Andrew S. Utada

Bio: Andrew S. Utada is an academic researcher from University of Tsukuba. The author has contributed to research in topics: Vibrio cholerae & Biofilm. The author has an hindex of 23, co-authored 40 publications receiving 7211 citations. Previous affiliations of Andrew S. Utada include University of California, Los Angeles & Bio-Rad Laboratories.

Monodisperse Double Emulsions Generated from a Microcapillary Device

Abstract: Double emulsions are highly structured fluids consisting of emulsion drops that contain smaller droplets inside. Although double emulsions are potentially of commercial value, traditional fabrication by means of two emulsification steps leads to very ill-controlled structuring. Using a microcapillary device, we fabricated double emulsions that contained a single internal droplet in a core-shell geometry. We show that the droplet size can be quantitatively predicted from the flow profiles of the fluids. The double emulsions were used to generate encapsulation structures by manipulating the properties of the fluid that makes up the shell. The high degree of control afforded by this method and the completely separate fluid streams make this a flexible and promising technique.

Dripping to jetting transitions in coflowing liquid streams.

Abstract: A liquid forced through an orifice into an immiscible fluid ultimately breaks into drops due to surface tension. Drop formation can occur right at the orifice in a dripping process. Alternatively, the inner fluid can form a jet, which breaks into drops further downstream. The transition from dripping to jetting is not understood for coflowing fluid streams, unlike the case of drop formation in air. We show that in a coflowing stream this transition can be characterized by a state diagram that depends on the capillary number of the outer fluid and the Weber number of the inner fluid.

Controllable monodisperse multiple emulsions.

Abstract: Multiple emulsions, in which dispersed drops contain smaller drops inside, are useful in a large number of commercial applications, including chemical synthesis and drug delivery. For many of these applications, it is critical to have control over the size and structure of multiple emulsion systems. The structure of multiple emulsion systems is in this case defined as the number of bubbles contained in each size "level" of larger bubbles.

Fabrication of Monodisperse Gel Shells and Functional Microgels in Microfluidic Devices

Abstract: Microgels are colloidal gel particles that consist of chemically cross-linked three-dimensional polymer networks; these networks are able to dramatically shrink or swell by expelling or absorbing large amounts of water in response to external stimuli. 2] The large change in size can be achieved, for example, by modifying the pH, temperature, or ionic strength of the medium, or by applying electric or magnetic fields; it is this response that makes microgels desirable for applications in drug delivery, biosensing, diagnostics, bioseparations, and optical devices. 10] To further expand their range of applicability, there have been efforts to generate microgels that have been complexed with preformed functionalized materials that impart additional desirable properties to the microgel. These preformed materials range from molecules to microparticles and are typically complexed with the gel matrix through specific interactions. The resulting complexed microgels usually show a drastic decrease in their physical response to external stimuli compared to that of the original cross-linked polymer networks; this is an undesirable side effect since the microgel performance for a given application is based on its sensitivity to external stimuli. In addition to functionality, the size distribution of a population of microgels is important; it is critical to provide a homogeneous distribution of microgels applying formulations and in controlling the release kinetics of encapsulates or adsorbents. From the standpoint of performance and applicability, there is a need for methods to generate monodisperse microgels that maintain high sensitivity to external stimuli irrespective of the materials that are incorporated to add complementary functions. Here, we describe a flexible and straightforward method for generating monodisperse suspensions of new microgelbased materials using a capillary microfluidic technique. This technique enabled us to generate and precisely control the size of the microgel-based particles without sacrificing the physical response of the resulting microgels. We generated two novel microgel structures: a spherical microgel shell and spherical microgel particles that retain their full sensitivity to external stimuli after being physically complexed with preformed colloidal particles. The overall size and thickness of the microgel shells can be tuned with temperature. We generated the spherical microgel particles in a single step, which allows us to freely incorporate functional materials into the polymer network. We used quantum dots, magnetic nanoparticles, and polymer microparticles as examples of the materials that can be added to provide specific chemical, physical, or mechanical properties to the original microgels. To generate the microgel particles, we constructed a capillary-based microfluidic device that generated pre-microgel drops, which were then polymerized in situ with a redox reaction. The capillary microfluidic device was made of three separate capillary tubes. The two internal cylindrical tubes served as injection and collection tubes and were coaxially aligned, as shown in the inset in Figure 1A. These tapered tubes were made by axially heating and pulling cylindrical capillaries. In the region near both tips, the outer fluid focuses both the middle and inner fluids through the collection tube to form a fluid thread that then breaks into drops as a result of hydrodynamic instabilities, as shown in Figure 1A. We typically used silicon oil with viscosity hOF= 125 mPas as the outer, or continuous-phase liquid. The middle fluid was an aqueous monomer solution that contained N-isopropylacrylamide (NIPAm, 15.5% w/v), a crosslinker (N,N’-methylenebisacrylamide, BIS, 1.5% w/v), a reaction accelerator (N,N,N’,N’-tetramethylethylenediamine, 2 vol%), and two co-monomers [2-(methacryloyloxy) ethyl trimethyl ammonium chloride (METAC, 2 vol%) and allylamine (1 vol%)]. METAC was added to increase the coil-toglobule transition temperature of poly(NIPAm), thereby facilitating homogeneous polymerization at room temperature. The allylamine adds amine groups to the network, which can subsequently be labeled with dyes after the formation of the microgel particles. The chemical formula [*] Dr. J. W. Kim, A. S. Utada, Dr. A. Fern ndez-Nieves, Prof. D. A. Weitz DEAS and Department of Physics Harvard University Cambridge, MA 02138 (USA) Fax: (+1)617-495-2875 E-mail: weitz@deas.harvard.edu

Sub-Diffraction-Limited Optical Imaging with a Silver Superlens

Abstract: Recent theory has predicted a superlens that is capable of producing sub–diffraction-limited images. This superlens would allow the recovery of evanescent waves in an image via the excitation of surface plasmons. Using silver as a natural optical superlens, we demonstrated sub–diffraction-limited imaging with 60-nanometer half-pitch resolution, or one-sixth of the illumination wavelength. By proper design of the working wavelength and the thickness of silver that allows access to a broad spectrum of subwavelength features, we also showed that arbitrary nanostructures can be imaged with good fidelity. The optical superlens promises exciting avenues to nanoscale optical imaging and ultrasmall optoelectronic devices.

Highly Parallel Genome-wide Expression Profiling of Individual Cells Using Nanoliter Droplets

Abstract: Cells, the basic units of biological structure and function, vary broadly in type and state. Single-cell genomics can characterize cell identity and function, but limitations of ease and scale have prevented its broad application. Here we describe Drop-seq, a strategy for quickly profiling thousands of individual cells by separating them into nanoliter-sized aqueous droplets, associating a different barcode with each cell's RNAs, and sequencing them all together. Drop-seq analyzes mRNA transcripts from thousands of individual cells simultaneously while remembering transcripts' cell of origin. We analyzed transcriptomes from 44,808 mouse retinal cells and identified 39 transcriptionally distinct cell populations, creating a molecular atlas of gene expression for known retinal cell classes and novel candidate cell subtypes. Drop-seq will accelerate biological discovery by enabling routine transcriptional profiling at single-cell resolution. VIDEO ABSTRACT.

Of Theory and Practice

Abstract: Much has been written about theory and practice in the law, and the tension between practitioners and theorists. Judges do not cite theoretical articles often; they rarely "apply" theories to particular cases. These arguments are not revisited. Instead the Essay explores the working and interaction of theory and practice, practitioners and theorists. The Essay starts with a story about solving a legal issue using our intellectual tools - theory, practice, and their progenies: experience and "gut." Next the Essay elaborates on the nature of theory, practice, experience and "gut." The third part of the Essay discusses theories that are helpful to practitioners and those that are less helpful. The Essay concludes that practitioners theorize, and theorists practice. They use these intellectual tools differently because the goals and orientations of theorists and practitioners, and the constraints under which they act, differ. Theory, practice, experience and "gut" help us think, remember, decide and create. They complement each other like the two sides of the same coin: distinct but inseparable.