^* Harnessing the Osteogenicity of In Vitro Stem Cell-Derived Mineralized Extracellular Matrix as 3D Biotemplate to Guide Bone Regeneration

Advanced biomaterials that are capable of guiding robust bone regeneration are highly demanded for translational therapy of bone defects or bone augmentation in clinics. One of the strategic approaches is to produce tissue engineering (TE) constructs that mediate bone regeneration by recapitulating the natural bone formation or healing process. In this study, we aimed at producing devitalized mineralized carriers with augmented bone forming capacity via a modified culture protocol (i.e., culture conditions with high calcium and/or phosphate concentrations) that first promotes cell growth and, subsequently, mineralized extracellular matrix (ECM) deposition by human periosteum-derived osteoprogenitor cells (hPDCs) on additive manufactured three-dimensional (3D) porous titanium (Ti)-based scaffolds. Qualitative and quantitative analysis was performed to characterize the physicochemical properties of the produced devitalized mineralized carriers, as well as their effects as carriers on in vitro cell growth and osteochondrogenic differentiation of hPDCs under a perfusion bioreactor culture set-up. The results showed that the modified culture protocol was useful to produce devitalized mineralized carriers with different amount, distribution, composition, and morphology of mineralized matrix that resembled hydroxyapatite, and exhibited different Ca²⁺ release kinetics, distinct human bone morphogenetic protein (hBMP)-2, human vascular endothelial growth factor (hVEGF) proteins, and collagen contents. The produced devitalized mineralized carriers supported 3D growth of hPDCs, with minor osteochondrogenic differentiation effects under the perfusion bioreactor culture condition. Subcutaneous implantation of hPDC-seeded devitalized mineralized carriers in athymic nude rats showed nearly five-fold augmentation in the ectopic bone-forming capacity, with no bone induction obtained for unseeded, devitalized mineralized carriers and plain Ti scaffolds. Implantation of devitalized mineralized carriers in critical-sized calvarial defects resulted in encouraging defect bridging as compared with limited defect bridging by plain Ti scaffolds or in empty defects. This defect bridging was not enhanced by implanting hPDC-seeded devitalized mineralized carriers. In conclusion, the investigated modified culture protocol was useful to produce devitalized mineralized carriers with augmented bone-forming capacity, which potentially could aid bone repair or augmentation in clinics.