Ph.D., Ryerson University, Canada, Biomedical Engineering
M.Sc., University of Calgary, Canada, Electrical Engineering
M.Sc., Sharif University of Technology, Iran, Mechanical Engineering
B.Sc., Ferdowsi University of Mashhad, Iran, Mechanical Engineering
Tim Stearns, Postdoctoral Faculty Sponsor
- Editorial on the Special Issue on Microelectrode Arrays and Application to Medical Devices. Micromachines 2020; 11 (8)
Magnetic water-in-water droplet microfluidics: Systematic experiments and scaling mathematical analysis
2020; 14 (2): 024101
A major barrier to the clinical utilization of microfluidically generated water-in-oil droplets is the cumbersome washing steps required to remove the non-biocompatible organic oil phase from the droplets. In this paper, we report an on-chip magnetic water-in-water droplet generation and manipulation platform using a biocompatible aqueous two-phase system of a polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer (PEG-PPG-PEG) and dextran (DEX), eliminating the need for subsequent washing steps. By careful selection of a ferrofluid that shows an affinity toward the DEX phase (the dispersed phase in our microfluidic device), we generate magnetic DEX droplets in a non-magnetic continuous phase of PEG-PPG-PEG. We apply an external magnetic field to manipulate the droplets and sort them into different outlets. We also perform scaling analysis to model the droplet deflection and find that the experimental data show good agreement with the model. We expect that this type of all-biocompatible magnetic droplet microfluidic system will find utility in biomedical applications, such as long-term single cell analysis. In addition, the model can be used for designing experimental parameters to achieve a desired droplet trajectory.
View details for DOI 10.1063/1.5144137
View details for Web of Science ID 000519010300001
View details for PubMedID 32161632
View details for PubMedCentralID PMC7056455
- Expansion-mediated breakup of bubbles and droplets in microfluidics PHYSICAL REVIEW FLUIDS 2020; 5 (1)
Dancing with the Cells: Acoustic Microflows Generated by Oscillating Cells
2020; 16 (9): e1903788
The interaction of a sound or ultrasound wave with an elastic object, such as a microbubble, can give rise to a steady-state microstreaming flow in its surrounding liquid. Many microfluidic strategies for cell and particle manipulation, and analyte mixing, are based on this type of flow. In addition, there are reports that acoustic streaming can be generated in biological systems, for instance, in a mammalian inner ear. Here, new observations are reported that individual cells are able to induce microstreaming flow, when they are excited by controlled acoustic waves in vitro. Single adherent cells are exposed to an acoustic field inside a microfluidic device. The cell-induced microstreaming is then investigated by monitoring flow tracers around the cell, while the structure and extracellular environment of the cell are altered using different chemicals. The observations suggest that the maximum streaming flow induced by an MDA-MB-231 breast cancer cell can reach velocities on the order of mm s-1 , and this maximum velocity is primarily governed by the overall cell stiffness. Therefore, such cell-induced microstreaming measurements, including flow pattern and velocity magnitude, may be used as label-free proxies of cellular mechanical properties, such as stiffness.
View details for DOI 10.1002/smll.201903788
View details for Web of Science ID 000502164600001
View details for PubMedID 31829522
AC Electrothermal Effect in Microfluidics: A Review
2019; 10 (11)
The electrothermal effect has been investigated extensively in microfluidics since the 1990s and has been suggested as a promising technique for fluid manipulations in lab-on-a-chip devices. The purpose of this article is to provide a timely overview of the previous works conducted in the AC electrothermal field to provide a comprehensive reference for researchers new to this field. First, electrokinetic phenomena are briefly introduced to show where the electrothermal effect stands, comparatively, versus other mechanisms. Then, recent advances in the electrothermal field are reviewed from different aspects and categorized to provide a better insight into the current state of the literature. Results and achievements of different studies are compared, and recommendations are made to help researchers weigh their options and decide on proper configuration and parameters.
View details for DOI 10.3390/mi10110762
View details for Web of Science ID 000502255300048
View details for PubMedID 31717932
View details for PubMedCentralID PMC6915365
Simultaneous Pumping and Mixing of Biological Fluids in a Double-Array Electrothermal Microfluidic Device
2019; 10 (2)
Transport and mixing of minute amounts of biological fluids are significantly important in lab-on-a-chip devices. It has been shown that the electrothermal technique is a suitable candidate for applications involving high-conductivity biofluids, such as blood, saliva, and urine. Here, we introduce a double-array AC electrothermal (ACET) device consisting of two opposing microelectrode arrays, which can be used for simultaneous mixing and pumping. First, in a 2D simulation, an optimum electrode-pair configuration capable of achieving fast transverse mixing at a microfluidic channel cross-section is identified by comparing different electrode geometries. The results show that by adjusting the applied voltage pattern and position of the asymmetrical microelectrodes in the two arrays, due to the resultant circular flow streamlines, the time it takes for the analytes to be convected across the channel cross-section is reduced by 95% compared to a diffusion-only-based transport regime, and by 80% compared to a conventional two-layer ACET device. Using a 3D simulation, the fluid transport (pumping and mixing) capabilities of such an electrode pair placed at different angles longitudinally relative to the channel was studied. It was found that an asymmetrical electrode configuration placed at an angle in the range of 30 ° ≤ θ ≤ 45 ° can significantly increase transversal mixing efficiency while generating strong longitudinal net flow. These findings are of interest for lab-on-a-chip applications, especially for biosensors and immunoassays, where mixing analyte solutions while simultaneously moving them through a microchannel can greatly enhance the sensing efficiency.
View details for DOI 10.3390/mi10020092
View details for Web of Science ID 000460798200017
View details for PubMedID 30696037
View details for PubMedCentralID PMC6413218
- Recent advances in AC electrokinetic sample enrichment techniques for biosensor development SENSORS AND ACTUATORS B-CHEMICAL 2018; 255: 3601–15
Periodic assembly of nanoparticle arrays in disclinations of cholesteric liquid crystals
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2017; 114 (9): 2137–42
An important goal of the modern soft matter science is to discover new self-assembly modalities to precisely control the placement of small particles in space. Spatial inhomogeneity of liquid crystals offers the capability to organize colloids in certain regions such as the cores of the topological defects. Here we report two self-assembly modes of nanoparticles in linear defects-disclinations in a lyotropic colloidal cholesteric liquid crystal: a continuous helicoidal thread and a periodic array of discrete beads. The beads form one-dimensional arrays with a periodicity that matches half a pitch of the cholesteric phase. The periodic assembly is governed by the anisotropic surface tension and elasticity at the interface of beads with the liquid crystal. This mode of self-assembly of nanoparticles in disclinations expands our ability to use topological defects in liquid crystals as templates for the organization of nanocolloids.
View details for DOI 10.1073/pnas.1615006114
View details for Web of Science ID 000395101200034
View details for PubMedID 28193865
View details for PubMedCentralID PMC5338481
- Optimized AC electrothermal micromixing design for biofluid systems SPIE-INT SOC OPTICAL ENGINEERING. 2017
- Microfluidic Studies of Polymer Adsorption in Flow MACROMOLECULAR CHEMISTRY AND PHYSICS 2017; 218 (2)
- AC electrothermal technique in microchannels SPIE-INT SOC OPTICAL ENGINEERING. 2017
A microfluidic study of liquid-liquid extraction mediated by carbon dioxide
LAB ON A CHIP
2016; 16 (14): 2710–18
Liquid-liquid extraction is an important separation and purification method; however, it faces a challenge in reducing the energy consumption and the environmental impact of solvent (extractant) recovery. The reversible chemical reactions of switchable solvents (nitrogenous bases) with carbon dioxide (CO2) can be implemented in reactive liquid-liquid extraction to significantly reduce the cost and energy requirements of solvent recovery. The development of new effective switchable solvents reacting with CO2 and the optimization of extraction conditions rely on the ability to evaluate and screen the performance of switchable solvents in extraction processes. We report a microfluidic strategy for time- and labour-efficient studies of CO2-mediated solvent extraction. The platform utilizes a liquid segment containing an aqueous extractant droplet and a droplet of a solution of a switchable solvent in a non-polar liquid, with gaseous CO2 supplied to the segment from both sides. Following the reaction of the switchable solvent with CO2, the solvent becomes hydrophilic and transfers from the non-polar solvent to the aqueous droplet. By monitoring the time-dependent variation in droplet volumes, we determined the efficiency and extraction time for the CO2-mediated extraction of different nitrogenous bases in a broad experimental parameter space. The platform enables a significant reduction in the amount of switchable solvents used in these studies, provides accurate temporal characterization of the liquid-liquid extraction process, and offers the capability of high-throughput screening of switchable solvents.
View details for DOI 10.1039/c6lc00597g
View details for Web of Science ID 000385291600016
View details for PubMedID 27327198
- A NOVEL AC ELECTROTHERMAL MICROPUMP FOR BIOFLUID TRANSPORT USING CIRCULAR INTERDIGITATED MICROELECTRODE ARRAY SPIE-INT SOC OPTICAL ENGINEERING. 2015
- FLUID FLOW STUDY OF AN AC ELECTROTHERMAL MICROPUMP CONSISTING OF MULTIPLE ARRAYS OF MICROELECTRODES FOR BIOFLUID APPLICATIONS SPIE-INT SOC OPTICAL ENGINEERING. 2015
- VIBRATION EFFECT ON CROSS-FLOW AND CO-FLOW FOCUSING MECHANISM FOR DROPLET GENERATION SPIE-INT SOC OPTICAL ENGINEERING. 2015
- HIGH EFFICIENT BIOFLUID MICROMIXING USING ULTRA-FAST AC ELECTROTHERMAL FLOW SPIE-INT SOC OPTICAL ENGINEERING. 2015
Breakup of microdroplets in asymmetric T junctions.
Physical review. E, Statistical, nonlinear, and soft matter physics
2013; 87 (5): 053003
Symmetric T junctions have been used widely in microfluidics to generate equal-sized microdroplets, which are applicable in drug delivery systems. A newly proposed method for generating unequal-sized microdroplets at a T junction is investigated theoretically and experimentally. Asymmetric T junctions with branches of identical lengths and different cross sections are utilized for this aim. An equation for the critical breakup of droplets at asymmetric T junctions and one for determining the breakup point of droplets are developed. A good agreement was observed between the theories (present and previous) and the experiments.
View details for DOI 10.1103/PhysRevE.87.053003
View details for PubMedID 23767616