Effect of Doping Element and Electrolyte’s pH on the Properties of Hydroxyapatite Coatings Obtained by Pulsed Galvanostatic Technique

Abstract

Hydroxyapatite (HAp) is the most widely used calcium phosphate as a coating on metal implants due to its biocompatibility and bioactivity. The aim of this research is to evaluate the effect of the pH’s electrolyte and doping element on the morphology, roughness, chemical, and phasic composition of hydroxyapatite-based coatings obtained by pulsed galvanostatic electrochemical deposition. As doping elements, both Sr and Ag were selected due to their good osseoinductive character and antibacterial effect, respectively. The electrolytes were prepared at pH 4 and 5, in which specific concentrations of Sr, Ag, and Sr + Ag were added. In terms of morphology, all coatings consist in ribbon-like crystals, which at pH 5 appear to be a little larger. Addition of Sr did not affect the morphology of HAp, while Ag addition has led to the formation of flower-like crystals agglomeration. When both doping elements were added, the flowers like agglomerations caused by the Ag have diminished, indicating the competition between Sr and Ag. X-Ray Diffraction analysis has highlighted that Sr and/or Ag have successfully substituted the Ca in the HAp structure. Moreover, at higher pH, the crystallinity of all HAp coatings was enhanced. Thus, it can be said that the electrolyte’s pH enhances to some extent the properties of HAp-based coatings, while the addition of Sr and/or Ag does not negatively impact the obtained features of HAp, indicating that by using pulsed galvanostatic electrochemical deposition, materials with tunable features dictated by the function of the coated medical device can be designed.

In Vitro Evaluation of Ag- and Sr-Doped Hydroxyapatite Coatings for Medical Applications

“…Our previous results [56], which showed that the Sr content reached 3.5 at.%, suggested that the Sr ions replaced part of the Ca(I) site. Similarly, Ag + ions substituted Ca 2+ ions within the HAp lattice, preferring the Ca(I) site, which led to an increment in the lattice parameters due to the greater ionic radius (0.128 nm vs. 0.099 nm) [28].…”

“…The electrolyte concentrations along with the electrochemical parameters used are presented in Table 1, and a full description of the electrochemical deposition is available in Ref. [56]. The coating deposition was carried out with a potentiostat/galvanostat PARSTAT MC equipped with a PMC-1000 module (Princeton Applied Research-AMETEK, Berwyn, PA, USA) using the galvanostatic pulse technique.…”

“…The electrolyte concentrations along with the electrochemical parameters used are presented in Table 1, and a full description of the electrochemical deposition is available in Ref. [56]. The coating thickness was determined by measuring the level difference at the substrate-coating interface with a stylus profilometer (DEKTAK 150, Veeco Instruments, The coating thickness was determined by measuring the level difference at the substrate-coating interface with a stylus profilometer (DEKTAK 150, Veeco Instruments, Plainview, NY, USA).…”

“…This study was a follow-up on previous research [56] investigating the influence of the electrolyte's pH level (pH 4 and pH 5) on the morphology, elemental and phasic composition, and roughness, based on which the layers obtained at pH 5 were selected due to their superior properties compared to the coatings obtained at pH 4. Thus, the aim of this study was to evaluate the electrochemical behavior, biomineralization, and biodegradation capacity in acellular media of cp-Ti and HAp-based coatings undoped and doped with Ag and/or Sr and the cellular response to these substrates.…”

Electrodeposition of Calcium Phosphate Coatings on Metallic Substrates for Bone Implant Applications: A Review

“…During deposition, the ionic substituents are integrated into the calcium phosphate lattice to enhance the biological properties of the coating. Several ions are described in the scientific literature with different biological effects [139][140][141][142][143][144][145][146][147].…”