Effect of temperature on the electroratation behavior of human red blood cells

The aim of this work is to analyze the effects of temperature on dielectric parameters of Human Red Blood Cells (HRBCs). The cells were suspended in external media with different conductivities and observed at different temperatures. An AC electric field was applied. The cell parameters were obtained by fitting the experimental points with the model. Effects on cell volume and cell radius led to a change in the interior ionic concentration. Cytoplasmic conductivity was calculated using the Debye-Hückel-Onsager relation. An exponential relationship of the conductivity to temperature was found

An Integrative Approach to Elucidating the Governing Mechanisms of Particles Movement under Dielectrophoretic and Other Electrokinetic Phenomena

Dielectrophoresis (DEP) has been a subject of active research in the past decades and has shown promising applications in Lab-on-Chip devices. Currently researchers use the point dipole method to predict the movement of particles under DEP and guide their experimental designs. For studying the interaction between particles, the Maxwell Stress Tensor (MST) method has been widely used and treated as providing the most robust and accurate solution. By examining the derivation processes, it became clear that both methods have inherent limitations and will yield incorrect results in certain occasions. To overcome these limitations and advance the theory of DEP, a new numerical approach based on volumetric-integration has been established. The new method has been proved to be valid in quantifying the DEP forces with both homogeneous and non-homogeneous particles as well as particle-particle interaction through comparison with the other two methods. Based on the new method, a new model characterizing the structure of electric double layer (EDL) was developed to explain the crossover behavior of nanoparticles in medium. For bioengineering applications, this new method has been further expanded to construct a complete cell model. The cell model not only captures the common crossover behavior exhibited by cells, it also explains why cells would initiate self-rotation under DEP, a phenomenon we first observed in our experiments. To take a step further, the new method has also been applied to investigate the interaction between multiple particles. In particular, this new method has been proved to be powerful in elucidating the underlying mechanism of the tumbling motion of pearl chains in a flow condition as we observed in our experiments. Moreover, it also helps shed some new insight into the formation of different alignments and configurations of ellipsoidal particles. Finally, with the consideration of the Faradic current from water electrolysis and effect of pH, a new model has been developed to explain the causes for the intriguing flow reversal phenomenon commonly observed (but not at all understood) in AC-electroosmosis (ACEO) with reasonable outcomes

A Microfluidic Device for Impedance Spectroscopy

Recently, microfluidics has become a versatile tool to investigate cellular biology and to build novel biomedical devices. Dielectric spectroscopy, on the other hand, allows non-invasive probing of biological cells. Information on the cell membrane, cytoplasm, and nucleus can be obtained by dielectric spectroscopy provided that appropriate tools are used in specific frequency ranges. This dissertation includes fabrication, characterization, and testing of a simple microfluidic device to measure cell dielectric properties. The dielectric measurements are performed on human T-cell leukemia (Jurkat), mouse melanoma (B16), mouse hepatoma (Hepa), and human costal chondrocyte cells. Dielectric measurements consist of measuring the complex impedance of cell suspensions as a function of frequency. Physical models are fitted to raw impedance data to obtain parameters for cell compartments. The dielectric measurements are further supported by dielectrophoresis (DEP) experiments. Crossover frequency, which is the applied frequency when the DEP force is equal to zero, is recorded for cells by changing buffer conductivity. Cell membrane properties are also estimated from the crossover frequency measurements. Sensing capability of the microfluidic device to external stimuli is tested with Jurkat, chondrocyte, and Hepa cells. Jurkat and chondrocyte cells are suspended in buffers with changing osmolarity, and cell membrane properties are probed. Results indicate osmotic swelling of Jurkat cells. Interestingly similar changes were not observed in chondrocyte cells. Ion efflux from Hepa cells is quantified by conductivity measurements, and ionic flux from an average cell is calculated. Finally, a separability parameter is introduced and plotted for Jurkat and B16 cells pair. The separability parameter is based on the difference of two cells\u27 Clausius-Mossotti factors, which is a function of the dielectric parameters of the cells, field frequency, and buffer conductivity. Using the separability maps one can choose the optimum conditions for cell separation using DEP

A Multifunctional Tool for the Electrokinetic Manipulation and Characterization of Cells

In a field dominated by risk assessment, diagnostics could greatly benefit from the use of electric characterization tools. Electric field based diagnostic tools are low risk to the patient, offer high throughputs, and are versatile in the diseases they can diagnose. Even if electrical characterization tools, aren’t yet equal in the diagnostic confidence level produced compared to more established FDA approved techniques like the agar plate, when a patients symptoms indicate the necessity for time efficient treatment, electrical characterization could provide a rapid, safe alternative diagnostic tool to be used in tandem with other existing techniques. The work presented in this dissertation will focus on gaining understanding for a single electrokinetic domain; Dielectrophoresis (DEP). DEP is a proven and reliable technique for the manipulation, separation, and enrichment of many microorganisms including but certainly not limited to bacteria, DNA and bloodborne pathogens [1–8]. DEP is a noncontact, non invasive technique that would pose low patient risk with regards to diagnosis. The versatility in the variety of microorganisms that exhibit a DEP response and its proven ability to separate cells are a promising characteristics that can be exploited for the development of a novel diagnostic tool

Electromechanics and electrorheology of fluid flow with internal micro-particle electrorotation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 283-287).The negative electrorheological responses of two dimensional Couette and Poiseuille flows with internal micro-particle electrorotation are modeled and analyzed via a set of "fully continuum mechanical modeling field equations" formulated in this thesis. By combining the theories of particle electromechanics and continuum anti-symmetric/couple stresses, general governing equations are presented to describe the physical aspects of mass conservation, linear momentum balance, angular momentum balance, and electro-quasi-static field of the negative electrorheological fluid flow. A "rotating coffee cup model" is also developed for the first time to derive the retarding polarization relaxation equation with its accompanying equilibrium retarding polarization in order to characterize the non-equilibrium motion effects of the continuum spin velocity, co, continuum linear velocity, v, and micro-particle rotation speed, n, on the polarization responses as well as the electrical body torque inputs in the negative electrorheological flow field. Using the general assumptions of steady, incompressible, fully developed, and two dimensional flows, we reduce and simplify the full general governing equations in the zero spin viscosity and the finite spin viscosity small spin velocity limits for both Couette and Poiseuille flow geometries. In the zero spin viscosity limit, expressions for the spin velocity and effective viscosity of Couette flow as well as the spin velocity, linear velocity, and two dimensional volume flow rate of Poiseuille flow are derived in terms of the applied direct current electric field strength, shear rate (for Couette flow), driving pressure gradient (for Poiseuille flow), and spatial coordinate by solving the simplified continuum linear and angular momentum equations with the linear flow velocity being subjected to the no-slip boundary condition. As for the finite spin viscosity small spin velocity limit, analytical solutions to the spin velocity, linear velocity, and effective viscosity of Couette flow as well as solutions to the spin velocity, linear velocity, and two dimensional volume flow rate of Poiseuille flow are obtained and expressed in terms of the applied direct current electric field strength, boundary condition selection parameter (p), spin viscosity, and driving shear rate (for Couette flow) or pressure gradient (for Poiseuille flow) by solving a set of differential equations coupling the linear and angular momentum balances of the negative electrorheological fluid flow subjected to the no-slip and co=0.5/Vxv (with 0 , 1) boundary conditions. After obtaining the solutions in the respective zero spin viscosity and finite spin viscosity small spin velocity limits, series of parametric studies are then performed on these solutions via varying the pertinent physical parameters involved in several parametric regimes of interest so as to illustrate the negative electrorheological behavior and fluid flow response due to internal micro-particle electrorotation. Modeling results in the two limits generally show that with a direct current electric field applied perpendicularly to the flow direction, the spin velocity is increased and the effective viscosity is decreased as compared to the zero electric field values of the electrorheological fluid flow in Couette geometries at a given driving shear rate. It is also found that with a constant driving pressure gradient, the internal micro-particle electrorotation induces increased continuum fluid spin velocity, linear flow velocity, and two-dimensional volume flow rate on the macroscopic level in Poiseuille flow geometries when a direct current electric field perpendicular to the direction of flow is applied. Results of the Couette effective viscosity and Poiseuille volume flow rate obtained from our present continuum mechanical formulation are further compared to the experimental measurements as well as modeling results from single particle dynamics based two-phase volume averaged effective medium analysis found in current literature. With the "rotating coffee cup" fluid polarization model, the present zero spin viscosity continuum solutions to the effective viscosity and volume flow rate agree with the theoretical solutions obtained from single particle dynamics analysis. The zero spin viscosity solutions to the Couette effective viscosity also fall closer to the experimental measurements reported in current literature for low to moderate direct current electric field strengths. Moreover, the present continuum mechanical formulation in the finite spin viscosity small spin velocity limit is more capable of accurately capturing the negative electrorheological flow responses in the low shear rate and low driving pressure gradient flow regimes characterized by the respective Couette effective viscosity and Poiseuille volume flow rate. These finite spin viscosity small spin velocity results agree better with previous experimental measurements reported in the literature and bring the theoretical modeling of the negative electrorheological flow phenomenon due to internal micro-particle electrorotation closer to physical reality-both of which were generally not possible in previous literature. This important improvement in modeling the negative electrorheological response considered in this thesis is due to our proposed "rotating coffee cup model," which is likely the first model to treat the continuum spin velocity and the micro-particle rotation speed as separate physical variables. Using the finite spin viscosity small spin velocity analysis, we also derive for the first time a characteristic length scale determined by the balances between the electrical body torque input and the angular momentum conversion between the linear and spin velocity fields, which can be used to explain why the present continuum zero spin viscosity solutions are very much similar to those obtained from single particle dynamics based two-phase volume averaged effective medium analysis found in current literature. Future work includes a more advanced modeling of the polarization relaxation processes in the negative electrorheological fluid flow, the full non-linear analysis of finite spin viscosity effects on the angular momentum balances within the electrorheological flow field without the restriction of the small spin velocity limit, and the search of possible applications of our proposed continuum mechanical modeling field equations theory in the research areas of micro/nano-fluidics, biofluid dynamics, and engineering torque-shear rate control systems.by Hsin-Fu Huang.Ph.D

Elucidating the Mechanisms of Two Unique Phenomena Governed by Particle-Particle Interaction Under DEP: Tumbling Motion of Pearl Chains and Alignment of Ellipsoidal Particles

Particle-particle interaction plays a crucial role in determining the movement and alignment of particles under dielectrophoresis (DEP). Previous research efforts focus on studying the mechanism governing the alignment of spherical particles with similar sizes in a static condition. Different approaches have been developed to simulate the alignment process of a given number of particles from several up to thousands depending on the applicability of the approaches. However, restricted by the simplification of electric field distribution and use of identical spherical particles, not much new understanding has been gained apart from the most common phenomenon of pearl chain formation. To enhance the understanding of particle-particle interaction, the movement of pearl chains under DEP in a flow condition was studied and a new type of tumbling motion with unknown mechanism was observed. For interactions among non-spherical particles, some preceding works have been done to simulate the alignment of ellipsoidal particles. Yet the modeling results do not match experimental observations. In this paper, the authors applied the newly developed volumetric polarization and integration (VPI) method to elucidate the underlying mechanism for the newly observed movement of pearl chains under DEP in a flow condition and explain the alignment patterns of ellipsoidal particles. The modeling results show satisfactory agreement with experimental observations, which proves the strength of the VPI method in explaining complicated DEP phenomena