Electrostatic Spray Deposition of Biomimetic Nanocrystalline Apatite Coatings onto Titanium

Titanium (Ti) and its alloys are widely used to manufacture orthopedic and dental implants due to their excellent mechanical properties and corrosion resistance. Although these materials are bioinert, improvement of biological properties (e.g., bone implant contact) can be obtained by the application of a coating made of nanostructured apatite. The aim of this study was to investigate the applicability of the electrostatic spray deposition (ESD) technique for the deposition of nanostructured apatite coatings onto commercially pure (cp) Ti substrates at room temperature. To that end, poorly crystalline, nano-sized, carbonate-apatite plate-like particles with dimensions similar to the nanocrystals present in bone were synthesized using wet-chemical precipitation techniques and their physicochemical properties were subsequently characterized thoroughly. The apatite suspensions were optimized for the ESD process in terms of dispersion, aggregation, and stability. Furthermore, relevant ESD processing parameters, including nozzle-to-substrate distance, relative humidity in the deposition chamber and deposition time were varied in order to study their effects on coating morphology. Porous films made of agglomerates of nano-sized apatite particles of similar to 50nm were generated, demonstrating the feasibility of the ESD technique for the deposition of thin apatite coatings with a nano-sized surface morphology onto titanium substrates. The ability of these nanocrystals to bind therapeutic agents for bone diseases and the capability of ESD to produce coating at physiological conditions makes this work a first step toward the set-up of coatings for bone implants based on surface-activated apatite with improved functionality.