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

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

Osseointegration plays the most important role in the success of an implant. One of the applications of hydroxyapatite (HAp) is as a coating for metallic implants due to its bioactive nature, which improves osteoconduction. The purpose of this research was to assess the in vitro behavior of HAp undoped and doped with Ag and/or Sr obtained by galvanostatic pulsed electrochemical deposition. The coatings were investigated in terms of chemical bonds, contact angle and surface free energy, electrochemical behavior, in vitro biomineralization in acellular media (SBF and PBS), and biocompatibility with preosteoblasts cells (MC3T3-E1 cell line). The obtained results highlighted the beneficial impact of Ag and/or Sr on the HAp. The FTIR spectra confirmed the presence of hydroxyapatite within all coatings, while in terms of wettability, the contact angle and surface free energy investigations showed that all surfaces were hydrophilic. The in vitro behavior of MC3T3-E1 indicated that the presence of Sr in the HAp coatings as a unique doping agent or in combination with Ag elicited improved cytocompatibility in terms of cell proliferation and osteogenic differentiation. Therefore, the composite HAp-based coatings showed promising potential for bone regeneration applications.

The influencing mechanism of phosphorus component on network structure and bioactivity of bioactive glass

(64-x)SiO₂-36CaO-xP₂O₅ (x = 0, 2, 4, 6, 8 mol%) bioactive glasses are successfully prepared by sol-gel method, and the effect of phosphorus (P) content on the network structure, phase composition and in vitro mineralization performance of bioactive glasses is investigated by the various characterization techniques. Results show that the as-prepared bioactive glass has the amorphous structure. With the increase of P content, it can be found in FT-IR spectra that the characteristic peaks of bending vibration corresponding to the P-O bond in PO₄^3- gradually appear. Among, the typical 60S4P has the highest percentage (73.81%) of bridging oxygen (BO), indicating its highest aggregation degree of silicate network. Besides, the introduction of P₂O₅ results in the formation of monophosphate, which enable the bioactive glasses to dissolve rapidly in water or simulate body fluids (SBF) and crystallize to form hydroxyapatite (HA), thereby enhancing its biological activity. After soaking in SBF for 3 days, the irregular cauliflower-like HA particles appear on the surface of bioactive glass, and the appropriate amount of P addition in glass could result in its high bioactivity. Therefore, this study could provide a theoretical reference for the relationship between the network structure and bioactivity of bioactive glass.

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

This review summaries more than three decades of scientific knowledge on electrodeposition of calcium phosphate coatings. This low-temperature process aims to make the surface of metallic bone implants bioactive within a physiological environment. The first part of the review describes the reaction mechanisms that lead to the synthesis of a bioactive coating. Electrodeposition occurs in three consecutive steps that involve electrochemical reactions, pH modification, and precipitation of the calcium phosphate coating. However, the process also produces undesired dihydrogen bubbles during the deposition because of the reduction of water, the solvent of the electrolyte solution. To prevent the production of large amounts of dihydrogen bubbles, the current density value is limited during deposition. To circumvent this issue, the use of pulsed current has been proposed in recent years to replace the traditional direct current. Thanks to breaking times, dihydrogen bubbles can regularly escape from the surface of the implant, and the deposition of the calcium phosphate coating is less disturbed by the accumulation of bubbles. In addition, the pulsed current has a positive impact on the chemical composition, morphology, roughness, and mechanical properties of the electrodeposited calcium phosphate coating. Finally, the review describes one of the most interesting properties of electrodeposition, i.e., the possibility of adding ionic substituents to the calcium phosphate crystal lattice to improve the biological performance of the bone implant. Several cations and anions are reviewed from the scientific literature with a description of their biological impact on the physiological environment.