Lin, T. ; Rubinstein, S. M. ; Korchev, A. ; Weitz, D. A. Pattern Formation of Charged Particles in an Electric Field. Langmuir 2014, 30, 12119-12123. Publisher's Version 2014_langmuir_charged_particles_in_e_field.pdf

PMID: 25227689

Rowat, A. C. ; Sinha, N. N. ; Sörensen, P. M. ; Campàs, O. ; Castells, P. ; Rosenberg, D. ; Brenner, M. P. ; Weitz, D. A. The kitchen as a physics classroom. Physics Education 2014, 49, 512. Publisher's VersionAbstract

Cooking is a tangible, familiar, and delicious tool for teaching physics, which is easy to implement in a university setting. Through our courses at Harvard and UCLA, each year we are engaging hundreds of undergraduate students, primarily non-science majors, in science concepts and the scientific research process. We find that weekly lectures by chefs and professors, paired with edible lab experiments, generate enthusiasm and provide strong motivation for students to learn physics. By the end of the course, students are able to conduct independent scientific research and present their results in a final science fair. Given the considerable broad appeal of food and cooking, the topic could be adapted to other post-secondary as well as secondary-level courses.

Polenz, I. ; Datta, S. S. ; Weitz, D. A. Controlling the Morphology of Polyurea Microcapsules Using Microfluidics. Langmuir 2014, ASAP. Publisher's Version 2014_langmuir_polyurea_microcapsules.pdf

doi: 10.1021/la503234z

Duncanson, W. J. ; Arriaga, L. R. ; Ung, L. W. ; Kopechek, J. ; Porter, T. ; Weitz, D. A. Microfluidic Fabrication of Perfluorohexane-Shelled Double Emulsions for Controlled Loading and Acoustic-Triggered Release of Hydrophilic Agents. Langmuir 2014, null. Publisher's Version 2014_langmuir_perfluorohexane_shelled_double_emulsions.pdf

PMID: 25340527

Jensen, K. E. ; Weitz, D. A. ; Spaepen, F. Local shear transformations in deformed and quiescent hard-sphere colloidal glasses. Physical Review E 2014, 90, 042305 -. Publisher's Version [PDF]
Zaburdaev, V. ; Biais, N. ; Schmiedeberg, M. ; Eriksson, J. ; Jonsson, A. - B. ; Sheetz, M.  P. ; Weitz, D.  A. Uncovering the Mechanism of Trapping and Cell Orientation during Neisseria gonorrhoeae Twitching Motility. 2014, 107, 1523 - 1531. Publisher's VersionAbstract

AbstractNeisseria gonorrheae bacteria are the causative agent of the second most common sexually transmitted infection in the world. The bacteria move on a surface by means of twitching motility. Their movement is mediated by multiple long and flexible filaments, called type IV pili, that extend from the cell body, attach to the surface, and retract, thus generating a pulling force. Moving cells also use pili to aggregate and form microcolonies. However, the mechanism by which the pili surrounding the cell body work together to propel bacteria remains unclear. Understanding this process will help describe the motility of N. gonorrheae bacteria, and thus the dissemination of the disease which they cause. In this article we track individual twitching cells and observe that their trajectories consist of alternating moving and pausing intervals, while the cell body is preferably oriented with its wide side toward the direction of motion. Based on these data, we propose a model for the collective pili operation of N. gonorrheae bacteria that explains the experimentally observed behavior. Individual pili function independently but can lead to coordinated motion or pausing via the force balance. The geometry of the cell defines its orientation during motion. We show that by changing pili substrate interactions, the motility pattern can be altered in a predictable way. Although the model proposed is tangibly simple, it still has sufficient robustness to incorporate further advanced pili features and various cell geometries to describe other bacteria that employ pili to move on surfaces.

Larsen, R. J. ; Kim, J. - W. ; Zukoski, C. F. ; Weitz, D. A. Fluctuations in flow produced by competition between apparent wall slip and dilatancy. Rheologica Acta 2014, 53, 333-347. Publisher's Version [PDF]
Jarosz, D.  F. ; Brown, J.  C. S. ; Walker, G.  A. ; Datta, M.  S. ; Ung, W.  L. ; Lancaster, A.  K. ; Rotem, A. ; Chang, A. ; Newby, G.  A. ; Weitz, D.  A. ; et al. Cross-Kingdom Chemical Communication Drives a Heritable, Mutually Beneficial Prion-Based Transformation of Metabolism. Cell 2014, 158, 1083 - 1093. Publisher's VersionAbstract

Summary In experimental science, organisms are usually studied in isolation, but in the wild, they compete and cooperate in complex communities. We report a system for cross-kingdom communication by which bacteria heritably transform yeast metabolism. An ancient biological circuit blocks yeast from using other carbon sources in the presence of glucose. [GAR+], a protein-based epigenetic element, allows yeast to circumvent this “glucose repression” and use multiple carbon sources in the presence of glucose. Some bacteria secrete a chemical factor that induces [GAR+]. [GAR+] is advantageous to bacteria because yeast cells make less ethanol and is advantageous to yeast because their growth and long-term viability is improved in complex carbon sources. This cross-kingdom communication is broadly conserved, providing a compelling argument for its adaptive value. By heritably transforming growth and survival strategies in response to the selective pressures of life in a biological community, [GAR+] presents a unique example of Lamarckian inheritance.

Wang, B. L. ; Ghaderi, A. ; Zhou, H. ; Agresti, J. ; Weitz, D. A. ; Fink, G. R. ; Stephanopoulos, G. Microfluidic high-throughput culturing of single cells for selection based on extracellular metabolite production or consumption. Nat Biotech 2014, 32, 473 - 478. Publisher's VersionAbstract

Phenotyping single cells based on the products they secrete or consume is a key bottleneck in many biotechnology applications, such as combinatorial metabolic engineering for the overproduction of secreted metabolites. Here we present a flexible high-throughput approach that uses microfluidics to compartmentalize individual cells for growth and analysis in monodisperse nanoliter aqueous droplets surrounded by an immiscible fluorinated oil phase. We use this system to identify xylose-overconsuming Saccharomyces cerevisiae cells from a population containing one such cell per 104 cells and to screen a genomic library to identify multiple copies of the xylose isomerase gene as a genomic change contributing to high xylose consumption, a trait important for lignocellulosic feedstock utilization. We also enriched L-lactate-producing Escherichia coli clones 5,800[times] from a population containing one L-lactate producer per 104D-lactate producers. Our approach has broad applications for single-cell analyses, such as in strain selection for the overproduction of fuels, chemicals and pharmaceuticals.

Pessi, J. ; Santos, H. A. ; Miroshnyk, I. ; JoukoYliruusi, ; Weitz, D. A. ; Mirza, S. Microfluidics-assisted engineering of polymeric microcapsules with high encapsulation efficiency for protein drug delivery. International Journal of Pharmaceutics 2014, 472, 82 - 87. Publisher's VersionAbstract

Abstract In this study, microfluidic technology was employed to develop protein formulations. The microcapsules were produced with a biphasic flow to create water–oil–water (W/O/W) double emulsion droplets with ultrathin shells. Optimized microcapsule formulations containing 1% (w/w) bovine serum albumin (BSA) in the inner phase were prepared with poly(vinyl alcohol), polycaprolactone and polyethylene glycol. All the particles were found to be intact and with a particle size of 23–47 μm. Furthermore, the particles were monodisperse, non-porous and stable up to 4 weeks. The encapsulation efficiency of \{BSA\} in the microcapsules was 84%. The microcapsules released 30% of their content within 168 h. This study demonstrates that microfluidics is a powerful technique for engineering formulations for therapeutic proteins.

Guo, M. ; Ehrlicher, A.  J. ; Jensen, M.  H. ; Renz, M. ; Moore, J.  R. ; Goldman, R.  D. ; Lippincott-Schwartz, J. ; Mackintosh, F.  C. ; Weitz, D.  A. Probing the Stochastic, Motor-Driven Properties of the Cytoplasm Using Force Spectrum Microscopy. Cell 2014, 158, 822 - 832. Publisher's Version 2014_cell_guo.pdf

doi: 10.1016/j.cell.2014.06.051

Datta, S. S. ; Abbaspourrad, A. ; Weitz, D. A. Expansion and rupture of charged microcapsules. Mater. Horiz. 2014, 1 92-95. Publisher's VersionAbstract

We study the deformations of pH-responsive spherical microcapsules - micrometer-scale liquid drops surrounded by thin{,} solid shells - under the influence of electrostatic forces. When exposed to a large concentration of NaOH{,} the microcapsules become highly charged{,} and expand isotropically. We find that the extent of this expansion can be understood by coupling electrostatics with shell theory; moreover{,} the expansion dynamics is well described by Darcy{'}s law for fluid flow through the microcapsule shell. Unexpectedly{,} however{,} below a threshold NaOH concentration{,} the microcapsules begin to disintegrate{,} and eventually rupture; they then expand non-uniformly{,} ultimately forming large{,} jellyfish-like structures. Our results highlight the fascinating range of behaviors exhibited by pH-responsive microcapsules{,} driven by the interplay between electrostatic and mechanical forces.

Carroll, N. J. ; Jensen, K. H. ; Parsa, S. ; Holbrook, M. N. ; Weitz, D. A. Measurement of Flow Velocity and Inference of Liquid Viscosity in a Microfluidic Channel by Fluorescence Photobleaching. Langmuir 2014, 30, 4868-4874. Publisher's Version [PDF]
Datta, S. S. ; Dupin, J. - B. ; Weitz, D. A. Fluid breakup during simultaneous two-phase flow through a three-dimensional porous medium. Physics of Fluids 2014, 26, n/a–n/a. Publisher's Version [PDF]
Chen, L. ; Li, Y. ; Fan, J. ; Bisoyi, H. K. ; Weitz, D. A. ; Li, Q. Photoresponsive Monodisperse Cholesteric Liquid Crystalline Microshells for Tunable Omnidirectional Lasing Enabled by a Visible Light-Driven Chiral Molecular Switch. Advanced Optical Materials 2014, n/a–n/a. Publisher's Version [PDF]
Arriaga, L. R. ; Datta, S. S. ; Kim, S. - H. ; Amstad, E. ; Kodger, T. E. ; Monroy, F. ; Weitz, D. A. Ultrathin Shell Double Emulsion Templated Giant Unilamellar Lipid Vesicles with Controlled Microdomain Formation. Small 2014, 10, 950–956. Publisher's VersionAbstract

A microfluidic approach is reported for the high-throughput, continuous production of giant unilamellar vesicles (GUVs) using water-in-oil-in-water double emulsion drops as templates. Importantly, these emulsion drops have ultrathin shells; this minimizes the amount of residual solvent that remains trapped within the GUV membrane, overcoming a major limitation of typical microfluidic approaches for GUV fabrication. This approach enables the formation of microdomains, characterized by different lipid compositions and structures within the GUV membranes. This work therefore demonstrates a straightforward and versatile approach to GUV fabrication with precise control over the GUV size, lipid composition and the formation of microdomains within the GUV membrane.

Cohen, S. I. A. ; Rajah, L. ; Yoon, C. H. ; Buell, A. K. ; White, D. A. ; Sperling, R. A. ; Vendruscolo, M. ; Terentjev, E. M. ; Dobson, C. M. ; Weitz, D. A. ; et al. Spatial Propagation of Protein Polymerization. Physical Review Letters 2014, 112, 098101. Publisher's Version [PDF]
Jensen*, M.  H. ; Morris*, E.  J. ; Gallant, C.  M. ; Morgan, K.  G. ; Weitz, D.  A. ; Moore, J.  R. Mechanism of Calponin Stabilization of Cross-Linked Actin Networks. Biophysical Journal 2014, 106, 793 - 800. Publisher's Version [PDF]
[*Equal contribution]
Datta, S. S. ; Ramakrishnan, T. S. ; Weitz, D. A. Mobilization of a trapped non-wetting fluid from a three-dimensional porous medium. Physics of Fluids 2014, 26, 022002. Publisher's Version [PDF]
Comunian, T. A. *; Abbaspourrad*, A. ; Favaro-Trindade, C. S. ; Weitz, D. A. Fabrication of solid lipid microcapsules containing ascorbic acid using a microfluidic technique. Food Chemistry 2014, 152, 271 - 275. Publisher's Version [PDF]
[*Equal contribution]