Vascular Perfusion and Biointegration of a Large Volume Synthetic Pedicled Flap Scaffold
Patrick S. Cottler, Ph.D., Ethan J. White, B.S., Lisa S. Salopek, B.S., Angela Pineros-Fernandez, M.D., Christopher A. Campbell, M.D..
University of Virginia, Charlottesville, VA, USA.
PURPOSE: Cell culture and bioprinting have been used to simulate micro-environments that recapitulate body systems biology. However, the thickness of these constructs is limited to the diffusion gradient of nutrients required for cellular growth. The use of the body as a bioreactor to vascularize implanted three-dimensional constructs and infiltrate them with cells can provide larger constructs that could later be transposed as autologous tissue flaps. Biologic scaffolds have been used in this manner to produce larger three-dimensional constructs but degrade too quickly for durable reconstructive applications. Our goal is to determine if a synthetic three-dimensional construct can be vascularized by a pedicle in vivo and incur host cellular in-growth, and potentially used as a vascularized flap for reconstructive indications.
METHODS: Three-dimensional constructs of polycaprolactone (PCL), poly lactic-co-glycolic acid (PLGA), and polypropylene (PP) were formed into tubular cuffs (5mm in diameter, 10mm in length and 2mm wall thickness) and analyzed for porous area fraction from SEM images. The superficial epigastric pedicles were dissected and isolated bilaterally in 6 Sprague-Dawley rats, with constructs of each material individually placed around the pedicles (4 constructs for each material). At 12 weeks, the constructs were harvested, dissected free and isolated on the proximal superficial epigastric vessels. The constructs were examined grossly, then imaged with indocyanin green (ICG) fluorescence videography using the SPY Elite system to measure perfusion compared to soft tissue control. The constructs were then fixed, sectioned for histology and immunohistochemistry (IHC) to evaluate vascular in-growth and cellular invasion.
RESULTS: Polymer cuffs were successfully produced with pore area fractions of 60.8% for PCL, 66.7% for PLGA, and 17.7% for PP. At 12 weeks, all constructs demonstrated gross evidence of surrounding tissue adherence with a uniform carpet of microvascular response. ICG perfusion at 20 seconds of PCL constructs demonstrated 101-116% of soft tissue control for roughly 2/3 of construct surface area. PLGA constructs demonstrated 109-116% of control involving 1/2 to 3/4 of the surface area of the constructs and PP constructs showed 39-47% of control for 3 of the 4 constructs while 1 construct yielded 100%. All constructs but 2 of the PP constructs were completely saturated by 100 seconds. Cross-sectional H&E slides of the construct reveal mononuclear cells dispersed throughout the construct, with a separate surrounding rim of cells at the edge of the synthetic material, with evidence of vascular growth. IHC staining reveals vascular ingrowth emanating from the pedicle, with VEGF expressed diffusely through the constructs. Macrophage staining and fibroblast lineage staining demonstrate that these cells emanate from both the pedicle and surrounding soft tissue.
CONCLUSION: Synthetic scaffolds containing a vascular pedicle are permeated with nascent vascular networks and macrophage and fibroblast lineage cells in a soluble factor-dependent manner. Perfusion imaging demonstrated a significant portion of the synthetic construct was vascularized for all groups but polypropylene. By varying the synthetic material, porosity and the inclusion of strategic cell types into the construct, different tissue types can be produced for autologous flap transfer.
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