HYDROXYAPATITE COATINGS ON TI PRODUCED BY HOT ISOSTATIC PRESSING

Plasma spraying is a technique currently used in the production of HA- coated titanium implants. These coatings have been shown to be porous; they dissolve and have a weak bond to the substrate. The long-term in terface strength has been questioned in particular. The aim of the pre sent work was to produce HA coatings without the shortcomings of those produced by plasma spraying. Hot isostatic pressing (HIP) at 850 degr ees C and 1000 bar with no holding time was applied for this purpose. Initially, the HA powder was mixed with water and air sprayed on the T i substrate. The Ti specimens were then cold-pressed, enclosed by a pr otective Pt foil, and encapsulated in an evacuated glass ampulla. Subs equent to HIP, the glass and the Pt-foil were removed. These coatings were denser than those produced by plasma spraying. The bonding was me asured to be > 62 MPa, which is considered to be satisfactory. The str ucture of the coating was checked by X-ray diffraction and IR spectros copy, and was found to correspond to that of HA. Some cracks were obse rved in the coating running predominantly vertical to the surface. Whe ther these are acceptable has to be verified by in vivo experiments. ( C) 1994 John Wiley and Sons, Inc.