The effect of surface preparation on the protective properties of Al2O3 and HfO2 thin films deposited on cp-titanium by atomic layer deposition

Atomic layer deposition (ALD), a method that allows the formation of thin and conformal films on substrates of interest, was employed to prepare thin films of alumina (Al2O3) and hafnia (HfO2), with the aim of protecting the surface of the commercially pure titanium (cp-Ti) used in biomedical applications. Prior to deposition, cp-Ti specimens have been prepared in two ways \u2013 grinding and grinding followed by polishing. Such surfaces have been denoted as rough and smooth, respectively. The thickness, composition, morphology and topography of alumina and hafnia films have been determined using ellipsometry, focused ion beam microscopy with energy dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry and 3D profilometry. A homogeneous stoichiometric composition of alumina and hafnia was obtained with a layer thickness of ca. 150 nm. The anti-corrosive properties of ALD thin films were measured in simulated body fluid solution, using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. The roughness of the cp-Ti surface plays an important role in the protective properties of these films, especially those of hafnia. In general, when deposited on a smooth surface, ALD films with better anti-corrosive properties were obtained, as evidenced by EIS long-term, 40-day tests. ALD films showed very low porosity, calculated from electrochemical parameters, and significantly lower corrosion current densities, compared with those from bare cp-Ti specimens. Lower porosity and slightly better protective properties were provided by films of hafnia. On the other hand, according to EIS long-term tests, alumina retained slightly greater impedance values than hafnia. Since both alumina and hafnia are biocompatible materials, this study confirms the possibility of their use to reduce the risk of failure of medical implants made of cp-Ti, in the human body environment

Effects of metal-on-metal wear on the host immune system and infection in hip arthroplasty

Methods We reviewed the available literature on the influence of degradation products of MOM bearings in total hip arthroplasties on infection risk. Results Wear products were found to influence the risk of infection by hampering the immune system, by inhibiting or accelerating bacterial growth, and by a possible antibiotic resistance and heavy metal co-selection mechanism. Interpretation Whether or not the combined effects of MOM wear products make MOM bearings less or more prone to infection requires investigation in the near future

The effect of copolymerisation on the performance of acrylate-based hybrid sol-gel coating for corrosion protection of AA2024-T3

The study was focused on the optimisation of the copolymerisation process of acrylate-based hybrid sol-gel coating to obtain long-lasting corrosion protection of AA2024-T3. The coating was synthesised using the radical copolymerisation process of methyl methacrylate (MMA) and 3-methacryloxypropyl trimethoxysilane (MAPTMS) performed under air and nitrogen (oxygen-free) atmospheres, followed by acidic hydrolysis and polycondensation in the presence of silica prepared from tetraethyl orthosilicate (TEOS). The sol synthesis was evaluated at various stages using real-time infrared spectroscopy, multinuclear liquid- and solid-state magnetic resonance spectroscopy and gel permeation chromatography. After deposition on AA2024-T3 substrate and curing, the coating properties were further evaluated by contact profilometer and focused ion beam/scanning electron microscopy coupled with energy-dispersive X-ray spectrometry. The corrosion performance was evaluated in 0.1 M NaCl solution using electrochemical impedance spectroscopy and salt spray chamber testing. The results indicated that the reaction performed in the nitrogen atmosphere increases the degree of the copolymerisation of acrylates groups, resulting in a larger molecular weight of the formed copolymer. After curing, both sol-gels formed continuous, smooth, 3c4 \u3bcm thick coatings that provided excellent barrier properties. However, when coating synthesised under nitrogen atmosphere, the coating provided better long-term corrosion resistance reaching almost 1 G\u3a9 cm2 after 6 months immersion in 0.1 M NaCl solution. Superior corrosion resistance was also confirmed in the salt spray chamber where the coating prepared under N2 atmosphere remained unchanged more than 500 hours

Al2O3and HfO2Atomic Layers Deposited in Single and Multilayer Configurations on Titanium and on Stainless Steel for Biomedical Applications

Thin films of alumina and hafnia were prepared by atomic layer deposition, with the aim of investigating the use of such films in biomedical applications. Films were deposited on commercially pure titanium and on medical stainless steel. Two configurations were prepared: single alumina films, 20 nm and 60 nm thick, and a multilayer film, 60 nm thick, consisting of alumina/hafnia/alumina layers, each 20 nm thick. The morphology, structure and composition of the coated alloys were characterized using scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. In addition, ellipsometry and atomic force microscopy coupled with scanning Kelvin probe force microscopy, were used to study the thickness and the topography with surface potential properties. An improvised method, involving the Vickers hardness test, was applied to assess the delamination of the deposited films. Coated specimens, as well as bare substrates, were tested at 37 C in simulated body fluid, using potentiodynamic polarization and electrochemical impedance spectroscopy as techniques for assessing corrosion susceptibility. In general, single and multilayer thin films possess excellent barrier properties and are worth investigating further for biomedical applications. The degree of protection is dependent mainly on film thickness and on the type of substrate, and less on configuration

The synergistic effect of cerium acetate and sodium sulphate on corrosion inhibition of AA2024-T3 at various temperatures

The present work examines the corrosion inhibition of aluminium alloy 2024-T3 immersed in NaCl+Ce(OAc)3 and NaCl+Ce(OAc)3+Na2SO4 solutions to evaluate the synergetic effect between cerium and sulphate ions at various temperatures (5 \ub0C, 25 \ub0C and 50 \ub0C). The electrochemical properties were studied using short-term potentiodynamic measurements and long-term electrochemical impedance measurements. The surface topography, morphology and composition of cerium deposits formed on the alloy surface after two days of immersion were evaluated using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results revealed an efficient long-term (up to 8 weeks) corrosion inhibition in NaCl+Ce(OAc)3 that was superior in the NaCl+Ce(OAc)3+Na2SO4 solution, especially at lower temperatures (5 \ub0C > 25 \ub0C > 50 \ub0C). The composition of the Ce-based film varied with the temperature and the presence of Na2SO4, resulting in different mixtures of Ce(III) and Ce(IV) species. The synergistic effect of cerium and sulphate ions on corrosion inhibition was reflected by a higher degree of cerium oxidation from Ce3+ to Ce4+ at a low temperature and the incorporation of sulphates into the formed film, which protected the surface from the corrosion medium more efficiently

Titanium nanostructures for biomedical applications

Titanium and titanium alloys exhibit a unique combination of strength and biocompatibility, which enables their use in medical applications and accounts for their extensive use as implant materials in the last 50 years. Currently, a large amount of research is being carried out in order to determine the optimal surface topography for use in bioapplications, and thus the emphasis is on nanotechnology for biomedical applications. It was recently shown that titanium implants with rough surface topography and free energy increase osteoblast adhesion, maturation and subsequent bone formation. Furthermore, the adhesion of different cell lines to the surface of titanium implants is influenced by the surface characteristics of titanium; namely topography, charge distribution and chemistry. The present review article focuses on the specific nanotopography of titanium, i.e. titanium dioxide (TiO2) nanotubes, using a simple electrochemical anodisation method of the metallic substrate and other processes such as the hydrothermal or sol-gel template. One key advantage of using TiO2 nanotubes in cell interactions is based on the fact that TiO2 nanotube morphology is correlated with cell adhesion, spreading, growth and differentiation of mesenchymal stem cells, which were shown to be maximally induced on smaller diameter nanotubes (15 nm), but hindered on larger diameter (100 nm) tubes, leading to cell death and apoptosis. Research has supported the significance of nanotopography (TiO2 nanotube diameter) in cell adhesion and cell growth, and suggests that the mechanics of focal adhesion formation are similar among different cell types. As such, the present review will focus on perhaps the most spectacular and surprising one-dimensional structures and their unique biomedical applications for increased osseointegration, protein interaction and antibacterial properties