Enhancement of Mechanical Properties and Testing of Nitinol Stents in Cerebral Aneurysm Simulation Models.

Stents are promising medical devices widely used in the prevention of cerebral aneurysm rupture. As the performance of stents depends on their mechanical properties and cell configuration, the aim of this study was to optimize the stent design and test the hemodynamic properties by using computational solid mechanics and computational fluid dynamics. In order to test their performance, computer-based cerebral aneurysm models that mimic the conditions present after implantation into the human brain were tested. The strut configuration selected was the closed-cell type, and nitinol was chosen as the material for stent manufacture because the innate characteristics of this material increase stent flexibility. Three ideal sample stent types with different cell configurations were manufactured. Computational solid mechanics analysis of the sample stents showed over 30% difference in flexibility between stents. Furthermore, using a cerebral aneurysm model simulation, we found that the stents eased the hemodynamic factors of the cerebral aneurysm and lessened the flow velocity influx into the sac. A decrease in flow velocity led to a 50-60% reduction in wall shear stress, which is expected to prevent aneurysm rupture under clinical conditions. Stent design optimization was carried out by simulation and electropolishing. Corrosion resistance and surface roughness were evaluated after electropolishing performed under variable conditions, but 40 V and 10 s were the most optimal.

Iterative control approach to high-speed force-distance curve measurement using AFM: time-dependent response of PDMS example.

Force-distance curve measurements using atomic force microscope (AFM) has been widely used in a broad range of areas. However, currently force-curve measurements are hampered the its low speed of AFM. In this article, a novel inversion-based iterative control technique is proposed to dramatically increase the speed of force-curve measurements. Experimental results are presented to show that by using the proposed control technique, the speed of force-curve measurements can be increased by over 80 times--with no loss of spatial resolution--on a commercial AFM platform and with a standard cantilever. High-speed force curve measurements using this control technique are utilized to quantitatively study the time-dependent elastic modulus of poly(dimethylsiloxane) (PDMS). The force-curves employ a broad spectrum of push-in (load) rates, spanning two-order differences. The elastic modulus measured at low-speed compares well with the value obtained from dynamic mechanical analysis (DMA) test, and the value of the elastic modulus increases as the push-in rate increases, signifying that a faster external deformation rate transitions the viscoelastic response of PDMS from that of a rubbery material toward a glassy one.

Miniaturized thermocycler based on thermoelectric heating for diagnosis of sexually transmitted disease by DNA amplification.

Sexually transmitted disease (STD) is among the most common infectious diseases; therefore, it is necessary to develop sensitive early diagnostic techniques. As the gold standard, polymerase chain reaction (PCR) has been most widely employed for STD diagnosis; however, PCR requires large and expensive instruments. In this study, miniaturized thermal cycler using Peltier modules was developed for the PCR analysis. In comparison with the conventional PCR instrument, the Peltier-based micro-PCR (P-mPCR) device developed in this study enables one to amplify and successfully distinguish between DNA of different sizes. Furthermore, by using the clinical vaginal sample collected with the vaginal swab and tampon, different kinds of STD bacteria could be detected with high accuracy (∼94.19%) and high sensitivity (∼95.6%). Therefore, the P-mPCR device will be applicable in STD diagnosis as well as the detection of other bacteria/viruses using DNA amplification in regions including those with limited resources.

Effect of gamma irradiation on the microbiological quality and antioxidant activity of fresh vegetable juice.

A fresh vegetable juice has become a new functional food available for dieting and health. However, it poses a microbiological hazard to the consumer because it is distributed and consumed without any cooking. In this study, we applied the radiation sterilization of fresh vegetable juice, and the effectiveness of gamma irradiation for inactivating Salmonella typhimurium and Escherichia coli in the carrot and kale juice was investigated. D((10)) values of S. typhimurium in the carrot and kale juice were 0.445+/-0.004 and 0.441+/-0.006 kGy, while those of E. coli were 0.301+/-0.005 and 0.299+/-0.006 kGy. The test organisms (inoculated at 10(7) cfu/ml) were eliminated by irradiation at 3 kGy. The total phenol contents of the irradiated juice during 3 days of storage at a cold chain temperature (10 degrees C) increased significantly (P<0.05), while those of the non-irradiated juice decreased (P<0.05). The antioxidant capacity of the irradiated carrot juice was higher than that of the non-irradiated control. Therefore, it was concluded that irradiation treatments of carrot and kale juice improve the microbiological safety with maintaining or even enhancing the antioxidative activity.