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Plasma and Blood Viscosity
Published in Gordon D. O. Lowe, Clinical Blood Rheology, 2019
The Wells-Brookfield viscometer (Baird and and Tatlock Ltd., London) was the first rotational viscometer to be produced commercially for blood viscosity measurement.80 A cone with a very obtuse angle is rotated on the surface of the flat plate of a sample cup, which it just fails to touch: the fluid under study fills the narrow gap between the cone and the plate. The cone not only applies the shear, but also measures the resultant torque mechanically by means of its spring suspension. Shear rates from 1.15 to 230/sec can be applied. The instrument gives reproducible results at high shear rates (CV less than 2%), but not at shear rates below 23/sec.81,82 This lack of reproducibility at low shear rates probably arises from the effects of red cell sedimentation and surface tension artifacts.17
Hyaluronic Acid Degradation Studies
Published in Robert A. Greenwald, CRC Handbook of Methods for Oxygen Radical Research, 2018
Robert A. Greenwald, Susan A. Moak
The two major types of instrumentation for performing viscometry are capillary viscometers and rotational devices. The latter are quite cumbersome to use and generally require large sample volumes, and they are therefore not readily suitable for biomedical experimentation. Capillary viscometry can be done in many ways, and it is tempting to take a pipet, make two scratch marks on the barrel, and time the flow of the solution between the two points. We believe that sophisticated capillary viscometry is not much harder to do than crude work, and that the data will be much more reproducible from run to run. The instrumentation required, however, costs a few dollars more than a jury-rigged pipet system.
Nature of Flow of a Liquid
Published in Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos, McDonald's Blood Flow in Arteries, 2022
In Poiseuille, or laminar, flow, concentric cylindrical layers of liquid undergo shearing or slide over one another. The force applied to the liquid layer is termed the “wall shear stress (WSS)”, and the velocity gradient obtained between adjacent layers of the liquid is the “shear rate” (Pearson, 2001). Resistance to flow arises from friction between the adjacent layers of the liquid; this frictional flow resistance is the liquid’s viscosity. “Viscosity” is defined as the ratio of WSS and shear rate (Samijo et al., 1997). Therefore, WSS is the product of viscosity and shear rate (Samijo et al., 1997). In general, the measurement of whole blood and plasma viscosity requires mechanical tests, such as the capillary tube viscometer (Çinar et al., 2001), where liquid is sheared by flow past the stationary inner wall of a capillary tube and the cone-and-plate viscometer (Eckmann et al., 2000; De Backer et al., 2002), where the test liquid is sheared between two surfaces, one fixed and one moving, with the torque being related to viscosity. The falling-ball, oscillating and concentric cylinder, and porous bed viscometers have also been used to measure viscosity (Crowley et al., 1991; Reinhart et al., 1998). Several novel methods designed to measure whole blood and plasma viscosity have been published recently. Using a rotational viscometer, Cecchi et al. (2009) demonstrated a significant and independent association between blood viscosity and infarct size in ST-segment elevation myocardial infarction patients after percutaneous coronary intervention. Kim et al. (2012) found that changes in whole blood viscosity at low shear rates correlated with intravascular volume changes during hemodialysis. These investigators used a scanning capillary tube viscometer (Kim et al., 2013; Holsworth et al., 2014) to measure blood viscosity. The development of a scanning capillary tube viscometer allows the measurement of blood viscosity in a clinical setting. Several other techniques for measuring blood viscosity have also been used (or evaluated) to monitor the physiological and pathological conditions of circulatory disorders. For example, a microfluidic device (Jun Kang et al., 2013), an electromagnetic spinning sphere viscometer (Furukawa et al., 2016) and a microviscometer (Kim et al., 2017) have been used.
Process parameters of microsphere preparation based on propylene carbonate emulsion-precursors
Published in Journal of Microencapsulation, 2021
The solubility of different grades of PLGA (RG 502H, RG 503H, RG 504H and RG 505) in PC was evaluated as follows: PLGA was added gradually to 1 mL of propylene carbonate under magnetic stirring until a clear solution or a high viscosity (>1000 mPas) was obtained. The solubility was determined by differential weighing and expressed as mass concentration [mg/mL]. All viscosity measurements were performed on a rotational viscometer (Roto Visco 1, Haake, Thermo Scientific, Germany) equipped with a 60 mm diameter plate-cone setup at 20 ± 0.2 °C. A constant stepwise increase in shear rate (18 s−1 step every 30 s) was used until a shear rate of 125 s−1 was achieved. At this constant shear rate all results were obtained. The viscosity of deionised and degassed water was used before each polymer type measurement to ensure the validity of the results.
Novel lipid–polymer hybrid nanoparticles incorporated in thermosensitive in situ gel for intranasal delivery of terbutaline sulphate
Published in Journal of Microencapsulation, 2020
Soha Mohamed, Mohamed Nasr, Abeer Salama, Hanan Refai
The rheological properties of the in situ gels were examined using cone and plate viscometer (Brookfield viscometer; type DVT-2, Brookfield Engineering Labs., Middleborough, MA). A sample (0.5 ml) was applied to the lower plate of the viscometer using a spatula. The experiments were done at 4 °C and 37 °C using spindle 52. The spindle was rotated at constant speed (10 rpm) then the viscosity determination was performed at different angular velocities (10, 20, 30, 40, and 50 rpm) with 10 s between each two successive speeds and then was repeated in a descending order of velocity (Zaki et al. 2007). The rheograms (shear rate versus shear stress) of the prepared formulae were plotted. The rheological data including ɳ min, ɳ max, Farrow’s constant “N” and hysteresis loop area were calculated for each in situ gel. Farrow's equation was applied to study the flow behaviour of the in situ gels (Tayel et al. 2013): D is the shear rate (sec−1), S is the shear stress (dyne/cm2), ɳ is the viscosity (cp), and N (Farrow’s constant) is the slope of log D against log S plot. N indicates the deviation from Newtonian flow. When N is bigger than 1, this indicates pseudoplastic flow, while if smaller than 1, dilatant flow is assured.
Mucoadhesive thermoreversible formulation of metoclopramide for rectal administration: a promising strategy for potential management of chemotherapy-induced nausea and vomiting
Published in Pharmaceutical Development and Technology, 2020
Mahmoud M. El-Sonbaty, Hatem R. Ismail, Alaa A. Kassem, Ahmed M. Samy, Mohamed A. Akl
The rheological parameters of the selected MCP HCl-LS formulations were estimated using cone/plate Wells viscometer (Brookfield®, HBDV-II + PROCP, 230 V, 50/60 Hz, Brookfield Engineering Laboratories, INC., USA), (Tung, 1994; Ban and Kim 2013). Sample (0.5 mL) was placed on the lower plate of the viscometer ensuring that formulation shearing was minimized, and permitted to be stabilized for at least 5 min before testing. The measurements were performed at 25 °C (RT) and 37 °C (rectal temperature) utilizing spindle 52 at a range of 5–400 rpm shear rate (SR). From the readings of the viscometer, the rheological parameters including share rate (SR) in s−1, shear stress (SS) in dyne/cm2 and the viscosity, ή in millipascal-second (MPa.S) were estimated, and fitted to the equation below for obtaining the flow index (n) and consistency index (m) characteristic for each formula.