Strength Of Hydroxyapatite Coatings Research Articles

Fabrication of Al2O3 by anodic oxidation and hydrothermal synthesis of strong-bonding hydroxyapatite coatings on its surface

Due to excellent mechanical properties and biocompatibility, A12O3 is considered as a promising biomaterial for biomedical applications. However, the inherent bio-inertness of A12O3 have limited its wider application. Although applying bioactive hydroxyapatite (HA) coatings on Al2O3 is an effective method to improve surface bioactivity, the bonding strength between the HA coatings and the flat A12O3 substrate is low. In this study, Al2O3 with micro-porous surface structure and hydrophilic surface was fabricated by anodic oxidation to improve the bonding strength between HA coatings and Al2O3. Then, strong-bonding HA coatings were prepared on the porous Al2O3 by hydrothermal synthesis. The results reveal the uniformity of pore distribution and the wettability of Al2O3 surface are significantly improved with the increase of current density and oxidation time. When the porous Al2O3 is prepared by anodic oxidation at 7 mA/cm2 for 4 h, the diameter of pores is 4.3–7.1 μm and the porous Al2O3 has a contact angle of 42.2 ± 2.6°. Nano-rod-like HA coatings completely and uniformly cover the surface of Al2O3 by hydrothermal synthesis at 180 °C for 24 h. The thickness of HA coatings is almost 30 ± 1.01 μm without delamination and/or cracking at the interface between HA coatings and Al2O3. The highest bonding strength of HA coatings on porous Al2O3 is 18.3 ± 2.4 MPa, which is higher than that of HA coatings formed on flat Al2O3 by other methods. In addition, simulated body fluid (SBF) immersion tests indicate that HA-coated Al2O3 possesses excellent biological activity in vitro. Hence, Al2O3 with bioactive HA coatings could be a candidate biomaterial for biomedical applications.

The Influence of Process Parameters on the Structure, Phase Composition, and Texture of Micro-Plasma Sprayed Hydroxyapatite Coatings

In this study, hydroxyapatite (HA) coatings were deposited on Ti-6Al-4V by micro-plasma spraying (MPS). The influence of the process parameters on the microstructure of HA coatings was investigated. The splat morphology and spreading behavior were examined to understand the influence of process parameters on the coating. The texture strength of HA coatings was characterized by X-ray diffraction (XRD). The texture coefficients were all applied to characterize the variation in texture. The morphology of splats and coatings were characterized by scanning electron microscopy (SEM). XRD pattern shows that the texture intensity of the c-axis of HA was greatly influenced by spraying distance and spraying current. SEM reveals the different texture strength of HA coatings with different ratios of columnar grains. The strongest c-axis texture was found in the coating by 60 mm spraying distance with a spraying current of 40 A. In the cross-section SEM images of the coating with the strongest c-axis texture, uniform distribution columnar grains were observed in the upper part (~100 μm). The investigation of splats indicates that columnar grain growth occurs after fully melted particles impact the heated substrate. By controlling the melting state prior to in-flight particle impacts, columnar grain growth can be achieved during slow solidification of the disk shape splat during MPS.

Significance of in-situ dry-ice blasting on the microstructure, crystallinity and bonding strength of plasma-sprayed hydroxyapatite coatings

To obtain hydroxyapatite (HA) coatings with high crystallinity which have long-term stability in clinical applications, coarse powders were usually injected to less energetic plasma. However, the HA coatings accumulated by partly melted particles usually have high porosity and poor mechanical properties, especially poor bonding strength. In this work, by profiting its quenching and mechanical impact, dry-ice blasting was in-situ employed during plasma spray process to improve the microstructure characterization and bonding strength of HA coatings. In addition, the influence of in-situ dry-ice blasting on the phase composition and crystallinity of plasma-sprayed HA coatings was investigated. The results show that a significant reduction of porosity and an apparent increase in bonding strength are revealed in plasma-sprayed HA coatings due to the cleaning effect of dry-ice blasting on the convex unmelted particles and splashing fragments. HA coatings prepared by the combination process of plasma spraying and dry-ice blasting have a compromise structure with minimum globular pores but with pronounced microcracks. The disappearance of CaO phase and the increase in crystallinity also derive from the application of dry-ice blasting.

Development of electrophoretically deposited hydroxyapatite coatings on anodized nanotubular TiO2 structures: Corrosion and sintering temperature

Hydroxyapatite (HA) coatings in and onto anodized TiO2 nanotube arrays were presented and prepared by electrophoretic deposition technique (EPD). Coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). EPD proved to be an innovative and versatile technique to coat HA on and into nanotubular structures of TiO2 with enhanced adhesion between nanotubes and HA particles provided by mechanical interlocking. After EPD of HA on TiO2 layer, samples were sintered at 400°C, 600°C and 800°C for 2h in an Ar atmosphere. Effect of EPD processing parameters on thickness of the deposits and rate of deposition was elucidated for HA coatings on the nanotubular TiO2 structures. It was shown that higher applied voltages increase deposition rate and thickness of the coatings. Potentiodynamic polarization measurements proved corrosion protection caused by both HA coating and nanotubular TiO2 structure in simulated body fluid (SBF). Effect of sintering temperature on adhesion strength of HA coatings on TiO2 nanotubes and their composition were also studied.

Electrodeposited hydroxyapatite coatings on the TiO2 nanotube in static magnetic field

Uniform hydroxyapatite (HA) grains were electrochemically deposited on the titania nanotube arrays (TNTs) in an electrolyte containing 0.042mol/L calcium nitrate (Ca(NO3)2) and 0.025mol/L ammonium dihydrogen phosphate (NH4H2PO4) in static magnetic field and then characterized by SEM, XRD, EDS, FTIR. To study the effect of magnetic fields on the morphology and adhesive strength of HA coatings on TNTs, the specimens were deposited in magnetic fields of different directions and intensities. The results indicate that the morphologies of HA crystals are plate-like, needle-like and spherical when the specimens were deposited in force-free magnetic field (B=0), in the magnetic field perpendicular (B⊥J) and parallel to the current direction (B∥J), respectively. Due to the action of the Lorentz force, which generates convection in the electrolyte, mass transport may increase significantly. This main effect in electrochemistry was called the magnetohydrodynamic (MHD) effect and is well-established. Additionally, increasing the intensity of magnetic fields improves the adhesive strength of HA coatings: as the intensity increases from 0.25T to 1T, the adhesive strengths of composite electrodeposited in perpendicular and parallel conditions, respectively, increase from 20.1MPa and 16.7MPa to approximately 26.5MPa and 24.7MPa that are almost 2.5 times as strong as the control specimen.

203 ハイドロキシアパタイト皮膜の密着強度評価

203 ハイドロキシアパタイト皮膜の密着強度評価

EFFECT OF STAND-OFF DISTANCE ON STRUCTURE AND MECHANICAL PROPERTIES OF HYDROXYAPATITE COATINGS PLASMA-SPRAYED ONTO CARBON/CARBON COMPOSITES

Plasma-spraying parameters are of crucial importance to the fabrication of high-quality hydroxyapatite (HA) coating for biomedical use. In this paper, hydroxyapaptite was coated onto carbon fiber reinforced carbon composites ( C/C composites) by a plasma spraying method. The effect of stand-off distances on the microstructure, phase composition and shear strength of hydroxyapatite coatings was studied. X-ray diffraction (XRD) was used to characterize the phase composition and scanning electron microscopy (SEM) examined the morphology of the sprayed surface and polished cross-sections. The shear strength of the HA coatings– C/C substrates was detected on a RGD-5 electric tension machine. The interface of the HA coating– C/C composites was also detected. Results showed that the extent of melting of particles increased with increasing stand-off distances, while the crystallinity of the HA decreased at a power level of 30 kW. Mechanical bonding plays a dominant role at the interface of the rough substrate and the deformed HA particles.

Grit blasting of Ti–6Al–4V alloy: Optimization and its effect on adhesion strength of plasma-sprayed hydroxyapatite coatings

The effect of grit blasting parameters on the surface roughness of Ti–6Al–4V alloy as the substrate for plasma-sprayed hydroxyapatite (HA) coatings was examined using the factorial and Taguchi designs of experiments. In this study, two grit materials (Al2O3 and SiO2) each at two sizes, and two types of blasting systems (pressure and suction) were used. An equivalent surface roughness of 3.51 μm was obtained in three optimum conditions. The results of the Taguchi designed experiments were analyzed using signal to noise ratio. The tensile bonding strength of HA coatings deposited on the roughened substrates at the three different optimum conditions was measured by the standard adhesion test (ISO 13779-4). As the crystallinity of the coating at the interface, evaluated by the XRD analysis, reduced the bonding strength of the coatings was increased. These findings suggest that the substrate surface topography significantly influences the properties of the coating at the interface.

Effect of Heat Treatment on Characteristics of Plasma Sprayed Hydroxyapatite Coatings

Bioactive hydroxyapatite (HA)-coated implants plasma sprayed on Ti6Al4V substrates have been widely used in load-bearing applications because of their biocompatibility and their intimate contact with bone. The improvement of the characteristics of HA coatings is concerned. The purpose of this work was to evaluate corrosion behavior and bond strength of HA coatings after post-deposition heat treatment at 500–700 � C. The results indicated that the heat treatment led to recrystallization of amorphous calcium phosphate of as-sprayed HA coatings. The reduction of layer defects associated with plasma-sprayed coatings and the enhancement of the resistance to corrosion took place after heat treatment. Bond strength of the heat-treated coatings was sensitive to the treatment temperature. It is concluded that the heat treatment at 600 � C for 1 h in air, endowing with increased crystallinity and the reduced defects without significantly reduced bond strength, provided a better corrosion protection than the other two treatment temperatures.

Titanium dioxide reinforced hydroxyapatite coatings deposited by high velocity oxy-fuel (HVOF) spray

Hydroxyapatite (HA) coatings with titania addition were produced by the high velocity oxy-fuel (HVOF) spray process. Mechanical properties of the as-sprayed coatings in terms of adhesive strength, shear strength and fracture toughness were investigated to reveal the effect of the titania reinforcement on HA. Qualitative phase analysis with X-ray diffraction (XRD) showed that mutual chemical reaction between TiO 2 and HA, that formed CaTiO 3 occurred during coating formation. Differential scanning calorimetry (DSC) analysis of the starting powders showed that the mutual chemical reaction temperature was ∼1410°C and the existence of TiO 2 can effectively inhibit the decomposition of HA at elevated temperatures. The positive influence of TiO 2 addition on the shear strength was revealed. The incorporation of 10 vol% TiO 2 significantly improved the Young's modulus of HA coatings from 24.82 (±2.44) GPa to 43.23 (±3.20) GPa. It decreased to 38.51 (±3.65) GPa as the amount of TiO 2 increased to 20 vol%. However, the addition of TiO 2 has a negative bias on the adhesive strength of HA coatings especially when the content of TiO 2 reached 20 vol%. This is attributed to the weak chemical bonding and brittle phases existing at the splats’ interface that resulted from mutual chemical reactions. The fracture toughness exhibited values of 0.48 (±0.08) MPa m 0.5, 0.60 (±0.07) MPa m 0.5 and 0.67 (±0.06) MPa m 0.5 for the HA coating, 10 vol% TiO 2 blended HA coating and 20 vol% TiO 2 blended HA coating respectively. The addition of TiO 2 in HA coating with the amount of less than 20 vol% is suggested for satisfactory toughening effect in HVOF HA coating.