PREDICTIVE MODEL AND IN VITRO ASSAY OF WOUND HEALING

Wound contraction is a hallmark in the healing of full-thickness wounds. Compelling evidence suggests that myofibroblasts are responsible for the forces driving wound contraction. These forces are almost certainly "traction forces", they cytoplasmic motility forces which are transmitted to ECM fibers by undulating cell pseudopods transiently adhering to or anchoring around the fibers, which are under intensive study using in vitro assays based on cell-induced compaction of reconstituted type I collagen gels. There is great motivation for understanding the interplay between the complex biochemical, cellular, and biomechanical phenomena which conspire to result in wound contraction since it can be a beneficial or deleterious consequence of wound healing. If a validated predictive model of wound healing were available, one which accounted for the salient phenomena and provided a framework to accommodate the emerging understanding of the relationship between wound healing and inflammation, then a rationale basis for the design and application of pharmacologic modulators of cell behavior to augment or mitigate wound contraction, as appropriate for the nature of the wound being managed, would be available. Unfortunately, a predictive in vivo dermal wound healing model does not exist, nor is there an in vitro assay that mimics dermal wound healing and allows the interplay to be quantitatively manipulated and characterized in the context of such a model. The aim of this proposal is to lay the foundation for an in vivo model by: (1) developing and validating a similar model based on a continuum theory of cell/ECM dynamics and mechanics, using an in vitro assay of traction forces exerted by fibroblasts dispersed throughout a microsphere of type I collagen gel for testing the model, (2) measuring directly with a rheometer the net traction force in a fibroblast-populated gel to establish the functional relationship between cell concentration, fibril concentration, and the macroscopic traction stress term in the theory, (3) applying the model to a novel in vitro dermal wound healing and contraction assay wherein fibroblasts repopulate the core of the microsphere in response to a diffusing bioactive factor, whose effect on the fibroblast behavior has been characterized in an independent assay, (4) using these results, extending the model to characterize the contraction behavior of idealized in vivo wounds (including known and speculated regulatory mechanisms related to inflammation and angiogenesis) and the consequences of modulating different cell and matrix parameters as a means of assessing the rationale of new therapies.