A Bioactive Coating Enhances Bone Allografts in Rat Models of Bone Formation and Critical Defect Repair

ABSTRACT Bone allografts are inferior to autografts for the repair of critical‐sized defects. Prior studies have suggested that bone morphogenetic protein‐2 (BMP‐2) can be combined with allografts to produce superior healing. We created a bioactive coating on bone allografts using polycondensed deoxyribose isobutyrate ester (PDIB) polymer to deliver BMP‐2 ± the bisphosphonate zoledronic acid (ZA) and tested its ability to enhance the functional utility of allografts in preclinical Wistar rat models. One ex vivo and two in vivo proof‐of‐concept studies were performed. First, PDIB was shown to be able to coat bone grafts (BGs). Second, PDIB was used to coat structural allogenic corticocancellous BG with BMP‐2 ± ZA ± hydroxyapatite (HA) microparticles and compared with PDIB‐coated grafts in a rat muscle pouch model. Next, a rat critical defect model was performed with treatment groups including (i) empty defect, (ii) BG, (iii) collagen sponge + BMP‐2, (iv) BG + PDIB/BMP‐2, and (v) BG + PDIB/BMP‐2/ZA. Key outcome measures included detection of fluorescent bone labels, microcomputed tomography (CT) quantification of bone, and radiographic healing. In the muscle pouch study, BMP‐2 did not increase net bone volume measured by microCT, however, fluorescent labeling showed large amounts of new bone. Addition of ZA increased BV by sevenfold (p