Electrochemical properties, chemical composition and thickness of passive film formed on novel Ti–20Nb–10Zr–5Ta alloy

Study on the Preparation and Corrosion-Wear Properties of TiN/Sn Coatings on the Ti-25Nb-3Zr-2Sn-3Mo Titanium Alloy

Due to its excellent specific strength, corrosion resistance, and biocompatibility, titanium alloy is often used as a biological implant material. In order to address the issues of low hardness and poor wear resistance of the Ti-25Nb-3Zr-2Sn-3Mo titanium alloy, a TiN/Sn coating with good biocompatibility was deposited on its surface using a new composite modification technology of surface mechanical strengthening + surface mechanical coating. By taking advantage of the wear resistance of TiN and the adhesiveness of Sn, a composite coating with corrosion-wear resistance was formed to improve its corrosion-wear resistance. Using TiN/Sn powders of different ratios (10% Sn, 20% Sn, 30% Sn, and 40% Sn) as media, the alloy was subjected to a combined strengthening treatment of surface mechanical attrition and solid-phase coating under a nitrogen atmosphere. The microstructure and mechanical properties of the composite-strengthened layer were tested by means of XRD, SEM-EDS, a nanoindentation tester, a white-light interferometer, and a reciprocating wear tester. Moreover, the corrosion-wear properties of the samples under different loads and electrochemical conditions were analyzed. The results show that the surface composite-strengthened layer of the alloy consisted of a TiN/Sn coating + a mechanical deformed layer. With an increase in the Sn content, the thickness of the TiN/Sn coating continuously increased, while the thickness of the mechanical deformed layer continuously decreased. The composite-strengthened layer had good comprehensive mechanical properties. In the SBF solution, the corrosion-wear resistance of the composite-strengthened samples improved; the degree of wear first decreased and then increased with the increase in the Sn content, and it reached the optimal value when the Sn content was 30%. Compared with the raw sample, the corrosion of the coating sample increased, but the wear significantly decreased. The corrosion-wear synergy factor κ value first increased and then decreased with the increase in the Sn content, reaching a maximum value at the 20% Sn content. This is the result of the combined effect of the corrosion resistance and wear resistance of the coating.

Effect of Ni and Nb Elements on Corrosion Resistance and Behavior of TC4 Alloy in Hydrochloric Acid

Due to the development of the petroleum industry, more severe mining conditions put forward higher corrosion resistance requirements for materials. In this paper, the corrosion resistance and corrosion behavior of four TC4-xNi-yNb (x, y = 0, 0.5) alloys were investigated in a 1 mol/L HCl solution through microscopic characterization, electrochemical tests and corrosion weight loss testing. The results demonstrated that the addition of Ni and Nb elements could improve the corrosion resistance of TC4 alloy to varying degrees. The addition of niobium formed niobium oxide in the passive film, while the addition of nickel thickened the passive film without formation of nickel oxides. The improvement of corrosion resistance of TC4 by nickel is more significant. Finally, a new highly corrosion resistant alloy TC4-0.5Ni-0.5Nb is preferred.

Functional medium entropy alloys for joint replacement: An atomistic perspective of material deformation and a correlation to wear, corrosion, and biocompatibility

The present study adopts a multi-facet approach to design bio inspired concentrated alloys for potential application as articulating surfaces in joint replacements. A series of equiatomic, Nb rich and Ti rich TiMoNbZr based medium entropy alloys (MEAs) were processed via arc melting and their mechanical, in-vitro corrosion, wear, and in vitro and in vivo biocompatibility were investigated. Equiatomic MEA had primarily bcc with minor hcp phases where the single bcc was achieved with the addition of Nb. The single bcc Nb rich alloy resulted in 13 % elongation, much higher than equiatomic or Ti rich alloy. All the MEAs showed comparatively higher yield strength due to the climb of edge dislocations which is the main rate limiting mechanism at 300 K, as evident molecular dynamics (MD) simulation. The locally fluctuating energy landscape promotes kinks on edge dislocation, and at local minima nanoscale segments gets pinned. Upon yielding the entangled kink leaves a trail of vacancies/interstitials and escapes via climb motion to render high yield strength. The higher corrosion and pitting resistance of Nb enriched alloys can be attributed to the stable ZrO2, Nb2O5, TiO2, and MoO3 oxides, high polarization resistance (106-105 Ωcm-2), and low defect densities (1016-1018). In vitro cell-materials interaction using MC3T3-E1 showed bioinert but cytocompatible nature of the MEAs. The wear rate of the MEAs was in the range of 7-9 × 10-5 mm3N-1m-1. The wear debris did not show any tissue necrosis when implanted in rabbit femur rather new bone regeneration can be seen around the particles. STATEMENT OF SIGNIFICANCE: In the present work, a noble Nb enriched MEAs with superior mechanical, in vitro wear, corrosion and cytocompatibility properties was designed for articulating surfaces in joint replacement.

Recent Advances in Processing of Titanium and Titanium Alloys through Metal Injection Molding for Biomedical Applications: 2013-2022

Metal injection molding (MIM) is one of the most widely used manufacturing processes worldwide as it is a cost-effective way of producing a variety of dental and orthopedic implants, surgical instruments, and other important biomedical products. Titanium (Ti) and Ti alloys are popular modern metallic materials that have revamped the biomedical sector as they have superior biocompatibility, excellent corrosion resistance, and high static and fatigue strength. This paper systematically reviews the MIM process parameters that extant studies have used to produce Ti and Ti alloy components between 2013 and 2022 for the medical industry. Moreover, the effect of sintering temperature on the mechanical properties of the MIM-processed sintered components has been reviewed and discussed. It is concluded that by appropriately selecting and implementing the processing parameters at different stages of the MIM process, defect-free Ti and Ti alloy-based biomedical components can be produced. Therefore, this present study could greatly benefit future studies that examine using MIM to develop products for biomedical applications.

Titanium and titanium alloys in dentistry: current trends, recent developments, and future prospects

Many implant materials have been used in various dental applications depending on their efficacy and availability. A dental implant must possess the required characteristics, such as biocompatibility, corrosion & wear resistance, adequate mechanical properties, osseointegration, etc., to ensure its safe and optimum use. This review analyzes various aspects of titanium (Ti) and Ti alloys, including properties, manufacturing processes, surface modifications, applications as dental implants, and limitations. In addition, it also presents a perception of recent advances in Ti-based implant materials and the futuristic development of innovative dental implants.

Effect of Ti on the Structure and Mechanical Properties of TixZr2.5-xTa Alloys

To determine the effects of Ti and mixing entropy (ΔS_mix) on the structure and mechanical proper-ties of Zr-Ta alloys and then find a new potential energetic structural material with good me-chanical properties and more reactive elements, Ti_xZr_2.5−xTa (x = 0, 0.5, 1.0, 1.5, 2.0) alloys were investigated. The XRD experimental results showed that the phase transformation of Ti_xZr_2.5−xTa nonequal-ratio ternary alloys depended not on the value of ΔS_mix, but on the amount of Ti atoms. With the addition of Ti, the content of the HCP phase decreased gradually. SEM analyses revealed that dendrite morphology and component segregation increasingly developed and then weakened gradually. When x increases to 2.0, Ti_xZr_2.5−xTa with the best mechanical properties can be ob-tained. The yield strength, compressive strength and fracture strain of Ti_2.0Zr_0.5Ta reached 883 MPa, 1568 MPa and 34.58%, respectively. The dependence of the phase transformation and me-chanical properties confirms that improving the properties of Zr-Ta alloys by doping Ti is feasible.

A more defective substrate leads to a less defective passive layer: Enhancing the mechanical strength, corrosion resistance and anti-inflammatory response of the low-modulus Ti-45Nb alloy by grain refinement

Orthopedic and dental implants made of β-type Ti alloys have low elastic modulus which can better relieve the stress shielding effects after surgical implantation. Nevertheless, clinical application of β-type Ti alloys is hampered by the insufficient mechanical strength and gradual release of pro-inflammatory metallic ions under physiological conditions. In this study, the β-type Ti-45Nb alloy is subjected to high-pressure torsion (HPT) processing to refine the grain size. After HPT processing, the tensile strength increases from 370 MPa to 658 MPa due to grain boundary strengthening and at the same time, the favorable elastic modulus is maintained at a low level of 61-72 GPa because the single β-phase is preserved during grain refinement. More grain boundaries decrease the work function and facilitate the formation of thicker and less defective passive films leading to better corrosion resistance. In addition, more rapid repair of the passive layer mitigates release of metallic ions from the alloy and consequently, the inflammatory response is suppressed. The results reveal a strategy to simultaneously improve the mechanical and biological properties of metallic implant materials for orthopedics and dentistry. STATEMENT OF SIGNIFICANCE: The low modulus Ti-45Nb alloy is promising in addressing the complication of stress shielding induced by biomedical Ti-based materials with too-high elastic modulus. However, its insufficient strength hampers its clinical application, and traditional strengthening via heat treatments will compromise the low elastic modulus. In the current study, we enhanced the ultimate tensile strength of Ti-45Nb from 370 MPa to 658 MPa through grain-refinement strengthening, while the elastic modulus was maintained at a low value (61-72 GPa). Moreover, substrate grain-refinement has been proved to improve the corrosion resistance of Ti-45Nb with reduced inflammatory response both in vitro and in vivo. A relationship between the substrate microstructure and the surface passive layer has been established to explain the beneficial effects of substrate grain-refinement.

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.

An In Vitro Evaluation of the Hierarchical Micro/Nanoporous Structure of a Ti3Zr2Sn3Mo25Nb Alloy after Surface Dealloying

A process to dealloy a Ti-3Zr-2Sn-3Mo-25Nb (TLM) titanium alloy to create a porous surface structure has been reported in this paper aiming to enhance the bioactivity of the alloy. A simple nanoporous topography on the surface was produced through dealloying the as-solution treated TLM alloy. In contrast, dealloying the as-cold rolled alloy created a hierarchical micro/nanoporous topography. SEM and XPS were performed to characterize the topography and element chemistry of both porous structures. The roughness, hydrophilicity, protein adsorption, cell adhesion, proliferation, and osteogenic differentiation were tested. The elements of Zr, Mo, Sn, and Nb were depleted at the nanoporous TLM surface with a diameter of 15.6 ± 2.3 nm. Dissolving the microscale α phase from the alloy surface contributed to the formation of the microscale grooves on the surface. The simple nanoporous topographical surface exhibited hydrophilicity and higher protein adsorption ability, which facilitated the early adhesion of osteoblasts compared with the hierarchical micro/nanoporous surface. On the other hand, the hierarchical micro/nanoporous surface improved cell proliferation and differentiation and still retained the contact guidance function, which implied good bonding for osseointegration. This research revealed the effect of phase composition on the surface morphology of dealloying titanium alloy and the synergistic effect of micron and nanometer topography on the function of osteoblasts. This paper therefore provides insights into the surface topological design of titanium-based biomaterials with improved biocompatibility.

Recent Development in Beta Titanium Alloys for Biomedical Applications

β-type titanium (Ti) alloys have attracted a lot of attention as novel biomedical materials in the past decades due to their low elastic moduli and good biocompatibility. This article provides a broad and extensive review of β-type Ti alloys in terms of alloy design, preparation methods, mechanical properties, corrosion behavior, and biocompatibility. After briefly introducing the development of Ti and Ti alloys for biomedical applications, this article reviews the design of β-type Ti alloys from the perspective of the molybdenum equivalency (Moeq) method and DV-Xα molecular orbital method. Based on these methods, a considerable number of β-type Ti alloys are developed. Although β-type Ti alloys have lower elastic moduli compared with other types of Ti alloys, they still possess higher elastic moduli than human bones. Therefore, porous β-type Ti alloys with declined elastic modulus have been developed by some preparation methods, such as powder metallurgy, additive manufacture and so on. As reviewed, β-type Ti alloys have comparable or even better mechanical properties, corrosion behavior, and biocompatibility compared with other types of Ti alloys. Hence, β-type Ti alloys are the more suitable materials used as implant materials. However, there are still some problems with β-type Ti alloys, such as biological inertness. As such, summarizing the findings from the current literature, suggestions forβ-type Ti alloys with bioactive coatings are proposed for the future development.

New Zr-25Ti-xMo alloys for dental implant application: Properties characterization and surface analysis

A series of Zr-25Ti-xMo (x = 0, 2.5, 5, 7.5, 10 and 12.5 wt %) as-cast alloys were designed to advance a new-brand Zr-based alloy with low Young's elastic, moderate compression strength, superior corrosion resistance and good wear behavior for the application of dental implant materials. In the present study, the microstructures of the alloys were evaluated by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The microhardness and uniaxial compression measurement were performed to evaluate the mechanical properties of the alloys. The electrochemical behaviors of the alloys was investigated in artificial saliva solution. The friction and wear performances of the Zr-25Ti-xMo alloys were examined by pin-on-disk under the load of 15 N. The results shows that the crystalline structure transforms from hexagonal close-pack (α phase, x = 0 wt %) to body-centered cubic structure (β phase, 5 ≤ x ≤ 12.5 wt %) through a α + β dual-phase region (x = 2.5 wt %). They exhibits excellent mechanical properties with low elastic modulus (from 17.7 to 24.4 GPa) and moderate compression strength (from 1154.4 to 1310.8 MPa). The Zr-25Ti-xMo alloys possess good corrosion resistance due to the formation of a protective passive film consisting mainly of ZrO₂, TiO₂ and minor MoO₃. Especially, the polarization curves demonstrates that the Zr-25Ti-7.5Mo alloy has a wider passive region than the other five alloys and it possesses the lower corrosion current density and corrosion rate. Furthermore, this alloy exhibits good abrasion resistance with the lowest coefficients of friction and volume wear loss. Thus, the Zr-25Ti-7.5Mo alloy has a combination of excellent mechanical properties such as low elastic modulus, moderate yield strength and the compression strength, good electrochemical stability and well wear resistance, it is considered a promising candidate for orthopedic materials as dental implant.

Investigation on ultrasonic cavitation erosion of TiMo and TiNb alloys in sulfuric acid solution

Two kinds of Ti-alloys, i.e., TiMo and TiNb alloys are manufactured in this paper, and their ultrasonic cavitation erosion behaviors in 0.1 M H₂SO₄ solution are evaluated by the mean depth erosion (MDE), SEM and white light photograph. The results show that MDE of TiMo and TiNb alloys obviously increase with increasing the cavitation erosion time, however, they evidently decrease with the increment of Mo or Nb content at each fixed cavitation erosion time, and even some large blank areas (uneroded areas) still exist on the sample surface after ultrasonic cavitation erosion for 2 h in the case of Ti10Mo and Ti20Nb samples, implying the enhanced anti-cavitation erosion property of Ti-alloy by adding Mo or Nb element. The MDE of Ti10Mo or Ti20Nb sample is lower than that of TC4 sample in the case of each cavitation erosion time, indicating the better cavitation erosion resistance of of Ti10Mo or Ti20Nb sample. The influences of Mo and Nb on the passivity of TiMo and TiNb alloys during the ultrasonic cavitation erosion are detected by potentiodynamic curves. The results display that Ti, TC4, TixMo (x = 1, 5, 10) and TixNb (x = 5, 10, 20) samples are all almost in the passive state within the potential region from 0V_SCE to 1.5V_SCE during ultrasonic cavitation erosion, and the passive current density evidently decreases with increasing Mo or Nb content, indicating the enhanced passive characteristic by adding Mo or Nb alloys during the ultrasonic cavitation erosion.

Tribocorrosion behaviour of pure titanium in bovine serum albumin solution: A multiscale study

Tribocorrosion behaviour of pure titanium in phosphate buffer saline (PBS) solution has been investigated systematically as a function of surface chemistry and bovine serum albumin (BSA) content in the solution. A ball-on-disk tribometer coupled with an electrochemical cell was used to study the effect of electrochemical conditions (i.e. anodic and cathodic applied potentials, as well as at open circuit potential) on the tribocorrosion response of titanium. It was found that the main material loss is due to mechanical wear caused by plastic deformation. The mechanical wear was higher under anodic conditions than under cathodic, partially due to an increased presence of debris particles at the sliding interface that act as third bodies. The effect of BSA on the interaction between alumina and titanium, as well as the behaviour of third bodies during the mechanical wear, were investigated in the nanoscale level using atomic force microscopy based force spectroscopy. It was found that the presence of BSA affects tribocorrosion in various ways. Firstly, it increases the repassivation rate of the oxide film by inhibiting the cathodic reactions and accelerating the anodic reactions. Secondly, it increases the mechanical wear by increasing the adhesion of debris onto the sliding interface, while at anodic conditions it increases the rolling efficiency of the debris particles that further enhances the mechanical wear.

On the Corrosion Behaviour of Low Modulus Titanium Alloys for Medical Implant Applications: A Review

The corrosion behaviour of new generation titanium alloys (β-type with low modulus) for medical implant applications is of paramount importance due to their possible detrimental effects in the human body such as release of toxic metal ions and corrosion products. In spite of remarkable advances in improving the mechanical properties and reducing the elastic modulus, limited studies have been done on the electrochemical corrosion behaviour of various types of low modulus titanium alloys including the effect of different beta-stabilizer alloying elements. This development should aim for a good balance between mechanical properties, design features, metallurgical aspects and, importantly, corrosion resistance. In this article, we review several significant factors that can influence the corrosion resistance of new-generation titanium alloys such as fabrication process, body electrolyte properties, mechanical treatments, alloying composition, surface passive layer, and constituent phases. The essential factors and their critical features are discussed. The impact of various amounts of α and β phases in the microstructure, their interactions, and their dissolution rates on the surface passive layer and bulk corrosion behaviour are reviewed and discussed in detail. In addition, the importance of different corrosion types for various medical implant applications is addressed in order to specify the significance of every corrosion phenomenon in medical implants.

Effect of DC Plasma Electrolytic Oxidation on Surface Characteristics and Corrosion Resistance of Zirconium

Zr is a valve metal, the biocompatibility of which is at least on par with Ti. Recently, numerous attempts of the formation of bioactive coatings on Zr by plasma electrolytic oxidation (PEO) in solutions that were based on calcium acetate and calcium β-glycerophosphate were made. In this study, the direct current (DC) PEO of commercially pure zirconium in the solutions that contained Ca(H₂PO₂)₂, Ca(HCOO)₂, and Mg(CH₃COO)₂ was investigated. The treatment was conducted at 75 mA/cm² up to 200, 300, or 400 V. Five process stages were discerned. The treatment at higher voltages resulted in the formation of oxide layers that had Ca/P or (Mg+Ca)/P ratios that were close to that of hydroxyapatite (Ca/P = 1.67), determined by SEM/EDX. The corrosion resistance studies were performed using electrochemical impedance spectroscopy (EIS) and DC polarization methods. R(Q[R(QR)]) circuit model was used to fit the EIS data. In general, the coatings that were obtained at 200 V were the most corrosion resistant, however, they lacked the porous structure, which is typical for PEO coatings, and is sought after in the biomedical applications. The treatment at 400 V resulted in the formation of the coatings that were more corrosion resistant than those that were obtained at 300 V. This was determined mainly by the prevailing plasma regime at the given process voltage. The pitting resistance of Zr was also improved by the treatment, regardless of the applied process conditions.

Surface Characterization, Corrosion Resistance and in Vitro Biocompatibility of a New Ti-Hf-Mo-Sn Alloy

A new superelastic Ti-23Hf-3Mo-4Sn biomedical alloy displaying a particularly large recovery strain was synthesized and characterized in this study. Its native passive film is very thick (18 nm) and contains very protective TiO_2, Ti₂O₃, HfO₂, MoO₂, and SnO₂ oxides (XPS analysis). This alloy revealed nobler electrochemical behavior, more favorable values of the corrosion parameters and open circuit potentials in simulated body fluid in comparison with commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy taken as reference biomaterials in this study. This is due to the favorable influence of the alloying elements Hf, Sn, Mo, which enhance the protective properties of the native passive film on alloy surface. Impedance spectra showed a passive film with two layers, an inner, capacitive, barrier, dense layer and an outer, less insulating, porous layer that confer both high corrosion resistance and bioactivity to the alloy. In vitro tests were carried out in order to evaluate the response of Human Umbilical Vein Endothelial Cells (HUVECs) to Ti-23Hf-3Mo-4Sn alloy in terms of cell viability, cell proliferation, phenotypic marker expression and nitric oxide release. The results indicate a similar level of cytocompatibility with HUVEC cells cultured on Ti-23Hf-3Mo-4Sn substrate and those cultured on the conventional CP-Ti and Ti-6Al-4V metallic materials.

Effect of anodization on the surface characteristics and electrochemical behaviour of zirconium in artificial saliva

The paper is focused on elaboration of ZrO2 films on pure zirconium via anodizing in phosphoric acid with and without fluoride at constant potentials of 30 V and 60 V. The structure and composition of the films were investigated using scanning electronic microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The composition of the oxides formed at both potentials can be identified as monoclinic ZrO2. In addition to Zr and O, the layers formed in phosphoric acid contain phosphorus originating from the phosphoric acid. When the phosphoric acid solution contains NaF, fluorine is also incorporated into the oxide layer. The oxides formed at a higher voltage have greater roughness than those formed at 30 V. Anodized samples exhibit smaller current densities during anodic polarization compared to the as-received zirconium covered with native oxide.

Corrosion behavior of Ti-39Nb alloy for dentistry

To increase an orthopedic implant's lifetime, researchers are now concerned on the development of new titanium alloys with suitable mechanical properties (low elastic modulus-high fatigue strength), corrosion resistance and good workability. Corrosion resistance of the newly developed titanium alloys should be comparable with that of pure titanium. The effect of medical preparations containing fluoride ions represents a specific problem related to the use of titanium based materials in dentistry. The aim of this study was to determine the corrosion behavior of β titanium alloy Ti-39Nb in physiological saline solution and in physiological solution containing fluoride ions. Corrosion behavior was studied using standard electrochemical techniques and X-ray photoelectron spectroscopy. It was found that corrosion properties of the studied alloy were comparable with the properties of titanium grade 2. The passive layer was based on the oxides of titanium and niobium in several oxidation states. Alloying with niobium, which was the important part of the alloy passive layer, resulted in no significant changes of corrosion behavior. In the presence of fluoride ions, the corrosion resistance was higher than the resistance of titanium.

Tribocorrosion behavior of beta titanium biomedical alloys in phosphate buffer saline solution

The tribo-electrochemical behavior of different β titanium alloys for biomedical applications sintered by powder metallurgy has been investigated. Different mechanical, electrochemical and optical techniques were used to study the influence of the chemical composition, Sn content, and the electrochemical conditions on the tribocorrosion behavior of those alloys Ti30NbxSn alloys (where "x" is the weight percentage of Sn content, 2% and 4%). Sn content increases the active and passive dissolution rate of the titanium alloys, thus increasing the mechanically activated corrosion under tribocorrosion conditions. It also increases the mechanical wear of the alloy. Prevailing electrochemical conditions between -1 and 2V influences the wear accelerated corrosion by increasing it with the applied potential and slightly increases the mechanical wear of Ti30Nb4Sn. Wear accelerated corrosion can be predicted by existing models as a function of electrochemical and mechanical parameters of the titanium alloys.

Quaternary Ti-20Nb-10Zr-5Ta alloy during immersion in simulated physiological solutions: formation of layers, dissolution and biocompatibility

Samples of the quaternary Ti-20Nb-10Zr-5Ta alloy were immersed in Hanks' simulated physiological solution and in minimum essential medium (MEM) for 25 days. Samples of Ti metal served as controls. During immersion, the concentration of ions dissolved in MEM was measured by inductively coupled plasma mass spectrometry, while at the end of the experiment the composition of the surface layers was analyzed by X-ray photoelectron spectroscopy, and their morphology by scanning electron microscopy equipped for chemical analysis. The surface layer formed during immersion was comprised primarily of TiO2 but contained oxides of alloying elements as well. The degree of oxidation differed for different metal cations; while titanium achieved the highest valency, tantalum remained as the metal or is oxidized to its sub-oxides. Calcium phosphate was formed in both solutions, while formation of organic-related species was observed only in MEM. Dissolution of titanium ions was similar for metal and alloy. Among alloying elements, zirconium dissolved in the largest quantity. The long-term effects of alloy implanted in the recipient's body were investigated in MEM, using two types of human cells-an osteoblast-like cell line and immortalized pulmonary fibroblasts. The in vitro biocompatibility of the quaternary alloy was similar to that of titanium, since no detrimental effects on cell survival, induction of apoptosis, delay of growth, or change in alkaline phosphatase activity were observed on incubation in MEM.