BMP-2-Loaded HAp:Ln3+ (Ln = Yb, Er, Gd) Nanorods with Dual-Mode Imaging for Efficient MC3t3-E1 Cell Differentiation Regulation

Effective bone tissue reconstitution improves the treatment success rate of dental implantation and preserves natural teeth during periodontal tissue repair. Hydroxyapatite (HAp) has received much attention in bone remodeling field because its mineralized structure is similar to that of the natural bone tissue. For this reason, it has been used as a carrier for growth factors. Although HAp possesses outstanding biomedical properties, its capacity of loading and releasing bone growth factors and promoting osteogenesis is not well understood. In this study, Ln3+ (Ln = Yb3+, Er3+, Gd3+)-doped HAp (HAp:Ln3+) nanorods were synthesized by one-step hydrothermal method. To improve its biocompatibility and surface properties, bone morphogenetic protein-2 (BMP-2) was loaded onto the surface of HAp:Ln3+ nanorods. The results showed that BMP-2 incorporation promoted bone formation and enhanced the expression of early bone-related gene and protein (RunX2, SP7, OPN). In addition, Yb3+- and Er3+-doped HAp nanorods were examined by upconversion luminescence with 980 nm near-infrared laser irradiation to monitor the delivery position of BMP-2 protein. Furthermore, due to the positive magnetism correlated with the concentration of Gd3+, HAp:Ln3+ with enhanced contrast brightening can be deemed as T1 MIR contrast agents. These findings indicate that HAp doped with rare-earth ions and loaded with BMP-2 has the potential to promote bone tissue repair and execute dual-mode imaging.