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. Aime, Stefano; M. Sabato, D. Weitz

Harvard University

DySH: measuring fast (sub)microscopic dynamics in 3D with no compromise on the field of view
Complex fluids, soft matter and biological systems often exhibit nontrivial microscopic dynamics both at rest and under the action of external stimuli, giving rise to complex flow patterns and collective behavior. It is for instance the case of flow instabilities such as shear banding, viscous fingering and viscoelastic turbulence, and of complex plasticity, yielding and fracture dynamics in viscoelastic solids. Quite generally, such dynamics are structured on multiple lenghthscales, ranging from the scale of the elementary constituents, often submicrometric, up to the whole system size, several orders of magnitude larger. A comprehensive understanding of such phenomena usually requires bridging between those widely different lengthscales, which is a challenging task for current imaging techniques, where a high spatial resolution, a large field of view, and a high acquisition rate are conflicting requirements, so that one cannot resolve minute displacements with good time resolution while imaging a large portion of the sample. Here we present Dynamic Speckle Holography (DySH), a novel optical technique able to access the 3D displacement field with sub-wavelength resolution and with no compromise on the field of view. Based on dynamic light scattering, this technique does not require the presence of trackable features such as tracer particles, and it is equally suitable for probing timescales as fast as milliseconds and as slow as hours. We demonstrate the power of DySH by unveiling the complex deformation field associated with the propagation and interaction of cracks in colloidal gels.
Keywords: Dynamic Speckle Holography, Light Scattering

2. Carmody, Caitlin; Jim Wilking

Montana State University

Ballistic Seed Dispersal in Leafy Spurge
Leafy spurge, an invasive weed found throughout North America, outcompetes native grasses and is poisonous to cattle and horses. Managing leafy spurge is expensive, and the estimated economic costs total more than $100 million annually between Montana, Wyoming, and the Dakotas. Leafy spurge spreads by explosive rupture of seed pods, which can launch millimeter-scale seeds up to 15 ft. To explore the physics of seed dispersal, we use high-speed imaging, force measurements, and microscopy. We find that the shells have a layered composite structure with layers that deform anisotropically in response to changes in humidity. Intriguingly, capillary forces appear to play an important role, and the stresses generated by drying are reversible. These ongoing experiments may lead to new strategies for managing and eradicating leafy spurge infestations.
Keywords: seed dispersal, high speed imaging, capillary forces, composite structure

3. Chakrabarti, Aditi; Aditi Chakrabarti, Gary P.T. Choi, L. Mahadevan

Harvard University

Spontaneous spin-sliding of volatile drops on swelling sheets
When a volatile solvent droplet is deposited on a freely floating swellable sheet, it can spontaneously become lobed, asymmetric, and either spin, slide or move via a combination of the two. This process of symmetry-breaking is a consequence of the solvent droplet swelling the membrane and its inhomogeneous evaporation from the membrane, coupled with the hydrodynamics within the droplet. By tuning the membrane thickness and the droplet size, we find a critical threshold that determines the transition from a quiescent spherical cap state to a self-piloted motile state. Simple scaling laws determine the angular and linear velocities of the droplets, and a 1D analog experiment confirms the relative roles of evaporation, swelling and viscoelastic dissipation.
Keywords: autonomous motion, droplets, thin films, swelling, evaporation

4. Chatterjee, Subhasish; Katherine Liu, Victoria Krovatin, Emma Breber, Emily Kornblum, Sapir Flank

Barnard College, Columbia University

Co-assembly of peptide motifs: Towards supramolecular materials design
The innate twenty–letter language of peptides has spurred the design of versatile bioinspired materials with wide-ranging applications in nanoscience and biomedicine. Molecular assembly is a key feature of natural and engineered supramolecular peptide materials. Molecular dynamics (MD) simulation offers an attractive tool for deconstructing the co-assembly of peptide-based structures that can be formed in solution as well as in the gel phase. We have used coarse-grained modeling and MD simulations to obtain information on morphology, molecular organization, internal mobility, and specific interactions of the constituents and molecular sites in tripeptide and tetrapeptide systems. Our findings illustrate the interplay between the morphology and mobility of peptide components, shedding light on the supramolecular frameworks that can be constructed by self-assembling peptide materials.
Keywords: self-assembly, peptides, coarse-grained modeling, MD simulation

5. Chen, Anqi; Liyuan Zhang, Bo Ri Seo, Berna Ozkale Edelmann, David Mooney, David Weitz

Harvard University

Mesenchymal stem cell encapsulation in alginate microcapsules for immunomodulation
Mesenchymal stem cells (MSCs) are multipotent cells characterized by the capability to differentiate into fat, cartilage and bone cells. They are first identified and isolated from the bone marrow, where they not only co-localize, but also interact with hematopoietic stem cells (HSCs), which give rise to the entire immune system. Inspired by the finding of MSC-HSC interactions, researchers have devoted tremendous effort in MSC therapy for immunomodulation in the past two decades, but are still challenged by the short in vivo persistence time (~48 hrs) of MSCs. In this study, we apply a microfluidic-based cell encapsulation strategy to create 200 um RGD-alginate capsules encapsulating MSCs inside. The capsule provides the cells with integrin binding sites for mechanical signaling and shields the injected cells from the host's immune system. In vivo mouse study shows our method extends the persistence time of subcutaneously injected MSCs to over two weeks.
Keywords: Mesenchymal stem cell, cell encapsulation, microfluidics

6. Cheng, Richard; Gertraud Eylert, Jean-Michel Gariepy, Sijin He, Hasan Ahmad, Yizhou Gao, Stephania Priore, Navid Hakimi, Marc G. Jeschke, Axel Guenther

University of Toronto

In-situ delivery of skin precursor hydrogel sheets for wound healing using a microfluidic handheld bioprinter
The current standard of care for patients with large area full-thickness burns involves grafting autologous meshed skin or the application of acellular dermal substitutes. Emerging options to accelerate wound healing include cell delivery via approaches such as direct spraying or injecting, but uniform coverage on clinically relevant wound topologies, orientations, and sizes remain a challenge. Here, we report the one-step in-situ formation of cell-containing hydrogel sheets using a handheld bioprinter which accommodates the topography of the wound. We use a transient fibrin-based biomaterial supplemented with hyaluronic acid to improve printability on non-flat surfaces while maintaining delivered stromal cell viability and proliferative activity. Porcine models of full-thickness burn indicate improved re-epithelialization, dermal cell repopulation, and neovascularization after treatment, suggesting clinical applications of this cell delivery approach to improve wound healing outcomes.
Keywords: tissue engineering, biomaterials, microfluidics, bioprinting, cell delivery

7. Cochard, Thomas; Y. Song, L. Xiao, D. A. Weitz

Harvard SEAS

Hydraulic fracture dynamics
Hydraulic fracking of shale reservoirs is a process where a highly pressurized fluid is injected into the shale matrix, inducing fractures that create a connected path between the pores filled with hydrocarbons. The dynamics of hydraulic fractures in high strength materials remain poorly understood, despite the widespread application of hydraulic fracking. Particularly related to mitigation of seismicity and aquifer pollution. Most of the research on hydraulic fracking is focused on the evolution of the pressure during the fracture propagation. In contrast, in our work, we are developing an energy balance approach that accounts for both the compressed volume and pressure of the injected fluid. Importantly, by only considering the pressure evolution within the system, the total volume of the injected fluid is neglected. Our results show that the volume of fluid cannot be neglected as the applied pressure upon fracture is at least 350 times the atmospheric pressure. To accomplish that, we designed a 3D-printed cube using a stereolithography apparatus with an injection system allowing us to initiate a systematic controlled hydraulic fracture. We use high speed imaging to follow the fracture propagation and measure the pressure evolution and the volume of injected fluid being compressed. Piezo electric sensors are set on the surface of the sample to measure the resulting deformation at 2 MHz with a high sensitivity. As a result, we can demonstrate that the desired volume of fractures can be triggered by the total volume of fluid used during the fracking process. In addition, we find that by using an energetic approach, we can estimate mechanical parameters in situ such as the fracture toughness of the material.
Keywords: Hydraulic fracture, high speed imaging, 3D printing, Seismic wave propagation

8. Dahl, Joanna; Cristina Rodriguez-Quijada

University of Massachusetts Boston

Non-Contact Microfluidic Mechanical Property Measurements of Single Apoptotic Bodies
Cells exchange information by secreting micro­ and nanosized extracellular vesicles (EVs), ranging from exosomes (30-100 nm) to apoptotic bodies (ABs, 1-5 µm). There is still much to understand about fundamental EV biological, physical, and chemical properties before clinical applications can be developed. EV mechanical properties have only been measured with atomic force microscopy with its problematic adhesion and hard substrate effects. To understand EV mechanical behavior in less extreme mechanical conditions relevant to blood flow and many soft tissue environments, a non-contact measurement technique is needed. We measured the mechanical properties of single microscale ABs derived from human blood plasma using non-contact microfluidics. The effective shear elastic modulus of ABs in non-contact flow conditions is approximately 5.9 ± 0.5 Pa, 7 orders of magnitude lower than previously reported AFM-measured biological exosome stiffnesses. Apoptotic bodies are very soft in fluid environments and exhibit lower effective stiffnesses than suspended cells. By measuring ABs in natural fluid environment and simplifying the deformation process to eliminate hard probes and surfaces, we achieved closer agreement with mechanical modeling assumptions and more accurate stiffness measurements.
Keywords: extracellular vesicle, microfluidics

9. Deveney, Brendan; Joerg Werner


Velcro surfactant
We have developed a new surfactant system capable of forming highly stable water/fluorinated oil emulsions. The surfactant forms an interfacial film that prevents drop coalescence in emulsions generated by droplet microfluidics. Using the surfactant, 200 micron diameter drops can be successfully thermocycled between 30°C and 90°C 45 times without loss of integrity, a feat unachievable with drops formed using traditional surfactants. Our surfactant is particularly well suited for single-cell biological assays employing PCR in microfluidic droplets, and should allow for unprecedented recovery of individual cell data.
Keywords: Interfacial film, drop stability

10. Dillavou, Sam; Shmuel Rubinstein, Mary Agaganian, Vincent Stin, Emily Brodsky, Amir Sagy


Table-top nucleation
The behavior of slip nucleation in extended frictional interfaces is an open question with significant implications to earthquake dynamics. We use a table-top setup to probe nucleation dynamics in 2D, slowing down the ruptures by using soft elastomers and filling the interface with sand.
Keywords: Earthquakes, Nucleation

11. Ding, Lijie; Robert A. Pelcovits, Thomas R. Powers

Brown University

Shapes of fluid membranes with chiral edges
We carry out Monte Carlo simulations of a colloidal fluid membrane composed of chiral rod-like viruses. The membrane is modeled by a triangular mesh of beads in which the bonds and beads are free to move at each Monte Carlo step. Since the constituent viruses are experimentally observed to twist only near the membrane edge, we use an effective free energy that favors a particular sign of the geodesic torsion of the edge. The effective energy also includes membrane bending stiffness, edge bending stiffness, and edge tension. We find three classes of membrane shapes resulting from the competition of the various terms in the free energy: branched shapes, chiral disks, and vesicles. Increasing the edge bending stiffness smooths the membrane edge, leading to correlations among the membrane normal at different points along the edge. We also consider membrane shapes under an external force by fixing the distance between two ends of the membrane, and find the shape for increasing values of the distance between the two ends. As the distance increases, the membrane twists into a ribbon, with the force eventually reaching a plateau.
Keywords: chirality, membranes, self-assembly

12. Ellis, Perry; Debojyoti Panda, Giridhar Anand, Sharad Ramanathan, David A. Weitz

Harvard University

Identifying pathogenic bacteria by phenotyping individual cells
Identifying pathogenic bacteria in natural samples has important consequences for human health. For example, 80% of foodborne illness comes from "unknown origin" --- there are either too few pathogenic bacteria in the sample to detect, or there doesn't exist a specific test for the pathogen at fault. To address these concerns we focus on high-throughput methods that require no prior knowledge of the bacteria to assess its pathogenicity. Our current approach relies on droplet microfluidics: we co-encapsulate human tissue with the bacteria of interest, forming a functional assay capable of screening 10^6 bacteria per day.
Keywords: Microfluidics, Screening, Pathogenicity, Droplets

13. Farokhirad, Samaneh; Ravi Radhakrishnan, David M. Eckmann, Andrew Tsourkas, Portonovo S Ayyaswamy

New Jersey Institute of Technology (NJIT)

Quantitative Basis for Design and Vascular Targeting of Flexible Polymeric Nanoparticles
We present a quantitative model for multivalent binding of ligand-coated flexible polymeric nanoparticles (NPs) to a flexible membrane expressing receptors. The model is developed using a multiscale computational framework by coupling a continuum field model for the cell membrane with a coarse-grained model for the polymeric NPs. The NP is modeled as a self-avoiding bead-spring polymer chain, and the cell membrane is modeled as a triangulated surface using the dynamically triangulated Monte Carlo method. The computational framework accounts for the mechanical properties of the NP as well as the target cell. We are able to demonstrate that NP transport and adhesion are sensitive to NP mechanics tuned from very soft NPs to rigid spheres. This sensitivity of NP targeting to NP mechanics arises out of the interplay between enthalpic and entropic terms mediating NP binding to the cell membrane. This new flexibility to use of NPs has translational importance in clinical medicine for early/correct treatment and diagnosis of progressive and treatable diseases.
Keywords: polymeric nanoparticle, cell membrane, drug delivery, coarse-grained modeling, Monte Carlo method

14. Gault, Zach; Zsolt Terdik, Peter Lu, Joerg Werner, David Weitz

Harvard University

Strain dependent hysteresis in nanoparticle aggregate dispersions visualized to explain origin of the Payne Effect and Spectral Hole Burning in cross-linked filled rubber
Filled rubbers are composite materials containing two interpenetrating phases: crosslinked elastomers, and a ‘filler’ consisting of nanoparticle particle aggregates. The nanoparticle aggregates form a system-spanning subnetwork that reinforces the elastomer network and introduces a new energy loss mechanism at low strains of only 1-5%. This loss mechanism, known as the Payne Effect, is one of the mechanical hallmarks of filled rubbers and is a major contributor to rolling friction in tires. We create a transparent model system to study the strain dependent hysteresis of nanoparticle aggregates. With this system we can directly observe microstructural changes of filler particle aggregates during in situ shear deformation. We complement these observations with bulk rheological tests, including spectral hole burning, to gain new insight into the microscopic structural changes that occur during cyclic deformation.

15. Han, Hee-Sun

University of Illinois, Urbana-Champaign

Single virus sequencing to reveal how
Virus is a collection of both infectious and non-infectious populations, 70-90% of virus particles. Non-infectious populations are dark but biologically active, which trigger an immune response. The defective interfering particles have a large internal deletion in their genomes, interfere with the production of fully infectious populations with a persistent infection in the host. The semi-infectious particles, the cells express a partial set of genes with complementation to phenotype mixing.

SVS enables quantitative analysis of viral populations. There are hidden subpopulations, which include the "dark" population, where the genome begins with ATCGTTGCCTCAAC... The evolutionary pathway includes mixing of an enzyme and virus. Successful amplification and barcoding of single influenza genome. RT in drops is as efficient as RT in bulk. All genome segments are successfully amplified and barcoded in drops.
Keywords: virus

16. 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

17. Hoppe Mezian, Carole

Harvard SEAS

my test title

18. Huang, Tina; Laura Arriaga, Anqi Chen, Ran Ran, Arash ManafiRad, David A.Weitz

Harvard University

Microfluidic Fabrication of Asymmetric Lipid and Polymer Vesicles
Lipid vesicles are aqueous volumes surrounded by a bilayer of lipid molecules, which are amphiphilic molecules with their head groups facing water and tail groups facing oil. These vesicles are simple models that mimic cell membranes and can be used for drug delivery. Similarly, block copolymers are amphiphilic molecules that form vesicles by themselves or when mixed with lipids. Like lipid vesicles, polymer vesicles can also be used for cell membrane mimicry and drug delivery. One interesting type of lipid/polymer vesicle is the asymmetric vesicle, in which its bilayer is composed of two dissimilar lipid monolayers or a lipid monolayer and a polymer monolayer. Importantly, all eukaryotic cell membranes exhibit this type of asymmetry and asymmetry is also proposed to enhance mechanical properties of the membrane. Here, we use microfluidics to fabricate mono disperse and highly controllable asymmetric vesicles, which unlike the conventional methods that often end up with highly poly disperse samples. To achieve this, asymmetric vesicles are produced using water/oil1/oil2/water emulsions in a glass capillary device, with different lipids/polymers immersed in two different volatile oil phases. Using the asymmetric vesicles, we are trying to measure how mechanical properties are affected by this asymmetry and also how to improve the degree of asymmetry in our vesicles even more. In future, we envision asymmetric lipid/polymer vesicles could open a new door in the field of drug delivery.
Keywords: Microfluidic, Lipid, Polymer, Asymmetry, Vesicle

19. Kapellos, George; Nicolas Kalogerakis, Patrick S. Doyle

MIT, TU-Crete

Tracking the biodegradation of hydrocarbon droplets by marine microbes
Natural seeps and accidental releases of crude oil in the sea result in clouds of droplets that are carried away by underwater sea currents. The fate of subsea droplet clouds is determined by natural attenuation processes, mainly dissolution into the seawater and biodegradation by oil-eating microbes. In this talk, I will briefly highlight our recent findings on the mechanisms underlying the biodegradation of individual oil droplets by marine microbes.

20. Keepseagle, Kayla; David A. Weitz

Harvard University

Mechanical Lysis of Single Bacteria
We are working on a mechanical method to break the cellular membrane of individual bacteria, also known as lysis. Single-cell analysis is incredibly important as it allows us to study rare populations and understand the differences between single bacteria in a large population. Lysis is the crucial step, and current chemical methods to carry out single-cell lysis limit the downstream applications. In contrast, this method is mechanical; it uses a focused acoustic pulse to lyse each single bacteria separately.
Keywords: Lysis, Bacteria, Single-cell

21. Kudrolli, Arshad; Bernny Ramirez

Clark Univ and Harvard Univ.

Burrowing dynamics in sediments
We discuss the dynamics of a California Blackworm as it burrows in water saturated granular matter, and contrast it with its swimming dynamics in water. This slender limbless aquatic worm can be found widely in ponds and marshes across America and Europe. By using transparent hydrogels, we track the strokes used in both mediums and show that the worm moves forward faster in the sediments compared to water while using the same undulatory and peristaltic strokes. We find that the observed speeds can be described by using resistive force theory and a dynamic anchor model of peristaltic motion.
Keywords: Biolocomotion, Burrowing, Granular Matter, Anchor Model

22. Lee, Garam; Abigail Taylor, Alan Luner, Jeremy Marzuola, Daniel Harris

Brown University, University of North Carolina at Chapel Hill

Dispersion control in deformable microchannels
In fully-developed pressure-driven flow, the spreading of a dissolved solute is enhanced in the flow direction due to transverse velocity variations in a phenomenon now commonly referred to as Taylor dispersion. It is well understood that the characteristics of the dispersion are sensitive to the channel’s cross-sectional geometry. Here we demonstrate a method for manipulation of dispersion properties in a single microchannel via controlled deformation of one of the channel's walls. Using a rapid-prototyped multi-layer microchip, the upper channel wall is deformed by an external pressure source allowing us to characterize the dependence of the dispersion on the deflection of the channel wall and overall channel aspect ratio. Our experimental measurements are compared directly with theoretical predictions.
Keywords: Deformable microchannel, Dispersion factor, Dispersion control

23. McKeown, Ryan; Rodolfo Ostilla-Monico, Alain Pumir, Michael P. Brenner, Shmuel M. Rubinstein

Harvard University

Turbulence generation through an iterative cascade of the elliptical instability
We demonstrate the existence of a novel mechanism in which two counter-rotating vortices violently collide and break down, leading to the rapid development of a turbulent energy cascade mediated by iterations of the elliptical instability. We probe the full 3D dynamics of this breakdown by conducting both experimental visualizations of colliding vortex rings and numerical simulations of colliding vortex rings and vortex tubes. We observe how the onset of the elliptical instability causes the vortex cores to develop antisymmetric perturbations, which give rise to an ordered array of secondary vortex filaments, perpendicular to the original cores. Adjacent secondary filaments counter-rotate and interact with each other in the same manner as the original configuration. In the high-Reynolds number limit, we observe another iteration of this instability, whereby a new generation of tertiary filaments forms perpendicular to the interacting secondary filaments. The energy spectrum of this turbulent breakdown exhibits Kolmogorov scaling, a hallmark of homogeneous isotropic turbulence. We find that the elliptical instability could play a role in the formation and sustenance of turbulent flows by providing a means through which energy is conveyed down to dissipative scales.
Keywords: Vortex rings, turbulent cascade

24. Milani, Matteo; Stefano Aime

Harvard SEAS

Droplet Deformation in Micro Channel with Constriction
The shape of a liquid droplet immersed in a second (immiscible) fluid flowing in a channel is determined by the competition between surface tension and the stress resulting from fluid flow. Analysis of the droplet shape combined with knowledge of the viscosities and the flow profile allows to infer the value of the surface tension itself. A similar analysis is also possible in presence of more complex rheological properties of either bulk phase, or of the interface. Therefore, the shape of droplets under flow encodes rich information that can be used to perform rheology experiments at high throughput and deformation rates using extremely small sample volumes. For this purpose, we build (or design, or work with) microfluidic channels with a well-defined undulating profile, to mimic the periodic deformation imposed by a rheometer: our preliminary experiments show encouraging results and give practical guidelines for the development of improved microfluidic rheometers.
Keywords: Droplet, microfluidic channels, rheometers, surface tension, fluid flow

25. Nelson, David R.

Harvard University

Statistical mechanics of dislocation pileups

26. Oliveira, Tania Thalyta Silva de ; Arijit Bose

University of Rhode Island

Tunable Carbon Black-Gold Nanoparticles for Surface-Enhanced Raman Spectroscopy
Surface-enhanced Raman scattering (SERs) is a powerful technique for the detection of a variety of molecules at very low concentrations. Consequently, the development and maximization of SERs substrates are intrinsically important in the detection field. Plasmonic nanostructures are a great tool to functionalize a diverse number of surfaces to be Raman active. Therefore, we have developed star shaped gold nanoparticles by using carbon black as a template and tuned them to different lasers wavelengths. Differences in the particle’s morphology as well as in the enhancement of the Raman signal were detected for the different tuned particles.
Keywords: Gold nanoparticles, Raman, tuned particles.

27. Sabato, Matteo; Stefano Aime

Harvard University

Microscopic aspects of crack dynamics in model soft solids
Failure and crack formation are extremely widespread phenomena that occur in both natural and artificial materials. Whether it is due to the action of an external force or just to aging, any object, at some point, breaks. However, despite its ubiquitous nature, our understanding of the microscopic features of crack propagation is still lacking, due to the challenge of probing the microscopic structural evolution as the crack spreads over long distances. For this reason, we developed Dynamic Speckle Holography (DySH), an innovative light scattering technique that allows us to measure the 3D deformation field produced by the crack with resolution down to the sub-micrometric scale while keeping a large field of view. Exploiting this technique, we are currently studying fractures in colloidal gels, model materials which can be easily tuned to exhibit a wide range of mechanical properties. In particular, we are focusing on various poorly understood features of crack propagation such as the determination of the size of the so-called plastic region and the interaction between cracks and defects (pre-existing cracks, bubbles, boundaries, etc.).
Keywords: cracks, soft solids, light scattering

28. Serra, Mattia; L. Mahadevan

Harvard University

Dynamic morphoskeletons in development
Morphogenetic flows in developmental biology are characterized by the coordinated motion of thousands of cells that organize into tissues, naturally raising the question of how this collective organization arises. Using only the kinematics of tissue deformation, which naturally integrates local and global mechanisms along cell paths, we identify the dynamic morphoskeletons behind morphogenesis, i.e., the evolving centerpieces of multi-cellular trajectory patterns. These features are model and parameter-free, frame-invariant, robust to measurement errors, and can be computed from unfiltered cell velocity data. It reveals the spatial attractors and repellers of the embryo by quantifying its Lagrangian deformation, information that is inaccessible to simple trajectory inspection or Eulerian methods that are local and typically frame-dependent. Computing these dynamic morphoskeletons in wild-type and mutant chick and fly embryos, we find that they capture the early footprint of known morphogenetic features, reveal new ones, and quantitatively distinguish between different phenotypes.
Keywords: Morphogenesis, Lagrangian frame, Finite Time Lyapunov Exponents, Fly, Chick

29. Shoaib, Mohammad; Erin Bobicki

University of Toronto

Effect of Acid Addition Scheme on Bentonite Rheology
Bentonite is a widely encountered swelling clay in several industries such as oil & Gas, mineral processing, nuclear waste disposal, etc. The edge of bentonite particles has an IEP between pH 6-7. Lowering the pH of bentonite suspensions below edge’s IEP results in an extremely aggregated system with high storage modulus and yield stresses. In this research, we report on how the scheme of acid addition affects the bentonite suspensions. Addition of acid before and after bentonite results in completely opposite systems, one with very low yield stresses and the other with very high yield stresses respectively.
Keywords: Bentonite, Swelling, Rheology

30. Stehnach, Michael

Tufts University

The Dispersal of Swimming Microalgae in Viscosity Gradients
Swimming cells often live in fluid environments characterized by spatial gradients of rheological properties, including biofilms and mucus layers. However, our understanding of cell motility and transport in such environments is lacking. We use microfluidic devices to generate a spatial concentration gradient of a Newtonian polymer suspension to form a viscosity gradient and video microscopy to quantify both the viscosity landscape and the cell motility. We demonstrate that swimming biflagellates (Chlamydomonas reinhardtii), at low viscosity gradients, accumulate in high viscosity regions due to a local change in swimming speed. However, in large gradients, a hydrodynamic "viscous torque" reorients the cells toward the low viscosity region, resulting in two distinct regimes of microbial transport in viscosity gradients.

31. Su, Yunxing; Andres Zambrano, Mingyu Wang, Mithun Ravisankar, Roberto Zenit

Brown University

Two-phase flow, biological flow and the fluid mechanics of artistic painting
We will briefly introduce the on-going projects in our lab. Specifically, we will be talking about the behaviors and interaction of bubbles in non-newtonian fluids, the swimming performance of magnetically driven micro-swimmers in various configurations (complex fluids, interface, etc.), the underlying fluid mechanics of artistic painting, including the instability of a viscous filament falling on a substrate.
Keywords: bubbles, droplets, micro-swimmer, viscous filament, coiling, non-newtonian fluids

32. Sun, Sijie; Sijie Sun, Dr Aime. Stefano, Prof. David, A, Weitz

harvard university

non-Brownian suspension flow with non-Newtonian fluid
Non-Brownian particle transport can lead to undesired particle sedimentation in many fluid-transport applications. Often, long-chain polymers are added to the transport liquid to inhibit particle sedimentation. However, the viscoelastic effects generated by the addition of long-chain polymers are not well-characterized. To address this question, we use flow-visualization to experimentally investigate the connection between the rheological behavior and the flow profile of defined particle and polymer solutions. We hope through our experiments to provide a deeper understanding of non-Brownian particle transport, as well as practical guidelines to improve and optimize fluid transport in industrial applications.
Keywords: Suspension Flow, Visco-elastic Liquid

33. Tang, Ray; Reda Karoum


Miniaturized inside-out NMR sensor for in-situ characterization of viscoelastic fluids
Mud is heavily engineered viscoelastic fluid used to aid the drilling of boreholes into the earth. The multiphastic complexities, consisting of brine, oil, lime, emulsifiers, organoclays, a multitude of polymers and micro-sized barite, are notorious difficult to characterize, not to mention under reservoir conditions. In this research, we construct a miniaturized inside-out NMR device operating up to 145 C, monitoring the fluid evolution in a static configuration. Through NMR relaxation measurements, we demonstrate the migration of chemical species in the fluid fabric, how they interact, and what they progress towards over time and space.
Keywords: NMR, in-situ measurement, viscoelastic fluid

34. Uzio, Jordy

Harvard University

Transport of Nanoscale zero-valent particles (nZVI) in model porous media
We are now in the Anthropocene era, the impact of mankind is observable at the Geological scale. Soil remediation has become an emergency, to be able to set up an efficient process Nanoscale zero-valent iron particles (nZVI) has been studied and have increasingly been applied for environmental remediation. To try to improve these methods we worked on the transport of nZVI particles in model porous media.

35. Wang, Mingyu; Mithun Ravisankar, Yunxing Su & Roberto Zenit

Brown University

Two phase flow: bubbles
Research on two in-line bubbles' motion in Newtonian and non-Newtonian fluid using experiments and use the phenomena to understand the motion of a bunch of bubbles.
Keywords: Bubble

36. Wu, Jiwei; T. Cochard, L. Xiao, D. A. Weitz

Harvard University

Experimental Investigations of Oil Transport in 2D Porous Media
The understanding of immiscible flow in porous media is a major interest for oil and gas recovery in conventional reservoir. After the secondary oil recovery (water flood), the oil network is disconnected in the pore structure. In order to understand how the single oil ganglia is being transported in such condition, we generate an artificial 2D porous media where we can trigger dominant parameters such as pore size, porosity and connectivity. Those artificial porous materials are then transferred into a PDMS chip. Thanks to our microfluidic design we can generate oil ganglia and look at its transport under certain condition: Type of fluids injected (polymer and surfactant mixture), surface properties of the PDMS device (change in wettability). Coupled with high speed imaging we can track the initial oil ganglia, look at its transport which can be achieved in several ways: continuous transport, break up into smaller ganglia but also study the coalescence of oil ganglia under certain conditions. New way of modelling the transport behavior are proposed and a framework of modelling the tertiary oil and gas recovery is suggested.
Keywords: artificial porous media; multiphasic flow; wettability; viscous flow; interfacial tension

37. Xiao, Ming; Jie Mao, Victoria Hwang, David Clarke, Vinothan Manoharan

Harvard University

Photonic glass based dielectric elastomer actuator enables wide-angle display
Structural color that was attempted on display faces problems including large angle dependence and slow response time. To address these challenges, we show the proof-of-concept that a photonic glass based dielectric elastomer actuator can mechanically deform and change colors rapidly upon a high electric voltage. The photonic glass shows much lower angle-independent colors compared to photonic crystals, providing a possible routine to make next generation wide-angle display.
Keywords: Structrul color, dielectric elastomer acurator, photonic glass, display

38. Xin, Weiyue; Hao Wu, Maria Santore

UMass Amherst

The impact of membrane tension and excess area on solid domains in membrane vesicles
Phase separation of phospholipids in biomolecular membranes is closely connected with signaling and trafficking in cells. This talk explores a fluid-solid coexistence system and pattern formation in phospholipid membranes, providing a new perspective on a classically studied system. The fluid-solid coexistence systems transcend biology to produce materials with potentially tunable interconnectivity and morphology. In our system, solid domains integrated into the fluid bilayer membrane on the curved contour of the vesicle, how curvature and tension in the fluid phase affect the arrangements of solid domains constitutes new physics that allows access to greater sophisticated interconnected patterns that form in response to touch.
Keywords: lipid membrane, fluid-solid coexistence system, domain arrangement

39. Yuan, Yuan; Julie Brouchon, J. Mauricio Calvo-Calle, Jing Xia, Li Sun, Xu Zhang, Fangfu Ye, David A. Weitz, John A. Heyman

Harvard university

Droplet encapsulation improves accuracy of immune cell cytokine capture assays
Cell-secreted molecules are important in cell-cell signaling and can often reveal cellular state and function. Quantification of cell-secreted molecules, e.g., cytokines, is fundamental to the characterization of immune responses. For example, at an infection site or in a tumor, the number of activated immune cells secreting IFN-γ can indicate the strength of the immune response. Cytokine capture assays that use engineered antibodies to anchor the secreted molecules to the secreting cells are widely used to characterize immune responses because they allow both sensitive identification and recovery of viable responding cells. However, if the cytokines diffuse away from the secreting cells, non-secreting cells will be identified as responding cells. Here we encapsulate immune cells in microfluidic droplets and perform in-droplet Cytokine capture assays to limit the diffusion of the secreted cytokines. We use microfluidic devices to rapidly encapsulate single natural killer NK-92 MI cells and their target K562 cells into microfluidic droplets. We perform in-droplet IFN-γ secretion assays and demonstrate that NK-92 MI cells recognize target cells within droplets and become activated to secrete IFN-γ. Droplet encapsulation prevents diffusion of secreted products to neighboring cells and dramatically reduces both false positives and false negatives, relative to assays performed without droplets. After cells are released from the droplets, secreted cytokine remains captured onto secreting immune cells, enabling FACS-isolation of populations highly enriched for activated effector immune cells. Droplet encapsulation can be used to reduce background and improve detection of any single-cell secretion assay.
Keywords: Droplet microfluidics, cytokine secretion, immune cell activation, cytokine capture assay, cell sorting

40. Zambrano, Andres; Yunxing Su, Roberto Zenit

Brown University

Biological Flow of Swimming Microorganisms
We will be discussing ongoing research in the Zenit group regarding the swimming of microorganisms in biological flows. We will also be mentioning other planned future work in bio-fluid mechanics.
Keywords: Biological, Flow, Swimming, microfluidics

41. Zarei, Zahra; Zahra Zarei, Chaitanya Joshi, Mike M. Norton, Michael Hagan, Seth Freden

Brandeis University

the role of boundaries in 2D active nematic
Defects play an important role in active-matter systems. They are nucleated because of the bend instability and in steady state are continuously created and annihilated. In this study we investigate a 2D active nematic confined in an annulus, which exhibits a rich dynamical behavior of the plus and minus half defects. The confinement effectively transforms the turbulent dynamics of the active nematic into coherent flow. We measure the positional-orientational distribution of defects in different confinements. We define three different states for the defects based on their positions and orientations, and calculate their transition rates.

42. Zhang, Liyuan; Liyuan Zhang, Shima Pasa, David A Weitz

Harvard University

Core-shell gel particles for conforamnce control
Conformance control during waterflooding in oil reservoir covers any technology that could redistribute water to increase the sweep efficiency and oil production. Using preformed gel particles can effectively redirect the flow by blocking the high permeability zones and forcing water into the low permeability zones where the crude oil is trapped. However, the large size of preformed gel particles, which is a result of pre-swelling and fabrication process, limits their wide application. Here, we fabricate core-shell nanohydrogels with programmable swelling behavior in aqueous solution and study their efficacy on the flow behavior in a three-dimensional (3D) micromodel porous medium. Using confocal microscopy, we directly visualize the spatial fluctuation of flow in the micromodel before and after nanohydrogel injection ¬and swelling. After swelling, the swollen nanohydrogel block some pores and significantly reduce the permeability of the 3D micromodel, resulting in diverting flow into unexplored regions of the porous medium. A core flooding test further confirms that the nanohydrogels can freely pass through a low permeability core, and significantly reduce the permeability with the possibility of diverting the flow into low permeability zones.

43. Zhang, Weixia; Liangliang Qu, Hao Pei, David Weitz

Harvard SEAS

Controllable Fabrication of Inhomogeneous Microcapsules for Triggered Release by Osmotic Pressure
Inhomogeneous microcapsules that can encapsulate various cargo for the controlled release triggered by osmotic shock are designed and reported. The microcapsules are fabricated using a microfluidic approach and the inhomogeneity of shell thickness in the microcapsules can be controlled by tuning the flow rate ratio of the middle phase to the inner phase. This study demonstrates the swelling of these inhomogeneous microcapsules begins at the thinnest part of the shell and eventually leads to rupture at the weak spot with low osmotic pressure. Systematic studies indicate the rupture fraction of these microcapsules increases with increasing inhomogeneity, while the rupture osmotic pressure decreases linearly with increasing inhomogeneity. The inhomogeneous microcapsules can be used for long-term storage of enzymes, which can be controllably released through osmotic shock without impairing their biological activity. The study provides a new approach to design effective carriers to encapsulate biomolecules and release them on-demand upon applying osmotic shock.
Keywords: Inhomogeneous Microcapsules, Controlled Release, Osmotic Pressure

44. Zhou, Zhiru; H. Susan Zhou, Qi Wen*

Worcester Polytechnic Insititute

A Microfluidic Approach for Study of Vimentin Effect on Cell Motility
Vimentin as an intermediate filament is of special interest in cell migration and epithelia-mesenchymal transition (EMT) of epithelial cancers. Although it is well acknowledged that vimentin knockdown or knockout attenuate the migration of fibroblast and that motile and invasive cell line express higher levels of vimentin, it is not tested in 3D in vitro environment. We designed and developed an innovative microfluidic device, capable of high-resolution time-lapse imaging of cells migrating through 3D precisely controlled microchannel geometries mimicking physiological confined environments. Using this microchannel assay, we demonstrated that knockdown of vimentin decreases 3T3 fibroblast cell directional migration speed in confined microchannels. Besides, cells formed dynamic membranes that define the leading edge of motile cells. We observed different leading-edge morphology of 3T3 fibroblast and 3T3 vimentin knockdown cells during migration, which may can be attributed to the role of vimentin in cytoskeletal organization and focal adhesion. The integration of our microfluidic device with quantitative measurements of both cell population level and single cell level provides a new approach for cell migration study under 3D narrow constrictions, which is strongly relevant to cancer metastasis process.

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© 2020 New England Complex Fluids Workshop
Supported by Harvard University's
Materials Research Science and Engineering Center