Plastic Surgery Research Council
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PSRC 60th Annual Meeting
Program and Abstracts

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Tissue Engineered, 3D Collagen Microsphere Scaffold (MSS) Expedites Cellular Invasion and Neovascularization
peipei zhang, M.D Ph.D, Ope Asanbe, M.D, Wilmina Landford, M.D, Adam Jacoby, B.A, Rachel Hooper, M.D, Abraham Stroock, Ph.D, Jason Spector, M.D FACS.
Weill Cornell Medical College, new york, NY, USA.

PURPOSE:Contemporary dermal substitutes are avascular and prone to high failure rates secondary to failure of incorporation or infection, especially when applied in complex wound beds, such as those previously irradiated or those with exposed hardware, bone or tendon. In order to overcome these shortcomings, we designed a novel hydrogel scaffold to guide and optimize cellular invasion and neovascularization, via the use of regularly spaced interfaces of differential collagen densities.
METHODS:Utilizing Kepler’s conjecture of sphere packing, which states that the arrangement of spheres in a 3 dimensional space has a density of 74%, we fabricated 7 mm diameter microsphere scaffolds (MSS) with a regular arrangement of density gradients. 1%, type I collagen microspheres were manufactured via a water-in-oil emulsion technique and their morphology was confirmed via scanning electron microscopy (SEM). MSS were fabricated by encasing higher density, 1% collagen microspheres into lower density, 0.3% collagen bulk so that 3/4 of the scaffold’s volume was comprised of microspheres and 1/4 of bulk collagen. MSS underwent thermal gelation at 37°C for 1 hour. Non-microsphere-containing 1% or 0.3% collagen scaffolds were fabricated as controls. Additionally, 7mm diameter Integra™ disks served as controls. All scaffolds were implanted subcutaneously in the dorsa of 8 week old WT C57bl/6 mice and harvested for histological and immunohistological analysis after 7, 14 or 28 days of implantation. The numbers of invading cells per unit area were determined.
RESULTS: SEM revealed the fabrication of smoothly contoured collagen microspheres, ranging 50 to 150 µm in diameter, with variable small lumps and minor irregularities. After 7, 14 and 28 days, fluorescent microscopy revealed MSS with robust cellular invasion spanning the scaffold depth. Comparatively, cells sporadically invaded 0.3% collagen scaffolds and failed to invade 1% collagen scaffolds altogether, remaining confined to the scaffold periphery. The number of cells in unit area was significantly higher in MSS samples (7d 6.767±3.032;14d 10.367±3.964) than those in 1% collagen scaffold samples (7d 2.829±0.934, p<0.01; 14d 5.52.938, p<0.01) and 0.3% collagen scaffold samples (7d 2.4±0.92, p<0.01; 14d 6.675±2.118, p<0.05). There was no difference in the number of invading cells when MSS was compared to Integra™. Immunohistochemical analysis identified CD31 expressing endothelial cells within MSS even after 7 days of implantation, with continued proliferation after 14 and 28 days of implantation, indicative of invading endothelial precursors and angiogenesis.
CONCLUSION:We successfully accelerated cellular invasion and neovascularization by enhancing mechanical and spatial cues of MSS through the regular arrangement of collagen density gradients. Our innovative, tissue engineered scaffolds are at least as effective as Integra™ and because of their relatively simple architecture, may become a cheap and easy to use next generation dermal replacement product.


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