Biological response of human bone cells to zinc-modified Ca-Si-based ceramics

Calcium silicate (CaSiO3) ceramics have received considerable attention in recent years due to their excellent bioactivity and degradability. However, their poor chemical stability limits their biological applications. Hardystonite (Ca2ZnSi2O7) ceramics are Ca-Si-based materials developed by incorporating zinc into the Ca-Si system to improve their chemical stability. However, the biological responses of Ca2ZnSi2O7 to bone cells are unknown. The objective of this study is to investigate and compare the in vitro responses of human osteoblast-like cells (HOBs) and osteoclasts when cultured on Ca2ZnSi2O7 and CaSiO3 ceramic disks. The ability of Ca2ZnSi2O7 ceramics to support HOB attachment, cytoskeleton organization, proliferation and differentiation was assessed by scanning electron microscopy, confocal microscopy, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, alkaline phosphatase activity and quantitative real-time polymerase chain reaction. Our results show that Ca2ZnSi2O7 supported HOB attachment with a well-organized cytoskeleton structure, and significantly increased cellular proliferation and differentiation compared to CaSiO3. In addition, Ca2ZnSi2O7 showed increased expression levels of osteoblast-related mRNAs (alkaline phosphatase, collagen type I, osteocalcin, receptor activator of NF kappa B ligand and osteoprotegerin) compared to CaSiO3. Ca2ZnSi2O7 ceramic supported the formation of mature and functional osteoclasts and formed resorption imprints. On CaSiO3 ceramics, the cells failed to differentiate from the monocytes into osteoclasts. Taken together, these results indicate that Hardystonite ceramics are conducive to both types of bone cells, osteoblast-like cells and osteoclasts, suggesting their potential use for skeletal tissue regeneration and as coatings onto currently available orthopedic and dental implants. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.