Nanocrystalline hydroxyapatite-based scaffold adsorbs and gives sustained release of osteoinductive growth factor and facilitates bone regeneration in mice ectopic model

Nanocrystalline hydroxyapatite (NHA) is a biocompatible, biodegradable, and osteoconductive bone graft material; however, it lacks osteoinductivity. The present study is aimed at investigating the feasibility of nanocrystalline hydroxyapatite (NHA) as an osteoinductive growth factor carrier. Bone morphogenic protein 2 (BMP2), an osteoinductive growth factor, was incorporated into NHA (BMP2-NHA) using a simple adsorption method. The growth factor loading and release kinetics were profiled using fluorescein-isothiocyanate-labeled bovine serum albumin (FITC-BSA) as a mimic of the osteoinductive growth factor BMP2. The effect of BMP2-NHA on the osteogenic differentiation of C2C12 cells and ectopic bone formation in mice were tested. Confocal laser-scanning microscopy showed that FITC-BSA was diffused throughout the porous structure of NHA. FITC-BSA was efficiently loaded in NHA and sustained release was observed up to 35 days in vitro. BMP2-NHA enhanced the expression of osteogenic markers Runx2, Osterix, Alp, and Col1α1 and ALP activity in C2C12 cells compared to NHA. Similarly, μ-CT and histological examinations showed that BMP2-NHA robustly induced ectopic bone formation in mice. This study suggests that NHA could be used as an effective carrier of osteoinductive growth factors, which ensures osteoinductivity of NHA via sustained release of the growth factor.