Abstract
Aggregation of human red blood cells (RBC) is central to various pathological conditions from bacterial infections to cancer. When left at low shear conditions or at hemostasis, RBCs form aggregates, which resemble stacks of coins, known as ‘rouleaux’. We experimentally examined the interfacial dielectric dispersion of aggregating RBCs. Hetastarch, an RBC aggregation agent, is used to mimic conditions leading to aggregation. Hetastrach concentration is incrementally increased in blood from healthy donors to measure the sensitivity of the technique. Time lapse electrical impedance measurements were conducted as red blood cells form rouleaux and sediment in a PDMS chamber. Theoretical modeling was used for obtaining complex permittivity of an effective single red blood cell aggregate at various concentrations of hetastarch. Time response of red blood cells’ impedance was also studied to parametrize the time evolution of impedance data. Single aggregate permittivity at the onset of aggregation, evolution of interfacial dispersion parameters, and sedimentation kinetics allowed us to distinguish differential aggregation in blood.
Highlights
Aggregation of human red blood cells (RBC) is central to various pathological conditions from bacterial infections to cancer
While α dispersion is due to the polarization of counterion cloud in the electrical double layer around a cell, existence of α dispersion for RBC suspensions is doubtful and a recent study did not observe α dispersion for b lood20. β dispersion, known as interfacial dispersion, is due to charging of the cell membrane. γ dispersion arises from reorientation of dipolar water molecules in an alternating electric field, and this dispersion in blood is different than that in pure water due to the presence of macromolecules, such as p roteins[20]
The dielectric spectra of four blood samples with changing amounts of RBC aggregation agent as well as whole blood and blood cells suspended in Phosphate Buffered Saline (PBS) were recorded in time series in independent experiments
Summary
Aggregation of human red blood cells (RBC) is central to various pathological conditions from bacterial infections to cancer. Human red blood cells (RBCs) have tendency to form aggregates at low shear or hemostasis conditions by joining face-to-face[1]. These aggregates, which resembles stacks of coins, are known as ‘rouleaux’. The evolution of RBC aggregates starts with formation of linear rouleaux, followed by branched network of rouleaux by face to side connections, compression and collapse of the RBC network, and sedimentation of the fragments All of these process have their unique time scales, and the main determinants of the ESR is the compression of the network and the settling of the network fragments[11]. Most electrical studies on the RBC sedimentation rate fell under β dispersion that has a relaxation frequency around 1 MHz and is a strong function of RBC volume fraction, RBC size and cell membrane capacitance
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