Bone grafts are used in various clinical settings to aid bone repair and regeneration. In recent years, the United States, as well as other countries worldwide, have experienced an increasingly high demand for functional bone grafts. This includes the US military and the VA healthcare systems, where there is a high demand for bone graft substitutes to repair critical-size bone defects, fracture non-unions, and orthopedic reconstruction incidents to battlefield trauma. Current repair processes use the patient’s own bone tissue harvested during reconstructive surgery. However, autograft donor sites are limited in the amount of tissue available, and secondary surgical sites are usually required. While allografts harvested from cadaveric sources eliminate the need for secondary surgical sites and have the advantage of being osteoconductive, they are associated with the risk of host rejection and accelerated graft resorption. The downsides of autograft and allograft bone techniques have impelled the development of bioengineered graft materials. As part of this quest, we developed apatite-based bone scaffolds through a VA SPiRE Grant (# 1I21RX003328-01A1). Our data showed that, in 12-weeks, the pores within the fluorapatite scaffolds became completely filled with viable new bone tissue, demonstrating the efficacy of these scaffolds in regenerating bone tissues. To further develop this novel material for clinical applications as an “autograft-like” bone scaffold for the repair of critical-size defects, we propose combining our scaffold with stromal vascular fraction cells as an osteogenic cell source. Thus, it is hypothesized that fluorapatite (FA) scaffoldings seeded with patients’ own stem cells, contained within the stromal vascular fraction (SVF) that is extracted from autologous fat tissue, will have the ability to generate new osseous tissue at a level comparable to that of autograft bone in both a non-weight bearing critical-size defect model and a weight-bearing fracture model. This hypothesis will be tested with three specific aims. Specific Aim 1 will determine the optimal number of SVF cells needed for repairing bone defects in a rat model. Specific Aim 2 will investigate the osteogenic potential and time-course of bone regeneration of FA scaffolds, with and without SVF, in a critical size bone defect in a sheep ilium model. mRNA-based techniques will be used to highlight the mechanistic differences in bone regeneration as a secondary outcome in the latter time-course study. Finally, Specific Aim 3 will investigate the efficacy of the FA scaffolds, with and/or without SVF, in a sheep weight- bearing tibial fracture model. FA with and without SVF will be compared to the clinical gold standard, autograft, as well as FDA-approved hydroxyapatite scaffold. It is expected that such a combination treatment of SVF and FA scaffolds will provide a potential source of “off-the-shelf” scaffolding materials for clinical bone repair and regeneration and im...