Electrochemical denitrification by a recyclable cobalt oxide cathode: Rapid recovery and selective catalysis

Cathodic aging and fouling have presented significant challenges in the realm of electrochemical denitrification for engineering applications. This study focused on the development of an economical and recyclable nanoporous Co3O4/Co cathode through anodization for nitrate reduction. What distinguished our cathode was its exceptional sustainability. Cobalt from the inactive catalyst could be reclaimed onto the substrate, enabling the regeneration of a new Co3O4 layer. This innovative approach resulted in an exceptionally low Co catalyst consumption, a mere 1.936 g/1 kg N, making it the most cost-effective choice among all Co-based cathodes. The Co3O4 catalyst exhibited a truncated octahedron structure, primarily composed of surface Co2+ ions. Density functional theory calculations confirmed that the bonding between the O atom in NO3- ions and the Co atom in Co3O4 was thermodynamically favorable, with a free energy of - 0.89 eV. Co2+ ions acted as "electron porters" facilitating electron transfer through a redox circle Co2+-Co3+-Co2+. However, the presence of two energy barriers (*NH2NO to *N2 and *N2 to N2) with respective heights of 0.83 eV and 1.17 eV resulted in a N2 selectivity of 9.84% and an NH3 selectivity of 90.02%. In actual wastewater treatment, approximately 78% of TN and 93% of NO3- were successfully removed after 3 h, consistent with the prediction kinetic model. This anodization-based strategy offers a significant advantage in terms of long-term cost and presents a new paradigm for electrode sustainability.

Electrochemical investigations and antimicrobial activity of Au nanoparticles photodeposited on titania nanoparticles

Titanium oxide nanopowder (TiO2 NPs) was synthesized via anodization in 0.7 M perchloric acid then annealed in nitrogen at 450 °C for 3 h to prepared the Titanium Oxide Nitrogen annealed nanoparticles (TiO2 NPs-N2) powder as catalytic support. Using a photodeposition process, gold was added with isopropanol as a sacrificial donor and H[AuCl4] acid, producing gold nanoparticles on nitrogen-annealed titanium oxide nanoparticles (Au-NPs on TiO2-NPs-N2). The mass loading of Au NPs was 2.86 × 10-4 (g/cm2). TEM images of Au NPs on TiO2-NPs-N2 suggest circular particles with a tendency to agglomerate. Cyclic voltammetry (CV) was used to investigate the electrocatalytic performance of the Au NPs/TiO2-NPs-N2 catalysts in ferrocyanide, KOH, and H2SO4, and the results were compared to those of a polycrystalline Au electrode that is readily accessible in the market. In KOH, H2SO4, and (2 M KOH + 0.1 M glycerol) solutions, the Au NPs/TiO2-NPs-N2 electrode displayed a startlingly high electrocatalytic performance. Using CV, the electrocatalytic oxygen reduction reaction (ORR) of Au NPs/TiO2-NPs-N2 and Au-NPs against glycerol oxidation in basic media was studied. The results indicated that Au NPs/TiO2-NPs-N2 is a promising support material for improving the electrocatalytic activity for acidic and basic oxidation. The electrode made of Au NPs/TiO2-NTs-N2 has steady electrocatalytic activity and may be reused repeatedly. TiO2 NPs and Au NPs/TiO2NPs-N2 showed satisfactory antibacterial activity against some human pathogenic bacteria using the disc diffusion method.

Fit and forget: The future of dental implant therapy via nanotechnology

Unlike orthopedic implants, dental implants require the orchestration of both osseointegration at the bone-implant interface and soft-tissue integration at the transmucosal region in a complex oral micro-environment with ubiquitous pathogenic bacteria. This represents a very challenging environment for early acceptance and long-term survival of dental implants, especially in compromised patient conditions, including aged, smoking and diabetic patients. Enabling advanced local therapy from the surface of titanium-based dental implants via novel nano-engineering strategies is emerging. This includes anodized nano-engineered implants eluting growth factors, antibiotics, therapeutic nanoparticles and biopolymers to achieve maximum localized therapeutic action. An important criterion is balancing bioactivity enhancement and therapy (like bactericidal efficacy) without causing cytotoxicity. Critical research gaps still need to be addressed to enable the clinical translation of these therapeutic dental implants. This review informs the latest developments, challenges and future directions in this domain to enable the successful fabrication of clinically-translatable therapeutic dental implants that would allow for long-term success, even in compromised patient conditions.

Nanotube patterning reduces macrophage inflammatory response via nuclear mechanotransduction

The inflammatory immune environment surrounding titanium bone implants determines the formation of osseointegration, and nanopatterning on implant surfaces modulates the immune microenvironment in the implant region. Among many related mechanisms, the mechanism by which nanopatterning controls macrophage inflammatory response still needs to be elucidated. In this paper, we found that inhibition of the nuclear envelope protein lamin A/C by titania nanotubes (TNTs) reduced the macrophage inflammatory response. Knockdown of lamin A/C reduced macrophage inflammatory marker expression, while overexpression of lamin A/C significantly elevated inflammatory marker expression. We further found that suppression of lamin A/C by TNTs limited actin polymerization, thereby reducing the nuclear translocation of the actin-dependent transcriptional cofactor MRTF-A, which subsequently reduced the inflammatory response. In addition, emerin, which is a key link between lamin A/C and actin, was delocalized from the nucleus in response to mechanical stimulation by TNTs, resulting in reduced actin organization. Under inflammatory conditions, TNTs exerted favourable osteoimmunomodulatory effects on the osteogenic differentiation of mouse bone marrow-derived stem cells (mBMSCs) in vitro and osseointegration in vivo. This study shows and confirms for the first time that lamin A/C-mediated nuclear mechanotransduction controls macrophage inflammatory response, and this study provides a theoretical basis for the future design of immunomodulatory nanomorphologies on the surface of metallic bone implants.

A short review of the electrochemical technologies for pit arrays fabricated on the surfaces of indium phosphide wafer

Fabricating a pit array on the surface of indium phosphide wafer can change its photoelectric properties, improve its photoelectric conversion efficiency, and expand its application range. There are few reviews devoted to the fabrication of regular hole arrays on the surface of indium phosphide wafers by electrochemical methods. In this paper, twelve electrochemical approaches for assembling pit arrays on the surface of indium phosphide wafers were introduced, the structure and experimental process of the electrochemical device were highlighted, and the resulting top and section views were also shown by animation. It can provide a useful reference guide for the large-scale fabrication of regular hole arrays on the surface of indium phosphide wafers.

Electrochemical treatment of electroplating wastewater using synthesized GO/TiO2 nanotube electrode

The graphene oxide (GO) deposited TiO₂ nanotube (GO/TiO₂) electrode on a titania plate was prepared using a simple anodization method. The morphological and structural properties of TiO₂ and GO/TiO₂ electrodes have been studied using field emission scanning electron microscopy energy dispersive spectroscopy (FESEM-EDS), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Raman spectroscopy, Fourier transform infrared spectra (FT-IR), and X-ray photoelectron spectroscopy (XPS). FESEM-EDS analysis confirmed that the 13.56% wt of GO nanoparticles was formed over the TiO₂ substrate, with the thickness of the wall to be ∼300 nm. The crystallite size of GO/TiO₂, i.e., 19.53 nm, was confirmed by XRD analysis. Analysis of the UV-DRS spectrum showed the bandgap of the synthesized GO/TIO₂ nanotube electrode to be 3.052 eV. Box-Behnken design (BBD) under response surface methodology (RSM) was used to design the experiments. The effect of operating input parameters like pH, current (i), and degradation time (t) on % COD degradation (X₁) and energy consumed (X₂) were also examined. At optimum process parameters, the value of X₁ and X₂ were 57.61% and 15.00 kWh/m³, respectively. Possible intermediates were identified based on the GC-MS data analysis. Scavenger tests showed that •OH radical plays a major role in electroplating effluents degradation. Based on the results, the EO process using GO/TiO₂ electrodes could be considered a promising technique for electroplating effluent degradation due to high degradation efficiency.

Enhanced pollutant photodegradation over nanoporous titanium-vanadium oxides with improved interfacial interactions

This study addressed the separation problem of colloidal catalytic powder from its solution and pore blockage of traditional metallic oxides by fabricating nanoporous composites of titanium (Ti)-vanadium (V) oxide via magnetron sputtering, electrochemical anodization, and annealing processes. The effect of V-deposited loading on the composite semiconductors was investigated by varying V sputtering power (20-250 W) to correlate their physicochemical properties to the photodegradation performance of methylene blue. The obtained semiconductors revealed circular and elliptical pores (14-23 nm) and formed different metallic and metallic oxide crystalline phases. Within the nanoporous composite layer, V ions substituted Ti⁴⁺, leading to Ti³⁺ formation accompanied by decreased band gap values and higher visible-light absorption. Thus, the band gap of TiO₂ was 3.15 eV, while that of Ti-V oxide with the maximum V content (at 250 W) was 2.47 eV. The interfacial separators between clusters in the mentioned composite created traps disrupting the charge carrier movements between crystallites, thereby decreasing the photoactivity. In contrast, the composite prepared with the minimum V content showed approximately 90% degradation efficiency under solar-simulated irradiation resulting from the homogeneous V dispersion and the lower recombination possibility, owing to its p-n heterojunction constituent. The nanoporous photocatalyst layers with their novel synthesis approach and outstanding performance can be applied in other environmental remediation applications.

Effects of Ceramic Thickness and Titanium Anodization on Esthetic Outcomes of Lithium Disilicate Ceramic Over Titanium Alloys

OBJECTIVE

In order to investigate the esthetic outcomes via color differences of various lithium disilicate ceramic thicknesses on various voltages of anodized titanium.

MATERIALS AND METHODS

28 lithium disilicate ceramic specimens (medium translucency) were arranged into four groups based on the thickness of the ceramic: 1.0, 1.5, 2.0, and 2.5 mm (n=7). Each group was tested with seven different materials (n=7): composite resin (A2-dentin shade, control), zirconia, titanium, 40 V (blue), 50 V (light yellow), 60 V (yellow) and 70 V (pink)-anodized titanium. All the specimens were measured with a spectrophotometer, and then compared with the composite resin (control) to establish the color differences. To be considered as clinically acceptable, the color differences must be lower than 2.7. The data obtained was statistically analyzed through ANOVA and a post hoc test (p=0.05).

RESULTS

Both the thickness of the lithium disilicate ceramics and the type of material had a significant effect on the color differences observed (p⟨0.05). When ceramics thickness more than 2.0 mm were used for zirconia or 2.5- mm ceramic thickness for yellow-shade (50 V and 60 V) of anodized titanium, the color differences obtained were below the clinical acceptability values.

CONCLUSIONS

yellowshade of anodized titanium tends to achieve esthetics in combination with adequate ceramic thickness.

Investigation of photocatalytic performance of titania based hybrid nanocomposite structure for dilapidation of organic contaminants

This research paper attempt to provide the photocatalytic performance of nitrogen ion (N⁺) entrenched anodized Ti with hydroxyapatite hybrid nano-sctructure meant for dilapidation of organic contaminant from the environment. The N⁺ was entrenched at 70 keV with varying doses (1 × 10¹⁶, 5 × 10¹⁶, 1 × 10¹⁷ and 2.5 × 10¹⁷ N⁺/cm²) into anodized Ti surface. Functional groups, phase structure, topographic and morphologic characterizations of the synthesized hybrid nano-sctructure were analyzed using Infra Red Spectroscopy, X-ray diffraction and Microscopic techniques, respectively. Wettability of the specimens was found out using contact angle measurements. The anodized Ti specimens without N⁺ have exhibited less surface energy than the specimens with N⁺. Porous shell gets smoothened after the entrenchment of N⁺. Compared to all the doses of nitrogen implantation, better performance was observed for 5 × 10¹⁶ N⁺/cm² dose. Moreover, the samples with N⁺ showed better charge transfer resistance indicating enhanced photocatalytic performance of N⁺ entrenched titania than other samples.

Photoreduction of Cr(VI) in wastewater by anodic nanoporous Nb2O5 formed at high anodizing voltage and electrolyte temperature

In this study, nanoporous anodic film was produced by anodization of niobium, Nb in a fluoride ethylene glycol electrolyte. The effect of anodization voltage and electrolyte temperature was studied to find an optimum condition for circular, ordered, and uniform pore formation. The diameter of the pores was found to be larger when the applied voltage was increased from 20 to 80 V. The as-anodized porous film was also observed to comprise of nanocrystallites which formed due to high field-induced crystallization. The nanocrystallites grew into orthorhombic Nb₂O₅ after post-annealing treatment. The Cr(VI) photoreduction property of both the as-anodized and annealed Nb₂O₅ samples obtained using an optimized condition (anodization voltage: 60 V, electrolyte temperature: 70 °C) was compared. Interestingly, the as-anodized Nb₂O₅ film was found to display better photoreduction of Cr(VI) than annealed Nb₂O_5. However, in terms of stability, the annealed Nb₂O₅ presented high photocatalytic efficiency for each cycle whereas the as-anodized Nb₂O₅ showed degradation in photocatalytic performance when used continually.

Comparison of surface aspects of turned and anodized titanium dental implant, or abutment material for an optimal soft tissue integration

Objectives

Soft tissue integration of dental implants lags behind natural biological integration of teeth mainly because of non-optimal surface features. Peri-implant infections resulting in loss of supporting bone jeopardize the success of implants. Our aim was to compare an anodized surface design with a turned one for a more optimal surface.

Methods

Morphological and chemical structures of turned and anodized Ti surfaces (grade 5: Ti6Al4V) discs were examined by scanning electron microscopy (SEM-EDS), energy dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). The hydrophilic or hydrophobic features of the surfaces were determined by dynamic contact angle measurement.

Results

SEM and AFM revealed significant differences in the morphology and roughness (R_a) of the samples. Anodized discs presented a granular structure, while turned ones had circular grooves. The roughness was significantly higher for the anodized samples compared to the turned ones. XPS and EDS confirmed typical elements for both Ti6Al4V samples. Due to anodization, the amount of Ti (IV) had increased and Ti (III) had decreased in the thicker oxide layer. Anodized samples resulted in a more hydrophilic surface than the turned ones.

Significance

The results suggest that the tested anodized samples present optimal surface characteristics to be used as abutment material for an optimal soft tissue integration.

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Optimization of soft tissue barrier is a crucial factor in long-term dental implant success and peri-implant health.

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The applied anodization is an easy-to-use process to change the color of titanium to a more favorable yellow.

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Changes in surface morphology and hydrophilic features were favorable for soft tissue attachment.

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Anodized samples presented optimal surface composition to be used as abutment material of dental implants.

Understanding the influence of electrolyte aging in electrochemical anodization of titanium

Titania nanotubes or nanopores self-ordered on electrochemically anodized (EA) titanium have been widely applied towards photocatalysis, solar cells, purification and biomedical implants. As a result, significant research has been focused towards optimizing anodization to fabricate controlled, stable and reproducible nanostructures. Among these, the use of organic-based electrolyte, like ethylene glycol (with NH₄F and water), to anodize Ti has been widely applied and researched. Interestingly, among the various influencing EA factors, electrolyte aging (repeated EA using non-target Ti, prior to EA of target Ti substrate) has been underexplored, with only few studies aiming to optimize electrolyte aging and its influence on the nanostructures fabricated. Moreover, many research laboratories utilize electrolyte aging in Ti anodization, but this practice is seldom reported. In this extensive and pioneering review, we discuss and detail electrolyte aging in Ti anodization to fabricate controlled nanostructures, and its influence on nanostructure characteristics including morphology, chemistry, stability and application-specific performance. This review will inform future research aimed at optimizing electrolyte aging and Ti anodization to fabricate controlled nanostructures catering to specific application needs.

Nanoporous anodic Nb2O5 with pore-in-pore structure formation and its application for the photoreduction of Cr(VI)

An anodic film with a nanoporous structure was formed by anodizing niobium at 60 V in fluorinated ethylene glycol (fluoride-EG). After 30 min of anodization, the anodic film exhibited a "pore-in-pore" structure; that is, there were smaller pores growing inside larger pores. The as-anodized film was weakly crystalline and became orthorhombic Nb₂O₅ after heat treatment. The energy band gap of the annealed nanoporous Nb₂O₅ film was 2.9 eV. A photocatalytic reduction experiment was performed on Cr(VI) under ultraviolet (UV) radiation by immersing the nanoporous Nb₂O₅ photocatalyst in a Cr(VI) solution at pH 2. The reduction process was observed to be very slow; hence, ethylenediaminetetraacetic acid (EDTA) was added as an organic hole scavenger, which resulted in 100% reduction after 45 min of irradiation. The photocatalytic reduction experiment was also performed under visible light, and findings showed that complete reduction achieved after 120 min of visible light exposure.

Evolution of anodised titanium for implant applications

Anodised titanium has a long history as a coating structure for implants due to its bioactive and ossified surface, which promotes rapid bone integration. In response to the growing literature on anodised titanium, this article is the first to revisit the evolution of anodised titanium as an implant coating. The review reports the process and mechanisms for the engineering of distinctive anodised titanium structures, the significant factors influencing the mechanisms of its formation, bioactivity, as well as recent pre- and post-surface treatments proposed to improve the performance of anodised titanium. The review then broadens the discussion to include future functional trends of anodised titanium, ranging from the provision of higher surface energy interactions in the design of biocomposite coatings (template stencil interface for mechanical interlock) to techniques for measuring the bone-to-implant contact (BIC), each with their own challenges. Overall, this paper provides up-to-date information on the impacts of the structure and function of anodised titanium as an implant coating in vitro and in/ex vivo tests, as well as the four key future challenges that are important for its clinical translations, namely (i) techniques to enhance the mechanical stability and (ii) testing techniques to measure the mechanical stability of anodised titanium, (iii) real-time/in-situ detection methods for surface reactions, and (iv) cost-effectiveness for anodised titanium and its safety as a bone implant coating.

Understanding and optimizing the antibacterial functions of anodized nano-engineered titanium implants

Nanoscale surface modification of titanium-based orthopaedic and dental implants is routinely applied to augment bioactivity, however, as is the case with other cells, bacterial adhesion is increased on nano-rough surfaces. Electrochemically anodized Ti implants with titania nanotubes (TNTs) have been proposed as an ideal implant surface with desirable bioactivity and local drug release functions to target various conditions. However, a comprehensive state of the art overview of why and how such TNTs-Ti implants acquire antibacterial functions, and an in-depth knowledge of how topography, chemistry and local elution of potent antibiotic agents influence such functions has not been reported. This review discusses and details the application of nano-engineered Ti implants modified with TNTs for maximum local antibacterial functions, deciphering the interdependence of various characteristics and the fine-tuning of different parameters to minimize cytotoxicity. An ideal implant surface should cater simultaneously to ossoeintegration (and soft-tissue integration for dental implants), immunomodulation and antibacterial functions. We also evaluate the effectiveness and challenges associated with such synergistic functions from modified TNTs-implants. Particular focus is placed on the metallic and semi-metallic modification of TNTs towards enabling bactericidal properties, which is often dose dependent. Additionally, there are concerns over the cytotoxicity of these therapies. In that light, research challenges in this domain and expectations from the next generation of customizable antibacterial TNTs implants towards clinical translation are critically evaluated. STATEMENT OF SIGNIFICANCE: One of the major causes of titanium orthopaedic/dental implant failure is bacterial colonization and infection, which results in complete implant failure and the need for revision surgery and re-implantation. Using advanced nanotechnology, controlled nanotopographies have been fabricated on Ti implants, for instance anodized nanotubes, which can accommodate and locally elute potent antibiotic agents. In this pioneering review, we shine light on the topographical, chemical and therapeutic aspects of antibacterial nanotubes towards achieving desirable tailored antibacterial efficacy without cytotoxicity concerns. This interdisciplinary review will appeal to researchers from the wider scientific community interested in biomaterials science, structure and function, and will provide an improved understanding of controlling bacterial infection around nano-engineered implants, aimed at bridging the gap between research and clinics.

Orchestrating soft tissue integration at the transmucosal region of titanium implants

Osseointegration at the bone-implant interface and soft tissue integration (STI) at the trans-mucosal region are crucial for the long-term success of dental implants, especially in compromised patient conditions. The STI quality of conventional smooth and bio-inert titanium-based implants is inferior to that of natural tissue (i.e. teeth), and hence various surface modifications have been suggested. This review article compares and contrasts the various modification strategies (physical, chemical and biological) utilized to enhance STI of Ti implants. It also details the STI challenges associated with conventional Ti-based implants, current surface modification strategies and cutting-edge nano-engineering solutions. The topographical, biological and therapeutic advances achievable via electrochemically anodized Ti implants with TiO₂ nanotubes/nanopores are highlighted. Finally, the status and future directions of such nano-engineered implants is discussed, with emphasis on bridging the gap between research and clinical translation.

In vivo and in simulated body fluid degradation behavior and biocompatibility evaluation of anodic oxidation-silane-chitosan-coated Mg-4.0Zn-0.8Sr alloy for bone application

With the development and progress of science and technology, magnesium and magnesium alloys have attracted more and more researchers' attention because of their excellent biocompatibility. However, rapid degradation rate of magnesium alloy in vivo seriously limits its application (Arthanari et al., n.d.; Cui et al., 2013 [1,2]). In order to solve this problem, the surface modification of Mg-4.0Zn-0.8Sr alloy was adopted in this paper. According to the requirements of orthopedic materials, anodizing coating (AO), silane coating (SA) and chitosan coating (CS) coating were prepared on its surface, and magnesium alloy was prepared into intramedullary nail, and the corrosion resistance and biocompatibility of the corresponding samples was evaluated. The experimental results show that the AO-SA-CS coating sample has higher corrosion resistance, in addition, it also shows good biocompatibility, such as lower hemolysis rate and normal platelet adhesion morphology. After implantation into the femur, the femur of rats recovered well and the kidney tissue was normal.

Mixed oxide nanotubes in nanomedicine: A dead-end or a bridge to the future?

Nanomedicine has seen a significant rise in the development of new research tools and clinically functional devices. In this regard, significant advances and new commercial applications are expected in the pharmaceutical and orthopedic industries. For advanced orthopedic implant technologies, appropriate nanoscale surface modifications are highly effective strategies and are widely studied in the literature for improving implant performance. It is well-established that implants with nanotubular surfaces show a drastic improvement in new bone creation and gene expression compared to implants without nanotopography. Nevertheless, the scientific and clinical understanding of mixed oxide nanotubes (MONs) and their potential applications, especially in biomedical applications are still in the early stages of development. This review aims to establish a credible platform for the current and future roles of MONs in nanomedicine, particularly in advanced orthopedic implants. We first introduce the concept of MONs and then discuss the preparation strategies. This is followed by a review of the recent advancement of MONs in biomedical applications, including mineralization abilities, biocompatibility, antibacterial activity, cell culture, and animal testing, as well as clinical possibilities. To conclude, we propose that the combination of nanotubular surface modification with incorporating sensor allows clinicians to precisely record patient data as a critical contributor to evidence-based medicine.

Formation of nanostructures on magnesium alloy by anodization for potential biomedical applications

In the present work, we have investigated the formation of nanostructures on AZ31 magnesium alloy using electrochemical anodization technique. The formed nanostructures were efficiently showed bone-like apatite formation followed by its gradual increase, when immersed in simulated body fluid (SBF) and it exhibited controlled degradation in 7 days. Cell viability study was performed using MG-63 cells (human osteosarcoma cell lines) and revealed that the nanostructured surface has excellent biocompatibility by enhancing both cell adhesion and cell growth. The detailed characterization of this anodized surface was evaluated by field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS). Furthermore, surface-corrosion before and after anodization was examined by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in SBF. The in-depth studies bring out the fact that native oxide in the sample is converted to a biocompatible nanostructure, which is created due to anodization in a particular electrolyte solution containing ethylene glycol and hybrid hydrofluoric acid mixture.

Highly efficient solid-phase microextraction of polycyclic aromatic hydrocarbons in water based on worm-like nickel-titanium oxide nanocomposites coating grown on a nickel-titanium alloy wire by low-voltage anodization

A novel worm-like nickel-titanium oxide nanocomposite coating was directly grown on a nickel-titanium alloy wire by low-voltage electrochemical anodization in alkaline ethylene glycol and water solution. The in situ growth of nickel-titanium oxide nanocomposites greatly depended on the volume ratio of ethylene glycol to water and temperature. Coupled to high-performance liquid chromatography with UV detection by static desorption in the mobile phase, the adsorption performance of the as-prepared fiber was evaluated for solid-phase microextraction of representative environmental analytes in water. The results indicate that the as-prepared fiber exhibits higher extraction capability for polycyclic aromatic hydrocarbons than commercial polydimethylsiloxane and polyacrylate fibers. After optimizing the extraction parameters, the calibration graphs of the developed method was linear in the range of 0.05-200 μg/L with correlation coefficients above 0.998. Limit of detection ranged from 0.013 to 0.145 μg/L for seven target analytes. Relative standard deviations of intraday and interday analyses varied from 4.0 to 5.3% and from 4.7 to 6.3% with the single fiber, respectively. The relative recoveries of 84.4-109% were achieved for highly efficient enrichment and determination of target analytes in spiked river and snow water. Moreover, the as-prepared fiber can be used more than 200 times.

Effects of the sources of calcium and phosphorus on the structural and functional properties of ceramic coatings on titanium dental implants produced by plasma electrolytic oxidation

Plasma Electrolytic Oxidation (PEO) is as a promising technique to modify metal surfaces by application of oxide ceramic coatings with appropriate physical, chemical and biological characteristics. Therefore, objective of this research was to find the simplest settings, yet able to produce relevant bioactive implant surfaces layers on Ti implants by means of PEO. We show that an electrolyte containing potassium dihydrogen phosphate as a source of P and either calcium hydroxide or calcium formate as a source of Ca in combination with a chelating agent, ethylenediamine tetraacetic acid (EDTA), is suitable for PEO to deliver coatings with desired properties. We determined surface morphology, roughness, wettability, chemical and phase composition of titanium after the PEO process. To investigate biocompatibility and bacterial properties of the PEO oxide coatings we used microbial and cell culture tests. The electrolyte based on Ca(OH)₂ and EDTA promotes active crystallization of apatites after PEO processing of the Ti implants. The PEO layers can increase electrochemical corrosion resistance. The PEO can be potentially used for development of bioactive surfaces with increased support of eukaryotic cells while inhibiting attachment and growth of bacteria without use of antibacterial agents.

Nanoporous thin films in optical waveguide spectroscopy for chemical analytics

Spectroscopy with planar optical waveguides is still an active field of research for the quantitative analysis of various supramolecular surface architectures and processes, and for applications in integrated optical chip communication, direct chemical sensing, etc. In this contribution, we summarize some recent development in optical waveguide spectroscopy using nanoporous thin films as the planar substrates that can guide the light just as well as bulk thin films. This is because the nanoporosity is at a spacial length-scale that is far below the wavelength of the guided light; hence, it does not lead to an enhanced scattering or additional losses of the optical guided modes. The pores have mainly two effects: they generate an enormous inner surface (up to a factor of 100 higher than the mere geometric dimensions of the planar substrate) and they allow for the exchange of material and charges between the two sides of the solid thin film. We demonstrate this for several different scenarios including anodized aluminum oxide layers for the ultrasensitive determination of the refractive index of fluids, or the label-free detection of small analytes binding from the pore inner volume to receptors immobilized on the pore surface. Using a thin film of Ti metal for the anodization results in a nanotube array offering an even further enhanced inner surface and the possibility to apply electrical potentials via the resulting TiO₂ semiconducting waveguide structure. Nanoporous substrates fabricated from SiN_x thin films by colloid lithography, or made from SiO₂ by e-beam lithography, will be presented as examples where the porosity is used to allow for the passage of ions in the case of tethered lipid bilayer membranes fused on top of the light-guiding layer, or the transport of protons through membranes used in fuel cell applications. The final example that we present concerns the replication of the nanopore structure by polymers in a process that leads to a nanorod array that is equally well suited to guide the light as the mold; however, it opens a totally new field for integrated optics formats for direct chemical and biomedical sensing with an extension to even molecularly imprinted structures. Graphical abstract.

Effect of anodized zirconium implants on early osseointegration process in adult rats: a histological and histomorphometric study

Since surface plays a key role in bioactivity, the response of the host to the biomaterial will determine the success or failure of the prosthesis. The purpose of this study is to make an exhaustive analysis of the histological and histochemical characteristics of new bone tissue around Zr implants anodized at 60 V (Zr60) supported by histomorphometric methods in a rat model. Fibrous tissue was observed around the control implants (Zr0) and osteoblasts were identified on the trabeculae close to the implantation site that showed typical cytological characteristics of active secretory cells, regardless of the surface condition. The histomorphometrical analysis revealed a significant increase in cancellous bone volume, trabecular thickness and in trabecular number together with a decrease in trabecular separation facing Zr60. TRAP staining showed that there was a relative increase in the number of osteoclasts for Zr60. In addition, a larger number of osteoclast with a greater number of nuclei were detected in the tibiae for Zr60. This research demonstrated that the new bone microarchitecture in contact with Zr60 is able to improve the early stages of the osseointegration process and consequently the primary stability of implants which is a crucial factor to reduce recovery time for patients.

Enhancing the photo-corrosion resistance of ZnO nanowire photocatalysts

Zinc oxide (ZnO) displays superior properties as a photocatalyst, compared to the more widely used TiO₂. However, widespread application of ZnO is hampered by its high photo-corrosion in aqueous environments under UV irradiation. A systematic investigation of the effect of (i) post-production annealing, (ii) dissolved oxygen levels during photocatalysis and (iii) reactor configuration on the stability and photocatalytic activity (PCA) of ZnO nanowires, grown on either flat or circular supports, was conducted. Results show, for the first time, that it is possible to significantly enhance the photo-corrosion resistance of ZnO in water under UV irradiation while also increasing PCA. Oxygen plasma post-annealing of ZnO nanowire films led to a 46% higher photocatalytic degradation of phenol compared to as-produced films. In oxygen-saturated solutions, both thermally and oxygen plasma annealed ZnO revealed similar photo-corrosion resistance. Switching from a batch to a flow-through reactor, tripled phenol photodegradation under the same irradiation conditions from 19 to 57% due to enhanced mass transfer, while significantly increasing the stability and re-usability of the ZnO, with 5 repeat uses over 3 days showing no decrease in PCA. These results pave the way to more widespread use of photo-corrosion resistant ZnO in the degradation of organic pollutants in water.

Ti plate with TiO2 nanotube arrays as a novel cathode for nitrate reduction

The purpose of this research is to investigate the possibility of using a Ti plate with TiO₂ nanotube arrays as a novel cathode for nitrate reduction. TiO₂ nanotube arrays were grown on a Ti plate by anodization in a glycerol based electrolyte and annealed to change their crystallographic structure. Morphological and crystallographic structures of Ti plates with a TiO₂ nanotubular layer were analysed before and after anodization or annealing by using energy-dispersive spectroscopy, Brunauer-Emmett-Teller analysis and X-ray diffraction. Cyclic voltammetry and electrochemical impedance spectroscopy were also performed to test the electrochemical reactivity towards nitrate reduction. A lab-scale electrochemical reactor with a RuO₂/Ti anode and a Ti plate with a TiO₂ nanotubular layer as a cathode was operated to treat synthetic wastewater containing up to 600 mg L^-1 of NO₃-N. The Ti plate with a TiO₂ nanotubular layer was compared with other cathodes such as Ti, Cu, Ni, and Stainless Steel. The Ti plate with an anatase TiO₂ nanotubular layer with a layer thicknesses greater than 45 μm was able to show the most efficient nitrate reduction.

Toward Robust Photoelectrochemical Operation of Cuprous Oxide Nanowire Photocathodes Using a Strategically Designed Solution-Processed Titanium Oxide Passivation Coating

To date, TiO₂ films prepared by atomic layer deposition are widely used to prepare Cu₂O nanowire (NW)-based photocathodes with photoelectrochemical (PEC) durability as this approach enables conformal coating and furnishes chemical robustness. However, this common approach requires complicated interlayers and makes the fabrication of photocathodes with reproducible performance and long-term stability difficult. Although sol-gel-based approaches have been well established for coating surfaces with oxide thin films, these techniques have rarely been studied for oxide passivation in PEC applications, because the sol-gel coating methods are strongly influenced by surface chemical bonding and have been mainly demonstrated on flat substrates. As a unique strategy based on solution processing, herein, we suggest a creative solution for two problems encountered in the conformal coating of surfaces with oxide layers: (i) how to effectively prevent corrosion of materials with hydrophilic surfaces by simply using a single TiO₂ surface protection layer instead of a complex multilayer structure and (ii) guaranteeing perfect chemical durability. A Cu(OH)₂ NW can be easily prepared as an intermediate phase by anodization of a Cu metal, where the former inherently possesses a hydrophilic hydroxylated surface and thus, enables thorough coating with TiO₂ precursor solutions. Chemically robust nanowires are then generated as the final product via the phase transformation of Cu(OH)₂ to Cu₂O via sintering at 600 °C. The coated NWs exhibit excellent PEC properties and a stable performance. Consequently, the perfect chemical isolation of the Cu₂O NWs from the electrolyte allows a remarkable PEC operation with the maintenance of the initial photocurrent for more than one day.

Highly efficient modified lead oxide electrode using a spin coating/electrodeposition mode on titanium for electrochemical treatment of pharmaceutical pollutant

In this study, Ti/TiO₂/PbO₂ anodes consisting of a PbO₂ coating growth on the TiO₂ interlayer deposited on titanium substrates were prepared combining different deposition technics: electrochemical method using anodization (Anod), electrodeposition (EL), and sol gel spin coating (SG). Different kinds of anodes have been tested for the removal of ampicillin, a pharmaceutical pollutant, from water. The structure and the surface morphology of the prepared multiple coatings were characterized by scanning electron microscopy and Energy-Dispersive X-ray spectroscopy respectively. Electrochemical impedance spectroscopy was also investigated in order to study the electrocatalytic activity of the anodes. The performance of the electrodes was evaluated through high performance liquid chromatography and chemical oxygen demand (COD) measurements. It was noticed that ampicillin could be mineralized by anodic oxidation process using Ti/TiO₂/PbO₂ anodes. The best results were obtained for Ti/TiO₂^SG/PbO₂^EL as anode with a 64% of COD removal after 300 min of treatment and a fast decrease in the amount of ampicillin was reached after almost one hour. Experimental results demonstrate that Ti/TiO₂^SG/PbO₂^EL anode presents the best ability for the degradation of ampicillin through anodic oxidation compared to the Ti/TiO₂^SG/PbO₂^SG and Ti/TiO₂^Anod/PbO₂^EL electrodes.

Effect of phosphate concentration, anions, heavy metals, and organic matter on phosphate adsorption from wastewater using anodized iron oxide nanoflakes

Phosphorus is a necessary nutrient for the growth and survival of living beings. Nevertheless, an oversupply of phosphorus in wastewater results in eutrophication. Therefore, its removal from wastewater is important. However, coexisting components, such as anions, heavy metals, and organic matter, might inhibit the phosphate-adsorption mechanism by competing for the active surface sites of the adsorbent. In this study, iron oxide nanoflakes (INFs) were fabricated on iron foil via anodization. The rate of phosphate adsorption from wastewater onto INFs in the presence of three different coexisting components-anions, heavy metals, and organic matter-was evaluated. The morphology of the INFs was analyzed by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The phosphate adsorption equilibrium time using INFs was found to be 1 h. The Elovich model (R² > 0.99) and the Langmuir model (R² >0.95) respectively provided the best description of the adsorption kinetics and isotherm, suggesting the chemisorption nature of adsorption. The estimated adsorption capacity of the INFs was 21.5 mg-P g^-1. The effect of anions (chloride, sulfate, nitrate, and carbonate) and heavy metals (Cd, As, Cr, and Pb) was studied at three different molar ratios (0.5:1, 1:1, and 1.5:1). The effect of different types of organic matter, such as citric acid, humic acid, and oxalic acid at concentrations of 100 and 200 mg L^-1, was also examined. In five regeneration cycles, the total amount of phosphate adsorbed and desorbed, and the recovery percentage were 6.51 mg-P g^-1, 5.16 mg-P g^-1, and 79.24%, respectively.

A facile synthesis of Cs loaded TiO2 nanotube photoelectrode for the removal of 4-chloroguaiacol

In this study, novel Cesium (Cs) doped TiO₂ nanotubes photoelectrode (Cs/TiO₂NTs) were synthesized by simple electrochemical anodization method and characterized by several physicochemical techniques. In particular, the photocatalytic (PC), electrocatalytic (EC) and photoelectrocatalytic (PEC) activity of newly synthesized Cs/TiO₂NTs electrodes was investigated using 4-Chloroguaiacol (4-CG). The effect of operating parameters like Cs concentration, electrolyte concentration, external current and pH on degradation efficacy was examined. PEC oxidation using Cs/TiO₂NTs lead to 92% degradation of 4-CG in 6 h of solar light irradiation under optimized conditions (2.5 mM Cs, 160 mg L^-1 Na₂SO₄, 0.03 A current and pH 3). A comparative assessment between PEC, PC and EC process manifested that PEC process was most efficient than the other two processes and Cs/TiO₂NTs exhibited higher PEC activity than bare-TiO₂ electrodes in terms of degradation and mineralization of organic pollutant. The generation of OH radicals was found to be highest in PEC when compared to EC and PC process. Possible intermediates/byproducts were identified by GC-MS technique and a corresponding tentative degradation pathway has been proposed. Cytotoxicity study showed that PEC has potential to detoxify 4-CG. Hence, combination of TiO₂ electrodes decorated with Cs metal can act as a highly efficient photoelectrode for the degradation of hazardous pollutants.

Electrochemical anodization of graphite oxide-TiO2 nanotube composite for enhanced visible light photocatalytic activity

The electrochemical anodization method was used to dope graphite oxide (GO) onto TiO₂ nanotubes (TNTs). This study focused on enhancement of the photocatalytic activity of TNTs in the visible light region. In this study, we have checked the effect of different GO concentrations and effect of GO doping time on photocatalytic efficiency of composite. The photocatalytic activity of the GO-TNT composite was tested by degradation of an organic compound. The organic compound was most severely degraded (95%) when the GO-TNT catalyst was doped at an anodization of 60 V for 13 min and GO concentration of 0.25 g L^-1. This degradation was 5.6 times higher than that of bare TiO₂. The as-prepared catalyst was characterized using FE-SEM, XRD, AES, PL, UV-Vis DRS, and Raman analysis. Recycling of the GO-TNT composite was also performed in order to examine the stability of the visible light catalyst. We observed that the doping of GO on the TNT surface can enhance the photocatalytic efficiency under visible light. Graphene acts as an electron transport; therefore, GO-TNTs were favorable for the separation of e^- and h⁺ charges. This promoted the formation of OH radicals, h⁺, and superoxides, all of which degrade organics.

Visible-light photoelectrodegradation of diuron on WO3 nanostructures

The degradation of pesticide diuron has been explored by photoelectrocatalysis (PEC) under visible light illumination using two different WO₃ nanostructures, obtained by anodization of tungsten. The highest degradation efficiency (73%) was obtained for WO₃ nanosheets synthesized in the presence of small amounts of hydrogen peroxide (0.05 M). For that nanostructure, the kinetic coefficient for diuron degradation was 133% higher than that for the other nanostructure (anodized in the presence of fluoride anions). These results have been explained by taking into account the different architecture and dimensions of the two WO₃ nanostructures under study.

Optimization of effective parameters in the synthesis of nanopore anodic aluminum oxide membrane and arsenic removal by prepared magnetic iron oxide nanoparicles in anodic aluminum oxide membrane via ultrasonic-hydrothermal method

In this study, a new anodized aluminum oxide (AAO) nanostructure membrane was synthesized by anodization process under a constant voltage, in oxalic acid solution that was improved with trace amounts of sulfuric acid at room temperature. The effect of various parameters on the morphology of the synthesized nanostructures such as voltage, electrolyte composition, anodization time and type of stripping solution were investigated. According to the results, corrosion of the walls, size regularity, diameter and number of the pores increased in the presence of sulfuric acid (0.018 mol.L^-1). Nitrogen adsorption-desorption analysis confirmed significant porosity, array and uniformity of the pore size in the synthesized nanoporous membrane. A new modification method was used based on ultrasonic-hydrothermal method to modify the synthesized AAO with Fe₃O₄/SiO₂ nanoparticles for metals and metalloids removal from aqueous solution. In this method, Fe₃O₄/SiO₂ nanoparticles were placed very regularly and uniformly on the surface and inside the pores. This modification was confirmed by characterization techniques. The modified AAO@Fe₃O₄/SiO₂ membrane showed excellent results for removing arsenic from aqueous media.

Titania nanopores with dual micro-/nano-topography for selective cellular bioactivity

This letter describes a simple surface modification strategy based on a single-step electrochemical anodization towards generating dual micro- and nano-rough horizontally-aligned TiO₂ nanopores on the surface of clinically utilized micro-grooved titanium implants. Primary macrophages, osteoblasts and fibroblasts were cultured on the nano-engineered implants, and it was demonstrated that the modified surfaces selectively reduced the proliferation of macrophages (immunomodulation), while augmenting the activity of osteoblasts (osseo-integration) and fibroblasts (soft-tissue integration). Additionally, the mechanically robust nanopores also stimulated osteoblast and fibroblast adhesion, attachment and alignment along the direction of the pores/grooves, while macrophages remained oval-shaped and sparsely distributed. This study for the first time reports the use of cost-effectively prepared nano-engineered titanium surface via anodization, with aligned multi-scale micro/nano features for selective cellular bioactivity, without the use of any therapeutics.

Visible-light-assisted photocatalytic activity of bismuth-TiO2 nanotube composites for chromium reduction and dye degradation

TiO₂ nanotubes (TNTs) were synthesized on a Ti sheet using the electrochemical anodization method. Bismuth (Bi) was coupled on the anodized TNTs via hydrothermal process. We verified the effect of different Bi concentrations on the photocatalytic properties of Bi-TNT composites. The obtained samples were characterized using field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, UV-Vis diffuse reflectance spectra, and photoluminescence spectra. The Bi-TNT photocatalysts exhibited higher activities by factors of 6.6 and 3.6 toward chromium reduction and methylene blue degradation, respectively, under visible light than the pure TNTs. The Bi-TNT material was recycled to examine the stability of the catalyst. The quantum efficiency of the photocatalytic system was calculated, and the synergistic effects of bismuth modification were discussed. The Bi-TNT composites were observed to be promising for separation of photoinduced e^- and h⁺ by decreasing charge recombination, and helped the formation of the hydroxyl radicals, h⁺, and superoxides used in the photocatalytic process.

Ultra-rapid fabrication of highly surface-roughened nanoporous gold film from AuSn alloy with improved performance for nonenzymatic glucose sensing

Using one-step anodization strategy, a nanoporous gold film (HNPG) with large surface area was rapidly fabricated on Au₈₀Sn₂₀ (wt%) alloy in just 80 s. The formation of highly surface-roughened nanoporous structures results from a complex process of electrochemical dealloying of Sn component from AuSn alloy, anodic electrodissolution, disproportion and deposition of Au component, and spontaneous redox reaction between electrodissolved Sn²⁺ and AuCl₄^－species at the applied anodic potential. As-prepared HNPG/AuSn shows enhanced electrochemical performance for glucose oxidation in alkaline electrolyte. At a low potential of 0.1 V (vs. SCE), it offers a short response time of 4 s, a wide linear detection range of 2 μM to 8.11 mM, an ultralow detection limit of 0.36 μM (S/N = 3), an ultrahigh sensitivity of 4374.6 μA cm^-2 mM^-1, and satisfactory selectivity and reproducibility. Specifically, after 6 weeks, no obvious loss of glucose amperometric signal was observed on HNPG/AuSn. The facile preparation and excellent sensing performance of HNPG/AuSn electrode make sure that it is a promising candidate for advanced enzyme-free glucose sensors.

Understanding and augmenting the stability of therapeutic nanotubes on anodized titanium implants

Titanium is an ideal material choice for orthopaedic and dental implants, and hence a significant amount of research has been focused towards augmenting the therapeutic efficacy of titanium surfaces. More recently the focus has shifted to nano-engineered implants fabricated via anodization to generate self-ordered nanotubular structures composed of titania (TiO₂). These structures (titania nanotubes/TNTs) enable local drug delivery and tailorable cellular modulation towards achieving desirable effects like enhanced osseointegration and antibacterial action. However, the mechanical stability of such modifications is often ignored and remains underexplored, and any delamination or breakage in the TNTs modification can initiate toxicity and lead to severe immuno-inflammatory reactions. This review details and critically evaluates the progress made in relation to this aspect of TNT based implants, with a focus on understanding the interface between TNTs and the implant surface, treatments aimed at augmenting mechanical stability and strategies for advanced mechanical testing within the bone micro-environment ex vivo and in vivo. This review article extends the existing knowledge in this domain of TNTs implant technology and will enable improved understanding of the underlying parameters that contribute towards mechanically robust nano-engineered implants that can withstand the forces associated with implant surgical placement and the load bearing experienced at the bone/implant interface.

Corrosion of titanium: Part 2: Effects of surface treatments

Titanium is well known as one of the most corrosion-resistant metals. However, it can suffer corrosion attacks in some specific aggressive conditions. To further increase its corrosion resistance, it is possible either to modify its surface, tuning either thickness, composition, morphology or structure of the oxide that spontaneously forms on the metal, or to modify its bulk composition. Part 2 of this review is dedicated to the corrosion of titanium and focuses on possible titanium treatments that can increase corrosion resistance. Both surface treatments, such as anodization or thermal or chemical oxidation, and bulk treatments, such as alloying, are considered, highlighting the advantages of each technique.

Fabrication of Uniform Nanoporous Oxide Layers on Long Cylindrical Zircaloy Tubes by Anodization Using Multi-Counter Electrodes

We have presented a method to prepare a uniform anodic nanoporous oxide film on the surface of a cylindrical zircaloy (Zr) tube. The distribution of the electric field around the Zr tube determines the distribution of the thickness of the anodic nanoporous oxide film. The electric field generated when a cylindrical Zr tube is electrochemically anodized was simulated by using commercial code COMSOL. When four Pt wires were used as counter electrodes, a uniform electric field was achieved with minimal use of Pt. Based on the simulation results, a cylindrical Zr tube was anodized and the distribution of the thickness of the anodic nanoporous oxide layer was measured by FESEM. Also, mass production of uniform nanoporous anodic oxide films was possible by symmetrically arranging the zircaloy tubes and Pt wires.

Anodization of magnesium for biomedical applications - Processing, characterization, degradation and cytocompatibility

This article reports anodization of Mg in KOH electrolyte and the associated surface, degradation, and biological properties for bioresorbable implant applications. The preparation procedures for electrodes and anodization setup significantly enhanced reproducibility of samples. The results of anodization performed at the applied potentials of 1.8, 1.9, or 2.0V showed that the sample anodized at 1.9V and annealed, referred to as the 1.9 AA sample, had homogenous surface microstructure and elemental composition, and a reduction in corrosion current density in the electrochemical testing. In comparison with Mg control, the 1.9 AA sample showed a distinct mode of degradation, e.g., continuous growth of a passivation layer enriched with Ca and P instead of typical localized pitting and undermining, and a greater release rate of Mg²⁺ ions when immersed in physiologically relevant media. In the direct culture with bone marrow derived mesenchymal stem cells (BMSCs) in vitro, the 1.9 AA sample did not affect BMSC adhesion and morphology under indirect contact; however, the 1.9 AA sample showed a reduction in cell spreading under direct contact. The change in surface topography/composition at the dynamic interface of the anodized-annealed Mg sample might have contributed to the change in BMSC morphology. In summary, this study demonstrated the potential of anodic oxidation to modulate the degradation behaviors of Mg-based biomaterials and BMSC responses in vitro, and confirmed the value of direct culture method for studying cytocompatibility of Mg-based biomaterials for medical implant applications.

STATEMENT OF SIGNIFICANCE

Magnesium (Mg)-based biomaterials have been specifically designed and actively explored for biodegradable implant applications since the early 2000s. To realize the benefits of Mg-based materials for medical implant applications, it is critical to control the rate of Mg degradation (i.e. corrosion) in the body. We investigated an environmentally friendly anodization process using KOH electrolyte for modifying the surface of Mg-based materials, and the resulted surface, degradation, and biological properties for biomedical applications. This study reported critical considerations that are important for repeatability of anodization process, homogeneity of surface microstructure and composition, and in vitro evaluations of the degradation and biological properties of surface treated Mg samples. The details in preparation of electrodes, anodization setup, annealing, and sample handling before and after surface treatment (e.g. re-embedding) reported in this article are valuable for studying a variety of electrochemical processes for surface treatment of Mg-based metals, because of enhanced reproducibility.

Synthesis and biological properties of Zn-incorporated micro/nano-textured surface on Ti by high current anodization

It is acknowledged that ideal implant coatings should possess micro/nano-textured surface, have good interfacial bonding, and can release bioactive elements. In this study, we fabricated a Zn-incorporated micro/nano-textured surface by one-step high current anodization (HCA) in an aqueous solution with 10g/L of NaOH and different concentrations of Zn(NO₃)₂ (4, 7, and 12g/L). The control group of Zn-free was fabricated in the electrolyte of 7g/L Zn(NO₃)₂. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and inductively coupled plasma mass spectroscopy (ICP-MS) were used to analyze the morphology, composition, microstructure, and Zn⁺ release kinetics of the micro/nano-textured coatings. The biological properties of the surface structure were evaluated by cytotoxicity assay, cell viability, cytoskeletal assembly and alkaline phosphatase activity. Our results show the micro/nano-textured surface is composed of TiO₂ mesoporous arrays, into which the Zn is demonstrated to be incorporated in the form of ZnO. The Zn content in the surface and release level of Zn²⁺ can be tailored through varying Zn(NO₃)₂ concentration in the electrolyte. In addition, the surface oxide layers show good interfacial bonding strength to the substrate. Compared with pure Ti and anodized Zn-free samples, the Zn-incorporated surface can upregulate osteoblast functions such as proliferation and alkaline phosphatase activity, which are assayed by MTT and ALP staining experiments, respectively. Collectively, this micro/nano-textured structure combined with high interfacial bonding strength and release of Zn²⁺ render the material surface promising as orthopedic implant coatings.

Investigation of the mechanical and chemical characteristics of nanotubular and nano-pitted anodic films on grade 2 titanium dental implant materials

OBJECTIVE

The objective of this study was to investigate the reproducibility, mechanical integrity, surface characteristics and corrosion behavior of nanotubular (NT) titanium oxide arrays in comparison with a novel nano-pitted (NP) anodic film.

METHODS

Surface treatment processes were developed to grow homogenous NT and NP anodic films on the surface of grade 2 titanium discs and dental implants. The effect of process parameters on the surface characteristics and reproducibility of the anodic films was investigated and optimized. The mechanical integrity of the NT and NP anodic films were investigated by scanning electron microscopy, surface roughness measurement, scratch resistance and screwing tests, while the chemical and physicochemical properties were investigated in corrosion tests, contact angle measurement and X-ray photoelectron spectroscopy (XPS).

RESULTS AND DISCUSSION

The growth of NT anodic films was highly affected by process parameters, especially by temperature, and they were apt to corrosion and exfoliation. In contrast, the anodic growth of NP film showed high reproducibility even on the surface of 3-dimensional screw dental implants and they did not show signs of corrosion and exfoliation. The underlying reason of the difference in the tendency for exfoliation of the NT and NP anodic films is unclear; however the XPS analysis revealed fluorine dopants in a magnitude larger concentration on NT anodic film than on NP surface, which was identified as a possible causative. Concerning other surface characteristics that are supposed to affect the biological behavior of titanium implants, surface roughness values were found to be similar, whereas considerable differences were revealed in the wettability of the NT and NP anodic films.

CONCLUSION

Our findings suggest that the applicability of NT anodic films on the surface of titanium bone implants may be limited because of mechanical considerations. In contrast, it is worth to consider the applicability of nano-pitted anodic films over nanotubular arrays for the enhancement of the biological properties of titanium implants.

Improved in vitro angiogenic behavior on anodized titanium dioxide nanotubes

Background

Neovascularization over dental implants is an imperative requisite to achieve successful osseointegration onto implanted materials. The aim of this study was to investigate the effects on in vitro angiogenesis of anodized 70 nm diameter TiO₂ nanotubes (NTs) on Ti6Al4V alloy synthesized and disinfected by means of a novel, facile, antibacterial and cost-effective method using super oxidized water (SOW). We also evaluated the role of the surface roughness and chemical composition of materials of materials on angiogenesis.

Methods

The Ti6Al4V alloy and a commercially pure Ti were anodized using a solution constituted by SOW and fluoride as electrolyte. An acid-etched Ti6Al4V was evaluated to compare the effect of micro-surface roughness. Mirror-polished materials were used as control. Morphology, roughness, chemistry and wettability were assessed by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy, atomic force microscopy, energy dispersive X-ray spectroscopy (EDX) and using a professional digital camera. Bovine coronary artery endothelial cells (BCAECs) were seeded over the experimental surfaces for several incubation times. Cellular adhesion, proliferation and monolayer formation were evaluated by means of SEM. BCAEC viability, actin stress fibers and vinculin cellular organization, as well as the angiogenic receptors vascular endothelial growth factor 2 (VEGFR2) and endothelial nitric oxide synthase (eNOS) were measured using fluorescence microscopy.

Results

The anodization process significantly increased the roughness, wettability and thickness of the oxidized coating. EDX analysis demonstrated an increased oxygen (O) and decreased carbon (C) content on the NTs of both materials. Endothelial behavior was solidly supported and improved by the NTs (without significant differences between Ti and alloy), showing that endothelial viability, adhesion, proliferation, actin arrangement with vinculin expression and monolayer development were evidently stimulated on the nanostructured surface, also leading to increased activation of VEGFR2 and eNOS on Ti6Al4V-NTs compared to the control Ti6Al4V alloy. Although the rougher alloy promoted BCAECs viability and proliferation, filopodia formation was poor.

Conclusion

The in vitro results suggest that 70 nm diameter NTs manufactured by anodization and cleaned using SOW promotes in vitro endothelial activity, which may improve in vivo angiogenesis supporting a faster clinical osseointegration process.

Self-organized double-wall oxide nanotube layers on glass-forming Ti-Zr-Si(-Nb) alloys

In this work, we report for the first time on the use of melt spun glass-forming alloys - Ti₇₅Zr₁₀Si₁₅ (TZS) and Ti₆₀Zr₁₀Si₁₅Nb₁₅ (TZSN) - as substrates for the growth of anodic oxide nanotube layers. Upon their anodization in ethylene glycol based electrolytes, highly ordered nanotube layers were achieved. In comparison to TiO₂ nanotube layers grown on Ti foils, under the same conditions for reference, smaller diameter nanotubes (~116nm for TZS and ~90nm for TZSN) and shorter nanotubes (~11.5μm and ~6.5μm for TZS and TZSN, respectively) were obtained for both amorphous alloys. Furthermore, TEM and STEM studies, coupled with EDX analysis, revealed a double-wall structure of the as-grown amorphous oxide nanotubes with Ti species being enriched in the inner wall, and Si species in the outer wall, whereby Zr and Nb species were homogeneously distributed.

Electrokinetic Properties of TiO2 Nanotubular Surfaces

Surface charge is one of the most significant properties for the characterisation of a biomaterial, being a key parameter in the interaction of the body implant with the surrounding living tissues. The present study concerns the systematic assessment of the surface charge of electrochemically anodized TiO2 nanotubular surfaces, proposed as coating material for Ti body implants. Biologically relevant electrolytes (NaCl, PBS, cell medium) were chosen to simulate the physiological conditions. The measurements were accomplished as titration curves at low electrolytic concentration (10(-3) M) and as single points at fixed pH but at various electrolytic concentrations (up to 0.1 M). The results showed that all the surfaces were negatively charged at physiological pH. However, the zeta potential values were dependent on the electrolytic conditions (electrolyte ion concentration, multivalence of the electrolyte ions, etc.) and on the surface characteristics (nanotubes top diameter, average porosity, exposed surface area, wettability, affinity to specific ions, etc.). Accordingly, various explanations were proposed to support the different experimental data among the surfaces. Theoretical model of electric double layer which takes into account the asymmetric finite size of ions in electrolyte and orientational ordering of water dipoles was modified according to our specific system in order to interpret the experimental data. Experimental results were in agreement with the theoretical predictions. Overall, our results contribute to enrich the state-of-art on the characterisation of nanostructured implant surfaces at the bio-interface, especially in case of topographically porous and rough surfaces.

Fast Growth of Highly Ordered TiO2 Nanotube Arrays on Si Substrate under High-Field Anodization

ABSTRACT

Highly ordered TiO₂ nanotube arrays (NTAs) on Si substrate possess broad applications due to its high surface-to-volume ratio and novel functionalities, however, there are still some challenges on facile synthesis. Here, we report a simple and cost-effective high-field (90-180 V) anodization method to grow highly ordered TiO₂ NTAs on Si substrate, and investigate the effect of anodization time, voltage, and fluoride content on the formation of TiO₂ NTAs. The current density-time curves, recorded during anodization processes, can be used to determine the optimum anodization time. It is found that the growth rate of TiO₂ NTAs is improved significantly under high field, which is nearly 8 times faster than that under low fields (40-60 V). The length and growth rate of the nanotubes are further increased with the increase of fluoride content in the electrolyte.

GRAPHICAL ABSTRACT

Highly ordered TiO₂ nanotube arrays (NTAs) on Si substrate have been fabricated by high-field anodization method. A high voltage (90-180 V) leads to a high growth rate of TiO₂ NTAs (35-47 nm s^-1), which is nearly 8 times faster than the growth rate under low fields (40-60 V). Furthermore, the current density-time curves recorded during the anodization provide a facial method to determine the optimal anodization parameters, leading to an easy obtaining of the desired nanotubes.

Biocompatibility of different nanostructured TiO2 scaffolds and their potential for urologic applications

Despite great efforts in tissue engineering of the ureter, urinary bladder, and urethra, further research is needed in order to improve the patient's quality of life and minimize the economic burden of different lower urinary tract disorders. The nanostructured titanium dioxide (TiO₂) scaffolds have a wide range of clinical applications and are already widely used in orthopedic or dental medicine. The current study was conducted to synthesize TiO₂ nanotubes by the anodization method and TiO₂ nanowires and nanospheres by the chemical vapor deposition method. These scaffolds were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. In order to test the urologic applicability of generated TiO₂ scaffolds, we seeded the normal porcine urothelial (NPU) cells on TiO₂ nanotubes, TiO₂ nanowires, TiO₂ nanospheres, and on the standard porous membrane. The viability and growth of the cells were monitored everyday, and after 3 weeks of culturing, the analysis with scanning electron microscope (SEM) was performed. Our results showed that the NPU cells were attached on all scaffolds; they were viable and formed a multilayered epithelium, i.e., urothelium. The apical plasma membrane of the majority of superficial NPU cells, grown on all three different TiO₂ scaffolds and on the porous membrane, exhibited microvilli; thus, indicating that they were at a similar differentiation stage. The maximal caliper diameter measurements of superficial NPU cells revealed significant alterations, with the largest cells being observed on nanowires and the smallest ones on the porous membrane. Our findings indicate that different nanostructured TiO₂ scaffolds, especially nanowires, have a great potential for tissue engineering and should be further investigated for various urologic applications.

OH radical generation in a photocatalytic reactor using TiO2 nanotube plates

In order to use TiO2 nanotubes grown on a Ti plate as a photocatalyst, self-organized oxide nanotube layers were grown by anodization in a glycerol based electrolyte. The ultimate conditions for the synthesis of the TiO2 nanotube array on the Ti plate were investigated by comparing the morphology, length, and inner diameter of the nanotubes. They were significantly affected by the applied anodic voltage, anodization time, and composition of the electrolyte such as the water and fluoride ion concentration. The crystallographic structures of TiO2 nanotubes before and after annealing were compared. The photocatalytic reactor used in this study consisted of two parallel and closely spaced TiO2 nanotube plates. The plates were squares while a UV lamp was inserted perpendicularly to them. OH radical generation in the photocatalytic reactor was monitored by using a probe compound, parachlorobenzoate (pCBA). The steady state OH radical concentration was compared depending on the length of nanotubes and crystallographic structure. The longer the nanotubes, the higher the steady state OH radical concentration.

Adhesive strength of bioactive oxide layers fabricated on TNTZ alloy by three different alkali-solution treatments

Bioactive oxide layers were fabricated on Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) by three different alkali solution treatments: hydrothermal (H), electrochemical (E), and hydrothermal-electrochemical (HE). The adhesive strength of the oxide layer to the TNTZ substrate was measured to determine whether this process achieves sufficient adhesive strength for implant materials. Samples subjected to the HE process, in which a current of 15mA/cm(2) was applied at 90°C for 1h (HE90-1h), exhibited a comparatively higher adhesive strength of approximately 18MPa while still maintaining a sufficiently high bioactivity. Based on these results, an oxide layer fabricated on TNTZ by HE90-1h is considered appropriate for practical biomaterial application, though thicker oxide layers with many cracks can lead to a reduced adhesive strength.

Controlled Fabrication of Nanoporous Oxide Layers on Zircaloy by Anodization

We have presented a mechanism to explain why the resulting oxide morphology becomes a porous or a tubular nanostructure when a zircaloy is electrochemically anodized. A porous zirconium oxide nanostructure is always formed at an initial anodization stage, but the degree of interpore dissolution determines whether the final morphology is nanoporous or nanotubular. The interpore dissolution rate can be tuned by changing the anodization parameters such as anodization time and water content in an electrolyte. Consequently, porous or tubular oxide nanostructures can be selectively fabricated on a zircaloy surface by controlling the parameters. Based on this mechanism, zirconium oxide layers with completely nanoporous, completely nanotubular, and intermediate morphologies between a nanoporous and a nanotubular structure were controllably fabricated.

Adherence of oral streptococci to nanostructured titanium surfaces

OBJECTIVES

Peri-implantitis and peri-mucositis pose a severe threat to the success of dental implants. Current research focuses on the development of surfaces that inhibit biofilm formation while not inferring with tissue integration. This study compared the adherence of two oral bacterial species, Streptococcus sanguinis and Streptococcus mutans to nanostructured titanium surfaces.

METHODS

The samples included TiO2 nanotubes formed by anodization of titanium foil of 100, 50 and 15nm diameter (NT15, NT50, NT100), a nanoporous (15nm pore diameter) surface and compact TiO2 control. Adherent surviving bacteria were enumerated after 1h in an artificial saliva medium containing bovine mucin.

RESULTS

Lowest numbers of adherent bacteria of both species were recovered from the original titanium foil and nanoporous surface and highest numbers from the Ti100 nanotubes. Numbers of attached S. sanguinis increased in the order (NT15<NT50<NT100), correlated with increasing percentage of surface fluoride. The lowest adhesion of S. sanguinis and S. mutans on TiO2 nanostructured surfaces was observed for small diameter nanoporous surfaces which coincides with the highest osteoblast adhesion on small diameter nanotubular/nanoporous surfaces shown in previous work.

SIGNIFICANCE

This study indicates that the adherence of oral streptococci can be modified by titanium anodization and nanotube diameter.