Fig. 7.

Force generation during early matrix contraction. (A) Collagen matrices were seeded with 10⁶ (HCF and HTF), or 7 × 10⁶ HSF fibroblasts per ml, floated in serum-supplemented medium and transferred to the culture force monitor stage. Cell-free matrices were prepared as negative controls to determine the baseline for the strain. The force associated with matrix contraction was recorded every second for 24 h, and measurements obtained over 1 min were averaged into one value. The average force reached after 7 h after matrix preparation (plateau phase, calculated from 6 to 13 h) in cell-free collagen matrices (5 experiments, total number of measurements recorded n = 1204) was subtracted from the values reached by the cell-seeded matrices (HCF: 6 experiments, n = 2166; HTF 7 experiments, n = 2527; HSF 1 experiment, n = 121), and the resulting figures corrected for the cell number to obtain the average maximum force generated by 10⁶ cells for each cell type. The graph shows the mean force and SEM over 16 h after matrix preparation. (B) Intrinsic cellular force. The force value measured at plateau phase for each cell type (7–13 h after matrix preparation) was divided by the mean cell volume (see Materials and methods) to obtain the amount of force per cell volume or intrinsic cellular force (nanodyne/μm³). Shown is mean ± SEM for HCF and HTF and single value for HSF.