Improvement of processability of poly(ε‐caprolactone) by radiation techniques

Improvement of processability of Poly(ε‐caprolactone) (PCL) was achieved by introduction of a branch structure using gamma‐irradiation from a ⁶⁰Co source. Irradiated PCL has higher molecular weight by producting a branch structure. Hence, the irradiation at a lower dose, such as 3 Mrad, leads to a higher melt viscosity. The branched structure gave improved properties for dynamic viscoelasticity and elongational viscosity. High elongational viscosity was observed by entanglement due to branch chain formed during irradiation, and the elongational viscosity for 3 Mrad is higher than 1.5 Mrad. Due to a higher elongational viscosity, PCL foam can be produced by a molding process. Foam produced from irradiated PCL pellets at 3 Mrad has honeycomb‐like structure, and the foam showed higher enzymatic degradation compared to film samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1815–1820, 1999     

Growth of ZnO crystal on sapphire and nitridated sapphire substrates at 1000 °C by halide vapor phase epitaxy

Using a halide vapor phase epitaxy (HVPE) technique in which the starting materials are ZnCl₂ generated by the reaction between high purity Zn metal (7 N grade) and Cl₂ gas, and H₂O, ZnO crystals have been grown at a high temperature of 1000 °C on sapphire substrates with and without surface nitridation treatment. It was found that the nitridation treatment resulted in a change of the (112?0) sapphire surface to a (0001) AlN structure, leading to two possible sets of orientations for (0001) ZnO crystals. In addition, the nitridation treatment leads to a smaller average ZnO grain size and a higher density of nuclei.     

High-oil-load encapsulation of medium-chain triglycerides and D-limonene mixture in modified starch by spray drying

Oil mixtures of medium-chain triglycerides (MCT) and D-limonene in mixing ratios from 10 to 100 wt% were encapsulated in modified starch (wall material) by spray drying to produce oil-rich powders. The oil load (mass ratio of oil mixture to wall material) of the infeed emulsion markedly influenced the properties of the infeed liquid and the characteristics of the resulting powder. The viscosity of the infeed liquid and the particle size of the powder exponentially decreased with increasing oil load, while the emulsion droplet size in the infeed liquid increased. In addition, retention of D-limonene during spray drying also decreased markedly with increasing oil load. Irrespective of the different oil loads and concentrations of the wall material, D-limonene retention was well correlated with the emulsion droplet diameter of the infeed liquid. The encapsulation efficiency of the oil mixture exhibited a maximum value (almost 100%) at an oil load between 0.5 and 1.0, before decreasing at higher oil loads. At an oil load of 2.0, the encapsulation efficiency of D-limonene was reduced to almost zero, while around 40% of the initial MCT was encapsulated in the powder. The increase in oil load also led to increased amounts of surface oil of MCT and D-limonene in the resulting powder due to the increasing emulsion droplet diameter of the infeed liquids. PRACTICAL APPLICATION: This study proposes the microencapsulation of medium-chain triglycerides under high-oil-load conditions by spray drying. The powders prepared by this process provide significant benefits in terms of rapid energy conversion after consumption without accumulation in the body. Important quality factors of the powder products such as the encapsulation efficiency and the amount of surface oil were examined to understand the optimum process conditions for spray drying.     

Colored Fluorescent Silk Made by Transgenic Silkworms

Silk is a protein fiber used to weave fabrics and as a biomaterial in medical applications. Recently, genetically modified silks have been produced from transgenic silkworms. In the present study, transgenic silkworms for the mass production of three colors of fluorescent silks, (green, red, and orange) are generated using a vector originating from the fibroin H chain gene and a classical breeding method. The suitability of the recombinant silks for making fabrics is investigated by harvesting large amounts of the cocoons, obtained from rearing over 20 thousand silkworms. The application of low temperature and a weakly alkaline solution for cooking and reeling enables the production of silk fiber without loss of color. The maximum strain tolerated and Young's modulus of the fluorescent silks are similar to those of ordinary silk, although the maximum stress value of the recombinant silk is slightly lower than that of the control. Fabrics with fluorescent color are demonstrated using the recombinant silk, with the color persisting for over two years. The results indicate that large amounts of genetically modified silk can be made by transgenic silkworms, and the silk is applicable as functional silk fiber for making fabrics and for use in medical applications.     

Comparison of side chain oxidation of potential C27-bile acid intermediates between mitochondria and peroxisomes of the rat liver: presence of beta-oxidation activity for bile acid biosynthesis in mitochondria

The oxidation of the side chains of two potential bile acid intermediates, 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) and 3 alpha,7 alpha-dihydroxy-5 beta-cholestanoic acid (DHCA), were investigated in rat liver mitochondria and peroxisomes. Both THCA and DHCA were efficiently oxidized to yield cholic acid and chenodeoxycholic acid, along with 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholest-24-enoic acid and 3 alpha,7 alpha-dihydroxy-5 beta-cholest-24-enoic acid, respectively, in both the mitochondria and peroxisomes. However, the spectrum of the metabolites in the mitochondria differed greatly from those in the peroxisomes. The major products from THCA and DHCA in the mitochondria were 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-chol-22-enoic acid and 3 alpha,7 alpha-trihydroxy-5 beta-chol-22-enoic acid, respectively, which were tentatively identified from the mass spectral data. However, the formation of these C24-unsaturated bile acids was not observed in the peroxisomes. These results strongly suggest that the cleavage of the side chain of the C27-intermediates for bile acid biosynthesis also occurs independently in the mitochondria, not due to the contamination of peroxisomes.     

Study on radiation vulcanization of natural rubber latex

The effect of dose rate of 60Co γ-ray on radiation vulacnization of natural rubber latex is studied using Malysian latex with 0.002 mass fraction KOH and 0.05 mass fraction n-BA.Results show that,when radiation doses are 20 and 15kGy,only that the dose rates are greater than 0.49 and 1.6 kGY/h,respectively can make the tensile strength of latex film meet the related standard;besides,storage time of radiation vulcanization latex has no effect on physical properties of the film.     

Expression profile of active genes in granulocytes

A number of genes active in granulocytes have been intensively studied as to the function of their products and their expression controls. However, the intensities and relative order of these gene activities have not been studied. This report describes an expression profile of 748 different species of active genes in human peripheral granulocytes obtained by analyzing a 3'-directed cDNA library that faithfully represents the mRNA population in the source cells. A significant fraction (20.3% of the total) of the expressed genes in granulocytes consisted of nuclear proteins such as DNA binding proteins, of secretory proteins such as cytokines, and of membrane proteins such as major histocompatibility complex (MHC) proteins and receptors. By comparing this expression profile with 11 profiles similarly obtained with unrelated human cells/tissues, we discovered 10 novel genes that are likely to act specifically in granulocytes. Comparison of this expression profile with that obtained with granulocytoids widely used as a granulocyte model by inducing a cultured promyelocytic leukemia cell line HL60 showed similarities and dissimilarities of gene expressions.     

Comparative studies of metabolism of simultaneously administered chenodeoxycholic acid and ursodeoxycholic acid in hamsters

We present the comparative studies of metabolism of chenodeoxycholic acid and ursodeoxycholic acid and their taurine conjugates in the liver and fecal culture from hamsters. When [24-14C]chenodeoxycholic acid and [11,12-3H]ursodeoxycholic acid were simultaneously instilled into the jujunal loop of bile fistula hamsters, both bile acids administered were recovered mainly as their conjugates with taurine and glycine in the fistula bile. The recovery of chenodeoxycholic acid was slightly but significantly higher than that of ursodeoxycholic acid. Chenodeoxycholic acid was more efficiently conjugated with glycine than ursodeoxycholic acid. The glycine/taurine ratio in the biliary chenodeoxycholic acid was 1.9, and that in ursodeoxycholic acid was 1.6. In addition, as much as 6.2% of ursodeoxycholic acid was excreted as the unconjugated form; on the other hand only 2.4% of unconjugated chenodeoxycholic acid was excreted. When [24-14C]chenodeoxycholyltaurine and [11,12-3H]ursodeoxycholyltaurine were simultaneously administered into the ileum loop of bile fistula hamsters, both bile salts were absorbed and secreted efficiently into the bile at the same rate. These results indicate that slightly lower recovery of ursodeoxycholic acid in the bile could be due to the less effective conjugation of ursodeoxycholic acid than chenodeoxycholic acid in the liver. Deconjugation by fecal culture from a hamster proceeded more rapidly in chenodeoxycholyltaurine than ursodeoxycholyltaurine. 7-Dehyroxylation to form lithocholic acid by fecal culture was also faster in chenodeoxycholic acid than ursodeoxycholic acid. The formation of 7-oxolithocholic acid from ursodeoxycholic acid was lesser than from chenodeoxycholic acid. In summary, bacterial deconjugation followed by 7-dehydroxylation to form lithocholic acid seems to be achieved more efficiently with chenodeoxycholic acid than ursodeoxycholic acid.     

Quantum distributed model of the resonant tunneling transistor

Two-dimensional simulation is crucial in the analysis of the transport characteristics of a resonant tunneling transistor that has a base electrode attached to the well region of a double barrier structure because of the transistor's two-dimensional heterogeneousness. We propose a novel numerical model of the resonant tunneling transistor that includes two-dimensional potential distribution and two-dimensional spatial current distribution. By using this mode in the present model, it is found that the transistor's I-V characteristics are strongly dependent on its internal well resistance     

Syntheses of hydroxypropyl methylcellulose phthalate gels in organic solvents by radiation crosslinking

Cellulose gels were prepared through the crosslinking of hydroxypropyl methylcellulose phthalate (HPMCP) with electron‐beam irradiation in concentrated organic solvent solutions. The effects of the solvent species, polymer concentration, and irradiation dose on the formation of the gels were investigated. Some organic solvents, such as alcohols with short alkyl chains, alkyl acetates, and ketones, were found to be suitable as media for the radiation crosslinking of the polymer. The prepared HPMCP gels showed excellent swelling in various organic solvents with medium hydrogen‐bonding abilities, such as pyridine, cresol (meta), acetic acid, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, 1,4‐dioxane, acetone, methyl ethyl ketone, methyl acetate, and chloroform. In an acetone/water mixture, the swelling ratio was significantly dependent on the solvent composition because of the coexistence of both hydrophilic and hydrophobic moieties in HPMCP. These results suggest that HPMCP gels have the potential to be superabsorbents for various kinds of organic solvents. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3002–3007, 2004