Microfluidics in Sickle Cell Disease Research: State of the Art and a Perspective Beyond the Flow Problem

Abstract

Sickle cell disease (SCD) is the monogenic hemoglobinopathy where mutated sickle hemoglobin molecules polymerize to form long fibers under deoxygenated state and deform red blood cells (RBCs) into predominantly sickle form. Sickled RBCs stick to the vascular bed and obstruct blood flow in extreme conditions, leading to acute painful vaso-occlusion crises (VOCs) – the leading cause of mortality in SCD. Being a blood disorder of deformed RBCs, SCD manifests a wide-range of organ-specific clinical complications of life (in addition to chronic pain) such as stroke, acute chest syndrome (ACS) and pulmonary hypertension in the lung, nephropathy, auto-splenectomy, and splenomegaly, hand-foot syndrome, leg ulcer, stress erythropoiesis, osteonecrosis and osteoporosis. The physiological inception for VOC was initially thought to be only a fluid flow problem in microvascular space originated from increased viscosity due to aggregates of sickled RBCs; however, over the last three decades, multiple molecular and cellular mechanisms have been identified that aid the VOC in vivo. Activation of adhesion molecules in vascular endothelium and on RBC membranes, activated neutrophils and platelets, increased viscosity of the blood, and fluid physics driving sickled and deformed RBCs to the vascular wall (known as margination of flow) – all of these come together to orchestrate VOC. Microfluidic technology in sickle research was primarily adopted to benefit from mimicking the microvascular network to observe RBC flow under low oxygen conditions as models of VOC. However, over the last decade, microfluidics has evolved as a valuable tool to extract biophysical characteristics of sickle red cells, measure deformability of sickle red cells under simulated oxygen gradient and shear, drug testing, in vitro models of intercellular interaction on endothelialized or adhesion molecule-functionalized channels to understand adhesion in sickle microenvironment, characterizing biomechanics and microrheology, biomarker identification, and last but not least, for developing point-of-care diagnostic technologies for low resource setting. Several of these platforms have already demonstrated true potential to be translated from bench to bedside. Emerging microfluidics-based technologies for studying heterotypic cell–cell interactions, organ-on-chip application and drug dosage screening can be employed to sickle research field due to their wide-ranging advantages.

Sequential quantification of blood and diluent using red cell sedimentation-based separation and pressure-induced work in a microfluidic channel

“…23,73 As sickle cell anemia had relative low level of hematocrit ( i.e. , 20%–25%), 74–77 the present method could be regarded as one of the promising potentials for detecting sickle cell anemia.…”

“…In the near future, if the issues raised by the proposed method are fully resolved (i.e., smartphone or portable pump), the proposed method can be considered as a promising method for monitoring blood samples circulating under an in vitro or ex vivo circuit. 23,73 As sickle cell anemia had relative low level of hematocrit (i.e., 20%-25%), [74][75][76][77] the present method could be regarded as one of the promising potentials for detecting sickle cell anemia.…”

Microfluidic Characterization of Red Blood Cells Microcirculation under Oxidative Stress

“…RBCs’ biophysical phenotyping is of great practical importance [ 51 , 52 ]. It has already been shown that microfluidic analysis can successfully register RBCs disorders [ 21 , 31 , 41 , 53 ]. For improving the analysis of the functional characteristics of RBCs, the microfluidic device must provide high sensitivity to deviations from the physiological norm and establish a standard experimental procedure.…”

“…Recently a microfluidic assay to measure RBCs occlusions under various conditions in vitro was developed to evaluate the clinical efficiency of different drug therapy [ 30 ]. Moreover, microfluidic analysis has been successfully used for the biophysical characterization of sickle cell erythrocytes, allowing in vitro modeling of an oxygen gradient, a trigger factor for developing occlusive crises during polymerization of hemoglobin S in these patients [ 31 ].…”

Microfluidics Approach to the Mechanical Properties of Red Blood Cell Membrane and Their Effect on Blood Rheology

“…In severe cases, ISCs obstruct microvessels, altering the normal circulation of blood. In the last decade, microfluidic devices have played the important role of determining the biophysical characteristics of sickle red cells [175], measuring the mechanical stresses on erythrocytes in sickle cell disease [176], studying vaso-oclusion [104,177,178], identifying biophysical markers [179,180], segregating sickle cells [181], and developing point-of-care diagnostic technologies for low-resource settings [182] and possible treatments [183].…”