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Vascular Perfusion and the Regenerative Response to Acellular Dermal Matrix
Joani M. Christensen, BA, John Pang, BS, Kakali Sarkar, PhD, Saami Khalifian, BS, Evan R. Langdale, BS, Karim Sarhane, MD, Damon S. Cooney, MD, PhD, Gerald Brandacher, MD, Stephen M. Belkoff, PhD, Justin M. Sacks, MD.
Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Human acellular dermal matrix (ADM) offers mechanical strength while being repopulated by both host cells and connective tissue. ADM is used in breast reconstruction to facilitate submuscular implant placement, allowing improved lower pole expansion and soft-tissue reinforcement. Cellular repopulation and revascularization are central to tissue integration, but the physiologic effect of placement of the ADM relative to muscle is unknown. We hypothesized that optimized placement of ADM relative to muscle in a small animal model would augment regenerative characteristics including revascularization and tensile strength.
A 2cm diameter hemispherical silicone implant was placed under the latissimus dorsi muscle of Lewis rats (n=40), creating a gap between the cut muscle edge and the midline muscular insertion. In half of the rats, ADM was placed as an inlay to bridge the gap. In the other half, ADM was placed as an overlay, with 0.5cm overlap between ADM and muscle edge on all sides. Half of the animals in each group were sacrificed on POD7, the remaining on POD28. Before sacrifice, vascular perfusion was assessed using indocyanine green fluorescent laser angiography (ICG-FLA). Fluorescence intensities of a region of interest (ROI) at the ADM interface were divided by intensity of a control ROI over local native musculature. Tissue from the interface zone was then harvested for mechanical strength testing (failure load normalized to specimen width) using a hydraulic materials testing device, angiogenesis gene expression analysis using a PCR array, and hematoxylin and eosin staining of paraffin embedded tissue sections.
ICG-FLA revealed a trend toward increased normalized fluorescence intensity of the interface region of the overlay group compared to the inlay group on POD7 (0.61 vs 0.51, respectively; p=0.17). At the POD7 and POD28 time points, there was a trend toward higher failure load at the overlay interface as compared to the inlay interface (POD7 0.39N vs. 0.28N, respectively; and POD28 0.58N vs. 0.49N, respectively). Gene expression analysis on POD7 showed expression of CXCL1, CXCL2, IFNG, and MMP3 > 2 fold higher than in the unoperated contralateral control in both inlay and overlay groups. Moreover, CXCL1, CXCL2, CCL2, EDN1, IL1b, IL6, TGFBR1 and MMP9 expression levels were significantly increased in the overlay group on POD28 compared to control. Expression was also upregulated in the inlay group at POD 28, but was not statistically significant. Decreased expression of F2 and FGF1 was seen in both inlay and overlay groups on POD7 and POD28. Hematoxylin and eosin staining revealed increased vascular structures in both groups from the POD28 time point compared to POD7 (8.4 vs. 6.7/hpf, respectively).
Early revascularization and interface strength may be improved when ADM has closer proximity to vascularized muscle. Vascularity of ADM increased when used as both an inlay and overlay. In addition, a significant upregulation of genes involved in angiogenesis including CXCL1, CXCL2, CCL2, EDN1, IL1b, IL6, TGFBR1 and MMP9 was observed in the overlay group suggesting proximity of vascularized tissue improved tissue integration. Further research is needed to explore revascularization for ADM tissue integration and soft-tissue reinforcement.
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