005 The Biomechanical Behavior of Scar Tissue and Uninjured Skin in a Porcine Model

Abstract

To investigate changes in the mechanical properties of skin with injury, tissue was evaluated 70 days following full thickness wounding in juvenile female Yorkshire pigs (N = 14). Samples were taken in the axial (cranial-caudal) and transverse (dorsal-ventral) directions, for both scar tissue and uninjured skin. The samples were evaluated mechanically in vitro using a protocol of stress relaxation followed by tensile failure, in an INSTRON universal test machine. Specimens were subjected to a 10% elongation and held for a 4-min isometric period, after which they were returned to the original length and failed in tension. Axial normal skin exhibited a smaller force at 10% elongation (−58%, p = 0.002), and higher failure load (p = 0.027) and displacement (p = 0.028) than transverse. Scarring reduced the failure strength on average by 60% in the axial and 65% in the transverse directions (p < 0.001), with large decreases (>50%) in displacement at failure in both directions (p < 0.001). Elongation of 10% produced a larger force in axial scars (p < 0.001) than their normal counterparts, indicating a reduction in small-displacement compliance. Axial scars exhibited greater failure strength (p = 0.009) than transverse scars, yet no significant differences were observed in elongation to failure or load at 10% elongation. These results indicate that normal skin exhibits higher compliance and failure strength in the axial direction. Following injury, the strength and compliance of the tissue are greatly reduced, and the strong compliance directionality originally observed, is lost. Therefore it appears that the healing response leads to increases in tissue stiffness, such that small displacements result in larger tissue loads. This is further complicated by the reduced ability of the scar to resist failure. Taken together, these findings illustrate the compounding negative effects of scar on tissue integrity and function. Acknowledgments: Alberta Ingenuity Fund, CIHR and NSERC