Heat-Treated Porous Fluorapatite Scaffolds with Adipose Derived Stem Cells for Bone Regeneration

Va Salt Lake City Healthcare System, Salt Lake City UT

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Abstract

Segmental bone loss due to high-energy trauma, such as battlefield injuries, are limb-threatening conditions, but there are limited treatment options available. Conventional treatments include bone grafts, vascularized bone transplant, and allografts. Bone repair using vascularized autografts is arguably the best current approach, because the repair process will proceed with the patient’s own tissue and blood supply, which can be harvested at the time of surgery. This eliminates many adverse outcomes associated with allografts and bioengineered bone substitutes. However, donor autograft sites are limited, and thus, its supply cannot meet the demand. It also requires a second surgical site, which could result in further comorbidities. Decellularized allografts harvested from cadaveric sources have the advantage of being osteoconductive. However, they are associated with risk of host rejection and accelerated graft resorption. Current bioengineered grafts focus on providing the necessary matrix to support bone regeneration by providing biocompatible, bioresorbable, and porous scaffolds made from materials such as hydroxyapatite, collagen and synthetic materials. It is now clear that bioengineered grafts also need a reliable source of osteogenic progenitor cells as well as osteogenic signals to be effective bone substitutes. To improve upon these initial designs, researchers made new scaffolds that integrated extracellular matrix proteins or growth factors, typically bone morphogenetic proteins (BMPs), but with limited success. Often the strength of the scaffolding remains the main hurdle for weight-bearing after surgery. To this end, we fabricated a fully interconnecting porous fluorapatite (FA) scaffold by adopting a “gel-casting” process, and then heat-treating to optimize the mechanical strength. As these surfaces are osteogenic, they also enhance osteoblast adhesion, proliferation, and differentiation. Interestingly, these scaffolds also possess the ability to differentiate stem cells (adipose derive stem cells) to an osteogenic lineage without any osteogenic signals (e.g. exogenous BMPs). More notably, the “gel-casting” technique allows custom fabrication of desired shapes and sizes of rigid scaffoldings to fit individual defects. Thus, we hypothesize that FA scaffoldings seeded with a patient’s own adipose tissue-derived stromal vascular fraction (SVF) stem cells will have the ability to regenerate osseous tissue. This hypothesis will be tested in three aims. Specific Aim 1 will investigate the mechanical, physical, and degradation properties of the porous fluorapatite scaffolds, which will be generated by the gel-casting technique. Specific Aim 2 will quantify the in vitro adhesion and differentiation properties of the SVF cells on porous FA surfaces. Specific Aim 3 will investigate the osteogenic potential of the FA scaffolding with and without SVF in a rat femoral condyle model. It is expected that such 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 improve the health and quality of life for a number of military personnel, veterans, and civilians. ! !