RF Magnetron Sputtering of Substituted Hydroxyapatite for Deposition of Biocoatings

Abstract

Functionalization of titanium (Ti)-based alloy implant surfaces by deposition of calcium phosphates (CaP) has been widely recognized. Substituted hydroxyapatites (HA) allow the coating properties to be tailored based on the use of different Ca substitutes. The formation of antibacterial CaP coatings with the incorporation of Zn or Cu by an RF magnetron sputtering is proposed. The influence of RF magnetron targets elemental composition and structure in the case of Zn-HA and Cu-HA, and the influence of substrate’s grain size, the substrate’s temperature during the deposition, and post-deposition heat treatment (HT) on the resulting coatings are represented. Sintering the targets at 1150 °C resulted in a noticeable structural change with an increase in cell volume and lattice parameters for substituted HA. The deposition rate of Cu-HA and Zn-HA was notably higher compared to stochiometric HA (10.5 and 10) nm/min vs. 9 ± 0.5 nm/min, respectively. At the substrate temperature below 100 °C, all deposited coatings were found to be amorphous with an atomic short-range order corresponding to the {300} plane of crystalline HA. All deposited coatings were found to be hyper-stochiometric with Ca/P ratios varying from 1.9 to 2.5. An increase in the substrate temperature to 200 °C resulted in the formation of equiaxed grain structure on both coarse-grained (CG) and nanostructured (NS) Ti. The use of NS Ti notably increased the scratch resistance of the deposited coatings from18 ± 1 N to 22 ± 2 N. Influence of HT in air or Ar atmosphere is also discussed. Thus, the deposition of Zn- or Cu-containing CaP is a complex process that could be fine-tuned using the obtained research results.

Influence of Cu Substitution on the Properties of Hydroxyapatite Targets and Deposited Coatings

“…Importantly, these coatings should be biocompatible and bioactive, supporting bone growth and accelerated healing. Calcium phosphate (CaP) biocoatings meet these requirements [16][17][18][19].…”

“…This technique enables the achievement of impressive adhesion between the coating and substrate while also offering control over the properties and morphology of CaP coatings. This control is crucial given the significant mechanical strain experienced by the surfaces of implant materials during the process of implantation [18,27,28]. Regarding the formation of CaP coatings via RF magnetron sputtering, targets play a pivotal role.…”

“…In our previous research [17,18,24], we used Cu-substituted powder manufactured by mechanochemistry when Cu content was introduced at small, doping concentrations in order to ensure manufacturing of a single-phase product. It is dictated by the fact that the CuO phase that might occur during synthesis, or that RF magnetron sputtering has drastically different bioactivity when compared to Cu [43].…”