Could the enrichment of a biomaterial with conditioned medium or extracellular vesicles modify bone-remodeling kinetics during a defect healing? Evaluations on rat calvaria with synchrotron-based microtomography.

Tissue engineering has been shown to offer promising approaches for bone regeneration, mostly based on replacement with biomaterials that provide specific environments and support for bone growth. In this context, we previously showed that mesenchymal stem cells (MSCs) and their derivatives, such as conditioned medium (CM) and extracellular vesicles (EV), when seeded on collagen membranes (COL) or poly- (lactide) (PLA) biomaterials, are able to favor bone tissue regeneration , especially evidenced in animal model calvary defects. In the present study, we investigated whether the enrichment of a rat calvary defect site with CM, EVs and polyethylenimine (PEI)-engineered EVs could substantially modify the bone remodeling kinetics during defect healing, as these products were reported to favor bone regeneration. In particular, we focused the study, performed by synchrotron radiation-based high resolution tomography, on the analysis of the bone mass density distribution. We proved that the enrichment of a defect site with CM, EVs and PEI-EVs substantially modifies, often accelerating, bone remodeling kinetics and the related mineralization process during defect healing. Moreover, different biomaterials (COL or PLA) in combination with stem cells of different origin (namely, human periodontal ligament stem cells-hPDLSCs and human gingival mesenchymal stem cells-hGMSCs.