A study on biological properties of titanium implants coated with multisubstituted hydroxyapatite

Abstract

In this work, it was found that the composition of hydroxyapatite coatings deposited on a titanium substrate depends on the temperature of detonation products and on the composition of the initial explosive mixture. Depending on the detonation mode, it was possible to obtain a coating of oxyhydroxyapatite containing or not containing an admixture of other calcium orthophosphates. It was shown for the first time that the structure of multisubstituted Zn–Si-hydroxyapatite and Ag–Zn–Si-hydroxyapatite with substitution degree x(Zn) = x(Si) = 0.2 and x(Ag) = 0.1 has lower thermal stability as compared to unsubstituted hydroxyapatite. The formation of a small amount of the α-Ca3(PO4)2 phase upon detonation deposition of the multisubstituted hydroxyapatites was obviously due to structural transformations that occurred when the material was heated by the detonation products. In vivo biological testing of titanium implants coated or not coated with hydroxyapatite revealed that the coating significantly accelerates osteogenesis in the gap between native bone and the implant; this acceleration improved implant fixation. In animals with the uncoated plates, fibrogenesis processes significantly outstripped the osteogenesis. The presence of Zn and Si ions in the apatite coating had a potentiating influence on the osteoinduction caused by hydroxyapatite. Osteogenesis in this case was more complete and characterized by pronounced processes of mineralization of the bone plates. The addition of Ag ions to the Zn–Si-hydroxyapatite at a concentration of 1 at.% did not impair its osteogenic activity and did not have a toxic effect on bone tissue, while imparting antibacterial properties to the material.