Microfluidic platforms for hemorheology and coagulation time analysis

Abstract

Blood is a non-Newtonian fluid consisting of plasma and cells that uninterruptedly circulate the body. Erythrocytes are deformable anucleated discoid blood cells with a viscoelastic membrane, constituting around half of blood volume. Hemorheology investigates blood flow characteristics determined by hemorheological properties comprising aggregation, sedimentation, and deformation of erythrocytes as well as blood/plasma viscoelasticity. These hemorheological properties are intricately interdependent. Hence, acquired or hereditary disorders affecting one hemorheological property (malaria, diabetes, anemia) lead to alterations in other properties. Available techniques lack the ability to measure these properties all-at-once and in physiologically relevant conditions. Blood coagulation is as essential as a healthy blood flow. This is a body defense mechanism involving the interplay of blood constituents for stable clot formation to stop bleeding. Sensitive and periodic measurement of coagulation time is critical for individuals who are under the risk of excessive bleeding or thrombus-originated vessel obstruction. Today, these conditions are responsible for 25 percent of all deaths worldwide. Unfortunately, the conventional practice for coagulation monitoring is fixed-interval hospital visits by patients. In this thesis, we present novel microfluidic platforms and measurement methods for the analysis of hemorheological properties and coagulation time parameters. The assays are based on optical quantification of erythrocyte dynamics inside miniaturized channels. The measurements require only 50 µl undiluted blood and are completed in less than 5 min. Firstly, we demonstrate optical measurement of erythrocyte aggregation and rapid measurement of erythrocyte sedimentation rate (ESR) using aggregation dynamics. Secondly, we present the results of clinical ESR tests performed in a local hospital and compare the performance of the developed platform with the conventional 1-hour test. Simultaneously obtained optical transmission signals and real-time microscopic observations of erythrocytes in custom-developed cartridges validate the proposed measurement principle. Thirdly, we present a method offering a holistic approach to blood flow characterization. The method enables simultaneous analysis of multiple hemorheological properties by optically investigating collective erythrocyte dynamics, primarily deformation, in a channel during unique damped oscillatory sample motion. We create a fluidic environment mimicking in vivo flow: confined, directional, and pulsatile movement of blood at flow rates and hematocrit comparable to physiological levels. Fourthly, we present a method for blood coagulation time measurement by optical quantification of erythrocyte aggregation. We demonstrate the fundamental relationship between aggregation and coagulation. Finally, we present an alternative, entirely disposable microfluidic platform for hemorheology and coagulation time analysis based on migration analysis of blood sample in microfluidic channels. Overall, the microfluidic platforms and measurement methods presented here will potentially initiate routine hemorheological and coagulation time analysis even in resource-poor setting.