Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session L6: Microfluids: Fluidic Devices II |
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Chair: Manu Prakash, Stanford University Room: 328 |
Monday, November 25, 2013 3:35PM - 3:48PM |
L6.00001: Mosquitoes meet microfluidics: High-throughput microfluidic tools for insect-parasite ecology in field conditions Manu Prakash, Haripriya Mukundarajan A simple bite from an insect is the transmission~mechanism for many deadly diseases worldwide --- including malaria, yellow fever,~west nile and~dengue. Very little is known about how populations of numerous~insect species and disease-causing parasites interact in their natural~habitats~due to a lack of measurement techniques.~At present, vector surveillance techniques involve manual capture by using humans as live bait, which is hard to justify on ethical grounds. Individual mosquitoes are manually dissected to isolate salivary glands to detect sporozites. With typical vector infection rates being very low even in endemic areas, it is almost impossible to get an accurate picture of disease distribution, in both space and time. Here we present novel high-throughput microfluidic tools for vector surveillance, specifically mosquitoes. A two-dimensional high density array with baits provide an integrated platform for multiplex PCR for detection of both vector and parasite species. Combining techniques from engineering and field ecology, methods and tools developed here will enable high-throughput measurement of infection rates for a number of diseases in mosquito populations in field conditions.~ [Preview Abstract] |
Monday, November 25, 2013 3:48PM - 4:01PM |
L6.00002: Scale reduction impact on bacterial growth David Lalanne-Aulet, Pierre Guillot, Annie Colin, Philippe Marchal Miniaturized tools for microbiological tests intensification have proven their impressive potential among the past decade and keep focusing a lot of researches. However, systematic comparison with usual tests is still lacking and prevents thus the implementation of these new methods. In this work, we study the scale effects on the growth of a bacterial population in order to identify growth-limiting parameters and determine ranges in which miniaturized tools really mimic usual tests. Incubations are performed in miniaturized droplets engineered in microfluidic devices with biocompatible fluorinated oil. This oil phase replaces the usual atmosphere as gas reservoir. The impact of size and environment modifications on microbial growth has to be evaluated. At first sight, system's size reduction is favorable because it minimizes nutrients diffusion times. However, the amount of needed gas available (O2) and the ability of storing undesirable gas (CO2) become limited. We show that oxygen does not limit the growth, whereas carbon dioxide accumulation can decrease growth yields by various mechanisms that will be discussed. Through this study we optimize growth conditions in miniaturized tools for long-term cultures. [Preview Abstract] |
Monday, November 25, 2013 4:01PM - 4:14PM |
L6.00003: Simulation of actuated synthetic cilia expelling microorganisms from a surface Henry Shum, Anurag Tripathi, Julia Yeomans, Anna Balazs The continual motion of cilia provides a defense against biofouling for a variety of marine organisms. Inspired by this natural solution, we perform numerical simulations to study the interactions between actuated, biomimetic cilia and model microswimmers that are hydrodynamically attracted to bare surfaces and therefore behave similarly to fouling organisms. The 3-dimensional fluid flow is coupled to the motion of the cilia and swimmers using an integrated lattice Boltzmann and immersed boundary method. We show that a sparse array of actuated cilia, through which the organisms are able to swim, is able to robustly expel swimmers. The average residence time of the swimmers in the ciliary layer is reduced if the motion of the cilia generates a net fluid flow, but for relatively fast swimmers, the steric interaction with the moving cilia alone is sufficient to ``knock'' the organisms away from the surface. As the demonstrated mechanisms for antifouling do not rely on specific chemical or physical properties of the surface or swimmer, actuated cilia can potentially protect microfluidic devices, filtration membranes or ship hulls from a wide range of fouling species. [Preview Abstract] |
Monday, November 25, 2013 4:14PM - 4:27PM |
L6.00004: Dancing Droplets Nate Cira, Manu Prakash Inspired by the observation of intricate and beautifully dynamic patterns generated by food coloring on corona treated glass slides, we have investigated the behavior of propylene glycol and water droplets on clean glass surfaces. These droplets exhibit a range of interesting behaviors including long distance attraction or repulsion, and chasing/fleeing upon contact. We present explanations for each of these behaviors, and propose a detailed model for the long distance interactions based on vapor facilitated coupling. Finally we use our understanding to create several novel devices which: passively sort droplets by surface tension, spontaneously align droplets, drive droplets in circles, and cause droplets to bounce on a vertical surface. The simplicity of this system lends it particularly well to application as a toy model for physical systems with force fields and biological systems such as chemotaxis and motility.~ [Preview Abstract] |
Monday, November 25, 2013 4:27PM - 4:40PM |
L6.00005: Synchronous Droplet Microfluidics: One ``Clock'' to rule them all Georgios Katsikis, Manu Prakash Controlling fluid droplets efficiently in the microscale is of great interest both from a basic science and a technology perspective. Here we demonstrate a general-purpose, highly scalable microfluidic control strategy through a single global clock signal that enables synchronous control of arbitrary number of droplets in a planar geometry. A rotating precessive magnetic field provides the clock signal, enabling simultaneous control of droplet position, velocity and trajectories. Using high-speed video capture and computational droplet tracking, we characterize a number of propagation circuits. Successful propagation depends on driving frequency and the size of the droplets, which is characterized as a regime diagram and rationalized in terms of Stokes and Capillary numbers. Novel interaction regimes for hydrodynamic interaction between droplets are also identified, paving the way for building complex synchronous fluidic circuits in the future. [Preview Abstract] |
Monday, November 25, 2013 4:40PM - 4:53PM |
L6.00006: Estimation of manipulation force for droplet in O/W system under photothermal interfacial control Masahiro Motosuke, Masakazu Muto Droplet-based microfluidics has been keenly investigated as a discrete operation of tiny amount of reagent or individual cell inside droplets. Noncontact maniplulation of droplets in a microfluidic platform can be achieved utilizing a photothermally induced interfacial tension gradient. Although this method could provide flexible and selective toolbox for droplet control using patterned light irradiation instead of complexed channel geometry. In this study, an experimental estimation of the manipulation force for droplet under photothermal interfacial control is presented. Temperature distribution in a PDMS microfluidic device was quantified by laser-induced fluorescence based on thermal quenching of fluorecein. Under trapped condition in a steady flow, the exerted force was determined considering a balance between the drag and the interfacial force. The results indicate that the nN-order force is available in the photothermal interfacial activation and imply the applicability of this method for a versatile droplet-based microfluidic platform. [Preview Abstract] |
Monday, November 25, 2013 4:53PM - 5:06PM |
L6.00007: ABSTRACT WITHDRAWN |
Monday, November 25, 2013 5:06PM - 5:19PM |
L6.00008: Two-phase droplet injectors for studies at X-ray free-electron laser facilities Claudiu Stan Hard X-ray free-electron lasers (XFEL) such as the recently developed Linac Coherent Light Source (LCLS) at SLAC deliver pulses with extremely short duration and intensities many orders of magnitude larger than previous sources, to enable visualization of the motion of single atoms within condensed matter. To circumvent X-ray damage, imaging experiments at LCLS are performed serially, with new samples being brought to the vacuum interaction region with X-ray pulses. Continuous liquid microjets in vacuum are currently the best way of carrying and regenerating the samples, but they consume inefficiently scarce samples, such as membrane protein microcrystals. To solve this problem, and to enhance the accuracy of pump-probe experiments, we are developing a two-liquid delivery method in which the sample is carried in disperse-phase drops contained in an immiscible continuous-phase liquid. We will report on (i) the phase-locked generation of sample-carrying droplets with an electrically-assisted axisymmetric flow-focusing device, (ii) methods to reduce the accumulation of phase jitter in the timing of drops during transport, and we will discuss methods for (iii) separating the continuous and disperse phases and (iv) ejection of sample-containing drops into air or vacuum. [Preview Abstract] |
Monday, November 25, 2013 5:19PM - 5:32PM |
L6.00009: Ink-jet patterned superhydrophobic paper for open-air surface microfluidic devices Mohamed Elsharkawy, Thomas Schutzius, Constantine Megaridis We present the production of superhydrophobic paper via polymer solution drop-casting on silicon carbide paper. The resulting substrate is patterned using household inkjet printers. The patterning process yields the ability to produce regions of varying wettability by simply controlling the intensity of ink deposited and surface area over which the ink is applied. By manipulating the two previously mentioned parameters we can develop surfaces that are capable of selective droplet sliding and adhesion. The mentioned methodology has produced superhydrophobic paper of advancing angles $157^{\circ} \pm 4.5^{\circ}$, receding angles $130^{\circ} \pm 6.3^{\circ}$, and droplet sliding angles of $13^{\circ} \pm 2.3^{\circ}$. We demonstrate the ability to vary the sliding angles of 10$\mu$L water droplets from $13^{\circ}$ to $40^{\circ}$ by printing lines of a constant intensity but varied width (.1 mm to 2 mm). It is thus possible to produce open-air surface microfluidic devices that are capable of pumpless transport, mixing, and rapid droplet sampling. The ease of the patterning technique allows for any imaginable 2D device to be printed, restricted only by the pattern usability and functionality. Lastly, post processing of printed areas using pH indicator solutions has demonstrated the use of these substrates in the area of Point-of-Care diagnostics. [Preview Abstract] |
Monday, November 25, 2013 5:32PM - 5:45PM |
L6.00010: Design of Micropost Array for Low Bubble Retention Mahshid Mohammadi, Kendra Sharp One of the well-known problems in microfluidic systems is the presence of immobile bubbles which may disturb the performance of the device. Bubbles moving through variable cross sectional areas such as regions between microposts are prone to getting stuck in the contractions. The minimal external pressure needed to overcome the capillary pressure and drive a bubble out of a contraction is called the clogging pressure. At low flow rates the clogging pressure for a bubble moving through contractions between microposts may be much larger than the pressure drop along the length of the bubble, and the chances of bubble stagnation are high. Large bubbles which come into contact with several microposts have the highest potential for geometry-based management. With an appropriate design it is possible to restrict a large bubble between two adjacent columns of microposts and force it to elongate along the direction of the flow. In that situation the bubble experiences a larger pressure drop along its length and is more likely to overcome the resistant capillary pressure. Preventing the bubbles from taking meandering paths is a key factor for keeping bubbles in motion toward the desired destination. Based on our experimental evidence we propose a design criterion that facilitates bubble mitigation in a micropost arrangement. The criterion places geometrical constraints on longitudinal, transverse, and diagonal pitches that need to be satisfied in order to have low bubble retention characteristics in a micropost array. [Preview Abstract] |
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