Challenge.GIF (211752 bytes)

From the perspective of rheological measurements, blood is a challenging complex fluid where reproducibility and accuracy of measurement can be affected by red blood cell sedimentation, measurement system confinement size and geometry.  The Vilastic oscillatory tube method rises above rotational instruments to meet these challenges.  

CHALLENGE:
Sedimentation of red blood cells can greatly affect the accuracy of measurement.
Vilastic Instruments Rotational Instruments

Because the vertical cylindrical tube contains large diameter reservoirs at each end, sedimentation during measurement is confined to the reservoir and does not affect the measurements in the tube.

The geometry of rotational instruments accelerates cell sedimentation during rotation (ref. 1).  The two phase fluid produced by sedimentation will negatively affect the accuracy of measurement.

CHALLENGE:
Reproducible, precision geometry is necessary for meaningful results.
Vilastic Instruments Rotational Instruments

The dimensions of the cylindrical tubes are fixed and permanent numerical constants and thus are not affected by handling, filling or measurement.

The dimensions of the fixtures used in rotation (cup-bob, cone-plate, plate-plate) must be carefully set for each sample, introducing the possibility of dimensional errors.

CHALLENGE:
The rheological properties of blood in small spaces can be affected by confinement geometry.  Small confinements can restrict cell orientation and local concentrations (ref. 2).
Vilastic Instruments Rotational Instruments

The cylindrical tube of the Vilastic-3 and BioProfiler have a uniform confinement space with a diameter >100 cell diameters.

The confinement space of rotational cone and plates are non-uniform.  The confinement space varies from apex to rim.   the blood properties at the apex will differ from those at the rim.

References:

1. H. Schmid-Schonbein, P. Gaehtgens and H. Hirsch, “On the shear rate dependence of red cell aggregation in vitro”, Journal of Clinical Investigation47, p1447-1453 (1968).
2. G. B. Thurston, “The viscosity and viscoelasticity of blood in small diameter tubes”, Microvascular Research11, 133-146 (1976).

For more information on blood and plasma rheology visit  Plasma Viscosity and Blood Viscoelasticity” and “FAQ-What is Blood Viscoelasticity” .  Detail specifications are available for instruments capable of measuring the blood viscoelasticity and plasma viscosity at  “BioProfiler” and  “Vilastic-3“. 

Vilastic Scientific, Inc. © 2006
www.vilastic.com
rheology@vilastic.com

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