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/mm²) 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/mm², 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/mm². 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 × 10³ to 4.38 × 10⁵ Ω cm² 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/mm² enhanced the surface properties (as passive current density is reduced) so that the materials may be suitable for the biomedical applications.     

Fabrication and characterization of bioactive composite coatings on Mg–Zn–Ca alloy by MAO/sol–gel

High corrosion rate and accumulation of hydrogen gas upon degradation impede magnesium alloys’ clinical application as implants. In this work, micro-arc oxidation (MAO) was used to fabricate a porous coating on magnesium alloys as an intermediate layer to enhance the bonding strength of propolis layer. Then the composite coatings were fabricated using sol–gel method by dipping sample into the solution containing propolis and polylactic acid at 40°C. The corrosion resistance of the samples was determined based on potentiodynamic polarization experiments and immersion tests. Biocompatibility was designed by observing the attachment and growth of wharton’s jelly-derived mesenchymal stem cells (WJCs) on substrates with MAO coating and substrates with composite coatings. The results showed that, compared with that of Mg–Zn–Ca alloy, the corrosion current density of the samples with composite coatings decreased from 5.37 × 10⁻⁵ to 1.10 × 10⁻⁶ A/cm² and the corrosion potential increased by 240 mV. Composite coatings exhibit homogeneous corrosion behavior and can promote WJCs cell adhesion and proliferation. In the meantime, pH value was relatively stable during the immersion tests, which may be significant for cellular survival. In conclusion, our results indicate that composite coatings on Mg–Zn–Ca alloy fabricated by MAO/sol–gel method provide a new type bioactive material.     

Calcium and titanium release in simulated body fluid from plasma electrolytically oxidized titanium

The release of titanium and calcium species to a simulated body fluid (SBF) at 37°C has been investigated for titanium treated by dc plasma electrolytic oxidation (PEO) in three different electrolytes, namely phosphate, silicate and calcium- and phosphorus-containing. The average rate of release of titanium over a 30 day period in immersion tests, determined by solution analysis, was in the range ~1.5–2.0 pg cm⁻² s⁻¹. Calcium was released at an average rate of ~11 pg cm⁻² s⁻¹. The passive current densities, determined from potentiodynamic polarization measurements, suggested titanium losses of a similar order to those determined from immersion tests. However, the possibility of film formation does not allow for discrimination between the metal releases due to electrochemical oxidation of titanium and chemical dissolution of the coating.     

Silver coated bioactive glass particles for wound healing applications

Bioactive glass particles (0.42SiO₂–0.15CaO–0.23Na₂O–0.20ZnO) of varying size (<90 μm and 425–850 μm) were synthesized and coated with silver (Ag) to produce Ag coated particles (PAg). These were compared against the uncoated analogous particles (Pcon.). Surface area analysis determined that Ag coating of the glass particles resulted in increased the surface area from 2.90 to 9.12 m²/g (90 μm) and 1.09–7.71 m²/g (425–850 μm). Scanning electron microscopy determined that the Ag coating remained at the surface and there was little diffusion through the bulk. Antibacterial (Escherichia coli—13 mm and Staphylococcus epidermidis—12 mm) and antifungal testing (Candida albicans—7.7 mm) determined that small Ag-coated glass particles exhibited the largest inhibition zones compared to uncoated particles. pH analysis determined an overall higher pH consider in the smaller particles, where after 24 h the large uncoated and Ag coated particles were 8.27 and 8.74 respectively, while the smaller uncoated and Ag coated particles attained pH values of 9.63 and 9.35 respectively.     

Corrosion behavior in SBF for titania coatings on Mg–Ca alloy

TiO₂ coating was obtained by sol–gel method to improve the corrosion resistance of Mg–Ca alloy in human body environment. The corrosion behavior of Mg–1.0 Ca alloy with TiO₂ coating was investigated by electrochemical tests and immersion tests in simulated body fluid (SBF). Bare Mg–1.0 Ca alloy suffered serious attack after immersed in simulated body fluid only for 48 h. While for the Mg–1.0 Ca alloy with TiO₂ coating, the surface almost maintained intact with only several collapses after immersed in SBF for 168 h. The electrochemical test results showed that the free corrosion current (i _corr) of Mg–1.0 Ca alloy substrate was 3.3275e−2A/cm², while the i _corr of TiO₂ coating was only 1.58549e−5A/cm². Therefore, TiO₂ coating significantly improved the corrosion resistance of Mg–1.0 Ca alloy in SBF. This enhances the potential of Mg–Ca alloy used as biodegradable orthopedic material.     

Bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid

The purpose of this study was to investigate bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid (SBF). Calcium phosphates were electrodeposited on commercially pure titanium substrates in the modified SBF at 60 °C for 1 h maintaining the cathodic potentials of − 1.5 V, − 2 V, and − 2.5 V (vs. SCE). Subsequently, the calcium phosphate coatings were transformed into apatites during immersion in the SBF at 36.5 °C for 5 days. The apatites consisted of needle-shaped crystallites distributed irregularly with different grain sizes. As the coatings were electrodeposited at higher cathodic potential, the crystallite of the apatites got denser and the grain sizes of the apatites became bigger during subsequent immersion in the SBF. However, as the coatings were electrodeposited at higher cathodic potential, the coatings were transformed into apatites with lower crystallinity and the Ca/P atomic ratio of the apatites got higher than 1.67, that of stoichiometric hydroxyapatite, after subsequent immersion in the SBF. In addition, CO₃²⁻ ions contained in the modified SBF were incorporated in the calcium phosphate coating during electrodeposition and had an influence on transforming the calcium phosphate into bonelike apatite during subsequent immersion in the SBF showing that CO₃²⁻ incorporated in the apatites disturbed crystallization of the apatites. These results revealed that the coating electrodeposited at − 2.0 V (vs. SCE) in the modified SBF containing CO₃²⁻ ions was the most bioactive showing transformation into carbonate apatite similar to bone apatite.     

Preparation, release profiles and antibacterial properties of vancomycin-loaded Ca-P coating titanium alloy plate

The aim of the study was to explore the feasibility of the Ca–P coating titanium alloy plate to be used as the vancomycin drug-delivery system by biomimetic coating technology. Through the X-ray diffraction study, the main components of the coatings were identified as octocalcium phosphate. The in vitro vancomycin release, bacteriostasis activity to Staphylococcus aureus (S. aureus), the scanning electron microscope (SEM) image and osteoblast adhesion and proliferation test of vancomycin-loaded Ca–P coating plate were evaluated. The bacteriostatic activity of the vancomycin-loaded Ca–P coating plate showed a continuous drug release and had an inhibitory effect on the growth of the S. aureus. In vitro osteoblast culture results showed that the Ca–P coating plate loaded with or without the vancomycin both obviously promoted the osteoblast attachment. It was suggested that the vancomycin-loaded Ca–P coating may be compounded in the surface of the internal fixators to reduce the incidence of the implant-associated infection.     

Corrosion resistance of model ultrafine-grained Al–Li alloys produced by severe plastic deformation

The influence of grain boundaries and fine precipitation on the corrosion behavior was investigated in two model aluminum–lithium alloys, namely (in wt%) Al–1.6Li (lithium in a solid solution) and Al–2.3Li (lithium in the form of Al₃Li precipitation), subjected to three different severe plastic deformation (SPD) treatments which refined the microstructure of the alloys to the ultrafine grain size. The SPD techniques used in the experiments were equal channel angular pressing (ECAP), hydrostatic extrusion (HE), and extrusion-torsion (ET). The corrosion behavior was examined using a potentiodynamic polarization test, electrochemical impedance spectroscopy, and an immersion test followed by a SEM surface analysis. The electrochemical tests were conducted in a 0.1 M Na₂SO₄ solution added with 100 ppm of Cl⁻. The immersion tests (48 h) were performed in a 3.5% NaCl solution at room temperature. The results indicate that the pitting potential, pit number, and stability of the passive layer formed on the surface of the substrates undergo changes depending on the average grain size and the presence of precipitation or its lack. The corrosion resistance, examined in the solution mentioned above, appears to increase with decreasing average grain size. The ET method gave the microstructure with the lowest corrosion resistance.     

Cu(II), Co(II) and Ni(II) complexes of –Br and –OCH<Subscript>2</Subscript>CH<Subscript>3</Subscript> substituted Schiff bases as corrosion inhibitors for aluminium in acidic media

A group of Cu(II), Ni(II) and Co(II) complexes of –Br and –OCH₂CH₃ substituted Schiff bases as a new class of corrosion inhibitors for aluminium has been studied in 0.1 M HCl by the addition of 10 ppm compound using potentiodynamic polarization, electrochemical impedance spectroscopy, linear polarization methods and gas evolution tests at 25 °C. The inhibition efficiencies obtained from all methods employed are in good agreement. Results show Ni(II) complex of –OCH₂CH₃ substituted Schiff bases was the best inhibitor with a mean efficiency of 69% at 10 ppm additive concentration. The potentiodynamic polarization curves showed both the cathodic and the anodic processes of aluminium corrosion were suppressed, and the Nyquist plots of impedance gave mainly a capacitive loop. Scanning electron microscopy (SEM) was done from the surface of the exposed sample indicating uniform film on the surface.     

The effects of calcium and yttrium additions on the microstructure,mechanical properties and biocompatibility of biodegradable magnesium alloys

In this study, the effects of calcium (Ca) and yttrium (Y) on the microstructure, mechanical properties, corrosion behaviour and biocompatibility of magnesium (Mg) alloys, i.e. Mg–xCa (x = 0.5, 1.0, 2.0, 5.0, 10.0, 15.0 and 20.0%, wt%, hereafter) and Mg–1Ca–1Y, were investigated. Optical microscopy, X-ray diffractometry (XRD), compressive and Vickers hardness testing were used for the characterisation and evaluation of the microstructure and mechanical properties. The in vitro cytotoxicity of the alloys was assessed using osteoblast-like SaOS2 cells. The corrosion behaviour of these alloys was evaluated by soaking the alloys in simulated body fluid (SBF) and modified minimum essential medium (MMEM) at 37 °C in a humidified atmosphere with 5% CO₂. Results indicated that the increase of the Ca content enhances the compressive strength, elastic modulus and hardness of the Mg–Ca alloys, but deteriorates the ductility, corrosion resistance and biocompatibility of the Mg–Ca alloys. The Y addition leads to an increase in the ductility; but a decrease in the compressive strength, hardness, corrosion resistance and biocompatibility of the Mg–1Ca–1Y alloy when compared to the Mg–1Ca alloy. Solutions of SBF and MMEM with the immersion of Mg–xCa and Mg–1Ca–1Y alloys show strong alkalisation. Our research results indicate that Mg–xCa alloys with Ca additions less than 1.0 wt% exhibited good biocompatibility, low corrosion rate as well as appropriate elastic modulus and strength; whilst the Y is not a proper element for Mg alloys for biomedical application due to its negative effects to the corrosion resistance and biocompatibility.     

Structure and electrochemical reactivity of new sulphur–silicon podands adsorbed on silver or gold surfaces

By the self-assembly monolayer (SAM) organization, three new podands belonging to silylpropanethiols have been tested as to their ability to form nanolayers protecting the noble metal surface (gold or silver) and to form complexes with monovalent metal cations on the metal surfaces. The stable self-assembled chemisorbed layers, providing protection to metal surface against electrooxidation and capable of blocking propylene carbonate (PC) electroreduction and Li electrodeposition were produced. Reflection-absorption infrared spectroscopy (RAIRS) indicated cleavage of the S–H bond upon adsorption of species 1–3 with the formation of S–Ag bonds on the metal surface. By cyclic voltammetry, it was found that the primary adsorbate formed on a Au electrode at E _ad (between −0.2 and −1.2 V vs. SCE) underwent reductive desorption at E < −1.3 V vs. SCE. The structures of 1–3 and their complexes with Na⁺ cations on the Ag surfaces were calculated and visualized by the AM1d semi-empirical method.     

A three-dimensional nanostructured PANI/MnOx porous microsphere and its capacitive performance

Three-dimensional nanostructured polyaniline (PANI) and manganese oxide (MnO _x ) composite porous microspheres were prepared by oxidizing aniline with KMnO₄ under interfacial chemical synthesis with 4-amino-thiophenol (4-ATP) as the structure-directing agent on the Au substrate. Surface morphology and chemical composition of PANI/MnO _x microsphere were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermo gravimetric-differential thermal analysis, and Fourier transform infrared spectrum. The result displayed that concentration of KMnO₄ played a key role in forming the 3D nanostructured porous microspheres. To obtain the regular shapes and uniform sizes of the porous microspheres, the optimal concentration of oxidant was 0.15 mol L⁻¹. The electrochemistry performances of PANI/MnO _x microsphere were determined by cyclic voltammograms, electrochemical impedance spectroscopy, and galvanostatic charge–discharge. The specific capacitance of the 3D nanostructured PANI–MnO _x porous microspheres exhibited a maximum value of 828 F g⁻¹ at current density of 2 mA cm⁻² over a potential range of 0.0–0.9 V versus SCE. It has improved 365 and 88 % comparing with that of PANI (178 F g⁻¹) and MnO _x (440 F g⁻¹) obtained at the similar condition. The charge–discharge tests showed the PANI/MnO _x microsphere possessed a good cycling stability. It maintained about 84.2 % of the initial capacitance after 1000 cycles at a current density of 2.0 mA cm⁻².     

Laser surface modification for synthesis of textured bioactive and biocompatible Ca–P coatings on Ti–6Al–4V

A textured calcium phosphate based bio-ceramic coating was synthesized by continuous wave Nd:YAG laser induced direct melting of hydroxyapatite precursor on Ti–6Al–4V substrate. Two different micro-textured patterns (100 μm and 200 μm line spacing) of Ca–P based phases were fabricated by this technique to understand the alignment and focal adhesion of the bone forming cells on these surfaces. X-ray diffraction studies of the coated samples indicated the presence of CaTiO₃, α-Ca₃(PO₄)₂, Ca(OH)₂, TiO₂ (anatase) and TiO₂ (rutile) phases as a result of the intermixing between the precursor and substrate material during laser processing. A two dimensional elemental mapping of the cross-section of the coated samples exhibited the presence of higher phosphorous concentration within the coating and a thin layer of calcium concentration only at the top of the coating. Improved in vitro bioactivity and in vitro biocompatibility was observed for the laser processed samples as compared to the control.     

In vitro dissolution and corrosion study of calcium phosphate coatings elaborated by pulsed electrodeposition current on Ti6Al4V substrate

Calcium-deficient hydroxyapatite (Ca-def-HAP) coatings on titanium alloy (Ti6Al4V) substrates are elaborated by pulsed electrodeposition. In vitro dissolution/precipitation process is investigated by immersion of the coated substrate into Dulbecco’s Modified Eagle Medium (DMEM) from 1 h to 28 days. Calcium and phosphorus concentrations evolution in the biological liquid are determined by Induced Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) for each immersion time. Physical and chemical characterizations of the coating are performed by scanning electron microscopy (SEM) associated to Energy Dispersive X-ray Spectroscopy (EDXS) for X-ray microanalysis. Surface modifications are investigated by an original method based on the three-dimensional reconstruction of SEM images (3D-SEM). Moreover, corrosion measurements are carried out by potentiodynamic polarization experiments. The results show that the precipitation rate of the Ca-def HAP coating is more pronounced in comparison with that of stoichiometric hydroxyapatite (HAP) used as reference. The precipitated bone-like apatite coating is thick, homogenous and exhibits an improved link to the substrate. Consequently, the corrosion behaviour of the elaborated prosthetic material is improved.     

Corrosion study of single crystal Ni–Mn–Ga alloy and Tb<Subscript>0.27</Subscript>Dy<Subscript>0.73</Subscript>Fe<Subscript>1.95</Subscript> alloy for the design of new medical microdevices

Once placed in a magnetic field, smart magnetic materials (SMM) change their shape, which could be use for the development of smaller minimally invasive surgery devices activated by magnetic field. However, the potential degradation and release of cytotoxic ions by SMM corrosion has to be determined. This paper evaluates the corrosion resistance of two SMM: a single crystal Ni–Mn–Ga alloy and Tb_0.27Dy_0.73Fe_1.95 alloy. Ni–Mn–Ga alloy displayed a corrosion potential (E _corr) of −0.58 V/SCE and a corrosion current density (i _corr) of 0.43 μA/cm². During the corrosion assay, Ni–Mn–Ga sample surface was partially protected; local pits were formed on 20% of the surface and nickel ions were mainly found in the electrolyte. Tb_0.27Dy_0.73Fe_1.95 alloy exhibited poor corrosion properties such as E _corr of −0.87 V/SCE and i _corr of 5.90 μA/cm². During the corrosion test, this alloy was continuously degraded, its surface was impaired by pits and cracks extensively and a high amount of iron ions was measured in the electrolyte. These alloys exhibited low corrosion parameters and a selective degradation in the electrolyte. They could only be used for medical applications if they are coated with high strain biocompatible materials or embedded in composites to prevent direct contact with physiological fluids.     

Structural, optical, and electric properties of BNT–BT0.08 thin films processed by sol–gel technique

Thin films with the composition [(Bi_0.5Na_0.5)TiO₃]_0.92–[BaTiO₃]_0.08 (hereafter BNT–BT_0.08) were deposited on Pt–Si by spin-coating from a stable sol precursor. The BNT–BT_0.08 film, crystallized on the Bi_0.5Na_0.5TiO₃ rhombohedral lattice, was obtained after annealing the film-gel at 700 °C. The films have a smooth surface (Rms = 2.76 nm) and grains with ferroelectric domains. The film showed a bandgap of 3.25 eV and a refractive index of 2.20 at a wavelength of 630 nm. The dielectric characteristics of BNT–BT_0.08 thin films were measured at room temperature and 10 kHz the dielectric constant (ε _r) was 243 and the loss tangent (tanδ) was 0.38. The remnant polarization (P _r) was 0.87 μC/cm² and the coercive field (E _c) was 220 kV/cm at 10 kHz and room temperature. The current density was approximately 2.7 × 10⁻⁵ A/cm² at low electric fields (100 kV/cm). BNT–BT_0.08 thin films shown piezoelectric properties (d _33eff = 100 pm/V) comparable to those of PZT thin films.     

Alumina coating formed on medical NiTi alloy by micro-arc oxidation

Al₂O₃ coatings were prepared on NiTi alloy by micro-arc oxidation in an aluminate solution. Thin-film X-ray diffraction (TF-XRD) indicated that the coating consisted of only Al₂O₃ crystal phase. Energy dispersive X-ray spectrometer (EDS) showed that there was about 2.53 at.% Ni in the surface layer, which was greatly lower than that of NiTi substrate. Scanning electron microscopy (SEM) showed that the coating exhibited a typical porous surface and excellent adhesive interface between the coating and the substrate. Direct pull-off test showed that the coating had a mean coating-substrate bonding strength of 28 ± 2 MPa. The results of electrochemical impedance spectroscopy (EIS) study and potentiodynamic polarization test indicated that the corrosion resistance of the coated sample was increased by two orders of magnitude compared with uncoated sample.     

High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W₂C–WC. The average roughness, R _a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m⁻¹ K⁻¹ are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 10⁷ W m⁻² K⁻¹. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.     

In vitro adhesion of staphylococci to diamond-like carbon polymer hybrids under dynamic flow conditions

This study compares the ability of selected materials to inhibit adhesion of two bacterial strains commonly implicated in implant-related infections. These two strains are Staphylococcus aureus (S-15981) and Staphylococcus epidermidis (ATCC 35984). In experiments we tested six different materials, three conventional implant metals: titanium, tantalum and chromium, and three diamond-like carbon (DLC) coatings: DLC, DLC–polydimethylsiloxane hybrid (DLC–PDMS-h) and DLC–polytetrafluoroethylene hybrid (DLC–PTFE-h) coatings. DLC coating represents extremely hard material whereas DLC hybrids represent novel nanocomposite coatings. The two DLC polymer hybrid films were chosen for testing due to their hardness, corrosion resistance and extremely good non-stick (hydrophobic and oleophobic) properties. Bacterial adhesion assay tests were performed under dynamic flow conditions by using parallel plate flow chambers (PPFC). The results show that adhesion of S. aureus to DLC–PTFE-h and to tantalum was significantly (P < 0.05) lower than to DLC–PDMS-h (0.671 ± 0.001 × 10⁷/cm² and 0.751 ± 0.002 × 10⁷/cm² vs. 1.055 ± 0.002 × 10⁷/cm², respectively). No significant differences were detected between other tested materials. Hence DLC–PTFE-h coating showed as low susceptibility to S. aureus adhesion as all the tested conventional implant metals. The adherence of S. epidermidis to biomaterials was not significantly (P < 0.05) different between the materials tested. This suggests that DLC–PTFE-h films could be used as a biomaterial coating without increasing the risk of implant-related infections.     

Comparison of oxidation resistance of NiCoCrAlTaY-coated and -uncoated Mar-M247 superalloys in the air at 1150 °C

Oxidation resistance of NiCoCrAlTaY coated and uncoated Mar-M247 superalloys were compared experimentally in the air at 1150 °C. It was found that the oxidation behavior of the NiCoCrAlTaY coated and uncoated Mar-M247 superalloys generally followed the parabolic kinetics with the rate of 1.5 and 9.8 × 10⁻³ mg²/cm⁴ h for each one. Microstructural observation and elemental analysis indicated that after 200 h the uncoated alloy covered with an oxide scale of 6–10 times thicker than the coated one, beneath which a fairly continuous and relatively thin α-Al₂O₃ could be found along the interface close to the substrate. Comparatively, the NiCoCrAlTaY coated alloy uniformly produced the continuous, dense and thick α-Al₂O₃ layer adhesive to the coating to prevent the metal elements against excessive oxidation, and finally formed the steady oxide scales: outer (Ni, Co)(Al, Cr)₂O₄ spinels, NiO, (Al, Cr)₂Ni₃; inner protective α-Al₂O₃ with a little Cr₂O₃. On the surface of the uncoated alloy, however, it mainly formed the Ni-rich oxides in which a large quantity of cracks propagated to result in the more oxidation.