A microfluidic gel valve device using reversible sol–gel transition of methyl cellulose for biomedical application

We have fabricated a microfluidic gel valve device that used reversible sol–gel transition of methyl cellulose (MC). A microheater and a microtemperature sensor were implemented in each microchannel in the gel valve device. Before evaluating the performance of the gel valve device, various properties of the MC solution were investigated using viscometer, spectrophotometer, and NMR. Gelation temperature was increased as the MC concentration was increased. Clear gel, an intermediate state between clear sol and turbid gel, was found at the temperature range from 30–40°C to 50–60°C. Temperature at each microchannel of the device was measured and the effect of the temperature difference on the valve operation was elucidated. In order to have normal operation of the gel valve, it was important to keep the temperature of the heated microchannel around 60°C while keeping the temperature of the flowing microchannel below 35°C. The temperature difference between two microchannels was about 23 K when fan forced cooling (FFC) method was used. For normal performance of the gel valve device, a temporary pause of fluid flow for at least 5 s was required to complete the local gelation in the microchannel. Stable gel valve performance was obtained at the flow rates larger than 5 μl/min. The gel valve device showed no leakage up to 2.07×10⁴ Pa.     

On intuitionistic fuzzy sub-hyperquasigroups of hyperquasigroups

The notion of intuitionistic fuzzy sets was introduced by Atanassov as a generalization of the notion of fuzzy sets. In this paper, we consider the intuitionistic fuzzification of the concept of sub-hyperquasigroups in a hyperquasigroup and investigate some properties of such sub-hyperquasigroups. In particular, we investigate some natural equivalence relations on the set of all intuitionistic fuzzy sub-hyperquasigroups of a hyperquasigroup.     

Isolation and characterization of phenol-degrading denitrifying bacteria

Phenol is a man-made as well as a naturally occurring aromatic compound and an important intermediate in the biodegradation of natural and industrial aromatic compounds. Whereas many microorganisms that are capable of aerobic phenol degradation have been isolated, only a few phenol-degrading anaerobic organisms have been described to date. In this study, three novel nitrate-reducing microorganisms that are capable of using phenol as a sole source of carbon were isolated and characterized. Phenol-degrading denitrifying pure cultures were obtained by enrichment culture from anaerobic sediments obtained from three different geographic locations, the East River in New York, N.Y., a Florida orange grove, and a rain forest in Costa Rica. The three strains were shown to be different from each other based on physiologic and metabolic properties. Even though analysis of membrane fatty acids did not result in identification of the organisms, the fatty acid profiles were found to be similar to those of Azoarcus species. Sequence analysis of 16S ribosomal DNA also indicated that the phenol-degrading isolates were closely related to members of the genus Azoarcus. The results of this study add three new members to the genus Azoarcus, which previously comprised only nitrogen-fixing species associated with plant roots and denitrifying toluene degraders.     

Effect of topical butyrate on rectal epithelial kinetics and mucosal enzyme activities

Public awareness and misunderstandings of lactose intolerance are at an all-time high. Many people erroneously believe they are lactose intolerant or develop gastrointestinal symptoms after intake of lactose. Consequently, lactose-containing foods such as milk and other dairy foods may be eliminated unnecessarily from the diet. Because these foods are a major source of calcium, low intake of them can compromise calcium nutriture. This, in turn, can increase the risk of major chronic diseases such as osteoporosis (porous bones) and hypertension. This review is intended to help dietetics professionals alleviate clients' fears about lactose intolerance and recommend dietary strategies to improve tolerance to lactose. Scientific findings indicate that the prevalence of lactose intolerance is grossly overestimated. Other physiologic and psychologic factors can contribute to gastrointestinal symptoms that mimic lactose intolerance. Scientific findings also indicate that people with laboratory-confirmed low levels of the enzyme lactase can consume 1 serving of milk with a meal or 2 servings of milk per day in divided doses at breakfast and dinner without experiencing symptoms. Several dietary strategies are available to help lactose maldigesters include milk and other dairy foods in their diet without experiencing symptoms.     

Counter-current air-water flow in narrow rectangular channels with offset strip fins

Counter-current two-phase flows of air-water in narrow rectangular channels with offset-strip fins have been experimentally investigated in a 760 mm long and 100 mm wide test section with 3.0 and 5.0 mm gap widths. The two-phase flow regime, channel-average void fractions and two-phase pressure gradients were studied. Flow regime transition occurred at lower superficial velocities of air than in the channels without fins. In the bubbly and slug flow regimes, elongated bubbles rose along the subchannel formed by fins without lateral movement. The critical void fraction for the bubbly-to-slug transition was about 0.14 for the 3 mm gap channel and 0.2 for the 5 mm gap channel, respectively. Channel-average void fractions in the channels with fins were almost the same as those in the channels without fins. Void fractions increased as the gap width increased, especially at high superficial velocity of air. The presence of fins enhanced the two-phase distribution parameter significantly in the slug How, where the effect of gap width was almost negligible. Superficial velocity of air dominated the two-phase pressure gradients. Liquid superficial velocity and channel gap width has only a minor effect on the pressure gradients.     

Preparation and properties of polyelectrolyte complex sponges composed of hyaluronic acid and chitosan and their biological behaviors

Polyelectrolyte complexes (PECs) composed of chitosan and hyaluronic acid (HA) were prepared in various pH regions and at different weight ratios. At low pHs, there was a strong ionic interaction between NH groups in chitosan and both COO^? and COOH groups in HA due to the deprotonation of HA, whereas weak linkages were formed at high pHs because only the carboxyl groups of HA could interact with NH groups in chitosan. The formation of PECs resulted in a decrease in the crystallinity and thermal stability caused by the interactions between polyions. With variations in the degree of ionization of polyions at various pH conditions, novel PEC sponges were prepared by the freeze drying of PEC solutions. Furthermore, for the evaluation of the wound‐healing effect of PEC sponges with or without an antimicrobial agent (silver sulfadiazine), they were applied to a full‐skin defect of a Wistar rat in vivo. The histology and computerized morphometric analysis of the epidermal healing confirmed the proliferation of fibroblasts in the wound bed and a distinct reduction in infectious agents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 925–932, 2003     

Faceting of High-Angle Grain Boundaries in Titanium-Excess BaTiO3

The grain boundaries in BaTiO₃ with excess Ti of 0.5, 0.3, and 0.1 at.% sintered at 1300° or 1250°C have been examined by scanning electron microscopy (SEM), electron backscattered diffraction pattern (EBSP), and transmission electron microscopy (TEM). In the 0.1% Ti-excess specimen, large grains growing abnormally form high-angle grain boundaries when they impinge on each other as verified by EBSP. A large fraction of these grain boundaries are faceted with hill-and-valley shapes. In the 0.5% Ti-excess specimen, large grains growing abnormally are elongated in the directions of their {111} double twins. These grains often form flat grain boundaries parallel to their {111} planes with the fine matrix grains, and the grain-boundary segments between the large impinging grains with high misorientation angles are often also parallel to the {111} planes of one of the grains. These grain boundaries are expected to be singular. Most of the grain boundaries between the randomly oriented fine-matrix grains in the 0.3 at.% Ti-excess specimen are also faceted with hill-and-valley shapes at finer scales when observed under TEM. The facet planes are parallel to {111}, {011}, and {012} planes of one of the grain pairs and are also expected to be singular. These high-angle grain boundaries lying on low index planes of one of the grain pairs are similar to those observed in other oxides and metals.     

Vitamin A microencapsulation within poly(methyl methacrylate)‐g‐polyethylenimine microspheres: Localized proton buffering effect on vitamin A stability

To stabilize vitamin A in a cosmetic/dermatological formulation, we present here a new encapsulation method based on polymer microspheres having a localized “proton‐buffering” capacity. Poly(methyl methacrylate)‐g‐polyethylenimine (PMMA‐g‐PEI) was prepared by direct condensation grafting of PEI onto poly(methyl methacrylate‐co‐methyl acrylic acid). The reaction was confirmed by FT‐IR analysis showing the amide vibration at 1,550 cm^?1. Elemental analysis indicated that the weight content of the grafted PEI was 1.6% (w/w). Vitamin A was encapsulated into PMMA‐g‐PEI microspheres by using an oil‐in‐water (O/W) single emulsion method. The presence of PEI moiety dramatically improved the chemical stability of vitamin A in microspheres. Vitamin A encapsulated within PMMA‐g‐PEI microspheres maintained 91% of its initial activity after 30‐day incubation at 40°C, while only maintaining 60% within plain PMMA microspheres. This study demonstrates that proton‐buffering within hydrophobic polymer matrix is a useful strategy for stabilizing “acid‐labile” active ingredients. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 517–522, 2004