Dissolution and adhesion behaviour of radio-frequency magnetron-sputtered Ca-P coatings

Radio-frequency magnetron sputtering deposition was used to produce calcium phosphate sputter coatings with th ree different thicknesses (0.1, 1 and 4 mu m) on titanium discs. Half of the as-sputtered coatings were subjected to an additional heat treatment for 2 h at 500 degrees C. X-ray diffraction demonstrated that annealing at 500 degrees C changed the amorphous 1 and 4 mu m sputtered coatings into an amorphous-crystalline structure, while the amorphous 0.1 mu m changed in a crystalline apatite structure. Further, sc anning electron microscopy (SEM) inspection demonstrated that annealing of the 1 and 4 mu m coatings resulted in the appearance of some cracks. The di ssolution behaviour of these Ca-P coatings was determined in a simulated bo dy fluid. It was found that after incubation for 4 weeks the dissolution wa s determined by the crystallinity of the deposited coating. SEM and Fourier transform infrared evaluation showed that all the heat-treated sputter coa ting appeared to be stable under the test conditions and a Ca-P precipitate was always deposited on the coating surface. On the other hand, the amorph ous 0.1 and 1 mu m coatings dissolved completely with in 4 weeks, while the amorphous 4 mu m coating sh owed only signs of surface dissolution. Scratc h testing demonstrated that there is a linear correlation between the criti cal load, L-c, and the coating thickness. A heat treatment for the CaP-4 co ating resulted in an additional decrease in the critical load. On the basis of these findings, we conclude that already a 0.1 mu m heat-treated Ca-P s putter coating is of sufficient thickness to show in-vitro adequate bioacti ve and adhesive properties. (C) 1998 Kluwer Academic Publishers.