A new blood compatible and permselective hollow fiber membrane for hemodialysis

The authors have prepared a blood compatible and highly permselective hemodialysis membrane composed of polyether segmented nylon. This block copolymer was synthesized by polycondensation of bis-3-aminopropyl-poly(tetramethylene oxide) (PTMO) and poly(imino-1,3-bismethyl-cyclohexyl-iminoisophtharoyl) (NyBl) prepolymer obtained by polycondensation of 1,3-bis(aminomethyl)cyclohexane (B) and isophthalic acid (I). The molecular weight (MW) calculated from the number of end-groups was 16,000-21,000. In vitro blood compatibility was evaluated in terms of platelet adhesion onto the surface. PTMO-NyBl surfaces showed excellent platelet adhesion preventing properties. The PTMO-NyBl hollow fiber membrane was obtained by a dry-wet spinning process. The membranes had higher permeability coefficients for macromolecules ranging from MW 10,000 to 20,000 than polysulfone hollow fiber membrane (PS membrane), and had acceptably low albumin permeability for use as a dialysis membrane. The ex vivo blood compatibilities of PTMO-NyBl membrane and PS membrane were investigated by extracorporeal circulation in a pig model. The PTMO-NyBl membrane gave excellent results when assessing hemodialysis leukopenia, oxidative burst, and free platelet count decrease.     

Observations of high-field domains in GaxIn1 ? xSb Gunn diodes

The properties of high-field domains in GaxIn1-xSb Gunn diodes (0.4 < x < 0.82) have been studied by measuring the surface potential on the diodes. The domain velocities vary with the Ga composition x, 5.3?6.1×106 cm/s for0.8 > x > 0.55 and 10×106 cm/s for x = 0.4, but they are almost independent of the applied voltage, even if the electron concentration is increased by the impact ionisation in the domain at high applied voltages for the small-x samples.     

Integration of GaAs m.e.s.f.e.t.s and Gunn elements in a 4 bit-gate device

A GaAs m.e.s.f.e.t. and a Schottky electrode-triggered Gunn element have been integrated into a single device which operated as a negative logic inhibitor. A monolithic device of four such inhibitors, connected in cascade, was operated in a stable manner, with a signal delay per gate as small as 40 ps.     

The chemistry of ‘alkali-aggregate’ reaction

To clarify ideas about the alkali aggregate reaction, the reaction between sodium hydroxide and various forms of silica has been studied. Variations with time in the sodium, hydroxyl and silica concentrations in solution have been followed and the volume change of solid silica immersed in solution has been measured.If the silica is an absorbant and reactive form such as silica gel, there is an immediate drop in both sodium and hydroxyl concentrations. Subsequently, as the silica dissolves, sodium concentration rises again. Both the final concentration of dissolved silica and the volume expansion of solid silicate pass through a maximum at an intermediate total Si0₂/Na₂0 mole ratio.     

Liquid mixing by large gas bubbles in bubble columns

Liquid mixing by large gas bubbles of spherical cup was investigated for co- and counter-current contact of air-water system with bubble columns of 5 and 10 cm dia. The results obtained are that for the column of 5 cm dia., the longitudinal dispersion coefficient ranges from 5 to 20 cm²/sec for superficial gas velocity from 0·07 to 8 cm/sec and that for the one of 10 cm in diameter it ranges from 9 to 45 cm²/sec for that from 0·035 to 8 cm/sec. Liquid mixing under the coexistence of large and small bubbles was also investigated and it was found that the gas holdup was fairly well explained by an equation derived on the assumption that the mixture of small bubbles and liquid behaves independently of large bubbles. The expansion model was applied to the experimental results on the longitudinal dispersion coefficient and it was observed that there should be the lower limit in the holdup of small bubbles where this model can be applied.     

Creep behavior of polyethylene melts

Creep behavior of branched polyethylene melts with various molecular weight distributions are examined experimentally. The order of the steady-state compliance is in accord with the prediction from the molecular weight distribution. The shear rate dependence of viscosity and steady-state compliance are analyzed according to Pao's theory.     

Acidophilic xylanase from Aureobasidium pullulans: efficient expression and secretion in Pichia pastoris and mutational analysis

A yeast-like fungus Aureobasidium pullulans var. melanigenum strain ATCC 20524 produces an extracellular acidophilic endo-1,4-beta-xylanase with an optimum pH of 2.0 [Ohta et al., J. Biosci. Bioeng., 92, 262-270 (2001)]. The xynI cDNA encoding the precursor protein (XynI) was expressed in the methylotrophic yeast Pichia pastoris under the control of the alcohol oxidase I gene promoter. The 34 amino acid prepro-signal peptide of the A. pullulans XynI directed the efficient secretion of 178 mg of active xylanase per liter of the culture medium. The secretion level of the xylanase with its own signal peptide was comparable to that of the mature protein fused to the prepro leader from Saccharomyces cerevisiae alpha-mating factor and twofold higher than that of the mature protein fused to the pre-type signal peptide from P. pastoris acid phosphatase. The N-terminal amino acid sequence and the apparent M(r) of 24 kDa of the secreted recombinant protein indicated the native-like processing of the A. pullulans XynI signal sequence in P. pastoris. The three-dimensional model and mutational analysis of the xynI gene product showed that Asp-73 and Glu-157 residues located at the upper and lower edges of the active site cleft, respectively, play a significant role in its low pH optimum.     

Two-dimensional multiarray formation of hepatocyte spheroids on a microfabricated PEG-brush surface

A two-dimensional microarray of ten thousand (100 x 100) hepatocyte heterospheroids, underlaid with endothelial cells, was successfully constructed with 100 microm spacing in an active area of 20 x 20 mm on microfabricated glass substrates that were coated with poly(ethylene glycol) brushes. Cocultivation of hepatocytes with endothelial cells was essential to stabilize hepatocyte viability and liver-specific functions, allowing us to obtain hepatocyte spheroids with a diameter of 100 microm, functioning as a miniaturized liver to secret albumin for at least one month. The most important feature of this study is that these substrates are defined to provide an unprecedented control of substrate properties for modulating cell behavior, employing both surface engineering and synthetic polymer chemistry. The spheroid array constructed here is highly useful as a platform of tissue and cell-based biosensors and detects a wide variety of clinically, pharmacologically, and toxicologically active compounds through a cellular physiological response.     

Transferred-electron negative-resistance amplifier

It has experimentally been shown that the travelling domain oscillations in an n type GaAs bulk element can be suppressed by applying externally a large microwave-signal electric field. A computer calculation indicates a possibility of amplifying the signal when the element mounted in a stripline is subject to such a relatively large microwave signal.     

Electrochemical protein chip with arrayed immunosensors with antibodies immobilized in a plasma-polymerized film

An electrochemical protein chip was microfabricated. A thin-film three-electrode system, including an array of 36 platinum working electrodes, a set of thin-film Ag/AgCl electrodes, and platinum auxiliary electrodes, was integrated on a glass substrate. Capture antibodies were immobilized in a 4.5-nm-thick double layer of a hexamethyldisiloxane plasma-polymerized film. Because of their highly cross-linked network structure, the capture antibodies could be firmly immobilized. No nonspecific adsorption was observed during a series of procedures to detect target proteins, and electrochemical cross talk between neighboring sites was negligible. The sandwich immunoassay was conducted on a single chip using model proteins, alpha-1-fetoprotein and beta2-microglobulin. A distinct current increase following the oxidation of hydrogen peroxide produced by the enzymatic reaction of glucose oxidase was observed, which indicates that the capture proteins could actually bind the target proteins. Two kinds of protein were detected independently on multiple sites with respective capture antibodies.