Abstract
Non-healing fractures can result from trauma, disease, or age-related bone loss. While many treatments focus on restoring bone volume, few try to recapitulate bone organization. However, the native architecture of bone is optimized to provide its necessary mechanical properties. Hyaluronic acid (HA) hydrogel scaffold systems with tunable degradation properties were developed for the controlled delivery of osteoinductive and angiogenic growth factors, thus affecting the quantity and quality of regenerated tissue. HA hydrogels were designed to degrade at fast, intermediate, and slow rates due to hydrolysis and further provided controlled release of cationic proteins due to electrostatic interactions. Scaffolds delivering bone morphogenetic protein-2 (BMP-2) were evaluated in a rat calvarial bone critical size defect model. BMP-2 delivery from the HA hydrogels had a clear osteoinductive effect in vivo and, for all hydrogel types, BMP-2 delivery resulted in significant mineralization compared to control hydrogels. The temporal progression of this effect could be modulated by altering the degradation rate of the scaffold. All three degradation rates tested resulted in similar amounts of mineral formation at the latest (six week) time point examined. Interestingly, however, the fastest and slowest degrading scaffolds seemed to result in more organized bone than the intermediate degrading scaffold, which was designed to degrade in 6-8 weeks to match the healing time. Additionally, healing could be enhanced by co-delivery of vascular endothelial growth factor along with BMP-2.