Manu Prakash

All Publications

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

  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 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

• 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

• 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 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 Prakash, M. OXFORD UNIV PRESS INC. 2012: E140-E140

  View details for Web of Science ID 000303165001028

• Flying in two dimensions 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 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