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

Abstract

Calcium silicate (CaSiO 3) 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 (Ca 2ZnSi 2O 7) 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 Ca 2ZnSi 2O 7 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 Ca 2ZnSi 2O 7 and CaSiO 3 ceramic disks. The ability of Ca 2ZnSi 2O 7 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 Ca 2ZnSi 2O 7 supported HOB attachment with a well-organized cytoskeleton structure, and significantly increased cellular proliferation and differentiation compared to CaSiO 3. In addition, Ca 2ZnSi 2O 7 showed increased expression levels of osteoblast-related mRNAs (alkaline phosphatase, collagen type I, osteocalcin, receptor activator of NF κB ligand and osteoprotegerin) compared to CaSiO 3. Ca 2ZnSi 2O 7 ceramic supported the formation of mature and functional osteoclasts and formed resorption imprints. On CaSiO 3 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.