Induction of delayed wound healing by irradiation with optional mechanical compression in swine.

A chronic wound or non-healing wound is one that fails to heal for at least 30 days after injury. This study was designed to create delayed wound healing induced by irradiation and mechanical compression using silicone block. Two female pigs received a single fraction of 20 Gy with 6-MeV electrons to a 22 × 60 cm field on the dorsal body skin 7 weeks before experimentation. A 30 × 30 mm sized wounds were created with preservation of muscle fascia on the dorsum. In groups of six, wounds were designated to be control (C) or test areas of irradiation only (T0), irradiation with silicone blocks for 1 week (T1), irradiation with silicone blocks for 2 weeks (T2), and irradiation with silicone blocks for 3 weeks (T3). Wound contraction, bacterial culture, and histological analysis were performed at 1-week intervals for 4 weeks. Control wounds displayed complete re-epithelialization at Weeks 4; however, all experimental groups (T0, T1, T2, and T3 groups) showed necrosis and delayed healing at Week 4. The number of bacterial strains in control wounds differed significantly from values recorded for all experimental groups from Weeks 1-3 (p < 0.05). However, in comparing the various test wounds (T0, T1, T2, and T3 groups), the numbers of strains did not differ significantly from Weeks 1-4. In the histological analysis, the control wound showed a peak influx of acute and chronic inflammatory cell and diminished inflammation thereafter. However, all experimental groups showed no peak in inflammatory score and prolonged chronic inflammation. In conclusion, radiation exposure alone, which triggers intense inflammation and extensive recruitment of inflammatory cells, proved sufficient to prevent re-epithelialization of skin at 30 days. Insertion of silicone blocks had limited effects on promoting delayed wound healing. Consequently, we now recommend using irradiation alone to simulate delayed wound healing in an experimental setting.