Mechanical properties of lower limb dermis following static and cyclic compression

Lower extremity amputations and foot ulcers are complications associated with diabetes, and have been shown to affect diabetic African Americans (AA) three times as often as diabetic non-Hispanic Whites (NHW). Possible causes for the increased risk include ethnic differences in structure and function within the dermis of the lower extremity. Testing this hypothesis requires studying the mechanical properties of skin from different ethnic groups with and without the diagnosis of noninsulin-dependent diabetes. The purpose of this study was to develop a testing method to investigate changes in tensile mechanical properties resulting from static and cyclic compression of dermis harvested from patients undergoing lower extremity amputations. Full thickness dermal samples were obtained from 15 patients undergoing below-knee amputations. Sections of each sample were conditioned with a compressive static pressure (170 mmHg) or cyclic pressures (110-170 mmHg) for 4 hours to elicit collagen bundle remodeling. Skin samples were then tested in tension to obtain sub-plastic stress vs. strain mechanical behavior. Length of the stress-strain toe-region was examined to quantify the effect of collagen bundle remodeling. Toe-region mean lengths were 0.141±0.041, 0.146±0.034, and 0.164±0.064 strains for the control, cyclic, and statically compressed samples respectively (p>.05). These results suggest that the preconditioning regimes did not produce sufficient collagen remodeling to affect the tensile properties of full-thickness dermis. Future work will examine histology from each specimen to identify microstructural features associated with this trend.