Effects of Combining Docosahexaenoic Acid and Eicosapentaenoic Acid with Sesame Lignan on Vascular Endothelial Function.

Vascular endothelial cells produce vasoactive substances, such as nitric oxide (NO), to regulate vascular relaxation and contraction. Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) enhance NO production in endothelial cells, and sesamin, a sesame lignan contained in sesame seeds, also promotes NO production. This study examined DHA, EPA, and sesamin's combined effects since it was expected that combining them would further enhance NO production in endothelial cells. Using a human umbilical vein endothelial cell (HUVEC), the NO amount secreted in the culture supernatant was analyzed. Sesamin metabolite (SC1) was used in the experiments because it is a major metabolite in human blood after sesamin absorption. When cells were treated with DHA or EPA alone, they increased NO production in a concentration-dependent manner, whereas no change in NO production was observed for SC1. NO production increased when DHA and EPA were treated in combination with SC1, although the low DHA and EPA concentrations showed no difference in NO production. In the concentrations in which the combined effect was observed, SC1 activated eNOS via calcium signaling, whereas DHA and EPA activated eNOS via alterations in the membrane lipid environment. The combined effect of the two pathways was considered to have enhanced the eNOS activity. These results suggested that combining DHA, EPA, and sesamin might improve vascular endothelial function.

Effects of Long-Chain Polyunsaturated Fatty Acids in Combination with Lutein and Zeaxanthin on Episodic Memory in Healthy Older Adults.

Arachidonic acid (ARA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), which are long-chain polyunsaturated fatty acids (LCPUFAs), as well as lutein (L) and zeaxanthin (Z), can potentially improve brain function. However, the effect of a combination of these components (LCPUFAs + LZ) on memory function in healthy older individuals remains unclear. This study aimed to determine if LCPUFAs + LZ-supplemented food could improve memory function. Exploratory and confirmatory trials (Trials 1 and 2, respectively) were conducted in healthy older Japanese individuals with memory complaints. We conducted randomized, double-blind, placebo-controlled, parallel-group trials. Participants were randomly allocated to two groups: placebo or LCPUFAs + LZ. LCPUFAs + LZ participants were provided with supplements containing ARA, DHA, EPA, L, and Z for 24 weeks in Trial 1 and 12 weeks in Trial 2. Memory functions were evaluated using Cognitrax before and after each trial. Combined analyses were performed for subgroups of participants with cognitive decline in Trials 1 and 2. The results showed that supplementation with LCPUFAs + LZ did not significantly affect memory function in healthy, non-demented, older individuals with memory complaints whereas it improved memory function in healthy, non-demented, older individuals with cognitive decline.

l-Anserine Increases Muscle Differentiation and Muscle Contractility in Human Skeletal Muscle Cells.

l-Anserine, an imidazole peptide, has a variety of physiological activities, but its effects on skeletal muscle differentiation and muscle contractile force remain unknown. Thus, in this study, we investigated the effect of l-anserine on muscle differentiation and muscle contractile force in human skeletal muscle cells. In two-dimensional culture, 1 µM l-anserine significantly increased the myotube diameters (26.5 ± 1.71, 27.7 ± 1.08, and 28.8 ± 0.85 µm with 0, 0.1, and 1 µM l-anserine, respectively) and the expression levels of genes involved in muscle differentiation and the sarcomere structure. In three-dimensional culture, 1 µM l-anserine significantly increased the contractile force of engineered human skeletal muscle tissues cultured on a microdevice (1.99 ± 0.30, 2.17 ± 0.62, 2.66 ± 0.39, and 3.28 ± 0.85 µN with 0, 0.1, 0.5, and 1 µM l-anserine, respectively). l-Anserine also increased the myotube diameters and the proportion of myotubes with sarcomere structures in the cultured tissues. Furthermore, the histamine receptor 1 (H1R) antagonist attenuated the l-anserine-induced increase in the contractile force, suggesting the involvement of H1R in the mechanism of action of l-anserine. This study showed for the first time that l-anserine enhances muscle differentiation and muscle contractility via H1R.

Sesamin Metabolites Suppress the Induction of Cellular Senescence.

Cellular senescence induces inflammation and is now considered one of the causes of organismal aging. Accumulating evidence indicates that age-related deterioration of mitochondrial function leads to an increase in reactive oxygen species (ROS) and DNA damage, which in turn causes cellular senescence. Thus, it is important to maintain mitochondrial function and suppress oxidative stress in order to inhibit the accumulation of senescent cells. Sesamin and its isomer episesamin are types of lignans found in sesame oil, and after being metabolized in the liver, their metabolites have been reported to exhibit antioxidant properties. However, their effects on cellular senescence remain unknown. In this study, the effects of sesamin, episesamin, and their metabolites SC1 and EC1-2 on replicative senescence were evaluated using human diploid lung fibroblasts, and TIG-3 cells. The results showed that sesamin and episesamin treatment had no effect on proliferative capacity compared to the untreated late passage group, whereas SC1 and EC1-2 treatment improved proliferative capacity and mitigated DNA damage of TIG-3 cells. Furthermore, other cellular senescence markers, such as senescence-associated secretory phenotype (SASP), mitochondria-derived ROS, and mitochondrial function (ROS/ATP ratio) were also reduced by SC1 and EC1-2 treatment. These results suggest that SC1 and EC1-2 can maintain proper mitochondrial function and suppress the induction of cellular senescence.

Effects of Quercetin Glycoside Supplementation Combined With Low-Intensity Resistance Training on Muscle Quantity and Stiffness: A Randomized, Controlled Trial.

Objective: Aging of skeletal muscle is characterized not only by a decrease of muscle quantity but also by changes in muscle quality, such as an increase in muscle stiffness. The present study aimed to investigate the effects of supplementation with quercetin glycosides (QGs), well-known polyphenolic flavonoids, combined with resistance exercise on muscle quantity and stiffness. Materials and Methods: A randomized, controlled trial was conducted in community-dwelling, Japanese people aged 50-74 years who were randomly allocated to exercise with placebo or 200 or 500 mg of QG supplementation. All participants performed low-intensity resistance training mainly targeting thigh muscles with 40% of 1-repetition maximum, 3 days per week for 24 weeks. Muscle cross-sectional area (CSA), lean mass, and vastus lateralis (VL) muscle stiffness were measured before and after the 24-week intervention. Results: Forty-eight subjects completed the 24-week intervention. There were no significant group × time interactions in thigh CSA for primary outcome, as well as lean mass. VL muscle stiffness in the stretched position was significantly lower in both the 200 mg and 500 mg QG groups than in the placebo group after the 24-week intervention (p < 0.05). No significant correlation was observed between changes of VL muscle CSA and stiffness during the 24-week intervention. Conclusion: Quercetin glycoside supplementation combined with low-intensity resistance exercise improved passive muscle stiffness independently of muscle quantity. Clinical Trial Registration: [www.umin.ac.jp/ctr/], identifier [UMIN000037633].

The association between long-chain polyunsaturated fatty acid intake and changes in brain volumes among older community-dwelling Japanese people.

The relationship between age-related brain atrophy and long-chain polyunsaturated fatty acid (LCPUFA) intake is not fully understood. This study investigated the association of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) intake and brain atrophy in non-demented older Japanese people (n = 810, aged 60-89 years) using data sets of a 2-year longitudinal study. Brain volumes were measured using 3D-MRI in the baseline and follow-up periods. The associations of multivariate-adjusted changes in brain volumes with baseline LCPUFA intake were assessed using a general linear model. Higher ARA intake was associated with a smaller decrease in frontal cortex volumes, which was accompanied by a lower risk of cognitive decline among the participants. In the subgroup analysis for low DHA and EPA intake, accounting for one-third of Japanese intake, DHA and EPA intake was positively correlated with preservation of the temporal cortex volume. These findings suggest that appropriate intake of LCPUFA may decelerate age-related brain atrophy and lead to the maintenance of brain health in older people.

Quercetin attenuates adipogenesis and fibrosis in human skeletal muscle.

Age-associated increase in ectopic fat degeneration and fibrosis in the skeletal muscle contribute to muscle degradation and weakness. Quercetin is a bioactive flavonoid with anti-inflammatory and anti-obesity effects. Thus, we aimed to investigate the effects of quercetin on adipogenesis and fibrosis in the human skeletal muscle, which have not yet been elucidated. Human muscle-derived PDGFRα+/CD201+ cells (mesenchymal progenitors) were incubated with various concentrations of quercetin (0, 0.3, 1, and 3 µM) under adipogenic or fibrogenic conditions. Lipid accumulation was visualized via Oil Red O staining. The expression of genes implicated in adipocyte or fibroblast differentiation and activation of signaling pathways was analyzed. The quercetin-treated PDGFRα+/CD201+ cells showed attenuated lipid accumulation and adipogenic gene expression (CEBPA and ADIPOQ) via the inhibition of CREB phosphorylation under adipocyte differentiation conditions. Additionally, quercetin treatment significantly attenuated the expression of fibrogenic genes (TIMP1, ACTA2, COL1A1 and COL3A1) by inhibiting Smad2 phosphorylation. Quercetin suppressed the differentiation of muscle-derived PDGFRα+/CD201+ cells to adipocytes and fibroblasts at concentrations achievable by dietary and dietary supplement intake, which indicated its preventive or therapeutic effect against the loss of muscle quality.

Differences in the effect of surface texturing on the wear loss of ß-type Ti-Nb-Ta-Zr and (α+ß)-type Ti-6Al-4V ELI alloys in contact with zirconia in physiological saline solution.

The effectiveness of dimple surface texturing via picosecond pulsed laser processing for reducing wear loss was investigated using two types of titanium alloys, ß-type Ti-29Nb-13Ta-4.6Zr (TNTZ) and α+ß-type Ti-6Al-4V ELI (Ti64). The two alloys showed different modes of wear against zirconia. As the sliding distance increased, the wear loss was observed to increase for Ti64, but not necessarily for TNTZ. The wear debris of Ti64 acted as abrasive particles, but that of TNTZ easily adhered to the surface, and the adhered wear debris turned into a hard wear-protective layer. Therefore, the dependence of wear loss on the sliding distance for these two titanium alloys could be attributed to the difference in the roles of wear debris between each titanium alloy and zirconia. Further, depending on this difference in wear mode, the effect of dimple surface texturing on the wear was found to be different in Ti64 and TNTZ. As the dimples can trap the wear debris, they are effective for reducing wear in Ti64 but are detrimental in TNTZ.

Osteoanabolic Implant Materials for Orthopedic Treatment.

Osteoporosis is becoming more prevalent due to the aging demographics of many populations. Osteoporotic bone is more prone to fracture than normal bone, and current orthopedic implant materials are not ideal for the osteoporotic cases. A newly developed strontium phosphate (SrPO4 ) coating is reported herein, and applied to Ti-29Nb-13Ta-4.6Zr (wt%), TNTZ, an implant material with a comparative Young's modulus to that of natural bone. The SrPO4 coating is anticipated to modulate the activity of osteoblast (OB) and osteoclast (OC) cells, in order to promote bone formation. TNTZ, a material with excellent biocompatibility and high bioinertness is pretreated in a concentrated alkaline solution under hydrothermal conditions, followed by a hydrothermal coating growth process to achieve complete SrPO4 surface coverage with high bonding strength. Owing to the release of Sr ions from the SrPO4 coating and its unique surface topography, OB cells demonstrate increased proliferation and differentiation, while the cellular responses of OC are suppressed, compared to the control case, i.e., bare TNTZ. This TNTZ implant with a near physiologic Young's modulus and a functional SrPO4 coating provides a new direction in the design and manufacture of implantable devices used in the management of orthopedic conditions in osteoporotic individuals.

Fabrication of low-cost beta-type Ti-Mn alloys for biomedical applications by metal injection molding process and their mechanical properties.

Titanium and its alloys are suitable for biomedical applications owing to their good mechanical properties and biocompatibility. Beta-type Ti-Mn alloys (8-17 mass% Mn) were fabricated by metal injection molding (MIM) as a potential low cost material for use in biomedical applications. The microstructures and mechanical properties of the alloys were evaluated. For up to 13 mass% Mn, the tensile strength (1162-938MPa) and hardness (308-294HV) of the MIM fabricated alloys are comparable to those of Ti-Mn alloys fabricated by cold crucible levitation melting. Ti-9Mn exhibits the best balance of ultimate tensile strength (1046MPa) and elongation (4.7%) among the tested alloys, and has a Young's modulus of 89GPa. The observed low elongation of the alloys is attributed to the combined effects of high oxygen content, with the presence of interconnected pores and titanium carbides, the formation of which is due to carbon pickup during the debinding process. The elongation and tensile strength of the alloys decrease with increasing Mn content. The Ti-Mn alloys show good compressive properties, with Ti-17Mn showing a compressive 0.2% proof stress of 1034MPa, and a compressive strain of 50%.

Microstructural evolution and mechanical properties of biomedical Co-Cr-Mo alloy subjected to high-pressure torsion.

The effects of severe plastic deformation through high-pressure torsion (HPT) on the microstructure and tensile properties of a biomedical Co-Cr-Mo (CCM) alloy were investigated. The microstructure was examined as a function of torsional rotation number, N and equivalent strain, εeq in the HPT processing. Electron backscatter diffraction analysis (EBSD) shows that a strain-induced martensitic transformation occurs by the HPT processing. Grain diameter decreases with increasing εeq, and the HPT-processed alloy (CCMHPT) for εeq=45 exhibits an average grain diameter of 47nm, compared to 70µm for the CCM alloy before HPT processing. Blurred and wavy grain boundaries with low-angle of misorientation in the CCMHPT sample for εeq<45 become better-defined grain boundaries with high-angle of misorientation after HPT processing for εeq=45. Kernel average misorientation (KAM) maps from EBSD indicate that KAM inside grains increases with εeq for εeq<45, and then decreases for εeq=45. The volume fraction of the ε (hcp) phase in the CCMHPT samples slightly increases at εeq=9, and decreases at εeq=45. In addition, the strength of the CCMHPT samples increases at εeq=9, and then decrease at εeq=45. The decrease in the strength is attributed to the decrease in the volume fraction of ε phase, annihilation of dislocations, and decrease in strain in the CCMHPT sample processed at εeq=45 by HPT.

Microstructures, mechanical properties and cytotoxicity of low cost beta Ti-Mn alloys for biomedical applications.

The microstructures, mechanical properties and biocompatibility of low cost ß-type Ti-(6-18)Mn alloys were investigated after solution treatment. Ti-9 Mn exhibits the best combination of tensile strength and elongation among the fabricated alloys, and its performance is comparable to or superior to those of Ti-6Al-4V ELI (Ti-64 ELI) in terms of every parameter evaluated. A hardness of 338 HV, a Young's modulus of 94 GPa, a 0.2% proof stress of 1023 MPa, an ultimate tensile strength of 1048 MPa and elongation of 19% were obtained for Ti-9 Mn. Furthermore, the cell viability and metallic ion release ratios are comparable to those of commercially pure titanium, making this alloy promising for biomedical applications. The Young's modulus is also lower than that of Ti-64 ELI (110 GPa), which can possibly reduce the stress shielding effect in implanted patients. STATEMENT OF SIGNIFICANCE: This study evaluates mechanical and biological performance of low cost solution treated ß-type Ti-(6, 9, 13 and 18 mass%)Mn alloys. It includes alloys containing a Mn content range higher than most previously published works (which is around or lower than 8 mass%). Furthermore, the effects of the ω phase and the ß phase stability of the alloys over some mechanical properties and microstructures are discussed. Ion release behavior under simulated body fluids and cell viability are also evaluated. For the case of the Ti-9 Mn, a mechanical and biological performance that is comparable to or superior than that of the widely used Ti-6Al-4V ELI and commercially pure Ti was observed.

Wear transition of solid-solution-strengthened Ti-29Nb-13Ta-4.6Zr alloys by interstitial oxygen for biomedical applications.

In previous studies, it has been concluded that volume losses (V loss) of the Ti-29Nb-13Ta-4.6Zr (TNTZ) discs and balls are larger than those of the respective Ti-6Al-4V extra-low interstitial (Ti64) discs and balls, both in air and Ringer's solution. These results are related to severe subsurface deformation of TNTZ, which is caused by the lower resistance to plastic shearing of TNTZ than that of Ti64. Therefore, it is necessary to further increase the wear resistance of TNTZ to satisfy the requirements as a biomedical implant. From this viewpoint, interstitial oxygen was added to TNTZ to improve the plastic shear resistance via solid-solution strengthening. Thus, the wear behaviors of combinations comprised of a new titanium alloy, TNTZ with high oxygen content of 0.89 mass% (89O) and a conventional titanium alloy, Ti64 were investigated in air and Ringer's solution for biomedical implant applications. The worn surfaces, wear debris, and subsurface damage were analyzed using a scanning electron microscopy and an electron probe microanalysis. V loss of the 89O discs and balls are smaller than those of the respective TNTZ discs and balls in both air and Ringer's solution. It can be concluded that the solid-solution strengthening by oxygen effectively improves the wear resistance for TNTZ materials. However, the 89O disc/ball combination still exhibits higher V loss than the Ti64 disc/ball combination in both air and Ringer's solution. Moreover, V loss of the disc for the 89O disc/Ti64 ball combination significantly decreases in Ringer's solution compared to that in air. This decrease for the 89O disc/Ti64 ball combination in Ringer's solution can be explained by the transition in the wear mechanism from severe delamination wear to abrasive wear.

ß-Type titanium alloys for spinal fixation surgery with high Young's modulus variability and good mechanical properties.

Along with a high strength, ductility, and work hardening rate, a variable Young's modulus is crucial for materials used as implant rods in spinal fixation surgery. The potential in this context of Ti-(9,8,7)Cr-0.2O (mass%) alloys is reported herein. The microstructural and mechanical properties of the alloys were systematically examined as a function of their chromium content, and the ion release of the optimized alloy was investigated to assess its suitability as an implant material. In terms of the deformation-induced ω-phase transformation required for a variable Young's modulus, the balance between ß-phase stability and athermal ω-phase content is most favorable in the Ti-9Cr-0.2O alloy. In addition, this composition affords a high tensile strength (>1000MPa), elongation at break (∼20%), and work hardening rate to solution-treated (ST) samples. These excellent properties are attributed to the combined effects of deformation-induced ω-phase transformation, deformation twinning, and dislocation gliding. Furthermore, the ST Ti-9Cr-0.2O alloy proves resistant to metal ion release in simulated body fluid. This combination of a good biocompatibility, variable Young's modulus and a high strength, ductility, and work hardening rate is ideal for spinal fixation applications. STATEMENT OF SIGNIFICANCE: Extensive efforts have been devoted over the past decades to developing ß-type titanium alloys with low Young's moduli for biomedical applications. In spinal fixation surgery however, along with excellent mechanical properties, the spinal-support materials should possess high Young's modulus for showing small springback during surgery to facilitate manipulation but low Young's modulus close to bone once implanted to avoid stress shielding. None of currently used metallic biomaterials can satisfy these abovementioned requirements. In the present study, we have developed a novel alloy, Ti-9Cr-0.2O. Remarkably variable Young's modulus and excellent mechanical properties can be achieved in this alloy via phase transformations and complex deformation mechanisms, which makes the Ti-9Cr-0.2O preferred material for spinal fixation surgery.

In vitro biocompatibility of Ti-Mg alloys fabricated by direct current magnetron sputtering.

Ti-xMg (x=17, 33, and 55 mass%) alloy films, which cannot be prepared by conventional melting processes owing to the absence of a solid-solution phase in the phase diagram, were prepared by direct current magnetron sputtering in order to investigate their biocompatibility. Ti and Mg films were also prepared by the same process for comparison. The crystal structures were examined by X-ray diffraction (XRD) analysis and the surfaces were analyzed by X-ray photoelectron spectroscopy. The Ti, Ti-xMg alloy, and Mg films were immersed in a 0.9% NaCl solution at 310 K for 7d to evaluate the dissolution amounts of Ti and Mg. In addition, to evaluate the formation ability of calcium phosphate in vitro, the Ti, Ti-xMg alloy, and Mg films were immersed in Hanks' solution at 310 K for 30 d. Ti and Mg form solid-solution alloys because the peaks attributed to pure Ti and Mg do not appear in the XRD patterns of any of the Ti-xMg alloy films. The surfaces of the Ti-17 Mg alloy and Ti-33 Mg alloy films contain Ti oxides and MgO, whereas MgO is the main component of the surface oxide of the Ti-55 Mg alloy and Mg films. The dissolution amounts of Ti from all films are below or near the detection limit of inductively coupled plasma-optical emission spectroscopy. On the other hand, the Ti-17 Mg alloy, Ti-33 Mg alloy, Ti-55 Mg alloy, and Mg films exhibit Mg dissolution amounts of approximately 2.5, 1.4, 21, and 41 µg/cm(2), respectively. The diffraction peaks attributed to calcium phosphate are present in the XRD patterns of the Ti-33 Mg alloy, Ti-55 Mg alloy, and Mg films after the immersion in Hanks' solution. Spherical calcium phosphate particles precipitate on the surface of the Ti-33 Mg film. However, many cracks are observed in the Ti-55 Mg film, and delamination of the film occurs after the immersion in Hanks' solution. The Mg film is dissolved in Hanks' solution and calcium phosphate particles precipitate on the glass substrate. Consequently, it is revealed that the Ti-33 Mg alloy film evaluated in this study is suitable for biomedical applications.

Mechanical properties and cytocompatibility of oxygen-modified ß-type Ti-Cr alloys for spinal fixation devices.

In this study, various amounts of oxygen were added to Ti-10Cr (mass%) alloys. It is expected that a large changeable Young's modulus, caused by a deformation-induced ω-phase transformation, can be achieved in Ti-10Cr-O alloys by the appropriate oxygen addition. This "changeable Young's modulus" property can satisfy the otherwise conflicting requirements for use in spinal implant rods: high and low moduli are preferred by surgeons and patients, respectively. The influence of oxygen on the microstructures and mechanical properties of the alloys was examined, as well as the bending springback and cytocompatibility of the optimized alloy. Among the Ti-10Cr-O alloys, Ti-10Cr-0.2O (mass%) alloy shows the largest changeable Young's modulus following cold rolling for a constant reduction ratio. This is the result of two competing factors: increased apparent ß-lattice stability and decreased amounts of athermal ω phase, both of which are caused by oxygen addition. The most favorable balance of these factors for the deformation-induced ω-phase transformation occurred at an oxygen concentration of 0.2mass%. Ti-10Cr-0.2O alloy not only exhibits high tensile strength and acceptable elongation, but also possesses a good combination of high bending strength, acceptable bending springback and great cytocompatibility. Therefore, Ti-10Cr-0.2O alloy is a potential material for use in spinal fixture devices.

Predominant factor determining wear properties of ß-type and (α+ß)-type titanium alloys in metal-to-metal contact for biomedical applications.

The predominant factor determining the wear properties of a new titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ) and a conventional titanium alloy, Ti-6Al-4V extra-low interstitial (Ti64) was investigated for TNTZ and Ti64 combinations in metal-to-metal contacting bio-implant applications. The worn surfaces, wear debris, and subsurface damages were analyzed using a scanning electron microscopy combined with energy-dispersive spectroscopy and electron-back scattered diffraction analysis. The volume loss of TNTZ is found to be larger than that of Ti64, regardless of the mating material. The wear track of TNTZ exhibits the galled regions and severe plastic deformation with large flake-like debris, indicative of delamination wear, which strongly suggests the occurrence of adhesive wear. Whereas, the wear track of Ti64 have a large number of regular grooves and microcuttings with cutting chip-like wear debris and microfragmentation of fine oxide debris, indicative of abrasive wear combined with oxidative wear. This difference in the wear type is caused by severe and mild subsurface deformations of TNTZ and Ti64, respectively. The lower resistance to plastic shearing for TNTZ compared to that of Ti64 induces delamination, resulting in a higher wear rate.

Hardening behavior after high-temperature solution treatment of Ag-20Pd-12Au-xCu alloys with different Cu contents for dental prosthetic restorations.

Ag-Pd-Au-Cu alloys have been used widely for dental prosthetic applications. Significant enhancement of the mechanical properties of the Ag-20Pd-12Au-14.5Cu alloy as a result of the precipitation of the ß' phase through high-temperature solution treatment (ST), which is different from conventional aging treatment in these alloys, has been reported. The relationship between the unique hardening behavior and precipitation of the ß' phase in Ag-20Pd-12Au-xCu alloys (x=6.5, 13, 14.5, 17, and 20mass%) subjected to the high-temperature ST at 1123K for 3.6ks was investigated in this study. Unique hardening behavior after the high-temperature ST also occurs in Ag-20Pd-12Au-xCu alloys (x=13, 17, and 20) with precipitation of the ß' phase. However, hardening is not observed and the ß' phase does not precipitate in the Ag-20Pd-12Au-6.5Cu alloy after the same ST. The tensile strength and 0.2% proof stress also increase in Ag-20Pd-12Au-xCu alloys (x=13, 14.5, 17, and 20) after the high-temperature ST. In addition, these values after the high-temperature ST increase with increasing Cu content in Ag-20Pd-12Au-xCu alloys (x=14.5, 17, and 20). The formation process of the ß' phase can be explained in terms of diffusion of Ag and Cu atoms and precipitation of the ß' phase. Clarification of the relationship between hardening and precipitation of the ß' phase via high-temperature ST is expected to help the development of more effective heat treatments for hardening in Ag-20Pd-12Au-xCu alloys.

Contribution of ß' and ß precipitates to hardening in as-solutionized Ag-20Pd-12Au-14.5Cu alloys for dental prosthesis applications.

Dental Ag-20Pd-12Au-14.5Cu alloys exhibit a unique hardening behavior, which the mechanical strengths enhance significantly which enhances the mechanical strength significantly after high-temperature (1123K) solution treatment without aging treatment. The mechanism of the unique hardening is not clear. The contribution of two precipitates (ß' and ß phases) to the unique hardening behavior in the as-solutionized Ag-20Pd-12Au-14.5Cu alloys was investigated. In addition, the chemical composition of the ß' phase was investigated. The fine ß' phase densely precipitates in a matrix. The ß' phase (semi-coherent precipitate), which causes lattice strain, contributes greatly to the unique hardening behavior. On the other hand, the coarse ß phase sparsely precipitates in the matrix. The contribution of the ß phase (incoherent precipitate), which does not cause lattice strain, is small. The chemical composition of the ß' phase was determined. This study reveals that the fine ß' phase precipitated by high-temperature solution treatment leads to the unique hardening behavior in dental Ag-20Pd-12Au-14.5Cu alloys in the viewpoints of the lattice strain contrast and interface coherency. It is expected to make the heat treatment process more practical for hardening. The determined chemical composition of ß' phase would be helpful to study an unknown formation process of ß' phase.

Bending springback behavior related to deformation-induced phase transformations in Ti-12Cr and Ti-29Nb-13Ta-4.6Zr alloys for spinal fixation applications.

The springback behavior of Ti-12Cr and Ti-29Nb-13Ta-4.6Zr (TNTZ) during deformation by bending was investigated; and the microstructures of the non-deformed and deformed parts of both alloys were systematically examined to clarify the relationship between microstructure and springback behavior. For the deformed Ti-12Cr alloy, deformation-induced ω-phase transformation occurs in both the areas of compression and tension within the deformed part, which increases the Young׳s modulus. With the deformed TNTZ alloy, deformation-induced ω-phase transformation is observed in the area of compression within the deformed part; while a deformation-induced α″ martensite transformation occurs in the area under tension, which is likely to be associated with the pseudoelasticity of TNTZ. Among these two alloys, Ti-12Cr exhibits a smaller springback and a much greater bending strength when compared with TNTZ; making Ti-12Cr the more advantageous for spinal fixation applications.