![]() This is the first step to compare healthy blood samples with diseased blood samples. Finally, comparing different donor samples, with different features of their red blood cells, we obtained a range of viscosity values that can be adjusted to a single curve, using a power law model. Later, we present a method that allows us to normalize the viscosity according to the shear rate. In order to validate the method, we compared this normalization process with typical constitutive models from Krieger and Dougherty and Quemada with a non-linear dependence on the hematocrit. Then, we study red blood cell crowding, presenting a normalization according to the hematocrit. We first define an effective viscosity, η e f f, as a function of the blood plasma of the sample. In this article, we present a method that allows one to distinguish between healthy blood samples according to the hematocrit and shear rate. Through a mathematical model, we relate the pressure applied to the fluid and its front velocity in the microchannel to determine the viscosity of blood. This method consist of tracking the velocity of the blood front (i.e., blood–air interface) moving inside a microfluidic channel using a pressure-driven flow. These altered values of the viscosity are due to a decrease in the concentration of red blood cells, to an increase of the rigidity of the membrane of red blood cell, or to alterations in the aggregation process.įor this work, the viscosity of blood has been measured using a front microrheology technique. ĭiseases such as malaria, sickle cell anemia, diabetes, and hemolytic syndromes, which affect the biomechanical properties, have shown differences in the expected values of their blood viscosities as they flow at a fixed shear rate. Furthermore, its has been mentioned that these properties are indicators of specific diseases related to RBCs and blood flow. These biomechanical properties have a fundamental contribution to blood viscosity. Meanwhile, from a micro-rheological point of view, blood flow is very sensitive to the elastic properties of individual RBC membranes and to red blood cells aggregation. However, the relation with blood pathologies is in many aspects an open problem for the development of reliable applications of microfluidics to Point of Care Diagnostics, where new approaches to rheometry using microfluidics are fundamental to create and improve PoC devices.įrom a macro-rheological point of view, it is known that, the viscosity of blood is directly proportional to the hematocrit (concentration of red blood cells), meaning that, an increase or decrease of the RBC concentration affects blood viscosity values, as well as its non-Newtonian behavior, which is lost at low hematocrit. Moreover, some works have been published on the possibility of coupling microscopy and microfluidics for diagnostic applications. Several experimental and numerical studies have analyzed the behavior of RBCs and their relation with the viscosity of whole blood using microfluidics. The rise of microfluidics in the past decades has opened alternative methods to measure the rheological properties of fluids, including blood. ![]() The viscosity of blood depends highly on its red blood cell (RBCs) concentration and biomechanical properties, such as aggregation and membrane elasticity. This characteristic of blood is known as shear thinning, which is the property of some complex fluids to decrease their viscosity as the shear rate increases (e.g., increasing its flow velocity), and it has been widely observed in blood. The rheological properties of blood have been studied for many years, and it has been clearly demonstrated that blood has a non-Newtonian behavior. By means of these normalization methods, we were able to determine the differences between the red blood cells of the samples and define a range where healthy blood samples can be described by a single behavior. ![]() The proposed methodology is able to predict the health conditions of the blood samples by introducing a non-dimensional coefficient that accounts for the response to shear rate of the different donors blood samples. In this work, we present two methods that successfully normalize the viscosity of blood for a single and for different donors, first according to the concentration of erythrocytes and second according to the shear rate. Using an experimental analysis of the interface advancement of blood in a microchannel, we determine the viscosity of different samples of blood. These properties affect the viscosity of blood as well as its shear thinning behavior. The rheological properties of blood depend highly on the properties of its red blood cells: concentration, membrane elasticity, and aggregation.
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