Electrochemical depositions of calcium phosphate film on commercial pure titanium and Ti–6Al–4V in two types of electrolyte at room temperature

Effects of Micro-Arc Oxidation Discharge Parameters on Formation and Biomedical Properties of Hydroxyapatite-Containing Flower-like Structure Coatings

The micro-arc oxidation (MAO) process was used to prepare hydroxyapatite-containing flower-like structure coatings on commercially pure titanium substrates with various values of the applied voltage (330, 390, 450 V), applied current (0.4, 0.5, 0.6 A), and duration time (1, 3, 5 min). It was found that the surface morphology of the coatings was determined primarily by the applied voltage. A voltage of 330 V yielded a flower-like/plate-like structure, while voltages of 390 V and 450 V produced a flower-like structure and a porous morphology, respectively. The applied current and duration time mainly affected the coating formation speed and petal size of the flower-like structures, respectively. The coatings prepared using voltages of 330 V and 390 V (0.6 A, 5 min) both contained Ti, TiO₂-A (anatase), TiO₂-R (rutile), DCPD (CaHPO₄·2H₂O, calcium hydrogen phosphate), and hydroxyapatite (HA). However, the latter coating contained less DCPD and had a higher HA/DCPD ratio and a Ca/P ratio closer to the ideal value of HA. The coating prepared with a voltage of 450 V consisted mainly of Ti, TiO₂-A, TiO₂-R, and CaTiO₃. For the coatings prepared with a voltage of 390 V, the flower-like structures consisted mainly of HA-containing compounds. DCPD plate-like structures were observed either between the HA-containing flower-like structures (330 V samples) or within the flower-like structures themselves (390 V samples). The coating surfaces with flower-like/plate-like or flower-like structures had a greater roughness, which increased their hydrophilicity and resulted in superior bioactivity (SBF immersion) and biocompatibility (MG-63 cell culture). The optimal biomedical performance was found in the 390 V coating due to its flower-like structure and high HA/DCPD ratio.

Rapid structural regulation, apatite-inducing mechanism and in vivo investigation of microwave-assisted hydrothermally treated titania coating

Owing to the poor bioactivity of microarc oxidation (MAO) coating and the rapid activation ability of the microwave hydrothermal (MH) technique, MH treatment was applied to optimize the in vivo interface status between MAO-treated titanium and bone. In this study, consequently, new outermost layers were prepared using hydroxyapatite (HA) nanorods, HA submicron pillars or sodium titanate nanosheets. The results revealed that the NaOH concentration significantly influenced the surface structure and phase constitution of the MAO samples. Moreover, on enhancing the NaOH concentration, the number of HA phases was decreased. Further, the influence of the NaOH concentration on the interfacial bonding strength was insignificant for concentrations ≤0.5 mol L⁻¹. Transmission electron microscopy (TEM) analysis showed that the induction of apatite was accompanied by the dissolution of the HA crystals and there was excellent crystallographic matching with the HA crystals. The in vitro and in vivo analyses revealed that the MH-treated MAO sample with the HA nanorods possessed superior apatite-formation ability and osseointegration, including a small amount of soft tissue and optimal bone–implant interfacial bonding force, thus signifying strong potential for the optimization of the bone–implant interfacial status.

In this work, the micro/nano scale structures of HA nanorods integrated on a titanium were prepared using MAO and MH treatment. The in vivo results indicate that HA crystals play a crucial role in the improvement of the osseointegration.

A mineral layer as an effective binder to achieve strong bonding between a hydrogel and a solid titanium substrate

This study has developed an effective strategy to bind a hydrogel with solid titanium by forming a CaCO₃ layer at their interface.

Effect of dissolution/precipitation on the residual stress redistribution of plasma-sprayed hydroxyapatite coating on titanium substrate in simulated body fluid (SBF)

The residual stress distributions in hydroxyapatite (HAp) coating with and without mixed hydroxyapatite/titanium (HAp/Ti) bond coating on commercially pure Titanium substrate (cp-Ti) were evaluated by Raman piezo-spectroscopy analysis. The Raman shifted position 962cm(-1), which is the symmetrical stretching of surrounded oxygen atoms with phosphorous atom ( [Formula: see text] ), was referred to analyses of stress dependency. The piezo-spectroscopic coefficient, which is a Raman shift value per stress (cm(-1)/GPa), was fitted from the result of four-points bending test of rectangular HAp bar and as-sprayed HAp on Zn plate. The calculated values were 3.89cm(-1)/GPa for the former and 7.11cm(-1)/GPa for the latter. By using these calibrations, the compressive residual stress in HAp coating with HAp/Ti bond coating (HA-B) has been found to be distributed in the range of -137MPa to -75MPa. For the heat-treated HAp coating (HA-B-HT) specimen, the compressive residual stresses placed in the range of -40--22MPa. The changes in the values of residual stress of the HAp coating after immersion in SBF were also evaluated. The residual stress in HA-WB specimens tend to change from compressive to tensile after 30 days immersion. The HA-B-HT specimens exhibited similar behavior and reached to zero stress after the immersion. The mechanism of the changes in residual stress would be the effect of stress redistribution around melted calcium phosphate particles to remained HAp splats.

In vivo cytotoxicity of MgO-doped nanobioactive glass particles and their anticorrosive coating on Ti–6Al–4V and SS304 implants for high load-bearing applications

Magnesium-doped NBG composites (SiO₂–CaO–P₂O₅–MgO) coated implant is found to be a potential nanocomposite for high load-bearing applications with better anticorrosive property and long-term stability.

Characteristics of Micro-Arc Treated Osseointegrated Porous Hydroxyapatite/Titanium Dioxide Coatings on Titanium Metal

A rapid and sufficient osseointegrating functions is obviously essential to the patients who suffered the bone reconstruction period. In order to perfectly target this issue, a single-stage micro-arc treated (MAT) coating beneficial from its inherent porous morphologies with controllable pore sizes, strong adhesive force between coatings and substrate and wide selections in electrolytes, is considered. Hydroxyapatite is extensively utilized and identified as mimic composition to human bone and an active bone ingrowth function. However, a controllable high-purity HAp phase via one-stage MAT has not yet been achieved. This study therefore prepares high-purity HAp coatings using one-stage MAT with the electrolyte combination of Calcium acetate and sodium biphosphate dihydrate on a titanium surface through a systematical evaluation of various MAT parameters, including Ca/P ratios of the electrolyte, electrolyte concentrations, working voltages, and treatment periods. Analytical results show that high-purity HAp can grow at a relatively high Ca/P ratio and electrolyte concentration when combined with a relatively high working voltage and long treatment time, which would otherwise grow with CaTiO3 and/or anatase TiO2 and/or rutile TiO2 simultaneously. Additionally, CaTiO3 acts a precursor phase for HAp formation. Ultimately, the highest purity of HAp coating is obtainable on metal titanium using a Ca/P ratio = 2.16 and applying a working voltage of 450 V for 10 min using one-stage MAT. This highest purity of HAp coating also presents excellent level of Ecorr than that on raw Ti alloys. The high Ecorr of HAp coating contributed from its thick and dense oxide layer by working voltage via one-stage MAT, consequently promises its satisfactory protection. The HAp coating demonstrated in this study not only provides the effective approach to produce the desired purity of HAp coatings but compromises its resistance to SBF. The bioactive HAp coating on Ti alloys via one-stage MAT, thus, considers as one significant surface modification for artificial hip joints and dental implants.

Failure behavior of plasma-sprayed HAp coating on commercially pure titanium substrate in simulated body fluid (SBF) under bending load

Four point bending tests with acoustic emission (AE) monitoring were conducted for evaluating failure behavior of the plasma-sprayed hydroxyapatite (HAp) top coat on commercially pure titanium (cp-Ti) plate with and without mixed HAp/Ti bond coat. Effect of immersion in simulated body fluid (SBF) on failure behavior of the coated specimen was also investigated by immersing the specimen in SBF. The AE patterns obtained from the bending test of the HAp coating specimens after a week immersion in SBF clearly showed the earlier stage of delamination and spallation of the coating layer compared to those without immersion in SBF. It was also found that the bond coating improved failure resistance of the HAp coating specimen compared to that without the bond coat. Four point bend fatigue tests under ambient and SBF environments were also conducted with AE monitoring during the entire fatigue test for investigating the influence of SBF environment on fatigue failure behavior of the HAp coating specimen with the mixed HAp/Ti bond coat. The specimens tested at a stress amplitude of 120 MPa under both ambient and SBF environments could survive up to 10⁷ cycles without spallation of HAp coating layer. The specimens tested under SBF environment and those tested under ambient environment after immersion in SBF showed shorter fatigue life compared to those tested under ambient environment without SBF immersion. Micro-cracks nucleated in the coating layer in the early stage of fatigue life and then propagated into the cp-Ti substrate in the intermediate stage, which unstably propagated to failure in the final stage. It was found from the XRD analysis that the dissolution of the co-existing phases and the precipitation of the HAp phase were taken place during immersion in SBF. During this process, the co-existing phases disappeared from the coating layer and the HAp phase fully occupied the coating layer. The degradation of bending strength and fatigue life of the HAp coating specimens tested under SBF environment would be induced by dissolution of the co-existing phases from the coating layer during immersion in SBF.

Electrochemical and mechanical behavior of laser processed Ti-6Al-4V surface in Ringer's physiological solution

Laser surface modification of Ti-6Al-4V with an existing calcium phosphate coating has been conducted to enhance the surface properties. The electrochemical and mechanical behaviors of calcium phosphate deposited on a Ti-6Al-4V surface and remelted using a Nd:YAG laser at varying laser power densities (25-50 W/mm(2)) have been studied and the results are presented. The electrochemical properties of the modified surfaces in Ringer's physiological solution were evaluated by employing both potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The potentiodynamic polarizations showed an increase in the passive current density of Ti-6Al-4V after laser modification at power densities up to 35 W/mm(2), after which it exhibited a decrease. A reduction in the passive current density (by more than an order) was observed with an increase in the laser power density from 25 to 50 W/mm(2). EIS studies at the open circuit potential (OCP) and in the passive region at 1.19 V showed that the polarization resistance increased from 8.274 × 10(3) to 4.38 × 10(5) Ω cm(2) with increasing laser power densities. However, the magnitudes remain lower than that of the untreated Ti-6Al-4V at OCP. The average hardness and modulus of the laser treated Ti-6Al-4V, evaluated by the nanoindentation method, were determined to be 5.4-6.5 GPa (with scatter <±0.976 GPa) and 124-155 GPa (with scatter <±13 GPa) respectively. The corresponding hardness and modulus of untreated Ti-6Al-4V were ~4.1 (±0.62) and ~148 (±7) GPa respectively. Laser processing at power densities >35 W/mm(2) enhanced the surface properties (as passive current density is reduced) so that the materials may be suitable for the biomedical applications.

Fatigue and Acoustic Emission Behavior of Plasma Sprayed HAp Top Coat and HAp/Ti Bond Coat with HAp Top Coat on Commercially Pure Titanium

In the conventional hydroxyapatite (HAp) coating, the surface of commercially pure titanium (Cp-Ti) is blasted with Al2O3 grid-blasting powders and then plasma-sprayed with HAp. To improve the adhesive strength of HAp coating, the grid-blasting with Al2O3 powders and subsequently wet-blasting by HAp/Ti mixed powders were applied on Cp-Ti substrate at ambient temperature. On the wet-blasted surface of Cp-Ti, two-layers of coating composed of HAp/Ti bond coat and HAp top coat were deposited by plasma spraying. Both types of HAp-coated specimen could survive up to 107 cycles without spallation of HAp coating at the stress amplitude of 120 MPa under four point bending fatigue test. In order to clarify mechanical failure behavior of the coatings and Ti substrate, acoustic emission (AE) signals during the entire fatigue process were observed. Relationship between AE behavior and cracking process of coated specimen was evaluated. HAp top coat with HAp/Ti bond coat strongly improved the adhesive and cohesive strength, where dense AE signals occurred at the early stage of fatigue test corresponded to plastic deformation of Ti substrate and micro-cracks in coated layers. AE signals occurred at the final stage corresponded to crack propagation in coated specimen and spallations of coated layers.

Electrodeposition on nanofibrous polymer scaffolds: Rapid mineralization, tunable calcium phosphate composition and topography

We developed a straightforward, fast, and versatile technique to fabricate mineralized nanofibrous polymer scaffolds for bone regeneration in this work. Nanofibrous poly(l-lactic acid) scaffolds were fabricated using both electrospinning and phase separation techniques. An electrodeposition process was designed to deposit calcium phosphate on the nanofibrous scaffolds. Such scaffolds contain a high quality mineral coating on the fiber surface with tunable surface topography and chemical composition by varying the processing parameters, which can mimic the composition and structure of natural bone extracellular matrix and provide a more biocompatible interface for bone regeneration.