Hydroxyapatite growth on anodic TiO2 nanotubes

Nanoengineering and Surface Modifications of Dental Implants

Dental implants are one of the most important and successful advancements in modern dentistry. One aspect of dental implant design that influences the rate and degree of osseointegration is implant surface features. Nano-engineering techniques are anticipated to improve titanium dentistry implants' surface characteristics, which in turn promote peri-implant osteogenesis. In this paper, we review the recent advances in nanosurface engineering techniques for enhancing the bioactivity of dental implants.

Tubular nanomaterials for bone tissue engineering

Nanomaterial composition, morphology, and mechanical performance are critical parameters for tissue engineering. Within this rapidly expanding space, tubular nanomaterials (TNs), including carbon nanotubes (CNTs), titanium oxide nanotubes (TNTs), halloysite nanotubes (HNTs), silica nanotubes (SiNTs), and hydroxyapatite nanotubes (HANTs) have shown significant potential across a broad range of applications due to their high surface area, versatile surface chemistry, well-defined mechanical properties, excellent biocompatibility, and monodispersity. These include drug delivery vectors, imaging contrast agents, and scaffolds for bone tissue engineering. This review is centered on the recent developments in TN-based biomaterials for structural tissue engineering, with a strong focus on bone tissue regeneration. It includes a detailed literature review on TN-based orthopedic coatings for metallic implants and composite scaffolds to enhance in vivo bone regeneration.

Effect of Hydrothermal and Vapor Thermal Treatments on Apatite Inductivity of Titanate Nanotubes on Anodized Ti-5Nb-5Mo Surface

Although titanium (Ti) alloys have been widely employed as biomedical materials, they cannot achieve satisfactory osseointegration when implanted in the human body due to their biologically inert nature. Surface modification can enhance both their bioactivity and corrosion resistance. The present study employed a Ti-5Nb-5Mo alloy with a metastable α″ phase. This alloy may undergo phase changes after conventional high-temperature heat treatment, which can deteriorate its properties. This study heat-treated the anodized Ti-5Nb-5Mo alloy by using a low-temperature hydrothermal or vapor thermal method to analyze the effects of heat treatment on its apatite induction. The results revealed that the porous nanotube structure on the surface of the alloy was transformed into anatase nanoparticles after hydrothermal or vapor thermal treatment at 150 °C for 6 h. After immersion in simulated body fluid (SBF) for 7 days, the amount of apatite deposited on the surface of the vapor thermal-treated alloy exceeded that on the hydrothermal-treated alloy. Therefore, post-heat treatment of anodized Ti-5Nb-5Mo by using the vapor thermal method can enhance its apatite inductivity without altering its structure.

Evaluation of the Cathodic Electrodeposition Effectiveness of the Hydroxyapatite Layer Used in Surface Modification of Ti6Al4V-Based Biomaterials

The important issue associated with the design and the fabrication of the titanium and titanium alloy implants is the increase of their biointegration with bone tissue. In the presented paper, the research results concerning the conditions used in the cathodic deposition of hydroxyapatite on the surface Ti6Al4V substrates primarily modified by the production of TiO₂ nanoporous coatings, TiO₂ nanofibers, and titanate coatings, are discussed. Despite excellent biocompatibility with natural bone tissue of materials based on hydroxyapatite (HA), their poor adhesion to the substrate caused the limited use in the implants' construction. In our works, we have focused on the comparison of the structure, physicochemical, and mechanical properties of coating systems produced at different conditions. For this purpose, scanning electron microscopy images, chemical composition, X-ray diffraction patterns, infrared spectroscopy, wettability, and mechanical properties are analyzed. Our investigations proved that the intermediate titanium oxide coatings presence significantly increases the adhesion between the hydroxyapatite layer and the Ti6Al4V substrate, thus solving the temporary delamination problems of the HA layer.

Tribocorrosion-Resistant Ti40Nb-TiN Composites Having TiO2-Based Nanotubular Surfaces

A novel multifunctional material was developed by hard TiN particle reinforcement addition to a β-type Ti40Nb alloy, followed by surface functionalization, yielding the formation of a nanotubular layer. Corrosion and tribocorrosion behaviors were investigated in a phosphate-buffered saline solution at body temperature. The results revealed that the Ti40Nb-TiN composites presented similar ipass and E(i=0) values together with relatively similar Rox and Cox. However, its tribocorrosion resistance drastically improved (wear volume is almost 15 times lower than an unreinforced alloy) as a consequence of the load-carrying effect given by the reinforcement phases. The corrosion and tribocorrosion behaviors were further improved through surface functionalization as observed by significantly lower ipass and higher Rox values and almost undetectable wear volume loss from tribocorrosion tests due to the formation of a well-adhered anatase-rutile TiO2-based nanotubular layer.

Improved Biocompatibility of TiO2 Nanotubes via Co-Precipitation Loading with Hydroxyapatite and Gentamicin

The antibacterial properties of titanium make it useful for clinical applications. Hydroxyapatite (HA) is widely utilized as a coating on orthopedic implants to improve osteointegration. Titanium oxide nanotubes (TNT) are recognized as a promising solution for local antibiotic therapy in bone implants. It is demonstrated that the utilization of HA-coated titanium can improve the biocompatibility of bone implants. This research aims to examine the antibacterial properties and biocompatibility of the TiO2 nanotubes by loading HA and gentamicin. In vitro testing, the characterization of drug release, cell adhesion and proliferation, bacteria culture, and antibacterial tests were conducted. During the in vivo experiments, Staphylococcus aureus was implanted into the femur of rats. The animals were sacrificed at four weeks followed by microbiological and clinical assessments on the bone, which were conducted by removing the implants followed by agar plating. The in vitro cell incubation demonstrated that the TiO2 nanotubes loaded with hydroxyapatite and gentamicin had better cellular compatibility compared to Cp–Ti. In addition, in vitro elution testing showed that gentamicin was released from the hydroxyapatite/TiO2 nanotubes for as long as 22 days. The release time was much longer than the TNT loaded with gentamicin at only 6 h. All animals in the gentamicin/HA/TNT group were free of infection compared to those in the Cp–Ti, TNT, and HA/gentamicin/TNT groups. There was a considerable reduction in the rates of infection among the rats with gentamicin-HA-TNT coatings compared to standard titanium. These results indicated that the co-precipitation of gentamicin and HA loading using the TNT method provided a novel prophylactic method against prosthetic infections and other biomedical applications.

Passive Layers and Corrosion Resistance of Biomedical Ti-6Al-4V and β-Ti Alloys

The high specific strength, good corrosion resistance, and great biocompatibility make titanium and its alloys the ideal materials for biomedical metallic implants. Ti-6Al-4V alloy is the most employed in practical biomedical applications because of the excellent combination of strength, fracture toughness, and corrosion resistance. However, recent studies have demonstrated some limits in biocompatibility due to the presence of toxic Al and V. Consequently, scientific literature has reported novel biomedical β-Ti alloys containing biocompatible β-stabilizers (such as Mo, Ta, and Zr) studying the possibility to obtain similar performances to the Ti-6Al-4V alloys. The aim of this review is to highlight the corrosion resistance of the passive layers on biomedical Ti-6Al-4V and β-type Ti alloys in the human body environment by reviewing relevant literature research contributions. The discussion is focused on all those factors that influence the performance of the passive layer at the surface of the alloy subjected to electrochemical corrosion, among which the alloy composition, the method selected to grow the oxide coating, and the physicochemical conditions of the body fluid are the most significant.

Assessment of Titanate Nanolayers in Terms of Their Physicochemical and Biological Properties

The surface modification of titanium substrates and its alloys in order to improve their osseointegration properties is one of widely studied issues related to the design and production of modern orthopedic and dental implants. In this paper, we discuss the results concerning Ti6Al4V substrate surface modification by (a) alkaline treatment with a 7 M NaOH solution, and (b) production of a porous coating (anodic oxidation with the use of potential U = 5 V) and then treating its surface in the abovementioned alkaline solution. We compared the apatite-forming ability of unmodified and surface-modified titanium alloy in simulated body fluid (SBF) for 1–4 weeks. Analysis of the X-ray diffraction patterns of synthesized coatings allowed their structure characterization before and after immersing in SBF. The obtained nanolayers were studied using Raman spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and scanning electron microscopy (SEM) images. Elemental analysis was carried out using X-ray energy dispersion spectroscopy (SEM EDX). Wettability and biointegration activity (on the basis of the degree of integration of MG-63 osteoblast-like cells, L929 fibroblasts, and adipose-derived mesenchymal stem cells cultured in vitro on the sample surface) were also evaluated. The obtained results proved that the surfaces of Ti6Al4V and Ti6Al4V covered by TiO₂ nanoporous coatings, which were modified by titanate layers, promote apatite formation in the environment of body fluids and possess optimal biointegration properties for fibroblasts and osteoblasts.

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.

Mechanical Properties of Different Nanopatterned TiO2 Substrates and Their Effect on Hydrothermally Synthesized Bioactive Hydroxyapatite Coatings

Nanotechnology is a very attractive tool for tailoring the surface of an orthopedic implant to optimize its interaction with the biological environment. Nanostructured interfaces are promising, especially for orthopedic applications. They can not only improve osseointegration between the implant and the living bone but also may be used as drug delivery platforms. The nanoporous structure can be used as a drug carrier to the surrounding tissue, with the intention to accelerate tissue–implant integration as well as to reduce and treat bacterial infections occurring after implantation. Titanium oxide nanotubes are promising for such applications; however, their brittle nature could be a significantly limiting factor. In this work, we modified the topography of commercially used titanium foil by the anodization process and hydrothermal treatment. As a result, we obtained a crystalline nanoporous u-shaped structure (US) of anodized titanium oxide with improved resistance to scratch compared to TiO₂ nanotubes. The US titanium substrate was successfully modified with hydroxyapatite coating and investigated for bioactivity. Results showed high bioactivity in simulated body fluid (SBF) after two weeks of incubation.

Comprehensive Survey on Nanobiomaterials for Bone Tissue Engineering Applications

One of the most important ideas ever produced by the application of materials science to the medical field is the notion of biomaterials. The nanostructured biomaterials play a crucial role in the development of new treatment strategies including not only the replacement of tissues and organs, but also repair and regeneration. They are designed to interact with damaged or injured tissues to induce regeneration, or as a forest for the production of laboratory tissues, so they must be micro-environmentally sensitive. The existing materials have many limitations, including impaired cell attachment, proliferation, and toxicity. Nanotechnology may open new avenues to bone tissue engineering by forming new assemblies similar in size and shape to the existing hierarchical bone structure. Organic and inorganic nanobiomaterials are increasingly used for bone tissue engineering applications because they may allow to overcome some of the current restrictions entailed by bone regeneration methods. This review covers the applications of different organic and inorganic nanobiomaterials in the field of hard tissue engineering.

Less known facts and findings about TiO2 nanotubes

Anodic TiO₂ nanotubes that are grown on Ti substrates by a simple anodization in various types of fluoride containing electrolytes have attracted scientific and technological interest due to their wide potential applications, and therefore, numerous research efforts have been dedicated to these self-ordered oxide structures in the past decade. The present mini-review highlights less known but important aspects, such as the formation of spaced nanotubes with adjustable interspacing that is achieved in a few specific organic electrolytes, and strong effects of the metallic Ti substrate which significantly affect the growth of the tubes. We discuss the formation of oxide nanotubes grown from adequately alloyed substrates and noble metal nanoparticle decoration of tubes. We describe how specific heat-treatment can introduce a nanotwinned boundary in the oxide tube walls of single-walled nanotubes obtained by a decoring process. All the facts and findings were studied in recent years and TiO₂ nanotubes can be upgraded with more optimized functionalities for their applications.

The Implication of Spatial Statistics in Human Mesenchymal Stem Cell Response to Nanotubular Architectures

INTRODUCTION

In recent years there has been ample interest in nanoscale modifications of synthetic biomaterials to understand fundamental aspects of cell-surface interactions towards improved biological outcomes. In this study, we aimed at closing in on the effects of nanotubular TiO2 surfaces with variable nanotopography on the response on human mesenchymal stem cells (hMSCs). Although the influence of TiO2 nanotubes on the cellular response, and in particular on hMSC activity, has already been addressed in the past, previous studies overlooked critical morphological, structural and physical aspects that go beyond the simple nanotube diameter, such as spatial statistics.

METHODS

To bridge this gap, we implemented an extensive characterization of nanotubular surfaces generated by anodization of titanium with a focus on spatial structural variables including eccentricity, nearest neighbour distance (NND) and Voronoi entropy, and associated them to the hMSC response. In addition, we assessed the biological potential of a two-tiered honeycomb nanoarchitecture, which allowed the detection of combinatory effects that this hierarchical structure has on stem cells with respect to conventional nanotubular designs. We have combined experimental techniques, ranging from Scanning Electron (SEM) and Atomic Force (AFM) microscopy to Raman spectroscopy, with computational simulations to characterize and model nanotubular surfaces. We evaluated the cell response at 6 hrs, 1 and 2 days by fluorescence microscopy, as well as bone mineral deposition by Raman spectroscopy, demonstrating substrate-induced differential biological cueing at both the short- and long-term.

RESULTS

Our work demonstrates that the nanotube diameter is not sufficient to comprehensively characterize nanotubular surfaces and equally important parameters, such as eccentricity and wall thickness, ought to be included since they all contribute to the overall spatial disorder which, in turn, dictates the overall bioactive potential. We have also demonstrated that nanotubular surfaces affect the quality of bone mineral deposited by differentiated stem cells. Lastly, we closed in on the integrated effects exerted by the superimposition of two dissimilar nanotubular arrays in the honeycomb architecture.

DISCUSSION

This work delineates a novel approach for the characterization of TiO2 nanotubes which supports the incorporation of critical spatial structural aspects that have been overlooked in previous research. This is a crucial aspect to interpret cellular behaviour on nanotubular substrates. Consequently, we anticipate that this strategy will contribute to the unification of studies focused on the use of such powerful nanostructured surfaces not only for biomedical applications but also in other technology fields, such as catalysis.

Nanotopographical Coatings Induce an Early Phenotype-Specific Response of Primary Material-Resident M1 and M2 Macrophages

Implants elicit an immunological response after implantation that results in the worst case in a complete implant rejection. This biomaterial-induced inflammation is modulated by macrophages and can be influenced by nanotopographical surface structures such as titania nanotubes or fractal titanium nitride (TiN) surfaces. However, their specific impact on a distinct macrophage phenotype has not been identified. By using two different levels of nanostructures and smooth samples as controls, the influence of tubular TiO2 and fractal TiN nanostructures on primary human macrophages with M1 or M2-phenotype was investigated. Therefore, nanotopographical coatings were either, directly generated by physical vapor deposition (PVD) or by electrochemical anodization of titanium PVD coatings. The cellular response of macrophages was quantitatively assessed to demonstrate a difference in biocompatibility of nanotubes in respect to human M1 and M2-macrophages. Depending on the tube diameter of the nanotubular surfaces, low cell numbers and impaired cellular activity, was detected for M2-macrophages, whereas the impact of nanotubes on M1-polarized macrophages was negligible. Importantly, we could confirm this phenotypic response on the fractal TiN surfaces. The results indicate that the investigated topographies specifically impact the macrophage M2-subtype that modulates the formation of the fibrotic capsule and the long-term response to an implant.

Enhanced bone healing in porous Ti implanted rabbit combining bioactive modification and mechanical stimulation

To improve the bone healing efficiency of porous titanium implants, desired biological properties of implants are mandatory, involving bioactivity, osteoconductivity, osteoinductivity and a stable environment. In this study, bare porous titanium (abbr. pTi) with the porosity of 70% was fabricated by vacuum diffusion bonding of titanium meshes. Hydroxyapatite-coated pTi (abbr. Hap-pTi) was obtained by successively subjecting pTi to alkali heat treatment, pre-calcification and simulated body fluid. Both pTi and Hap-pTi were respectively implanted into the tibia defect model (ϕ10 mm × 6 mm) in New Zealand white rabbits, then subjected to non-invasively axial compressive loads at high-magnitude low-frequency (HMLF), which were denoted as F-pTi and F-Hap-pTi, respectively. Bone repairing efficiencies were analyzed by postoperative X-ray examination, optical observation and HE staining after 14 and 30 days of implantation. ALP and OCN contents in serum were also examined at 30 days. Results showed that the sham group and sham group with mechanical stimulation (abbr. F-sham) preferably caused bone fractures. Qualitatively, Hap-pTi reduced the risk of bone fractures and enhanced bone healing slightly more effectively compared to bared pTi. However, both Hap-pTi combined with mechanical stimulation and F-pTi in the case of bioactive modification could result in a higher bone healing efficiency (F-Hap-pTi). The molecular signaling investigation of ALP and OCN contents in serum further revealed a probable synergistic effect of Hap coating coupling with HMLF compression on improving bone repairing efficiency. It provides a candidate of clinically applicable therapy for osseous defects.

A Review on the Electrochemically Self-organized Titania Nanotube Arrays: Synthesis, Modifications, and Biomedical Applications

Titania nanotubes grown by anodic oxidation have intrigued the material science community by its many unique and potential properties, and the synthesis of technology is merging to its mature stage. The present review will focus on TiO2 nanotubes grown by self-organized electrochemical anodization from Ti metal substrate, which critically highlights the synthesis of this type of self-organized titania nanotube layers and the means to influence the size, shape, the degree of order, and crystallized phases via adjusting the anodization parameters and the subsequent thermal annealing. The relationship between dimensions and properties of the anodic TiO2 nanotube arrays will be presented. The latest progress and significance of the research on formation mechanism of anodic TiO2 nanotubes are briefly discussed. Besides, we will show the most promising applications reported recently in biomedical directions and modifications carried out by doping, surface modification, and thermal annealing toward improving the properties of anodically formed TiO2 nanotubes. At last, some unsolved issues and possible future directions of this field are indicated.

Application of quality by design for 3D printed bone prostheses and scaffolds

3D printing is an emergent manufacturing technology recently being applied in the medical field for the development of custom bone prostheses and scaffolds. However, successful industry transformation to this new design and manufacturing approach requires technology integration, concurrent multi-disciplinary collaboration, and a robust quality management framework. This latter change enabler is the focus of this study. While a number of comprehensive quality frameworks have been developed in recent decades to ensure that the manufacturing of medical devices produces reliable products, they are centred on the traditional context of standardised manufacturing techniques. The advent of 3D printing technologies and the prospects for mass customisation provides significant market opportunities, but also presents a serious challenge to regulatory bodies tasked with managing and assuring product quality and safety. Before 3D printing bone prostheses and scaffolds can gain traction, industry stakeholders, such as regulators, clients, medical practitioners, insurers, lawyers, and manufacturers, would all require a high degree of confidence that customised manufacturing can achieve the same quality outcomes as standardised manufacturing. A Quality by Design (QbD) approach to custom 3D printed prostheses can help to ensure that products are designed and manufactured correctly from the beginning without errors. This paper reports on the adaptation of the QbD approach for the development process of 3D printed custom bone prosthesis and scaffolds. This was achieved through the identification of the Critical Quality Attributes of such products, and an extensive review of different design and fabrication methods for 3D printed bone prostheses. Research outcomes include the development of a comprehensive design and fabrication process flow diagram, and categorised risks associated with the design and fabrication processes of such products. An extensive systematic literature review and post-hoc evaluation survey with experts was completed to evaluate the likely effectiveness of the herein suggested QbD framework.

Influence of shape and dispersion media of titanium dioxide nanostructures on microvessel network and ossification

Titanium dioxide nanoparticles (TiO₂ NPs) production has been used for pigment, food and cosmetic industry and more recently, shaped as belts for treatment of contaminated water, self-cleaning windows and biomedical applications. However, the toxicological data have demonstrated that TiO₂ NPs inhalation induce inflammation in in vivo models and in vitro exposure leads to cytotoxicity and DNA damage. Dermal exposure has limited adverse effects and the possible risks for implants used for tissue regeneration is still under research. Then, it has been difficult to establish a straight statement about TiO₂ NPs toxicity since route of exposure and shapes of nanoparticles play an important role in the effects. In this study we aimed to investigate the effect of three different types of TiO₂ NPs (industrial, food-grade and belts) dispersed in fetal bovine serum (FBS) and saline solution (SS) on microvessel network, angiogenesis gene expression and femur ossification using a chick embryo model after an acute exposure of NPs on the day 7 after eggs fertilization. Microvascular density of chorioallantoic membrane (CAM) was analyzed after 7days of NPs injection and vehicles induced biological effects per se. NPs dispersed in FBS or SS have slight differences in microvascular density, mainly opposite effect on angiogenesis gene expression and no effects on femur ossification for NPs dispersed in SS. Interestingly, NPs shaped as belts dramatically prevented the alterations in ossification induced by FBS used as vehicle.

New Interface for Purification of Proteins: One-Dimensional TiO2 Nanotubes Decorated by Fe3O4 Nanoparticles

In this work, a high surface area interface, based on anodic one-dimensional (1D) TiO₂ nanotubes homogeneously decorated by Fe₃O₄ nanoparticles (TiO₂NTs@Fe₃O₄NPs) is reported for the first time for an unprecedented purification of His-tagged recombinant proteins. Excellent purification results were achieved from the model protein mixture, as well as from the whole cell lysate (with His-tagged ubiquitin). Compared to a conventional immobilized-metal affinity chromatography (IMAC) system, specific isolation of selected His-tagged proteins on behalf of other proteins was significantly enhanced on TiO₂NTs@Fe₃O₄NPs interface under optimized binding and elution conditions. The combination of specific isolation properties, magnetic features, biocompatibility, and ease of preparation of this material consisting of two basic metal oxides makes it a suitable candidate for future purification of recombinant proteins in biotechnology. The principally new material bears a large potential to open new pathways for discoveries in nanobiotechnology and nanomedicine.

TiO2 Nanotubes on Ti Dental Implant. Part 1: Formation and Aging in Hank’s Solution

Self-organized TiO2 nanotube layer has been formed on titanium screws with complex geometry, which are used as dental implants. TiO2 nanotubes film was grown by potentiostatic anodizing in H3PO4 and HF aqueous solution. During anodizing, the titanium screws were mounted on a rotating apparatus to produce a uniform structure both on the peaks and on the valleys of the threads. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX) and electrochemical characterization were used to evaluate the layer, chemical composition and electrochemical properties of the samples. Aging in Hank’s solution of both untreated and nanotubes covered screw, showed that: (i) samples are covered by an amorphous oxide layer, (ii) the nanotubes increases the corrosion resistance of the implant, and (iii) the presence of the nanotubes catalyses the formation of chemical compounds containing Ca and P.

Ultra-structural evaluation of an anodic oxidated titanium dental implant

Anodic oxidation is used for the surface treatment of commercial implants to improve their functional properties for clinical success. Here we conducted ultrastructural and chemical investigations into the micro- and nanostructure of the anodic oxide film of a titanium implant. The anodic oxidized layer of a Ti6Al4V alloy implant was examined ultrastructurally by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). They were also analyzed using energy dispersive X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). The TEM revealed that the oxide layer of the Ti6Al4V implant prepared through anodic oxidation was separated into two layers. Al and V were not present on the top surface of the anodic oxide. This can be attributed to the biocompatibility of the anodic oxidized Ti6Al4V alloy implant, because the release of harmful metal ions such as Al and V can be suppressed by the biocompatibility.

Cytocompatibility and antibacterial activity of titania nanotubes incorporated with gold nanoparticles

TiO2 nanotubes prepared by electrochemical anodization have received considerable attention in the biomedical field. In this work, different amounts of gold nanoparticles were immobilized onto TiO2 nanotubes using 3-aminopropyltrimethoxysilane as coupling agent. Field emission scanning electron microscopy and X-ray photoelectron spectroscopy were used to investigate the surface morphology and composition. Photoluminescence spectra and surface zeta potential were also measured. The obtained results indicate that the surface modified gold nanoparticles can significantly enhance the electron storage capability and reduce the surface zeta potential compared to pristine TiO2 nanotubes. Moreover, the surface modified gold nanoparticles can stimulate initial adhesion and spreading of rat bone mesenchymal stem cells as well as proliferation, while the osteogenous performance of TiO2 nanotubes will not be reduced. The gold-modified surface presents moderate antibacterial effect on both Staphylococcus aureus and Escherichia coli. It should be noted that the surface modified fewer gold nanoparticles has better antibacterial effect compared to the surface of substantial modification of gold nanoparticles. Our study illustrates a composite surface with favorable cytocompatibility and antibacterial effect and provides a promising candidate for orthopedic and dental implant.

Photocatalytic Deposition of Hydroxyapatite onto a Titanium Dioxide Nanotubular Layer with Fine Tuning of Layer Nanoarchitecture

A new effective method of photocatalytic deposition of hydroxyapatite (HA) onto semiconductor substrates is proposed. A highly ordered nanotubular TiO2 (TNT) layer formed on titanium via its anodization is chosen as the photoactive substrate. The method is based on photodecomposition of the phosphate anion precursor, triethylphosphate (TEP), on the semiconductor surface with the following reaction of formed phosphate anions with calcium cations presented in the solution. HA can be deposited only on irradiated areas, providing the possibility of photoresist-free HA patterning. It is shown that HA deposition can be controlled via pH, light intensity, and duration of the process. Energy-dispersive X-ray spectroscopy profile analysis and glow discharge optical emission spectroscopy of HA-modified TNT prove that HA deposits over the entire TNT depth. High biocompatibility of the surfaces is proven by protein adsorption and pre-osteoblast cell growth.

Self-organized ZnO nanorods prepared by anodization of zinc in NaOH electrolyte

Regular ZnO nanorods were obtained by anodization using NaOH aqueous electrolytes which is affected by voltage, anodization time and electrolyte concentration.

Probing Water and CO₂ Interactions at the Surface of Collapsed Titania Nanotubes Using IR Spectroscopy

Collapsed titania nanotubes (cTiNT) were synthesized by the calcination of titania nanotubes (TiNT) at 650 °C, which leads to a collapse of their tubular morphology, a substantial reduction in surface area, and a partial transformation of anatase to the rutile phase. There are no significant changes in the position of the XPS responses for Ti and O on oxidation or reduction of the cTiNTs, but the responses are more symmetric than those observed for TiNTs, indicating fewer surface defects and no change in the oxidation state of titanium on oxidative and/or reductive pretreatment. The interaction of H₂O and CO₂ with the cTiNT surface was studied. The region corresponding to OH stretching absorptions extends below 3000 cm(-1), and thus is broader than is typically observed for absorptions of the OH stretches of water. The exchange of protons for deuterons on exposure to D₂O leads to a depletion of this extended absorption and the appearance of new absorptions, which are compatible with deuterium exchange. We discuss the source of this extended low frequency OH stretching region and conclude that it is likely due to the hydrogen-bonded OH stretches. Interaction of the reduced cTiNTs with CO₂ leads to a similar but smaller set of adsorbed carbonates and bicarbonates as reported for reduced TiNTs before collapse. Implications of these observations and the presence of proton sources leading to hydrogen bonding are discussed relative to potential chemical and photochemical activity of the TiNTs. These results point to the critical influence of defect structure on CO₂ photoconversion.

Improved Osteoblast and Chondrocyte Adhesion and Viability by Surface-Modified Ti6Al4V Alloy with Anodized TiO₂ Nanotubes Using a Super-Oxidative Solution

Titanium (Ti) and its alloys are amongst the most commonly-used biomaterials in orthopedic and dental applications. The Ti-aluminum-vanadium alloy (Ti6Al4V) is widely used as a biomaterial for these applications by virtue of its favorable properties, such as high tensile strength, good biocompatibility and excellent corrosion resistance. TiO₂ nanotube (NTs) layers formed by anodization on Ti6Al4V alloy have been shown to improve osteoblast adhesion and function when compared to non-anodized material. In his study, NTs were grown on a Ti6Al4V alloy by anodic oxidation for 5 min using a super-oxidative aqueous solution, and their in vitro biocompatibility was investigated in pig periosteal osteoblasts and cartilage chondrocytes. Scanning electron microscopy (SEM), energy dispersion X-ray analysis (EDX) and atomic force microscopy (AFM) were used to characterize the materials. Cell morphology was analyzed by SEM and AFM. Cell viability was examined by fluorescence microscopy. Cell adhesion was evaluated by nuclei staining and cell number quantification by fluorescence microscopy. The average diameter of the NTs was 80 nm. The results demonstrate improved cell adhesion and viability at Day 1 and Day 3 of cell growth on the nanostructured material as compared to the non-anodized alloy. In conclusion, this study evidences the suitability of NTs grown on Ti6Al4V alloy using a super-oxidative water and a short anodization process to enhance the adhesion and viability of osteoblasts and chondrocytes. The results warrant further investigation for its use as medical implant materials.

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.

TiO2 nanotubes: interdependence of substrate grain orientation and growth rate

Highly ordered arrays of TiO2 nanotubes can be produced by self-organized anodic growth. It is desirable to identify key parameters playing a role in the maximization of the surface area, growth rate, and nanotube lengths. In this work, the role of the crystallographic orientation of the underlying Ti substrate on the growth rate of anodic self-organized TiO2 nanotubes in viscous organic electrolytes in the presence of small amounts of fluorides is studied. A systematic analysis of cross sections of the nanotubular oxide films on differently oriented substrate grains was conducted by a combination of electron backscatter diffraction and scanning electron microscopy. The characterization allows for a correlation between TiO2 nanotube lengths and diameters and crystallographic parameters of the underlying Ti metal substrate, such as planar surface densities. It is found that the growth rate of TiO2 nanotubes gradually increases with the decreasing planar atomic density of the titanium substrate. Anodic TiO2 nanotubes with the highest aspect ratio form on Ti(-151) [which is close to Ti(010)], whereas nanotube formation is completely inhibited on Ti(001). In the thin compact oxide on Ti(001), the electron donor concentration and electronic conductivity are higher, which leads to a competition between oxide growth and other electrochemical oxidation reactions, such as the oxygen evolution reaction, upon anodic polarization. At grain boundaries between oxide films on Ti(hk0), where nanotubes grow, and Ti(001), where thin compact oxide films are formed, the length of nanotubes decreases most likely because of lateral electron migration from TiO2 on Ti(001) to TiO2 on Ti(hk0).

Titania nanotubes from weak organic acid electrolyte: fabrication, characterization and oxide film properties

In this study, TiO2 nanotubes were fabricated using anodic oxidation in fluoride containing weak organic acid for different durations (0.5h, 1h, 2h and 3h). Scanning electron microscope (SEM) micrographs reveal that the morphology of titanium oxide varies with anodization time. Raman spectroscopy and X-ray diffraction (XRD) results indicate that the as-formed oxide nanotubes were amorphous in nature, yet transform into crystalline phases (anatase and rutile) upon annealing at 600°C. Wettability measurements show that both as-formed and annealed nanotubes exhibited hydrophilic behavior. The electrochemical behavior was ascertained by DC polarization and AC electrochemical impedance spectroscopy (EIS) measurements in 0.9% NaCl solution. The results suggest that the annealed nanotubes showed higher impedance (10(5)-10(6)Ωcm(2)) and lower passive current density (10(-7)Acm(-2)) than the as-formed nanotubes. In addition, we investigated the influence of post heat treatment on the semiconducting properties of the oxides by capacitance measurements. In vitro bioactivity test in simulated body fluid (SBF) showed that precipitation of Ca/P is easier in crystallized nanotubes than the amorphous structure. Our study uses a simple strategy to prepare nano-structured titania films and hints the feasibility of tailoring the oxide properties by thermal treatment, producing surfaces with better bioactivity.

Nanotubular surface modification of metallic implants via electrochemical anodization technique

Due to increased awareness and interest in the biomedical implant field as a result of an aging population, research in the field of implantable devices has grown rapidly in the last few decades. Among the biomedical implants, metallic implant materials have been widely used to replace disordered bony tissues in orthopedic and orthodontic surgeries. The clinical success of implants is closely related to their early osseointegration (ie, the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant), which relies heavily on the surface condition of the implant. Electrochemical techniques for modifying biomedical implants are relatively simple, cost-effective, and appropriate for implants with complex shapes. Recently, metal oxide nanotubular arrays via electrochemical anodization have become an attractive technique to build up on metallic implants to enhance the biocompatibility and bioactivity. This article will thoroughly review the relevance of electrochemical anodization techniques for the modification of metallic implant surfaces in nanoscale, and cover the electrochemical anodization techniques used in the development of the types of nanotubular/nanoporous modification achievable via electrochemical approaches, which hold tremendous potential for bio-implant applications. In vitro and in vivo studies using metallic oxide nanotubes are also presented, revealing the potential of nanotubes in biomedical applications. Finally, an outlook of future growth of research in metallic oxide nanotubular arrays is provided. This article will therefore provide researchers with an in-depth understanding of electrochemical anodization modification and provide guidance regarding the design and tuning of new materials to achieve a desired performance and reliable biocompatibility.

Surface Characterization of Magnesium Anodized in a 10M KOH Electrolyte

Magnesium (Mg) is a promising implant material for orthopedic applications due to its biodegradability and desirable mechanical properties. However, in order for Mg to have widespread clinical applications, engineering solutions that address the rapid degradation in physiological environments and promote bone-forming activity are needed. The objective of this study was to develop an anodization process using a toxicant-free electrolyte to modulate nanoscale surface features and surface chemistry on Mg. Anodic polarization and potentiostatic anodization tests were used to evaluate the effect of applied potential on surface morphology of Mg in a 10 M KOH electrolyte. Nucleation of oxides as a function of anodization duration was also investigated in order to optimize the synthesis process. The alkaline electrolyte used for anodization of Mg offers an alternative to commercial processes that use hazardous elements. The anodized samples were annealed to investigate the effect of thermal treatments on surface morphology and chemical composition. The nanostructure and chemical composition of the anodized and annealed Mg substrates were characterized using scanning electron microscopy and energy dispersive X-ray spectroscopy. Our results showed that the nanostructures and chemical composition of anodically-generated oxide layers on Mg are specific to each oxidation process in a 10 M KOH electrolyte. Furthermore, results indicated that anodization durations of two hours generated surface oxide layers with homogeneous topography on the Mg substrates atapplied potentials of 0.5 V, 1.5 V and 2 V.. This study showed a promising approach for creating nanoscale surface features on Mg for improved bioactivity and degradation property.

Fabrication of anti-aging TiO2 nanotubes on biomedical Ti alloys

The primary objective of this study was to fabricate a TiO2 nanotubular surface, which could maintain hydrophilicity over time (resist aging). In order to achieve non-aging hydrophilic surfaces, anodization and annealing conditions were optimized. This is the first study to show that anodization and annealing condition affect the stability of surface hydrophilicity. Our results indicate that maintenance of hydrophilicity of the obtained TiO2 nanotubes was affected by anodization voltage and annealing temperature. Annealing sharply decreased the water contact angle (WCA) of the as-synthesized TiO2 nanotubular surface, which was correlated to improved hydrophilicity. TiO2 nanotubular surfaces are transformed to hydrophilic surfaces after annealing, regardless of annealing and anodization conditions; however, WCA measurements during aging demonstrate that surface hydrophilicity of non-anodized and 20 V anodized samples decreased after only 11 days of aging, while the 60 V anodized samples maintained their hydrophilicity over the same time period. The nanotubes obtained by 60 V anodization followed by 600 °C annealing maintained their hydrophilicity significantly longer than nanotubes which were obtained by 60 V anodization followed by 300 °C annealing.

Effects of TiO2 nanotube layers on RAW 264.7 macrophage behaviour and bone morphogenetic protein-2 expression

OBJECTIVES

To investigate behaviour and osteogenic cytokine expression of RAW264.7 macrophages grown on TiO2 nanotube layers.

MATERIALS AND METHODS

The murine macrophage cell line RAW 264.7 was cultured on TiO2 nanotubes of varying diameter; macrophage morphology was examined using scanning electron microscopy. Cell adhesion and viability were assessed with the aid of the MTT method and BMP-2 and TGF-β gene expression were examined by RT-PCR analysis. Levels of BMP-2, TGF-β1 and ICAM-1 proteins secreted into the supernatant were measured by ELISA assay.

RESULTS

Macrophages cultured on nanotube layers had spread out morphology, the largest (120 nm) nanotube layer eliciting an elongation by 24 h. Macrophages adhered significantly less to 120 nm TiO2 nanotubes than to control discs at 4 h after application; after 24 h incubation, macrophages were sufficiently viable (P < 0.05) on 30 and 70 nm nanotube layers. Increasing nanotube diameter led to increased BMP-2 protein secretion and increased BMP-2 mRNA expression.

CONCLUSION

These results demonstrate that nanoscale topography of TiO2 nanotube layers can affect macrophage morphology, adhesion, viability and BMP-2 expression. Macrophages grown on layers of large nanotubes had the highest potential to enhance bone formation during bone healing.