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TECHNICAL PAPERS: Fluids/Heat/Transport

Precision Assessment of Biofluid Viscosity Measurements Using Molecular Rotors

[+] Author and Article Information
Walter J. Akers

Department of Biological Engineering,  University of Missouri-Columbia, 252 Ag Engineering Building, Columbia, MO 65211

Mark A. Haidekker

Department of Biological Engineering,  University of Missouri-Columbia, 252 Ag Engineering Building, Columbia, MO 65211HaidekkerM@missouri.edu

J Biomech Eng 127(3), 450-454 (Jan 31, 2005) (5 pages) doi:10.1115/1.1894366 History: Received August 02, 2004; Revised December 20, 2004; Accepted January 31, 2005

Blood viscosity changes with many pathologic conditions, but its importance has not been fully investigated because the current methods of measurement are poorly suited for clinical applications. The use of viscosity-sensitive fluorescent molecular rotors to determine fluid viscosity in a nonmechanical manner has been investigated recently, but it is unknown how the precision of the fluorescence-based method compares to established mechanical viscometry. Human blood plasma viscosity was modulated with high-viscosity plasma expanders, dextran, pentastarch, and hetastarch. The samples were divided into a calibration and a test set. The relationship between fluorescence emission and viscosity was established using the calibration set. Viscosity of the test set was determined by fluorescence and by cone-and-plate viscometer, and the precision of both methods compared. Molecular rotor fluorescence intensity showed a power law relationship with solution viscosity. Mechanical measurements deviated from the theoretical viscosity value by less than 7.6%, while fluorescence-based measurements deviated by less than 6%. The average coefficient of variation was 6.9% (mechanical measurement) and 3.4% to 3.8% (fluorescence-based measurement, depending on the molecular rotor used). Fluorescence-based viscometry exhibits comparable precision to mechanical viscometry. Fluorescence viscometry does not apply shear and is therefore more practical for biofluids which have apparent non-Newtonian properties. In addition, fluorescence instrumentation makes very fast serial measurements possible, thus promising new areas of application in laboratory and clinical settings.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Chemical structures of the molecular rotors used in this study, 9-[(2-Cyano-2-hydroxy carbonyl)vinyl]julolidine triethyleneglycol ester (CCVJ-TEG) and 9-[(2-Cyano-2-hydroxy carbonyl)vinyl]julolidine (CCVJ)

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Figure 2

Reference viscosity (line) of plasma-hetastarch mixture computed from mechanically measured viscosity at 24°C (data points). Error bars indicate standard deviation.

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Figure 3

Error analysis of blood plasma viscosity as measured using cone-plate rheometer at indicated shear rates at 24°C. Error bars indicate standard deviation. Deviation is lower and non-Newtonian behavior is minimal at higher shear rates.

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Figure 7

Comparison of viscosity measurements made by cone-plate rheometer with fluorescence viscometery from calibration curve

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Figure 6

Log log comparison of CCVJ fluorescence versus plasma–hetastarch mixture viscosity. Error bars indicate standard deviation.

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Figure 5

Absorption spectra of CCVJ stained and unstained plasma-pentastarch mixtures. Solution absorbance at 490 nm and above is attributable to plasma alone, not dye.

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Figure 4

Viscosity values for plasma-hetastarch mixtures obtained with cone-and-plate rheometer at various shear rates using ramp-up, ramp-down protocol. Highest viscosity solution exceeded instrument limits at 750s−1.

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