Monodisperse nanoparticles of poly(ethylene glycol) macromers and N‐isopropyl acrylamide for biomedical applications

Poly(ethylene glycol)‐based nanoparticles have received significant attention in the field of biomedicine. When they are copolymerized with pH‐ or temperature‐sensitive comonomers, their small size allows them to respond very quickly to changes in the environment, including changes in the pH, ionic strength, and temperature. In addition, the high surface‐to‐volume ratio makes them highly functionalized. In this work, nanoparticles composed of temperature‐sensitive poly(N‐isopropylacrylamide), poly(ethylene glycol) 400 dimethacrylate, and poly(ethylene glycol) 1000 methacrylate were prepared by a thermally initiated, free‐radical dispersion polymerization method. The temperature‐responsive behavior of the hydrogel nanoparticles was characterized by the study of their particle size with photon correlation spectroscopy. The size of the nanoparticles varied from 200 to 1100 nm and was a strong function of the temperature of the system, from 5 to 40°C. The thermal, structural, and morphological characteristics were also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1678–1684, 2003     

Wasserabsorptionseigenschaften natürlicher polyionenkomplexe

As the cationic component of natural polymer polyionic complexes, polysaccharide chitosan or polypeptide polylysine, and as the anionic component, polysaccharide carboxymethyl cellulose (=CMC) or polypeptide poly(glutamic acid) (PGA) were used. The degree of chitosan/CMC or polylysine/PGA complex film swelling was minimum, when the amounts of the cationic and anionic groups in these polymers were balanced at 1 : 1 ratio. On the other hand, the degree of chitosan/PGA film swelling was minimum at the ratio with excess of PGA which is a linear flexible chain. Comparing the enthalpies estimated by DSC analysis, it was suggested that the larger quantity of water in the form of nonfreezable bound water was absorbed in the complex films with polysaccharide which is a chain of ring structure. Further, the compressive moduli of swollen complex films were high, when the complex consisted of polysaccharide components.     

Temperature and frequency dependence of dielectric loss of Ba(Mg1/3Ta2/3)O3 microwave ceramics

Ba(Mg_1/3Ta_2/3)O₃ ceramic possessing extremely high Q × f value of more than 300 THz at microwave frequency was developed in our previous study. It is of great interest to understand the mechanism of microwave absorption in such a practical material. In the present study we report on the temperature dependence of the dielectric loss in the Ba(Mg_1/3Ta_2/3)O₃. The mechanism of the microwave absorption is discussed using two phonons difference process. The samples were prepared by conventional solid state reaction and sintered at 1893 K in oxygen atmosphere. Dielectric properties in the microwave range were measured by Hakki & Colemann and resonant cavity methods in the temperature range of 20–300 K. Whispering gallery mode technique was used for the measurement of the dielectric properties at the millimeter wave frequency. Dielectric loss of the Ba(Mg_1/3Ta_2/3)O₃ at the microwave frequency increases with temperature between 200 and 300 K in general agreement with the theory of intrinsic dielectric loss derived from the two phonon difference process. However below 200 K, the dielectric loss has shown a distinctive behavior with a loss peak at 40 K. It was inferred that the loss peak of the Ba(Mg_1/3Ta_2/3)O₃ was caused by the local orientation polarization having dispersion at the microwave frequency.     

Photoelectric properties of ABA‐type triblock copolymers designed using fluorine‐containing polyimide macroinitiators with polyhedral oligomeric silsesquioxane

4,4′‐(Hexafluoro‐isopropylidene) diphthalic anhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (6FDA‐TeMPD) was synthesized and reacted with polyhedral oligomeric silsesquioxane (POSS) to form an ABA‐type triblock copolymer by atom transfer radical polymerization. The solid‐state and optical properties of the resulting copolymers were systematically investigated, and their electronic states were analyzed. As the POSS concentration increased, the transparency across the entire wavelength range increased. In the ABA‐type triblock copolymers, a new transition was observed between the highest occupied molecular orbital in POSS and the lowest unoccupied molecular orbital in 6FDA‐TeMPD because of their high molecular size dispersion. Since the refractive index of 6FDA‐TeMPD decreased linearly as the POSS concentration increased, the refractive index of the ABA‐type triblock copolymers of 6FDA‐TeMPD with POSS could be easily controlled. POLYM. ENG. SCI., 57:1207–1213, 2017. © 2017 Society of Plastics Engineers     

Electrode conditioning characteristics in vacuum under impulse voltage application in nonuniform electric field

In this paper, we quantitatively investigated the impulse conditioning mechanism under nonuniform electric field electrodes in a vacuum. A negative standard lightning impulse voltage was applied between rod and plane electrodes whose materials were Cu-Cr, stainless steel and Cu and the gap lengths were d=5 and 10 mm, respectively. Experimental results revealed the transition of the breakdown (BD) sport region on the rod electrode and the corresponding BD field strength in the conditioning process. As a result, we found that the BD spot region started at the tip of the rod electrode and moved to the wider region of the rod electrode with lower electric field as the shots of the voltage application increased before the saturation of the BD voltage. Finally, by analyzing the results with an electric field strength, we propose that "the conditioning degree" along the electrode surface distributed directly proportional to the electric field distribution under a nonuniform electric field in a vacuum, irrespective of the electrode materials     

Influence of seat characteristics on occupant motion in low-speed rear impacts

To analyze the effect of the seat characteristics on dummy motions and human volunteer motions, sled tests simulating low-speed rear impacts were conducted with some seats which had different characteristics. Volunteer's cervical vertebral motions were photographed with an X-ray cineradiographic system at a speed of 90 frames/s as well as the visible motions of dummy's and volunteer's were recorded. Although the tests were conducted under limited conditions, the results indicated the relationship between the occupant's visible motions, which are assumed to be closely related to the whiplash injury mechanism, and seat characteristics. It should be noted that the volunteer sled tests were discussed and approved by the Tsukuba University Ethics Committee and the volunteer submitted his informed consent in writing in line with the Helsinki Declaration.     

Cloning of a gene for D-sorbitol dehydrogenase from Gluconobacter oxydans G624 and expression of the gene in Pseudomonas putida IFO3738

We have cloned a novel gene for d-sorbitol dehydrogenase (SLDH), which efficiently converted D-sorbitol to L-sorbose, from Gluconobacter oxydans G624 (FERM BP-4415). A cosmid library of the genomic DNA was screened by assaying SLDH activity. The inserted DNA from a positive clone was downsized by subcloning into charomid and pUCP plasmid, successively. Sequencing analysis of the DNA responsible for SLDH activity revealed an open reading frame of 1455 bp coding for 485 amino acid residues with a calculated molecular mass of 53,642 Da. The amino acid sequence showed 42.2% identity with a NAD+-dependent mannitol dehydrogenase (MDH), which catalyzed conversion of d-sorbitol to d-fructose, from Pseudomonas fluorescens DSM50106. Since the intact SLDH was found to be very unstable during isolation and purification, this SLDH fused to 6 x His-tag was expressed in Pseudomonas putida IFO3738 and purified by immobilized metal affinity chromatography using cobalt-based resins. The 6 x His-tag SLDH catalyzed the oxidation of D-sorbitol to L-sorbose and exhibited 15 times higher activity in the presence of NADP+ than that of NAD+. These results indicate that the SLDH is a novel kind of dehydrogenase distinct from MDH previously reported.