Manu Prakash

All Publications

• Coupled Active Systems Encode an Emergent Hunting Behavior in the Unicellular Predator Lacrymaria olor. Current biology : CB Coyle, S. M., Flaum, E. M., Li, H., Krishnamurthy, D., Prakash, M. 2019

  Abstract

  Many single-celled protists use rapid morphology changes to perform fast animal-like behaviors. To understand how such behaviors are encoded, we analyzed the hunting dynamics of the predatory ciliate Lacrymaria olor, which locates and captures prey using the tip of a slender "neck" that can rapidly extend more than seven times its body length (500mum from its body) and retract in seconds. By tracking single cells in real-time over hours and analyzing millions of sub-cellular postures, we find that these fast extension-contraction cycles underlie an emergent hunting behavior that comprehensively samples a broad area within the cell's reach. Although this behavior appears complex, we show that it arises naturally as alternating sub-cellular ciliary and contractile activities rearrange the cell's underlying helical cytoskeleton to extend or retract the neck. At short timescales, a retracting neck behaves like an elastic filament under load, such that compression activates a series of buckling modes that reorient the head and scramble its extensile trajectory. At longer timescales, the fundamental length of this filament can change, altering the location in space where these transitions occur. Coupling these fast and slow dynamics together, we present a simple model for how Lacrymaria samples the range of geometries and orientations needed to ensure dense stochastic sampling of the immediate environment when hunting to locate and strike at prey. More generally, coupling active mechanical and chemical signaling systems across different timescales may provide a general strategy by which mechanically encoded emergent cell behaviors can be understood or engineered.

  View details for DOI 10.1016/j.cub.2019.09.034

  View details for PubMedID 31679941

• Collective intercellular communication through ultra-fast hydrodynamic trigger waves. Nature Mathijssen, A. J., Culver, J., Bhamla, M. S., Prakash, M. 2019

  Abstract

  The biophysical relationships between sensors and actuators1-5 have been fundamental to the development of complex life forms. Swimming organisms generate abundant flows that persist in aquatic environments6-13, and responding promptly to external stimuli is key to survival14-19. Here we present the discovery of 'hydrodynamic trigger waves' in cellular communities of the protist Spirostomum ambiguum that propagate-in a manner similar to a chain reaction20-22-hundreds of times faster than their swimming speed. By coiling its cytoskeleton, Spirostomum can contract its long body by 60% within milliseconds23, experiencing accelerations that can reach forces of 14g. We show that a single cellular contraction (the transmitter) generates long-ranged vortex flows at intermediate Reynolds numbers that can, in turn, trigger neighbouring cells (the receivers). To measure the sensitivity to hydrodynamic signals in these receiver cells, we present a high-throughput suction-flow device for probing mechanosensitive ion channels24 by back-calculating the microscopic forces on the cell membrane. We analyse and quantitatively model the ultra-fast hydrodynamic trigger waves in a universal framework of antenna and percolation theory25,26, and reveal a phase transition that requires a critical colony density to sustain collective communication. Our results suggest that this signalling could help to organize cohabiting communities over large distances and influence long-term behaviour through gene expression (comparable to quorum sensing16). In more immediate terms, because contractions release toxins27, synchronized discharges could facilitate the repulsion of large predators or immobilize large prey. We postulate that numerous aquatic organisms other than protists could coordinate their behaviour using variations of hydrodynamic trigger waves.

  View details for DOI 10.1038/s41586-019-1387-9

  View details for PubMedID 31292551

• Ultrafast epithelial contractions provide insights into contraction speed limits and tissue integrity. Proceedings of the National Academy of Sciences of the United States of America Armon, S., Bull, M. S., Aranda-Diaz, A., Prakash, M. 2018

  Abstract

  By definition of multicellularity, all animals need to keep their cells attached and intact, despite internal and external forces. Cohesion between epithelial cells provides this key feature. To better understand fundamental limits of this cohesion, we study the epithelium mechanics of an ultrathin (25 mum) primitive marine animal Trichoplax adhaerens, composed essentially of two flat epithelial layers. With no known extracellular matrix and no nerves or muscles, T. adhaerens has been claimed to be the "simplest known living animal," yet is still capable of coordinated locomotion and behavior. Here we report the discovery of the fastest epithelial cellular contractions known in any metazoan, to be found in T. adhaerens dorsal epithelium (50% shrinkage of apical cell area within one second, at least an order of magnitude faster than other known examples). Live imaging reveals emergent contractile patterns that are mostly sporadic single-cell events, but also include propagating contraction waves across the tissue. We show that cell contraction speed can be explained by current models of nonmuscle actin-myosin bundles without load, while the tissue architecture and unique mechanical properties are softening the tissue, minimizing the load on a contracting cell. We propose a hypothesis, in which the physiological role of the contraction dynamics is to resist external stresses while avoiding tissue rupture ("active cohesion"), a concept that can be further applied to engineering of active materials.

  View details for PubMedID 30309963

• Two-component marangoni-contracted droplets: friction and shape SOFT MATTER Benusiglio, A., Cira, N. J., Prakash, M. 2018; 14 (37): 7724–30

  View details for DOI 10.1039/c7sm02361h

  View details for Web of Science ID 000448354800018

• Two-component marangoni-contracted droplets: friction and shape. Soft matter Benusiglio, A., Cira, N. J., Prakash, M. 2018

  Abstract

  When a mixture of propylene glycol and water is deposited on a clean glass slide, it forms a droplet of a given apparent contact angle rather than spreading as one would expect on such a high-energy surface. The droplet is stabilized by a Marangoni flow due to the non-uniformity of the components' concentrations between the border and the apex of the droplet, itself a result of evaporation. These self-contracting droplets have unusual properties such as absence of pinning and the ability to move under an external humidity gradient. The droplets' apparent contact angles are a function of their concentration and the external humidity. Here we study the motion of such droplets sliding down slopes and compare the results to normal non-volatile droplets. We precisely control the external humidity and explore the influence of the volume, viscosity, surface tension, and contact angle. We find that the droplets suffer a negligible pinning force so that for small velocities the capillary number (Ca) is directly proportional to the Bond number (Bo): Ca = Bosinalpha with alpha the angle of the slope. Lastly we study the successive shapes the droplets take when sliding at larger and larger velocities.

  View details for PubMedID 30191241

• The principles of cascading power limits in small, fast biological and engineered systems SCIENCE Ilton, M., Bhamla, M., Ma, X., Cox, S. M., Fitchett, L. L., Kim, Y., Koh, J., Krishnamurthy, D., Kuo, C., Temel, F., Crosby, A. J., Prakash, M., Sutton, G. P., Wood, R. J., Azizi, E., Bergbreiter, S., Patek, S. N. 2018; 360 (6387): 397-+

  Abstract

  Mechanical power limitations emerge from the physical trade-off between force and velocity. Many biological systems incorporate power-enhancing mechanisms enabling extraordinary accelerations at small sizes. We establish how power enhancement emerges through the dynamic coupling of motors, springs, and latches and reveal how each displays its own force-velocity behavior. We mathematically demonstrate a tunable performance space for spring-actuated movement that is applicable to biological and synthetic systems. Incorporating nonideal spring behavior and parameterizing latch dynamics allows the identification of critical transitions in mass and trade-offs in spring scaling, both of which offer explanations for long-observed scaling patterns in biological systems. This analysis defines the cascading challenges of power enhancement, explores their emergent effects in biological and engineered systems, and charts a pathway for higher-level analysis and synthesis of power-amplified systems.

  View details for PubMedID 29700237

• Synchronous magnetic control of water droplets in bulk ferrofluid SOFT MATTER Katsikis, G., Breant, A., Rinberg, A., Prakash, M. 2018; 14 (5): 681–92

  Abstract

  We present a microfluidic platform for magnetic manipulation of water droplets immersed in bulk oil-based ferrofluid. Although non-magnetic, the droplets are exclusively controlled by magnetic fields without any pressure-driven flow. The fluids are dispensed in a sub-millimeter Hele-Shaw chamber that includes permalloy tracks on its substrate. An in-plane rotating magnetic field magnetizes the permalloy tracks, producing local magnetic gradients, while an orthogonal magnetic field magnetizes the bulk ferrofluid. To minimize the magnetostatic energy of the system, the water droplets are attracted towards the locations on the tracks where the bulk ferrofluid is repelled. Using this technique, we demonstrate synchronous generation and propagation of water droplets, study the kinematics of propagation, and analyze the flow of the bulk ferrofluid. In addition, we show controlled break-up of droplets and droplet-to-droplet interactions. Finally, we discuss future applications owing to the potential biocompatibility of the droplets.

  View details for PubMedID 29205244

• Ultra Fast Contractions and Emergent Dynamics in a Living Active Solid - The Epithelium of the Primitive Animal Trichoplax adhaerens Armon, S., Prakash, M. CELL PRESS. 2018: 649A

  View details for Web of Science ID 000430563300236

• Local Epithelial Fracture and Healing Mechanics Dictate Morphogenesis and Asexual Reproduction in Trichoplax adhaerens Prakash, V. N., Bhargava, A., Prakash, M. CELL PRESS. 2018: 651A–652A

  View details for Web of Science ID 000430563300252

• Using mobile phones as acoustic sensors for high-throughput mosquito surveillance ELIFE Mukundarajan, H., Hol, F., Castillo, E., Newby, C., Prakash, M. 2017; 6

  Abstract

  The direct monitoring of mosquito populations in field settings is a crucial input for shaping appropriate and timely control measures for mosquito-borne diseases. Here, we demonstrate that commercially available mobile phones are a powerful tool for acoustically mapping mosquito species distributions worldwide. We show that even low-cost mobile phones with very basic functionality are capable of sensitively acquiring acoustic data on species-specific mosquito wingbeat sounds, while simultaneously recording the time and location of the human-mosquito encounter. We survey a wide range of medically important mosquito species, to quantitatively demonstrate how acoustic recordings supported by spatio-temporal metadata enable rapid, non-invasive species identification. As proof-of-concept, we carry out field demonstrations where minimally-trained users map local mosquitoes using their personal phones. Thus, we establish a new paradigm for mosquito surveillance that takes advantage of the existing global mobile network infrastructure, to enable continuous and large-scale data acquisition in resource-constrained areas.

  View details for PubMedID 29087296

• Flowtrace: simple visualization of coherent structures in biological fluid flows JOURNAL OF EXPERIMENTAL BIOLOGY Gilpin, W., Prakash, V. N., Prakash, M. 2017; 220 (19): 3411–18

  Abstract

  We present a simple, intuitive algorithm for visualizing time-varying flow fields that can reveal complex flow structures with minimal user intervention. We apply this technique to a variety of biological systems, including the swimming currents of invertebrates and the collective motion of swarms of insects. We compare our results with more experimentally difficult and mathematically sophisticated techniques for identifying patterns in fluid flows, and suggest that our tool represents an essential 'middle ground' allowing experimentalists to easily determine whether a system exhibits interesting flow patterns and coherent structures without resorting to more intensive techniques. In addition to being informative, the visualizations generated by our tool are often striking and elegant, illustrating coherent structures directly from videos without the need for computational overlays. Our tool is available as fully documented open-source code for MATLAB, Python or ImageJ at www.flowtrace.org.

  View details for PubMedID 28729343

• Generation of droplet arrays with rational number spacing patterns driven by a periodic energy landscape PHYSICAL REVIEW E Rinberg, A., Katsikis, G., Prakash, M. 2017; 96 (3): 033108

  Abstract

  The generation of droplets at low Reynolds numbers is driven by nonlinear dynamics that give rise to complex patterns concerning both the droplet-to-droplet spacing and the individual droplet sizes. Here we demonstrate an experimental system in which a time-varying energy landscape provides a periodic magnetic force that generates an array of droplets from an immiscible mixture of ferrofluid and silicone oil. The resulting droplet patterns are periodic, owing to the nature of the magnetic force, yet the droplet spacing and size can vary greatly by tuning a single bias pressure applied on the ferrofluid phase; for a given cycle period of the magnetic force, droplets can be generated either at integer multiples (1, 2, ...), or at rational fractions (3/2, 5/3, 5/2, ...) of this period with mono- or multidisperse droplet sizes. We develop a discrete-time dynamical systems model not only to reproduce the phenotypes of the observed patterns but also to provide a framework for understanding systems driven by such periodic energy landscapes.

  View details for PubMedID 29346989

• Vortex arrays and ciliary tangles underlie the feeding-swimming trade-off in starfish larvae NATURE PHYSICS Gilpin, W., Prakash, V. N., Prakash, M. 2017; 13 (4): 380-386

  View details for DOI 10.1038/NPHYS3981

  View details for Web of Science ID 000398262900018

• Schistosoma mansoni cercariae swim effciently by exploiting an elastohydrodynamic coupling NATURE PHYSICS Krishnamurthy, D., Katsikis, G., Bhargava, A., Prakash, M. 2017; 13 (3): 266-271

  View details for DOI 10.1038/NPHYS3924

  View details for Web of Science ID 000395814000018

• Mapping Load-Bearing in the Mammalian Spindle Reveals Local Kinetochore Fiber Anchorage that Provides Mechanical Isolation and Redundancy. Current biology : CB Elting, M. W., Prakash, M., Udy, D. B., Dumont, S. 2017; 27 (14): 2112–22.e5

  Abstract

  Active forces generated at kinetochores move chromosomes, and the dynamic spindle must robustly anchor kinetochore fibers (k-fibers) to bear this load. The mammalian spindle bears the load of chromosome movement far from poles, but we do not know where and how-physically and molecularly-this load distributes across the spindle. In part, this is because probing spindle mechanics in live cells is difficult. Yet answering this question is key to understanding how the spindle generates and responds to force and performs its diverse mechanical functions. Here, we map load-bearing across the mammalian spindle in space-time and dissect local anchorage mechanics and mechanism. To do so, we laser-ablate single k-fibers at different spindle locations and in different molecular backgrounds and quantify the immediate relaxation of chromosomes, k-fibers, and microtubule speckles. We find that load redistribution is locally confined in all directions: along the first 3-4 μm from kinetochores, scaling with k-fiber length, and laterally within ∼2 μm of k-fiber sides, without detectable load sharing between neighboring k-fibers. A phenomenological model suggests that dense, transient crosslinks to the spindle along k-fibers bear the load of chromosome movement but that these connections do not limit the timescale of spindle reorganization. The microtubule crosslinker NuMA is needed for the local load-bearing observed, whereas Eg5 and PRC1 are not detectably required, suggesting specialization in mechanical function. Together, the data and model suggest that NuMA-mediated crosslinks locally bear load, providing mechanical isolation and redundancy while allowing spindle fluidity. These features are well suited to support robust chromosome segregation.

  View details for PubMedID 28690110

• Hand-powered ultralow-cost paper centrifuge NATURE BIOMEDICAL ENGINEERING Bhamla, M., Benson, B., Chai, C., Katsikis, G., Johri, A., Prakash, M. 2017; 1 (1)

  View details for DOI 10.1038/s41551-016-0009

  View details for Web of Science ID 000418850600009

• USING MOBILE PHONES AS ACOUSTIC SENSORS FOR HIGH-THROUGHPUT SURVEILLANCE OF MOSQUITO ECOLOGY Mukundarajan, H., Hol, F., Castillo, E., Newby, C., Prakash, M. AMER SOC TROP MED & HYGIENE. 2017: 21

  View details for Web of Science ID 000423215202065

• Wetting: Bumps lead the way. Nature materials Prakash, M. 2016; 15 (4): 378-379

  View details for DOI 10.1038/nmat4612

  View details for PubMedID 27005915

• Surface tension dominates insect flight on fluid interfaces. journal of experimental biology Mukundarajan, H., Bardon, T. C., Kim, D. H., Prakash, M. 2016; 219: 752-766

  Abstract

  Flight on the 2D air-water interface, with body weight supported by surface tension, is a unique locomotion strategy well adapted for the environmental niche on the surface of water. Although previously described in aquatic insects like stoneflies, the biomechanics of interfacial flight has never been analysed. Here, we report interfacial flight as an adapted behaviour in waterlily beetles (Galerucella nymphaeae) which are also dexterous airborne fliers. We present the first quantitative biomechanical model of interfacial flight in insects, uncovering an intricate interplay of capillary, aerodynamic and neuromuscular forces. We show that waterlily beetles use their tarsal claws to attach themselves to the interface, via a fluid contact line pinned at the claw. We investigate the kinematics of interfacial flight trajectories using high-speed imaging and construct a mathematical model describing the flight dynamics. Our results show that non-linear surface tension forces make interfacial flight energetically expensive compared with airborne flight at the relatively high speeds characteristic of waterlily beetles, and cause chaotic dynamics to arise naturally in these regimes. We identify the crucial roles of capillary-gravity wave drag and oscillatory surface tension forces which dominate interfacial flight, showing that the air-water interface presents a radically modified force landscape for flapping wing flight compared with air.

  View details for DOI 10.1242/jeb.127829

  View details for PubMedID 26936640

  View details for PubMedCentralID PMC4811005

• Synchronous universal droplet logic and control NATURE PHYSICS Katsikis, G., Cybulski, J. S., Prakash, M. 2015; 11 (7): 588-596

  View details for DOI 10.1038/NPHYS3341

  View details for Web of Science ID 000357197300026

• Diagnosis of Schistosoma haematobium Infection with a Mobile Phone-Mounted Foldscope and a Reversed-Lens CellScope in Ghana AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE Ephraim, R. K., Duah, E., Cybulski, J. S., Prakash, M., D'Ambrosio, M. V., Fletcher, D. A., Keiser, J., Andrews, J. R., Bogoch, I. I. 2015; 92 (6): 1253-1256

  Abstract

  We evaluated two novel, portable microscopes and locally acquired, single-ply, paper towels as filter paper for the diagnosis of Schistosoma haematobium infection. The mobile phone-mounted Foldscope and reversed-lens CellScope had sensitivities of 55.9% and 67.6%, and specificities of 93.3% and 100.0%, respectively, compared with conventional light microscopy for diagnosing S. haematobium infection. With conventional light microscopy, urine filtration using single-ply paper towels as filter paper showed a sensitivity of 67.6% and specificity of 80.0% compared with centrifugation for the diagnosis of S. haematobium infection. With future improvements to diagnostic sensitivity, newer generation handheld and mobile phone microscopes may be valuable tools for global health applications.

  View details for DOI 10.4269/ajtmh.14-0741

  View details for Web of Science ID 000355785400028

  View details for PubMedID 25918211

• Vapour-mediated sensing and motility in two-component droplets. Nature Cira, N. J., Benusiglio, A., PRAKASH, M. 2015; 519 (7544): 446-450

  Abstract

  Controlling the wetting behaviour of liquids on surfaces is important for a variety of industrial applications such as water-repellent coatings and lubrication. Liquid behaviour on a surface can range from complete spreading, as in the 'tears of wine' effect, to minimal wetting as observed on a superhydrophobic lotus leaf. Controlling droplet movement is important in microfluidic liquid handling, on self-cleaning surfaces and in heat transfer. Droplet motion can be achieved by gradients of surface energy. However, existing techniques require either a large gradient or a carefully prepared surface to overcome the effects of contact line pinning, which usually limit droplet motion. Here we show that two-component droplets of well-chosen miscible liquids such as propylene glycol and water deposited on clean glass are not subject to pinning and cause the motion of neighbouring droplets over a distance. Unlike the canonical predictions for these liquids on a high-energy surface, these droplets do not spread completely but exhibit an apparent contact angle. We demonstrate experimentally and analytically that these droplets are stabilized by evaporation-induced surface tension gradients and that they move in response to the vapour emitted by neighbouring droplets. Our fundamental understanding of this robust system enabled us to construct a wide variety of autonomous fluidic machines out of everyday materials.

  View details for DOI 10.1038/nature14272

  View details for PubMedID 25762146

• Vapour-mediated sensing and motility in two-component droplets NATURE Cira, N. J., Benusiglio, A., Prakash, M. 2015; 519 (7544): 446-?

  View details for DOI 10.1038/nature14272

  View details for Web of Science ID 000351602800051

  View details for PubMedID 25762146

• Punch card programmable microfluidics. PloS one Korir, G., Prakash, M. 2015; 10 (3)

  Abstract

  Small volume fluid handling in single and multiphase microfluidics provides a promising strategy for efficient bio-chemical assays, low-cost point-of-care diagnostics and new approaches to scientific discoveries. However multiple barriers exist towards low-cost field deployment of programmable microfluidics. Incorporating multiple pumps, mixers and discrete valve based control of nanoliter fluids and droplets in an integrated, programmable manner without additional required external components has remained elusive. Combining the idea of punch card programming with arbitrary fluid control, here we describe a self-contained, hand-crank powered, multiplex and robust programmable microfluidic platform. A paper tape encodes information as a series of punched holes. A mechanical reader/actuator reads these paper tapes and correspondingly executes operations onto a microfluidic chip coupled to the platform in a plug-and-play fashion. Enabled by the complexity of codes that can be represented by a series of holes in punched paper tapes, we demonstrate independent control of 15 on-chip pumps with enhanced mixing, normally-closed valves and a novel on-demand impact-based droplet generator. We demonstrate robustness of operation by encoding a string of characters representing the word "PUNCHCARD MICROFLUIDICS" using the droplet generator. Multiplexing is demonstrated by implementing an example colorimetric water quality assays for pH, ammonia, nitrite and nitrate content in different water samples. With its portable and robust design, low cost and ease-of-use, we envision punch card programmable microfluidics will bring complex control of microfluidic chips into field-based applications in low-resource settings and in the hands of children around the world.

  View details for DOI 10.1371/journal.pone.0115993

  View details for PubMedID 25738834

  View details for PubMedCentralID PMC4349784

• Punch card programmable microfluidics. PloS one Korir, G., Prakash, M. 2015; 10 (3)

  View details for DOI 10.1371/journal.pone.0115993

  View details for PubMedID 25738834

• Emergent mechanics of biological structures MOLECULAR BIOLOGY OF THE CELL Dumont, S., Prakash, M. 2014; 25 (22): 3461-3465

  View details for DOI 10.1091/mbc.E14-03-0784

  View details for Web of Science ID 000344236800007

• Emergent mechanics of biological structures. Molecular biology of the cell Dumont, S., Prakash, M. 2014; 25 (22): 3461-3465

  Abstract

  Mechanical force organizes life at all scales, from molecules to cells and tissues. Although we have made remarkable progress unraveling the mechanics of life's individual building blocks, our understanding of how they give rise to the mechanics of larger-scale biological structures is still poor. Unlike the engineered macroscopic structures that we commonly build, biological structures are dynamic and self-organize: they sculpt themselves and change their own architecture, and they have structural building blocks that generate force and constantly come on and off. A description of such structures defies current traditional mechanical frameworks. It requires approaches that account for active force-generating parts and for the formation of spatial and temporal patterns utilizing a diverse array of building blocks. In this Perspective, we term this framework "emergent mechanics." Through examples at molecular, cellular, and tissue scales, we highlight challenges and opportunities in quantitatively understanding the emergent mechanics of biological structures and the need for new conceptual frameworks and experimental tools on the way ahead.

  View details for DOI 10.1091/mbc.E14-03-0784

  View details for PubMedID 25368421

  View details for PubMedCentralID PMC4230603

• Foldscope: Origami-Based Paper Microscope PLOS ONE Cybulski, J. S., Clements, J., Prakash, M. 2014; 9 (6)

  View details for DOI 10.1371/journal.pone.0098781

  View details for Web of Science ID 000338508200010

• Probing the Mechanical Coupling of the Cell Membrane to the Nucleus with Vertical Nanopillar Arrays 57th Annual Meeting of the Biophysical-Society Hanson, L., Urzay, J., Lin, Z., Zhao, W., Prakash, M., Cui, B. CELL PRESS. 2013: 546A–546A

  View details for Web of Science ID 000316074305286

• Hydraulic stress induced bubble nucleation and growth during pupal metamorphosis Annual Meeting of the Society-for-Integrative-and-Comparative-Biology (SICB)/Symposium on New Frontiers from Marine Snakes to Marine Ecosystems Prakash, M. OXFORD UNIV PRESS INC. 2012: E140–E140

  View details for Web of Science ID 000303165001028

• Flying in two dimensions Annual Meeting of the Society-for-Integrative-and-Comparative-Biology (SICB)/Symposium on New Frontiers from Marine Snakes to Marine Ecosystems Prakash, M., Donald, K. OXFORD UNIV PRESS INC. 2012: E141–E141

  View details for Web of Science ID 000303165001029

• The hungry fly: Hydrodynamics of feeding in the common house fly PHYSICS OF FLUIDS Prakash, M., Steele, M. 2011; 23 (9)

  View details for DOI 10.1063/1.3640023

  View details for Web of Science ID 000295621800010

• Face-selective electrostatic control of hydrothermal zinc oxide nanowire synthesis NATURE MATERIALS Joo, J., Chow, B. Y., Prakash, M., Boyden, E. S., Jacobson, J. M. 2011; 10 (8): 596-601

  Abstract

  Rational control over the morphology and the functional properties of inorganic nanostructures has been a long-standing goal in the development of bottom-up device fabrication processes. We report that the geometry of hydrothermally grown zinc oxide nanowires can be tuned from platelets to needles, covering more than three orders of magnitude in aspect ratio (~0.1-100). We introduce a classical thermodynamics-based model to explain the underlying growth inhibition mechanism by means of the competitive and face-selective electrostatic adsorption of non-zinc complex ions at alkaline conditions. The performance of these nanowires rivals that of vapour-phase-grown nanostructures, and their low-temperature synthesis (<60 °C) is favourable to the integration and in situ fabrication of complex and polymer-supported devices. We illustrate this capability by fabricating an all-inorganic light-emitting diode in a polymeric microfluidic manifold. Our findings indicate that electrostatic interactions in aqueous crystal growth may be systematically manipulated to synthesize nanostructures and devices with enhanced structural control.

  View details for DOI 10.1038/NMAT3069

  View details for Web of Science ID 000293000000019

  View details for PubMedID 21743451

• Hydraulic stress induced bubble nucleation and growth during pupal metamorphosis Annual Meeting of the American-Society-for-Cell-Biology (ASCB) PRAKASH, M. AMER SOC CELL BIOLOGY. 2011

  View details for Web of Science ID 000305505501236

• Face-selective electrostatic control of nanowire synthesis Nature Materials Joo, J., Chow, B., Prakash, M., Boyden, E., Jacobson, J. 2011; 10: 596-601
• Interfacial Propulsion by Directional Adhesion International Journal of Non-Linear Mechanics Manu Prakash, John W. M. Bush 2011; 46 (4): 607-615
• On a tweezer for droplets Advances in Colloid and Interface Science Bush, J., Peaudecerf, F., Prakash, M., Quere, D. 2010; 161: 10-14
• Drop propulsion in tapered tubes Euro Physics Letters, Renvoise, P., Bush, J., Prakash, M., Quere, D. 2009; 86: 1-5
• Surface tension transport of prey by feeding shorebirds: The capillary ratchet SCIENCE Prakash, M., Quere, D., Bush, J. W. 2008; 320 (5878): 931-934

  Abstract

  The variability of bird beak morphology reflects diverse foraging strategies. One such feeding mechanism in shorebirds involves surface tension-induced transport of prey in millimetric droplets: By repeatedly opening and closing its beak in a tweezering motion, the bird moves the drop from the tip of its beak to its mouth in a stepwise ratcheting fashion. We have analyzed the subtle physical mechanism responsible for drop transport and demonstrated experimentally that the beak geometry and the dynamics of tweezering may be tuned to optimize transport efficiency. We also highlight the critical dependence of the capillary ratchet on the beak's wetting properties, thus making clear the vulnerability of capillary feeders to surface pollutants.

  View details for DOI 10.1126/science.1156023

  View details for Web of Science ID 000255868300042

  View details for PubMedID 18487193

• Microfluidic bubble logic SCIENCE Prakash, M., Gershenfeld, N. 2007; 315 (5813): 832-835

  Abstract

  We demonstrate universal computation in an all-fluidic two-phase microfluidic system. Nonlinearity is introduced into an otherwise linear, reversible, low-Reynolds number flow via bubble-to-bubble hydrodynamic interactions. A bubble traveling in a channel represents a bit, providing us with the capability to simultaneously transport materials and perform logical control operations. We demonstrate bubble logic AND/OR/NOT gates, a toggle flip-flop, a ripple counter, timing restoration, a ring oscillator, and an electro-bubble modulator. These show the nonlinearity, gain, bistability, synchronization, cascadability, feedback, and programmability required for scalable universal computation. With increasing complexity in large-scale microfluidic processors, bubble logic provides an on-chip process control mechanism integrating chemistry and computation.

  View details for DOI 10.1126/science.1136907

  View details for Web of Science ID 000244069000065

  View details for PubMedID 17289994

• The Integument of Water-walking Arthropods: Form and Function Advances in Insect Physiology John W. M. Bush, David L. Hu, Manu Prakash 2007; 34: 117-192
• Water walking devices Experiments in Fluids Hu, D., Prakash, M., Chan, B., Bush, J. 2007; 43: 769-778
• Microfludic Bubble Logic Science Prakash, M., Gershenfeld, N. 2007; 315: 832-835
• Personal fabrication Telektronikk Gershenfeld, N., Prakash, M. 2004; 3: 22-26