Plasma and Blood Viscosity
Gordon D. O. Lowe in 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
Robert A. Greenwald in CRC Handbook of Methods for Oxygen Radical Research, 2018
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.
Bioresponsive Hydrogels for Controlled Drug Delivery
Deepa H. Patel in Bioresponsive Polymers, 2020
Rheological parameters of sample measure structural viscosity and kinetics of volatile components loss. Viscosity test is mostly performed using a cone plate digital rheometer (Brookfield viscometer) under constant temperature at 4°C [26].
A novel thermo-sensitive hydrogel-based on poly(N-isopropylacrylamide)/hyaluronic acid of ketoconazole for ophthalmic delivery
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
The test tube inverting method was used to determine the sol-gel transition temperatures of the copolymer sol in water [19]. Each sample at a given concentration was prepared by dissolving the copolymer in distilled water in a vial and stored at 4 °C for 24 h. The vials containing 20 ml copolymer sol were immersed in an oil bath at different setting temperatures and allowed to reach equilibrium. The sample was regarded as a “gel” when flow was no longer visually observed within 30 s by inverting the vial with a temperature increment of 2 °C per step. Then, the viscosity of the formulation, either in solution or in gel, was determined with a rotational viscometer using a proper sample. Measurements were performed using suitable spindle number at different rotation rates. The viscosity was read directly from the viscometer display. All measurements were made in triplicate.
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.
Design and evaluation of novel topical formulation with olive oil as natural functional active
Published in Pharmaceutical Development and Technology, 2018
Ana Henriques Mota, Catarina Oliveira Silva, Marisa Nicolai, André Baby, Lídia Palma, Patrícia Rijo, Lia Ascensão, Catarina Pinto Reis
To incorporate the olive oil-loaded beads into topical formulations, we prepared two different bases: the Beeler and the Lanette Wax Cream. To prepare 500 g of Beeler base, 75 g of cetyl alcohol, 5 g of white wax, 50 g of propylene glycol, 10 g of sodium lauryl sulphate, and 360 g of purified water were gentle mixed. Firstly, cetyl alcohol and white wax were incubated in a water bath at 65–70 °C (Termofin, J.P. Selecta, Barcelona, Spain). After melting, an aqueous phase with sodium lauryl sulfate, purified water and propylene glycol was added to the oil phase. To prepare 500 g of Lanette Wax Cream, 120 g of cetearylalcohol (Lanette Wax SX®), 80 g of decyloleate (Cetiol®) were weighed and melted in a water bath at 70–75 °C. After melting, 300 g of water was added to the oil phase. Olive oil beads were incorporated in these cosmetic bases after manual mixing (1:1, w/w) using a metal spatula to facilitate the homogenous dispersion of the hydrated beads. The obtained cream was then characterized in terms of aspect (color and homogeneity), odor and pH by using a pH electrode meter (827 pH Lab, Metrohm, Switzerland), calibrated daily with buffer solutions pH 4.00 ± 0.02 and 7.00 ± 0.02 (20 °C) ST (Panreac, Spain). The viscosity was also measured using a DV-I + Viscometer (Brookfield Engineering Labs, Middleboro, MA, USA).
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