Formation of calcium phosphate coatings on titanium and polymer substrates using gas-detonation deposition

The use of medical implants is becoming more widespread, which is attracting great interest in the development of new technologies for their production. Titanium-based implants are the most common now, but the polymer polyetheretherketone (PEEK) is studied as a substitute. Despite the biotolerance to titanium and PEEK, their implantation in the human body is often accompanied by some negative effects. This problem is solved by depositing biocompatible coatings on the implant's surface, in particular, calcium phosphates (CPs). CP coatings on implants are produced by different techniques, each of which has its own disadvantages related to both the quality of the formed coatings and their cost.

Biocompatible coatings based on hydroxyapatite (HAP) on metal and polymer implants were obtained by gas-detonation deposition (GDD). This method consists ofthe acceleration of HAP powder by a detonation wave resulting from the explosion of a mixture of acetylene and oxygen. HAP powder particles are introduced into the detonation wave and accelerate to high speeds and form a coating on the implants. Among the main advantages of GDD are its high productivity, the ability to form layers of different thickness on large-area substrates in a few minutes, the possibility of varying the coating composition, the high adhesion with low energy consumption of the process and, accordingly, the low cost.

HAP coatings with a thickness ~ 200 microns on titanium and PEEK substrates were studied by Raman spectroscopy, XRD and microscopic analysis. This study showed the formation of a porous coating on the titanium substrate, which consisted of crystalline and partially amorphous HAP. The latter was transformed into a crystalline one during annealing at 600 ^oC. The HAP coating on PEEK was shown to consist of HAP with a small admixture of tricalcium phosphate. The appearance of the latter is explained by the partial transformation of HAP microparticles into tricalcium phosphate when they collide with the surface.