Development of an injectable slow release system for bone morphogenetic protein-2

In this thesis, development of a bone regeneration therapy using biomaterials and growth factors is described. Initially, collagen I based recombinant protein (RCP) microspheres were developed for BMP-2 delivery. Among several parameters investigated, size and crosslinking of microspheres affected the BMP-2 release. To improve bone formation, we have combined microspheres with in-situ gelling hydrogels. Two types of alginate, high mannuronate (SLM) and high guluronate (SLG), and one type of thermosensitive hyaluronic acid were developed for this study. These hydrogels were designed not only to deliver and keep the microspheres at the site but also to act as a scaffold for the regenerating tissue and to fill a defect. The SLG alginate-RCP microspheres formulation was selected for further studies in ectopic and orthotopic bone formation models in rats. First, the effect of BMP-2 dose delivered was tested in the ectopic bone model using 10, 3, 1, 0.3 and 0 μg BMP-2 per implant. In a subsequent calvarial defect experiment, 50 μg/mL and 5 μg/mL BMP-2 containing hydrogels were tested. This study showed that the effective concentration of BMP-2 to induce both ectopic and orthotopic bone is optimally between 15-50 μg/mL.