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An atom is cooled by a standing-wave light field between two high-quality mirrors. Cavity cooling avoids the usual light scatter into the surroundings. Instead, the light leaking out of the mirrors is blue-shifted to a higher frequency (image credit: Pepijn Pinkse Max Planck Institute of Quantum Optics)
Artist's impression of an atom cooling device
NECF Meeting Abstracts

79th New England Complex Fluids Meeting
UMass Boston | Friday, June 7, 2019
Registration deadline: Wednesday, June 5, 2019

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Abstracts for Invited Talks and Sound Bites:

Invited Talks

1. Brenner, Michael

Harvard University
"The quest to observe the turbulent cascade in real time"

2. Brown, Keith A.

Boston University
"Exploring Smart Fluids from Particles to Properties"

3. Celli, Jon

UMass Boston
"Modeling biophysical determinants of pancreatic tumor growth, invasion and therapeutic response in 3D cell cultures"
Cancer progression is regulated not only by the molecular biology and genetics of the disease but also by the physical properties of the tumor and surrounding tissues. For pancreatic tumors in particular, the development of mechanically rigid fibrous stroma is a defining feature which has been shown to play complex roles both promoting and constraining disease progression. It remains poorly understood however, how this altered mechanical landscape, which is dynamically remodeled during tumor progression and invasion, regulates susceptibilities to cancer therapeutics. Several projects in our group examine how biophysical interactions with the tumor microenvironment impact upon phenotypic changes which determine therapeutic response. This work is enabled by the use of in vitro 3D tumor models with tunable and rheologically-characterized extracellular matrix (ECM). Combined with imaging-based analyses of phenotype and in situ microrheology measurements of dynamic matrix remodeling, this platform provides a means to co-register rigidity-dependent cell shape, mechanics, and motility with response to therapeutic intervention. We use this system to specifically contrast classical chemotherapy agents with photodynamic therapy (PDT), in which light activation of a photosensitizing agent leads to cell death by local generation of reactive oxygen species. Interestingly, our recent results show that while modulation of ECM composition to promote increased invasive motility imparts resistance to chemotherapy, the same chemoresistant populations exhibit increased sensitivity to PDT. These and other emergent findings will be discussed in the broader context of connecting cancer biophysics with cancer therapeutics.

4. Fraden, Seth

Brandeis University
"Programmable self-assembly of capsids based on the principles of virus structure"

5. Invited, Speaker; Alexey Veraksa

UMass Boston
"Cellular movements during organism development"

6. Ross, Jennifer

UMass Amherst
"Self-Organization and Self-Propulsion of Biological Building Blocks"
The cell is a complex autonomous machine taking in information, performing computations, and responding to the environment. Much of the internal structure and architecture is transient and created through active processes. Recent advances in active matter physics with biological elements are opening new insights into the physics behind how cellular organizations are generated, maintained, and destroyed. I will present two short stories with enzymes at the heart of the activity driving organization and transport. The first will discuss self-organization of microtubules in the presence of "weakly interacting" crosslinkers. The second will discuss possible mechanisms for the cell to mix itself using self-propelled single molecule enzymes. These works illustrate the importance of the fundamental physics to build structures and propel matter inside living cells while informing on new physics we can learn from biological elements and materials.

Sound Bites

1. Drybread, Erik; Prof. Mohamed Amine Gharbi

University of Massachusetts, Boston
"The Diffusion of Colloids in Simple and Complex Fluids"
In this project, we seek to understand the difference in the diffusion of colloidal particles in simple fluids versus complex fluids. The diffusion of colloids is caused by Brownian motion, which is the erratic and unpredictable movement affected by the viscosity of the liquid. However, the diffusion depends on the properties of the solvent where the colloids are immersed. We have developed a technique of image processing based on the tracking of particles using the package Trackpy in Python to understand how spherical particles diffuse in isotropic fluids: water and glycerol. Then, we have compared the results to the diffusion of particles in an anisotropic material, a nematic liquid crystal. We concluded the Brownian motion of colloidal particles is very sensitive to the viscosity of the fluid that can be controlled by changing the temperature of the system, and the order of molecules within the studied phase. For the next step of the project, we wish to investigate the effect of particle size and shape on the Brownian motion of particles.

2. George, Elizabeth; Ryan Preusse, Dr. Mohamed Amine Gharbi

University of Massachusetts Boston
"Engineered Topological Defects in Smectic Liquid Crystal at Curved Interfaces"
In this project we explore the effect of curvature on the organization of defects in a smectic liquid crystal. The experimental system is comprised of 4 n-Octyl-4-Cyano-Biphenyl (8CB) liquid crystal on an undulated interface with hybrid anchoring. We create surfaces with controlled morphologies and curvature to investigate the role of geometry in controlling defects in smectic liquid crystal. The goal of our work is to explore the way in which the curvature of the undulated surface affects the order and geometric confinement of the liquid crystal. Our preliminary results indicate that curved interfaces play an import role in controlling the formation of defects in both the nematic and the smectic mesophases. The structure formed by these defects can be used to direct the assembly of functional nanomaterials and biomaterials to create a new generation of smart materials. A fuller understanding of the mechanisms that govern the relationship between defects in the nematic and defects in the smectic are underway.  
Keywords: liquid crystal, focal conic domains, smectic, nematic

3. Hristov, Delyan R.; Cristina Rodriguez-Quijada, Kimberly Hamad-Schifferli

University of Massachusetts Boston
"Optimising the synthesis and properties of immunoprobes used in paper based assays for detection of infectious diseases"
The ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to end users) outlined by the WHO in 2012 aimed to provide a framework for the development of point of care (POC) devices to be used for same day diagnostics in a wide variety of diseases. Paper based assays, such as lateral flow assays (LFAs) and microfluidic paper-based analytical devices (μPADs) have garnered a lot of attention in the diagnostics community in the past decade as they may fulfill the WHO requirements. Though different versions exist, the most basic form of paper based assays do not require electricity or external equipment, cost ~$5 per unit, can detect target molecules in the or below nM concentration range and give users a straight forward yes/no answer within minutes. However, such systems have seen limited commercial release due to challenges related to development and optimization generally observed as lack of reliability, specificity and/or sensitivity. Among the biggest challenges of such devices is the design and development of nanoparticle probes used to capture the target and as labeling agent. Less than optimal design can result in undesirable non-specific interactions leading to probe aggregation or loss of specificity and/or function. Research focuses on identifying and resolving key aspects of the nanoparticle probe surface which could reduce non-specific interactions and improve test reliability.
Keywords: LFA, Paper-based assay, immunoprobe, biosensors, rapid diagnostics

4. Preusse, Ryan; Mohamed Amine Gharbi, Elizabeth George

University of Massachusetts, Boston
"Role of Curvature in Controlling the Arrangement of Defects in Smectic Liquid Crystals"
Defects are highly sought after in liquid crystals and have various technological applications. They can be used to act as a microlens as well as direct the assembly of nanomaterials and biomaterials, alongside various other energy applications. A uniform smectic liquid crystal exhibits no defects under matching boundary conditions, and uniform defects under hybrid boundary conditions. The goal of this work is to control defects through geometric confinement on different types of undulated surfaces under hybrid boundary conditions. It was found that defect size has a direct correlation to the depth of the sample. It was also found that line defects remain after the phase transition from the nematic. With two different types of defects forming in the sample, a more complex method of directed assembly can be implemented.
Keywords: Defects, Smectic, Curvature

5. Stolovicki, Elad; Elad Stolovicki, Lloyd Ung, Roy Ziblat and David A. Weitz

Harvard John A. Paulson School of Engineering and Applied Sciences
"Drop chemostats: White biotechnology on a chip"
White biotechnology, the production of chemicals using cells or enzymes, is increasingly employed as it results in higher, overall greener chemical processes. Bio-production is also ideally suited in cases where the selectivity of enzymes for a specific molecule enantiomer (chirality) is critical. By using an emulsion of small drops of growth medium in oil as a micro-reactor, we can optimize the production yield of a desired bio-product, preforming toxicity tests or response-resistance assays. Another key feature of our system is that each, individual droplet emulates a larger-scale bioreactor that can be grown using batch, fed-batch or continuous culture methods. Thus, drop micro-reactors have the advantages of reducing R&D production time and cost by having thousands of parallel experiments, greatly reduced quantities of reagents, and compact space requirements.
Keywords: White biotechnology, bio-production, drop micro-reactors, microfluidics

6. Wadhwa, Navish; Rob Phillips, Howard C. Berg

Harvard University/California Institute of Technology
"Tunable self-assembly of the bacterial flagellar motor"
Multisubunit protein complexes are ubiquitous in biology and perform many of life’s essential functions. Scientific literature often treats such assemblies as static: their function is assumed to be independent of their manner of assembly, and they are assumed to remain intact until damaged or degraded. Recent observations of the bacterial flagellar motor bring these notions into question. The torque-generating stator units of the motor assemble and disassemble in response to changes in viscous load. We used electrorotation to drive tethered cells forward, which decreases motor load, and measured the resulting stator dynamics. No disassembly occurred while the torque remained high, but all of the stator units were released when the motor was spun near the zero-torque speed. When the electrorotation was turned off, so that the load was again high, stator units were recruited, increasing motor speed in a stepwise fashion. A model in which speed affects the binding rate and torque affects the free energy of bound stator units captures the observed torque-dependent stator assembly dynamics, providing a quantitative framework for the environmentally regulated self-assembly of a major macromolecular machine.
Keywords: Self-assembly, bacterial flagellar motor, multisubunit complex, molecular motor

7. Zhang, Kaixuan; Zhen Li, Martin Maxey, Shuo Chen, George Karniadakis

Brown university/Tongji University
"Self-cleaning of textured hydrophobic surfaces by coalescence-induced wetting transition"
The superhydrophobic leaves of a lotus plant and other natural surfaces with self-cleaning function have been studied intensively for the development of artificial biomimetic surfaces. The surface roughness generated by hierarchical structures is a crucial property required for superhydrophobicity and self-cleaning. Here, we demonstrate a novel self-cleaning mechanism of textured surfaces attributed to a spontaneous coalescence-induced wetting transition. We focus on the wetting transition as it represents a new mechanism, which can explain why droplets on rough surfaces are able to change from the highly adhesive Wenzel state to the low adhesion Cassie−Baxter state and achieve selfcleaning. In particular, we perform many-body dissipative particle dynamics simulations of liquid droplets (with a diameter of 89 μm) sitting on mechanically textured substrates. We quantitatively investigate the wetting behavior of an isolated droplet as well as coalescence of droplets for both Cassie−Baxter and Wenzel states. Our simulation results reveal that droplets in the Cassie−Baxter state have much lower contact angle hysteresis and smaller hydrodynamic resistance than droplets in the Wenzel state. When small neighboring droplets coalesce into bigger ones on textured hydrophobic substrates, we observe a spontaneous wetting transition from the Wenzel state to the Cassie−Baxter state, which is powered by the surface energy released upon coalescence of the droplets. For superhydrophobic surfaces, the released surface energy may be sufficient to cause a jumping motion of droplets off the surface, in which case adding one more droplet to the coalescence may increase the jumping velocity by one order of magnitude. When multiple droplets are involved, we found that the spatial distribution of liquid components in the coalesced droplet can be controlled by properly designing the overall arrangement of droplets and the distance between them. These findings offer new insights for designing effective biomimetic self-cleaning surfaces by enhancing spontaneous Wenzel-to-Cassie wetting transitions, and additionally, for developing new noncontact methods to manipulate liquids inside the small droplets via multiple-droplet coalescence.
Keywords: Self cleaning, Droplet coalescence, Wetting transition

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