@inbook {1582722,
	title = {Control over the Shell Thickness of Core/Shell Drops in Three-Phase Glass Capillary Devices},
	booktitle = {UK Colloids 2011: An International Colloid and Surface Science Symposium},
	volume = {139},
	year = {2012},
	pages = {115-118},
	abstract = {
	
		Monodisperse core/shell drops with aqueous core and poly(dimethylsiloxane) (PDMS) shell of controllable thickness have been produced using a glass microcapillary device that combines co-flow and flow-focusing geometries. The throughput of the droplet generation was high, with droplet generation frequency in the range from 1,000 to 10,000 Hz. The size of the droplets can be tuned by changing the flow rate of the continuous phase. The technique enables control over the shell thickness through adjusting the flow rate ratio of the middle to inner phase. As the flow rate of the middle and inner phase increases, the droplet breakup occurs in the dripping-to-jetting transition regime, with each double emulsion droplet containing two monodisperse internal aqueous droplets. The resultant drops can be used subsequently as templates for monodisperse polymer capsules with a single or multiple inner compartments, as well as functional vesicles such as liposomes, polymersomes and colloidosomes.
	

},
	url = {https://link.springer.com/chapter/10.1007/978-3-642-28974-3_20},
	author = {Vladisavljevi{\'c}, Goran T. and Shum, Ho Cheung and Weitz, DavidA.}
}
@inbook {Vladisavljevi{\'c}2012,
	title = {Fabrication of Biodegradable Poly(Lactic Acid) Particles in Flow-Focusing Glass Capillary Devices},
	booktitle = {UK Colloids 2011: An International Colloid and Surface Science Symposium},
	volume = {139},
	year = {2012},
	pages = {111{\textendash}114},
	publisher = {Springer Berlin Heidelberg},
	organization = {Springer Berlin Heidelberg},
	address = {Berlin, Heidelberg},
	abstract = {Monodisperse poly(dl-lactic acid) (PLA) particles with a diameter in the range from 12 to 100 $μ$m were fabricated in flow focusing glass capillary devices by evaporation of dichloromethane (DCM) from emulsions at room temperature. The dispersed phase was 5\% (w/w) PLA in DCM containing a small amount of Nile red and the continuous phase was 5\% (w/w) poly(vinyl alcohol) in reverse osmosis water. Particle diameter was 2.7 times smaller than the size of the emulsion droplet template indicating that the particle porosity was very low. SEM images revealed that the majority of particle pores are in the sub-micron region but in some instances these pores can reach 3 $μ$m in diameter. Droplet diameter was influenced by the flow rates of the two phases and the entry diameter of the collection capillary tube; droplet diameters decreased with increasing values of the flow rate ratio of the dispersed to continuous phase to reach constant minimum values at 40{\textendash}60\% orifice diameter. At flow rate ratios less than 5, jetting can occur, giving rise to large droplets formed by detachment from relatively long jets (\textasciitilde10 times longer than droplet diameter).},
	isbn = {978-3-642-28974-3},
	doi = {10.1007/978-3-642-28974-3_19},
	url = {http://dx.doi.org/10.1007/978-3-642-28974-3_19},
	author = {Vladisavljevi{\'c}, Goran T. and Henry, J. V. and Duncanson, Wynter J. and Shum, Ho C. and Weitz, DavidA.},
	editor = {Starov, Victor and Griffiths, Peter}
}
@article {jensen2012conformational,
	title = {The conformational state of actin filaments regulates branching by actin-related protein 2/3 (Arp2/3) complex},
	journal = {Journal of Biological Chemistry},
	volume = {287},
	number = {37},
	year = {2012},
	pages = {31447{\textendash}31453},
	publisher = {ASBMB},
	abstract = {
	
		Actin is a highly ubiquitous protein in eukaryotic cells that plays a crucial role in cell mechanics and motility. Cell motility is driven by assembling actin as polymerizing actin drives cell protrusions in a process closely involving a host of other actin-binding proteins, notably the actin-related protein 2/3 (Arp2/3) complex, which nucleates actin and forms branched filamentous structures. The Arp2/3 complex preferentially binds specific actin networks at the cell leading edge and forms branched filamentous structures, which drive cell protrusions, but the exact regulatory mechanism behind this process is not well understood. Here we show using\&nbsp;in vitro\&nbsp;imaging and binding assays that a fragment of the actin-binding protein caldesmon added to polymerizing actin increases the Arp2/3-mediated branching activity, whereas it has no effect on branch formation when binding to aged actin filaments. Because this caldesmon effect is shown to be independent of nucleotide hydrolysis and phosphate release from actin, our results suggest a mechanism by which caldesmon maintains newly polymerized actin in a distinct state that has a higher affinity for the Arp2/3 complex. Our data show that this new state does not affect the level of cooperativity of binding by Arp2/3 complex or its distribution on actin. This presents a novel regulatory mechanism by which caldesmon, and potentially other actin-binding proteins, regulates the interactions of actin with its binding partners.
	

},
	url = {https://www.jbc.org/article/S0021-9258(20)63089-7/fulltext},
	author = {Jensen, Mikkel Herholdt and Morris, Eliza J. and Huang, Renjian and Rebowski, Grzegorz and Dominguez, Roberto and Weitz, David A and Moore, Jeffrey R. and Wang, Chih-Lueh Albert}
}
@article {156436,
	title = {Asymmetric functionalization of colloidal dimer particles with gold nanoparticles},
	journal = {Chemical Communications},
	volume = {48},
	number = {72},
	year = {2012},
	pages = {9056-9058},
	abstract = {We present a method to asymmetrically functionalize dimer particles with gold nanoparticles. Our method enables the fabrication of asymmetrically functionalized dimer particles on a large scale.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/cc/c2cc33449f$\#$!divAbstract},
	author = {Yoon, Kisun and Lee, Daeyeon and Kim, Jin Woong and Kim, Jaeyun and Weitz, David A}
}
@article {155611,
	title = {High throughput production of single core double emulsions in a parallelized microfluidic device},
	journal = {Lab on a Chip},
	volume = {12},
	number = {4},
	year = {2012},
	pages = {802-807},
	abstract = {Double emulsions are useful templates for microcapsules and complex particles, but no method yet exists for making double emulsions with both high uniformity and high throughput. We present a parallel numbering-up design for microfluidic double emulsion devices, which combines the excellent control of microfluidics with throughput suitable for mass production. We demonstrate the design with devices incorporating up to 15 dropmaker units in a two-dimensional or three-dimensional array, producing single-core double emulsion drops at rates over 1 kg day(-1) and with diameter variation less than 6\%. This design provides a route to integrating hundreds of dropmakers or more in a single chip, facilitating industrial-scale production rates of many tons per year.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/lc/c2lc21033a$\#$!divAbstract},
	author = {Romanowsky, Mark B. and Abate, Adam R. and Rotem, Assaf and Holtze, Christian and Weitz, David A}
}
@article {155366,
	title = {Direct visualization of three-dimensional crystallization behavior in microgels},
	journal = {Physical Review E},
	volume = {85},
	number = {2},
	year = {2012},
	pages = {021405},
	abstract = {We use confocal microscopy to study the three-dimensional (3D) structure of colloidal crystals formed by poly(N-isopropylacrylamide)-co-(acrylic acid) microgels of diameter 1.0-1.5 mu m. The confocal images are tracked to locate particle positions in 3D, which are used to compute pair-correlation functions g(r), bond order parameters, and structure factors s(q). We find that the structure remains fcc for a range of charge, size, and concentration of the particles. When the particles are weakly attractive and are at low concentrations, polycrystalline solids result. In addition, owing to the compressibility of the colloids, the crystals display remarkable structural stability when subjected to external stress.},
	url = {https://journals.aps.org/pre/abstract/10.1103/PhysRevE.85.021405},
	author = {Muluneh, Melaku and Weitz, David A}
}
@article {155316,
	title = {Does size matter? Elasticity of compressed suspensions of colloidal- and granular-scale microgels},
	journal = {Soft Matter},
	volume = {8},
	number = {1},
	year = {2012},
	pages = {156-164},
	abstract = {We investigate the mechanics of dense packing of very small, colloidal-scale, and larger, granular-scale microgel particles. At low particle concentration, thermally induced Brownian motion of the particles is important for the colloidal-scale systems; in contrast, such Brownian motion is irrelevant at particle packing fractions beyond jamming. As a consequence, colloidal and granular systems behave very similarly under these conditions. At sufficiently high compression of the microgel particles, their polymeric nature sets the scale of the osmotic pressure and shear modulus of the whole packing, in direct analogy with macroscopic, continuous polymer gels. This observation suggests that the particulate nature of microgels is inconsequential for their linear elasticity in a highly packed state. In contrast, the particulate nature of the microgels does become essential when the packed suspensions are forced to yield and flow; here, the differences between colloidal-and granular-scale particles are marked.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/sm/c1sm06355c$\#$!divAbstract},
	author = {Menut, Paul and Seiffert, Sebastian and Sprakel, Joris and Weitz, David A}
}
@article {155246,
	title = {Protein expression, aggregation, and triggered release from polymersomes as artificial cell-like structures},
	journal = {Angewandte Chemie-International Edition},
	volume = {51},
	number = {26},
	year = {2012},
	pages = {6416-6420},
	abstract = {
	Bringing droplets to life: A cytoskeletal protein (red dots, see scheme) is expressed in artificial cells composed of biocompatible polymersomes, which encapsulate expression machinery and amino acid building blocks. Release of the expressed proteins can be triggered by a negative osmotic shock.

},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201201443},
	author = {Martino, Chiara and Kim, Shin-Hyun and Horsfall, Louise and Abbaspourrad, Alireza and Rosser, Susan J. and Cooper, Jonathan and Weitz, David A}
}
@article {155176,
	title = {Characterizing concentrated, multiply scattering, and actively driven fluorescent systems with confocal differential dynamic microscopy},
	journal = {Physical Review Letters},
	volume = {108},
	number = {21},
	year = {2012},
	pages = {218103},
	abstract = {We introduce confocal differential dynamic microscopy (ConDDM), a new technique yielding information comparable to that given by light scattering but in dense, opaque, fluorescent samples of micron-sized objects that cannot be probed easily with other existing techniques. We measure the correct wave vector q-dependent structure and hydrodynamic factors of concentrated hard-sphere-like colloids. We characterize concentrated swimming bacteria, observing ballistic motion in the bulk and a new compressed-exponential scaling of dynamics, and determine the velocity distribution; by contrast, near the coverslip, dynamics scale differently, suggesting that bacterial motion near surfaces fundamentally differs from that of freely swimming organisms.},
	url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.108.218103},
	author = {Lu, Peter J. and Giavazzi, Fabio and Angelini, Thomas E. and Zaccarelli, Emanuela and Jargstorff, Frank and Schofield, Andrew B. and Wilking, James N. and Romanowsky, Mark B. and Weitz, David A and Cerbino, Roberto}
}
@article {155161,
	title = {Non-coalescence of oppositely charged droplets in pH-sensitive emulsions},
	journal = {Proceedings of the National Academy of Sciences of the United States of America},
	volume = {109},
	number = {2},
	year = {2012},
	pages = {384-389},
	abstract = {Like charges stabilize emulsions, whereas opposite charges break emulsions. This is the fundamental principle for many industrial and practical processes. Using micrometer-sized pH-sensitive polymeric hydrogel particles as emulsion stabilizers, we prepare emulsions that consist of oppositely charged droplets, which do not coalesce. We observe noncoalescence of oppositely charged droplets in bulk emulsification as well as in microfluidic devices, where oppositely charged droplets are forced to collide within channel junctions. The results demonstrate that electrostatic interactions between droplets do not determine their stability and reveal the unique pH-dependent properties of emulsions stabilized by soft microgel particles. The noncoalescence can be switched to coalescence by neutralizing the microgels, and the emulsion can be broken on demand. This unusual feature of the microgel-stabilized emulsions offers fascinating opportunities for future applications of these systems.},
	url = {https://www.pnas.org/content/109/2/384},
	author = {Liu, Tingting and Seiffert, Sebastian and Thiele, Julian and Abate, Adam R. and Weitz, David A and Richtering, Walter}
}
@article {155116,
	title = {Structures, stresses, and fluctuations in the delayed failure of colloidal gels},
	journal = {Soft Matter},
	volume = {8},
	number = {13},
	year = {2012},
	pages = {3657-3664},
	abstract = {Sample-spanning networks of aggregated colloidal particles have a finite stiffness and deform elastically when subjected to a small shear stress. After some period of creep, these gels ultimately suffer catastrophic failure. This delayed yielding is governed by the association and dissociation dynamics of interparticle bonds and the strand structure of the gel. We derive a model which connects the kinetics of the colloids to the erosion of the strand structure and ultimately to macroscopic failure. Importantly, this model relates time-to-failure of the gel to an applied static stress. Model predictions are in quantitative agreement with experiments. It is predicted that the strand structure, characterized by its mesh size and strand coarseness, has a significant impact on delay time. Decreasing the mesh size or increasing the strand thickness makes colloidal gels more resilient to delayed yielding. The quench and flow history of gels modifies their microstructures. Our experiments show that a slow quenching increases the delay time due to the coarsening of the strands; by contrast, preshear reduces the delay time, which we explain by the increased mesh size as a result of shear-induced fracture of strands.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/SM/c2sm06723d$\#$!divAbstract},
	author = {Lindstrom, Stefan B. and Kodger, Thomas E. and Sprakel, Joris and Weitz, David A}
}
@article {154926,
	title = {Skating on a film of air: Drops impacting on a surface},
	journal = {Physical Review Letters},
	volume = {108},
	number = {7},
	year = {2012},
	pages = {074503},
	abstract = {The commonly accepted description of drops impacting on a surface typically ignores the essential role of the air that is trapped between the impacting drop and the surface. Here we describe a new imaging modality that is sensitive to the behavior right at the surface. We show that a very thin film of air, only a few tens of nanometers thick, remains trapped between the falling drop and the surface as the drop spreads. The thin film of air serves to lubricate the drop enabling the fluid to skate on the air film laterally outward at surprisingly high velocities, consistent with theoretical predictions. Eventually this thin film of air breaks down as the fluid wets the surface via a spinodal-like mechanism. Our results show that the dynamics of impacting drops are much more complex than previously thought, with a rich array of unexpected phenomena that require rethinking classic paradigms.},
	url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.108.074503},
	author = {Kolinski, John M and Rubinstein, Shmuel M and Mandre, Shreyas and Michael P. Brenner and Weitz, David A and Mahadevan, L}
}
@article {154936,
	title = {Surface roughness directed self-assembly of patchy particles into colloidal micelles},
	journal = {Proceedings of the National Academy of Sciences of the United States of America},
	volume = {109},
	number = {27},
	year = {2012},
	pages = {10787-10792},
	abstract = {Colloidal particles with site-specific directional interactions, so called "patchy particles", are promising candidates for bottom-up assembly routes towards complex structures with rationally designed properties. Here we present an experimental realization of patchy colloidal particles based on material independent depletion interaction and surface roughness. Curved, smooth patches on rough colloids are shown to be exclusively attractive due to their different overlap volumes. We discuss in detail the case of colloids with one patch that serves as a model for molecular surfactants both with respect to their geometry and their interactions. These one-patch particles assemble into clusters that resemble surfactant micelles with the smooth and attractive sides of the colloids located at the interior. We term these clusters "colloidal micelles". Direct Monte Carlo simulations starting from a homogeneous state give rise to cluster size distributions that are in good agreement with those found in experiments. Important differences with surfactant micelles originate from the colloidal character of our model system and are investigated by simulations and addressed theoretically. Our new "patchy" model system opens up the possibility for self-assembly studies into finite-sized superstructures as well as crystals with as of yet inaccessible structures.},
	url = {https://www.pnas.org/content/109/27/10787},
	author = {Kraft, Daniela J. and Ni, Ran and Smallenburg, Frank and Hermes, Michiel and Yoon, Kisun and Weitz, David A and van Blaaderen, Alfons and Groenewold, Jan and Dijkstra, Marjolein and Kegel, Willem K.}
}
@article {154656,
	title = {Droplet microfluidics for high-throughput biological assays},
	journal = {Lab on a Chip},
	volume = {12},
	number = {12},
	year = {2012},
	pages = {2146-2155},
	abstract = {Droplet microfluidics offers significant advantages for performing high-throughput screens and sensitive assays. Droplets allow sample volumes to be significantly reduced, leading to concomitant reductions in cost. Manipulation and measurement at kilohertz speeds enable up to 10(8) samples to be screened in one day. Compartmentalization in droplets increases assay sensitivity by increasing the effective concentration of rare species and decreasing the time required to reach detection thresholds. Droplet microfluidics combines these powerful features to enable currently inaccessible high-throughput screening applications, including single-cell and single-molecule assays.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/LC/c2lc21147e$\#$!divAbstract},
	author = {Guo, Mira T. and Rotem, Assaf and Heyman, John A. and Weitz, David A}
}
@article {154356,
	title = {Microfluidic synthesis of advanced microparticles for encapsulation and controlled release},
	journal = {Lab on a Chip},
	volume = {12},
	number = {12},
	year = {2012},
	pages = {2135-2145},
	abstract = {We describe droplet microfluidic strategies used to fabricate advanced microparticles that are useful structures for the encapsulation and release of actives; these strategies can be further developed to produce microparticles for advanced drug delivery applications. Microfluidics enables exquisite control in the fabrication of polymer vesicles and thermosensitive microgels from single and higher-order multiple emulsion templates. The strategies used to create the diversity of microparticle structures described in this review, coupled with the scalability of microfluidics, will enable fabrication of large quantities of novel microparticle structures that have potential uses in controlled drug release applications.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/LC/c2lc21164e$\#$!divAbstract},
	author = {Duncanson, Wynter J. and Lin, Tina and Abate, Adam R. and Seiffert, Sebastian and Shah, Rhutesh K. and Weitz, David A}
}
@article {154361,
	title = {Microfluidic synthesis of monodisperse porous microspheres with size-tunable pores},
	journal = {Soft Matter},
	volume = {8},
	number = {41},
	year = {2012},
	pages = {10636-10640},
	abstract = {We use a perfluorinated-dendrimer-dye complex that stabilizes microbubbles as a novel pore-forming agent. We use microfluidics to produce monodisperse emulsions containing a polymer matrix material, a model active, and the perfluorinated complex; upon drying, the emulsions form porous microspheres. This porosity causes the encapsulated model active to be released faster than from non-porous microspheres. Moreover, because of the fluorous features of the pores, we can also attach an additional guest molecule to the pores which is released with a profile that is distinct from that of the encapsulated active. These porous microspheres can encapsulate and controllably release multiple actives; this makes them valuable for applications such as drug delivery and imaging.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/SM/c2sm25694k$\#$!divAbstract},
	author = {Duncanson, Wynter J. and Zieringer, Maximilian and Wagner, Olaf and Wilking, James N. and Abbaspourrad, Alireza and Haag, Rainer and Weitz, David A}
}
@article {154351,
	title = {Monodisperse gas-filled microparticles from reactions in double emulsions},
	journal = {Langmuir},
	volume = {28},
	number = {17},
	year = {2012},
	pages = {6742-6745},
	abstract = {We present a strategy for preparing size-controlled gas-filled microparticles using two aqueous components that chemically react to produce the gas. We use a dual-bore microfluidic device to isolate the reactants of two gas-producing reactions until they are encapsulated in the outer droplet. The reactants in the monodisperse droplets merge and produce the gas bubbles, which are stabilized with a surfactant and form the core of the microparticles. The number and size of the generated gas bubbles are governed by the gas-forming reaction used. Our versatile strategy can be applied to a wide range of gas-producing reactions.},
	url = {https://pubs.acs.org/doi/10.1021/la300915p},
	author = {Duncanson, Wynter J. and Abbaspourrad, Alireza and Shum, Ho Cheung and Kim, Shin-Hyun and Adams, Laura L. A. and Weitz, David A}
}
@article {154266,
	title = {Delayed buckling and guided folding of inhomogeneous capsules},
	journal = {Physical Review Letters},
	volume = {109},
	number = {13},
	year = {2012},
	pages = {134302},
	abstract = {Colloidal capsules can sustain an external osmotic pressure; however, for a sufficiently large pressure, they will ultimately buckle. This process can be strongly influenced by structural inhomogeneities in the capsule shells. We explore how the time delay before the onset of buckling decreases as the shells are made more inhomogeneous; this behavior can be quantitatively understood by coupling shell theory with Darcy{\textquoteright}s law. In addition, we show that the shell inhomogeneity can dramatically change the folding pathway taken by a capsule after it buckles.},
	url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.109.134302},
	author = {Datta, Sujit S. and Kim, Shin-Hyun and Paulose, Jayson and Abbaspourrad, Alireza and David R. Nelson and Weitz, David A}
}
@article {154091,
	title = {Use of micro-emulsion technology for the directed evolution of antibodies},
	journal = {Methods},
	volume = {58},
	number = {1},
	year = {2012},
	pages = {28-33},
	abstract = {Affinity reagents, such as antibodies, are needed to study protein expression patterns, sub-cellular localization, and post-translational modifications in complex mixtures and tissues. Phage Emulsion, Secretion, and Capture (ESCape) is a novel micro-emulsion technology that utilizes water-in-oil (W/O) emulsions for the identification and isolation of cells secreting phage particles that display desirable antibodies. Using this method, a large library of antibody-displaying phage will bind to beads in individual compartments. Rather than using biopanning on a large mixed population, phage micro-emulsion technology allows us to individually query clonal populations of amplified phage against the antigen. The use of emulsions to generate microdroplets has the promise of accelerating phage selection experiments by permitting fine discrimination of kinetic parameters for binding to targets. In this study, we demonstrate the ability of phage micro-emulsion technology to distinguish two scFvs with a 300-fold difference in binding affinities (100 nM and 300 pM, respectively). In addition, we describe the application of phage microemulsion technology for the selection of scFvs that are resistant to elevated temperatures. (C) 2012 Published by Elsevier Inc.},
	url = {https://www.sciencedirect.com/science/article/abs/pii/S1046202312001624?via\%3Dihub},
	author = {Buhr, Diane L. and Acca, Felicity E. and Holland, Erika G. and Johnson, Katie and Maksymiuk, Gail M. and Vaill, Ada and Kay, Brian K. and Weitz, David A and Weiner, Michael P. and Kiss, Margaret M.}
}
@article {153961,
	title = {Photo- and thermoresponsive polymersomes for triggered release},
	journal = {Angewandte Chemie-International Edition},
	volume = {51},
	number = {50},
	year = {2012},
	pages = {12499-12503},
	abstract = {
	Microfluidics: Thermo- and photoresponsive polymersomes are assembled using capillary microfluidic devices. Encapsulants can be selectively released from the thermoresponsive polymersomes if they are incubated at and above temperatures of 40 {\textdegree}C, whereas the photoresponsive polymersomes selectively release encapsulants if illuminated with laser light (see picture; NP=nanoparticle).

},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201206531},
	author = {Amstad, Esther and Kim, Shin-Hyun and Weitz, David A}
}
@article {153936,
	title = {Single step emulsification for the generation of multi-component double emulsions},
	journal = {Soft Matter},
	volume = {8},
	number = {41},
	year = {2012},
	pages = {10719-10724},
	abstract = {We successfully encapsulate two, three, and four different inner drops inside double emulsions by means of a single-step emulsification technique. The microfluidic device fabrication is simple and the emulsification process highly robust. Optical microscopy images of double emulsion generation and of monodisperse double emulsions with discrete numbers of inner drops indicate the achievement of a high level of control with this technique. When the middle fluid transitions from dripping to jetting, two additional variations of double emulsions are produced: highly packed double emulsions and double emulsions with different sizes of inner drops. Finally, we successfully coalesce inner drops confined in a wax shell by applying heat. This demonstrates that these multi-component double emulsions may be useful as micro-reactors.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/SM/c2sm25953b$\#$!divAbstract},
	author = {Adams, L. L. A. and Kodger, Thomas E. and Kim, Shin-Hyun and Shum, Ho Cheng and Franke, Thomas and Weitz, David A}
}
@article {153856,
	title = {Experimental validation of plugging during drop formation in a T-junction},
	journal = {Lab on a Chip},
	volume = {12},
	number = {8},
	year = {2012},
	pages = {1516-1521},
	abstract = {At low capillary number, drop formation in a T-junction is dominated by interfacial effects: as the dispersed fluid flows into the drop maker nozzle, it blocks the path of the continuous fluid; this leads to a pressure rise in the continuous fluid that, in turn, squeezes on the dispersed fluid, inducing pinch-off of a drop. While the resulting drop volume predicted by this "squeezing{\textquoteright}{\textquoteright} mechanism has been validated for a range of systems, as of yet, the pressure rise responsible for the actual pinch-off has not been observed experimentally. This is due to the challenge of measuring the pressures in a T-junction with the requisite speed, accuracy, and localization. Here, we present an empirical study of the pressures in a T-junction during drop formation. Using Laplace sensors, pressure probes we have developed, we confirm the central ideas of the squeezing mechanism; however, we also uncover other findings, including that the pressure of the dispersed fluid is not constant but rather oscillates in anti-phase with that of the continuous fluid. In addition, even at the highest capillary number for which monodisperse drops can be formed, pressure oscillations persist, indicating that drop formation in confined geometries does not transition to an entirely shear-driven mechanism, but to a mechanism combining squeezing and shearing.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/LC/c2lc21263c$\#$!divAbstract},
	author = {Abate, Adam R. and Mary, Pascaline and van Steijn, Volkert and Weitz, David A}
}
@article {153826,
	title = {Measuring the elastic modulus of microgels using microdrops},
	journal = {Soft Matter},
	volume = {8},
	number = {39},
	year = {2012},
	pages = {10032-10035},
	abstract = {Two microgel particles are encapsulated in a microdrop having a spherical diameter smaller than the sum of the diameters of the microgels; this causes the microgels to be squeezed together by the oil-water interface of the drop, in turn, making the drop ellipsoidal in shape. By modeling the force applied to the microgels by the drop and equating this to the Hertz contact force of their deformation, we are able to estimate their elastic modulus. By varying the surface tension and shape of the drops, we are able to measure the modulus of the microgels under different loads. This provides a simple technique for quantifying the elasticity of small, deformable objects, including liquid drops, microgels, and cells.},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/SM/c2sm26108a$\#$!divAbstract},
	author = {Abate, Adam R. and Han, Lloyd and Jin, Lihua and Zhigang Suo and Weitz, David A}
}
@article {155671,
	title = {Colloidal gelation of oppositely charged particles},
	journal = {Soft Matter},
	volume = {8},
	number = {33},
	year = {2012},
	pages = {8697-8703},
	abstract = {
	Colloidal gelation has been extensively studied for the case of purely attractive systems, but little is understood about how colloidal gelation is affected by the presence of repulsive interactions. Here we demonstrate the gelation of a binary system of oppositely charged colloids, in which repulsive interactions compete with attractive interactions. We observe that gelation is controlled by varying the total volume fraction, the interaction strength, and the new tuning parameter of the mixing ratio of the two particle types, and present a state diagram of gelation along all these phase-space coordinates. Contrary to commonly studied purely attractive gels, in which weakly quenched gels are more compact and less tenuous, we find that particles in these binary gels form fewer contacts and the gels become more tenuous as we approach the gel point. This suggests that a different mechanism governs gel formation and ultimate structure in binary gelation: particles are unable to form additional favorable contacts through rearrangements, due to the competition of repulsive interactions between similarly charged colloids and attractive interactions between oppositely charged colloids.

},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/SM/c2sm25901j$\#$!divAbstract},
	author = {Russell, Emily R. and Sprakel, Joris and Kodger, Thomas E. and Weitz, David A}
}
@article {155631,
	title = {Controlled synthesis of cell-laden microgels by radical-free gelation in droplet microfluidics},
	journal = {Journal of the American Chemical Society},
	volume = {134},
	number = {10},
	year = {2012},
	pages = {4983-4989},
	abstract = {
	Micrometer-sized hydrogel particles that contain living cells can be fabricated with exquisite control through the use of droplet-based microfluidics and bioinert polymers such as polyethyleneglycol (PEG) and hyperbranched polyglycerol (hPG). However, in existing techniques, the microgel gelation is often achieved through harmful reactions with free radicals. This is detrimental for the viability of the encapsulated cells. To overcome this limitation, we present a technique that combines droplet microfluidic templating with bio-orthogonal thiol-ene click reactions to fabricate monodisperse, cell laden microgel particles. The gelation of these microgels is achieved via the nucleophilic Michael addition of dithiolated PEG macro-cross-linkers to acrylated hPG building blocks and does not require any initiator. We systematically vary the microgel properties through the use of PEG linkers with different molecular weights along with different concentrations of macromonomers to investigate the influence of these parameters on the viability and proliferation of encapsulated yeast cells. We also demonstrate the encapsulation of mammalian cells including fibroblasts and lymphoblasts.

},
	url = {https://pubs.acs.org/doi/10.1021/ja300460p},
	author = {Rossow, Torsten and Heyman, John A. and Ehrlicher, Allen J. and Langhoff, Arne and Weitz, David A and Haag, Rainer and Seiffert, Sebastian}
}
@article {155636,
	title = {Drop formation in non-planar microfluidic devices},
	journal = {Lab on a Chip},
	volume = {12},
	number = {21},
	year = {2012},
	pages = {4263-4268},
	abstract = {
	Microfluidic devices can be used to produce single or multiple emulsions with remarkably precise control of both the contents and size of the drops. Since each level of a multiple emulsion is formed by a distinct fluid stream, very efficient encapsulation of materials can be achieved. To obtain high throughput, these devices can be fabricated lithographically, allowing many devices to operate in parallel. However, to form multiple emulsions using a planar microfluidic device, the wettability of its surface must switch from hydrophobic to hydrophilic on the scale of micrometers where the drops are formed; this makes the fabrication of the devices very difficult. To overcome this constraint, we introduce non-planar microfluidic devices with graduated thicknesses; these can make drops even when their wetting properties do not favor drop formation. Nevertheless, the dependence of drop formation on the device geometry, the flow rates and the properties of the fluids, particularly in the case of unfavorable wetting, is very complex, making the successful design of these devices more difficult. Here we show that there exists a critical value of flow of the continuous phase above which drop formation occurs; this value decreases by two orders of magnitude as the wetting to the device wall of the continuous phase improves. We demonstrate how this new understanding can be used to optimize device design for efficient production of double or multiple emulsions.

},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/LC/c2lc40546f$\#$!divAbstract},
	author = {Rotem, Assaf and Abate, Adam R. and Utada, Andrew S. and van Steijn, Volkert and Weitz, David A}
}
@article {156081,
	title = {Emulsion templating of poly(lactic acid) particles: Droplet formation behavior},
	journal = {Langmuir},
	volume = {28},
	number = {36},
	year = {2012},
	pages = {12948-12954},
	abstract = {
	Monodisperse poly(DL-lactic acid) (PLA) particles of diameters between 11 and 121 mu m were fabricated in flow focusing glass microcapillary devices by evaporation of dichloromethane (DCM) from emulsion droplets at room temperature. The dispersed phase was 5\% (w/w) PLA in DCM containing 0.1-2 mM Nile Red and the continuous phase was 5\% (w/w) poly(vinyl alcohol) in reverse osmosis water. Particle diameter was 2.7 times smaller than the diameter of the emulsion droplet template, indicating very low particle porosity. Monodisperse droplets have only been produced under dripping regime using a wide range of dispersed phase flow rates (0.002-7.2 cm(3).h(-1)), continuous phase flow rates (0.3-30 cm(3).h(-1)), and orifice diameters (50-237 mu m). In the dripping regime, the ratio of droplet diameter to orifice diameter was inversely proportional to the 0.39 power of the ratio of the continuous phase flow rate to dispersed phase flow rate. Highly uniform droplets with a coefficient of variation (CV) below 2\% and a ratio of the droplet diameter to orifice diameter of 0.5-1 were obtained at flow rate ratios of 4-25. Under jetting regime, polydisperse droplets (CV \&gt; 6\%) were formed by detachment from relatively long jets (between 4 and 10 times longer than droplet diameter) and a ratio of the droplet size to orifice size of 2-5.

},
	url = {https://pubs.acs.org/doi/10.1021/la302092f},
	author = {Vladisavljevic, Goran T. and Duncanson, Wynter J. and Shum, Ho Cheung and Weitz, David A}
}
@article {154816,
	title = {High-yield cell ordering and deterministic cell-in-droplet encapsulation using Dean flow in a curved microchannel},
	journal = {Lab on a Chip},
	volume = {12},
	number = {16},
	year = {2012},
	pages = {2881-2887},
	abstract = {
	In this article high-yield (77\%) and high-speed (2700 cells s(-1)) single cell droplet encapsulation is described using a Dean-coupled inertial ordering of cells in a simple curved continuous microchannel. By introducing the Dean force, the particles will order to one equilibrium position after travelling less than 1 cm. We use a planar curved microchannel structure in PDMS to spatially order two types of myeloid leukemic cells (HL60 and K562 cells), enabling deterministic single cell encapsulation in picolitre drops. An efficiency of up to 77\% was reached, overcoming the limitations imposed by Poisson statistics for random cell loading, which yields only 37\% of drops containing a single cell. Furthermore, we confirm that \&gt; 90\% of the cells remain viable. The simple planar structure and high throughput provided by this passive microfluidic approach makes it attractive for implementation in lab on a chip (LOC) devices for single cell applications using droplet-based platforms.

},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/LC/c2lc00013j$\#$!divAbstract},
	author = {Kemna, Evelien W. M. and Schoeman, Rogier M. and Wolbers, Floor and Vermes, Istvan and Weitz, David A and van den Berg, Albert}
}
@article {155331,
	title = {Low intensity ultrasound perturbs cytoskeleton dynamics},
	journal = {Soft Matter},
	volume = {8},
	number = {8},
	year = {2012},
	pages = {2438-2443},
	abstract = {
	Therapeutic ultrasound is widely employed in clinical applications but its mechanism of action remains unclear. Here we report prompt fluidization of a cell and dramatic acceleration of its remodeling dynamics when exposed to low intensity ultrasound. These physical changes are caused by very small strains (10(-5)) at ultrasonic frequencies (10(6) Hz), but are closely analogous to those caused by relatively large strains (10(-1)) at physiological frequencies (10(0) Hz). Moreover, these changes are reminiscent of rejuvenation and aging phenomena that are well-established in certain soft inert materials. As such, we suggest cytoskeletal fluidization together with resulting acceleration of cytoskeletal remodeling events as a mechanism contributing to the salutary effects of low intensity therapeutic ultrasound.

},
	url = {https://pubs.rsc.org/en/content/articlelanding/2012/SM/c2sm07246g$\#$!divAbstract},
	author = {Mizrahi, Natalya and Zhou, Enhua H. and Lenormand, Guillaume and Krishnan, Ramaswamy and Weihs, Daphne and James P. Butler and Weitz, David A and Jeffrey J. Fredberg and Kimmel, Eitan}
}
@article {155856,
	title = {Microfluidic fabrication of water-in-water (w/w) jets and emulsions},
	journal = {Biomicrofluidics},
	volume = {6},
	number = {1},
	year = {2012},
	pages = {012808},
	abstract = {
	We demonstrate the generation of water-in-water ( w/w) jets and emulsions by combining droplet microfluidics and aqueous two-phase systems ( ATPS). The application of ATPS in microfluidics has been hampered by the low interfacial tension between typical aqueous phases. The low tension makes it difficult to form w/w droplets with conventional droplet microfluidic approaches. We show that by mechanically perturbing a stable w/w jet, w/w emulsions can be prepared in a controlled and reproducible fashion. We also characterize the encapsulation ability of w/w emulsions and demonstrate that their encapsulation efficiency can be significantly enhanced by inducing formation of precipitates and gels at the w/w interfaces. Our work suggests a biologically and environmentally friendly platform for droplet microfluidics and establishes the potential of w/w droplet microfluidics for encapsulation-related applications. (C) 2012 American Institute of Physics. [doi:10.1063/1.3670365]

},
	url = {https://aip.scitation.org/doi/10.1063/1.3670365},
	author = {Shum, Ho Cheung and Varnell, Jason and Weitz, David A}
}
@article {155626,
	title = {Origin of de-swelling and dynamics of dense ionic microgel suspensions},
	journal = {Journal of Chemical Physics},
	volume = {136},
	number = {12},
	year = {2012},
	pages = {124905},
	abstract = {
	A direct consequence of the finite compressibility of a swollen microgel is that it can shrink and deform in response to an external perturbation. As a result, concentrated suspensions of these particles exhibit relaxation dynamics and rheological properties which can be very different with respect to those of a hard sphere suspension or an emulsion. We study the reduction in size of ionic microgels in response to increasing number of particles to show that particle shrinkage originates primarily from steric compression, and that the effect of ion-induced de-swelling of the polymer network is negligible. With increasing particle concentration, the single particle dynamics switch from those typical of a liquid to those of a super-cooled liquid and finally to those of a glass. However, the transitions occur at volume fractions much higher than those characterizing a hard sphere system. In the supercooled state, the distribution of displacements is non-Gaussian and the dependence of the structural relaxation time on volume fraction is describable by a Volger-Fulcher-Tammann function. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697762]

},
	url = {https://aip.scitation.org/doi/10.1063/1.3697762},
	author = {Romeo, Giovanni and Imperiali, Luna and Kim, Jin-Woong and Fernandez-Nieves, Alberto and Weitz, David A}
}
@article {155661,
	title = {Osmotic pressure can regulate matrix gene expression in Bacillus subtilis},
	journal = {Molecular Microbiology},
	volume = {86},
	number = {2},
	year = {2012},
	pages = {426-436},
	abstract = {
	Many bacteria organize themselves into structurally complex communities known as biofilms in which the cells are held together by an extracellular matrix. In general, the amount of extracellular matrix is related to the robustness of the biofilm. Yet, the specific signals that regulate the synthesis of matrix remain poorly understood. Here we show that the matrix itself can be a cue that regulates the expression of the genes involved in matrix synthesis in Bacillus subtilis. The presence of the exopolysaccharide component of the matrix causes an increase in osmotic pressure that leads to an inhibition of matrix gene expression. We further show that non-specific changes in osmotic pressure also inhibit matrix gene expression and do so by activating the histidine kinase KinD. KinD, in turn, directs the phosphorylation of the master regulatory protein Spo0A, which at high levels represses matrix gene expression. Sensing a physical cue such as osmotic pressure, in addition to chemical cues, could be a strategy to non-specifically co-ordinate the behaviour of cells in communities composed of many different species.

},
	url = {https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2958.2012.08201.x},
	author = {Rubinstein, Shmuel M and Kolodkin-Gal, Ilana and Mcloon, Anna and Chai, Liraz and Kolter, Roberto and Losick, Richard and Weitz, David A}
}
@article {155781,
	title = {Osmotic spreading of Bacillus subtilis biofilms driven by an extracellular matrix},
	journal = {Proceedings of the National Academy of Sciences of the United States of America},
	volume = {109},
	number = {4},
	year = {2012},
	pages = {1116-1121},
	abstract = {
	Bacterial biofilms are organized communities of cells living in association with surfaces. The hallmark of biofilm formation is the secretion of a polymeric matrix rich in sugars and proteins in the extracellular space. In Bacillus subtilis, secretion of the exopolysaccharide (EPS) component of the extracellular matrix is genetically coupled to the inhibition of flagella-mediated motility. The onset of this switch results in slow expansion of the biofilm on a substrate. Different strains have radically different capabilities in surface colonization: Flagella-null strains spread at the same rate as wild type, while both are dramatically faster than EPS mutants. Multiple functions have been attributed to the EPS, but none of these provides a physical mechanism for generating spreading. We propose that the secretion of EPS drives surface motility by generating osmotic pressure gradients in the extracellular space. A simple mathematical model based on the physics of polymer solutions shows quantitative agreement with experimental measurements of biofilm growth, thickening, and spreading. We discuss the implications of this osmotically driven type of surface motility for nutrient uptake that may elucidate the reduced fitness of the matrix-deficient mutant strains.

},
	url = {https://www.pnas.org/content/109/4/1116},
	author = {Seminara, Agnese and Angelini, Thomas E. and Wilking, James N. and Vlamakis, Hera and Ebrahim, Senan and Kolter, Roberto and Weitz, David A and Michael P. Brenner}
}
@article {154746,
	title = {Rapid growth of large, defect-free colloidal crystals},
	journal = {Soft Matter},
	volume = {9},
	number = {1},
	year = {2012},
	pages = {320-328},
	abstract = {
	We demonstrate controlled growth of face-centered cubic (FCC), monodisperse hard-sphere colloidal crystals by centrifugation at up to 3000g onto FCC (100) templates. Such rapid deposition rates often result in an amorphous sediment. Surprisingly, however, growth onto (100) templates results only in single crystals with few or no extended defects. By contrast, deposition onto flat, (111), or (110) templates causes rapid disordering to an amorphous sediment if the dimensionless flux (particle volume fraction x Peclet number) exceeds a critical value. This crystalline-to-amorphous crossover results from the degeneracy of possible stacking positions for these orientations. No such degeneracy exists for growth onto (100). After growth, extended defects can nucleate and grow only if the crystal exceeds a critical thickness that depends on the lattice misfit with the template spacing. The experimental observations of the density of misfit dislocations are accounted for by the Frank-van der Merwe theory, adapted for the depth-dependent variation of lattice spacing and elastic constants that results from the gravitational pressure.

},
	url = {https://pubs.rsc.org/en/content/articlelanding/2013/SM/C2SM26792F$\#$!divAbstract},
	author = {Jensen, K. E. and Pennachio, D. and D. Recht and Weitz, D. A. and F. Spaepen}
}
