Electrothermal transport in biological systems : an analytical approach for electrokinetically-modulated peristaltic flow

A mathematical model is developed to investigate the combined viscous electro-osmotic flow and heat transfer in a finite length micro-channel with peristaltic wavy walls. The influence of Joule heating is included. The unsteady two-dimensional conservation equations for mass, momentum and energy conservation with viscous dissipation, heat absorption and electro-kinetic body force, are formulated in a Cartesian co-ordinate system. The Joule heating term appears as a quadratic function of axial electrical field in the energy conservation equation. The axial momentum and energy equations are coupled via the thermal buoyancy term. The peristaltic waves propagating along the micro-channel walls are simulated via a time-dependent co-sinusoidal wave function for the transverse vibration of the walls. Both single and train wave propagations are considered. Constant thermo-physical properties are prescribed and a Newtonian viscous model is employed for the fluid. The electrical field terms are rendered into electrical potential terms via the Poisson-Boltzmann equation, Debye length approximation and ionic Nernst Planck equation. The dimensionless emerging linearized electro-thermal boundary value problem is solved using integral methods. A parametric study is conducted to evaluate the impact of isothermal Joule heating term on axial velocity, temperature distribution, pressure difference, volumetric flow rate, skin friction and Nusselt number. The modification in streamline distributions with Joule heating and electro-osmotic velocity is also addressed to elucidate trapping bolus dynamics

Direct current insulator based dielectrophoresis (DC-iDEP) microfluidic chip for blood plasma separation

Lab-on-a-Chip (LOC) integrated microfluidics has been a powerful tool for new developments in analytical chemistry. These microfluidic systems enable the miniaturization, integration and automation of complex biochemical assays through the reduction of reagent use and enabling portability.Cell and particle separation in microfluidic systems has recently gained significant attention in many sample preparations for clinical procedures. Direct-current insulator-based dielectrophoresis (DC-iDEP) is a well-known technique that benefits from the electric field gradients generated by an array of posts for separating, moving and trapping biological particle samples. In this thesis a parametric optimization is used to determine the optimum radius of the post for particle separation. Results that are used to design a microfluidic device that with a novel combination of hydrodynamic and di-electrophoretic techniques can achieve plasma separation in a microfluidic channel from fresh blood and for the first time allows optical real-time monitoring of the components of plasma without pre or post processing. Finally, all the results are integrated to create a novel microfluidic chip for blood plasma separation, which combines microfluidics with conventional lateral flow immune chromatography to extract enough plasma to perform a blood panel. The microfluidic chip design is a combination of cross-flow filtration with a reversible electroosmotic flow that prevents clogging at the filter entrance and maximizes the amount of separated plasma. The main advantage of this design is its efficiency, since with a small amount of sample (a single droplet ~10µL) a considerable amount of plasma (more than 1µL) is extracted and collected with high purity (more than 99%) in a reasonable time (5 to 8 minutes). To validate the quality and quantity of the separated plasma and to show its potential as clinical tool, the microfluidic chip has been combined with lateral flow immune chromatography technology to perform a qualitative detection of the TSH (thyroid-stimulating hormone) and a blood panel for measuring cardiac Troponin and Creatine Kinase MB. The results obtained from the microfluidic system are comparable to previous commercial lateral flow assays that required more sample for implementing less tests.Els dispositius Lab-on-a-Chip (LOC) són una eina de gran abast per als nous desenvolupaments de química analítica. Aquests sistemes de microfluids permeten la miniaturització, la integració i automatització d'assajos bioquímics complexos a través de la reducció del consum de reactiu i són portables. La separació de partícules i cél.lules mitjançant sistemes de microfluids ha guanyat recentment una atenció significativa en la preparació de mostres per als procediments clínics. La dielectroforesis amb corrent continu basada amb aïllants (DC-IDEP) és una tècnica ben coneguda que es beneficia dels gradients de camp elèctric generats per una sèrie de columnes d'aïllants que permeten la separació, el moviment i la captura de mostres de partícules biològiques. En aquesta tesis una optimització paramètrica s'utilitza per determinar el radi òptim de la columna necessària per a la separació de partícules. Resultats que s'utilitzen per dissenyar un dispositiu de microfluids que amb una nova combinació de tècniques hidrodinàmiques i di-electroforètiques pot aconseguir la separació de plasma en un microcanal a partir de sang fresca que per primera vegada permet la monitorització en temps real òptica dels components del plasma sense pre o post processament. Finalment, tots els resultats s'integren per crear un nou microxip per a la separació de plasma de la sang, que combina la microfluídica amb cromatografia de flux lateral convencional per extreure suficient plasma per dur a terme un panell de sang. El disseny del microxip és una combinació de filtració de flux creuat amb un flux electroosmòtic reversible que evita l'obstrucció a l'entrada del filtre i maximitza la quantitat de plasma separat. El principal avantatge d'aquest disseny és la seva eficiència, ja que amb una petita quantitat de mostra (una sola gota ~ 10µL) s'extreu una quantitat considerable de plasma (més de 1µL) i es recull amb gran puresa (més de 99%) en temps raonable (de 5 a 8 minuts). Per validar la qualitat i quantitat del plasma separat i per mostrar el seu potencial com a eina clínica, el xip de microfluids s'ha combinat amb la tecnologia de cromatografia de flux lateral per a realitzar una detecció qualitativa de la TSH (hormona estimulant de la tiroide) i un panell de sang per mesura la troponina cardíaca i la creatina quinasa MB. Els resultats obtinguts del sistema de microfluids són comparables als assajos de flux lateral comercials anteriors que requerien més mostra per a la realització de menys proves

Wetting, roughness and hydrodynamic slip

The hydrodynamic slippage at a solid-liquid interface is currently at the center of our understanding of fluid mechanics. For hundreds of years this science has relied upon no-slip boundary conditions at the solid-liquid interface that has been applied successfully to model many macroscopic experiments, and the state of this interface has played a minor role in determining the flow. However, the problem is not that simple and has been revisited recently. Due to the change in the properties of the interface, such as wettability and roughness, this classical boundary condition could be violated, leading to a hydrodynamic slip. In this chapter, we review recent advances in the understanding and expectations for the hydrodynamic boundary conditions in different situations, by focussing mostly on key papers from past decade. We highlight mostly the impact of hydrophobicity, roughness, and especially their combination on the flow properties. In particular, we show that hydrophobic slippage can be dramatically affected by the presence of roughness, by inducing novel hydrodynamic phenomena, such as giant interfacial slip, superfluidity, mixing, and low hydrodynamic drag. Promising directions for further research are also discussed.Comment: 36 pages, 19 figures. This chapter would be a part of "Nanoscale liquid interfaces" boo

Tensorial hydrodynamic slip

We describe a tensorial generalization of the Navier slip boundary condition and illustrate its use in solving for flows around anisotropic textured surfaces. Tensorial slip can be derived from molecular or microstructural theories or simply postulated as an constitutive relation, subject to certain general constraints on the interfacial mobility. The power of the tensor formalism is to capture complicated effects of surface anisotropy, while preserving a simple fluid domain. This is demonstrated by exact solutions for laminar shear flow and pressure-driven flow between parallel plates of arbitrary and different textures. From such solutions, the effects of rotating a texture follow from simple matrix algebra. Our results may be useful to extracting local slip tensors from global measurements, such as the permeability of a textured channel or the force required to move a patterned surface, in experiments or simulations.Comment: 10 page

Transverse magnetic field driven modification in unsteady peristaltic transport with electrical double layer effects

The influence of transverse magnetic field on time-dependent peristaltic transport of electrically-conducting fluids through a microchannel under an applied external electric field with induced electric field effect is considered, based on lubrication theory approximations. The electrohydrodynamic (EHD) problem is also simplified under the Debye linearization. Closed-form solutions for the linearized dimensionless boundary value problem are derived. With increasing Hartmann number, the formation of bolus in the regime (associated with trapping) is inhibited up to a critical value of magnetic field. Flow rate, axial velocity and local wall shear stress are strongly decreased with greater Hartmann number whereas pressure difference is enhanced with higher Hartmann number at low time values but reduced with greater elapse in time. With greater electro-osmotic parameter (i.e. smaller Debye length), maximum time-averaged flow rate is enhanced, whereas the axial velocity is reduced. An increase in electrical field parameter (i.e. maximum electro-osmotic velocity) causes an increase in maximum time-averaged flow rate. The simulations find applications in electromagnetic peristaltic micro-pumps in medical engineering and also “smart” fluid pumping systems in nuclear and aerospace industries

Dielectrophoretic characterization of particles and erythrocytes

Medical lab work, such as blood testing, will one day be near instantaneous and inexpensive via capabilities enabled by the fast growing world of microtechnology. In this research study, sorting and separation of different ABO blood types have been investigated by applying alternating and direct electric fields using class=SpellE\u3edielectrophoresis in microdevices. Poly(dimethylsiloxane) (PDMS) microdevices, fabricated by standard photolithography techniques have been used. Embedded perpendicular platinum (Pt) electrodes to generate forces in AC dielectrophoresis were used to successfully distinguish positive ABO blood types, with O+ distinguishable from other blood types at \u3e95% confidence. This is an important foundation for exploring DC dielectrophoretic sorting of blood types. The expansion of red blood cell sorting employing direct current insulative class=SpellE\u3edielectrophoresis (DC-iDEP) is novel. Here Pt electrodes were remotely situated in the inlet and outlet ports of the microdevice and an insulating obstacle generates the required dielectrophoretic force. The presence of ABO antigens on the red blood cell were found to affect the class=SpellE\u3edielectrophoretic deflection around the insulating obstacle thus sorting cells by type. To optimize the placement of insulating obstacle in the microchannel, COMSOL Multiphysics® simulations were performed. Microdevice dimensions were optimized by evaluating the behaviors of fluorescent polystyrene particles of three different sizes roughly corresponding to the three main components of blood: platelets (2-4 µm), erythrocytes (6-8 µm) and leukocytes (10-15 µm). This work provided the operating conditions for successfully performing size dependent blood cell insulator based DC dielectrophoresis in PDMS microdevices. In subsequent studies, the optimized microdevice geometry was then used for continuous separation of erythrocytes. The class=SpellE\u3emicrodevice design enabled erythrocyte collection into specific channels based on the cell’s deflection from the high field density region of the obstacle. The channel with the highest concentration of cells is indicative of the ABO blood type of the sample. DC resistance measurement system for quantification of erythrocytes was developed with single PDMS class=SpellE\u3emicrochannel system to be integrated with the DC- class=SpellE\u3eiDEP device developed in this research. This lab-on-a-chip technology application could be applied to emergency situations and naturalcalamities for accurate, fast, and portable blood typing with minimal error

Analysis, Design and Fabrication of Micromixers

This book includes an editorial and 12 research papers on micromixers collected from the Special Issue published in Micromachines. The topics of the papers are focused on the design of micromixers, their fabrication, and their analysis. Some of them proposed novel micromixer designs. Most of them deal with passive micromixers, but two papers report studies on electrokinetic micromixers. Fully three-dimensional (3D) micromixers were investigated in some cases. One of the papers applied optimization techniques to the design of a 3D micromixer. A review paper is also included and reports a review of recently developed passive micromixers and a comparative analysis of 10 typical micromixers

Dielectrophoretic characterization of particles and erythrocytes

Medical lab work, such as blood testing, will one day be near instantaneous and inexpensive via capabilities enabled by the fast growing world of microtechnology. In this research study, sorting and separation of different ABO blood types have been investigated by applying alternating and direct electric fields using class=SpellE\u3edielectrophoresis in microdevices. Poly(dimethylsiloxane) (PDMS) microdevices, fabricated by standard photolithography techniques have been used. Embedded perpendicular platinum (Pt) electrodes to generate forces in AC dielectrophoresis were used to successfully distinguish positive ABO blood types, with O+ distinguishable from other blood types at \u3e95% confidence. This is an important foundation for exploring DC dielectrophoretic sorting of blood types. The expansion of red blood cell sorting employing direct current insulative class=SpellE\u3edielectrophoresis (DC-iDEP) is novel. Here Pt electrodes were remotely situated in the inlet and outlet ports of the microdevice and an insulating obstacle generates the required dielectrophoretic force. The presence of ABO antigens on the red blood cell were found to affect the class=SpellE\u3edielectrophoretic deflection around the insulating obstacle thus sorting cells by type. To optimize the placement of insulating obstacle in the microchannel, COMSOL Multiphysics® simulations were performed. Microdevice dimensions were optimized by evaluating the behaviors of fluorescent polystyrene particles of three different sizes roughly corresponding to the three main components of blood: platelets (2-4 µm), erythrocytes (6-8 µm) and leukocytes (10-15 µm). This work provided the operating conditions for successfully performing size dependent blood cell insulator based DC dielectrophoresis in PDMS microdevices. In subsequent studies, the optimized microdevice geometry was then used for continuous separation of erythrocytes. The class=SpellE\u3emicrodevice design enabled erythrocyte collection into specific channels based on the cell’s deflection from the high field density region of the obstacle. The channel with the highest concentration of cells is indicative of the ABO blood type of the sample. DC resistance measurement system for quantification of erythrocytes was developed with single PDMS class=SpellE\u3emicrochannel system to be integrated with the DC- class=SpellE\u3eiDEP device developed in this research. This lab-on-a-chip technology application could be applied to emergency situations and naturalcalamities for accurate, fast, and portable blood typing with minimal error