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Powder flow in an automated uniaxial tester and an annular shear cell: a study of pharmaceutical excipients and analytical data comparison.

Drug development and industrial pharmacy (2012-10-10)
Martin Kuentz, Peter Schirg
ABSTRACT

An automated version of uniaxial powder flow testing has recently been developed and there is a need for experimental data from pharmaceutical powders. To compare the novel testing method with an annular shear cell using different pharmaceutical excipients. A particular aim was to gain an improved understanding of potential differences in the obtained flow results. Nine excipients were studied with both flow testers at different consolidation levels. Unconfined yield strengths were determined at similar major consolidation stresses. Finally, an anisotropic stress factor was calculated and the fractal character of the powders was assessed by means of image analysis in a rotating drum. Data correlated generally well; however, the unconfined yield strength from uniaxial testing resulted mostly in lower values compared to annular shear cell testing. Differences were specific for the given excipients and mannitol demonstrated the highest discrepancy of measured flow parameters. The differences were first discussed by considering wall friction, anisotropy of forces, brittleness as well as the fractal nature of the powder surface. This heterogeneity of the powder as well as the anisotropy of forces was also found to be important for the relative flow index. The automated uniaxial method demonstrated faster and more reproducible flow testing as compared to an annular shear cell. Therefore, the new method has a high potential in pharmaceutics for example in the quality-control of powders.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Polyvinylpyrrolidone, average mol wt 40,000
Sigma-Aldrich
D-Mannitol, ≥98%
Sigma-Aldrich
Polyvinylpyrrolidone, average mol wt 10,000
Sigma-Aldrich
Polyvinylpyrrolidone, K 30
Sigma-Aldrich
Methyl cellulose, viscosity: 4,000 cP
Supelco
Poly(vinylpolypyrrolidone), ~110 μm particle size
Sigma-Aldrich
Polyvinylpyrrolidone, mol wt (number average molecular weight Mn 360)
Supelco
Mannitol, Pharmaceutical Secondary Standard; Certified Reference Material
Sigma-Aldrich
Polyvinylpyrrolidone, average Mw ~1,300,000 by LS
Sigma-Aldrich
Methyl cellulose, viscosity: 400 cP
Supelco
Lactose, Anhydrous, Pharmaceutical Secondary Standard; Certified Reference Material
Sigma-Aldrich
Methyl cellulose, viscosity: 15 cP, BioReagent, suitable for cell culture
Sigma-Aldrich
(Hydroxypropyl)methyl cellulose, viscosity 2,600-5,600 cP, 2 % in H2O(20 °C)(lit.)
Sigma-Aldrich
Polyvinylpyrrolidone, K 90
Sigma-Aldrich
D-Mannitol, ACS reagent
Sigma-Aldrich
Polyvinylpyrrolidone, powder, average Mw ~55,000
Sigma-Aldrich
Lactose, tested according to Ph. Eur.
Sigma-Aldrich
Polyvinylpyrrolidone, for molecular biology, nucleic acid hybridization tested, mol wt 360,000
Sigma-Aldrich
(Hydroxypropyl)methyl cellulose
Sigma-Aldrich
D-Mannitol, meets EP, FCC, USP testing specifications
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Polyvinylpyrrolidone, powder, BioXtra, suitable for mouse embryo cell culture
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Methyl cellulose, viscosity: 1,500 cP
Sigma-Aldrich
Hypromellose, meets USP testing specifications
Sigma-Aldrich
D-Mannitol, BioXtra, ≥98% (HPLC)
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(Hydroxypropyl)methyl cellulose, viscosity 80-120 cP, 2 % in H2O(20 °C)(lit.)
Sigma-Aldrich
D-Mannitol, suitable for plant cell culture
Sigma-Aldrich
(Hydroxypropyl)methyl cellulose, viscosity 40-60 cP, 2 % in H2O(20 °C)(lit.)
Sigma-Aldrich
Kollidon® 25
Sigma-Aldrich
Polyvinylpyrrolidone, powder, average Mw ~29,000
Sigma-Aldrich
Methocel® A4M, viscosity 3000-5500 mPa.s, 2 % in H2O(20 °C)