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At least 145 records · Page 8Linked to original sources
PubMed1989

A stopped-flow mixer device for a batch microcalorimeter application to NAD-NADase reaction.

A new molded polypropylene, diamond-like carbon (DLC)-coated mixing cell has been developed for use in the batch microcalorimeter. Reagent volume can be varied from 25 microliters to 100 microliters. A 10 microcalorie reaction heat can be measured to 5%. Repeat reactions can be done as often as every 10 min for a fast reaction. Reactions can be started within 1 h or less after loading. A pre-equilibrator and a temperature-controlled syringe drive unit permit solutions to be stored at 4 degrees C while being run at any temperature from -20 degrees C to 40 degrees C. The kinetics and enthalpy of reaction of NAD-NADase have been measured. delta H is about 21 kcal/mol endothermic.

Calorimetry↗
PubMed1987

Diffusion-controlled association of a dye, 1-anilinonaphthalene-8-sulfonic acid, to a protein, bovine serum albumin, using a fast-flow microsecond mixer and stopped-flow.

The kinetic constants of the two fastest reactions of 1-anilinonaphthalene-8-sulfonic acid binding to bovine serum albumin are derived from the results of experiments with a microsecond fast-flow mixing technique and a stopped-flow method. The experiments are interpreted in terms of rapid bimolecular diffusion-controlled associations to two independent regions on the protein surface; this reaction mechanism contrasts with previous kinetic studies of ligand binding to bovine serum albumin which have not demonstrated the fastest kinetic processes.

Anilino Naphthalenesulfonates↗
PubMed1986

NACA overview on assessment of mixer-loader-applicator exposure to pesticides. National Agricultural Chemical Association.

An overview is given of the involvement of the National Agricultural Chemical Association (NACA) in the research of field worker exposure and in the drafting of a protocol for performing exposure studies. Specific field methods are discussed and criteria for the utilization of biological monitoring are given. A generic exposure data base is being developed together with the Environmental Protection Agency (EPA).

Absorption↗
PubMed2004

Qualitative proof of liquid dispersion and penetration-involved granule formation in a high shear mixer.

The origination of granules in the early seconds is an important aspect of high shear granulation. To elucidate these mechanisms, a substandard amount (1.5% w/w) of an aqueous hydroxypropyl cellulose solution was added to four different lactose mixtures: (1) lactose 100 M (d(4,3) approximately 170 microm), (2) lactose 200 M (d(4,3) approximately 50 microm), and (3, 4) 10% magnesium stearate/lactose 100 or 200 M. Between 1 and 15 s after binder addition samples were taken, which were immediately frozen in liquid nitrogen. The frozen sample was sieved into granular (> 280 microm) and non-granular-material (< 280 microm). The binder distribution in these fractions was determined. The observed binder distribution behaviour revealed that three different nucleation mechanisms can occur: (I) For lactose 100 M holds that all the binder is initially located in the granules. These granules are subsequently broken again. (II) The lactose 200 M granules also contain 100% of the added binder liquid. Contrary to lactose 100 M the lactose 200 M granules remain intact during the process. It is argued that in both cases liquid penetration is responsible for the accumulation of all liquid in the granules. A theoretical evaluation also confirmed that liquid penetration leads to the formation of the primary granules (III) No liquid penetration is possible in the hydrophobic magnesium stearate/lactose mixtures and the binder is completely dispersed in the non-granular material.

Chemistry, Pharmaceutical↗
PubMed2004

The effect of vessel material on granules produced in a high-shear mixer.

In this study the effect of different vessel wall materials on the granule size distributions obtained during high-shear granulation of different materials is investigated. The distributions obtained in glass and stainless steel vessels differ from those obtained in PMMA (polymethyl methacrylate) and PTFE (polytetrafluoroethylene) vessels. The high contact angle of PMMA forces all liquid immediately into the more easily wetted powder bed. In this vessel a fast liquid absorbing powder nucleates in the droplet controlled regime, leading to a narrow particle size distribution. In a vessel with a low contact angle (glass or stainless steel) a liquid layer can be formed on the wall surface. This liquid causes an inhomogeneous distribution of liquid over the powder bed; a broader granule size distribution is the result. With a powder that slowly absorbs liquid, local overwet areas can be created, resulting in large granules. This results in broader granule size distributions as well. In conclusion; the contact angle of the vessel material and the wetting rate of the powder used determine the granule growth process and the resulting granule size distribution.

Algorithms↗
PubMed2000

Effect of process parameters on compressibility of granulation manufactured in a high-shear mixer.

Various processing variables that can influence granulation characteristics of a lactose-based formulation were evaluated using a Plackett-Burman experimental design. These parameters were impeller speed, granulating solution addition rate, total amount of water added in the granulation step, wet massing time, moisture content of the granulation after drying, and screen size used for the dry milling. Results showed that granulation growth was enhanced by the increase in the amount of added water, high impeller speed, and short wet massing time. On the other hand, moisture content had the largest impact on granulation compressibility, followed by the wet massing time and impeller speed. Increasing moisture content of the granulation and decreasing wet massing time or impeller speed increased granulation compressibility. Increasing impeller speed and/or wet massing time decreased granule porosity and fragmentation propensity, which led to decreased granulation compressibility. Granulation compressibility was extremely sensitive to processing conditions. Tablets from all runs showed acceptable weight variation and friability, suggesting that the parameters evaluated had little effect on these responses in the ranges tested.

Drug Compounding↗
PubMed2002

Time-resolved UV resonance Raman investigation of protein folding using a rapid mixer: characterization of kinetic folding intermediates of apomyoglobin.

The 244-nm excited transient UV resonance Raman spectra are observed for the refolding intermediates of horse apomyoglobin (h-apoMb) with a newly constructed mixed flow cell system, and the results are interpreted on the basis of the spectra observed for the equilibrium acid unfolding of the same protein. The dead time of mixing, which was determined with the appearance of UV Raman bands of imidazolium upon mixing of imidazole with acid, was 150 micros under the flow rate that was adopted. The pH-jump experiments of h-apoMb from pH 2.2 to 5.6 conducted with this device demonstrated the presence of three folding intermediates. On the basis of the analysis of W3 and W7 bands of Trp7 and Trp14, the first intermediate, formed before 250 micros, involved incorporation of Trp14 into the alpha-helix from a random coil. The frequency shift of the W3 band of Trp14 observed for this process was reproduced with a model peptide of the A helix when it forms the alpha-helix. In the second intermediate, formed around 1 ms after the start of refolding, the surroundings of both Trp7 and Trp14 were significantly hydrophobic, suggesting the formation of the hydrophobic core. In the third intermediate appearing around 3 ms, the hydrophobicity was relaxed to the same level as that of the pH 4 equilibrium intermediate, which was investigated in detail with the stationary state technique. The change from the third intermediate to the native state needs more time than 40 ms, while the appearance of the native spectrum after the mixing of the same solutions was confirmed separately.

Animals↗
PubMed2005

Optically fabricated three dimensional nanofluidic mixers for microfluidic devices.

This paper describes a simple technique for fabricating complex, but well defined, three-dimensional (3D) networks of nanoscale flow paths in the channels of microfluidic systems. Near field scanning optical measurements reveal the optics associated with the fabrication process and the key features that enable its application to the area of microfluidics. Confocal studies of microfluidic devices that incorporate 3D nanostructures formed using this approach show that they function as efficient passive mixing elements, particularly at low Reynolds numbers. This application and others such as separation and extraction inmicrofluidic total analysis systems or lab on a chip devices represent promising areas for 3D nanostructures of this general type.

Equipment Design↗
PubMed2003

Electrowetting-based droplet mixers for microfluidic systems.

Mixing of analytes and reagents is a critical step in realizing a lab-on-a-chip. However, mixing of liquids is very difficult in continuous flow microfluidics due to laminar flow conditions. An alternative mixing strategy is presented based on the discretization of liquids into droplets and further manipulation of those droplets by electrowetting. The interfacial tensions of the droplets are controlled with the application of voltage. The droplets act as virtual mixing chambers, and mixing occurs by transporting the droplet across an electrode array. We also present an improved method for visualization of mixing where the top and side views of mixing are simultaneously observed. Microliters of liquid droplets are mixed in less than five seconds, which is an order of magnitude improvement in reported mixing times of droplets. Flow reversibility hinders the process of mixing during linear droplet motion. This mixing process is not physically confined and can be dynamically reconfigured to any location on the chip to improve the throughput of the lab-on-a-chip.

Electrochemistry↗
PubMed2003

Fabrication of microfluidic mixers and artificial vasculatures using a high-brightness diode-pumped Nd:YAG laser direct write method.

This paper describes a direct write laser technology, which is fast and flexible, for fabricating multiple-level microfluidic channels. A high brightness diode-pumped Nd-YAG laser with slab geometry was used for its excellent beam quality. Channels with flat walls and staggered herringbone ridges on the floor have been successfully fabricated and their ability to perform passive mixing of liquid is discussed. Also, a multi-width multi-depth microchannel has been fabricated to generate biomimetic vasculatures whose channel diameters change according to Murray's law, which states that the cube of the radius of a parent vessel equals the sum of the cubes of the radii of the daughters. The multi-depth architecture allows for flow patterns to resemble physiological vascular systems with lower overall resistance and more uniform flow velocities throughout the network compared to planar patterning techniques which generate uniformly thin channels. The ability to directly fabricate multiple level structures using relatively straightforward laser technology enhances our ability to rapidly prototype complex lab-on-a-chip systems and to develop physiological microfluidic structures for tissue engineering and investigations in biomedical fluidics problems.

Biomimetics↗