Regulation of Osteogenic Markers at Late Stage of Osteoblast Differentiation in Silicon and Zinc Doped Porous TCP

Calcium phosphates (CaPs) are one of the most widely used synthetic materials for bone grafting applications in the orthopedic industry. Recent trends in synthetic bone graft applications have shifted towards the incorporation of metal trace elements that extend the performance of CaPs to have osteoinductive properties. The objective of this study is to investigate the effects of silicon (Si) and zinc (Zn) dopants in highly porous tricalcium phosphate (TCP) scaffolds on late-stage osteoblast cell differentiation markers. In this study, an oil emulsion method is utilized to fabricate highly porous SiO2 doped β-TCP (Si-TCP) and ZnO doped β-TCP (Zn-TCP) scaffolds through the incorporation of 0.5 wt.% SiO2 and 0.25 wt.% ZnO, respectively, to the β-TCP scaffold. Reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) is utilized to analyze the mRNA expression of osteoprotegerin (OPG), receptor activator of nuclear kappa beta ligand (RANKL), bone morphogenetic protein 2 (BMP2), and runt-related transcription factor 2 (Runx2) at the later stage of osteoblast differentiation, day 21 and day 28. Results show that the addition of Si and Zn to the β-TCP structure inhibited the β to α-TCP phase transformation and enhance the density without affecting the dissolution properties. Normal BMP-2 and Runx2 transcriptions are observed in both Si-TCP and Zn-TCP scaffolds at the initial time point, as demonstrated by RT-qPCR. Moreover, the addition of both Si and Zn positively regulate the osteoprotegerin: receptor activator of nuclear factor k-β ligand (OPG:RANKL) ratio at 21-days for Si-TCP and Zn-TCP scaffolds. These results demonstrate the effects of Si and Zn doped porous β-TCP scaffolds on the upregulation of osteoblast marker gene expression including OPG, RANKL, BMP-2, and Runx2, indicating the role of trace elements on the effective regulation of late-stage osteoblast cell differentiation markers.