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In the era of tissue engineering, the physiologic process of skin graft revascularization remains unclear, preventing the successful development of skin substitutes. Therefore, the authors developed a new in vivo model with which to visualize the process of engraftment and its microvascular architecture. The aim of this study was to specifically investigate the vascular transformations within the skin graft to gain applicable knowledge on how vascular processes during engraftment occur.Microsurgical preparation of the modified dorsal skinfold chamber including autologous skin grafting was performed in male C57BL/6J mice (n = 10). In addition, immunohistochemistry of angiogenic factors, endothelial cells, and pericytes, and corrosion casting were performed to further characterize the specific mechanisms.The graft exhibited capillary widening starting at day 3, resulting in the temporary formation of spherical protrusions at the graft capillary divisions starting in the center of the graft 24 to 48 hours after revascularization. Confocal microscopy showed the simultaneous expression of CD31 and desmin. Corrosion casting and evaluation by light microscopy and scanning electron microscopy showed the three-dimensional formation of capillaries in the wound bed that connected to the preexisting capillary loops of the skin graft.The authors were able to show for the first time a temporary angiogenic response within the capillaries of the skin graft. This most likely represents a reaction to reperfusion allowing the supply of proangiogenic factors to the hypoxic skin graft. The detection of an angiogenic response within the graft capillaries is for the first time made possible in the newly developed model and is therefore completely novel.

BACKGROUND: Models of skin graft revascularization are based mostly on histologic evaluations but lack the possibility of analyzing the vascular biology in vivo. The aim of the present study was therefore to develop an animal model that allows continuous monitoring of the microcirculation during skin graft healing. METHODS: Skin and subcutaneous tissue were removed from the back of dorsal skinfold chamber preparations in mice, leaving one layer of striated muscle and subcutaneous tissue as a wound bed (n = 5). A corresponding full-thickness skin graft was harvested from the groin and sutured into the defect in the back of the chamber. To study graft healing, repetitive intravital microscopy was performed during the first 10 days after engraftment. RESULTS: Capillary widening in the wound bed appeared at day 1 after grafting and increased until day 4. Capillary buds and sprouts first appeared at day 2. Blood filling of autochthonous graft capillaries occurred at day 3, resulting in almost complete restoration of the original skin microcirculation on day 5. This was achieved by interconnections between the microvasculature of the wound bed and the skin graft through a temporary angiogenic response. In principle, angiogenic blood vessel growth originated in the wound bed and was directed toward the graft. CONCLUSIONS: This new model allows for repetitive analysis of the microcirculation during skin graft healing. It provides ideal in vivo conditions to further delineate the exact mechanisms of blood vessel interconnection during the complex process of angiogenesis, and may also allow study of the vascularization of tissue-engineered skin substitutes.