Novel Titania Nanocoatings Produced by Anodic Oxidation with the Use of Cyclically Changing Potential: Their Photocatalytic Activity and Biocompatibility

Engineered titania nanomaterials in advanced clinical applications

Significant advancement in the field of nanotechnology has raised the possibility of applying potent engineered biocompatible nanomaterials within biological systems for theranostic purposes. Titanium dioxide (titanium(IV) oxide/titania/TiO₂) has garnered considerable attention as one of the most extensively studied metal oxides in clinical applications. Owing to the unique properties of titania, such as photocatalytic activity, excellent biocompatibility, corrosion resistance, and low toxicity, titania nanomaterials have revolutionized therapeutic approaches. Additionally, titania provides an exceptional choice for developing innovative medical devices and the integration of functional moieties that can modulate the biological responses. Thus, the current review aims to present a comprehensive and up-to-date overview of TiO₂-based nanotherapeutics and the corresponding future challenges.

Study on the photoelectrical performance of anodized titanium sheets

Anodization is a widely used method to obtain multicoloured oxidized titanium sheets. However, most researchers paid great attention to the colour-related properties instead of photoelectrical properties of titanium oxide film obtained by anodization. In this work, to study their photoelectrical properties, a series of multicoloured oxidized titanium sheets were prepared by anodization method, and UV-vis absorption and photocurrents were tested. The relationship between anodization voltages/anodization durations and photocurrents of titanium sheets was studied. Results show that titanium sheets have excellent photoelectrical performance. With the increase of anodization voltage, the number of UV-vis absorption peaks increased under visible light which means increasing absorption. When anodization duration increased, absorption band edge also increased in the visible light region, which means the band gap needed to produce charge transfer transition decreased. Under simulated sunlight and applied voltage of +0.4 V, photocurrent increased with the increase of either anodization voltage or anodization duration, and can be expressed by linear equations. In addition, anodization currents were recorded during anodization. Morphology, crystal structure and photoelectrical properties of anodized titanium sheets were characterized. The anodized titanium sheets can not only be used as decorative material in jewellery and architecture fields etc. but also are supposed to be used as photoelectrical catalyst in further work.

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.

Oxygen Content-Controllable Synthesis of Non-Stoichiometric Silicon Suboxide Nanoparticles by Electrochemical Anodization

A facile route to producing non-stoichiometric silicon suboxide nanoparticles (SiO_x NPs, 0 < x < 1) with an adjustable oxygen content is proposed. The process is based on electrochemical anodization involving the application of a strong electric field near the surface of a Si electrode to directly convert the Si electrode into SiO_x NPs. The difference in ion mobility between oxygen species (O²⁻ and OH⁻), formed during anodization, causes the production of non-stoichiometric SiO_x on the surface of the Si while, simultaneously, fluoride ions in the electrolyte solution etch the formed SiO_x layer, generating NPs under the intense electric field. The adjustment of the applied voltage and anodization temperature alters the oxygen content and the size of the SiO_x NPs, respectively, allowing the characteristics of the NPs to be readily controlled. The proposed approach can be applied for mass production of SiO_x NPs and is highly promising in the field of batteries and optoelectronics.

In Vitro Studies on Nanoporous, Nanotubular and Nanosponge-Like Titania Coatings, with the Use of Adipose-Derived Stem Cells

In vitro biological research on a group of amorphous titania coatings of different nanoarchitectures (nanoporous, nanotubular, and nanosponge-like) produced on the surface of Ti6Al4V alloy samples have been carried out, aimed at assessing their ability to interact with adipose-derived mesenchymal stem cells (ADSCs) and affect their activity. The attention has been drawn to the influence of surface coating architecture and its physicochemical properties on the ADSCs proliferation. Moreover, in vitro co-cultures: (1) fibroblasts cell line L929/ADSCs and (2) osteoblasts cell line MG-63/ADSCs on nanoporous, nanotubular and nanosponge-like TiO₂ coatings have been studied. This allowed for evaluating the impact of the surface properties, especially roughness and wettability, on the creation of the beneficial microenvironment for co-cultures and/or enhancing differentiation potential of stem cells. Obtained results showed that the nanoporous surface is favorable for ADSCs, has great biointegrative properties, and supports the growth of co-cultures with MG-63 osteoblasts and L929 fibroblasts. Additionally, the number of osteoblasts seeded and cultured with ADSCs on TNT5 surface raised after 72-h culture almost twice when compared with the unmodified scaffold and by 30% when compared with MG-63 cells growing alone. The alkaline phosphatase activity of MG-63 osteoblasts co-cultured with ADSCs increased, that indirectly confirmed our assumptions that TNT-modified scaffolds create the osteogenic niche and enhance osteogenic potential of ADSCs.

Comprehensive Evaluation of the Biological Properties of Surface-Modified Titanium Alloy Implants

An increasing interest in the fabrication of implants made of titanium and its alloys results from their capacity to be integrated into the bone system. This integration is facilitated by different modifications of the implant surface. Here, we assessed the bioactivity of amorphous titania nanoporous and nanotubular coatings (TNTs), produced by electrochemical oxidation of Ti6Al4V orthopedic implants' surface. The chemical composition and microstructure of TNT layers was analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). To increase their antimicrobial activity, TNT coatings were enriched with silver nanoparticles (AgNPs) with the chemical vapor deposition (CVD) method and tested against various bacterial and fungal strains for their ability to form a biofilm. The biointegrity and anti-inflammatory properties of these layers were assessed with the use of fibroblast, osteoblast, and macrophage cell lines. To assess and exclude potential genotoxicity issues of the fabricated systems, a mutation reversal test was performed (Ames Assay MPF, OECD TG 471), showing that none of the TNT coatings released mutagenic substances in long-term incubation experiments. The thorough analysis performed in this study indicates that the TNT5 and TNT5/AgNPs coatings (TNT5-the layer obtained upon applying a 5 V potential) present the most suitable physicochemical and biological properties for their potential use in the fabrication of implants for orthopedics. For this reason, their mechanical properties were measured to obtain full system characteristics.

Titania Nanofiber Scaffolds with Enhanced Biointegration Activity-Preliminary In Vitro Studies

The increasing need for novel bone replacement materials has been driving numerous studies on modifying their surface to stimulate osteogenic cells expansion and to accelerate bone tissue regeneration. The goal of the presented study was to optimize the production of titania-based bioactive materials with high porosity and defined nanostructure, which supports the cell viability and growth. We have chosen to our experiments TiO2 nanofibers, produced by chemical oxidation of Ti6Al4V alloy. Fibrous nanocoatings were characterized structurally (X-ray diffraction (XRD)) and morphologically (scanning electron microscopy (SEM)). The wettability of the coatings and their mechanical properties were also evaluated. We have investigated the direct influence of the modified titanium alloy surfaces on the survival and proliferation of mesenchymal stem cells derived from adipose tissue (ADSCs). In parallel, proliferation of bone tissue cells-human osteoblasts MG-63 and connective tissue cells - mouse fibroblasts L929, as well as cell viability in co-cultures (osteoblasts/ADSCs and fibroblasts/ADSCs has been studied. The results of our experiments proved that among all tested nanofibrous coatings, the amorphous titania-based ones were the most optimal scaffolds for the integration and proliferation of ADSCs, fibroblasts, and osteoblasts. Thus, we postulated these scaffolds to have the osteopromotional potential. However, from the co-culture experiments it can be concluded that ADSCs have the ability to functionalize the initially unfavorable surface, and make it suitable for more specialized and demanding cells.

Synthesis of Nanoporous TiO2 with the Use of Diluted Hydrogen Peroxide Solution and Its Application in Gas Sensing

The chemical routes of metal oxidation in presence of hydrogen peroxide solutions are tailor-made for the synthesis of biocompatible metal oxide surfaces with clean intermediate and end products, such as oxides, hydroxides, hydrogen and water. The hydrolysis of titanium in hydrogen peroxide solutions is particularly interesting for medical applications, forming micro- and nanoscale titania surfaces. In this paper, the content of the hydrolysis solution is revised, allowing the fabrication of gas sensor devices based on nanoporous titania. Nanopore and microcrack formations were discussed in detail by monitoring the structural changes on the thin film surface with field-emission scanning electron microscopy (FE-SEM). A stable rutile crystalline phase was detected by glancing incidence X-ray diffraction (GI-XRD) measurement after repetitive hydrothermal processes. Electrical conductance measurements were carried out at high temperatures (400–600 °C) under humid airflow (40% RH@20 °C) with the injection of various concentrations of a wide set of test compounds (C2H3N, CO, H2, NO2, C2H6O), to observe the sensing capabilities of the material. Furthermore, the humidity effects on the sensing properties toward H2, CO, and C2H6O have been discussed.

Photocatalytic Activity of Nanostructured Titania Films Obtained by Electrochemical, Chemical, and Thermal Oxidation of Ti6Al4V Alloy—Comparative Analysis

Three different Ti6Al4V surface oxidation methods have been applied to obtain three types of titania materials of different nanoarchitecture. Electrochemical oxidation of titanium alloy allowed for obtaining titania nanotubes (TNT), chemical oxidation led to obtain titania nanofibers (TNF), and thermal oxidation gave titania nanowires (TNW). My earlier investigations of these nanomaterials were focused mainly on the estimation of their bioactivity and potential application in modern implantology. In this article, the comparative analysis of the photocatalytic activity of produced systems, as well as the impact of their structure and morphology on this activity, are discussed. The activity of studied nanomaterials was estimated basis of UV-induced degradation of methylene blue and also acetone, and it was determined quantitatively according to the Langmuir–Hinshelwood reaction mechanism. The obtained results were compared to the activity of Pilkington Glass ActivTM (reference sample). Among analyzed systems, titania nanofibers obtained at 140 and 120 °C, possessing anatase and anatase/amorphous structure, as well as titania nanowires obtained at 475 and 500 °C, possessing anatase and anatase/rutile structure, were better photocatalyst than the reference sample. Completely amorphous titania nanotubes, turned out to be an interesting alternative for photocatalytic materials in the form of thin films, however, their photocatalytic activity is lower than for Pilkington Glass ActivTM.

The Morphology, Structure, Mechanical Properties and Biocompatibility of Nanotubular Titania Coatings before and after Autoclaving Process

The autoclaving process is one of the sterilization procedures of implantable devices. Therefore, it is important to assess the impact of hot steam at high pressure on the morphology, structure, and properties of implants modified by nanocomposite coatings. In our works, we focused on studies on amorphous titania nanotubes produced by titanium alloy (Ti6Al4V) electrochemical oxidation in the potential range 5⁻60 V. Half of the samples were drying in argon stream at room temperature, and the second ones were drying additionally with the use of immersion in acetone and drying at 396 K. Samples were subjected to autoclaving and after sterilization they were structurally and morphologically characterized using Raman spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and scanning electron microscopy (SEM). They were characterized in terms of wettability, mechanical properties, and biocompatibility. Obtained results proved that the autoclaving of amorphous titania nanotube coatings produced at lower potentials (5⁻15 V) does not affect their morphology and structure regardless of the drying method before autoclaving. Nanotubular coatings produced using higher potentials (20⁻60 V) require removal of adsorbed water particles from their surface. Otherwise, autoclaving leads to the destruction of the architecture of nanotubular coatings, which is associated with the changing of their mechanical and biointegration properties.