Preparation and osteocompatibility of hydroxyapatite coated on titanium from the reaction of sputtered CaO and vaporized P 2 O 5

Hydroxyapatite (HA) and other calcium phosphates were synthesized on titanium plates by a solid–gas state reaction of sputtered CaO and vaporized P₂O₅. The calcium phosphates formed were HA, β‐tricalcium phosphate (β‐TCP; Ca₃(PO₄)₂), β‐calcium pyrophosphate (β‐PYR; Ca₂P₂O₇), and β‐calcium metaphosphate (β‐MET; Ca₂(PO₃)₂). Their formation depended on the ratio of the sputtered CaO and the reacting P₂O₅. For a mole ratio of CaO/P₂O₅=4 (Ca/P=2), an HA film was synthesized. The surface roughness increased by over seven times after the solid–gas state reaction from Ra = 0.16±0.02 μm (for the CaO film) to Ra = 1.15±0.25 μm (for the reacted film). The synthesized HA film‐coated titanium plates and control non‐coated titanium plates were implanted in the femora of two dogs for a period of two, four and 12 weeks, and observed using a soft X‐ray radiograph and histological sections. New bone formation was observed without any connective tissue at four weeks around the HA film, whereas over the 12 week experimental period, there was no new bone formation around the control and connective tissue was observed over all periods, reaching a thickness of more than 200 μm at 12 weeks.