Formation Of Hydroxyapatite Coatings Research Articles

Influence of Concentration of Potassium Hydroxide in Electrolyte on Formation of Hydroxyapatite Coatings on Titanium

Influence of Concentration of Potassium Hydroxide in Electrolyte on Formation of Hydroxyapatite Coatings on Titanium

Evaluation of the effect of surface modification of Ti64 and 316 L by addition of calcium phosphate through electrical discharge machining process

In this investigation, the EDM process was applied to modify the surfaces of Ti-6Al-4 V alloy and AISI 316 L steel by the formation of hydroxyapatite coatings with the objective of providing a favorable environment for osseointegration of implants. The EDM process has the advantage of simultaneously machining and increasing surface roughness increasing surface contact area with bone tissue and implant anchorage. The hydroxyapatite coatings were formed during EDM currents of 30 A and 40 A with calcium phosphate additions. The coatings were analyzed in terms of hardness, roughness, surface profile, wear and tribological characteristics (pin on disk) and were characterized SEM/EDS and XRD. It was possible to show that on all processed surfaces the development of apatite coatings was achieved. Coating thickness and hardness were approximately 120 µm, 700HV and 12 µm, 300HV for the Ti-alloy and stainless steel, respectively. On both substrates, a significant increase in surface roughness was observed after EDM. The pin on disk tests revealed that the coefficient of friction varied from 0.54 to 0.80, and superior wear resistance of the coating formed on the AISI 316 L steel.

Tunable Microstructure and Morphology of the Self-Assembly Hydroxyapatite Coatings on ZK60 Magnesium Alloy Substrates Using Hydrothermal Methods

Hydroxyapatite coatings have been widely used to improve the corrosion resistance of biodegradable magnesium alloys. In this paper, in order to manufacture the ideal hydroxyapatite (HA) coating on the ZK60 magnesium substrate by hydrothermal method, formation mechanism of enhanced hydroxyapatite (HA) coatings, influence of pH values of the precursor solution on the HA morphology, corrosion resistance and cytotoxicity of HA coatings have been investigated. Results show that the growth pattern of the HA is influenced by the local pH value. HA has a preferential c-axis and higher crystallinity in the alkaline environment developing a nanorod-like structure, while in acid and neutral environments it has a preferential growth along the a(b)-plane with a lower crystallinity, developing a nanosheet-like structure. The different morphology and microstructure lead to different degradation behavior and performance of HA coatings. Immersion and electrochemical tests show that the neutral environment promote formation of HA coatings with high corrosion resistance. The cell culture experiments confirm that the enhanced corrosion resistance assure the biocompatibility of the substrate-coating system. In general, the HA coating prepared in neutral environment shows great potential in surface modification of magnesium alloys.

Quantitative texture analysis of a hydroxyapatite coatings plasma-sprayed on titanium substrates at different temperatures

Artificial hydroxyapatite exhibits an excellent biocompatibility with tissues of human body. However, poor mechanical properties of hydroxyapatites and low reliability in wet environments restrict their use. These limitations can be overcome by applying the hydroxyapatite as a coating onto metallic implants. X-ray diffraction analysis (restoration of orientation distribution function from pole figures and the Rietveld method) and scanning electron microscopy have been used to study thick (~330 μm) plasma-sprayed hydroxyapatite coatings. The coatings were deposited onto Ti – 2Al – 1Mn alloy substrates, one of which was held at room temperature (20°C) whereas the other substrate was preheated to 550°C. The texture of the coating deposited on substrate held at room temperature is characterized by the (001)[510] orientation, the volume fraction of which is 0.08, while the coating deposited on preheated substrate has the (001)[410] orientation, the volume fraction of which is 0.10. Results of texture analysis are qualitatively supported by the Rietveld refinement data. The problem of the formation of basal texture in plasma-sprayed hydroxyapatite coatings is discussed in terms of quantitative texture analysis in relation to the differences in the substrate temperature and spraying parameters. It was concluded that the quantitative texture analysis is of importance for deeper understanding the effect of spraying parameters on the formation of hydroxyapatite coatings.

Formation of Hydroxyapatite Coatings on Titanium by Plasma-Electrolytic Oxidation in Alkaline Electrolytes

We study the influence of the voltage (100–180 V) of plasma-electrolytic oxidation on the formation of hydroxyapatite coatings on VT1-0 commercially pure titanium in alkaline electrolytes (hydroxyapatite + 1 M potassium hydroxide). We analyze the physical and chemical characteristics of hydroxyapatite coatings (phase composition, thickness, porosity, and surface roughness) and establish the conditions of formation of coatings for which the ratio Ca/P is close to the values typical of biological hydroxyapatite.

Formation of hydroxyapatite coatings with addition of chitosan from aqueous solutions by thermal substrate method

Formation of hydroxyapatite coatings with addition of chitosan from aqueous solutions by thermal substrate method

Nucleation and growth of hydroxyapatite on arc-deposited TiO2 surfaces studied by quartz crystal microbalance with dissipation

Understanding of nucleation and growth kinetics of biomimetically deposited hydroxyapatite (HA) on crystalline TiO2 surfaces is important with respect to the application and performance of HA as functional implant coatings. Arc-evaporation was used to deposit TiO2 coatings dominated by anatase phase, rutile phase or their mixtures. Subsequent formation of HA from phosphate buffered saline solution (PBS) was investigated in real-time using in situ quartz crystal microbalance with dissipation technique (QCM-D). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to characterize the presence, morphology and crystal structure of TiO2 coatings and the formed HA. Increasing temperature of the PBS, increasing flow rate and applying a higher ion concentration in solution were found to accelerate HA nucleation process and hence affect growth kinetics. Lower PBS temperature resulted in the formation of HA coatings with flake-like morphology and increasing HA porosity. All TiO2 coatings under study enabled HA formation at body temperature, while in contrast Ti reference surfaces only supported HA nucleation and growth at elevated temperatures. QCM-D technique is a powerful tool for studying the impact of process parameters during biomimetic coating deposition on coating structure evolution in real time and provides valuable information for understanding, optimizing as well as tailoring the biomimetic HA growth processes.

Numerical Investigation on Particle Velocity in Cold Spraying of Hydroxyapatite Coating

Hydroxyapatite (HA) is a calcium phosphate ceramics and HA coating is essential for the medical metallic implants. This paper presents a novel cold spraying method for the formation of HA coatings instead of the commonly used thermal spraying method. The HA particle velocity in the cold spraying process is investigated numerically using a computational fluid dynamics (CFD) program, FLUENT. Stress is laid on how the geometric parameters of the nozzle and the process parameters influence the particle velocity. A Taguchi’s orthogonal array is employed to arrange the simulation conditions and the simulation results are analyzed by analysis of variance (ANOVA) method to reveal the main factors influencing HA particle acceleration significantly. The changes of the HA particle velocity under different cold spraying conditions are simulated to clarify the effects of the nozzle geometry, accelerating gas condition and property of particle itself on HA particle acceleration.

Preparation and characterization of hydroxyapatite coatings on human enamel by electrodeposition

Thin hydroxyapatite (HA) coatings, approximately from 1 μm to 10 μm in thickness, had been prepared on human enamel by electrodeposition with the current density of 0.5 mA/cm 2 at 55 °C in 1 h. They exhibited an acicular morphology and had a tight contact with the substrate by scanning electron microscope and transmission electron microscope observation. The comparison was made between the enamel specimens with HA coatings in this study and the sound enamel. In this comparison, while the Vickers micro-hardness showed a similar value, the antibacterial activities improved significantly after the formation of HA coatings. In conclusion, electrodeposition was proved to be an effective method for preparing HA coatings on human enamel and could be considered as a promising method to restore the initial enamel lesions in clinic.

A study of the process and kinetics of electrochemical deposition and the hydrothermal synthesis of hydroxyapatite coatings.

Hydroxyapatite (HAp) coatings were prepared using electrochemical deposition and post-hydrothermal synthesis. The composition and morphology of coatings at each processing step was studied through the application of scanning electron microscopy (SEM), X-ray diffraction (XRD) and infra-red spectroscopy (IR). The mechanism and kinetics of hydrothermal synthesis were considered in particular, and the influence of the temperature and time on the HAp formation rate was also investigated. The results show that the electrochemical deposition coatings are composed of CaHPO42H2O crystals which are converted into needle-like HAp crystals after post-hydrothermal treatment. The HAp content of the coatings increases with the treatment temperature and time. The synthesis rate also increases with the pH value of the water. The formation of HAp coatings is considered to be a combination of several reactions. An Arrhenius relationship was found between the HAp formation rate and the temperature, and an apparent activation energy of 94.4 KJ/mol was obtained by calculation.

The effect of electric field on the formation of hydroxyapatite coatings

A method using the action of an electric field on a continuously precipitating solution of calcium phosphate has been used to obtain reproducible hydroxyapatite coatings (1–2 μm) on a stainless steel substrate. The effect of changing various parameters on the nature of the coating was ascertained including constant current and constant voltage conditions, temperature, supersaturation and electrode spacing. The resultant coatings were characterised using electron microscopical and X-ray diffraction techniques. The mechanical properties were tested using a microhardness indentation technique, the results from which were used to give some indication of the strength and adhesion of the coatings. A model has been proposed to explain the observed phenomena in the precipitation and deposition processes. Amorphous calcium phosphate forms initially in the form of spheres. These spheres coalesce to form gel-like sheets in which hydroxyapatite nucleates. The gel sheets are attracted electrophoretically to the cathode where they are deposited as cells. Each cell wall comprises a number of 100 nm sized crystals oriented with their c-axis perpendicular to the substrate surface.