Development of MRI Artifact-Free Alloys for Biomedical Applications

MRIで金属アーチファクトを生じない医療用デバイスを作製するには，周囲の組織に近い体積磁化率を示す反磁性の金属材料が必要である．我々は，生体親和性の高い反磁性元素であるAuをベースとし，目標磁化率と高強度を同時に発揮する合金の開発を進めており，Ti-6Al-4V合金やCo-Cr-Mo合金と同等以上の強さを示すAu合金が得られる可能性が見えてきた．MRI artifact-free biomedical devices require diamagnetic metals indicating small volume-magnetic-susceptibility mismatch between the metal and surrounding tissues. The authors have developed new alloys based on Au, a biocompatible diamagnetic element, demonstrating susceptibility values close to surrounding tissues and high strength, simultaneously. And they found candidate Au alloys exhibiting strength similar to or higher than Ti-6Al-4V alloy and Co-Cr-Mo alloy

イオン液体含有レジン添加型グラスアイオノマーセメントの通電によるせん断接着強度低下 : オンデマンド剥離可能な歯科用スマートセメントのコンセプトと実証

With improvement of bonding strength of recent dental cement, it is difficult nowadays to remove restorations without excessive force or vibration to tooth, occasionally resulting in damage of dentin, enamel, and dental root. Therefore, “smart” dental cement indicating strong bonding and easy debonding-on-demand simultaneously is required. In this research, resin-modified glass-ionomer-cement containing an ionic-liquid, tris(2-hydroxyethyl)methylammonium methylsulfate was produced, and the shear bonding strength before and after direct current application were evaluated. The prototype cement containing 15 to 20 mass% ionic-liquid indicated simultaneously no significant reduction of shear bonding strength from that of the original cement not containing ionic-liquid, and significant reduction of bonding strength to approximately 20% of that of the original cement after direct current application of more than 2 mmC/mm2. The prototype cement in this research demonstrated that the concept of smart dental cement electrically debonding-on-demand is feasible

MRIに適合した生体医療用Au-Ta合金とAu-Nb合金の体積磁化率設計と硬さ

The volume magnetic susceptibility (χv) and Vickers hardness (HV) of Au–Ta and Au–Nb alloys were investigated for use as magnetic resonance imaging (MRI)-compatible alloys for biomedical applications. χv of the Au–Ta alloys did not depend on the phase constitution but did depend on the alloy composition. Therefore, heat treatment hardly affected χv of the Au–Ta alloys, and only alloys with Ta contents near 15 were possibly MRI-compatible. In contrast, χv of the Au–Nb alloys depended on the phase constitution. Therefore, both the alloy composition and heat treatment can be used to widely control χv of Au–Nb alloys, and Au–xNb alloys (x≥6.8) can be made MRI-compatible by optimizing χv using heat treatment. HV of the Au–15Ta alloy was smaller than that of pure Ti even after heat treatment, whereas HV of the MRI-compatible Au–Nb alloys was possibly higher than that of pure Ti after heat treatment. The saturated χv values of the Au–Nb alloys after heat treatment at 800 °Care compatible with the hypothesis that χv of an alloy is the average χv of each phase of the alloy based on the rule of mixtures. This hypothesis supports the tailoring of χv by controlling the alloy composition and heat treatment

強度と注入性に優れるβ-TCP基セメントへのジルコニア添加の効果

Injectable calcium phosphate cements (CPCs) exhibit many advantages as bone substitution materials. However, the strength of injectable CPCs after setting are often insufficient. In our previous studies, mechano-chemically modification of β-tricalcium phosphate cement powder through a planetary ball-milling process exhibited simultaneous improvement in the strength and injectability of CPC. Two plausible effects of this process are: changes in the CPC powder properties and zirconia abrasion powder contamination from the milling pot and balls. The objective of the present study is to separately evaluate these two effects on the strength and injectability of CPCs. The calculated injectability of the cement paste with and without the addition of zirconia powder were higher than 65% at 6 h after mixing. These values were much higher than that of the CPC paste without mechano-chemically modification, and similar to that of CPC with zirconia abrasion powder contamination. By contrast, the compression strength of the set CPC with zirconia powder additives were higher than that without the addition, and similar to that of CPC with zirconia abrasion powder contamination. These results suggest that the changes in the CPC powder properties due to mechano-chemically modification mainly affected the injectability of the CPC paste, and the zirconia abrasion powder contamination of the CPC powder affected the strength of the set CPC

生体医用応用を目的としたTi合金中のα相とβ相の体積磁化率の評価

Metallic medical devices in the human body cause serious artifacts in magnetic resonance imaging owing to the volume magnetic susceptibility (χν) mismatch between the device and tissue around the device. To reduce artifacts, medical devices produced from alloys with χν values of approximately −9 × 10−6 are required. Controlling the phase constitution is a basic technique used to control the χν value of an alloy, and the χν value of each phase is a fundamental property. In this study, an α+β-type Ti alloy and two β-type Ti alloys were investigated. The estimated χν values of the α-phase of the alloys were similar to or smaller than that of pure Ti. In contrast, the estimated χν values of the β-phase of the alloys were larger than that of pure Ti. Since the χν value of pure Ti is much larger than −9 × 10−6, the χν values of the β-phases suggested that increasing the volume fraction of the β-phase was not appropriate for producing a Ti alloy with a lower χν value

レジン添加型グラスアイオノマーセメントの通電後の剪断強度減少に対するイオン液体含有の有無と水中浸漬の影響

The enhancement in the bonding strength of advanced dental cements has enabled long-lasting dental restorations. However, the high bonding strength can cause difficulty in removing these restorations. Therefore, “smart” dental cements with simultaneous strong bonding and easy on-demand debonding ability are required. A resin-modified glass-ionomer-cement (RMGIC) with an ionic liquid (IL) has demonstrated significant reduction in the bonding strength with current application (CA). This research investigates the effects of immersion in distilled water on the electric conductivity and bonding strength of RMGIC with and without an IL and CA. The RMGIC without the IL exhibited significant electric conductivity after immersion, and a significant decrease in bonding strength with CA. In comparison, the electric conductivity after immersion and the decrease in bonding strength with CA were greater for RMGIC with the IL. Thus, the feasibility of smart dental cements capable of electrically debonding-on-demand is indicated

レジン添加型グラスアイオノマーセメントの電気伝導度と通電によるせん断試験強度低下に塩化ナトリウム溶液浸漬が与える影響

Advancements in dental cements have considerably improved their bond strengths. However, high bond strength often makes the removal of restorations difficult. Thus, smart dental cements that show controllable bond strength are required. A conventional resin-modified glass-ionomer-cement demonstrated a significant reduction in the bond strength after current application. However, for this system, the ions in the cement are released into the oral cavity, resulting in a reduction of the electrical conductivity and in losses of the expected on-demand debonding property. Herein, the effects of immersion in 0.9 and 15% NaCl solutions on the electrical conductivity and debonding properties were investigated. The cement immersed in 0.9% NaCl solution from 1 to 28 days maintained similar bond strength reductions after current application, whereas that in 15% NaCl solution initially showed no bond strength reduction after 1 day but exhibited an increase in the bond strength reduction after immersion for 28 days

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Effects of poloxamer additives on strength, injectability, and shape stability of beta-tricalcium phosphate cement modified using ball-milling

A new CPC was developed in this study using a β-TCP powder mechano-chemically modified by ball-milling. The prototype CPC exhibits excellent fluidity for easy injection into bone defects; however, there is a risk of leakage from the defects immediately after implantation due to its high fluidity. The addition of poloxamer, an inverse thermoresponsive gelling agent, into CPC optimizes the fluidity. At lower temperatures, it forms a sol and maintains good injectability, whereas at the human body temperature, it transforms to a gel, reducing the fluidity and risk of leakage. In this study, the effects of poloxamer addition of 3, 5, and 10 mass% on the injectability, shape stability, and strength of the prototype CPC were evaluated. The calculated injectability of the prototype CPC pastes containing three different poloxamer contents was higher than that of the CPC paste without poloxamer for 15 min at 37 °C. Furthermore, the shape stability immediately after injection of the three CPC pastes with poloxamer was higher than that of the CPC paste without poloxamer. After 1 week of storage at 37 °C, the compressive strength and diametral tensile strength of the CPC compacts containing 10 mass% poloxamer were similar to those of the CPC compact without poloxamer. Additionally, the CPC compacts containing 10 mass% poloxamer exhibited clear plastic deformation after fracture. These results indicate that the addition of poloxamer to the prototype CPC could reduce the risk of leakage from bone defects and improve the fracture toughness with maintaining the injectability and strength