Single and Dual Growth Factor Delivery from Poly-E-caprolactone Scaffolds for Pre-Fabricated Bone Flap Engineering.

Abstract

Autografts are utilized to reconstruct large craniofacial bone defects; however, they result in donor site morbidity and defect geometry mismatch. Pre-fabricating a bone flap overcomes these drawbacks by integrating a patient specific scaffold with biologics, implanting it in the latissimus dorsi for a period of time and then transplanting it to the defect site as a partially remodeled construct. Polycaprolactone (PCL) is a biocompatible polymer that has mechanical properties suitable for bone tissue engineering. It must be integrated with biologics, however, to stimulate bone formation. The purpose of this work was to investigate bone regeneration using PCL and dual protein delivery. Bone morphogenetic protein-2 (BMP2) was adsorbed or conjugated onto a PCL scaffold in a clinically applicable setting (1 hour exposure at room temperature). Adsorbed BMP2 had a small burst release and was bioactive as indicated by C2C12 alkaline phosphatase expression. Interestingly, conjugated BMP2 had a sustained release but was not bioactive. When implanted subcutaneously, adsorbed BMP2 had increased bone volume (BV), elastic modulus, and ingrowth when compared to conjugation. Next, a collagen sponge was fabricated inside of a BMP2-adsorbed PCL scaffold to deliver vascular endothelial growth factor (VEGF). In addition, a modular PCL scaffold was developed in which the inner and outer modular portions were adsorbed with BMP2 and VEGF, respectively. In both systems, the VEGF was bioactive as indicated by increased endothelial cell proliferation. Dual delivery of BMP2+VEGF significantly increased BV from 4 to 8 weeks in an ectopic location, whereas, BMP2 alone did not. Finally, erythropoietin (EPO) and BMP2 were delivered from the outer and inner portions of the modular scaffold, respectively. The adsorbed EPO was bioactive as indicated by increased endothelial cell proliferation. At 4 weeks, dual EPO+BMP2 delivery significantly increased BV and ingrowth when compared to BMP2 alone. In conclusion, adsorbing BMP2 onto PCL may be optimal for clinical use. Delivering VEGF with BMP2 increases the bone regeneration rate from 4 to 8 weeks, and delivering EPO with BMP2 increases the BV at 4 weeks when compared to BMP2 alone, making multiple biologics delivery a promising method to increase the regenerated bone for pre-fabricated flaps.