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B16.03 - The Development and Characterization of a Biomimetic Neovascularization-Inducing Cortical Bone Scaffold 
December 4, 2014   2:00pm - 2:15pm

Bone loss and skeletal deficiencies due to disease, traumatic injury, and abnormal development are major problems worldwide. In the U.S. alone, over 3 million orthopaedic procedures are performed every year; approximately 500,000 of these are bone-grafting procedures. Autograft, the gold standard treatment, requires an invasive second surgery and can lead to donor site morbidity. Allografts (bone donated from cadaver) are another popular option, but they can illicit an unfavorable immune response and exhibit a 30-50% failure rate over a period of 10 years. With the drawbacks witnessed from biological grafts, there has been a shift in paradigm towards tissue engineered (TE) bone grafts. The limitless supply and ability to utilize TE scaffolds as carriers for stem cells or growth factors delivery make them advantageous, but the lack of vascularization and nutrients to the graft implant leads to the graft’s failure in vivo. Current directions to enhance vascularization in bone regeneration are largely aimed at enhancing early vascular support using pre-vascaularization of tissue-engineered constructs. Bone vascularization is housed within mineralized collagenous tubes called osteons that are fused together to form cortical bone. This study focuses on the development of fabricated osteons using nanoscale fabrication techniques and promoting early angiogenesis within the biomimetic osteonic (haversian) canals. We fabricated the biomimetic osteons by electrospinning poly-l-lactic acid (PLLA) with 10% gelatin (from bovine skin) and poly-d-lactic acid (PDLA) nanofibers onto a rotating polyethylene oxide (PEO) and PLLA twist until an approximate scaffold diameter of 500μm was reached. PEO is used because it is extremely water-soluble. The electrospun tubes were crosslinked with the FDA approved enzymatic crosslinking agent Transglutaminase (mTG) to increase strength and prevent gelatin leaching. After crosslinking, the inner twist was dissolved out leaving behind a scaffold mimicking the osteonic structure. Human umbilical vein endothelial cells (HUVECs) were seeded inside the hollow scaffolds and evaluated over a 28-day span. SEM images of the fabricated osteon yielded an average inner diameter of 0.495mm±44μm. Actin/DAPI stain exhibited circumferential cellular proliferation in confocal microscopy z-stack images. Additionally, preliminary SEM results demonstrated the presence of new ECM indicating the beginning stages of guided neovascularization. Ongoing studies will further characterize the vasculature lumen development within the osteon scaffold over an 8-week time period using a variety of techniques including immunofluorescence staining for CD31 and VE-Cadherin and qPCR assay for expression of endothelial genes such as collagen type 1, elastin, vascular endothelial growth factor type A, and angiopoietin 1. Our ultimate goal is to develop a TE pre-vascularized full-thickness and structurally relevant bone graft for large bone defects.

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