Preparation of spherical calcium phosphate granulates suitable for the biofunctionalization of active brazed titanium alloy coatings.

Titanium-based alloys can be actively brazed onto bio-inert ceramics and potentially be used as biocompatible coatings. To further improve their bioactivity in vivo, introduction of calcium phosphate (CaP)-based granulates onto their surface layer is possible. For this, mechanically stable CaP-based granulates need to be able to withstand the demand of the brazing process. In this study, spherical granulates, made of a calcium phosphate composite composed primarily of ß-tricalcium phosphate and hydroxyapatite, a bioactive glass, and a mixture of the previous two, were manufactured by spray drying. The influence of organic additives (Dolapix CE64, trisodium citrate) and solids content (30-80 wt%) in the slurry on the physical characteristics of granulates was investigated. X-ray diffraction, Brunauer, Emmett, Teller specific surface area standard method, scanning electron microscopy, granulate size analysis, and single granule strength were performed. Our results showed that trisodium citrate permitted the production of granulates with regular morphology, high density, and increased failure stress values. The strong granules also withstood the brazing process. These results show that CaP bioactive agents can be generated and be integrated during the demanding metallurgical processes, allowing for one-step bioactivation of metal brazes.