  Contraction assay based on surface measurement have been widely used to
evaluate cell contractility in 3D models. This method is straightforward and
requires no specific equipment, but it does not provide quantitative data about
contraction forces generated by cells. We expanded this method with a new
biomechanical model, based on the work-energy theorem, to provide
non-destructive longitudinal monitoring of contraction forces generated by
cells in 3D.We applied this method on hydrogels seeded with either fibroblasts
or osteoblasts. Hydrogel mechanical characteristics were modulated to enhance
(condition HCA$_{High}$: hydrogel contraction assay high contraction) or limit
(condition HCA$_{Low}$: hydrogel contraction assay low contraction) cell
contractile behaviors. Macroscopic measures were further correlated with cell
contractile behavior and descriptive analysis of their physiology in response
to different mechanical environments. Fibroblasts and osteoblasts contracted
their matrix up to 47% and 77% respectively. Contraction stress peaked at day 5
with 1.1 10$^{-14}$Pa for fibroblasts and 3.5 10$^{-14}$Pa for osteoblasts,
which correlated with cell attachment and spreading. Negligible contraction was
seen in HCA$_{Low}$. Both fibroblasts and osteoblasts expressed $\alpha$-SMA
contractile fibers in HCA$_{High}$ and HCA$_{Low}$. Failure to contract
HCA$_{Low}$ was attributed to increased cross-linking and resistance to
proteolytic degradation of the hydrogel.
