Hajime Katou

Kinetics of solvent extraction/evaporation process for PLGA microparticle fabrication.

Organic solvent extraction/evaporation from an o/w-dispersion has been widely used for the fabrication of PLGA microparticles. The purpose of this work was to elucidate the kinetics of the solvent extraction/evaporation process. A mathematical diffusion model was developed and applied to predict the duration of the solvent extraction. As the diffusion coefficient, D(p), plays a major role in the modeled process, a new and experimentally simple method for estimating D(p) was developed. Both the experimental method and the mathematical model were validated through PLGA microparticle fabrication experiments. For microparticles of mode diameters of 2 and 20 microm, the solvent was extracted in approximately 10 s. Sufficient hardening of the microparticles required, however, the evaporation of solvent from the extraction phase. Residual solvent in extraction phase exerted a strong effect on the morphology of the final product as demonstrated by scanning electron microscopy. Only if most solvent was removed from the aqueous extraction phase, a powdery product of individual microparticles was obtained. At residual organic solvent concentration of above 0.2% in the extraction phase, the microparticles strongly aggregated during collection on a membrane filter and final drying. The presented methods may be useful for better controlling microparticle fabrication processes by solvent extraction/evaporation.

Integrated Immunoassay System Using Multichannel Microchip for Simultaneous Determination

Immunoassay system was integrated on a multichannel microchip. The chip, which has branching channel patterns with weirs, was fabricated by single step wet etching. To prevent contamination of up-flowed samples, pneumatic valves made of silicone rubber were set on a chip. By using the system, 4 assays were successfully performed at a time. We concluded that the system should be practicable.

Development on a Non-Contact Mixing Device for Micro-Liquids

We have developed a new device that can mix a micro-liquid without contact (i.e., one without a paddle or a screw). Essentially, non-contact mixing does not cause any cross-contamination or carryover, therefore it should be applied to a chemical analyzer, where high accuracy is needed. In the field of chemical analysis, especially for medical diagnostics using blood, decreasing the volume of samples and reagents is very important. Chemical analysis at low sample and reagent volumes will bring several merits: 1) Low sample volume will reduce indisposition in patients. 2) Low sample volume will allow analysis in babies or infants, from whom large samples can’t be collected the supply of. 3) Low reagent volume will reduce the cost of testing. 4) Low reagent volume will reduce exhausting liquids after tests. In our laboratory, we have found that a liquid in a vessel can flow when a proper wave on a free surface is generated. Using this phenomenon, we developed a non-contact mixing device for micro-liquids. To generate a wave on a free surface, we used an ultrasound. The free surface is pushed out when the ultrasound propagating in the liquid reaches the free surface. This effect is due to the radiation pressure caused by an ultrasound. Our developed mixing device consists of only two mechanical components: a vessel and a sound source. The vessel used in our demonstration was rectangular. A cross section of the vessel was 3.8 × 5.6 mm, with a depth of 20 mm and walls 0.6 mm thick. Thus, this vessel can be filled with about 400 μ L of liquid. Actually, because a portion is needed to hold the vessel, we used less than 12 mm of the depth (250 μ L liquid). The frequency of the ultrasound we used was 1.6 MHz, and the sound source for emitting the ultrasound was made of PZT. To obtain its effective power, the PZT thickness resonance was used. Therefore, we made the PZT plate 1.1 mm thick. The sound source was arranged outside the vessel, and it emitted ultrasound toward the free surface in the vessel. Emitted ultrasound permeates through the wall of a vessel and reaches the free surface of a liquid. When it is pulsatile, the ultrasound reaching the free surface generates a wave. In the liquid under the wavy free surface, a circulating flow occurs. The intensity of the flow depends on the amplitude and frequency of the surface. From our theoretical and experimental study, we found that the best pulsating frequency was 20 Hz for our vessel. We measured the velocity of the circulating flow under this condition by using PIV. The results were that a maximum velocity of 300 mm/sec was observed. In the next step, we applied our device to mixing a real sample and reagent. A serum of a horse was used as the sample. In general, there is a difference in refractive index between the sample and reagent. By using the Schlieren visualization method, we observed the mixing process between the sample and reagent, and evaluated the mixing time needed for them to be fully homogeneous. Our results demonstrated that 250 μ L of liquid can be mixed within 1.8 sec.Copyright

238 超音波を応用した微量液の非接触攪拌技術 : 気-液界面のハンドリングによる流動制御

СФЕРА ДЕЙСТВИЯ СТАТЬИ 238 УК РФ В ОБЛАСТИ ЗАЩИТЫ ЗДОРОВЬЯ, ЖИЗНИ И ПРАВ ПОТРЕБИТЕЛЕЙ В статье исследуются критерии соотношения безопасного и небезопасного товара, а также рассматриваются правовые конструкции защиты жизни, здоровья и прав потребителя от приобретения некачественного товара, по средствам правовых норм отраженных в статье 238 УК РФ. Адрес статьи: www.gramota.net/materials/3/2008/1/22.html