Chapter 13 Microfluidic Approaches for Biomechanics of Red Blood Cells E. Du Abstract Studies of cellular mechanics have led to important advances in our understanding of the physiological processes of human diseases as well as provided adjunct biophysical markers for disease diagnosis and therapeutic evaluations. Microfluidic assays allow novel manipulations of single cells quickly and effectively under a physiologically appropriate environment. This paper briefly summarizes our two recently developed microfluidic techniques for probing mechanics of diseased human red blood cells (RBCs). In particular, the in vitro microvascular model allowed characterization of blood micro-rheology in terms of cellular velocity and capillary obstructions under transient hypoxic conditions. These analyses suggested novel mechanics indicators of disease severity and drug treatment in sickle cell anemia. The second microfluidic technique allowed rapid characterization of electrically coupled mechanics of cell membranes from a dielectrophoresisinduced uniaxial stretching of single RBCs. The obtained force-deformation curves agreed well with the independent studies reported in literature for both healthy RBCs and those influenced by Plasmodium falciparum. These findings clearly demonstrated the capabilities of microfluidics in quantitative, mechanical measurements of RBCs and can be potentially applied to other cell types. Keywords Microfluidics • Cellular mechanics • Red blood cell • Sickle cell anemia • Malaria 13.1 Introduction Normal red blood cells (RBCs) have a biconcave disc shape, about 8 μm in diameter and 2 μm in thickness; they must undergo severe passive deformation while maintaining mechanical stability during circulation, where they are subjected to intensive mechanical stimulation in blood flow or when squeezing through micro capillaries and splenic sinusoids [1]. The remarkable deformability of RBCs largely attributes to the mechanical properties of the membrane, its only structural component. During the repeated passages of several hundred 1000 times in their 120-day normal lifespan, RBCs lose their membrane integrity, become rigid, and are degraded by the mononuclear phagocyte system [2]. Various pathological and physiological conditions can accelerate this process, such as hereditary hemolytic anemias [3], extracorporeal circulation for hemodialysis [4], cardiopulmonary bypass [5], and cold storage of RBC products for transfusion purposes [6, 7]. Many engineering techniques, such as micropipette aspiration [8], atomic force microscopy [9, 10], optical tweezers [11–13], diffraction phase microscopy [14–16], magnetic twisting cytometry [17], have enabled high-precision mechanical measurements of individual cells and cellular components. These studies have demonstrated critical roles of cellular mechanics in various pathophysiological processes and provided novel biophysical markers for disease diagnosis and drug efficacy testing, in malaria [18–20], sickle cell disease [16, 21, 22], and cancer [23–25]. These techniques have advantages in high resolutions of force and displacement for probing single-cells and subcellular components. Despite the intense studies in cellular mechanics, limited measurements have yet been obtained at the single-cell level. It remains a challenging task to measure single cells under physiological conditions close to their in vivo microenvironments. However, it is crucial to measure large quantities of cells in order to account for the statistical dispersion in nature among the biological cells. Implementation of such measurements will lead to a better understanding of cellular dynamics and intercellular heterogeneity in their native biological context. Microfluidics has been demonstrated to be an versatile tool for high throughput single-cell studies [20, 26–30], as well as intercellular communications in response to mechanical stimuli [31]. In order to recreate the specific factors that cells are exposed to in vivo, microfluidic systems can be designed to incorporate controls of flow, temperature, gas, chemical E. Du (*) Department of Ocean and Mechanical Engineering, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA e-mail: edu@fau.edu #The Society for Experimental Mechanics, Inc. 2017 C.S. Korach et al. (eds.), Mechanics of Biological Systems and Materials, Volume 6, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-41351-8_13 89
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