The compressive, shear, biochemical, and histological characteristics of diabetic and non-diabetic plantar skin are minimally different

Diabetes is associated with lower limb co-morbidities, including ulceration and subsequent amputation. As a systemic disease, diabetes affects the microstructure of soft tissues, and material microstructural changes are known to affect the macroscale mechanics. However, the associations between diabetes-related disruptions to essential microstructural components and mechanical changes in plantar skin with diabetes has not been thoroughly characterized. Plantar skin specimens were collected from four diabetic and eight non-diabetic donors at six plantar locations (hallux; first, third, and fifth metatarsals; lateral midfoot; calcaneus) from matched pairs. Mechanical testing was performed on fresh frozen specimens from one foot, and histomorphological measurement and biochemical quantification were performed on specimens from the other foot. Mechanical (compressive and shear moduli and viscoelastic slopes) and biochemical/histological (total quantity of collagen and elastin; dermal and epidermal thickness) parameters were correlated using linear mixed effects regression. There were no significant differences by disease state. Skin thicknesses were positively correlated with initial compression modulus and all three shear moduli. The final compressive modulus was significantly lower at the third metatarsal than the fifth metatarsal, lateral midfoot, and calcaneus, while the final shear modulus was significantly higher at the calcaneus than at the hallux, first, and third metatarsals. Epidermal thickness was significantly higher at the calcaneus compared to all other locations. While differences were not significant by disease state, the strong differences by locations and significant but weak correlations between skin thickness and mechanics can inform future research to understand the mechanism of ulcer formation in the diabetic foot.