Two-Step attached contraction model
There are different culture models to study the ability of fibroblasts to re-organize and contract in collagen matrices in vitro.
In the floating contraction model, a freshly polymerized collagen matrix containing cells and detached from the culture dish and left free in the culture medium. The contraction is therefore in the absence of external mechanical load and without appearance of stress fibers in the cells.
In the model with attached matrix, a polymerized collagen matrix containing cells remains attached to the culture dish during contraction. Mechanical tension develops during contraction and stress fibers appear.
The two-step model combines an initial contraction period of the attached matrix leading to a mechanical load, followed by the release of the matrices, resulting in additional mechanical unloading and contraction as the mechanical stress dissipates.
The signaling mechanisms used by fibroblasts to regulate contraction of the collagen matrix depend on whether the cells are mechanically loaded or unloaded at the time of initiation of the contraction or growth factor used to initiate contraction. For example, fibroblast stimulation by lysophosphatidic acid (LPA) but not by platelet-derived growth factor (PDGF) causes robust force generation in restricted matrices, whereas LPA and PDGF stimulate both contraction of the floating matrix.