Mechanical Properties, Corrosion Resistance and Bioactivity of Oxide Layers Formed by Isothermal Oxidation of Ti-6Al-7Nb Alloy

Effect of Temperature on Thermal Oxidation Behavior of Ti-6Al-4V ELI Alloy

In this paper, the morphological, micromechanical and tribological characteristics of the Ti-6Al-4V ELI alloy after thermal oxidation (TO) were identified. TO was carried out at temperatures of 848 K, 898 K and 948 K over a period of 50 h. Microscopic examination revealed that an increase in temperature resulted in an improved uniformity of coverage and an increased oxide grain size. Micromechanical tests showed that TO of the Ti-6Al-4V ELI alloy led to an increase in hardness and deformation resistance. Following oxidation, a decrease (by approximately 10-22%) was observed in the total mechanical work of indentation, Wtotal, compared to the as-received material. The formation of protective oxide films on the Ti-6Al-4V ELI alloy also led to the improvement of tribological characteristics, both when tested under dry friction conditions and in Ringer's solution. The sliding wear resistance increased with an increase in the oxidation temperature. However, a greater degree of wear reduction (by approximately 30-50%) was found for the lubricated contact in comparison with the dry friction tests. Surface roughness also increased with the increase in temperature.

Study on Osseointegration Capability of β-Type Ti-Nb-Zr-Ta-Si Alloy for Orthopedic Implants

Osseointegration is the basic condition for orthopedic implants to maintain long-term stability. In order to achieve osseointegration, a low elastic modulus is the most important performance indicator. It is difficult for traditional titanium alloys to meet this requirement. A novel β-titanium alloy (Ti-35Nb-7Zr-5Ta)98Si2 was designed, which had excellent strength (a yield strength of 1296 MPa and a breaking strength 3263 MPa), an extremely low elastic modulus (37 GPa), and did not contain toxic elements. In previous in vitro studies, we confirmed the good biocompatibility of this alloy and similar bioactivity to Ti-6Al-4V, but no in vivo study was performed. In this study, Ti-6Al-4V and (Ti-35Nb-7Zr-5Ta)98Si2 were implanted into rabbit femurs. Imaging evaluation and histological morphology were performed, and the bonding strength and bone contact ratio of the two alloys were measured and compared. The results showed that both alloys remained in their original positions 3 months after implantation, and neither imaging nor histological observations found inflammatory reactions in the surrounding bone. The bone-implant contact ratio and bonding strength of (Ti-35Nb-7Zr-5Ta)98Si2 were significantly higher than those of Ti-6Al-4V. The results confirmed that (Ti-35Nb-7Zr-5Ta)98Si2 has a better osseointegration ability than Ti-6Al-4V and is a promising material for orthopedic implants.

Electrophoretic Deposition of Multi-Walled Carbon Nanotube Coatings on CoCrMo Alloy for Biomedical Applications

Carbon nanotubes are a promising material for use in innovative biomedical solutions due to their unique chemical, mechanical, electrical, and magnetic properties. This work provides a method for the development of ultrasonically assisted electrophoretic deposition of multi-walled carbon nanotubes on a CoCrMo dental alloy. Functionalization of multi-walled carbon nanotubes was carried out by chemical oxidation in a mixture of nitric and sulfuric acids. The modified and unmodified multi-walled carbon nanotubes were anaphoretically deposited on the CoCrMo alloy in an aqueous solution. Chemical composition was studied by Fourier transform infrared spectroscopy. Surface morphology was examined by scanning electron microscopy. The mechanism and kinetics of the electrochemical corrosion of the obtained coatings in artificial saliva at 37 °C were determined using the open-circuit potential method, electrochemical impedance spectroscopy, and anodic polarization curves. The capacitive behavior and high corrosion resistance of the tested electrodes were revealed. It was found that the kinetics of electrochemical corrosion of the CoCrMo electrode significantly decreased in the presence of the functionalized multi-walled carbon nanotube coating. Electrophoretic deposition was shown to be an effective, low-cost, and fast method of producing nanotubes with controlled thickness, homogeneity, and packing density.

Effect of Artificial Saliva Modification on Pitting Corrosion and Mechanical Properties of the Remanium®-Type Orthodontic Archwire

The pitting corrosion of orthodontic apparatus elements in the oral environment is an interest of both clinicians and scientists dealing with the assessment of the biocompatibility of medical materials. This work presents a study on the effect of ready-to-use Listerine® and Meridol® mouthwashes and sodium fluoride on the resistance of the commercial Remanium®-type orthodontic archwire to pitting corrosion in artificial saliva at 37 °C. XRD, SEM, EDS, mechanical properties, and microhardness measurements were used to characterize the archwire. The in vitro corrosion resistance of the archwire was examined using the open-circuit potential method, electrochemical impedance spectroscopy, and anodic polarization curves. The physicochemical characteristics confirmed the presence of a bi-phase alloy with a mixed austenite/ferrite structure containing Fe 74.4(7) at.%, Cr 18.4(4) at.%, and Ni 7.2(4) at.%. The Fe-Cr-Ni alloy was characterized by high tensile strength and Vickers microhardness. EIS revealed the capacitive behavior with high corrosion resistance. It was found that the kinetics of pitting corrosion in the artificial saliva decreased in the presence of NaF and mouthwashes. The potentiodynamic characteristics confirmed the decrease in susceptibility to pitting corrosion after the modification of artificial saliva. The pitting corrosion mechanism of the self-passive oxide layer on the surface of the Fe-Cr-Ni electrode in the biological environment containing chloride ions was discussed in detail. Mechanical properties after corrosion tests were weakened.

Biological Activity and Thrombogenic Properties of Oxide Nanotubes on the Ti-13Nb-13Zr Biomedical Alloy

The success of implant treatment is dependent on the osseointegration of the implant. The main goal of this work was to improve the biofunctionality of the Ti-13Nb-13Zr implant alloy by the production of oxide nanotubes (ONTs) layers for better anchoring in the bone and use as an intelligent carrier in drug delivery systems. Anodization of the Ti-13Nb-13Zr alloy was carried out in 0.5% HF, 1 M (NH₄)₂SO₄ + 2% NH₄F, and 1 M ethylene glycol + 4 wt.% NH₄F electrolytes. Physicochemical characteristics of ONTs were performed by high-resolution electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS), and scanning Kelvin probe (SKP). Water contact angle studies were conducted using the sitting airdrop method. In vitro biological properties and release kinetics of ibuprofen were investigated. The results of TEM and XPS studies confirmed the formation of the single-walled ONTs of three generations on the bi-phase (α + β) Ti-13Nb-13Zr alloy. The ONTs were composed of oxides of the alloying elements. The proposed surface modification method ensured good hemolytic properties, no cytotoxity for L-929 mouse cells, good adhesion, increased surface wettability, and improved athrombogenic properties of the Ti-13Nb-13Zr alloy. Nanotubular surfaces allowed ibuprofen to be released from the polymer matrix according to the Gallagher-Corrigan model.

In Vitro Bioelectrochemical Properties of Second-Generation Oxide Nanotubes on Ti-13Zr-13Nb Biomedical Alloy

Surface charge and in vitro corrosion resistance are some of the key parameters characterizing biomaterials in the interaction of the implant with the biological environment. Hence, this work investigates the in vitro bioelectrochemical behavior of newly developed oxide nanotubes (ONTs) layers of second-generation (2G) on a Ti-13Zr-13Nb alloy. The 2G ONTs were produced by anodization in 1 M (NH₄)₂SO₄ solution with 2 wt.% of NH₄F. The physical and chemical properties of the obtained bamboo-inspired 2G ONTs were characterized using scanning electron microscopy with field emission and energy dispersive spectroscopy. Zeta potential measurements for the examined materials were carried out using an electrokinetic analyzer in aqueous electrolytes of potassium chloride, phosphate-buffered saline and artificial blood. It was found that the electrolyte type and the ionic strength affect the bioelectrochemical properties of 2G ONTs layers. Open circuit potential and anodic polarization curve results proved the influence of anodizing on the improvement of in vitro corrosion resistance of the Ti-13Zr-13Nb alloy in PBS solution. The anodizing conditions used can be proposed for the production of long-term implants, which are not susceptible to pitting corrosion up to 9.4 V.

Influence of Anodizing Conditions on Biotribological and Micromechanical Properties of Ti-13Zr-13Nb Alloy

The biomedical Ti-13Zr-13Nb bi-phase (α + β) alloy for long-term applications in implantology has recently been developed. The porous oxide nanotubes' (ONTs) layers of various geometries and lengths on the Ti-13Zr-13Nb alloy surface can be produced by anodizing to improve osseointegration. This work was aimed at how anodizing conditions determinatine the micromechanical and biotribological properties of the Ti-13Zr-13Nb alloy. First-generation (1G), second-generation (2G), and third-generation (3G) ONT layers were produced on the Ti-13Zr-13Nb alloy surface by anodizing. The microstructure was characterized using SEM. Micromechanical properties were investigated by the Vickers microhardness test under variable loads. Biotribological properties were examined in Ringer's solution in a reciprocating motion in the ball-on-flat system. The 2D roughness profiles method was used to assess the wear tracks of the tested materials. Wear scars' analysis of the ZrO₂ ball was performed using optical microscopy. It was found that the composition of the electrolyte with the presence of fluoride ions was an essential factor influencing the micromechanical and biotribological properties of the obtained ONT layers. The three-body abrasion wear mechanism was proposed to explain the biotribological wear in Ringer's solution for the Ti-13Zr-13Nb alloy before and after anodizing.

Mechanical Characteristics and Bioactivity of Nanocomposite Hydroxyapatite/Collagen Coated Titanium for Bone Tissue Engineering

In the present study, we have analyzed the mechanical characteristics and bioactivity of titanium coating with hydroxyapatite/bovine collagen. Hydroxyapatite (HAp) was synthesized from a Pinctada maxima shell and has a stoichiometry (Ca/P) of 1.72 and a crystallinity of 92%, suitable for coating materials according to ISO and Food and Drug Administration (FDA) standards. Titanium (Ti) substrate coatings were fabricated at HAp concentrations of 1% (Ti/HAp-1) and 3% (Ti/HAp-3) and a bovine collagen concentration of 1% (Ti/HAp/Coll) by the electrophoresis deposition (EPD) method. The compressive strength of Ti/HAp-1 and Ti/HAp-3 was 87.28 and 86.19 MPa, respectively, and it increased significantly regarding the control/uncoated Ti (46.71 MPa). Furthermore, the Ti/HAp-coll (69.33 MPa) has lower compressive strength due to collagen substitution (1%). The bioactivity of Ti substrates after the immersion into simulated body fluids (SBF) for 3-10 days showed a high apatite growth (Ca²⁺ and PO43-), according to XRD, FTIR, and SEM-EDS results, significantly on the Ti/HAp-coll.

Effect of oxide layers formed by thermal oxidation on mechanical properties and NaCl-induced hot corrosion behavior of TC21 Ti-alloy

In the current study on TC21 Ti-alloy (6.5Al-3Mo-1.9Nb-2.2Sn-2.2Zr-1.5Cr), the thermal oxidation formed oxide layers that considerably influenced mechanical properties (hardness and wear). TC21 specimens were oxidized at 600, 700, 800, and 900 °C for 5, 20, and 50 h. NaCl-induced hot corrosion testing was carried out on raw (un-oxidized) and oxidized specimens at 600 and 800 °C for 50 h. The cyclic testing was performed at 600 °C for durations of 5, 10, 20, 30, 40, and 50 h. The average thickness of the layer grew with increasing oxidation time and temperature. A thin oxide layer (average 0.16 µm) was generated by oxidation at a temperature of 600 °C for a duration of 5 h, and at 800 °C, a large oxide layer of 10.8 µm thickness was formed. The most significant surface hardness of 1000 ± 150 HV0.05 was produced for the layer oxidized at 900 °C. On the other hand, the lowest hardness of 360 ± 150 HV0.05 was recorded for the raw materials. Best wear resistance had been achieved for specimens oxidized at 800 °C. During NaCl hot corrosion test, the weight loss of the raw specimen was 6.4 mg/cm2 due to the flaking off of the corrosion product. However, for specimens oxidized at 600 °C for 50 h, weight loss after corrosion testing was 0.54 mg/cm2, less than that of the specimen before corrosion. Oxidized specimens at 800 °C exhibited the best mechanical characteristics and corrosion resistance.

In-vitro biocompatibility evaluation of cast Ni–Ti alloy produced by vacuum arc melting technique for biomedical and dental applications

The investigated cast Ni50–Ti50 shape memory alloy was prepared using a vacuum arc furnace. The cast samples were subjected to in-vitro biocompatibility studies according to ISO 10993-12:2004, and compared to other samples Ni–Ti orthodontic wires commercially available at the dental market. The cast samples were hydroxyapatite-coated using the electrodeposition technique. The effect of surface treatment on the coating quality was addressed. The hydroxyapatite-coated samples were investigated using electrochemical impedance (EIS) and potentiodynamic techniques. Coated samples were also examined using a scanning electron microscope to inspect the coating morphology. Cytotoxicity tests on MG63 and H9C2 cell lines showed the safety and biocompatibility of the cast NiTi alloy, with a direct relationship between the incubation period of the tested samples and cell viability. Well-adhered hydroxyapatite coating was obtained on the surface-treated NiTi samples using the electrodeposition technique. EDS analysis showed a hydroxyapatite coating having a calcium to phosphorus ratio close to that of the natural bone. Electrochemical tests indicated that the highest corrosion resistance was obtained for the uncoated samples followed by the anodized sample and finally the hydroxyapatite-coated samples due to their high porosity.

Investigation of Dry Sliding Friction, Wear and Mechanical Behavior of the Ti-6Al-7Nb Alloy after Thermal Oxidation

The mechanical and tribological characteristics of the Ti-6Al-7Nb alloy were investigated within a wide range of temperature and time parameters of thermal oxidation. The hardness, H_IT, and indentation modulus, E_IT, of the alloy in question, with and without an anti-wear oxide layer, were determined. The tribological properties of sliding couples were studied under technically dry friction conditions, using a ball-on-disc tribometer. The test pieces were non-oxidized and oxidized Ti-6Al-7Nb alloy discs, and Al₂O₃, ZrO_2, and 100Cr6 balls were used as counter specimens. After thermal oxidation, the surface of the titanium alloy was characterized by a significantly higher hardness, H_IT (8-10 GPa), compared to the surface not covered with oxide layers (3.6 GPa). The study showed that the curvature of the loading segments increased with an increasing oxidation temperature, indicating a strong positive dependence of hardness on the thermal oxidation temperature. The value of the indentation modulus, E_IT, was also found to increase with the increasing oxidation temperature. The intensity of the tribological processes was strictly dependent on the oxidation parameters and the couple's material (Al₂O₃, ZrO₂, 100Cr6). It has been shown that the thermal oxidation process makes it possible to control, within a wide range, the friction-wear characteristics of the Ti-6Al-7Nb alloy.

Production and Characterization of the Third-Generation Oxide Nanotubes on Ti-13Zr-13Nb Alloy

In the group of vanadium-free titanium alloys used for applications for long-term implants, the Ti-13Zr-13Nb alloy has recently been proposed. The production of a porous layer of oxide nanotubes (ONTs) with a wide range of geometries and lengths on the Ti-13Zr-13Nb alloy surface can increase its osteoinductive properties and enable intelligent drug delivery. This work concerns developing a method of electrochemical modification of the Ti-13Zr-13Nb alloy surface to obtain third-generation ONTs. The effect of the anodizing voltage on the microstructure and thickness of the obtained oxide layers was conducted in 1 M C₂H₆O₂ + 4 wt% NH₄F electrolyte in the voltage range 5–35 V for 120 min at room temperature. The obtained third-generation ONTs were characterized using SEM, EDS, SKP, and 2D roughness profiles methods. The preliminary assessment of corrosion resistance carried out in accelerated corrosion tests in the artificial atmosphere showed the high quality of the newly developed ONTs and the slight influence of neutral salt spray on their micromechanical properties.

Insights into oxidative stress in bone tissue and novel challenges for biomaterials

The presence of Reactive Oxygen Species (ROS) in bone can influence resident cells behaviour as well as the extra-cellular matrix composition and the tissue architecture. Aging, in addition to excessive overloads, unbalanced diet, smoking, predisposing genetic factors, lead to an increase of ROS and, if it is accompanied with an inappropriate production of scavengers, promotes the generation of oxidative stress that encourages bone catabolism. Furthermore, bone injuries can be triggered by numerous events such as road and sports accidents or tumour resection. Although bone tissue possesses a well-known repair and regeneration capacity, these mechanisms are inefficient in repairing large size defects and bone grafts are often necessary. ROS play a fundamental role in response after the implant introduction and can influence its success. This review provides insights on the mechanisms of oxidative stress generated by an implant in vivo and suitable ways for its modulation. The local delivery of active molecules, such as polyphenols, enhanced bone biomaterial integration evidencing that the management of the oxidative stress is a target for the effectiveness of an implant. Polyphenols have been widely used in medicine for cardiovascular, neurodegenerative, bone disorders and cancer, thanks to their antioxidant and anti-inflammatory properties. In addition, the perspective of new smart biomaterials and molecular medicine for the oxidative stress modulation in a programmable way, by the use of ROS responsive materials or by the targeting of selective molecular pathways involved in ROS generation, will be analysed and discussed critically.

Production, Characterization and Application of Oxide Nanotubes on Ti-6Al-7Nb Alloy as a Potential Drug Carrier

This work concerns the development of a method of functionalization of the surface of the biomedical Ti–6Al–7Nb alloy by producing oxide nanotubes (ONTs) with drug-eluting properties. Shaping of the morphology, microstructure, and thickness of the oxide layer was carried out by anodization in an aqueous solution of 1 M ethylene glycol with the addition of 0.2 M NH₄F in the voltage range 5–100 V for 15–60 min at room temperature. The characterization of the physicochemical properties of the obtained ONTs was performed using SEM, XPS, and EDAX methods. ONTs have been shown to be composed mainly of TiO₂, Al₂O₃, and Nb₂O₅. Single-walled ONTs with the largest specific surface area of 600 cm² cm⁻² can be obtained by anodization at 50 V for 60 min. The mechanism of ONT formation on the Ti–6Al–7Nb alloy was studied in detail. Gentamicin sulfate loaded into ONTs was studied using FTIR, TG, DTA, and DTG methods. Drug release kinetics was determined by UV–Vis spectrophotometry. The obtained ONTs can be proposed for use in modern implantology as carriers for drugs delivered locally in inflammatory conditions.