NECF Meeting Abstracts
76th New England Complex Fluids Meeting
Brandeis University | Friday, September 21, 2018
Registration deadline: Tuesday, September 18, 2018
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Abstracts for Invited Talks and Sound Bites:Invited Talks
Beltramo; Peter Beltramo
"Engineering soft matter interfaces: Particle stabilized foams to biomembranes"
Soft matter interfaces are ubiquitous across living systems, foods, personal care products, and the environment. They occur whenever surface-active molecules or particles appear at fluid interfaces, giving the interface distinct properties in response to flow, deformation, and concentration gradients. This talk will cover two such systems: arresting coalescence using particle stabilized foams and a new technique to measure the biophysical properties of biomembranes. Interfacial particle monolayers self-assemble due to variations in shape or topological heterogeneity that causes three phase contact line undulations that lead to lateral capillary interactions. The structures which result from this have exceptional mechanical properties and can be used to stabilize high interface systems and even arrest dissolution. In a first part of the talk, a strategy to halt dissolution of particle coated air bubbles in water based on interfacial rheology design will be presented. Whereas previously a dense monolayer was believed to be required for such an “armored bubble” to resist dissolution, in fact engineering a two-dimensional yield stress interface suffices to achieve such performance at sub-monolayer particle coverages. The link between interfacial rheology and macroscopic dissolution of ∼100μm bubbles coated with ∼1μm PS-PVP particles is presented and discussed. The results imply a generic design rationale that can be applied to successfully inhibit Ostwald ripening in a multitude of foam and emulsion applications. Nature’s most ubiquitous self-assembled interface is the phospholipid bilayer, which comprises all cell and organelle membranes. In the second part of the talk, I will discuss a new technique to study model bilayers in a platform where the membrane properties can be controlled and interrogated in a rational manner. Several examples highlighting the advantages and versatility of the approach will be given, including measurements of bilayer elasticity, membrane tension, phospholipid phase separation, and membrane protein/peptide pore formation.
Bourouiba; Lydia Bourouiba
"Unsteady fluid fragmentation"
Secondary droplets are ubiquitous and important for understanding, prediction, and control of a range of industrial, environmental, and health processes. Despite the complexity and diversity of modes of fluid fragmentation leading to the formation of secondary droplets, universality across geometry and fluid systems emerges. We will discuss results from our recent joint experimental and theoretical investigations elucidating the particular role of unsteadiness in shaping a neglected class of fluid fragmentation problems ubiquitous in a range of health and food safety applications.
Keywords: surface tension, fragmentation, hydrodynamic instabilities
Elrad; Oren Elrad
Invited; Andrew Ward
Research Director, Confer Health
Link; Darren Link
Nassar; Roger A. Nassar
Founder & CEO, RAN Biotechnologies
Nikova; Ani Nikova
Research Project Leader, Cabot Corp.
Busupalli; Joanna B Dahl
University of Massachusetts Boston
"Vibrational spectroscopy to probe membrane dynamics in lipid vesicles"
Sophisticated vibrational spectroscopic methods are being employed as tools to investigate the membrane dynamics in synthetic vesicles such as lipid vesicles in recent years. In our most recent experimental studies we made observations related to how the lipid vesicle membrane behaves when subjected to osmotic pressure gradient across it. We employed Raman and FTIR spectroscopy to investigate the same in addition to the optical microscopy to visually observe the same. With easy access to the advanced vibrational spectroscopy instruments at Umass Boston we are investigating this in depth now.
Keywords: lipid vesicles, membrane dynamics, vibrational spectroscopy
Chen; Tina Huang, David Weitz
"Microfluidic generation of multiple emulsion-templated lipid vesicles"
Giant lipid vesicles(GUV) are elegant models to study the biophysical properties of biomembranes as well as competent cargo carriers for biological applications. Traditional self-assembly-based methods of vesicle fabrication suffer from inhomogeneity in vesicles compositions and structures. However, the interests from both fundamental research and biomedical application sides urgently demand a well-controlled vesicle fabrication method to provide reliable and reproducible experimental results. Here we present a microfluidic emulsion-templated method to generate monodispersed GUVs. Compared to other emulsion-templated methods, our protocol allows a wider range of lipid choices, eliminates the influence of residual solvents, requires a shorter incubation time for solvent evaporation, and supports fabrication of GUVs with more complicated structures. Thus our method opens up more opportunities for GUVs as quantitative experimental tools to study lipid bilayer physics, also as important components in synthetic biology and biomedical vehicle constructions.
Keywords: Microfluidics; Giant Unilamellar Lipid Vesicles
Clark; Morgan Taylor, Matthew J. Panzer, Peggy Cebe
"Thermal characterization of a fully zwitterionic copolymer"
Lithium ion batteries have become ubiquitous in portable electronics due to their high electrochemical energy storage, and ability to be recharged many times. Current liquid electrolytes used in lithium ion batteries result in batteries that are both volatile and flammable. A unique alternative to conventional electrolytes is to use ionic liquids (which are very ion dense by definition) immobilized into a solid gel via a cross-linked polymer scaffold. However typical polymer species are semi-crystalline and insulating, leading to a decrease in ion mobility of a bound ionic liquid. Zwitterionic polymers are a promising solution, as they are mostly amorphous, and the zwitterionic side groups promote ion mobility. In this study, the fundamental thermal properties of a group of zwitterionic copolymers polymerized in an ionic liquid solution are investigated using conventional differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The polymers are comprised of sulfobetaine vinylimidazole (SBVI) and 2-methacryloyloxyethyl phosphorylcholine (MPC) in varying molar ratios with the ionic liquid EMI TFSI. TGA reveals the degradations of the copolymers and identifies the main degradations as being a result of the individual homopolymer degradations. Interestingly TGA also shows a degradation event due to the ionic liquid. DSC was used in order to identify the glass transition of these materials, showing a decrease in Tg with addition of SBVI, with no visible T¬¬g for the homopolymer SBVI. A melting endotherm due to EMI TFSI was identified which disappeared upon reheating the samples, except in the homopolymer SBVI. Fitting to the Fox equation provides an estimate for the T¬g for the homopolymer SBVI.
Keywords: Copolymer, zwitterion
Das; Jennifer A Mitchel2, Dapeng Bi1, Jin-Ah Park2
Northeastern University1, Harvard T.H. Chan School of Public Health2
"Different modes of fluidization in Human Bronchial Epithelial Cells -- the Unjamming Transition vs. the Epithelial-Mesenchymal Transition"
Epithelial tissues form the lining of every organ surface and cavity in our body. In these tissues the cells are largely confluent with strong apico-basal polarity. They remain non-migratory under homeostatic conditions which has been compared with a jammed system in recent literature. Using a culture of human lung epithelial tissue we compare a newly discovered mode of fluidization of jammed cells – the unjamming transition (UJT) – with the canonical epithelial-mesenchymal transition (EMT). We show that in the UJT, the cells exhibit large-scale dynamic collective motion when subjected to compressive stress from apical to basal side. To induce EMT, on the other hand, we treat the cells with TGF-beta1 which makes them lose the epithelial character, disrupt the cell-cell junctions and express a host of mesenchymal markers. We show that not only the UJT proceeds without expression of any of these markers, the cell-cell junctions remain intact and the cells preserve their confluent epithelial nature with only some elongation of the apical surfaces. In addition, measurements of cell shapes and cellular dynamics reveal the emergence of large and fast moving nematic swirls accompanying the UJT which are not observed during EMT. We use a dynamic vertex model (DVM) to capture the essential ingredients of these two dynamical behaviors and propose how the UJT could be an alternative route to fluidization of jammed epithelial tissues, independent of EMT. The DVM differs from previous vertex models in that edges can now become curved, tortuous and ruffled, thus reflecting the effects of forces acting on the edge locally, and their competition. These forces include cortical tension, intracellular-pressure differences, and polarized motility forces.
Keywords: sold-fluid transition;dynamic vertex model; collective motion
Duclos; Pooja Chandrakar, Zvonimir Dogic
Brandeis Univiersity, Physics department
"Generic bend instability in extensile active materials"
The cellular cytoskeleton is an active polymer network that is driven out of equilibrium by molecular motors. Although most out-of-equilibrium collective phenomena in living cells and their potential engineering applications take place in complex 3D environments, majority of the recent experimental and theoretical work exploring the self-organization of active biological materials has been restricted to two-dimensional systems. Here, we explore how active cytoskeleton networks behave and self-organize in 3D and present our recent efforts to describe the emergence of flows in biomimetic 3D active gels composed of purified microtubules and Kinesin-1 molecular motors. In particular, today, I will describe the generic bend instability that emerges in a flow-aligned 3D active gel and show how the wavelength and the growth rate of this activity driven instability are controlled by the interplay between material properties and confinement in 3D.
Keywords: active matter, liquid crystals
Harvard University, SEAS
"Interaction of spin-labeled HPMA-based nanoparticles with human blood plasma proteins – the introduction of protein-corona-free polymer nanomedicine"
We revised the current understanding of the protein corona that is created on the surface of nanoparticles in blood plasma after an intravenous injection. We have focused on nanoparticles that have
a proven therapeutic outcome. These nanoparticles are based on two types of biocompatible amphiphilic copolymers based on N-(2-hydroxypropyl)methacrylamide (HPMA): a block copolymer, poly(ε-caprolactone) (PCL)-b-poly(HPMA), and a statistical HPMA copolymer bearing cholesterol moieties, which have been tested both in vitro and in vivo. We studied the interaction of nanoparticles with blood plasma and selected blood plasma proteins by electron paramagnetic resonance (EPR), isothermal titration calorimetry,
dynamic light scattering, and cryo-transmission electron microscopy. The copolymers were labeled with TEMPO radicals at the end of hydrophobic PCL or along the hydrophilic HPMA chains to monitor changes in polymer chain dynamics caused by protein adsorption. By EPR and other methods, we were able to probe
specific interactions between nanoparticles and blood proteins, specifically low- and high-density lipoproteins, immunoglobulin G, human serum albumin (HSA), and human plasma. It was found that individual proteins and plasma have very low binding affinity to nanoparticles. We observed no hard corona around HPMA-based
nanoparticles; with the exception of HSA the proteins showed no detectable binding to the nanoparticles. Our study confirms that a classical “hard corona–soft corona” paradigm is not valid for all types of nanoparticles and each system has a unique protein corona that is determined by the nature of the NP material.
Keywords: protein corona, nanoparticles, blood plasma, nanomedicine, N-(2-hydroxypropyl)methacrylamide (HPMA)
Gharbi; Elizabeth George
University of Masschussetts, Boston
"Smectic flowers: Growing tunable liquid crystal lenses on curved surfaces "
Materials based on liquid crystals have had a profound impact on modern technology. Only recently have these materials been used in the fabrication of items such as smart windows, optical structures, and sensors. In particular, smectic liquid crystals have recently drawn much attention because of their defect structures, known as focal conic domains (FCDs). In recent works, we have developed an original method to create structures with high degrees of symmetry based on the spontaneous arrangement of smectic defects (FCDs). The system was designed to create flower-like patterns of FCDs at curved interfaces. These flowers can capture and focus light and act as microlenses by constructing composite 3D images from a different depth of field, similar to insects’ eyes. We seek to perfect the approach of making smectic “compound eyes” by growing smectic flowers on tailored surfaces in a single-step approach. The designed systems will permit sophisticated self-assembled patterns that can be used to guide assembly of functional nanomaterials and biomaterials.
Keywords: Smectic flowers, self-assembly, lenses, biomaterials
Giso; Timothy Atherton
"Packing Particles on a Sphere Under Gravity"
Packings on curved surfaces may resolve geometric frustration by introducing defects or elastic deformations. Here, I investigate the scenario where the surface is only partially covered. Soft, spherical particles are constrained to a sphere under the force of gravity and a Hertzian interaction and low-energy structures are found by simulated annealing. The defect structures obtained depend crucially on the coverage fraction and the elasticity of the particles.
Keywords: Packing, defect, structures
Govinna; Nelaka Govinna, Papatya Kaner, Davette Ceasar, Anita Dhungana, Cody Moers, Katherine Son, Ayse Asatekin, Peggy Cebe
"Fouling resistant electrospun fiber membranes for oil-water separation"
Non-woven super-hydrophobic fiber membranes have potential applications in oil-water separation. The membranes are blends comprising poly(vinylidene fluoride), PVDF, and random zwitterionic copolymers of poly(methyl methacrylate), PMMA and sulfobetaine methacrylate, SBMA, and sulfobetaine-2-vinylpyridine, SB2VP. PVDF imparts mechanical strength to the membrane, while the copolymers enhance membrane roughness and introduces fouling resistance. Blend composition was varied by controlling the PVDF content of the blends. Non-woven fiber membranes were obtained by electrospinning solutions of PVDF and the copolymers, at 20% w/v in a mixed solvent, N,N-dimethylacetamide/acetone, 7/3 v/v. The crystal phases and crystallinities of the blends were studied using wide angle X-ray diffraction and differential scanning calorimetry. The degradation profiles were determined using thermogravimetry and the degradation temperatures varied systematically with the composition of the blends. The hydrophobicity of the fibrous membranes was determined using contact angle testing. Addition of both copolymers showed significant decrease of fouling and at 10% of PMMA-r-SB2VP, fouling resistance rose to excellence with a five-fold decrease of foulants retained.
Keywords: PVDF, SBMA, SB2VP, Zwitterion, filtration membrane, electrospinning
Harvard T.H. Chan School of Public Health
"The dipole approximation for droplets in Hele-Shaw flows"
For the past decade, the interaction force between droplets flowing in a Hele-Shaw cell has been modelled as a dipole despite the fact that such interactions do not satisfy the no-flux boundary condition required at the droplet interfaces. Yet, correspondence between experiments and the dipole model is striking. To explain this, we approximate the exact solution of a two-droplet system. We show that at large spacing, the dipole approximation is the leading order solution and this approximation can be expanded to a lattice of an arbitrary number of droplets.
Keywords: Hele-Shaw flows, low-Reynolds-number flows, microfluidics
Hensley; W. Benjamin Rogers
"Measuring crystal nucleation and growth of DNA-grafted colloidal particles"
Grafting DNA onto microscopic colloidal particles can `program' them with information that tells them exactly how to self-assemble. Advances in our understanding of these specific interactions have enabled the assembly of a wide variety of crystal structures. However, the dynamic pathways by which these crystals self-assemble from the fluid phase are largely unknown. In this soundbite I will present recent progress on an experimental study of the nucleation and growth of colloidal crystals due to DNA hybridization. Specifically, I will describe a microfluidics-based approach in which we produce hundreds of monodisperse, isolated droplets filled with colloidal particles and then track the formation of crystals within each drop as a function of time. By examining the statistical behavior of the system as a whole, we measure the rate of nucleation for different interaction strengths and colloid concentrations. We also simultaneously measure the crystal growth kinetics by tracking the change in scattered-light intensity of the individual drops as particles are consumed by the growing crystals and through direct imaging of the crystals. We hope that these experimental findings help us better understand how characteristic properties of different lattices such as the density and coordination number affect nucleation and growth, thus improving our ability to design more complicated self-assembled structures in the future.
Keywords: Self-Assembly, Colloids, Crystals, Nucleation, Microfluidics
Huang; Yanran Li, Ping Mu
Harvard University, Xiamen University
"Micropatterning of TiO2 Nanotubes for High-throughput Screening"
TiO2 nanotubes (TNTs) have attracted extensive attention by virtue of the similarity of their highly ordered nanotubular structure to that of cortical bone. Recent studies have indicated that titanium nanotubes are superior to pure titanium in terms of bone regeneration, blood compatibility and corrosion resistance. However, the optimal properties of TNTs for certain applications remain mystery. For example, the nanotube dimension ranges from several nanometers to hundreds of nanometers. The existing literature reports biological responses to confined dimensions owing to the technique difficulties in evaluating hundreds of TNTs with different properties at the same time. In this study, TNT gradients with different properties were fabricated and applied for high-throughput study. Results showed that TNT gradients provide facile platforms for high-throughput screening of biological responses, including cell responses, protein adsorption, bacterial adhesion, and et al.
Keywords: TiO2 nanotubes, high-throughput screening; biological responses
Hunter; Mike Norton, Youssef Fahmy, Lanijah Flagg, Seth Fraden
Brandeis University Fraden lab
"Synchronizing nonlinear, microfluidics chemical oscillators"
Networks of nonlinear oscillators, such as neural networks, are of clear importance to comprehend. Observation of many such biological systems, and theoretical works have developed many theories as to how such networks form patterns, essential in biological systems. These have provided potential methods for rational design of fully synthetic, actuation systems with the robustness of biological ones. A model nonlinear oscillatory system, the Belousov–Zhabotinsky (BZ) reaction, confined to diffusively coupled, microfluidic reactors was developed at Brandeis to experimentally realize this goal. Work on producing robust synchronization within networks of these oscillators will be presented. This will include description of thermal control of the micronscale chemical reactors, and methods used to maximize diffusive fluxes between microfluidic reactors.
Keywords: Microfluidic reactors, Neural dynamics, Complex networks, Thermal control
"76th New England Complex Fluids Meeting"
Jhe; Seongsoo Kim, Dohyun Kim, Sangmin An, Jongwoo Kim
Seoul National University
"Curvature Dependence of Surface Tension and Test of Kelvin Equation at Molecular Scale"
Capillary condensation is the vapor-to-liquid phase transition occurring in confined geometries. Such heterogeneous nucleation has been well described by the Kelvin equation, but its applicability at nanoscale is still unresolved. We show it is valid down to 0.5 nm scale when the curvature-dependent surface tension is considered. Our results that unify the validity of the Kelvin equation and the curvature effect of surface tension may provide a better understanding of nucleation phenomena.
Keywords: nucleation, surface tension, kelvin equation
"Implantable Hydrogel Optical Fibers for In-vivo Sensing"
In vivo optical sensing provides a robust platform to understand the dynamic process underlying both health conditions and diseases. Efficient light transmission through biological tissues remains a challenge in optogenetics and photomedicine. Owing to high stiffness and less flexibility, commonly used solid-state optical waveguides are fragile and incompatible with soft tissues that restrict the clinical utility. Here, a step-index core/cladded hydrogel optical fiber was created. By integrating with a solid-state silica fiber coupler, the hydrogel optical fiber could achieve efficient light delivery in vivo. Functionalized with phenylboronic acid molecules, the hydrogel optical fiber could allow for continuous and quantitative glucose sensing in vivo.
Li; Amit Das, Dapeng Bi
"Biological tissue-inspired tunable photonic fluid"
We design an amorphous material with a full photonic band gap inspired by how cells pack in biological tissues. A physical parameter based by how cells adhere with one another and regulate their shapes can continuously tune the photonic band gap size as well as the bulk mechanical properties of the material. The photonic band gap persists well through a solid-fluid phase transition characterized by a vanishing shear modulus. This property gives rise to a photonic fluid which overcomes many of the limitations of previously proposed photonic materials due to its insensitivity to structural defects and robustness with respect to fluid flow, rearrangements and thermal fluctuations. This design should immediately catch the attention of experimentalists. Unlike previous works which use hard-sphere packing protocol or artificial interactions to design rigid and static photonic solids, the design proposed here uses a physical interaction that can be realized in experiment via self-assembly engineering. In particularly, emulsion droplets or nanoparticles grafted with polymers should be ideal for constructing such structures.
Keywords: photonic materials, tissue mechanics, bioinspired materials
Liu; Michael Hagan
"Inferring Capsid Assembly Kinetics from Experimental Observation"
Capsid assembly and packaging of the genome are essential steps in the formation of an infectious virus. Despite its importance, viral assembly is difficult to study experimentally due to the small sizes and fast kinetics of the assembly intermediates. Recently, there is an exciting experimental breakthrough which makes it possible to visualize the assembly of individual capsids around RNA molecules. However, the resolution is still not enough to distinguish the assembly intermediates with different structures. Here, we propose a computational approach to infer the information about assembly intermediates that are not directly accessible from experimental data. We develop a Hidden-Markov model for the capsid assembly experiment where the hidden states are assembly intermediates and the observations correspond to the total amount of capsid proteins bound to the RNA as measured in light scattering experiments. By calculating the posterior probability distribution, we demonstrate that the assembly kinetics can be inferred from experimental data with a simple model of self-assembly. We also explore the possibility of extending this strategy to perform machine learning of experimental parameters.
Keywords: self-assembly, Hidden Markov Model, bayesian inference
Liu; Mike Norton, Pengyu Hong, Seth Fraden
"Studying the Topological Defects in Confined Active 2D Nematics with Deep Learning"
The active nematics we are researching is made up of microtubules(MT) bundles bound together by kinesin clusters. Due to the constant input of ATP, the active nematics continuously flows in a turbulent-like manner. Under certain confinement conditions, we observe a special circulating state in which two, topologically-required +1/2 defects co-rotate around each other. This circulating state is regularly disturbed by the nucleations of new defects near the boundary followed by annihilations of old defects. We quantify the dynamics of the material by tracking the motions of these topological defects. An algorithm utilizing a 31-layer Deep Convolutional Neural Network (D-CNN) is proposed. The architecture is based on the state-of-the-art object detection algorithm—YOLO. The network is trained using 40,000 total instances of the +1/2 and -1/2 defects, and nucleation events. Currently, we’ve reached an overall F1-score of 0.65 on detection results, where the F1-scores for +1/2 defects, -1/2 defects and nucleation events are 0.80, 0.43 and 0.29, respectively. We are trying multiple methods to optimize the training process to reach better detection results. Looking forward, we also want to construct a Deep Recurrent Neural Network (D-RNN) used to predict the appearance of nucleation of defects by looking at previous few frames.
Keywords: active nematics, topological defects, deep learning, pattern recognition
Lowensohn; W. Benjamin Rogers
"Linker-mediated binding of DNA-coated colloids"
The possibility of prescribing interactions between nano- and microscopic components that direct them to assemble in a predictable fashion is a central goal of nanotechnology research. In my soundbite I describe the self-assembly of DNA-functionalized colloidal particles that interact via linker oligonucleotides dispersed in solution. We find a phase diagram that differs from phase diagrams typical of DNA-functionalized colloidal particles that interact by direct hybridization, and develop a new theory that predicts the observed experimental phase boundaries quantitatively without any fitting parameters. Taken together, these experiments and model lay the groundwork for future research in programmable self-assembly, ushering in the possibility of programming the hundreds of specific interactions needed to assemble arbitrary, mesoscopic structures, while also expanding our fundamental understanding of the unique phase behavior possible in colloids.
Keywords: Colloids, DNA, Linker, Self-Assembly
Miller; Doug Hall, Joanna Robaszewski, Michael Hagan, Greg Grason, Zvonimir Dogic
"Raft edge twist in colloidal membranes depends on size"
Colloidal membranes are composed of micron-long chiral rods in the presence of a depletant polymer. When short rods are added to the membrane, they assemble into finite-sized raft structures with twist at their edges that decays into the membrane background. Previous work has shown that this twist controls raft interactions for background membranes of varying chirality. Here we show that the twist magnitude depends non-monotonically on raft size, an effect which will presumably lead to size-dependent interactions.
Keywords: Self-Assembly, Colloids, Membranes, Chirality
Mohajerani; Michael F. Hagan
"Simulating Hepatitis B Virus antiviral agents"
The infectivity of a virus depends on the complete assembly of a protein shell (capsid) around the viral nucleic acid. Molecules which block or alter assembly pathways have the potential to be used as antiviral agents. Recent in vitro experiments have identified a class of small molecules (assembly effectors) that accelerate assembly of Hepatitis B virus (HBV) capsids. In vivo experiments have shown that this acceleration of assembly in vitro correlates to antiviral activity in cells. However, the mechanism by which these molecules alter assembly pathways is unclear. In this talk I will describe a computational model which allows extremely efficient simulation of assembly dynamics of large protein shells. I will then show how application of this model to HBV assembly can elucidate the mechanism of action of assembly effectors. In particular, I will describe how the assembly effectors result in malformed capsid shapes, as seen in experiments.
Keywords: self assembly - assembly effectors - HBV
Norton; Achini Opathalage, Michael Juniper, Blake Langeslay, S. Ali Aghvami, Zvonimir Dogic, Seth Fraden
"Transition to turbulence in a confined active nematic suspension"
Confining an active nematic suspension composed of microtubules and kinesin motor clusters to a disk below a critical diameter tames the otherwise turbulent flows observed in bulk into a single, system-sized vortex. Active nematic suspensions are inherently unstable complex fluids that spontaneously produce motile topological defects. Hydrodynamic theory predicts that in order to cohere the system into a single, circulating vortex, the material must be confined to length scales commensurate with the intrinsic defect spacing. However, we experimentally observe this coherence to occur at much larger scales. Theory and experiment will be compared and contrasted in this talk and possible mechanisms for the discrepancy discussed.
Keywords: active matter, complex fluids, nonlinear dynamics, liquid crystals
Sharma; John C MacDonald, Anjani Kumar, Rajendra K Shukla
"“Observance of Induced Glass Transition in Ge S Sb Glassy Alloys”"
This study presents observance of induced glass transition in Ge25S75-xSbx (where x=0%,5%). These chalcogenide glasses were made under vacuum of 10-5 Torr with 12 hours rocking and then quenching technique. It was seen that three multi endothermic peaks were appeared around 70 – 120 oC in x = 0% which then with addition of Sb got flattened and spread more widely with lower enthalpy.
Keywords: Calorimetry, glasses, alloys, vacuum.
Keywords: Glasses, Calorimetry, Alloys, Vacuum
Simonetti; Mike Norton, Seth Fraden
"Applying Perturbations in Light Intensity to Change Dynamical Attractors of a 3-Ring Network of Chemical Oscillators"
Chemical networks comprised of coupled Belousov-Zhabotinsky reactors exhibit rich dynamical pattern formation. The BZ reaction is a limit cycle oscillator with many dynamical attributes comparable to neurons; networks of BZ oscillators can therefore yield insights into neuronal networks and, more generally, to diffusively coupled oscillator networks. One network of particular interest is composed of a ring of three inhibitor-coupled wells which possesses two stable dynamical steady states: clockwise and counterclockwise traveling wave states. It is possible to force the system to change chirality (switch from one steady state to the other) by applying perturbations that change the wells’ intrinsic frequencies. This can be accomplished experimentally using a photo-sensitive variant of the BZ chemistry and applying spatially varying light to the network. Using the Kuramoto model for weakly coupled oscillators, the system’s steady states as a function of applied light gradient are explored. These results serve as the starting point for the application of optimal control theory to find the most efficient way of driving the system from one attractor to another.
Keywords: Oscillatory Networks, Nonlinear Dynamics, Optimal Control
Stolovicki; Elad Stolovicki, Roy Ziblat and David A. Weitz
"Throughput enhancement of parallel step emulsifier devices by shear-free and efficient nozzle clearance"
Step emulsification is an attractive method for production of monodisperse drops. Its main advantage is the ability to parallelize many step emulsifier nozzles to achieve high production rates. However, step emulsification is sensitive to any obstructions at the nozzle exit. At high production rates, drops can accumulate at nozzle exits, disturb the formation of subsequent drops and impair monodispersity. As a result, parallelized step emulsifier devices typically do not work at maximum productivity. Here a design is introduced that parallelizes hundreds of step emulsifier nozzles, and effectively removes drops from the nozzle exits. The drop clearance is achieved by an open collecting channel, and is aided by buoyancy. Importantly, this clearance method avoids the use of a continuous phase flow for drop clearance and hence no shear is applied on the forming drops. The method works well for a wide range of drops, sizing from 30 to 1000 μm at production rates of 0.03 and 10 L per hour and achieved by 400 and 120 parallelized nozzles respectively.
Keywords: Step emulsification
Su; K. Bieniek, M. A. Constantino, S. Decker, B. Turner, R. Bansil
"The effect of varying pH on the microrheology of porcine gastric mucin and the motility of Helicobacter pylori"
Helicobacter pylori, a pathogen known to inhabit the gastric mucus in the stomach of more than half of the global population, can lead to ulcers and gastric cancer. The naturally occurring pH gradient present in the protective gastric mucus lining varies from 2-4 on the lumen to 7 on the epithelial cell surface. The mucus also has a pH-dependency on its viscoelasticity; at low pH the mucus forms a gel-barrier, whereas at higher pH it is solution-like. In order to survive and colonize the host system, the non-acidophile bacteria must traverse the gradient and the mucus gel, away from the low pH, to reach the epithelial cells. Previous studies have shown that H. pylori were immobile in porcine gastric mucin (PGM) solutions below pH 4. How much of this effect was due to gelation of PGM at pH below 4 and how much due to the effects of pH on flagellar motors which pump protons was unclear. To investigate the extent to which pH influences the bacterial motility we used phase contrast microscopy to follow the translation and rotational motion of the bacteria in PGM and in Brucella broth at different pHs. In broth, H. pylori swimming speed increased as pH lowered from pH 7 to 4, followed by a dramatic drop in speed below pH 4, and bacteria became immobile below pH 3, indicating the collapse of proton motive force. In contrast, in PGM the bacteria swam slower overall at higher pH, and the speed peaked at pH5 and only slowed down slightly between pH 5 to 4, indicating the increase in viscosity in PGM dominating the motility. The bacteria were embedded in PGM gel and rotating without translational motion at pH 3.5.
Keywords: microrheology, particle tracking, bacterial motility
Xie; Timothy J. Atherton
" Order and percolation of hard ellipsoidal particles packing on sphere"
Packing problems can help understand the structure and properties of granular media. While there exists a lot of literature analyzing sphere packing, ellipsoidal particles packing draw a lot of attention. By adding an extra orientational degree of freedom, it can produce unique properties, for example denser packing and orientational order. Previous simulation work focused on ellipsoids packing in 2D or 3D Euclidean space. In this work we look at ellipsoids packing on curved surface-sphere as a start-by simulation. We calculated nematic order of the system to check the existence of phase transition due to the increase of aspect ratio. The deviation from sphere generates more defects, i.e. particles with non-six neighbors, and these defects would form one whole network as aspect ratio increases. Hence we tested the percolation transition of the system.
Keywords: ellipsoids, order, percolation
Yamani; Gareth McKinley; Irmgard Bischofberger
" Schlieren Imaging of Mixing and Turbulence in Dilute Polymer Solutions"
Dilute synthetic polymer solutions have the potential to reduce turbulent drag in pipelines and around marine structures. Biopolymeric extracts such as plant mucilage have recently been proposed as alternative material sources for drag reducing polymers due to their cost-effectiveness and lower environmental hazards. The very low concentrations of polymer employed in drag reduction studies makes direct imaging of the new flow structures that develop an outstanding challenge. Here, we employ Schlieren imaging to enable direct flow visualization of the mixing dynamics and recirculating regions that develop in complex flows of dilute aqueous polymer solutions. With this technique we are able to detect density differences of order 0.001% for dilute aqueous solutions of polyethylene oxide (PEO) as well as for polysaccharide exudates extracted from the husks of flax seed. This promising visualization capability is used to help understand the vortical structures associated with turbulent drag reduction of polymer solutions. In our experiments, the turbulent mixing of high speed dilute polymer jets is visualized for different values of Reynolds number, polymer concentration, and molecular weight. We compare these visualization results with previous theoretical studies of mixing layer development and experimental reports of the turbulent drag reducing properties of different polymer solutions.
Keywords: Schlieren imaging, Dilute polymer solutions, mixing, turbulence, biopolymers
Yuan; Yuan Yuan, Brouchon Julie, Jing Xia, John Heyman, David Weitz
"Droplet-based assay for activated immune cell detection and sorting"
When talking about self-protection, the first idea comes to our mind might be our immune system. It is a defense system of our body to fight against disease and it comprises many immune cells and responses. When pathogen comes, some cells work well to fight against pathogens while others may not. Insufficient functioning cells may lead to inadequate immune response. And many severe diseases like cancer and viral infections are thought to be caused by it. We really need better ways to find individual immune cells that function well so that we can take full advantage of the immune system. Based on the droplet technique, we developed a quick assay by co-encapsulating individual immune cells and target cells into one drop. And Immune cells are pre-treated with cytokine catch reagent so that the secreted cytokines could be captured and enriched on the surface of immune cells. This in-drop assay greatly reduces the cross-contamination in bulk. As compatible with flow cytometry, thousands of cells with signals could be sorted and recovered for further analysis in our assay.
Keywords: Droplet microfluidics, Immune therapy, single-cell quick assay
Zhang; • X. Zhang. J. Heyman, L Qu, J Werner, D. Weitz, E. Appel.
Harvard University; Stanford University
"Stable Vaccines Encapsulation& Single Injection Technology"
Our project is to generate a transformational strategy for vaccination/drugs in a single injection. According to the World Health Organization, 18.7 million children were incompletely vaccinated for diphtheria-tetanus-pertussis vaccine (DTP) in 2014, where 40% of those children had received the first dose of the vaccine, but were unable to complete the 3-dose series.1.5 million children still die each year from vaccine-preventable diseases. Improving vaccination technology can be truly transformational in the prevention of infectious disease. The majority of vaccines require multiple doses to elicit full immunization, which increases both the cost and complexity of reaching the entire globe. Moreover, vaccines/drugs are generally formulations of biologics, which are highly susceptible to denaturation and subsequent loss of activity, thus complicating their global distribution and storage. A stable single-administration vaccine would reduce the number of required interventions, thereby preventing the unnecessary spreading of infectious disease, especially amongst rural population, who must often travel far to reach their closest healthcare clinic. The enhanced convenience and reduced costs associated with this approach will certainly be welcomed in the developed world. We are developing a single administration vaccination platform using advanced micro-fluidic double emulsion technology along with a novel hydrogel excipient to create tunable, pulsatile release of vaccines.
Keywords: Single Injection; Vaccines; Encapsulation
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