Increasing Bioactivity of Cancellous Bone Allografts Using Growth Factor Delivery through a Polymer Coating

Bone grafts are incorporated in over 2 million orthopedic surgeries worldwide every year. (Janhangir) When a defect is large enough that the body cannot properly heal on its own, a bone graft is surgically implanted into the defect site. Allografts, though commonly used, show poor bioactivity and often require the incorporation of molecules such as growth factors to achieve significant bone formation in defect sites. This study used a degradable polymer, poly(lactide-co-glycolide) (PLGA), to coat allografts and load multiple growth factors to be released. Bone morphogenetic protein-2 (BMP-2) was physically encapsulated for extended release, while vascular endothelial growth factor (VEGF) was surface adsorbed to achieve a burst release. The antibiotic gentamicin was also tested in surface adsorption as an alternative application. Results showed a thin, continuous coating was able to extend throughout the entirety of the allograft while maintaining the native porosity of the allograft. Surface adsorption of VEGF and gentamicin both showed a burst release with the majority of the release occurring in the first 24 hours. Encapsulation of BMP-2 showed an extended release, with a smaller initial burst compared to surface adsorption. This combination shows ability to create short and long term kinetics similar to that of the natural healing process in bone. It was also shown that the volume of coating, and therefore release of the growth factors, was affected by a change in the concentration of the polymer. Results show a system with potential capability to increase bioactivity of allografts in bone healing, as well as possible mitigation of infection following surgery.