Microstructure of ceramic coating on titanium surface as a result of hydrothermal treatment.

Hydroxyapatite coating on commercially pure titanium has been produced by a biomimetic method in order to improve osteointegration for medical implant purposes. A specific chemical treatment by etching titanium substrate with different concentrations of NaOH aqueous solution at 130 degrees C in an autoclave, followed by heat treatment at 600 degrees C was selected to obtain an activated titanium substrate. The microporous surface obtained has allowed the nucleation and growth of a calcium phosphate layer by soaking the substrate in a simulated body fluid (SBF). Scanning electron microscopy (SEM) together with energy dispersive analyzer for X-ray (EDS), X-ray diffraction (XRD) as well as Fourier transform infrared spectroscopy (FT-IR) were employed to evaluate the hydroxyapatite coating. A homogeneous structure coating without cracks defined the chemical treatment condition of the substrate.

Nucleation and growth of hydroxyapatite on titanium pretreated in NaOH solution: experiments and thermodynamic explanation.

Titanium was submitted to chemical attack with sodium hydroxide solution under hydrothermal (SBF) conditions and then kept for 4 weeks in simulated body fluid after heat treatment. The resultant coating titanium samples were characterized regarding nucleation and growth of hydroxyapatite on their surfaces using scanning electron microscopy and energy dispersive spectroscopy, as well as low angle X-ray diffraction. In order to obtain a thermodynamic explanation of same results, Eh-pH diagrams of Na-Ti-H2O and Ca-Ti-H2O systems at 25, 100, 200, and 300 degrees C were built for selected activities of the species in aqueous solutions. Values of pairs corresponding to the predominance limit of the species in solution at equilibrium with 0.21 atm of oxygen pressure were taken from these Eh-pH diagrams for subsequent building of the pNa-pH and pCa-pH diagrams of the same systems at each referred temperature (pi = -log10ai). In addition, the titanate-apatite free energy of formation was estimated and then a pCa-pH diagram of the Ca-P-Ti-H2O system at 25 degrees C was built. Examination of the resultant diagrams could elucidate the thermodynamic viability of the process.

Solution effects on the surface reactions of three bioactive glass compositions.

The in vitro five-stage surface reactions of two bioactive glass compositions, 45S5 and 52S4.6, and one bioinert glass, 60S3.8, exposed to three simulated body fluids (SBF) were analyzed using Fourier Transform infrared Spectroscopy (FTIR). There was little effect of SBF composition on ion exchange, silica hydrolysis, and silica polymerization (stages 1-3) of glass with silica content up to 52 wt%. However, calcium and phosphate ions in SBF accelerated the formation of an amorphous calcium-phosphate (a-CP) layer (stage 4), and crystallization (stage 5) of the hydroxycarbonate apatite (HCAp) layer. The magnesium ions had a retardation effect on the kinetics of stages 4 and 5, but little effect on stages 1-3. In SBF solutions which contained calcium and phosphate ions an amorphous calcium-phosphate (a-CaP) layer formed on even a 60S3.8 glass which was not bioactive in vivo. However, the a-CaP layer did not crystallize to form HCAp. Thus, there is a significant contribution from the ions present in the SBF solutions to the HCAP formation and crystallization of HCAp on bioactive glasses. Also, silanol repolymerization is necessary for rapid crystallization of HCAp.

Solution effects on the surface reactions of a bioactive glass.

The in vitro surface reactions of a 45S5 bioactive glass in three simulated body fluids (SBF) are analyzed using Fourier transform infrared (FTIR) spectroscopy. Five reaction stages are observed. Calcium and phosphate ions in SBF accelerate to a small extent the repolymerization of silica (Stage 3) and formation of an amorphous calcium-phosphate (a-CP) layer (Stage 4) on the glass surface. The a-CaP layer is crystallized to form hydroxy-carbonate apatite (HCAp) (Stage 5) more rapidly in the Ca- and P-containing SBF solutions (in 90 min rather than 120 min). However, Mg ions in SBF slow down formation of the a-CaP layer and greatly retard crystallization of HCAp on the glass surface.