Effects of phase constitution on magnetic susceptibility and mechanical properties of Zr-rich Zr-Mo alloys

Nanoscale osseointegration of zirconia evaluated from the interfacial structure between ceria-stabilized tetragonal zirconia and cell-induced hydroxyapatite

BACKGROUND

The osseointegration of zirconia implants has been evaluated based on their implant fixture bonding with the alveolar bone at the optical microscopic level. Achieving nano-level bonding between zirconia and bone apatite is crucial for superior osseointegration; however, only a few studies have investigated nanoscale bonding. This review outlines zirconia osseointegration, including surface modification, and presents an evaluation of nanoscale zirconia-apatite bonding and its structure.

HIGHLIGHT

Assuming osseointegration, the cells produced calcium salts on a ceria-stabilized zirconia substrate. We analyzed the interface between calcium salts and zirconia substrates using transmission electron microscopy and found that 1) the cell-induced calcium salts were bone-like apatite and 2) direct nanoscale bonding was observed between the bone-like apatite and zirconia crystals without any special modifications of the zirconia surface.

CONCLUSION

Structural affinity exists between bone apatite and zirconia crystals. Apatite formation can be induced by the zirconia surface. Zirconia bonds directly with apatite, indicating superior osseointegration in vivo.

Electrospun PCL Wires Loaded with Vancomycin on Zirconium Substrate

The current study presents research about electrodeposition in relation to electrospinning PCL wires on a Zr substrate and loading the coating with vancomycin. The structural composition of the coatings was investigated via FT-IR analysis. The morphology evaluated using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, for the composition (SEM-EDS), evidenced the presence of the polymer wires, with and without drug vancomycin loading. The wettability of the coatings was evaluated from the hydrophobic-hydrophilic point of view, and the characterization was completed with mechanical and electrochemical tests. All the electrochemical tests performed in simulated body fluid highlighted that PCL represents a barrier against corrosion processes. The quantitative method to evaluate the loading efficiency shows that almost 80% of the total loaded vancomycin is released within 144 h; after the initial burst at 24 h, a steady release of vancomycin is observed over 7 days. A kinetic model of the drug release was also constructed.

Advancing dental implants: Bioactive and therapeutic modifications of zirconia

Zirconium-based implants have gained popularity in the dental implant field owing to their corrosion resistance and biocompatibility, attributed to the formation of a native zirconia (ZrO₂) film. However, enhanced bioactivity and local therapy from such implants are desirable to enable the earlier establishment and improved long-term maintenance of implant integration, especially in compromised patient conditions. As a result, surface modification of zirconium-based implants have been performed using various physical, chemical and biological techniques at the macro-, micro-, and nano-scales. In this extensive review, we discuss and detail the development of Zr implants covering the spectrum from past and present advancements to future perspectives, arriving at the next generation of highly bioactive and therapeutic nano-engineered Zr-based implants. The review provides in-depth knowledge of the bioactive/therapeutic value of surface modification of Zr implants in dental implant applications focusing on clinical translation.

Athermal ω Phase and Lattice Modulation in Binary Zr-Nb Alloys

To further explore the potential of Zr-based alloys as a biomaterial that will not interfere with magnetic resonance imaging (MRI), the microstructural characteristics of Zr-xat.% Nb alloys (10 ≤ x ≤ 18), particularly the athermal ω phase and lattice modulation, were investigated by conducting electrical resistivity and magnetic susceptibility measurements and transmission electron microscopy observations. The 10 Nb alloy and 12 Nb alloys had a positive temperature coefficient of electrical resistivity. The athermal ω phase existed in 10 Nb and 12 Nb alloys at room temperature. Alternatively, the 14 Nb and 18 Nb alloys had an anomalous negative temperature coefficient of the resistivity. The selected area diffraction pattern of the 14 Nb alloy revealed the co-occurrence of ω phase diffraction and diffuse satellites. These diffuse satellites were represented by gβ + q when the zone axis was [001] or [113], but not [110]. These results imply that these diffuse satellites appeared because the transverse waves consistent with the propagation and displacement vectors were q = <ζ ζ¯ 0>* for the ζ~1/2 and <110> directions. It is possible that the resistivity anomaly was caused by the formation of the athermal ω phase and transverse wave. Moreover, control of the athermal ω-phase transformation and occurrence of lattice modulation led to reduced magnetic susceptibility, superior deformation properties, and a low Young’s modulus in the Zr-Nb alloys. Thus, Zr-Nb alloys are promising MRI-compatible metallic biomaterials.

Evaluation of cytocompatibility and osteoconductivity of Zr-14Nb-5Ta-1Mo alloy with MC3T3-E1 cells

The cytocompatibility and osteoconductivity of the Zr-14Nb-5Ta-1Mo alloy were investigated using a mouse osteoblastic cell line (MC3T3-E1) to promote the application of this newly developed alloy in dental/medical treatment. The initial cell-attached morphology was visualized by fluorescent staining, and cells cultured on the Zr alloy showed similar cell adhesion behavior to cells cultured on titanium (Ti). In our 5-day proliferation investigation, similar cell numbers were obtained with both Zr alloy and Ti. These results indicate that the cytocompatibility of Zr alloy is similar to that of Ti. In addition, the similar results in the evaluation of alkaline phosphatase (ALP) activity and staining of deposited calcium using alizarin red S with both Zr alloy and Ti indicated that the osteoconductivity of the Zr alloy is similar to that of Ti. Our results prove the good cytocompatibility and osteoconductivity of the Zr-14Nb-5Ta-1Mo alloy, enabling its promotion for use in dental/medical applications.

Novel Biocompatible Zr-Based Alloy with Low Young's Modulus and Magnetic Susceptibility for Biomedical Implants

The microstructure, mechanical properties, magnetic susceptibility, electrochemical corrosion performance, in vitro cell compatibility and blood consistency of Zr-16Nb-xTi (x = 0, 4, 8, 12 and 16 wt.%) materials were investigated as potential materials for biomedical implants. X-ray diffraction (XRD) and Transmission electron microscopy (TEM) analyses revealed the secondary phase martensite α' formed during the quenching process. The phase composition contained metastable β and martensite α', resulting from Ti addition. These phase constitutions were the main causes of a low Young's modulus and magnetic susceptibility. The in vitro cytocompatibility analysis illustrated that the MG63 cells maintained high activity (from 91% to 97%) after culturing in Zr-16Nb-xTi extraction media for 12 days due to the high internal biocompatibility of Zr, Nb and Ti elements, as well as the optimal corrosion resistance of Zr-16Nb-xTi. On the basis of Inductively coupled plasma optical emission spectrometry (ICP-OES) ion release studies, the concentration of Zr, Nb and Ti was noted to reach the equipment detective limit of 0.001 mg/L, which was much lower than pure Ti. With respect to the corrosion behavior in Hank's solution, Zr-16Nb-16Ti displayed superior properties, possessing the lowest corrosion current density and widest passivation region, attributed to the addition of Ti. The blood compatibility test illustrated that the Zr-16Nb-xTi materials were nonhemolytic, and the platelets maintained a spherical shape, with no aggregation or activation on Zr-16Nb-xTi. Overall, Ti addition has obvious effects on the developed Zr-16Nb-xTi alloys, and Zr-16Nb-4Ti exhibited low magnetic susceptibility, low modulus, good biocompatibility and proper corrosion properties, demonstrating the potential of use as implant biomaterials.

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.

Appraising the potential of Zr-based biomedical alloys to reduce magnetic resonance imaging artifacts

This study compared Zr-Mo alloys with commercial metallic biomaterials. It was observed that the Zr-Mo alloys exhibited favourable mechanical properties, particularly the Zr-10Mo alloy, which showed the highest strength to Young's modulus ratio among all evaluated metals. These alloys also exhibited the lowest magnetic susceptibilities, which are important for magnetic resonance imaging (MRI). However, both Zr- and Ti-based metals yielded comparable artifacts. It was concluded that the magnetic susceptibility must differ considerably to afford significantly improved MRI quality owing to the increased importance of non-susceptibility-related artifacts when comparing materials with relatively similar magnetic susceptibilities.

Torque property of titanium alloy cerebral aneurysm clips in a magnetic resonance scanner

Titanium (Ti) alloys have been introduced in magnetic resonance (MR) safe implantable medical devices because the susceptibility of Ti is approximately 1/10 that of the Co-Cr-Ni alloy (Elgiloy), which was the previously preferred MR-safe material. The torque applied to metallic materials in an MR imaging (MRI) scanner is commonly believed to increase with the susceptibility of the material. However, a visual inspection showed that the torque applied to Ti alloy cerebral aneurysm clips is comparable with that in the case of those of Elgiloy. In this study, we measured the torque applied to the small test pieces of rods and aneurysm clips quantitatively in a 3-T MRI using an accurate self-developed torque measurement apparatus. The maximum torques of Ti alloy and Elgiloy rod test pieces were comparable as 1.1 and 1.2 µN·m, respectively. The values for Ti alloy aneurysm clips were distinctly higher than the values for those of Elgiloy. These contradictory results of a larger torque for smaller-susceptibility products could be explained by our new theory, which takes into account the crystal susceptibility anisotropy in addition to the conventional torque due to the shape anisotropy.

Reduction of magnetic resonance image artifacts of NiTi implant by carbon coating

A paramagnetic NiTi substrate was coated with diamagnetic carbon materials, i.e., graphene, graphene oxide (GO), and carbon nanotubes (CNTs), in order to reduce magnetic resonance (MR) image artifacts of NiTi implants. The present study focused on the effect of magnetic susceptibility variations in NiTi caused by the carbon coating on MR image artifacts. In the case of the graphene and GO coatings, the reduction of the magnetic susceptibility was greater along the perpendicular direction than the parallel direction. In contrast, the CNT coating exhibited a larger reduction along the parallel direction. The reduction of magnetic susceptibility measured in CNT-coated NiTi (CNT/NiTi) was smaller than the theoretical prediction especially when measured along the parallel direction, because CNTs on the NiTi surface were randomly arranged, rather than in a single direction. MR image artifacts were substantially reduced in all carbon-coated NiTi specimens, which is due to the reduction of magnetic susceptibility in NiTi by the carbon coating. This method can also be applied to other paramagnetic bio-metallic materials such as Co-Cr.

Synthesis, spectral and extended spectrum beta-lactamase studies of transition metal tetraaza macrocyclic complexes

Urinary tract infections commonly occur in humans due to microbial pathogens invading the urinary tract, which can bring about a range of clinical symptoms and potentially fatal sequelae. The present study is aimed at addressing the development of a new antimicrobial agent against extended spectrum beta lactamase (ESBL) producing E. coli bacteria. We have synthesised some biologically potent (NNNN) donor macrocycles (L ₁  = dibenzo[f,n]dipyrido[3,4-b:4',3'-j][1,4,9,12]tetraazacyclohexadecine-6,11,18,23(5H,12H, 7H, 24H)-tetraone, and L ₂  = 6,12,19,25-tetraoxo-4,6,11,12,16,18,23,24-octahydrotetrabenzo [b,g,k,p][1,5,10,14]tetra azacyclooctadecine-2,13-dicarboxylic acid) and their Ti and Zr metal complexes in alcoholic media using microwave protocol. Macrocyclic ligands were synthesised by incorporating of 3,5-diaminobenzoic acid, phthalic acid and 3,4-diaminopyridine in 1:1:1 molar ratio. The macrocyclic ligands and their metal complexes have been characterised by elemental analysis, conductance measurement, magnetic measurement and their structure configurations have been determined by various spectroscopic (FTIR, ¹H/¹³C NMR, UV-Vis, LC-MS mass, XRD and TGA) techniques. [ZrL₂Cl₂]Cl₂ metal complex shows excellent antibacterial activity against ESBLs. A zone of inhibition and minimum inhibitory concentration was determined by McFarland and the dilution method, respectively. The spectral studies confirm the binding sites of the nitrogen atom of the macrocycles. An octahedral geometry has been assigned to the metal complexes based on the findings.

MRI compatibility of several early transition metal based alloys and its influencing factors

Magnetic resonance imaging (MRI) compatibility of three early transition metal (ETM) based alloys was assessed in vitro with agarose gel as a phantom, including Zr-20Nb, near-equiatomic (TiZrNbTa)₉₀ Mo₁₀ and Nb-60Ta-2Zr, together with pure tantalum and L605 Co-Cr alloy for comparison. The artifact extent in the MR image was quantitatively characterized according to the maximum area of 2D images and the total volume in reconstructed 3D images with a series of slices under acquisition by fast spin echo (FSE) sequence and gradient echo (GRE) sequence. It was indicated that the artifacts extent of L605 Co-Cr alloy with a higher magnetic susceptibility (χ_v ) was approximately 3-fold greater than that of the ETM-based alloys with χ_v in the range of 160-250 ppm. In the ETM group, the MRI compatibility of the materials can be ranked in a sequence of Zr-20Nb, pure tantalum, (TiZrNbTa)₉₀ Mo₁₀ and Nb-60Ta-2Zr. In addition, using a rabbit cadaver with the implanted tube specimens as a model for ex vivo assessment, it was confirmed that the artifact severity of Nb-60Ta-2Zr alloy is significantly reduced in comparison with the L605 alloy. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 377-385, 2018.

Magnetic susceptibility, artifact volume in MRI, and tensile properties of swaged Zr-Ag composites for biomedical applications

Zr-Ag composites were fabricated to decrease the magnetic susceptibility by compensating for the magnetic susceptibility of their components. The Zr-Ag composites with a different Zr-Ag ratio were swaged, and their magnetic susceptibility, artifact volume, and mechanical properties were evaluated by magnetic balance, three-dimensional (3-D) artifact rendering, and a tensile test, respectively. These properties were correlated with the volume fraction of Ag using the linear rule of mixture. We successfully obtained the swaged Zr-Ag composites up to the reduction ratio of 96% for Zr-4, 16, 36, 64Ag and 86% for Zr-81Ag. However, the volume fraction of Ag after swaging tended to be lower than that before swaging, especially for Ag-rich Zr-Ag composites. The magnetic susceptibility of the composites linearly decreased with the increasing volume fraction of Ag. No artifact could be estimated with the Ag volume fraction in the range from 93.7% to 95.4% in three conditions. Young's modulus, ultimate tensile strength (UTS), and 0.2% yield strength of Zr-Ag composites showed slightly lower values compared to the estimated values using a linear rule of mixture. The decrease in magnetic susceptibility of Zr and Ag by alloying or combining would contribute to the decrease of the Ag fraction, leading to the improvement of mechanical properties.

Differences in the calcification of preosteoblast cultured on sputter-deposited titanium, zirconium, and gold

In this study, osteogenic differentiation and calcification of preosteoblast (MC3T3-E1) cultured on sputter-deposited titanium (Ti), zirconium (Zr), and gold (Au) on cover glasses were evaluated to understand the differences in bone formation ability among these three metals; these metals show the same high corrosion resistance, but Ti and Zr are covered by surface passive oxide film while Au is not covered by the oxide film. Ti and Zr promoted cellular proliferation without osteogenic differentiation. Cells cultured on Ti and Zr expressed higher levels of Runx2, Col1α1, and Akp2 at an earlier stage, which indicated faster promotion of osteogenic differentiation, as compared to those cultured on Au. Moreover, after 21 days of culture, the Bglap1 and Ifitm5 expression peaks in cells cultured on Ti and Zr were higher than those in cells cultured on Au, which indicated faster promotion of calcification. Cells cultured on Ti showed an advantage in osteogenic differentiation at an early stage, while cells on Zr showed better calcification promotion with a long-term culture. The amount of extracellular calcified deposits was in good agreement with the gene expression results. On the other hand, the intracellular calcium content of cells on Au specimens was higher than that of cells on Ti and Zr specimens. The results indicate that preosteoblasts on Ti and Zr showed faster osteogenic differentiation and calcification than those on Au, whereas Au improved the intracellular calcium content. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 639-651, 2016.

Evaluation of the shear bond strength of dental porcelain and the low magnetic susceptibility Zr-14Nb alloy

The aim of this study was to investigate the bond strength of dental porcelain and the preheated Zr-14Nb alloy, and compare this strength with that of titanium. White oxide layers, which were predominantly composed of monoclinic zirconia, were formed on the preheated sample groups, and exhibited a greater roughness than the control samples. At the metal-ceramic interface, a greater Nb diffusion range was observed than in the control samples. The bond strengths of the samples subjected to 20min preheating treatment were the lowest (33.6 ± 3.2 MPa), which may be ascribed to the formation of a brittle thick oxide layer under excessive heat treatment. The samples subjected to this heat treatment for 5 min exhibited the highest mean bond strength (43.7 ± 5.9 MPa), which was significantly higher than that of titanium (35.3 ± 3.5 MPa). Thus, the Zr-14Nb alloy is a promising candidate for fixed dental prosthesis, as long as the appropriate treatment conditions are adopted.

Surface characteristics and castability of Zr-14Nb alloy dental castings

The purpose of this study was to evaluate mechanical properties, surface characteristics and castability of Zr-14Nb dental castings. The mean 0.2% proof and ultimate tensile strengths of Zr-14Nb were approximately 68% and 76% those of Ti-6Al-7Nb, respectively, while they were comparable to Co-29Cr-6Mo. Elongation of Zr-14Nb was the highest of all alloys tested. The hardened reaction layer was formed on the surfaces of the Zr-14Nb castings. The layer consisted of oxygen and aluminum originating form investment. The castability of Zr-14Nb was comparable to that of Ti-6Al-7Nb. Dental castings of Zr-14Nb reveal mechanical properties that were within the range of the other dental alloys. Further improvements in castability and minimization of the surface reaction layer are needed for applications in dental prostheses.

Fabrication of titanium alloy frameworks for complete dentures by selective laser melting

STATEMENT OF PROBLEM

Casting difficulties have led to the limited use of titanium in dental prostheses. The selective laser melting system was recently developed to fabricate biomedical components from titanium alloys. However, the fabrication of a titanium alloy framework for a maxillary complete denture by selective laser melting has not yet been investigated.

PURPOSE

The purpose of the study was to fabricate thin titanium alloy frameworks for a maxillary complete denture with a selective laser melting system and to evaluate their hardness and microstructure.

MATERIAL AND METHODS

A cast of an edentulous maxilla was scanned with a dental 3-dimensional cone-beam computed tomography system, and standard triangulation language data were produced with the DICOM Viewer (Digital Imaging and Communications in Medicine). Two types of metal frameworks for complete dentures were designed with 3-dimensional computer-aided design software. Two titanium alloy frameworks, SLM-1 and SLM-2, were fabricated from these designs with the selective laser melting system. Plate-shaped specimens were cut from the central flat region of SLM-1, SLM-2, and as-cast Ti-6Al-4V (As-cast). Vickers hardness testing, optical microscopy, and x-ray diffraction measurements were performed.

RESULTS

Thin titanium alloy frameworks for maxillary complete dentures could be fabricated by selective laser melting. The hardness values for SLM-1 and SLM-2 were higher than that for the as-cast specimen. Optical microscopy images of the SLM-1 and SLM-2 microstructure showed that the specimens did not exhibit pores, indicating that dense frameworks were successfully obtained with the selective laser melting process. In the x-ray diffraction patterns, only peaks associated with the α phase were observed for SLM-1 and SLM-2. In addition, the lattice parameters for SLM-1 and SLM-2 were slightly larger than those for the as-cast specimen.

CONCLUSIONS

The mechanical properties and microstructure of the denture frameworks prepared by selective laser melting indicate that these dentures are appropriate for clinical use.

Formation of white oxide layer on Zr-14Nb alloy using thermal treatment

This study aimed to develop a novel abutment material with good esthetic and mechanical properties by producing a white oxide layer on a zirconium-14 mass% niobium (Zr-14Nb) alloy substrate using a thermal oxidation process. Oxidation temperatures ranged 700-1000°C and oxidation time ranged 30-180 min. The color of the oxide layer varied depending on temperature and time. A white oxide layer was obtained under appropriate conditions. The oxide layer thickness increased with increased temperature and time, as revealed by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Moreover, X-ray diffraction and X-ray photoelectron spectroscopy revealed that the oxide layer was predominantly monoclinic ZrO2, tetragonal ZrO2, and Nb2O5. The oxide layer revealed good abrasion resistance and high adhesion to the substrate. This novel process for producing white materials with good mechanical properties will be useful for abutments and prostheses in dental implant treatment.

A Comparative Evaluation between New Ternary Zirconium Alloys as Alternative Metals for Orthopedic and Dental Prosthetic Devices

Purpose

We assessed in vitro the corrosion behavior and biocompatibility of four Zr-based alloys (Zr97.5 Nb1.5 VM1.0 ; VM, valve metal: Ti, Mo, W, Ta; at%) to be used as implant materials, comparing the results with grade-2 titanium, a biocompatible metal standard.

Methods

Corrosion resistance was investigated by open circuit potential and electrochemical impedance spectroscopy measurements as a function of exposure time to an artificial physiological environment (Ringer's solution). Human bone marrow stromal cells were used to evaluate biocompatibility of the alloys and their influence on growth kinetics and cell osteogenic differentiation through histochemical and gene expression analyses.

Results

Open circuit potential values indicated that Zr-based alloys and grade-2 Ti undergo spontaneous passivation in the simulated aggressive environment. High impedance values for all samples demonstrated improved corrosion resistance of the oxide film, with the best protection characteristics displayed by Zr97.5 Nb1.5 Ta1.0. Cells seeded on all surfaces showed the same growth kinetics, although matrix mineralization and alkaline phosphatase activity were maximal on Zr97.5 Nb1.5 Mo1.0 and Zr97.5 Nb1.5 Ta1.0. Markers of ongoing proliferation, however, such as podocalyxin and CD49f, were still overexpressed on Zr97.5 Nb1.5 Mo1.0 even upon osteoinduction. No relevant effects were noted for the CD146-expressing population of bone progenitors. Nonetheless, the presence of a more differentiated cell population on Zr97.5 Nb1.5 Ta1.0 samples was inferable by comparing mineralization data and transcript levels of osteogenic markers (osteocalcin, osteopontin, bone sialoprotein, and RUNX2).

Conclusions

The combination of passivation, corrosion resistance and satisfactory biotolerance to bone progenitors make the Zr-based alloys promising implant materials. Among those we tested, Zr97.5 Nb1.5 Ta1.0 seems to be the most appealing.

Screening on binary Zr-1X (X = Ti, Nb, Mo, Cu, Au, Pd, Ag, Ru, Hf and Bi) alloys with good in vitro cytocompatibility and magnetic resonance imaging compatibility

In this study, the microstructures, mechanical properties, corrosion behaviors, in vitro cytocompatibility and magnetic susceptibility of Zr-1X alloys with various alloying elements, including Ti, Nb, Mo, Cu, Au, Pd, Ag, Ru, Hf and Bi, were systematically investigated to explore their potential use in biomedical applications. The experimental results indicated that annealed Zr-1X alloys consisted entirely or primarily of α phase. The alloying elements significantly increased the strength and hardness of pure Zr and had a relatively slight influence on elastic modulus. Ru was the most effective enhancing element and Zr-1Ru alloy had the largest elongation. The results of electrochemical corrosion indicated that adding various elements to Zr improved its corrosion resistance, as indicated by the reduced corrosion current density. The extracts of the studied Zr-1X alloys produced no significant deleterious effects on osteoblast-like cells (MG 63), indicating good in vitro cytocompatibility. All except for Zr-1Ag alloy showed decreased magnetic susceptibility compared to pure Zr, and Zr-1Ru alloy had the lowest magnetic susceptibility value, being comparable to that of α' phase Zr-Mo alloy and Zr-Nb alloy and far lower than that of Co-Cr alloy and Ti-6Al-4V alloy. Among the experimental Zr-1X alloys, Zr-1Ru alloy possessing high strength coupled with good ductility, good in vitro cytocompatibility and low magnetic susceptibility may be a good candidate alloy for medical devices within a magnetic resonance imaging environment.

An overview of recent advances in designing orthopedic and craniofacial implants

Great deal of research is still going on in the field of orthopedic and craniofacial implant development to resolve various issues being faced by the industry today. Despite several disadvantages of the metallic implants, they continue to be used, primarily because of their superior mechanical properties. In order to minimize the harmful effects of the metallic implants and its by-products, several modifications are being made to these materials, for instance nickel-free stainless steel, cobalt-chromium and titanium alloys are being introduced to eliminate the toxic effects of nickel being released from the alloys, introduce metallic implants with lower modulus, reduce the cost of these alloys by replacing rare elements with less expensive elements etc. New alloys like tantalum, niobium, zirconium, and magnesium are receiving attention given their satisfying mechanical and biological properties. Non-oxide ceramics like silicon nitride and silicon carbide are being currently developed as a promising implant material possessing a combination of properties such as good wear and corrosion resistance, increased ductility, good fracture and creep resistance, and relatively high hardness in comparison to alumina. Polymer/magnesium composites are being developed to improve mechanical properties as well as retain polymer's property of degradation. Recent advances in orthobiologics are proving interesting as well. This paper thus deals with the latest improvements being made to the existing implant materials and includes new materials being introduced in the field of biomaterials.

Three-dimensional quantification of susceptibility artifacts from various metals in magnetic resonance images

Susceptibility artifacts generated in magnetic resonance (MR) images were quantitatively evaluated for various metals using a three-dimensional (3-D) artifact rendering to demonstrate the correlation between magnetic susceptibility and artifact volume. Ten metals (stainless steel, Co-Cr alloy, Nb, Ti, Zr, Mo, Al, Sn, Cu and Ag) were prepared, and their magnetic susceptibilities measured using a magnetic balance. Each metal was embedded in a Ni-doped agarose gel phantom and the MR images of the metal-containing phantoms were taken using 1.5 and 3.0 T MR scanners under both fast spin echo and gradient echo conditions. 3-D renderings of the artifacts were constructed from the images and the artifact volumes were calculated for each metal. The artifact volumes of metals decreased with decreasing magnetic susceptibility, with the exception of Ag. Although Sn possesses the lowest absolute magnetic susceptibility (1.8×10(-6)), the artifact volume from Cu (-7.8×10(-6)) was smaller than that of Sn. This is because the magnetic susceptibility of Cu was close to that of the agarose gel phantom (-7.3×10(-6)). Since the difference in magnetic susceptibility between the agarose and Sn is close to that between the agarose and Ag (-17.5×10(-6)), their artifact volumes were almost the same, although they formed artifacts that were reversed in all three dimensions.

Magnetic susceptibility and hardness of Au-xPt-yNb alloys for biomedical applications

Metal devices in the human body induce serious metal artifacts in magnetic resonance imaging (MRI). Metals artifacts are mainly caused by a volume magnetic susceptibility (χv) mismatch between a metal device and human tissue. In this research, Au-xPt-yNb alloys were developed for fabricating MRI artifact-free biomedical metal devices. The magnetic properties, hardness and phase constitutions of these alloys were investigated. The Au-xPt-8Nb alloys showed satisfactory χv values. Heat treatments did not clearly change the χv values for Au-xPt-8Nb alloys. The Vickers hardness (HV) of these two alloys was much higher than that of high-Pt alloys; moreover, aging at 700°C increased the HV values of these two alloys. A dual phase structure consisting of face-centered cubic α1 and α2 phases was observed and aging at 700°C promoted phase separation. The Au-5Pt-8Nb and Au-10Pt-8Nb alloys showed satisfactory χv values and high hardness and are thus suggested as candidates for MRI artifact-free alloys for biomedical applications.

Microstructure, mechanical property, corrosion behavior, and in vitro biocompatibility of Zr-Mo alloys

In this study, the microstructure, mechanical properties, corrosion behaviors, and in vitro biocompatibility of Zr-Mo alloys as a function of Mo content after solution treatment were systemically investigated to assess their potential use in biomedical application. The experimental results indicated that Zr-1Mo alloy mainly consisted of an acicular structure of α' phase, while ω phase formed in Zr-3Mo alloy. In Zr-5Mo alloy, retained β phase and a small amount of precipitated α phase were observed. Only the retained β phase was obtained in Zr-10Mo alloy. Zr-1Mo alloy exhibited the greatest hardness, bending strength, and modulus among all experimental Zr-Mo alloys, while β phase Zr-10Mo alloy had a low modulus. The results of electrochemical corrosion indicated that adding Mo into Zr improved its corrosion resistance which resulted in increasing the thermodynamic stability and passivity of zirconium. The cytotoxicity test suggested that the extracts of the studied Zr-Mo alloys produced no significant deleterious effect to fibroblast cells (L-929) and osteoblast cells (MG 63), indicating an excellent in vitro biocompatibility. Based on these facts, certain Zr-Mo alloys potentially suitable for different biomedical applications were proposed.

Development of new metallic alloys for biomedical applications

New low modulus β-type titanium alloys for biomedical applications are still currently being developed. Strong and enduring β-type titanium alloy with a low Young's modulus are being investigated. A low modulus has been proved to be effective in inhibiting bone atrophy, leading to good bone remodeling in a bone fracture model in the rabbit tibia. Very recently β-type titanium alloys with a self-tunable modulus have been proposed for the construction of removable implants. Nickel-free low modulus β-type titanium alloys showing shape memory and super elastic behavior are also currently being developed. Nickel-free stainless steel and cobalt-chromium alloys for biomedical applications are receiving attention as well. Newly developed zirconium-based alloys for biomedical applications are proving very interesting. Magnesium-based or iron-based biodegradable biomaterials are under development. Further, tantalum, and niobium and its alloys are being investigated for biomedical applications. The development of new metallic alloys for biomedical applications is described in this paper.