Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session M30: Microfluids: Fluidic Devices II |
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Chair: Zachary Gagnon, Johns Hopkins University Room: Ballroom IV |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M30.00001: Microfluidic Controlled Conformal Coating of Particles Scott Tsai, Jason Wexler, Jiandi Wan, Howard Stone Coating flows are an important class of fluid mechanics problems. Typically a substrate is coated with a moving continuous film, but it is also possible to consider coating of discrete objects. In particular, in applications involving coating of particles that are useful in drug delivery, the coatings act as drug-carrying vehicles, while in cell therapy a thin polymeric coating is required to protect the cells from the host's immune system. Although many functional capabilities have been developed for lab-on-a-chip devices, a technique for coating has not been demonstrated. We present a microfluidic platform developed to coat micron-size spheres with a thin aqueous layer by magnetically pulling the particles from the aqueous phase to the non-aqueous phase in a co-flow. Coating thickness can be adjusted by the average fluid speed and the number of beads encapsulated inside a single coat is tuned by the ratio of magnetic to interfacial forces acting on the beads. [Preview Abstract] |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M30.00002: Self-assembling particles of various shapes and sizes into adjustable monolayers at liquid-fluid interfaces Sai Nudurupati, Muhammad Janjua, Nadine Aubry, Pushpendra Singh Capillarity induced self-assembly of particles trapped at a fluid-liquid interface has been widely used to fabricate self-assembled monolayers. Capillarity alone, however, cannot be used to form ultra-thin membranes, made of submicron or nanosized particles, or membranes with a non-close packed structure whose properties could be adjusted. To address these shortcomings, we apply an external electric field which generates electric field induced capillary forces which are non-negligible even on very small particles for which capillary forces based on their buoyant weight alone are nearly zero. In addition, particles experience repulsive electric forces which lead to expanded lattices whose constant can be adjusted by varying the strength and/or frequency of the applied electric field. In addition to forces, torques are involved in the case of non-spherical particles which then reorient themselves as they self-assemble. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M30.00003: Electric field induced self-assembly of particles at liquid-liquid interfaces M. Hossain, B. Dalal, S. Gurupatham, I. Fischer, P. Singh, N. Aubry We have recently shown that virtually defect-free monolayers of particles can be assembled at air-liquid interfaces by applying an electric field normal to the interface. Particles rearrange themselves under the influence of interfacial and electrostatic forces to form hexagonal monolayers with long-range order. The lattice spacing can be varied by changing the electric field intensity and frequency. In this talk we present similar results for the self-assembly of particles on the interfaces between two liquids. It is shown that the monolayer arrangement depends on the radii of the particles, the dielectric properties of the fluids and particles, and the applied electric-field intensity. [Preview Abstract] |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M30.00004: Capillary flow driven gradient generation in fluid stripes for biomaterial and biomedical applications Matthew Hancock, Jiankang He, Francesco Piraino, Gulden Camci-Unal, Ali Khademhosseini A simple and inexpensive bench-top method is presented employing passive mechanisms to generate centimeters-long gradients of molecules and particles in under a second with only a coated glass slide and a micropipette. By patterning hydrophilic regions on a substrate, a stripe of prepolymer solution is held in place on a glass slide by a hydrophobic boundary. Adding a droplet to one end of this ``pre-wet'' stripe causes a rapid capillary flow that spreads the droplet along the stripe to generate a gradient in the relative concentrations of the droplet and pre-wet solutions. Experiments and theoretical models characterize the flows and gradient profiles and their dependence on the fluid volumes, properties, and stripe geometry. A bench-top rapid prototyping method allows the user to design and fabricate the coated slides using only tape and hydrophobic spray. Gradient biomaterials are produced by crosslinking gradients of prepolymer solutions. Applications include producing a soluble drug gradient over cells in shear-protected microwells, generating a concentration gradient of cells encapsulated in three dimensions within a homogeneous biopolymer, and synthesizing a biomaterial with encapsulated cells exhibiting a gradient in cell spreading. [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M30.00005: Self-similar flow channel designs for parallel multiscale transport of multiple fluid species Kenneth Lee, Omer Savas The need for multiscale fluid transport arises in a number of engineering applications involving fluid delivery or collection over a range of different lengthscales. A ``tree-shaped" system of flow channels has been an efficient transport solution commonly practiced by biomimetics. There has been much work in optimizing these dendritic flow systems, primarily for cooling applications. However, most designs can be costly to manufacture and limited in scalability. Moreover, most systems are restricted to the transport of a single fluid species. This work explores the feasibility of self-similar flow channel designs to provide parallel multiscale transport of multiple fluid species. The self-similar characteristic of these designs simplifies manufacturing and allows for flexible scalability. Prototypes for the parallel transport of one and two independent fluid species are supported with analytical theory and experimental work. Designs for three and four species are presented as well. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M30.00006: Propulsion and Trapping of Micro-particles by Active Cilia Arrays Amitabh Bhattacharya, Gavin Buxton, O. Berk Usta, Anna Balazs Hair-like cilia are vital for transporting fluid and particulates within and around biological organisms. While the coordinated motion of the cilia is effective at propelling the surrounding fluid, adhesive interaction between the cilia and particulates can be crucial for controlling particle movement. Here, we model transport of a microscopic particle via a regular array of beating elastic cilia, whose tips experience an adhesive interaction with the particle's surface. At optimal adhesion strength, the average particle velocity is maximized. Using simulations spanning a range of cilia stiffness, particle radius, and cilia-particle adhesion strength, we explore the parameter space over which the particle can be ``released,'' ``propelled'' or ``trapped'' by the cilia. We use a semi-analytical theory to predict parameters for which the cilia are able to attach themselves to the particle. This is the first study that shows how both stiffness and adhesion strength are crucial for the manipulation of particles by active cilia arrays. These results can ultimately facilitate the design of synthetic cilia that integrate adhesive and hydrodynamic interactions to selectively trap or repel particulates. [Preview Abstract] |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M30.00007: Experiment and Modeling of Spatially Indexed Microbead Arrays for High-Throughput Screening Applications Thomas Leary, Charles Maldarelli, Alexander Couzis The development of platforms for multiplexed, high throughput screening of the binding interactions of target biomolecules against a library of potential binding probes enables progress in many areas in medicine and biology. Formats in which probes are linked to microbeads arrayed in a microfluidic channel offer high sensitivity, reduced reagent consumption and are easily parallelized for multiplexed detection. This presentation describes a microfluidically assembled microbead array in which beads are streamed through a channel with an array of wells inscribed in the floor of the channel. The beads are captured in the wells via gravity. We demonstrate that an array of beads displaying different receptors can be assembled in this format, indexed by sequential depostion and used for a prototype assay. Solutions for a two dimensional mass transfer model of the conjugation of the probe to the receptor on the bead surface identify kinetically limited regimes which are used to measure the binding kinetics of the prototype assay. [Preview Abstract] |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M30.00008: Isotachophoretic Preconcentration of Cardiac Proteins from Human Serum Prashanta Dutta, Mohammad Hossan, Talukder Jubery, Danny Bottenus, Cornelius Ivory Cationic isotachophoresis (ITP) is used to concentrate and detect a cardiac biomarker, cardiac troponin I (cTnI), spiked into depleted human serum in a cascade poly(methyl methacrylate) (PMMA) microfluidic channel. PMMA microchannel was formed using solvent imprinting and temperature-assisted bonding. A 100x reduction in cross-sectional area is implemented by gradually decreasing the channel width and height to increase the sensitivity of ITP. The ITP was performed in peak mode with potassium ion as the leading electrolyte and hydronium ions as the terminating electrolyte. The cross-sectional area reductions in combination with ITP allowed visualization of lower concentrations of fluorescently labeled cTnI. Experimental results show that ITP can detect cTnI at initial concentrations as low as 46 ng/mL in the presence of human serum proteins, and ITP can obtain cTnI concentrations factors as high as 10,000. This demonstrates the detection of cTnI in depleted human serum at clinically relevant concentrations without the use of antibodies and relying solely on ITP in a cascade microchip. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M30.00009: Acoustically Generated Flows in Flexural Plate Wave Sensors: a Multifield Analysis Ersin Sayar, Bakhtier Farouk Acoustically excited flows in a microchannel flexural plate wave device are explored numerically with a coupled solid-fluid mechanics model. The device can be exploited to integrate micropumps with microfluidic chips. A comprehensive understanding of the device requires the development of coupled two or three-dimensional fluid structure interactive (FSI) models. The channel walls are composed of layers of ZnO, Si$_{3}$N$_{4}$ and Al. An isothermal equation of state for the fluid (water) is employed. The flexural motions of the channel walls and the resulting flowfields are solved simultaneously. A parametric analysis is performed by varying the values of the driving frequency, voltage of the electrical signal and the channel height. The time averaged axial velocity is found to be proportional to the square of the wave amplitude. The present approach is superior to the method of successive approximations where the solid-liquid coupling is weak. [Preview Abstract] |
Tuesday, November 22, 2011 9:57AM - 10:10AM |
M30.00010: Electric field-enhanced water dissociation in nanoporous membranes Devin Conroy, Richard Craster, Omar Matar, Hsueh-Chia Chang The dissociation of water with a PN junction is investigated theoretically. The model accounts for the the voltage potential and transport of ions using the Nernst-plank and Maxwell's equations respectively and solved numerically and asymptotically in the small reaction limit. The advantage of the PN junction is that the electric field is very large, which enhances the product yield far from the thermodynamic value. Further, the junction causes the charge of the ions to be separated onto the oppositely charged membrane, forming a travelling wave the has a constant velocity. Preliminary work indicates that the travelling wave undergoes a mobility gradient driven instability, for sufficiently large electric fields, that leads to the formation of fingers. [Preview Abstract] |
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