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.
Highlights
In the past years, the use of implants has grown considerably, driven by ageing of populations and the desire of the patients to maintain the same level of activity and quality of life [1].Among the metallic biomaterials, titanium is the most used due to its excellent properties such as the modulus of elasticity close to that of bone, biocompatibility, and excellent corrosion resistance, being considered the “gold standard” [2,3]
Since a more acidic pH leads to the formation of a higher quantity of hydrogen on macroscopic images of the coatings after deposition, it can be observed that all coatings gas and the reactions are more energetic [31]
Because the coatings are are fully covering the surface of the cp-Ti metallic substrate, and no defects were visible deposited in pulses, the repeatedly interrupted process of nucleation and growth of preto the naked eye
Summary
Titanium is the most used due to its excellent properties such as the modulus of elasticity close to that of bone, biocompatibility, and excellent corrosion resistance, being considered the “gold standard” [2,3]. Due to its bioinert character does not favor the formation of a direct connection with the hard tissue nor the initiation of the bone remodeling mechanism in the early stages after implantation [4]. Imparting multifunctionality of bioinert metals such as Ti and its alloys is generally achieved through surface modification techniques [5], such as coating the metallic biomaterials with bioactive ceramics and/or polymers to improve their osseointegration and bioactivity [6]. Hydroxyapatite (HAp) is a calcium phosphate-based ceramic that is found in the structure of hard tissues along with collagen and minerals [7]. Due to its resemblance to its natural homologue, HAp can be doped with a large variety of ions such as Mg, Sr, Zn, Mn, and Si found in the structure of hard tissues [8,9]
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