Nanoparticulate Mineralized Collagen Scaffolds Induce In Vivo Bone Regeneration Independent of Progenitor Cell Loading or Exogenous Growth Factor Stimulation

Purpose:  Current strategies for skeletal regeneration often require co-delivery of scaffold technologies, growth factors, and cellular material.  However, isolation and expansion of stem cells can be time consuming, costly, and requires an additional procedure for harvest. Further, the introduction of supraphysiologic doses of growth factors may result in untoward clinical side effects, warranting pursuit of alternative methods for stimulating osteogenesis. 

Methods:  Primary rabbit bone marrow stromal cells (BMSCs) isolated from the iliac crest of New Zealand rabbits were differentiated on non-mineralized and nanoparticulate mineralized collagen glycosaminoglycan scaffolds in osteogenic differentiation medium.  Osteogenic gene expression, mineralization, and activation of intracellular signalling molecules were examined.  In vivostudies using scaffolds, scaffolds loaded ex vivo with BMSCs, and scaffolds loaded with BMSCs and BMP-2 were implanted in critical sized rabbit cranial defects and evaluated for bone healing after 12 weeks.  Gross, histologic, and radiographic examinations were performed on explanted skulls.

Results:  Nanoparticulate mineralized collagen glycosaminoglycan scaffolds (MC-GAG) induced activation of osteogenic gene expression and mineralization in vitro.  In vivo, MC-GAG induced healing of critical-sized rabbit cranial defects without addition of expanded stem cells or exogenous growth factors.  Bone healing correlated to activation of the canonical BMP receptor signalling and autogenous production of BMP-2 and -9 early and BMP-4 later during differentiation.

Conclusions: Nanoparticulate mineralized collagen glycosaminoglycan scaffolds may provide a novel growth factor-free and ex vivo progenitor cell culture-free implantable method for bone regeneration.