Du, Sarah

Sickle Cell Disease (SCD) is a genetic disease that affects approximately 100,000 people in the USA and millions worldwide. The disease is defined by a mutation in hemoglobin, the red blood cell’s oxygen carrying component. Under hypoxic (low oxygen) conditions, the mutated hemoglobin (known as HbS) polymerizes into rigid fibers that stretch the cell into a sickle shape. These rigid cells can occlude blood vessels and cause an individual immense pain. Currently, no point-of-care devices exist in the market for assisting those with SCD. Using microfluidics with custom designed portable impedance measuring hardware we can achieve label-free in vitro analyses of SCD rheology.
This dissertation presents two impedance-based devices for finger-prick volume blood testing, including a microflow cytometer for SCD diagnostics and a vaso-occlusion tester for monitoring blood flow activities. First, the microflow cytometer is validated by measuring the electrical impedance of individual cells flowing through a narrow microfluidic channel. Cellular impedance is interpreted by changes in subcellular components due to oxygen association-dissociation of hemoglobin, using an equivalent circuit model and Multiphysics simulation. Impedance values of sickle cells exhibit remarkable deviations from normal blood cells. Such deviation is quantified by a conformity score, which allows for measurement of SCD heterogeneity, and potentially disease severity. Findings from this study demonstrate the potential for SCD screening via electrical impedance. Second, a vaso-occlusion tester is validated by measuring the impedance response of blood flow within a microfluidic mimic of capillary bed.

Mass transport is important for all biological functions to protect the cell’s environment and to keep its balance of nutrients, proteins and keep the organism alive. We are motivated to study two different types of mass transport, glucose and oxygen that are critical in human system. Specifically, this study focused on mass and oxygen transport in human placenta and oxygen transport in transfusion of artificial oxygen carriers. Studying these processes in vivo or ex vivo are difficult due to ethical or technical challenges.
In this dissertation, Organ-on-a-chip devices were used to simulate placental barrier and blood vessels. In first device, 3D placenta–on-a-chip device consists of a polycarbonate membrane and two Poly dimethylsiloxane microchannels was used. Human umbilical vein endothelial cells were cultured in microfluidic devices and mass transport was measured. In the second device, 3-lane OrganoPlate was used to develop the placental barrier model. The human umbilical vein endothelial cells and trophoblast cells cultured in two microchannels compartmented by polycarbonate membrane (first device) and extracellular matrix gel (second device) to mimic the placental barrier in vitro. Finally, the glucose transfer across the placental barrier affected by malaria parasite was investigated. The results of this study can be used for better understanding of placental malaria pathology and drug efficacy testing.

Human red blood cells (RBCs) must undergo severe deformation to pass through narrow capillaries and submicronic splenic slits for several hundred thousand times in their normal lifespan. Studies of RBC biomechanics have been mainly focused on cell deformability measured from a single application of stress using classical biomechanical techniques, such as optical tweezers and micropipette aspiration. Mechanical fatigue effect on RBCs under cyclic loadings of stress that contributes to the membrane failure in blood circulation is not fully understood. This research developed a new experimental method for mechanical fatigue testing of RBCs using amplitude-modulated electro-deformation technique. Biomechanical parameters of individually tracked RBCs show strong correlations with the number of the loading cycles. Effects of loading configurations on the cellular fatigue behavior of RBCs is further studied. The results uniquely establish the important role of mechanical fatigue in influencing physical properties of biological cells. They further provide insights into the accumulated membrane damage during blood circulation, paving the way for further investigations of the eventual failure of RBCs in various hemolytic pathologies.

Sickle cell disease is an inherited blood cell disorder that affects about 100,000 people
in the US and results in high cost of medical care exceeding $1.1 billion annually. Sickle
cell patients suffer from unpredictable, painful vaso-occlusive crises. Portable, costeffective
approaches for diagnosis and monitoring sickle blood activities are important for
a better management of the disease and reducing the medical cost.
In this research, a mobile application controlled, impedance-based flow cytometer is
developed for the diagnosis of sickle cell disease. Calibration of the portable device is
performed using a component of known impedance value. The preliminary test results are
then compared to those obtained by a commercial benchtop impedance analyzer for further
validation. With the developed portable flow cytometer, experiments are performed on two
sickle cell samples and a healthy cell sample. The acquired results are subsequently
analyzed with MATLAB scripts to extract single-cell level impedance information as well as statistics of different cell conditions. Significant differences in cell impedance signals
are observed between sickle cells and normal cells, as well as between sickle cells under
hypoxia and normoxia conditions.