One and two-step electrodeposition of composite films of calcium-deficient hydroxyapatite matrix with nanoscale Ag- and Zn-based particles

Abstract

A fundamental study regarding the electrochemical synthesis of composite coatings with application in the orthopaedic field has been conducted. In particular, the electrodeposition of calcium phosphate coatings with Ag nanoparticles (AgNPs) from either a single electrolyte (one-step, 1S) or two electrolytes (two-step, 2S) on a β-Ti alloy (Ti-18Mo-6Nb-4Ta in wt%) was investigated. Pulse current deposition was implemented to produce the composite coatings by the 1S approach from a simple solution containing 42 mM Ca(NO3)2·4H2O, 25 mM NH4H2PO4, and 0.5 mM AgNO3 at 65°C. Meanwhile, the calcium phosphate matrix was also deposited by pulse current, and Ag was afterwards grown by direct current from 0.1 M KNO3 + x mM AgNO3 (x = 5, 10) at 25 °C (2S approach). The Ca/P ratio of the matrix was compatible with the formation of calcium-deficient hydroxyapatite (CDHA). The resulting Ag content in the composites could be varied between 4 and 13 wt% as a function of the working conditions. The 2S-derived coatings produced by electroplating Ag at j = –20.8 mA/cm2 from 0.1 M KNO3 + 10 mM AgNO3 furnished an optimal dispersion of the AgNPs on top of the CDHA matrix, while aggregation and/or dendritic growth was observed in other cases. Glow discharge optical emission spectrometry (GDOES) measurements indicated that a given amount of AgNPs becomes engulfed in the CDHA matrix during the 1S electrodeposition, whereas most of them decorate its outer surface in the 2S-derived coatings. The applicability of the two approaches was extended to the case of zinc oxide. ZnO-containing CDHA coatings in which the Zn element was homogeneously distributed across the film surface were obtained from 42 mM Ca(NO3)2·4H2O, 25 mM NH4H2PO4 and 1 mM Zn(NO3)2·6H2O at 65 °C (1S approach). On the contrary, ZnO-NPs could be clearly observed when deposition from 5 mM KNO3 + 5 mM Zn(NO3)2 was performed at 70 °C on top of previously grown CDHA (2S approach). The results indicated that the percentage and location of the antibacterial element (Ag, Zn) in the calcium phosphate matrix can be tuned on demand to a great extent by electrochemical means.