BMP-2, PDGF-BB, and bone marrow mesenchymal cells in a macroporous β-TCP scaffold for critical-size bone defect repair in rats

The aim of this work was to study the bone repair induced by bone morphogenetic protein-2 (BMP-2), rat mesenchymal stem cells (rMSCs), and platelet-derived growth factor (PDGF-BB) incorporated in a macroporous beta-tricalcium phosphate (beta-TCP) system fabricated by robocasting, and to identify the most beneficial combination in a critical rat calvaria defect. BMP-2 was formulated in microspheres to provide a prolonged, local concentration, whereas PDGF-BB, which acts during the initial stage of defect repair, was incorporated in a thin layer of crosslinked alginate. Approximately 80% of PDGF-BB and 90% of BMP-2 were released into the defect during the first 2 d and 3 weeks, respectively. Histological analyses indicated a minor synergistic effect in the BMP-2-MSC groups. In contrast, significant antagonism was found with combined BMP-2 and PDGF-BB defect treatment. The high-grade repair induced by BMP-2 rules out any advantage from combining BMP-2 with PDGF-BB or MSCs, at least with this scaffold and defect model.