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.

Chloride Electrolyte-Sintered Cathode Anode System Chemism Study of Titanium Dioxide in Calcium Chloride

The electrochemical process of the solid titanium dioxide develops in the complex system: TiO2 (solid, sintered cathode) � CaCl2 (liquid, electrolyte) � C (anode, graphite). As a consequence of the chemical and electrochemical reactions which take place in this system, with determined conditions of temperature and potential, are finally formed solid metallic titanium (at the cathode) and oxygen (at the anode). The general reaction of the process is: TiO2(s) = Ti(s)+O2(g). A series of other reactions, implying the presence of other components (elements and compounds), as Ca, CaO, CaTiO3, C, CO, CO2, etc., are possible in certain conditions and stages of the process. In the paper are analyzed the main reactions which occur in the process, by their thermodynamic study. Through mathematical processing of thermodynamic data for the main reactions in the system, recently published in the literature, there was determined the temperature dependence of the Free Gibbs Energy, and based on it the values of the electrode potential were computed. In this manner was possible to prove that chemical reactions that could not spontaneously evolve, can develop in the electrochemical process by means of a corresponding voltage applied on the electrolysis cell.