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Despite profound expertise and advanced surgical techniques, ischemia-induced complications ranging from wound breakdown to extensive tissue necrosis are still occurring, particularly in reconstructive flap surgery. Multiple experimental flap models have been developed to analyze underlying causes and mechanisms and to investigate treatment strategies to prevent ischemic complications. The limiting factor of most models is the lacking possibility to directly and repetitively visualize microvascular architecture and hemodynamics. The goal of the protocol was to present a well-established mouse model affiliating these before mentioned lacking elements. Harder et al. have developed a model of a musculocutaneous flap with a random perfusion pattern that undergoes acute persistent ischemia and results in ~50% necrosis after 10 days if kept untreated. With the aid of intravital epi-fluorescence microscopy, this chamber model allows repetitive visualization of morphology and hemodynamics in different regions of interest over time. Associated processes such as apoptosis, inflammation, microvascular leakage and angiogenesis can be investigated and correlated to immunohistochemical and molecular protein assays. To date, the model has proven feasibility and reproducibility in several published experimental studies investigating the effect of pre-, peri-and postconditioning of ischemically challenged tissue.

Burn wound progression (BWP) leads to vertical and horizontal injury extension. The “burn comb model” is commonly used, in which a full-thickness burn with intercalated unburned interspaces is induced. We aimed to establish an injury progressing to the intermediate dermis, allowing repeated wound evaluation. Furthermore, we present a new dorsal frame that enables topical drug application. 8 burn field and 6 interspaces were induced on each of 17 rats’ dorsa with a 10-second burn comb application. A developed 8-panel aluminum frame was sutured onto 12 animals and combined with an Elizabethan collar. Over 14 days, macroscopic & histologic wound assessment and Laser-Speckle-Contrast-Imaging (LSCI) were performed besides evaluation of frame durability. The 10-second group was compared to 9 animals injured with a full-thickness 60-second model. Frame durability was sufficient up to day 4 with 8 of 12 frames (67%) still mounted. The 60-second burn led to an increased extent of interspace necrosis (p=0.002). The extent of necrosis increased between days 1 and 2 (p=0.001), following the 10-second burn (24%±SEM 8% to 40%±SEM 6%) and the 60-second burn (57%±SEM 6% to 76%±SEM 4%). Interspace LSCI perfusion was higher than burn field perfusion. It earlier reached baseline levels in the 10-second group (on day 1: 142%±SEM 9% vs. 60%±SEM 5%; p<0.001). Within day 1, the 10-second burn showed histological progression to the intermediate dermis, both in interspaces and burn fields. This burn comb model with its newly developed fixed dorsal frame allows investigation of topical agents to treat BWP in partial-thickness burns.

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