Separated Flows in Artificial Organs

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Abstract
Separated flow is unavoidable in artificial blood-wetted devices. Surfaces bound by separated flows cause abnormal protein adsorption, then platelet adhesion and activation, and eventually thrombogenesis and embolization. A prolonged abnormal adsorption pattern is expected, especially in separated flows, as blood first displaces a wetting liquid during start-up of a device. The authors obtained patterns of immunoglobulin G (IgG), fibrinogen, and high molecular weight kininogen (HMK) adsorption in and near a separated flow. The flow was induced in flowing saline, replaced at time zero by plasma. The separated flow was induced behind a 4 mm bar introduced into a steady shear flow (Re = 26.4) in an apparatus designed so that the surface behind the bar was a standard glass microscope slide. The staining technique revealed the distribution of each protein of interest over the surface of the slide, and was applied to slides residing in the flow for 1, 5, 10, 30, and 60 min after the introduction of plasma (final dilution, 3.5% and 8.5%). Results show the expected, rapid disappearance of fibrinogen from surfaces near (but not in) the separated region, and prolonged appearance and even more prolonged disappearance of fibrinogen from the surface bounding the separated region. Slides removed from the apparatus, when exposed to a platelet suspension, showed that platelets adhered where fibrinogen was present on the surface.

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