figs. S5 and S6).