108. Integration of Biologic Matrices in Wounds With Avascular Structures

PURPOSE: Soft tissue defects with exposed critical structures usually require reconstruction with well-vascularized tissues, the gold standard being flaps. Yet, these procedures result in additional scarring and functional loss. Biologic wound matrices have become an important part of wound reconstruction, however, given their lack of blood supply and dependence on nutrients from the wound bed, they may not be as reliable and durable as flaps. There is paucity of direct, comparative clinical data comparing wound matrices with conventional tissue transfer, especially in wound beds with poorly vascularized structures. We propose a study that aims to evaluate the ability of three commercially available biologics from different sources to integrate over an avascular structure, and assess where their viability falls compared to skin grafts and free-flaps. METHODS: We created 20x20 mm full-thickness wounds on the dorsum of Lewis rats and secured 1-mm-thick silicone sheets sized one-fourth of the wound’s surface area. A custom-made 3D-printed wound contraction frame was placed around the wound bed to isolate the wound environment. The following groups were assessed: (1) split-thickness skin graft, (2) free-flap anastomosed to neck vessels, 3) bovine tendon collagen and glycosaminoglycan (Integra Matrix Wound Dressing single-layer), (4) porcine urinary bladder matrix (Cytal Wound Matrix 1-Layer), (5) acellularized human skin (AlloDerm™ Regenerative Tissue Matrix) were used to completely cover the defects. The rats were followed for 4 weeks with weekly photography. At the 4-week time-point, tissue viability was assessed with scratch and sheer force testing, and samples were retrieved for histologic analysis with H&E, Trichrome, and immunofluorescence staining. RESULTS: Total wound sizes were constant throughout the duration of the experiment in all groups. Gradual necrosis of the portion of the skin graft and wound matrices corresponding to the silicone sheet was observed with exposure of the silicone sheet at the 4-week timepoint. At the 4-week endpoint, near complete necrosis of the portion of Cytal and Integra covering the silicone was observed (mean viable percent over silicone=8.2%, SD=8.8%; mean=15.4%, SD=7.7%, respectively). Alloderm showed intact integrity but no viability over the silicone sheet (mean=0%, SD=0%). All matrices performed worse than skin grafts and free-flaps, which achieved 93.1% (SD=4.2%) and 100% (SD=0%) tissue coverage and viability over the silicone sheet (p<0.05). Upon sheer force, Cytal and Integra necrotic portions corresponding to the silicone sheet were sloughed off, while Alloderm, free-flap, and skin graft withstood the test. Scratching the remnant tissue of Cytal and Integra over the silicone yielded visible bleeding. The skin graft and free-flap group manifested visible bleeding upon scratching any area of the wound. Histology showed mostly no vascularity of all matrices over the silicone sheet, except at the silicone edges. CONCLUSION: Biological wound matrices did not survive over an avascular structure as towel as free-flaps or skin grafts. Our model’s affordability, reproducibility, and modifiability allows us to further test the survival of those or novel matrices under different controlled conditions such as a closed wet wound design or with adjunctive therapies, such as cell therapy.