Development of novel hierarchical designs for skin graft simulants with high expansion potential.

Skin graft designs play an essential role in healing severe burn injuries. Split-thickness skin grafting (STSG) is one of the commonly used techniques for treating large burn injuries. In STSG, parallel cuts are projected onto a small portion of excised healthy skin for expansion and covering a larger burn area. To date, expansions reported for STSG are very low and insufficient to cover large burn areas. In this work, novel traditional and auxetic hierarchical cuts were designed on skin graft simulants, which were mechanically tested to study their expansion potential. Additive manufacturing and a two-part polymeric material were employed to fabricate the skin graft simulants. The nonlinear mechanical behavior of the hierarchical skin graft simulants was characterized using hyperelastic models. The effective Poisson's ratio, meshing ratios, and induced stresses in first and second-order hierarchical cut patterns were estimated across all skin graft simulants for up to 300% strain. Also, Statistical analysis was performed to calculate the significance among the groups. From the analysis, the skin graft simulants with second-order auxetic incision patterns were found to exhibit the lowest induced stresses and maximum expansion of approximately four times, at 300% strain. To date, traditional skin grafts have only been able to achieve up to three times expansion. Therefore, the expansions realized with the novel hierarchical skin graft simulants is unprecedented, with the potential to generate ground-breaking advances in burn injury treatment.