Assessing the biocompatibility of NiTi shape memory alloys used for medical applications

The present paper reviews aspects related to the biocompatibility of NiTi shape memory alloys used for medical applications. These smart metallic materials, which are characterised by outstanding mechanical properties, have been gaining increasing importance over the last two decades in many minimal invasive surgery and diagnostic applications, as well as for other uses, such as in orthodontic appliances. Due to the presence of high amounts of Ni, the cytotoxicity of such alloys is under scrutiny. In this review paper we analyse work published on the biocompatibility of NiTi alloys, considering aspects related to: (1) corrosion properties and the different methods used to test them, as well as specimen surface states; (2) biocompatibility tests in vitro and in vivo; (3) the release of Ni ions. It is shown that NiTi shape memory alloys are generally characterised by good corrosion properties, in most cases superior to those of conventional stainless steel or Co–Cr–Mo-based biomedical materials. The majority of biocompatibility studies suggest that these alloys have low cytotoxicity (both in vitro and in vivo) as well as low genotoxicity. The release of Ni ions depends on the surface state and the surface chemistry. Smooth surfaces with well-controlled structures and chemistries of the outermost protective TiO₂ layer lead to negligible release of Ni ions, with concentrations below the normal human daily intake.     

Electroreduction of α-glucose on CNT/graphite electrode modified by Zn and Zn–Fe alloy

Electroreduction of -glucose to form sorbitol on Zn/CNTs and Zn alloy/CNTs electrodes has been investigated in this paper. Carbon nanotubes (CNTs) used in this paper are grown directly on graphite disks by chemical vapor deposition. Zn and Zn alloy are electrodeposited on the activated CNTs/graphite electrode by pulse galvanostatic method. The micrographs of Zn/CNTs and Zn alloy/CNTs electrodes are characterized by scanning electron microscopy. The results show that the current efficiency of -glucose reduction on CNTs electrodes is much better than that on flat Zn electrodes. The order of the current efficiency on different electrodes is as follows: Zn/CNT (0.58) Zn–Fe/CNT (0.57)>Zn–Ni/CNT (0.43) Zn/graphite (0.42)>Zn (0.40). It indicates that CNTs have good potential application in electrosynthesis. Additionally, effects of some operating parameters, such as pH, temperature and -glucose concentration, on the current efficiency of -glucose reduction are also discussed.     

Pulse plating effect on microstructure and corrosion properties of Zn–Ni alloy coatings

The influence of pulse plating parameters on the surface morphology, grain size, lattice imperfection and corrosion properties of Zn–Ni alloy has been studied. The coatings were electrodeposited in an alkaline cyanide-free solution. AFM was applied for surface morphology examination, XRD measurements were carried out for phase composition and texture analysis, electron probe microanalysis was used for alloy chemical composition studies, while electrochemical techniques were applied for corrosion performance evaluation. The pulse plated Zn–Ni coatings appeared to consist of the γ-Zn₂₁Ni₅ phase and the composition of the alloy depended on the plating parameters. The grain size, lattice imperfection and homogeneity of grain distribution were established to be the main factors determining corrosion behaviour of the coating. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005     

混合稀土对ZL108铝合金组织与性能的影响

对稀土处理前后的ZL108合金进行了机械性能测试和断口分析, 表明稀土处理有利于提高合金的塑性和强度. 对稀土处理前后合金中氢总量进行了分析, 未加稀土的合金内氢总量与稀土处理后的合金相当, 结合性能与断口形态, 从侧面表明稀土改变了氢的存在形式.     

Iron-Cobalt-Silica Aerogel Nanocomposite Materials

Iron-Cobalt-Silica nanocomposites were prepared in form of aerogels. X-ray diffraction, transmission electron microscopy and N₂ physisorption at 77 K were used to investigate the structure, size and dispersion of the nanocrystals and the porous structure in the aerogels and in the final composites. The variation of the supercritical drying conditions gives rise to differences in the morphological features of the aerogels. These differences influence the size of the cobalt oxide nanoparticles in the aerogels. On the other hand, after the reduction treatment the average size of the alloy nanoparticles is the same in all the aerogel nanocomposites. The effect of reduction temperature on alloy formation and particle size is also discussed.     

Spectrophotometric determination of zinc in copper-base alloys with TAN

TAN reacts with zinc(II) forming a red complex with composition 1:2 Zn(II)-TAN and absorption maximum at 582 nm. Zinc can be determined with this reagent in the presence of Triton X-100, in the pH range 6.20-8.00 with a molar absorptivity of 4.5×10⁴ l/mol/cm Beer's Law was obeyed up to least 1.55 g/ml. Copper interference was eliminated with a mixture of thiosulfate and ascorbic acid and nickel separated by precipitation with dimethylglyoxime. The proposed method was used for zinc determination in several copper-base alloys and the results of analysis in comparison with certified values indicated that the procedure was accurate and precise. A derivative procedure is also proposed, allowing zinc determination with high sensitivity (5-400 ng/ml).     

Magnetic susceptibility of liquid gold-indium-zinc alloys

Summary Alloys of the ternary system gold-indium-zinc with a variable content of goldx _Au at a constant ratio ofx _In:x _Zn=1:1 have been investigated by susceptibility measurements from 300 K up to 1500 K with emphasis on the liquid state. The magnetic susceptibilities of the homogeneous liquids were found to vary in a non-linear manner with temperature and composition. At temperatures close to the liquid-solid transition, the susceptibilities pass through a characteristic minimum which tends to disappear with increasing temperature. The anomaly located atx _Au 0.6 seems to be related to a particular valence electron concentration ofe/a 1.6.

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Magnetische Suszeptibilität von flüssigen Gold-Indium-Zink-Legierungen

Zusammenfassung Legierungen des ternären Systems Gold-Indium-Zink mit einem variablen Goldgehaltx _Au bei konstantem Indium-Zink-Verhältnis (x _In:x _Zn=1:1) wurden zwischen 300 und 1500 K auf ihre magnetische Suszeptibilität untersucht. Das Hauptaugenmerk wurde dabei auf den flüssigen Zustand gelegt. Die magnetischen Suszeptibilitäten der homogenen Schmelzen variieren nichtlinear mit Temperatur und Zusammensetzung. Bei Temperaturen nahe dem übergang flüssig-fest tritt ein charakteristisches Minimum der Suszeptibilität auf, das mit steigender Temperatur verschwindet. Die Anomalie bei einemx _Au vonca. 0.6 scheint mit einer speziellen Valenzelektronenkonzentration (e/a) von etwa 1.6 verknüpft zu sein.

     

温度对贮氢合金MlNi3.75Co0.65Mn0.4Al0.2动力学性能的影响

在-20℃～85℃的范围内系统地研究了温度对贮氢合金MINi3.75Co0.65Mn0.4Al0.2动力学性能的影响.结果表明:该贮氢合金电极的电化学反应电阻Rt,欧姆内阻Ro,阴极极化过电位,阳极极化过电位,阳极极化过程中的电化学反应过电位ηa和浓差极化过电位ηa均随温度的升高而减小,该电极的交换电流密度i0,对称因子β和电极中氢的扩散系数D随温度的升高而增大.当放电电流密度较低时,电化学反应是整个电极过程的速度控制步骤;当放电电流密度较高时,氢的扩散是整个电极过程的速度控制步骤;在中等放电电流密度下,电极过程由电化学过程和氢的扩散过程混合控制.该电极中电化学反应过程和氢扩散过程的活化能分别为28.1 kJ·mol-1和19.9 kJ·mol-1.     

往复挤压准晶增强快速凝固Mg92.5Zn6.4Y1.1合金

采用往复挤压工艺将快速凝固Mg92.5Zn6.4Y1.1合金薄带在330℃挤压2道次和4道次,然后正挤压制成Φ10 mm的棒材。用OM,TEM,XRD及DTA研究了往复挤压过程中准晶相I-Mg3YZn6弥散析出及对力学性能的影响。研究表明,往复挤压有利于快速凝固Mg92.5Zn6.4Y1.1合金薄带的焊合,获得组织致密、均匀、高强韧合金。往复挤压2道次,相组成为-αMg和准晶I-Mg3YZn6,脱溶析出纳米准晶相较少;4道次相组成为-αMg和准晶I-Mg3YZn6及MgZn相,脱溶弥散析出的纳米I-Mg3YZn6准晶相及MgZn相较多。往复挤压提高材料的拉伸性能,其主要原因是细晶强化和析出强化。     

低钴AB5型稀土系贮氢电极合金的研究

为了进一步降低AB5型混合稀土系贮氢合金的成本,采用Cr,Si,Cu替代Co和调节化学计量比的方法制备低钴AB5型贮氢合金。结果表明:3种取代元素在寿命方面的效果依次为Si>Cr>Cu,在放电容量和活化性能方面依次是Cu>Cr>Si。Cr,Cu,Si只有少量的替代才可能发挥其有利影响;通过非化学计量比的调节,低钴混合稀土系贮氢电极合金的放电容量、活化性能及倍率放电能力都能较好地达到实用要求,但是循环寿命有待提高。