Engineer BMP-2 and Sonic Hedgehog-Slow Releasing Nanogels to Enhance Osteoinduction

Objectives: There are >150 million new bone fractures globally each year. The current standard treatments using autografts and allografts have limitations of donor shortage, high cost and/or poor healing function. The goal of this work is to develop a nanotherapy that can sustain release bone morphogenetic protein-2 (BMP-2) and sonic hedgehog (SHH) for large scale bone regeneration. The objectives are to use dental pulp stem cell (DPSCs) and mouse hindlimb muscle pocket models to evaluate the osteoinductive effects of the nanotherapy in vitro and in vivo, respectively.
Methods: Nanogels composed of poly(N-isopropylacrylamide)-dextran-poly(lactate-2-hydroxyethyl-methacrylate) were loaded with BMP-2 and SHH in aqueous solution via UV-emulsion polymerization. The size, morphology and degradation of the nanogels were characterized by dynamic light scattering, atomic force microscopy and Fourier transform infrared spectroscopy, respectively. The release kinetics and bioactivity of BMP-2 and SHH from the nanogels were studied using ELISA and cellular reporter BRE-luc assay, respectively. The cytotoxicity of the nanogels to DPSCs was assessed by MTT assay. The osteoinduction of the BMP-2- and SHH-nanogels to DPSCs was evaluated via mineralization and alkaline phosphatase (ALP) assays. The in vivo effects of the BMP-2 and SHH-loaded nanogels on mineralization are being assessed by implanting the nanogels imbedded in the collagen sponge in the mice hindlimb muscle pocket.
Results: The BMP-2 and SHH-nanogels were monodispersed ~60 nm with 80-95% encapsulation efficiency. The nanogels degraded with time for at least 21 days, sustained the release of biologically active BMP-2 and SHH for >7 weeks, and were not cytotoxic to DPSCs at 5 mg/mL^-1. The BMP-2-nanogels enhanced the osteodifferentiation of DPSCs and the SHH-loaded nanogels further augmented the osteodifferentiation of the BMP-2-nanogels.
Conclusions: The BMP-2 and SHH-nanogels have synergetic effects on osteoinduction of DPSCs and have great potential to be developed into an effective nanotherapy for large scall bone regeneration