Influence of coating strain on calcium phosphate thin-film dissolution

The success of calcium phosphate (CaP) coatings used to accelerate initial bone growth onto dental implants can vary depending on the CaP phases prese nt in the coating. In this study, the effect of CaP coating crystal structu re and morphology on dissolution rates was investigated. RF magnetron-sputt ered CaP coatings (NTC) were compared to a less strained coating (HTC) obta ined from heat treatment of sputtered samples at 550 degreesC. Coating stra in differences were apparent in XRD spectra where hydroxyapatite-like plane s shifted by 0.5 degrees 2 theta and 0.05 degrees 2 theta for Che NTC and H TC coatings, respectively. HTC XRD peak widths were broader than NTC peak w idths, indicating smaller crystals or grain sizes. These differences in gra in size were corroborated by imaging with scanning probe microscopy. NTC co atings dissolved at a 300% faster rate than HTC coatings. A major factor co ntributing to this kinetic effect was the level of strain in both coatings. These results suggest an alternate design for CaP coatings can be obtained through the manipulation of coating strain. Using this approach, delivery of different ionic gradients from CaP coatings to surrounding tissue enviro nments can be obtained from surfaces having similar chemistries. (C) 2001 J ohn Wiley & Sons, Inc.