The modulation of osteogenesis in vitro by calcium titanium phosphate coatings

Calcium phosphate coated titanium and titanium alloy are widely used as dental and orthopaedic implants. This study examines the effect of novel calcium titanium and calcium titanium zirconium phosphates suitable for plasma-spraying onto titanium substrata on the expression of bone-related genes and proteins by human bone-derived cells (HBDC) and compares this behavior to that on native titanium and hydroxyapatite-coated titanium. Test materials were an acid etched and sand-blasted titanium surface (Ti-DPS), a plasma-sprayed hydroxyapatite coating (HA), and five materials which were created from CaTi4(PO4)6 (CTP) and CaZr4(PO4)6 (CZP): sintered CaTi4(PO4)6 (CTP-S1), sintered 46CaO•23TiO2•31P2O5 (CTP-S2), sintered CaTiZr3(PO4)6, (CTZP-S1), sintered 46CaO•23ZrO2•31P2O5 (CTZP-S2) and sintered 55CaO•20TiO2•31P2O5 (CTP-S3). HBDC were grown on the substrata for 3, 7, 14 and 21 d, counted and probed for various mRNAs and proteins (type I collagen, osteocalcin, osteopontin, osteonectin, alkaline phosphatase and bone sialoprotein). All substrates significantly affected cellular growth and the temporal expression of an array of bone-related genes and proteins. At 14 and 21 d, cells on CTP-S3 displayed significantly enhanced expression of all osteogenic mRNAs. Surfaces of CTP-S1 and CTP-S3 had the most effect on osteoblastic differentiation inducing a greater expression of an array of osteogenic markers than recorded for cells grown on Ti-DPS and HA, suggesting that these novel materials may possess a higher potency to enhance osteogenesis.