Structure and apatite formation of microarc oxidized TiO2-based films before and after alkali-treatment by various alkali concentrations

Alkali-treatment was performed to modify the surface of the TiO₂-based film containing Ca and P prepared by microarc oxidation (MAO) technique for improving the apatite-forming ability of the MAO film. Before alkali-treatment, in the MAO film amorphous and crystalline regions with main composition of Ti, Ca, P and Al both were observed; and in the latter TiO₂ nanocrystals were randomly distributed in Ca- and P-doped matrix. After alkali-treatment, the surfaces of the MAO films become rough, and the Ca and P concentrations decrease with increasing the concentration of NaOH solution (1, 3 and 5 mol/L). When 5 mol/L NaOH solution was used, amorphous calcium titanate hydrogel was formed on the surface, showing a nanoflake-like morphology. In vitro experiment indicates that the ability to induce apatite formation of the alkali-treated MAO films increase with increasing the concentration of NaOH solution, which is associated with the formation of Ti-OH groups during the incubation process in a simulated body fluid.     

The nature of the copper sulfide film grown on copper in aqueous sulfide and chloride solutions

In this paper, the properties of copper sulfide films formed both anodically and naturally in deaerated/anoxic aqueous sulfide and chloride solutions were investigated using a series of electrochemical and surface analytical techniques. A combination of cyclic voltammetric, corrosion potential (E_corr), and cathodic stripping voltammetric experiments showed that the sulfide film growth kinetics and film morphologies were controlled by the supply of SH⁻ from the bulk solution to the copper surface. There was no passive barrier layer observed on the copper surface under either electrochemical or corrosion conditions. The film morphology was dependent on the type and concentration of anions (SH⁻, Cl⁻) present in the solution. Scanning electron microscopy on both surfaces and focused ion beam-cut cross-sections showed the growth of a thin, but porous, base layer of chalcocite (Cu₂S) after short immersion periods (up to 2 hr) and the continuous growth of a much thicker crystalline outer deposit over longer immersion periods (≥36 hr), suggesting a solution species transport-based film formation process and the formation of an ineffective thin “barrier-type” layer on copper.     

XPS study on potential suppression factors of suppressing in vitro apatite formation on anatase films prepared on various substrates

Multilayer anatase films were coated by sol-gel technology on various substrates such as stainless-steel, alumina, and glass, respectively. Their in vitro apatite-forming ability was examined by immersion in Kokubo's simulated body fluid (SBF; pH 7.4, 36.5 °C). Although on anatase layer on alkali-free glass apatite was deposited within 7 d, no apatite was found on anatase deposited onto stainless steel, alumina or glass substrates within 7 d to prove they were bioinert. X-ray photoelectron spectroscopy was able to detect chromium, aluminum, or sodium on the surface of the anatase films. This indicated that these ions possibly inhibited the in vitro apatite-forming ability.     

Effect of Ti-OH formation on bioactivity of vacuum plasma sprayed titanium coating after chemical treatment

The effect of Ti-OH groups on bioactivity of NaOH treated titanium coating was investigated in this paper. The NaOH-heat treatment was also applied to modify the titanium coating for comparison. The results show that the amount of Ti-OH groups was important to induce apatite formation on the treated titanium coating. When the NaOH treated titanium coating was exposed to SBF, it released Na⁺ ions from the sodium titanate layer on its surface into the SBF via exchanging with H₃O⁺ ions in the fluid and Ti-OH groups were rapidly formed on the surface. So the NaOH treated titanium coating has good bioactivity in simulated body fluid (SBF). The amount of Ti-OH groups on the titanium coating was reduced after heat treatment, so the bioactivity of NaOH-heat treated titanium coating was obviously affected.     

Preparation and in vitro characterization of crack-free mesoporous titania films

Crack-free mesoporous titania films (MTFs) on Ti6Al4V demonstrated potential application for implanting and bone regeneration materials in the future. The MTFs were prepared on Ti6Al4V substrate by an evaporation-induced self-assembly (EISA) process. The BET surface area, pore volume, and pore size of the MTFs samples were calculated to be 190 m²/g, 0.31 cm³/g, and 4.8 nm, respectively. The apatite-forming ability of the MTFs was evaluated by immersing them in simulated body fluid (SBF). After immersion in SBF for 5 days, bone-like apatite was induced on the surface of the MTFs. With increasing immersion time, the apatite would continue to grow and cover the surface of the MTFs. The apatite induced by MTFs contains Mg and Na ions, carbonated moieties and nano-network structure. In this work, preliminary investigation of the MG63 cell proliferation on the surface of the MTFs was also conducted. The cell experiment indicated that the MTFs possessed good biocompatibility and can thus provide a surface suitable for MG63 cell proliferation. The effects of surface properties and mesostructure on inducing apatite and cell proliferation were also discussed.     

Biomimetic apatite induction of P-containing titania formed by micro-arc oxidation before and after hydrothermal treatment

Phosphorous (P)-containing titania films were prepared by micro-arc oxidation (MAO) of titanium (Ti) in an electrolyte containing β-glycerol phosphate disodium salt pentahydrate (β-GP, C₃H₇Na₂O₆P^.5H₂O), and their apatite inducing ability in a simulated body fluid (SBF) was investigated. Macro-porous titania films were formed, consisting of only anatase phase, and the P content in the films increased up to 8 at.% with an increasing applied voltage. During hydrothermal treatment, the P in the films was diffused out to the surface and hydrolyzed to form the hydrogen phosphate (HPO₄²⁻) group. When immersed in SBF, no apatite was induced in any of the P-containing MAO specimens for up to 28 days. However, after a hydrothermal treatment at 250 °C, apatite was induced on the titania surfaces as early as 9 h immersion, and the entire exposed surface was covered with the apatite globules after 36 h immersion, which was much faster than the apatite induction on Ca-containing titania. The higher apatite-inducing ability of P-containing titania after hydrothermal treatment was believed to be due to the crystal structure (anatase) and presence of HPO₄²⁻ group on the surface.     

Apatite formation in Hanks' solution on β-Ca2SiO4 films prepared by MOCVD

β-Ca₂SiO₄ film in a single phase was prepared by metalorganic chemical vapor deposition (MOCVD) and immersed in Hanks' solution to evaluate the apatite formation ability. Apatite formed on the surface of the β-Ca₂SiO₄ film after immersion for 1 d. A dense apatite layer covered the β-Ca₂SiO₄ film surface after immersion for 7 d. CO₃²⁻ and PO₄³⁻ groups were identified by Fourier transform-infrared spectroscopy (FT-IR) after immersion for 1 d. The shape of apatite changed from granular to needle-like to densely packed granular with increasing immersion time from 1 d to 14 d.     

Effects of plasma treatment on bioactivity of TiO2 coatings

In this work, nano-TiO₂ powders were deposited on titanium alloy substrates by atmospheric plasma spraying, followed by plasma immersion ion implantation (PIII) using hydrogen, oxygen and ammonia gases. The bioactivities of PIII-treated TiO₂ coatings were evaluated by the formation of apatite on their surface after soaked in simulated body fluids (SBF) for a period of time. As-sprayed TiO₂ coating is composed of rutile, anatase and TiO_2−x (most of them is Ti₃O₅). After immersion in SBF for two weeks, the hydrogen PIII-treated TiO₂ coating can induce bone-like apatite formation on its surface but apatite cannot be formed on the surface of as-sprayed and oxygen, ammonia PIII-treated TiO₂ coatings. The results obtained indicated that a hydrogenated surface plays a very important role to induce bioactivity of TiO₂ coatings.     

Effect of heat treatment on the structure and in vitro bioactivity of microarc-oxidized (MAO) titania coatings containing Ca and P ions

Microarc oxidized (MAO) coating containing TiO₂ and amorphous calcium phosphate was formed on Ti6Al4V in an electrolyte containing EDTA-Ca and phosphate. Subsequent heat treatment has significant effects on the structure and in vitro bioactivity of the MAO coating. After heat treatment (400-800 °C), the crystallinity of TiO₂ increases, and micropore numbers of the MAO coating decline. Moreover, Ca₃(PO₄)₂ is formed on the surfaces of the MAO coatings after heat treatment at 700 and 800 °C. The SEM and ICP-OES results indicate that the abilities of apatite-forming and Ca and P releasing of the MAO coating decrease after heat treatment. The apatite-forming ability of the MAO coating is associated with the crystallinities of titanium oxide and calcium phosphate. The MAO coating containing TiO₂ with a low crystallinity and amorphous calcium phosphate facilitates the apatite formation in vitro. In addition, the induced biomimetic apatite by the MAO coating without heat treatment exhibits carbonated structure, controllable crystallinity and pore networks on the nanometer scale.     

Biomimetic deposition of apatite coatings on micro-arc oxidation treated biomedical NiTi alloy

The biomedical NiTi alloy was treated by micro-arc oxidation in an electrolytes containing sodium aluminate and sodium hypophosphite at 400 V constant voltages for 30 min. The MAO-treated NiTi has a porous microstructure on its surface and coatings consisting only of the γ-Al₂O₃ phase. The ceramic coating prepared by micro-arc oxidation is composed of Al, Ti, Ni, O, and P with the atomic concentration of 26.98%, 3.67%, 3.33%, 65.30% and 0.72%, respectively. The MAO-treated NiTi was soaked in a simulated body fluid (1.0SBF) to investigate the biomimetic deposition of apatite on the surface of Al₂O₃ coated NiTi alloy. It was found that Al₂O₃ coated NiTi alloy shows an excellent apatite-forming ability after soaking in a simulated body fluid (1.0SBF) for 14 days, while no apatite-forming ability was observed on bared NiTi alloy even though soaking time is up to 28 days.     

Surface structure changes on aluminosilicate microspheres at the interface with simulated body fluid

Aluminosilicate microspheres obtained by spray drying were investigated in prospect of their potential biomedical applications. The as-prepared microspheres are amorphous. TEM and AFM were used to examine the morphology of the samples before and after immersion in simulated body fluid (SBF). The local structure changes as a function of microspheres composition and due to their immersion in SBF were investigated by ²⁹Si and ²⁷Al MAS–NMR. After SBF immersion, the silica network partially depolymerised by hydration/hydroxylation and the completely changed aluminium environment suggest a phylosilicate-like structure. ³¹P MAS–NMR analysis evidenced phosphorus ions incorporated in a new crystalline phase developed during SBF immersion.     

Effect of a bioactive glass-ceramic on the apatite nucleation on titanium surface modified by micro-arc oxidation

The aim of this work was to evaluate the ability of a bioactive glass-ceramic to induce the apatite nucleation on the titanium oxide layer produced by micro-arc oxidation. “In vitro” tests were carried out on a simulated body fluid solution in two different manners: one group was soaked in the SBF, while the other group was soaked together with the bioactive glass-ceramic. Results revealed that after 7 days, the specimens soaked in SBF were covered with an amorphous calcium phosphate layer, while the specimens soaked in SBF plus glass-ceramic formed a crystalline apatite layer, suggesting thus, that the glass-ceramic provides silanol groups that accelerated the hydroxyapatite apatite precipitation on the anodic TiO₂ layer.     

Surface modification of titanium by chemical and thermal methods – electrochemical impedance spectroscopic studies

Abstract

The surface modification of untreated, alkali treated and alkali heat treated titanium has been investigated by electrochemical impedance spectroscopic technique. The substrates were treated with 10M NaOH aqueous solutions and subsequently heat treated at 600°C, a thin sodium titanium layer was formed on their surfaces. Thus, the treated substrates formed a dense and uniform bone-like apatite layer on their surfaces in simulated body fluid (SBF) solution. This indicates that the alkali and heat treated titanium bond to living bone through the bonelike apatite layer formed on their surface in the body. Electrochemical impedance spectroscopic (EIS) experiments were performed in SBF solution as a function of immersion time. Data of EIS were taken for untreated and the results revealed the formation of one additional layer along with the barrier layer. In case of alkali treated sample, titania gel layer alone dissolves completely and forms apatite and barrier layers, whereas, the alkali and heat treated samples showed three layers namely apatite, gel and barrier layers. The nature of these layers has been obtained by fitting the EIS data to suitable equivalent electrical circuit models. The alkali heat treated titanium results in the faster apatite nucleation and growth on the surface. Immersion in SBF solution exhibited higher apatite film resistance compared to alkali treated and untreated titanium substrate.     

In vitro bioactivity and osteoblast response on chemically modified biomedical porous NiTi synthesized by capsule-free hot isostatic pressing

Porous biomedical NiTi with an average porosity of 56% and a general pore size of 50-800 μm was synthesized by capsule-free hot isostatic pressing (CF-HIP) with NH₄HCO₃ as a space holder. In order to enhance the surface bioactivity, the porous alloy was subjected to H₂O₂ to form a TiO₂ coating followed by a NaOH treatment. Scanning electron microscopy (SEM), thin film X-ray diffraction (TF-XRD), and X-ray photoelectron spectroscopy (XPS) revealed that a porous sodium titanate (Na₂TiO₃) film formed on the surface of the porous NiTi due to the chemical reaction between NaOH and pre-formed TiO₂ at the interface between the NaOH solution and porous NiTi. An apatite layer was formed on the film after immersion in simulated body fluids (SBF) at 37 °C while no apatite could be found on the surface of the untreated porous NiTi. Formation of the apatite layer indicates that the chemically treated porous NiTi possesses excellent bioactivity and this bodes well for applications in bone implants. In our preliminary cell culture tests, osteoblast cells were found to attach and proliferate better on the chemically treated samples compared to the untreated alloys.     

The inhibition effect of two commercial compounds on interface steel/natural softened water

The protection against the corrosion of the carbon steel in aqueous environment by commercial inhibitors, based of nitrite and alkanolamine, has been studied by electrochemical impedance spectroscopy (EIS) and several analytic methods. An inhibitor’s efficiency has been determined with the two compounds on polished surface in presence of softened water. The results show that the two inhibitors act by the formation of protective layer on interface steel/electrolyte but the efficiency is more important in the case of the nitrite compound thanks to the formation of film with thickness estimated by Atomic force microscopy (AFM) at 0.8 μm after 102 days of immersion. In the case of the nitrites, the inhibitor film is a porous layer, weak conductor and presents a considerable increase of the charge transfer resistance with time. This is a result of an interest protection of the surface against corrosion. The low frequencies limit (L _LF) reaches about 150 kOhm cm² after 59 days of immersion. In the case of the alkanolamine, XPS (X-Rray Spectroscopy) show that the film formed is richer of Fe ions but is offered a considerable protection of the interface, its thickness is about 0.26 μm and L _LF reaches about 35.5 kOhm cm² after 61 days of immersion. The influence of surface state is discussed in this paper, in fact on raw surface steel, no inhibitor efficiency is observed. A few protections are given with a crude surface in contact with water softened in presence of the nitrite compound.     

Carbo-oxidising of titanium by diffusion treatment in carbon–oxygen containing media

Abstract

The surface engineering of titanium with TiC_xO_1?x coatings through diffusion carbo-oxidising from graphite in oxygen containing media is investigated. The effect of oxygen partial pressure on phase composition of coatings during carbo-oxidising is evaluated. The interval of oxygen partial pressure allowing the carbo-oxide TiC_xO_1?x to form is defined as 10^?2–10³ Pa. The effects of process temperature and time on evolution of TiC_xO_1?x composition and morphology of surface layer have been investigated. It is determined that increases in temperature and process time favour an increase in carbon content in TiC_xO_1?x. It is revealed that at temperatures above the transformation temperature T_α?β, TiC_xO_1?x is formed not only in coating but also throughout grain boundaries of diffusion layer. The stages of carbo-oxide formation during diffusion carbo-oxidising of commercially pure titanium are explained as follows: surface saturation with oxygen; formation of TiO₂ film; oxide dissolution and formation of diffusion layer; formation of non-stoichiometric TiC_x and TiO_x and their interaction resulting in TiC_xO_1?x formation. Corrosion properties of carbo-oxide coatings tested in 80%H₂SO₄ are compared with nitride and oxide coatings. It is revealed that carbo-oxide coating demonstrates better corrosion resistance. The tribological properties of carbo-oxide, nitride and oxide coatings tested with bronze counterbody are compared, and carbo-oxide coating demonstrates better wear resistance.     

New generation hopeite coating on Ti6Al4V (TC4) by radio frequency magnetron sputtering for prosthetic-orthopaedic implant applications: synthesis and characterisation

ABSTRACT

Bioceramic coatings with multifunctionality have emerged as an effective alternative to conventional coatings, owing to their combination of various properties that are essential for bio-implants, such as osseointegration and antibacterial character. In the present study, thin hopeite coatings were synthesised by radio frequency magnetron sputtering on TC4 substrates. The obtained hopeite coatings were thermally treated at 500°C in ambient air and characterised in terms of surface morphology, phase composition, surface roughness, adhesion strength, antibacterial efficacy, apatite forming ability, surface wettability and corrosion resistance by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Atomic Force Microscopy(AFM), Tensometer, Fluorescence-Activated Cell Sorting (FACS), Simulated Body Fluid (SBF) immersion, Contact Angle Goniometer and potentiostatic polarisation respectively. It was observed that the post-deposition annealing increases the crystallinity of the synthesised hopeite coatings. SEM analysis showed deposited particles are spherical in shape and small in dimensions (<1?μm in diameter). XRD results confirm the deposited coating is crystalline in nature. AFM analysis reveals deposited hopeite coating has an average surface roughness value of 8.66?nm. Tensile pullout experiments indicated that the adhesive strength of the hopeite coating is 21.75?±?2.1?MPa. FACS study confirms the deposited hopeite coating possesses antibacterial character. SBF immersion experiments clearly demonstrate apatite growth on the surface of the deposited hopeite coating. The surface wettability test showed that the deposited coatings are hydrophobic in character having an average contact angle value of 136.65°. Potentiodynamic polarisation experiments in SBF showed a significant improvement in corrosion resistance (R_p?=?7945.87?Ω?cm²) of hopeite coated samples. In summary, it can be concluded that the new generation multifunctional hopeite coating synthesised by an alternative new process route of radio frequency magnetron sputtering on TC4 substrates is an effective alternative to conventional coatings. This is largely attributed to the strong osseointegration and antibacterial character of deposited hopeite coating ensuring the overall stability of metallic orthopaedic implants.     

Structure of calcium titanate/titania bioceramic composite coatings on titanium alloy and apatite deposition on their surfaces in a simulated body fluid

In this study, TiO₂-based coatings containing Ca and P ions were prepared on titanium alloy surfaces by microarc oxidation (MAO). After soaking in aqueous NaOH solution and subsequent heat treatment at 700 and 800 °C, calcium titanate/titania bioceramic composite (CTBC) coatings were obtained. The results show that the outer layers (0–1.5 μm) of the CTBC coatings are mainly composed of Ca, Ti, O and Na constituents with a uniform distributions with increasing the depth near the surfaces. The surface phase compositions of the CTBC coating formed at 700 °C are anatase, rutile and CaTi₂₁O₃₈ phases, as well as a few CaTiO₃, while those of the CTBC coating formed at 800 °C are anatase, rutile and CaTiO₃. When incubated in a simulated body fluid (SBF), apatite was deposited on the CTBC coatings probably via formation of hydroxyl functionalized surface complexes on the CTBC coating surfaces by ionic exchanges between (Ca²⁺, Na⁺) ions of the CTBC coatings and H₃O⁺ ions in the SBF. The CTBC coating formed at 800 °C seems to facilitate the deposition of Ca and P probably due to the good crystallographic match between perovskite CaTiO₃ and HA on specific crystal planes.     

In situ growth of Mg–Al hydrotalcite conversion film on AZ31 magnesium alloy

In situ growth of Mg–Al hydrotalcite conversion film on AZ31 alloy has been developed by a two-step method. The characteristics of the films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electronic microscope (SEM) observation, electrochemical and immersion tests. The film formation process was proposed based on the open circuit potential (OCP) measurements and surface analysis. A precursor film with network cracks is first formed and then this film is transformed into a compact and uniform hydrotalcite (Mg₆Al₂(OH)₁₆CO₃·4H₂O) film after the post treatment. This dense Mg–Al hydrotalcite film can provide effective protection to the AZ31 alloy.     

可降解血管支架用Mg-4.0Zn-0.2Mn-0.2Ca微细管的体外降解行为

通过浸泡实验和电化学测试研究了Mg-4.0Zn-0.2Mn-0.2Ca（质量分数）微细管的体外降解行为与腐蚀机理。结果表明,退火处理可以提高微细管的耐腐蚀性。长期浸泡实验表明腐蚀过程相对均匀,退火微细管在Hank''s溶液中的腐蚀速率约为0.30 mm/a。在浸泡初期,退火管材表面生成Mg(OH)₂,形成保护膜,阻碍腐蚀进行。虽然Mg(OH)₂膜上形成的羟基磷灰石（HA）可以进一步降低腐蚀速率,但是镁基体中粗大的第二相会增强电偶腐蚀效应,并且生成的大量氢气,从而破坏HA膜,使腐蚀继续进行。