Evaluation of BMP-2 tethered polyelectrolyte coatings on hydroxyapatite scaffolds in vivo

The goal of this in vivo study was to evaluate the osteoinductive and angio-inductive properties of a porous hydroxyapatite (HAp) scaffold with immobilized recombinant bone morphogenetic protein-2 (rhBMP-2) on the surface. It was hypothesized in this study that the use of a rhBMP-2 incorporated polyelectrolyte coating on the HAp scaffold would allow for controlled exposure of rhBMP-2 into the tissue and would provide a sound platform for tissue growth. The scaffolds were characterized for porosity and interconnectivity using pycnometry, scanning electron microscopy and micro-ct. These scaffolds were then divided into the following four groups: (a) HAp scaffold (n-HAp group), (b) rhBMP-2 physically adsorbed on HAp scaffold (HAp-BMP-2 Group), (c) polyelectrolyte coating on HAp scaffold without rhBMP-2 (HAp-PEI Scaffold Group), and (d) polyelectrolyte coating tethered with rhBMP-2 on HAp scaffold (HAp-PEI-BMP-2 Scaffold Group). Using 18 skeletally matured New Zealand white rabbits, these scaffolds were evaluated in a nonload bearing femoral condyle plug model. The negative controls for this study have defects that were left untreated and the positive controls have defects that were filled with autologous bone graft harvested from epsilateral iliac crest. Bone induction, vessel growth, and scaffold-bone contact were analyzed after 8-week implantation using micro-CT and histomorphometry. It was concluded from this study that the use of scaffold with an attached rhBMP-2 increased the vascularization around the implant when compared with the uncoated n-HAp scaffold, a necessary step of bone regeneration. The open-pore HAp scaffold was also concluded to provide a platform for tissue growth, drug loading, and tissue interaction.