Biocompatibility and Surface Properties of TiO₂ Thin Films Deposited by DC Magnetron Sputtering

Integral Algorithms to Evaluate TiO2 and N-TiO2 Thin Films' Cytocompatibility

Titanium oxide (TiO₂) and oxynitride (N-TiO₂) coatings can increase nitinol stents' cytocompatibility with endothelial cells. Methods of TiO₂ and N-TiO₂ sputtering and cytocompatibility assessments vary significantly among different research groups, making it difficult to compare results. The aim of this work was to develop an integral cytocompatibility index (ICI) and a decision tree algorithm (DTA) using the "EA.hy926 cell/TiO₂ or N-TiO₂ coating" model and to determine the optimal cytocompatible coating. Magnetron sputtering was performed in a reaction gas medium with various N₂:O₂ ratios and bias voltages. The samples' morphology was studied by scanning electron microscopy (SEM) and Raman spectroscopy. The cytocompatibility of the coatings was evaluated in terms of their cytotoxicity, adhesion, viability, and NO production. The ICI and DTA were developed to assess the cytocompatibility of the samples. Both algorithms demonstrated the best cytocompatibility for the sample sputtered at U_bias = 0 V and a gas ratio of N₂:O₂ = 2:1, in which the rutile phase dominated. The DTA provided more detailed information about the cytocompatibility, which depended on the sputtering mode, surface morphology, and crystalline phase. The proposed mathematical models relate the cytocompatibility and the studied physical characteristics.

Blood Coagulation on Titanium Dioxide Films with Various Crystal Structures on Titanium Implant Surfaces

Background: Titanium (Ti) is one of the most popular implant materials, and its surface titanium dioxide (TiO₂) provides good biocompatibility. The coagulation of blood on Ti implants plays a key role in wound healing and cell growth at the implant site; however, researchers have yet to fully elucidate the mechanism underlying this process on TiO₂. Methods: This study examined the means by which blood coagulation was affected by the crystal structure of TiO₂ thin films (thickness < 50 nm), including anatase, rutile, and mixed anatase/rutile. The films were characterized in terms of roughness using an atomic force microscope, thickness using an X-ray photoelectron spectrometer, and crystal structure using transmission electron microscopy. The surface energy and dielectric constant of the surface films were measured using a contact angle goniometer and the parallel plate method, respectively. Blood coagulation properties (including clotting time, factor XII contact activation, fibrinogen adsorption, fibrin attachment, and platelet adhesion) were then assessed on the various test specimens. Results: All of the TiO₂ films were similar in terms of surface roughness, thickness, and surface energy (hydrophilicity); however, the presence of rutile structures was associated with a higher dielectric constant, which induced the activation of factor XII, the formation of fibrin network, and platelet adhesion. Conclusions: This study provides detailed information related to the effects of TiO₂ crystal structures on blood coagulation properties on Ti implant surfaces.

Effect of Treated Time of Hydrothermal Etching Process on Oxide Layer Formation and Its Antibacterial Properties

Inspired by natural materials, we developed an antibacterial surface on titanium (Ti) using hydrothermal etching techniques and examined the effect of treated time on oxide layer formation, its antibacterial properties, and surface defects. Hydrothermal etching was conducted on Grade 2 commercially pure Ti immersed in 5M NaOH at 250 °C during a range of time of 0–12 h. Nanopillars generated on the surface had ~100 nm thickness, which resulted in decreased attachment and rupturing of the attached bacteria. The results also showed that 6 h and 8 h of etching time provided a desirable uniform nanopillar structure with the most effective prevention of bacterial adherence on the surface. Multiscale SEM observations revealed that the longer the etching was conducted, the more cracks propagated, which led to an increase in dissociated fragments of the oxide layer. In the 12 h of etching, a higher density of bacterial adherence was observed than that of the untreated and the shorter time treated samples, indicating that etching took longer than 10 h worsened the antibacterial properties of the nano-patterned surface of Ti. This study demonstrated that the optimal time duration is 6–8 h for the oxide layer formation to maximize antibacterial activity and minimize cracking formation on the surface. For future studies, we suggest exploring many possible conditions to generate a more uniform nanopattern without structural defects to secure the integration between a newly deposited oxide layer and the substrate.

PLGA-Based Composites for Various Biomedical Applications

Polymeric materials have been extensively explored in the field of nanomedicine; within them, poly lactic-co-glycolic acid (PLGA) holds a prominent position in micro- and nanotechnology due to its biocompatibility and controllable biodegradability. In this review we focus on the combination of PLGA with different inorganic nanomaterials in the form of nanocomposites to overcome the polymer’s limitations and extend its field of applications. We discuss their physicochemical properties and a variety of well-established synthesis methods for the preparation of different PLGA-based materials. Recent progress in the design and biomedical applications of PLGA-based materials are thoroughly discussed to provide a framework for future research.

Self-cleaning structural colors by TiO2/Ti nanostructures

Structural colors are fascinating due to their stability in comparison with dyes and pigments; nevertheless, environmental pollutants contaminate surfaces and redefine structural colors. To overcome this problem, cleaning of the surface is necessary at regular intervals, which is cumbersome and costly. We have circumvented this issue in this article and fabricated scalable self-cleaning structural colors. The structural colors are generated by TiO₂ nanorods and thin films on Ti sputtered glass and flexible polyethylene terephthalate substrates employing a glancing angle deposition (GLAD) technique. Theoretical calculations based on thin film interference validate the experimental results and suggest Al, Ni, Co, and Cu as an alternative of Ti for generating structural colors. Structural colors are transformed to a superhydrophilic state, i.e., a self-cleaning state, via UV exposure and annealing at elevated temperatures. In addition to a self-cleaning state, annealing could control the opaqueness and color tunability of the structural colors. A permanent wettability state in between the superhydrophobic and superhydrophilic states of the structural colors is controlled by the GLAD technique. Moreover, the structural colors are demonstrated for information encryption and optical ethanol sensing applications.

Anatase Incorporation to Bioactive Scaffolds Based on Salmon Gelatin and Its Effects on Muscle Cell Growth

The development of new polymer scaffolds is essential for tissue engineering and for culturing cells. The use of non-mammalian bioactive components to formulate these materials is an emerging field. In our previous work, a scaffold based on salmon gelatin was developed and tested in animal models to regenerate tissues effectively and safely. Here, the incorporation of anatase nanoparticles into this scaffold was formulated, studying the new composite structure by scanning electron microscopy, differential scanning calorimetry and dynamic mechanical analysis. The incorporation of anatase nanoparticles modified the scaffold microstructure by increasing the pore size from 208 to 239 µm and significantly changing the pore shape. The glass transition temperature changed from 46.9 to 55.8 °C, and an increase in the elastic modulus from 79.5 to 537.8 kPa was observed. The biocompatibility of the scaffolds was tested using C2C12 myoblasts, modulating their attachment and growth. The anatase nanoparticles modified the stiffness of the material, making it possible to increase the growth of myoblasts cultured onto scaffolds, which envisions their use in muscle tissue engineering.

Fabrication of Microporous Coatings on Titanium Implants with Improved Mechanical, Antibacterial, and Cell-Interactive Properties

The success of an orthopedic implant therapy depends on successful bone integration and the prevention of microbial infections. In this work, plasma electrolytic oxidation (PEO) was performed to deposit TiO₂ coatings enriched with Ca, P, and Ag on titanium to improve its surface properties and antibacterial efficacy while maintaining normal biological functions and thus to enhance the performance of orthopedic implants. After PEO treatment, the surface of Ti was converted to anatase and rutile TiO₂, hydroxyapatite, and calcium titanate phases. The presence of these crystalline phases was further increased with an increased Ag content in the coatings. The developed coatings also exhibited a more porous morphology with an improved surface wettability, roughness, microhardness, and frictional coefficient. In vitro antibacterial assays indicated that the Ag-doped coatings can significantly prevent the growth of both Staphylococcus aureus and Escherichia coli by releasing Ag⁺ ions, and the ability to prevent these bacteria was enhanced by increasing the Ag content in the coatings, resulting in a maximal 6-log reduction of E. coli and a maximal 5-log reduction of S. aureus after 24 h of incubation. Moreover, the in vitro cytocompatibility evaluation of the coatings showed that the osteoblast (MC3T3) cell integration on the PEO-based coatings was greatly improved compared to untreated Ti and no notable impact on their cytocompatibility was observed on increasing the amount of Ag in the coating. In conclusion, the coating with favorable physicochemical and mechanical properties along with controlled silver ion release can offer an excellent antibacterial performance and osteocompatibility and can thus become a prospective coating strategy to face current challenges in orthopedics.

Dynamics of water trapped in transition metal oxide-graphene nano-confinement

Motivated by practical implementation of transition-metal oxide-graphene heterostructures, we use all atom molecular dynamics simulations to study dynamics of water in a nano slit bounded by a transition metal oxide surface, namely, TiO2termination of SrTiO3, and graphene. The resultant asymmetric, strong confinement produces square ice-like crystallites of water pinned at TiO2surface and drives enhanced hydrophobicity of graphene via the proximity effect to the hydrophilic TiO2surface. This importantly brings in dynamic heterogeneity, both in translational and rotational degrees of freedom, due to coupling between the slow relaxing, strongly adsorbed water layer at the hydrophilic oxide surface, and faster relaxation of subsequent water layers. The heterogeneity is signalled in the ruggedness of the effective free energy landscapes. We discuss possible implications of our findings in drug delivery.

A novel pathway to produce biodegradable and bioactive PLGA/TiO2 nanocomposite scaffolds for tissue engineering: Air-liquid foaming

Poly (lactate-co-glycolate) (PLGA) is a typical biocompatible and biodegradable synthetic polymer. The addition of TiO₂ nanoparticles has shown to improve compressive modulus of PLGA scaffolds and reduced fast degradation. A novel method has been applied to fabricate PLGA/TiO₂ scaffolds without using any inorganic solvent, with aim of improving the biocompatibility, macroscale morphology, and well inter-connected pores efficacy: Air-Liquid Foaming. Field Emission Scanning Electron Microscopy (FESEM) revealed an increase in interconnected porosity of up to 98%. As well the compressive testing showed enhancement in modulus. Bioactivity and in vitro degradation were studied with immersion of scaffolds in Simulated Body Fluid (SBF) and incubation in Phosphate Buffered Saline (PBS), respectively. Formation of apatite layer corroborated the bioactivity after soaking in SBF. Degradation rate of scaffolds was increased with excessive addition of TiO₂ contents withal. The in vitro cultured human-like MG63 ostoblast cells showed attachment, proliferation, and nontoxcitiy in contact, using MTT assay [3-(4, 5-Dimethylthiazol-2-yl)-2, 5-Diphenyltetrazolium Bromide]. According to the results, the novel method utilized in this study generated porous viable tissue without using any inorganic solvent or porogen can be a promising candidate in further treatment of orthopedic patients effectively.

Effect of the Thickness of TiO2 Films on the Structure and Corrosion Behavior of Mg-based Alloys

This article discusses the influence of the thickness of TiO₂ films deposited onto MgCa2Zn1 and MgCa2Zn1Gd3 alloys on their structure, corrosion behavior, and cytotoxicity. TiO₂ layers (about 200 and 400 nm thick) were applied using magnetron sputtering, which provides strong substrate adhesion. Such titanium dioxide films have many attractive properties, such as high corrosion resistance and biocompatibility. These oxide coatings stimulate osteoblast adhesion and proliferation compared to alloys without the protective films. Microscopic observations show that the TiO₂ surface morphology is homogeneous, the grains have a spherical shape (with dimensions from 18 to 160 nm). Based on XRD analysis, it can be stated that all the studied TiO₂ layers have an anatase structure. The results of electrochemical and immersion studies, performed in Ringer’s solution at 37 °C, show that the corrosion resistance of the studied TiO₂ does not always increase proportionally with the thickness of the films. This is a result of grain refinement and differences in the density of the titanium dioxide films applied using the physical vapor deposition (PVD) technique. The results of 24 h immersion tests indicate that the lowest volume of evolved H₂ (5.92 mL/cm²) was with the 400 nm thick film deposited onto the MgCa2Zn1Gd3 alloy. This result is in agreement with the good biocompatibility of this TiO₂ film, confirmed by cytotoxicity tests.

A novel BSA immobilizing manner on modified titanium surface ameliorates osteoblast performance

Surface modification of medical and dental devices, to improve their biocorrosion resistance and biocompatibility, can be achieved with the multidisciplinary field of biomaterials. Nanostructured titanium dioxide (TiO₂) has been employed as surface modifier of titanium-based biomaterials because it can prevent the failure of the devices due to wear mechanisms. Moreover, this oxide surface is mostly terminated by hydroxyl groups (-OH) that can be directly functionalized with biomolecules to improve the biocompatibility of these devices. We explored the influence of 3-aminopropyltrimethoxysilane (APTMS) molecules as spacers in bovine serum albumin (BSA) protein immobilization on the physically hydroxylated surfaces of rutile phase TiO₂ films grown by reactive Radio Frequency (RF) magnetron sputtering. X-ray Photoelectron Spectroscopy (XPS) was used to examine the adsorption of BSA and APTMS on the hydroxylated surface of TiO₂ thin films. For biological tests, BSA was directly immobilized on the film surface and on the APTMS monolayer. Biological analysis found better osteoblast performance considering gene markers related to cell adhesion after interacting directly with the surface modified by the immobilization of BSA, especially on the surface where this protein was immobilized by APTMS. Additionally, we addressed the relevance of this biointerfaces on extracellular matrix remodeling by zymography analysis. Altogether, our data provides new insights about the cellular and molecular mechanisms covering the improved osteoblastic response of the proposed surface modification.

TiO2 as Photosensitizer and Photoinitiator for Synthesis of Photoactive TiO2-PEGDA Hydrogel Without Organic Photoinitiator

The replacement of potentially toxic photoinitiators is of increasing interest regarding the synthesis of biomaterials by photopolymerization. Therefore, we present a new method for the preparation of UV polymerized hydrogels with TiO2 as a photoinitiator. Titania is known to be an excellent photoactive compound which is non-toxic, inert, and cheap. The so-formed hydrogels possess excellent mechanical properties, a high swelling ratio, and high thermal stability. Furthermore, no TiO2 is released from the hydrogels. Thus, the material is highly suitable for medical applications. Additionally, the present TiO2 in the hydrogels remains photoactive as demonstrated by degradation of methylene blue. This enables the application of TiO2-hydrogels in photodynamic therapy.

Titanium surface bio-functionalization using osteogenic peptides: Surface chemistry, biocompatibility, corrosion and tribocorrosion aspects

Titanium (Ti) is widely used in biomedical devices due to its recognized biocompatibility. However, implant failures and subsequent clinical side effects are still recurrent. In this context, improvements can be achieved by designing biomaterials where the bulk and the surface of Ti are independently tailored. The conjugation of biomolecules onto the Ti surface can improve its bioactivity, thus accelerating the osteointegration process. Ti was modified with TiO₂, two different spacers, 3-(4-aminophenyl) propionic acid (APPA) or 3-mercaptopropionic acid (MPA) and dentin matrix protein 1 (DMP1) peptides. X-ray photoelectron spectroscopy analysis revealed the presence of carbon and nitrogen for all samples, indicating a success in the functionalization process. Furthermore, DMP1 peptides showed an improved coverage area for the samples with APPA and MPA spacers. Biological tests indicated that the peptides could modulate cell affinity, proliferation, and differentiation. Enhanced results were observed in the presence of MPA. Moreover, the immobilization of DMP1 peptides through the spacers led to the formation of calcium phosphate minerals with a Ca/P ratio near to that of hydroxyapatite. Corrosion and tribocorrosion results indicated an increased resistance to corrosion and lower mass loss in the functionalized materials, showing that this new type of functional material has attractive properties for biomaterials application.

Atomic layer deposition of nano-TiO2 thin films with enhanced biocompatibility and antimicrobial activity for orthopedic implants

Titanium (Ti) and its alloys have been extensively used as implant materials in orthopedic applications. Nevertheless, implants may fail due to a lack of osseointegration and/or infection. The aim of this in vitro study was to endow an implant surface with favorable biological properties by the dual modification of surface chemistry and nanostructured topography. The application of a nanostructured titanium dioxide (TiO2) coating on Ti-based implants has been proposed as a potential way to enhance tissue-implant interactions while inhibiting bacterial colonization simultaneously due to its chemical stability, biocompatibility, and antimicrobial properties. In this paper, temperature-controlled atomic layer deposition (ALD) was introduced for the first time to provide unique nanostructured TiO2 coatings on Ti substrates. The effect of nano-TiO2 coatings with different morphology and structure on human osteoblast and fibroblast functions and bacterial activities was investigated. In vitro results indicated that the TiO2 coating stimulated osteoblast adhesion and proliferation while suppressing fibroblast adhesion and proliferation compared to uncoated materials. In addition, the introduction of nano-TiO2 coatings was shown to inhibit gram-positive bacteria (Staphylococcus aureus), gram-negative bacteria (Escherichia coli), and antibiotic-resistant bacteria (methicillin-resistant Staphylococcus aureus), all without resorting to the use of antibiotics. Our results suggest that the increase in nanoscale roughness and greater surface hydrophilicity (surface energy) together could contribute to increased protein adsorption selectively, which may affect the cellular and bacterial activities. It was found that ALD-grown TiO2-coated samples with a moderate surface energy at 38.79 mJ/m2 showed relatively promising antibacterial properties and desirable cellular functions. The ALD technique provides a novel and effective strategy to produce TiO2 coatings with delicate control of surface nanotopography and surface energy to enhance the interfacial biocompatibility and mitigate bacterial infection, and could potentially be used for improving numerous orthopedic implants.

Parallel patterning of SiO2 wafer via near-field electrospinning of metallic salts and polymeric solution mixtures

This paper describes a near-field electrospinning technique combined with heat treatment process used to directly align parallel metal oxide and metal nitride fibers on silicon dioxide substrate. The effects of near-field electrospinning parameters (including collector-to-needle distance, applied voltage and the moving speed of the collector) on the morphology of the resulted fibers have been studied. Metallic salt-contained precursor fibers are individually aligned via near-field electrospinning of metallic salts and polymeric solution mixtures. After applying calcination process to these well aligned precursor fibers, patterning by metal oxide and metal nitride fibers such as ZnO, Ga₂O₃, TiO₂, GaN and TiN is successfully obtained. The optical microscope images and the scanning electron microscopy show the presence of fiber patterns, whose crystalline structure is characterized by x-ray diffraction and Raman spectroscopy measurement. The results demonstrate the potential of this approach for assembling ceramic fibers into parallel arrays with controllable orientation and position.

The Bioactivity and Photocatalytic Properties of Titania Nanotube Coatings Produced with the Use of the Low-Potential Anodization of Ti6Al4V Alloy Surface

Titania nanotube (TNT) coatings were produced using low-potential anodic oxidation of Ti6Al4V substrates in the potential range 3-20 V. They were analysed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The wettability was estimated by measuring the contact angle when applying water droplets. The bioactivity of the TNT coatings was established on the basis of the biointegration assay (L929 murine fibroblasts adhesion and proliferation) and antibacterial tests against Staphylococcus aureus (ATCC 29213). The photocatalytic efficiency of the TNT films was studied by the degradation of methylene blue under UV irradiation. Among the studied coatings, the TiO₂ nanotubes obtained with the use of 5 V potential (TNT5) were found to be the most appropriate for medical applications. The TNT5 sample possessed antibiofilm properties without enriching it by additional antimicrobial agent. Furthermore, it was characterized by optimal biocompatibility, performing better than pure Ti6Al4V alloy. Moreover, the same sample was the most photocatalytically active and exhibited the potential for the sterilization of implants with the use of UV light and for other environmental applications.

Optimized composition of nanocomposite scaffolds formed from silk fibroin and nano-TiO2 for bone tissue engineering

Natural silk fibroin (SF) polymer has biomedical and mechanical properties as a biomaterial for bone tissue engineering scaffolds. Freeze-dried porous nanocomposite scaffolds were prepared from silk fibroin and titanium dioxide (TiO₂) nanoparticles as a bioactive reinforcing agent by a phase separation method. In order to fabricate SF/TiO₂ scaffolds, 5, 10, 15 and 20wt% of the TiO₂ were added to the SF. The phase structure, functional groups and morphology of the scaffolds were evaluated using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy techniques, respectively. Porosity of the scaffolds was measured by Archimedes' Principle. In addition, mechanical properties of prepared scaffolds were evaluated by measuring the compressive strength and compressive modulus. The bioactivity property of these scaffolds was examined for 7, 14, 21 and 28days immersion in simulated body fluid (SBF) at 37°C and the in vitro degradation was studied by incubation in phosphate buffered saline (PBS) at 37°C and pH7.4 for up to 30days. Moreover, the scaffolds' biocompatibility was evaluated by seeding and culture of SaOS-2 osteoblast-like cells and assessment of their proliferation with MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. Results showed that the prepared scaffolds had directional porosity and the reduction of porosity in composite scaffolds with higher contents of TiO₂ nanoparticles resulted to an improvement of the mechanical strength. The macroporous structures with open interconnected and directional pores were successfully obtained without applying any porogen or inorganic solvent. The bioactivity of these scaffolds was confirmed by scanning electron microscopy (SEM) showing surface crystallization of the apatite layer proportional to the duration of immersion in the SBF and the degradation rate of scaffolds were increased by increasing the TiO₂ content. The osteoblast-like cells showed a high attachment and proliferation on these scaffolds and their viability was increased with increasing the SF content. Finally, an optimum composition of SF/TiO₂ nanocomposite scaffolds was selected.

IR spectroscopic investigations of chemical and photochemical reactions on metal oxides: bridging the materials gap

In this review, we highlight recent progress (2008–2016) in infrared reflection absorption spectroscopy (IRRAS) studies on oxide powders achieved by using different types of metal oxide single crystals as reference systems.

Cytotoxicity Evaluation of Anatase and Rutile TiO₂ Thin Films on CHO-K1 Cells in Vitro

Cytotoxicity of titanium dioxide (TiO₂) thin films on Chinese hamster ovary (CHO-K1) cells was evaluated after 24, 48 and 72 h of culture. The TiO₂ thin films were deposited using direct current magnetron sputtering. These films were post-deposition annealed at different temperatures (300, 500 and 800 °C) toward the anatase to rutile phase transformation. The root-mean-square (RMS) surface roughness of TiO₂ films went from 2.8 to 8.08 nm when the annealing temperature was increased from 300 to 800 °C. Field emission scanning electron microscopy (FESEM) results showed that the TiO₂ films’ thickness values fell within the nanometer range (290–310 nm). Based on the results of the tetrazolium dye and trypan blue assays, we found that TiO₂ thin films showed no cytotoxicity after the aforementioned culture times at which cell viability was greater than 98%. Independently of the annealing temperature of the TiO₂ thin films, the number of CHO-K1 cells on the control substrate and on all TiO₂ thin films was greater after 48 or 72 h than it was after 24 h; the highest cell survival rate was observed in TiO₂ films annealed at 800 °C. These results indicate that TiO₂ thin films do not affect mitochondrial function and proliferation of CHO-K1 cells, and back up the use of TiO₂ thin films in biomedical science.