NECF Workshop

Abstracts for Invited Talks and Soundbites

81st New England Complex Fluids Meeting
Harvard University | Friday, December 6, 2019
Registration deadline: Wednesday, December 4, 2019

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Invited Talks

1. Angelini, Thomas

University of Florida

Investigating cell behavior in 3D with 3D printed experiments"
The remarkable differences between cells grown on plates and cells in vivo or in 3D culture are well-known. At the physical level, cell shape, structure, motion, and mechanical behavior in 3D are totally different from those in the dish and are far less explored. At the molecular level, cells grown in monolayers exhibit gene expression profiles that do not correlate or are anticorrelated with those of cells grown in 3D culture or xenograft animal models. However, our understanding of cell biology has been heavily shaped by the culture plate, whether viewed through the lens of gene expression profiles, signaling pathways, morphological characterization, or mechanical behaviors. Closing this major gap between 2D in vitro culture and in vivo biology requires a tunable and flexible method for creating 3D cell assemblies and performing experiments on cells in 3D environments. In this talk I will describe how we use a bioprinter in combination with a 3D culture medium made from jammed microgels to perform a wide range of 3D experiments. I will demonstrate this ability of this experimental platform to print structures made from multiple cell types or extracellular matrix with predictable feature sizes down to the scale of a few cell bodies. I will also present data from numerous types of experiments performed in 3D, designed to explore collective cell behavior and cell-cell interactions. For example, recent results will be presented from a 3D immunotherapy model in which we investigate how antigen-specific T cells attack 3D printed brain tumoroids. Our results demonstrate that, in parallel to pursuing the long-standing goals shared by those within the 3D bioprinting field, the current state of bioprinting technology can be leveraged to perform a wide diversity of experiments.

2. Chang, Connie

Montana State University

Examining heterogeneous populations of microbes at the single cell level using stabilized emulsions"
Conventional methods in microbiology can be limited by long assay execution and analysis times, large reagent volumes, and high single-use supply costs. These limitations can be overcome using drop-based microfluidics in which picoliter-sized, water-in-oil emulsions serve as independent microreactors, allowing for the compartmentalization of microbes and high-throughput assaying at the single cell level. Here, drop-based microfluidics is used to interrogate the physiological heterogeneity of P. aeruginosa cells in a microbial population using a technique we name DropSOAC (Drop Stabilization On A Chip). The DropSOAC method stabilizes the position and volume of monodisperse water-in-oil drops with diameters <20 µm within a monolayer array on a microfluidic chip for 24 h. The stability of drops is maintained by soaking the device in a reservoir containing both water and oil in thermodynamic equilibrium. This ensures that phase equilibrium of the drop emulsion fluids within the porous PDMS material structure is maintained during drop incubation and imaging. The results presented here show the potential of drop-based microfluidics for high-throughput assaying of heterogeneous populations of microbes at the single cell level.

3. Fernandez-Nieves, Alberto

Georgia Tech and University of Barcelona

Columns and waves of fire ants"
In this talk, I will present recent experiments in my group with dense fire ant collectives. I will first discuss how confining ants to 2D vertical columns results in an initial expansion, followed by the spontaneous generation of ant waves. These waves propagate at a speed that depends on amplitude and are not just density waves but rather activity waves. I will then focus on 3D cylindrical columns and revisit the behavior of granular matter and how it changes as a result of ant activity.

4. Invited, Speaker; Allison M. Sweeney

University of Pennsylvania

The evolution of equilibrium: Thermodynamic pattern formation outside of living cells"
Implicitly and in general, the project of biomaterials and biomimetics considers structures formed in the topologically extracellular space of organisms: beetle carapace, feathers, butterfly wings, and wood are all extracellular materials. Our work seeks to make this implicit assumption explicit, and understand the material pattern formation that imbues function in these materials via equilibrium thermodynamic theories. This talk will look at two pattern-forming biomaterial systems, plant pollen and squid lenses, in which the relevant pattern and function emerges from equilibration of biological components in the extracellular space. Squid lenses have evolved to explore the patchy particle phase diagram, while pollen patterns form from a phase transition modulated by membrane elasticity. Quantifying the evolution of these systems can provide further insight into molecular function, which can in turn inform efforts to realize these principles in engineered systems.

5. Invited, Speaker; Michael E. Cates

University of Cambridge

Shear thickening in dense suspensions"
Recent years have seen a new understanding of how dense suspensions, such as corn-starch in water, undergo a sudden transition from a flowable to a jammed state upon increasing stress. Interparticle stresses overcome repulsive barriers to create frictional contacts between particles; the resulting extra constraints on particle motion cause partial or complete rigidification. So far we have a simple predictive model that captures this picture for steady flows, which I will outline. However, new physics emerges for flows with a transverse oscillatory component (which can maintain the unjammed state) and for reversing flows. I will outline recent progress towards a full constitutive model that may capture some of these effects.

Sound Bites

1. Henshaw, Richard; Jeffrey Guasto

Tufts University

Shepherding bacterial flocks using magnetotactic alignment in active suspensions"
A prominent open questions in the active matter community concerns how large numbers of individual active agents, such as flocks of birds or schools of fish, are able to organise and shepherd their collective motion through the local environment and its hazards. Dense suspensions of swimming bacteria have emerged as a model system of collective motion which is mediated by nematic interactions and self-propulsion. This so called “bacterial turbulence” can be characterized by emergent spatial and temporal scales several orders of magnitude greater than the individual agent. Here, we are studying the effect of rotational control of a sub-population of bacterial agents in the suspension to influence the collective properties of the system. A small number of magnetotactic bacteria are introduced into a dense suspension of non-magnetotactic swimming bacteria and the alignment of the magnetotactic agents to an external magnetic field biases long-range velocity correlations. The ability to control this otherwise stochastic transport process could provide new insight into fundamental microbial processes with far-reaching potential applications including manipulating biofilm production and microrobotic guidance.
Keywords: Collective motion, magnetotaxis, bacterial suspensions, active matter, bacterial turbulence

2. Hoppe Mezian, Carole

Harvard SEAS

my test title"

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© 2019 New England Complex Fluids Workshop
Supported by Harvard University's
Materials Research Science and Engineering Center