Expansion potential of skin grafts with alternating slit based auxetic incisions

Abstract

Due to a dearth of skin substitutes, severe burn injuries result in millions of deaths every year. Split thickness skin grafting, which involves the projection of a parallel incision pattern on a small section of excised healthy skin, is commonly used to improve the expansion and cover a large burn site. The true expansion capacity of such grafts is currently limited to less than three times, which is insufficient for treating severe burn damage. In this work, we investigated the expansion potential of skin grafts using alternating slit based auxetic incision designs, with the hypothesis that this would lead to greater expansion than standard graft models. Nine two-layer skin graft models were developed with varying slit lengths and spacing, and the Poisson's ratio, meshing ratios, and induced stresses were estimated under uniaxial and biaxial load tests. For up to 100% applied strains, the Poisson's ratio increased with increase in the unit cell spacing. For the biaxial tests, equal lengths of the slits of the pattern, with a high unit cell spacing, was found to lead to a greater skin cover and lower stress localization in the graft models. However, when the graft models were tested up to the ultimate tensile strength of skin, a low unit cell spacing was found to be more desirable. Maximum uniaxial and biaxial meshing ratios, approximately 13 and 5 times higher than that of traditional grafts respectively, were quantified. Such expansion potentials and stress estimations with skin grafts have not been reported previously and would be indispensable for ground breaking advances in burn surgery research.