A novel implantable collagen gel assay for fibroblast traction and proliferation during wound healing

Background. A novel implantable assay for studying cellular behavior in the wound environment was developed. The assay is unique in that it combines the more quantitative nature of in vitro assays with the greater physiological relevance of in vivo wound healing models. Materials and methods. Cells were seeded in a physiologically relevant biological matrix, a collagen gel, contained within a semipermeable tube, and then exposed to soluble factors of the wound environment at different stages of the wound healing response. Gels were harvested at prescribed time points, and cell proliferation rates and gel compaction were measured. These data were combined with our theory for cell-matrix mechanical interactions to estimate the cell traction exerted by the cells leading to gel compaction. Cell morphology and α-smooth muscle actin expression were also characterized. Results. The proliferation of and traction exerted by fibroblasts exposed to the soluble wound environment were different from those in similar collagen gels maintained in culture in complete medium. Proliferation and traction also varied over the course of the wound healing response. Traction was higher and proliferation lower in day 1-5 wounds compared to day 7-11 wounds. Recovered cells no longer stained for α-smooth muscle actin, in contrast to cells maintained in culture. Conclusions. Changes in the soluble wound environment that occur as the wound healing response proceeds alter fibroblast traction and migration. We have developed a new assay that employs a physiologically relevant biological matrix and allows the effects of the dynamic soluble wound environment on cellular traction, proliferation, and other phenomena such as protein expression to be quantified.