The responses of osteoblasts, osteoclasts and endothelial cells to zirconium modified calcium-silicate-based ceramic

In this study we have developed Ca₃ZrSi₂O₉ (Baghdadite) ceramics by incorporating Zirconium in Ca-Si system and determined their biological properties. Ca₃ZrSi₂O₉ ceramics possess apatite-formation ability in simulated body fluid, indicating their potential bioactivity. The response of human osteoblast like cells (HOB), osteoclast and endothelial cells when cultured on Ca₃ZrSi₂O₉ ceramics was investigated. Scanning electron microscopy and immunofluorescence studies demonstrated that this material supports HOB cell attachment with organized cytoskeleton structure. Compared to CaSiO₃, Ca₃ZrSi₂O₉ ceramics induced increased HOB proliferation and differentiation as shown by increased methyltetrazidium salt (MTS), alkaline phosphatase activity, and mRNA expression levels of bone-related genes (Collagen type I, alkaline phosphatase, Bone Sialoprotein, receptor activator of NF-κB ligand and osteoprotegerin). Ca₃ZrSi₂O₉ ceramics supported the fusion of monocytes to form functional osteoclasts with their characteristic features of f-actin ring structures and the expression of α_vβ₃ integrin consistent with functional activity. Osteoclasts cultured on Ca₃ZrSi₂O₉ expressed increased levels of osteoclast-related genes; Cathepsin K, Carbonic Anhydrase II, Matrix metalloproteinase-9, receptor activator of NF-κB and Calcitonin Receptor, consistent with the formation of functional osteoclasts. In addition to HOB and osteoclasts, Ca₃ZrSi₂O₉ supported the attachment of endothelial cells, which expressed the endothelial cell markers; ZO-1 and VE-Cadherin. Results presented here indicate that Ca₃ZrSi₂O₉ ceramics have the potential for applications in bone tissue regeneration.