Native multipotential stromal cell colonization and graft expander potential of a bovine natural bone scaffold

Graft expanders are bone scaffolds used, in combination with autografts, to fill large bone defects in trauma surgery. This study investigates the graft expander potential of a natural bone substitute Orthoss by studying its ability to support attachment, growth and osteogenic differentiation of neighboring multipotential stromal cells (MSCs). Material consisting of bone marrow (BM) aspirate and reamer-irrigator-aspirator (RIA)-harvested autograft bone was co-cultured with commercially available Orthoss granules. Native MSCs attached to Orthoss were expanded and phenotypically characterized. MSCs egress from neighboring cancelous bone was assessed in 3D Matrigel co-cultures. MSC differentiation was evaluated using scanning electron microscopy and measuring alkaline phosphatase (ALP) activity per cell. CD45(+) hematopoietic lineage cells and highly proliferative CD90(+) CD73(+) CD105(+) MSCs preferentially colonized Orthoss granules, over RIA bone chips. MSC colonization was followed by their intrinsic osteogenic differentiation, assessed as mineral deposition and gradual rise in ALP activity, even in the absence of osteogenic stimuli. When in contact with mixed cell populations and RIA chips, Orthoss granules support the attachment, growth and osteogenic differentiation of neighboring MSCs. Therefore, natural bone substitutes similar to Orthoss can be used as void fillers and graft expanders for repairing large bone defects in conjunction with autologous BM aspirates and autografts.