Saud Khashan

Numerical simulation of biomagnetic fluid downstream an eccentric stenotic orifice

Biomagnetic fluid dynamics is the study of the interaction of biological fluids with an applied steady magnetic field. The composition of the biological fluid is considered nonconducting; however, it has magnetic moment. The magnetic moment of the biological fluid can be enhanced by tagging superparamagnetic particles. Several biomedical applications recently developed utilize the magnetic labeling of cellular components. In this paper, the biomagnetic fluid downstream an eccentric stenotic orifice is considered. An external magnetic field is applied at different locations down stream the stenotic orifice. It is found that based on the location of the magnetic field, the reattachment point downstream the stenotic orifice changes; it is also found that the shear stress will be affected based on the magnetic field location. Major changes in the flow pattern have been also observed based on the magnetic field strength.

Computational Analysis of Enhanced Magnetic Bioseparation in Microfluidic Systems with Flow-Invasive Magnetic Elements

A microfluidic design is proposed for realizing greatly enhanced separation of magnetically-labeled bioparticles using integrated soft-magnetic elements. The elements are fixed and intersect the carrier fluid (flow-invasive) with their length transverse to the flow. They are magnetized using a bias field to produce a particle capture force. Multiple stair-step elements are used to provide efficient capture throughout the entire flow channel. This is in contrast to conventional systems wherein the elements are integrated into the walls of the channel, which restricts efficient capture to limited regions of the channel due to the short range nature of the magnetic force. This severely limits the channel size and hence throughput. Flow-invasive elements overcome this limitation and enable microfluidic bioseparation systems with superior scalability. This enhanced functionality is quantified for the first time using a computational model that accounts for the dominant mechanisms of particle transport including fully-coupled particle-fluid momentum transfer.

Coupled particle-fluid transport and magnetic separation in microfluidic systems with passive magnetic functionality

A study is presented of coupled particle–fluid transport and field-directed particle capture in microfluidic systems with passive magnetic functionality. These systems consist of a microfluidic flow cell on a substrate that contains embedded magnetic elements. Two systems are considered that utilize soft- and hard-magnetic elements, respectively. In the former, an external field is applied to magnetize the elements, and in the latter, they are permanently magnetized. The field produced by the magnetized elements permeates into the flow cell giving rise to an attractive force on magnetic particles that flow through it. The systems are studied using a novel numerical/closed-form modelling approach that combines numerical transport analysis with closed-form field analysis. Particle–fluid transport is computed using computational fluid dynamics (CFD), while the magnetic force that governs particle capture is obtained in closed form. The CFD analysis takes into account dominant particle forces and two-way momentum transfer between the particles and the fluid. The two-way particle–fluid coupling capability is an important feature of the model that distinguishes it from more commonly used and simplified one-way coupling analysis. The model is used to quantify the impact of two-way particle–fluid coupling on both the capture efficiency and the flow pattern in the systems considered. Many effects such as particle-induced flow-enhanced capture efficiency and flow circulation are studied that cannot be predicted using one-way coupling analysis. In addition, dilute particle dispersions are shown to exhibit significant localized particle–fluid coupling near the capture regions, which contradicts the commonly held view that two-way coupling can be ignored when analysing high-gradient magnetic separation involving such particle systems. Overall, the model demonstrates that two-way coupling needs to be taken into account for rigorous predictions of capture efficiency, especially for applications involving high particle loading and/or low flow rates. It is computationally more efficient and accurate than purely numerical models and should prove useful for the rational design and optimization of novel magnetophoretic microsystems.

Modeling solute transport affected by heterogeneous sorption kinetics using single-rate nonequilibrium approaches

Single-rate transport models are commonly used for interpreting sorption-related mass transfer in porous media, often with the intention of approximating the kinetics of the sorption process. Among the most commonly used single-rate models are the two-site first-order (TSFO) and the two-site radial diffusion (TSRD) models. We fitted the parameters of the TSFO and TSRD models to simulated breakthrough data of hypothetical column experiments in which sorption rates were described by a γ-distributed sorption sites (GS) model. Our objective was to determine the conditions under which the assumption of a single-rate sorption parameter will be applicable to systems with heterogeneous sorption rates. We were further interested in knowing in what manner the fitted single-rate nonequilibrium model parameters depend upon the conditions under which the data were obtained. The considered hypothetical cases covered a range of experimental conditions and involved compounds with different sorption characteristics. The study revealed that the goodness of fit of the single rate models in simulating the transport of solutes exhibiting heterogeneous sorption rates is affected by solute residence time and pulse injection duration. Compared to the TSFO model, the TSRD model generally results in better prediction of solute transport affected by heterogeneous sorption kinetics. In addition, for such systems, the nonequilibrium parameters fitted using the TSFO model and their counterparts in the TSRD model are highly correlated. Moreover, an increase in the fitted mass transfer timescale of each of the single-rate models is coupled with an increase in the associated fraction of instantaneous sorption sites. A strong correlation was found between the time of the experiment and the product of the fitted characteristic time for mass transfer, pulse duration, and solute residence time. The correlation explains many of the variations in the mass transfer timescale encountered when single-rate sorption approaches were utilized to model solute transport in previous miscible displacement studies.

Lab-on-chip for liquid biopsy (LoC-LB) based on dielectrophoresis

This short communication presents the proof-of-concept of a novel dielectrophoretic lab-on-chip for identifying/separating circulating tumor cells for purposes of liquid biopsy. The device consists of a polydimethylsiloxane layer, containing a microchannel, bonded on a glass substrate that holds two sets of planar interdigitated transducer electrodes. The lab-on-chip is operated at a frequency that enables dielectrophoretic force to sort cells, based on type, along the lateral direction. The operating frequency ensures attraction force toward the electrodes on cancer cells and repulsion force toward the center of the microchannel on other cells. Initial tests for demonstrating proof-of-concept have successfully identified/separated green fluorescent protein-labelled MDA-MB-231 breast cancer cells from a mixture of the same and regular blood cells suspended in low conductivity sucrose/dextrose medium.

Microfluidic Platforms for Bio-applications

This chapter provides a brief overview of three actuation mechanisms that are relevant for biomedical applications of microfluidics. Actuation mechanisms are employed in the field of microfluidics for realizing unit operations such as focusing, switching, and separation. The topics dealt with in this chapter include dielectrophoresis, acoustophoresis, and magnetophoresis. The first section provides an introduction to these and related topics while the second section deals specifically on dielectrophoresis. The third and fourth sections detail acoustophoresis and magnetophoresis, respectively. This chapter concludes by providing a quick comparison of these different actuation methods.

Microfluidics Based Magnetophoresis: A Review

Magnetophoresis, the manipulation of trajectory of micro-scale entities using magnetic forces, as employed in microfluidic devices is reviewed at length in this article. Magnetophoresis has recently garnered significant interest due to its simplicity, in terms of implementation, as well as cost-effectiveness while being efficient and biocompatible. Theory associated with magnetophoresis is illustrated in this review along with different sources for creating magnetic field gradient commonly employed in microfluidic devices. Additionally, this article reviews the state-of-the-art of magnetophoresis based microfluidic devices, where positive- and negative-magnetophoresis are utilized for manipulation of micro-scale entities (cells and microparticles), employed for operations such as trapping, focusing, separation, and switching of microparticles and cells. The article concludes with a brief outlook of the field of magnetophoresis.

Trajectory of microparticles actuated with standing surface acoustic waves in microfluidic devices

This article deals with the development of a two-dimensional dynamic model for predicting the trajectory of microparticles in an acoustic field, associated with standing surface acoustic wave, on a continuous flow microfluidic device. The model consists of two governing equations, each describing the motion of the microparticle. The model is solved using finite difference method; the solution provides the displacements of the microparticles, in the two directions, for the time duration of interest. The model is subsequently employed for parametric study. The parameters considered include the width of the microchannel, radius of microparticles, initial transverse displacement of the microparticle and volumetric flow rate. The primary application of this model article would be in the design process.

Modeling and simulation of the multiphase flow involving magnetophoresis-based microfluidic systems

In this study, we use the Lagrangian-Eulerian model, usually termed as Discrete Particle Model(DPM), and the Eulerian mixture model to numerically simulate the magnetophoresis-based separation of magnetic beads in a microfluidic system. The separation is based on High Gradient Magnetic Separation (HGMS) principle. A comparative assessment of both computational models was conducted. Mixture model provides a solution similar to that obtained using the DPM but with reduced computational time. However, the fidelity of mixture model can be attained only by the proper modeling of the slip velocity between the particle and the carrier fluid. For both of DPM and mixture approaches, the appropriate constitutive physics models for drag, lift, slip were resolved.

Microfabrication of multi-layered electrodes for dielectrophoresis-based field flow fractionation

This article details the process layout required for realizing a three-dimensional arrangement of electrodes in a microfluidic device for field flow fractionation based on dielectrophoresis. The metal electrodes are placed horizontally, in a stair-case arrangement, and pass through the bulk of the fluid. Several standard microfabrication processes are employed, in realizing this microdevice, including multi-layer photolithography, casting and plasma bonding. Thus the process layout is repeatable and reproducible. The feasibility of this process layout is demonstrated using three electrodes arranged in aforementioned manner; nevertheless, this process can be extended to as many electrodes as desired in the horizontal direction. This process layout can will make applications possible that were not possible till date due to the inability in microfabricating three-dimensional horizontal metal electrodes that run through the entire width of the microchannel.