355 Establishing Ovine Model of Burn Wounds Grafted with Cadaver Skin

Abstract

Shortage in autograft skin to cover burn wounds require a frequent use of cadaver skin as a temporary cover. Cadaver skin graft prevents infection and dehydration and prepares the wound bed for subsequent skin autograft or application of autologous tissue engineered skin constructs. The aim of this study was to establish an ovine model of burn wound healing using ovine cadaver skin. Quality and efficacy of fresh and frozen cadaver skins were evaluated comparing to skin autograph. Cadaver skin samples were harvested from sheep used for different studies at necropsy. The cadaver skin preparation process consisted of 4 steps: preparation for recovery by wool shaving and applying primary disinfection, collection, disinfection, and cryopreservation. First, to fully characterize fresh and frozen cadaver skin, the harvested skin was evaluated based on microbial screening, skin thickness, viability, and cell proliferation in in vitrocondition. The froze skin was evaluated after 10 and 40 days of freezing. Then we compared acceptance/rejection of autograft, freshly prepared and frozen cadaver skins overlaid onto burn ovine wounds. Full thickness skin burns (5X5cm) were induced in sheep dorsum. After 24 hrs, burned skins were excised and wounds were allocated to following groups: 1) Fresh ovine cadaver skin, 2) Frozen cadaver skin, 3) Autograft, 4) No cover. Pictorial record and skin biopsies were collected 7, 14 and 20 days after grafting cadaver skin. Prepared cadaver (fresh & frozen) skins were negative for bacterial growth. Thethickness was comparable between the freshly prepared and frozen skins for 10 or 40 days. Significant reduction in skin viability was detected in frozen skin after freezing for 40 days. Histological analysis of burn wounds biopsies showed that skin autograft maintains normal skin structure at different time points. However, fresh cadaver skin graft showed signs (vacuoles in epidermis) of rejection starting from day 7 as evidenced by microscopic analysis. At day 14, the epidermis was mostly rejected, and the rejection was completed by day 20. Histologically, signs of immunoreaction and presence of many immune cells were noted. Frozen Cadaver skin followed the same pattern of fresh cadaver skin rejection rate. Viability of fresh frozen cadaver skin before grafting was significantly higher vs. frozen (40 days). However, on average both fresh or frozen ovine cadaver skins were rejected within 8.5 days that mimics rejection time in humans (~8.4 days), suggesting that ovine model of burn wound grafted with cadaver skin can successfully be used in burn wound research mimicking clinical scenario. Establishing a clinically relevant ovine model for burn wounds grafted with cadaver skin is a potential contribution to the burn research.