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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

77th New England Complex Fluids Meeting
Harvard University | Friday, November 30, 2018
Registration deadline: Wednesday, November 28, 2018

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abstract list | attendees list

Abstracts for Invited Talks and Sound Bites:

Invited Talks

1. Carroll, Nick James

University of New Mexico
"Programming assemblies of phase-separated polypeptide liquid"
Aqueous multi-phase systems comprising immiscible biopolymer solutions are ubiquitous in biological cells. However, the structure-to-function relationship and the physics describing the behavior of these polymer systems are, in general, not well understood. For example, almost all proteins have a specific three-dimensional structure that maintains its specific activity in the cell. One class of phase separating proteins, which has flown under the radar for decades, do not. They are referred to as intrinsically disordered proteins (IDPs). Their role in the cell appears to be to spontaneously associate with other proteins in phase separated compartments to activate them collectively. This is an important function to include in the design of a synthetic cell and for integration with cellular regulatory systems. Our work explores how we can leverage the blue print provided by the cell to engineer biological systems comprising phase-separated liquids with applications spanning areas of tissue culture, gene delivery, microfluidic colloid synthesis and engineered synthetic cells. Potential advancements include understanding how these interactions affect the regulation of gene expression and cell metabolism, understanding how dysfunctional interactions are linked to neurodegenerative disorders, and the design of synthetic cellular systems to create membraneless organelles to control a variety of biological processes at the molecular level.

2. Codd, Sarah

Montana State University
"Magnetic Resonance of Complex Fluids - RheoNMR and dynamics of polymer-solvent phase transitions"
The dissipative, heterogeneous and non-equilibrium nature of the microscale dynamics in most soft matter systems impact the macroscale material response. The role of NMR relaxation, diffusion and imaging in the study of soft matter systems will be overviewed with emphasis on rheological responses of micellar polymer solutions and solvent dynamics in a weak gel of a concentrated polymer-solvent system.

RheoNMR allows Couette cells to be placed inside the NMR spectrometer and MRI velocity maps quantify the local spatial shear rate response to an imposed stress. The memory effect in wormlike micelles subject to different preshear measurement history are demonstrated and fluctuations during start-up are resolved with time resolutions on the order of seconds. Using large angle oscillatory shear, data on a range of fluids from Newtonian to yield-stress have been acquired to demonstrate the potential of LAOS RheoNMR. The data provides the velocity across the gap of the Couette cell as a function of the oscillatory shear. Interpretation of the data in the context of LAOS shear stress-shear rate correlations could provide novel insight into material response. Phase transitions during solvent evaporation drying of biopolymer solutions (e.g. HPMC) are important in food science and pharmaceutical production processes. NMR relaxation and diffusion measurements can characterize the structure of glassy polymer solutions and gels and provide insight into the transport processes within these systems and study the molecular dynamics of phase transitions during the solvent evaporative drying process.

3. Invited, Speaker; Thomas C. Halsey

"Erosion of unconsolidated beds by turbidity currents"

Turbidity currents are gravity flows of fluids with suspended, denser sediment, which remains aloft due to turbulence generated by the current motion itself. To remain active, turbidity currents must have an ability to entrain material from their base to counteract the sedimentation of particles from the current to the base. A number of decades ago, Bagnold, Engelund, and Fredsøe proposed a physical picture for erosion as a function of the overall velocity of the turbidity current (bed stress). Recently, it has been argued that the high-velocity form of this law is critical in determining the overall mechanics of turbidity currents, particularly their predeliction to erode or deposit sediment in different locations. I re-examine the Bagnold-Engelund-Fredsøe picture, and determine the corresponding erosion law in a way that is consistent with turbidity current mechanics, and has a high-velocity plateau that determines the qualitative features of turbidity current deposition and erosion*.

*T.C. Halsey, Phys. Rev. Fluids 3, 104303 (2018)


4. McKinley, Gareth; M. Geri, B. Keshavarz, T. Divoux, C. Clasen, and D. Curtis

"Optimal Fourier Transform Rheology for Probing the Linear Viscoelasticity of Gels and Time-Evolving Soft Materials"
Numerous approaches have been proposed for developing time-resolved oscillatory rheometric protocols that can provide both time- and frequency-resolved measurements on an aging, curing, drying or crosslinking gel system. Previous approaches include multiwave techniques, random/white noise sequences, short-time Fourier transforms, and repeated step strain pulses. Here we revisit an audio signal processing sequence known as the exponential chirp, which offers a number of benefits including a frequency-independent amplitude and a continuously-varying phase. This sequence enables the linear viscoelastic properties of a "mutating" (or time-evolving) gel to be rapidly determined over several decades in frequency in ~30-100s, and has been claimed to be an "optimal" Fourier transform sequence. However, closer investigation of high-resolution calibration data on a model polymer network shows that regardless of choice of the time-frequency bandwidth parameter, measurement precision can be severely compromised at the highest and lowest frequencies by "leakage" of material information into side-lobes of the chirp power spectrum. Taking inspiration from the chirp sequences used by bats in echolocation, we illustrate how these inaccuracies can be resolved through convolution of the chirp sequence with a carefully-chosen windowing function or envelope. The resulting waveforms can be readily encoded and then used to drive a controlled-strain rheometer. Numerical computations and experimental measurements show that the error magnitude can, in fact, be reduced exponentially with correct selection of the window parameters plus implementation of careful signal conditioning protocols. We present experimental measurements on a semi-dilute entangled polymer solution, a worm-like micellar fluid and a time-evolving cross-linked biopolymer gel, to show that the resulting Optimally-Windowed Chirp (or OWCh!) can indeed rapidly and accurately extract the entire linear viscoelastic spectrum of a time-evolving complex material in less than 15s, the time typically required to obtain the complex modulus at a single low frequency.


5. Shum, Ho Cheung (Anderson)

Hong Kong University
"Assembly at aqueous-aqueous interfaces"
Liquid-liquid interfaces have been shown as versatile substrates to form material structures. Aqueous-aqueous liquid interfaces, which are characterized by tunable properties, such as interfacial tension and affinity partitioning, have inspired new opportunities to assemble particles, macromolecules and biological cells. In this talk, I will share our works in assembling material structures with unconventional properties at these interfaces.

Sound Bites

1. Abbasi, Akram; Geoffrey D. Bothun, Arijit Bose

University of Rhode Island
"Gold on Fractal Nanoparticles as Highly Active Surface-Enhanced Raman Scattering Substrate"
A unique gold nanostructure on para-amino benzoic acid (PABA)-terminated carbon black nanoparticle has been synthesized through a cationic polyelectrolyte templating technique and shown to be an excellent substrate for surface-enhanced Raman scattering (SERS) applications. Fractal particles coated with poly-L-lysine (PLL) were suspended in a tetrachloroauric acid (HAuCl4) solution. PLL enriched the interface with AuCl4- anions and ascorbic acid was added as the reducing agent, forming a thin layer of gold (Au) on the carbon black particles. Surface coverage and absorbance spectra of the nanoparticles was tuned by controlling the HAuCl4 and PLL concentration. SERS enhancement of the gold-coated carbon black has been successfully demonstrated for the detection of 4-nitrobenzenethiol(4-NBT), crystal violet as a model polycyclic aromatic hydrocarbon (PAH), and nitrate as a model small anionic molecule. Many nanoscale features of the gold layer, as well as the adsorption capacity of the underlying carbon template, significantly enhance SERS signals. Our results suggest that gold on carbon fractal nanoparticles are new, highly sensitive SERS substrates.
Keywords: Gold, Surface-enhanced Raman scattering, Carbon

2. Aime, Stefano

"Impact of interfacial rheology on two-phase flow in porous media"
Two-phase flow in porous media is a fascinating open problem, with huge implications in many fields, including oil recovery. Despite the efforts of an ever-increasing scientific community, its complexity keeps challenging our understanding, while its industrial relevance calls for practical guidelines to improve the economic, social and environmental impact of current oil extraction techniques. Among the many challenges faced by experimental as well as numerical approaches, one is certainly the complex rheological properties of interface of crude oil with the displacing fluid, which are highly simplified in current models relying on the existence of well-defined (constant) viscosities and contact angles. While there is some ongoing effort to extend current models to take bulk viscoelasticity into account, to the best of our knowledge no attempt has been done to account for nontrivial rheological properties of the water/oil interface. Our preliminary experimental data demonstrate that, unlike most model oils used in benchtop experiments, crude oil does exhibit interesting interfacial rheology, which should be taken into account by models aiming at a quantitative description of crude oil recovery.

3. Arango, Maria Torres; Ruipeng Li, Gregory Doerk, Lutz Wiegart

Brookhaven National Laboratory
"Understanding Nano-scale Dynamics in Nano-Composite Inks during 3D Printing Processes"
There is currently a common interest from industry and academia in novel additive manufacturing (AM) based printing techniques that enable new materials and device architectures, with properties and performance expected to exceed those achievable with conventional manufacturing techniques. Inherent to printing are the anisotropy and the out-of-equilibrium nature of this process, causing nanoscale materials transformations during the different processing stages. In particular, for continuous-flow direct writing (CDW), the materials, formulated as colloidal inks, exhibit a strong dependence on the colloidal/matrix interactions, which determine their rheological behavior. Concomitantly, the materials’ nano- and meso-structure are influenced by the out-of-equilibrium processing pathways, opening new routes for material engineering. Despite the importance of the printing process and the associated material transformations, fundamental understanding of the underlying principles governing such relationships remains a challenge. At the National Synchrotron Light Source – II, Brookhaven National Laboratory, we conduct operando studies of the out-of-equilibrium processes accompanying CDW, by combining X-ray photon correlation spectroscopy (XPCS), and CDW at the Coherent Hard X-Ray Scattering (11ID) Beamline. The length and time scales that can be probed through XPCS are suited for the study of these fluids, by capturing the materials dynamics from the millisecond to the hundreds-of-seconds range, encountered during the deposition, subsequent relaxation, and drying/curing stages of the processing. Similarly, XPCS covers material length scales from tens to hundreds of nanometers, sufficient to resolve typical heterogeneities in CDW. These observations are complemented by rheology and post-printing studies of the materials microstructure and compositional changes. We expect our studies to shed light on the mechanisms of geometric fidelity and self-assembly of materials, contributing to the theoretical understanding and modelling of AM processes, and exploring new opportunities by applying such transient out-of-equilibrium states engineering materials with novel properties.
Keywords: 3D printing, colloidal inks, ink dynamics, XPCS, X-ray photon correlation spectroscopy, direct writing, additive manufacturing

4. Brouchon, Julie; Julie Brouchon, Yuan Yuan, John Heyman, Jaime M. Calvo-Calle, David A. Weitz

Harvard university
"Microfluidics for high-throughput single-cell analysis of immune cells"
Isolation of antigen-specific T cells is fundamental to study autoimmune diseases and to develop immunotherapies. Unfortunately, these cells are rare and cannot be easily identified by surface markers. We overcome these challenges by compartmentalizing cells into microfluidic droplets and performing a functional assay relying on T cell-target cell interaction and subsequent fluorescent detection of cytokine secretion. In one day we can screen several million cells to isolate live, antigen-specific T cells.

5. Chen, Anqi; Tina Huang, David Weitz

Harvard University
"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

6. Cochard, Thomas

Harvard University, Weitz lab
"Hydraulic fracturing dynamics in natural and artificial low-permeability porous media"
Despite the impact that hydraulic fracturing has on the energy sector, the physical mechanisms that control its efficiency and environmental impacts remain poorly understood in part because of the complex heterogeneous structures of the natural low permeability formations. We developed an experimental approach to study the hydraulic fracture propagation in both natural and model low-permeability media. Natural shale sample, thin sections of Mancos Shale, and engineered gels have been hydro-fractured under controlled conditions. The combination of high-speed imaging during the process and X-ray tomography before and after allows us to monitor the fracture propagation and gives insight on how heterogeneities drive hydraulic fracturing dynamics.
Keywords: Hydraulic fracking, porous media, heterogeneity

7. Cui, Naiwen; Huidan Zhang; Haichuan Hu; Yamei Cai; David Weitz

HARVARD UNIVERSITY; Mass General Hospital
"Ultra High-Throughput Targeted sequencing in single cells using droplet barcoding microfluidics"
Single cell targeted sequencing is a powerful tool for genetic mutation detection, which play an important role in studying genetic heterogeneity and clonal evolution in many complex illness and diseases. Studies show that clonal evolution can contribute to treatment failure, drug resistance and metastasis in cancer. For example, Intratumoural EGFR heterogeneity in Non-Small Cell Lung Cancer (NSCLC) revealed a close relationship with tumor shrinkage under chemotherapy treatment. To provide a good representation of the whole tumor, large number of cells need to be processed due to large number of tumor cells present. Current technology could only study 96 cells at a time using plate based assays or commercially available platform, which is very difficult and expansive to scale up. We have developed a droplet-based microfluidics technology that is capable of first encapsulating single cells in droplet, amplifying multiple targeted genes in each drop and then molecularly barcode them using hydrogel barcoded beads with very high efficiency. The ability to barcode tens of thousands of cells in each experiment with such low cost makes this a great tool for many clinical applications. 
Keywords: single cell; sequencing; drop-based microfluidics

8. Dehkharghani, Amin; Nicolas Waisbord, Thomas Coons, Jeffrey S. Guasto

Tufts University
"Navigation of magnetotactic bacteria is impaired by porous microstructure "
Using microfluidics experiments, we study the impact of porous microstructure on both the diffusive and directed transport of magnetotactic bacteria (MTB). MTBs are used as a model biological system because they share motility mechanisms with many other bacterial species, and their swimming direction is easily manipulated via an external magnetic field. We show that the cells’ effective diffusion coefficient without a magnetic field decreases markedly in the presence of porous microstructure compared to bulk fluid. Applying a guiding external field greatly enhances the mobility of the migrating cells through the media, an effect that is enhanced with increasing magnetic field strength. These results are an important step toward understanding the physical ecology of swimming cells in quiescent porous media as well as for controlling micro-robots in complex environments.
Keywords: swimming cells, active matter, transport, porous media

9. Dillavou, Sam; Shmuel Rubinstein, John Kolinski

Harvard University
"Virtual Frame Technique: Ultrafast Imaging with Any Camera"
Many phenomena of interest in nature and industry occur rapidly and are difficult and cost-prohibitive to visualize properly without specialized cameras. The Virtual Frame Technique (VFT), is a simple, useful, and accessible form of compressed sensing that increases the frame acquisition rate of any camera by several orders of magnitude by leveraging its dynamic range. VFT is a powerful tool for capturing rapid phenomenon where the dynamics facilitate a transition between two states, and are thus binary. We have used the VFT on a variety of processes including fracture, liquid, and solid, and biological interaction with a hard surface, and tape peeling. The performance of the VFT - even with a 'slow' camera - exceeds that of any commercial high speed camera not only in rate of imaging but also in field of view, for example, videos at 65MHz with 4MPx resolution. In principle, modern cell phones can achieve imaging rates of over a million frames per second using the VFT.
Keywords: high-speed imaging, technique, rapid phenomena, impact, fracture

10. Ellis, Perry; Giridhar Anand, David A. Weitz, Sharad Ramanathan

Harvard University
"Identifying pathogenic bacteria by phenotyping individual cells"
While estimates give the number of bacterial species on this earth to be greater than 10^10, we have currently cataloged fewer than 10^7. Of all the species we have cataloged, only 10^3 are pathogenic. As even a single pathogenic bacterium can colonize humans and cause disease, identifying pathogenic bacteria in natural sample has important consequences for human health. We work to address this problem using high-throughput methods. Our goal is to identify even a single pathogenic bacterium in a collection of 10^6 bacteria obtained from a natural sample. 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.

11. Feng, Yujun

Sichuan University
"Smart Viscoelastic Soft Materials for Enhancing Oil Recovery"
While more than 2/3 of crudes were trapped in the oil reservoirs, further increase of oil recovery was largely impeded due to the lack of promising materials used in harsh oil reservoir environment, such as high temperature and high salinity, acidic and basic conditions during CO2 and ASP flooding. Here we demonstrate the idea "smart soft materials" whose properesties especially viscoelasticity can comply and environmental situation and be tuned by the intrsinsic heat, salinity and pH exsited in the reservoirs.
Keywords: Smart Materrials; Soft Materials; Viscoelasticity; EOR

12. Filippov, Sergey; Leonid I. Kaberov, Bart Verbraeken, Anna Riabtseva, Richard Hoogenboom

Harvard University, SEAS
"Fluorophilic-lipophilic-hydrophilic poly-2-oxazolines block copolymers as MRI contrast agents: from synthesis to self-assembly"
This work focused on the synthesis and self-assembly of triphilic poly(2-oxazoline) triblock copolymers with high fluorine content towards our future aim of developing poly(2-oxazoline) MRI contrast agents. A highly fluorinated 2-substituted-2-oxazoline monomer, namely 2-(1H,1H,2H,2H-perfluorooctyl)-2-oxazoline was synthesized using the Grignard reaction. The polymerization kinetics of the synthesized monomer was studied and it was used for the preparation of triblock copolymers with hydrophilic 2-methyl-2-oxazoline, hydrophobic 2-octyl-2-oxazoline and fluorophilic blocks by Cationic Ring-Opening Polymerization yielding polymer with low relatively dispersity (1.2-1.4). The presence of the blocks with the different nature in one copolymer structure facilitated self-assembly of the copolymers in water and dimethylsulfoxide as observed by dynamic light scattering, cryotransmition electron microscopy, and small-angle neutron scattering. The nanoparticle morphology is strongly influenced by the order and length of each block and the nature of solvent, leading to nanoparticles with core-shell structure as confirmed by small angle neutron scattering. The reported poly(2-oxazoline) block copolymers with high fluorine content have high potential for future development of MRI contrast agents.
Keywords: poly(2-oxazoline)s, fluorine, self-assembly, DLS, SANS, Cryo-TEM, MRI

13. Garry, Ryan; Julie Brouchon, Kirk Mutafopulous, Dave Weitz

Harvard University
"High-throughput hydro-gel encapsulated cell sorting using Traveling Surface Acoustic Waves (TSAW)"
Isolation of immune cells with desired specificity is essential for the development of immunotherapy. These cells can be identified using a microfluidic in-drop assay: cells are encapsulated into water-in-oil picoliter droplets and a fluorescent signal is generated if the cell has the desired specificity.Based on this fluorescent signal, droplets containing the desired cells need to be sorted and isolated at high thoughput. We are developing a sorter using traveling surface acoustic waves. This technology has the potential to sort and isolate droplet at high-throughput and recovery while maintaining cell purity and viability.
Keywords: Traveling Sound Acoustic Wave (TSAW), Hydrogel

14. Giso, Mathew; Haoda Zhao, Patrick T. Spicer, Timothy J. Atherton

Tufts University
"Sculpting high aspect ratio particles from oil-in-water emulsions"
We present a process to sculpt elongated oil crystals from an oil-in-water emulsion. Oil droplets are crystallized in a controlled manner by reducing the temperature at a specific rate. With the addition of surfactants, it is possible to induce dewetting of the crystals by their own liquid phase. Tuning the relative rates of dewetting and crystallization produces a rich variety of crystal shapes in an easily scalable process using controlled interfacial hydrodynamics. We explain these experimental findings using a non-equilibrium Monte Carlo model that captures both the crystallization and dewetting processes. Our results reproduce the wide range of shapes seen in experiment.
Keywords: Emulsions, Colloids, Non-Equilibrium, Monte Carlo, Potts

15. Green, Yoav

Harvard T.H. Chan School of Public Health
"Current rectification in nanochannel systems"
Permselective nanochannels can rectify the electric current transported through them similar to solid-state diodes. The rectification is due to symmetry breaking related to distribution of the nanochannels surface charge as well the geometry. Here, I will explain what is the origin of the current rectification and review the numerous ways to rectify the current.
Keywords: Nanochannels, electrokinetics flows, concentration polarization

16. Guzman, Edward; A. Green, N. Clark, D. Walba

University of Colorado, Boulder
"Nano-phase Segregating Groups in Bent-Core SmAP Mesogens"
Since the rediscovery of bent-core liquid crystals and “Banana-mania” in the late 1990s and early 2000s, the interplay between chirality and polarity in smectic liquid crystals has been re-evaluated. In 2011, the first reported achiral orthogonal polar liquid crystal phase, the SmAPf, was reported by the Walba and Clark groups in the bent-core mesogen W586 [1]. Two key molecular design principles to induce the phase were the inclusion of only one “tail,” and the addition of a linear tricarbosilane moiety at the tail terminus, a combination that was expected to favor the formation of an orthogonal ferroelectric phase. A variety of derivatives and homologs of W586 were synthesized since to study the structure-property relationships of the phase. Prior to the start of this project the effects of the nano-phase segregating group have on SmAP phase properties had not been investigated, motivating studies of the structural features responsible for the formation of ferro or antiferroelectric SmAP phases. A series of SmAP mesogens with different carbosilane moieties have been synthesized and studied to probe the role nano-phase segregating groups have on phase formation and phase properties. [1] R. A. Reddy, C. Zhu, R. Shao, E. Korblova, T. Gong, Y. Shen, E. Garcia, M. A. Glaser, J. E. Maclennan, D. M. Walba, and N. A. Clark, Science 332, 72- 77(2011).
Keywords: Liquid Crystals, Ferroelectric, Antiferroelectric

17. Haney, Bobby Tyrell; Joerg Werner, David A. Weitz, Subramanian Ramakrishnan

Florida A&M University, Harvard University
"Stable Pickering Emulsions Using Amphiphilic Microgel Particles via Microfluidics "
Pickering emulsions are important in systems where controlled confinement of an oil or water phase is needed. For example, micro-capsules incased by particles can serve as rigid vehicles for drugs or precious food ingredients. These coated emulsions can harbor oils in water or even water in oils. Nonetheless, the stability of the Pickering emulsions depend on the wetting properties of the particle. Amphiphilic, “Janus”, particles with two distinct surface chemistries are ideal for stabilizing emulsions due to the ability to tune wetting properties by changing the chemistry. Microfluidic techniques are used to create Janus particles to form stable water in oil as well as oil in water Pickering emulsions. These particles are composed of polyethylene glycol hydrogel as the hydrophilic side and polypropylene glycol as the hydrophobic side. The hydrogel and hydrophobic polymer’s abilities to respectively absorb the water and oil in an emulsion system enable the particles stronger attachment to the oil-water interface. The flowrates in a glass capillary device are varied to demonstrate complete control over particle sizes and hydrophilic to hydrophobic domain ratios. Using UV light, these droplets are cross-linked via photo-polymerization to form monodispersed particles. By manipulating the inner-phase flowrate, larger sized particles are fabricated which give larger stable emulsions. By adjusting the ratio of inner-phase hydrophilic fluid to hydrophobic fluid, the sizes of the two individual sections of the Janus particle are controlled. Emulsion stability is tested via centrifugation. Use of these larger particles to stabilize the emulsions allows direct visual observation, which lead to better understanding of how factors such as the particle orientations at the L-L interface affect Pickering emulsion stability.
Keywords: Pickering Emulsion, Hydrogel, Microfluidics, Amphiphilic

18. Huang, Tina; Laura Arriaga, David Weitz

Harvard University
"Microfluidic Fabrication of Asymmetric Lipid 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. One interesting type of lipid vesicle is the asymmetric vesicle, in which its bilayer is composed of two dissimilar lipid monolayers. 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 lipid 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 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 vesicles could open a new door in the field lipid based drug delivery systems.
Keywords: Lipid Vesicle, Cell Membrane, Microfluidics

19. Ionkin, Nikolay P; Daniel Harris

Brown University
"A versatile 3D-printed droplet-on-demand generator"
There is a rapid and persistent growth in the study of dynamical behavior of droplets, however, the precise generation of these droplets over a range of sizes can be challenging. A versatile 3D- printed droplet-on-demand generator is presented for laboratory use. The design is modeled off of an existing design [Harris et al., Experiments in Fluids, 56:83 (2015)] but is tested with an extended range of working fluids and the manufacturing process is greatly simplified by 3D-printing the principal components. The present device is tested with deionized water and water-glycerol mixtures, and was reliably able to produce single droplets-on-demand of diameters 0.65-1.32 mm with an overall variability of less than 1%.
Keywords: Drops, Droplet-on-demand, Piezoelectric, Rapid prototyping

20. Jewel, Rausan Atik; Ram Sharma, Arshad Kudrolli

Clark University
"Finger like instability due to granular beads in miscible fluids"
We discuss fingering instability due to accumulation of granular beads in the Hele-Shaw cell. A neutrally buoyant mixture of polystyrene beads and salt water is injected into a Hele-Shaw filled with water of different densities. The invading fluid front is stable if the densities of injecting fluid and the ambient fluid are same. A small difference in the densities give rise to instability due to particle deposition. Accumulation of beads in the front makes a band with a higher concentration of particles giving rise to a viscosity difference. This band fingers creating similar patterns to the Saffman-Taylor instability of low viscosity fluid pushed into a higher viscosity fluid.

21. Jiang, Nan; Guoliang Ying, Yu Shrike Zhang*

Harvard University
"Three-dimensional (3D) Bioprinted Porous Hydrogels by Using Aqueous Two-Phase Emulsion Bioink"
The 3D bioprinting technology has been unprecedentedly progressed during the past decades in the field of regenerative medicine and disease modeling. By using programmable and customizable platforms, the 3D bioprinting technology enables engineered cell-laden constructs in a spatial-controllable manner. However, the conventional 3D encapsulated cells are always restricted in spreading and proliferation by the dense hydrogels. In this talk, we will introduce a novel approach to construct a 3D bioprinted porous cell-laden hydrogel by using a newly developed bioink. The bioink is consist of two aqueous phases, namely cell-laden gelatin methacryloyl (GelMA) solution and poly(ethylene oxide) (PEO) solution. The interconnected micropores within the 3D bioprinted cell-laden constructs were formed by photocrosslinking and subsequent PEO removal process. Both of extrusion bioprinting or digital micromirror device-based stereolithographic bioprinting allow for patterned cell-laden hydrogel constructs with high cell viability, spreading and proliferation. This new 3D bioprinting technique offers a robust and versatile platform to modeling human tissues.
Keywords: Aqueous two-phase emulsion, 3D bioprinting, bioink, porous hydrogel, gelatin methacryloyl (GelMA), tissue engineering

22. Kim, Jeong-Hyun; Daniel M. Harris

Brown University
"Deposition of micrometric water droplets on rough hydrophobic surfaces"
In this talk, we present new experimental observations of a droplet sliding down an inclined, rough hydrophobic surface. Periodic micrometer-scale grooves were fabricated on smooth PDMS surfaces using a commercial laser cutter. A millimetric water droplet was then deposited on the inclined surface and the resulting contact-line dynamics were visualized using high-speed imaging. We found that a micro-capillary bridge was formed at each structure, which ultimately ruptured at the trailing edge of the sliding water droplet. This detachment mechanism resulted in the deposition of a trail of uniform micrometric droplets on top of the periodic substrate. The size of the isolated droplets was sensitive to both the droplet sliding velocity and the dimensions of the grooved structures; in particular, the size of the droplet increases with increasing droplet velocity as well as the spacing between the structures.

23. Kim, Seongsoo; Dohyun Kim, Jongwoo Kim, Sangmin An, Wonho Jhe

Harvard University
"Experimental verification of the curvature dependent surface tension in nanoscale"
Surface tension plays crucial role in diverse fields of science such as microfluidics, granular media and colloidal science. Despite its importance, physical understanding of the surface tension at molecular scale is still in open question. In 1948, Tolman predicted that pure water droplet would have lower surface tension than the bulk value when its radius of curvature gets down to few nanometers. However, its direct experimental verification was lacked due to the difficulty of observing single nanometer-size droplet. Here, we overcome this limitation by capturing the first moment of phase transition. We use quartz tuning fork-based atomic force microscopy and measure the critical distance at which single meniscus is condensed between two hydrophilic surfaces. By having statistical analysis of the critical distance at different humidity, we measured a slight deviation from the classical nucleation theory described as the Kelvin equation and found the deviation can be accounted by the curvature dependent surface tension. We experimentally determined the Tolman length, an important parameter for curvature dependent surface tension. Our results may provide deep understanding of the molecular mechanism of the surface tension and its effect on general nucleation phenomena.
Keywords: surface tension, curvature effect, nucleation, liquid-vapor phase transition

24. LaMascus, Parker; Lisa Lee, Jovana Andrejovic, Shmuel Rubinstein, Chris Rycroft

Harvard SEAS
"Exploring the State Variable of Crumpling Paper: Scaling and Machine Learning"
Crumpled paper, though a commonplace occurrence, is a paradigm of physical complexity. Work by Gottesman, Andrejevic, et al has demonstrated that, for repeatedly crumpled sheets of paper, the evolution of their damage networks can be modeled using "mileage", a state variable that is the sum of crease length for all prior crumples. This work extends their findings by testing this state variable in new environments -- by changing the length scales of the experiments, we hypothesize that the mileage will vary by inverse proportion. These findings have application in complex systems like protein folding, plate tectonics, and the buckling of thin shells.
Keywords: complex physics; machine learning

25. Lee, Lisa

Harvard SEAS
"Growing and healing of air-liquid biofilms"
Biofilms are structured communities of bacteria that exhibit complex spatio-temporal dynamics. In liquid media, Bacillus subtilis produces an opaque floating biofilm, or a pellicle. Biofilms are generally associated with an interface, but the ability of Bacillus subtilis to swim means the bacteria are additionally able to reside within the liquid phase. We report a well-defined sequence of developmental events that occurs in the liquid phase for a growing pellicle. We also study the ability of these floating biofilms to repair damage imposed upon them.

26. Lima, Nicolle; Shima Parsa, Marcio Carvalho

"Foam formation during drainage of a surfactant solution by gas injection"
Foam can be used in enhanced oil recovery to maximize oil production and solve problems caused by either a thief zone or gravity override. The presence of liquid lamellae between gas bubbles in the foam reduces the gas mobility; the resistance imposed by drag on moving lamellae resembles a shear-thinning viscosity behavior and leads to a more stable oil displacement flow. The flow mobility is a function of the pore geometry and foam properties. Foams can be injected in the reservoir or produced in-situ in the gas-liquid flow through the pore space. The goal of this research is to study foam formation during drainage of a two- dimensional porous media glass model by visualizing the pore scale displacement flow of a surfactant solution by injected gas. Image processing is used to study the evolution of the phase distribution and foam characteristics as a function of pore space geometry and flow conditions.
Keywords: foam, surfactant, porous media, EOR

27. McKeown, Ryan; Rodolfo Ostilla-Monico, Alain Pumir, Michael Brenner, Shmuel Rubinstein

Harvard University
"From Rings to Smoke: Visualizing the Breakdown of Colliding Vortex Rings "
The turbulent cascade, or the means by which the energy of a flow is conveyed from large to small scales, is governed by the interactions between vortices over many scales. In order to better understand the mechanisms that govern the close-range interactions between vortices, we experimentally examine the head-on collision of two vortex rings. By seeding the vortex rings with fluorescent dye and imaging their collision with a high-speed scanning laser sheet, we visualize the breakdown dynamics of the flow in full 3D. For weak collisions at low Reynolds numbers, the colliding rings stretch radially, develop long-wavelength perturbations, and reconnect into a tiara of secondary vortex rings. Conversely, for violent collisions at high Reynolds numbers, the rings rapidly develop short-wavelength perturbations as they stretch radially before erupting into a turbulent cloud of fine-scale vortex filaments. Initiated by these instabilities, the colliding vortices break down through various distinct processes and lead to the generation of small-scale flow structures. Thus, the close-range interactions of the colliding vortices could provide new insights into the mechanistic underpinnings of the turbulent cascade.
Keywords: Vortex Rings, Vortex Dynamics, Turbulence

28. Meles, Abraham

Navajo Technical University
"Physics in Navajo Technical University"
I, with my Physics students at the Navajo Technical University are interested in Bio-Physics of cell membranes, in analysing contamination of Uranium in abandoned mines, and Nuclear physics.

29. Menesses, Mark; Matthieu Roche, Laurent Royon, James C. Bird

Boston University, Universite Paris Diderot
"Evaporation induced stabilization of bubbles at the free surface of volatile liquids"
When a bubble rises to the free surface of a liquid, a thin film is formed separating the gas within the bubble from the outside atmosphere. The persistence of this film is typically determined by a balance of viscous stresses with gravitational and capillary drainage. The presence of surfactants at the interfaces can alter these drainage dynamics; however, the rupture of this film is traditionally considered unavoidable. Here we present air bubbles at the free surfaces of liquids which appear to defy these traditional drainage rules and can avoid rupture, persisting for hours until dissolution. We find that liquid volatility plays a key role in stabilizing in these bubbles.
Keywords: thermocapillary flow, surface bubble

30. Nawar, Saraf ; Joerg Werner, Wenshan Zheng, David Weitz

Harvard SEAS
"Wettability Patterning of PDMS Microfluidic Dropmakers using Surfactants"
Microfluidics enables facile fabrication of multiple emulsions with precise control over structural parameters. A typical material of choice for making microfluidic chips is polydimethylsiloxane (PDMS), given its ease of chip prototyping. PDMS, however, is hydrophobic, and as such, in order to produce multiple emulsions composed of different liquid phases, requires spatial wettability patterning of hydrophilic regions. Here, we use hydrophilic surfactants to modify the bulk properties of PDMS to render its surface hydrophilic. We incorporate this surfactant-modified PDMS as part of PDMS double emulsion dropmakers with spatially patterned hydrophilic wettability, which enables the production of monodisperse water-in-oil-in-water double emulsions. Our approach for the spatial patterning of microchannel hydrophilicity using surfactant-modified PDMS enables facile modification of parallel microfluidic dropmakers, thus providing us with a viable approach for scaling up the production of multiple emulsions.
Keywords: surfactants, microfluidics, wettability

31. Nguyen, Khoi; Madhusudhan Venkadesan

"Fluid-to-solid transition in muscles"
Muscle exhibits either solid-like or fluid-like properties depending on the biomechanical task at hand. For example, an activated muscle behaves as a solid-like strut to maintain body posture and a minimally activated muscle yields against its antagonist muscle as a fluid to allow for rapid movement. Both solid-like and fluid-like behaviors result from actomyosin crossbridges that cycle between a stress-bearing attached state and a stress-dissipating detached state. An activation-dependent fluid-to-solid transition of muscles is inevitable given these behavioral examples, but how it may arise from crossbridge dynamics remains a poorly recognized and studied physical process. We find that current mean-field models of Huxley-based crossbridges fail to capture the transition, and thus postulate in analogy to jamming transitions that potential nonequilibrium crossbridge dynamics underlie a muscle fluid-to-solid transition. Furthermore, an individual muscle cell containing thousands of crossbridges is a contractile cell with minimal non-contractile elements. It may therefore present itself as a tractable system to view the underlying physics of fluid-to-solid transitions in active and out-of-equilibrium systems.
Keywords: Muscles, crossbridges, fluid-to-solid

32. Owens, Crystal; Gareth H. McKinley, A. John Hart

"3D printing of custom, disposable vanes for measurements of yield-stress fluids"
We constructed vanes with an assortment of typical and novel geometries for rheological measurements using stereolithographic 3D printing (Form2, Formlabs Inc) which works by UV-crosslinking a methacrylate-based liquid photopolymer to build a solid object layer by layer. The SLA printing process permits straightforward creation of complex structures with dimensional resolution <200 µm, over several cm in length, from materials having wide chemical compatibility and high mechanical stability. The low cost of production allows vanes to be disposable, allowing measurement of caustic materials such as battery slurries. Enabled by the 3D printing process, we introduce novel geometries designed to improve the typical 4-armed vane by creating a more homogeneous shear profile in the unknown test material, including a fractal structure and a ribbed hollow cylinder. The end of each vane connects to the spindle of a rheometer (Discovery Hybrid, TA Instruments) via an M4 helicoil threaded insert. A 3D printed cup with a ribbed inner surface is used to hold the sample fluid, and disassembles for ease of cleaning. Finally, we designed and compared conversion equations that translate measured torque to material shear stress as a function of the vane geometry, and measured viscosity of silicone oils within 5% of the true value for all vanes. We reproduced material flow curves for complex fluids with mean average error below 2% when compared to baseline flow curves measured with a cone and plate geometry, showing ultimately that the designs are useful for experiments, and not just made in vane.
Keywords: Rheology, vanes, yield stress


The recalcitrance exhibit by biofilm-associated infections, with sessile persister cells (PC) surviving in the presence of high concentrations of antifungal drugs (ATF), leads to treatment failure and infection recurrence. Novel strategies are necessary to achieve the complete eradication of biofilms and one promising approach to combating is based on nanotechnology. In this context, ATF activity of metallic nanoparticles (NP) was studied. Gold (Au) NP showed a percentage of biofilm reduction (% R) up to 90%, with an overproduction of reactive metabolites, mainly ROS. Antioxidant systems activation was not enough to avoid oxidative imbalance and biomass reduction. Comparison with Au NP conjugated to the antioxidant molecule cysteine (Au-cis NP), which showed a lower activity than the Au NP, evidenced a direct relationship between the observed ATF effect and the oxidative stress induction as a mechanism of action of NP. Finally, biomass and EPS matrix reduction and the impact on cellular morphology, was demonstrated by Scanning Electron Microscopy (SEM), observing multiple cell wall protuberances of sessile cells treated with Au NP.

34. Parsa, Shima; David Weitz

Harvard University
"Emulsions in porous media"
We measure the cooperative dynamics of mono-disperse emulsion droplets in porous media. Using particle tracking and confocal microscopy we track each drop and its impact on the surrounding pores and eventually long-range correlation between pores.
Keywords: Emulsion, Porous media

35. Saenz, Pedro; Jörn Dunkel, John Bush

"Spin lattices of walking droplets"
Understanding the self-organization principles and collective dynamics of non-equilibrium matter remains a major challenge despite considerable progress over the last decade. In this talk, I will introduce a hydrodynamic analog system that allows us to investigate simultaneously the wave-mediated self-propulsion and interactions of effective spin degrees of freedom. Millimetric liquid droplets can walk across the surface of a vibrating fluid bath, self-propelled through a resonant interaction with their own guiding wave fields. A walking droplet, or `walker’, may be trapped by a submerged circular well at the bottom of the fluid bath, leading to a clockwise or counter-clockwise angular motion centered at the well. When a collection of such wells is arranged in a 1D or 2D lattice geometry, a thin fluid layer between wells enables wave-mediated interactions between neighboring walkers. Through experiments and mathematical modeling, we demonstrate the spontaneous emergence of coherent droplet rotation dynamics for different types of lattices. For sufficiently strong pair-coupling, wave interactions between neighboring droplets may induce local spin flips leading to ferromagnetic or antiferromagnetic order. Transitions between these two forms of order can be controlled by tuning the lattice parameters or by imposing a Coriolis force mimicking an external magnetic field. More generally, our results reveal a number of surprising parallels between the collective spin dynamics of wave-driven droplets and known phases of classical condensed matter systems. This suggests that our hydrodynamic analog system can be used to explore universal aspects of active matter and wave-mediated particle interactions, including spin-wave propagation and topologically protected dynamics far from equilibrium.
Keywords: walking droplets, collective dynamics

36. Sharma, Dipti; J C MacDonald, N. Mehta

"Multiple Kinetics of New Generation Glassy Alloy Se76Te20Sn2Cd2"
This current research reports multiple activated kinetics of a New Generation Glassy Alloy Se76Te20Sn2Cd2. This glassy alloy contains Sn and Cd as guest members by 2% of composition made by quenching technique under vacuum. Calorimetric technique was used to study thermal behavior of material and it was found that multiple glass transition, crystallization, melting transition appeared on heating and multiple cool crystallization was also observed. When SeTe based glassy alloys were studied with either Sn or Cd, not all transitions appeared as multiple peaks/dips but in the present composition each transition was appeared multiple times. Further research is under process and we like to show our current data we observed so far.
Keywords: Calorimetry, Glassy Alloys, New Generation Material

37. Shayegan, Marjan; Yinan Shen, David Weitz

Postdoctoral fellow
"Active multi-point microrheology of biopolymer networks "
Rheology is the field that can describe viscoelastic behavior of a material in response to applied force or deformation. Active microrheology is a technique in which particles can be manipulated by an external force, in contrast to the passive one, in which thermal fluctuations of particles are recorded. One experimental approach to active microrheology uses optical tweezers, which trap a μm-sized particle located within the material and excite it with an oscillating force. In this study, we use optical tweezers to oscillate a particle inside reconstituted biopolymer networks and by measuring the response of multiple neighboring particles to the excitation of a reference particle, we are able to measure the frequency-dependent viscoelastic response of the material at various length scales.

38. Shen, Yinan; Marjan Shayegan, Arturo Moncho, Hui Li, Huayin Wu, Dianzhuo Wang, Weichao Shi, Songlei Liu, Jing Xia, Liheng Cai, Meng Zhang, Ruihua Ding, Frederick MacKintosh, David A. Weitz

Harvard University Weitz Lab
"Microrheology of Microtubule-Actin-Vimentin Composite Cytoskeletal Networks"
Mechanics of the cytoskeleton is known to be responsible for maintaining cell mechanical integrity and determining cellular functions. We develop a method that enables us to reconstruct a three-component in-vitro network composed of intermediate filaments (vimentin filaments), microtubules and F-actin filaments, which are three fundamental cytoskeletal components. This composition is more physiologically relevant compared with any of the previously reconstituted cytoskeletal networks, which are composed of one or two components only. We investigate the structure and mechanical properties of this multicomponent cytoskeletal network using a combination of several microscopies and microrheology. We show that vimentin filaments couple the other cytoskeletal filaments together by introducing steric constraints between cytoskeletal polymers; these inter-network interactions extend the composite network elastic behavior to a longer time scale, prolong the network relaxation time, and facilitate the stress propagation within the network. These findings are helpful to deepen our understanding of the mechanical role vimentin plays in regulating cellular activities.
Keywords: Cytoskeleton, Microrheology

39. Shen, Zhiqiang; Huilin Ye, Martin Kroger, Ying Li

University of Connecticut
"Aggregation of polyethylene glycol polymers suppresses receptor-mediated endocytosis of PEGylated liposomes"
The PEGylated liposome, composed of an aqueous core and a fluid state lipid bilayer shell, is one of the few Food and Drug Administration (FDA) approved drug delivery platforms. To prevent the absorption of serum proteins, the surface of a liposome is decorated by hydrophilic and bio-compatible polyethylene glycol (PEG) polymers, which can significantly extend the blood circulation time of liposomes. In this work, with the help of dissipative particle dynamics (DPD) simulations, we explore how the tethered PEG polymers will affect the membrane wrapping process of PEGylated liposomes during endocytosis. Specifically, we compare the membrane wrapping process of a PEGylated rigid nanoparticle (NP) with a PEGylated liposome under identical conditions. Due to the mobility of grafted PEG polymers on the liposome's surface, the complete wrapping of a PEGylated liposome can be dramatically delayed and blocked, in comparison with a PEGylated rigid NP. For the first time, we observe the aggregation of PEG polymers in the contact region between a PEGylated liposome and the membrane, which in turn leads to a ligand-free region on the surface of the liposome during endocytosis. Subsequently, the partially wrapped PEGylated liposome can be bounced back to a less wrapped state. Through free energy analysis, we find that the aggregation of PEG polymers during the membrane wrapping process of a PEGylated liposome introduces a dramatic free energy penalty of about ∼800kBT, which is almost twice that of a PEGylated rigid NP. Here kB and T are the Boltzmann constant and temperature, respectively. Such a large energy barrier and the existence of a ligand-free region on the surface of PEGlylated liposomes prevent their membrane wrapping, thereby reducing the chance of internalization by tumor cells. Therefore, our DPD simulation results provide a possible explanation for the inefficient cellular uptake of PEGylated liposomes. In addition, we suggest that by increasing the repulsive interactions between grafted PEG polymers it might be possible to limit their aggregation, and in turn, facilitate the internalization of PEGylated liposomes. The current study provides fundamental insights into the endocytosis of PEGylated liposomes, which could help to design this platform with high efficacy for drug delivery.
Keywords: PEGylated Liposome, endocytosis

40. Sintes, Guillaume; Philippe Bourrianne, Irmgard Bischofberger

"Drying of colloidal droplets: the influence of particle concentration"
The interplay between the microscopic transport of particles and macroscopic mechanical instabilities occurring during the evaporation of a colloidal suspension leads to a rich variety of final deposit patterns. At low volume fraction of colloids, the pinning of the contact line induces the well-known coffee-stain effect. At higher volume fraction, the contact line is no longer pinned, which leads to a more homogeneous particle deposition and to the formation of radial cracks. We investigate the transition between these two regimes over a large range of volume fractions and show the emergence of two additional drying patterns.
Keywords: Drying, Colloidal droplet

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

Harvard universty
"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: Keywords: White biotechnology, bio-production, drop micro-reactors, microfluidics

42. Tanjeem, Nabila; Vinothan N. Manoharan

Harvard University
"2D crystal in confinement: How non-equilibrium defects appear from equilibrium crystal growth "
To understand the effect of confinement in crystal growth, we studied colloidal crystals confined to the surface of a finite sized cylinder. The finite size constraint imposes a periodic boundary condition on a maximally packed crystal on a cylinder surface. The effect of this constraint was previously explored using theory and simulation, predicting ground state crystal structure with chirality and line-slip defects. We demonstrate an experimental system where submicron-sized colloidal spheres self-assemble into hexagonal lattices on a silica fiber with a diameter of a few micrometers. We confirmed the formation of chirality and line-slips defects. We also found that most line-slip defects have kinks in them which can be recognized from a discontinuity in the line-slip structure. The number of kinks in a line-slip defect does not change significantly over long time, but instead shows small fluctuations. We show how the roughness of a 2D crystal boundary is responsible for the formation of the kinks and find that the average kink density in a line-slip defect can be related to the average roughness of equilibrium 2D crystal on a flat surface.
Keywords: Colloidal crystal, cylinder, line-slip defect

43. Terdik, Zsolt; David Weitz, Frans Spaepen

Harvard University
"Stresses and Strains in Colloidal Glass"
Micron-sized hard-sphere colloidal particles can be used to form dense amorphous packings. Due to the large size and slow dynamics of colloidal particles, confocal microscopy can be used to investigate the 3D structure and dynamics of these glasses at the particle level. Previous studies have directly visualized both the inhomogeneous particle level strains in deformed colloidal glasses (i.e. STZs), and surrounding continuum strain fields. Measuring the stress in colloidal glasses during deformation, however, is a significant challenge due to the large size and thermal interaction energies, colloidal solids have very small elastic moduli. We introduce a new technique, traction force rheology, to directly measure the mechanical response of colloidal glasses while simultaneously visualizing the microstructure using a confocal microscope. The method consists of a bilayer of colloidal glass atop a well calibrated soft polymer gel of slightly greater shear modulus. The composite bilayer is sheared and the shear stresses are inferred from the displacement of embedded tracer particles in the calibrated polymer gel. Using these stress measurements, we show that under cyclic applied shear the colloidal glass goes through a sequence of reversible and irreversible microscopic rearrangements which are related to the spatially correlated heterogeneities in the stress field.

44. Thiele, Julian

Leibniz Institute of Polymer Research Dresden
"Design of microscopic polymer materials by droplet microfluidics and additive manufacturing for cell-free biotechnology"
The structural diversity of natural and synthetic macromolecular building blocks allows for designing polymer materials with tailored size, shape, porosity, degradability, stimuli-sensitivity and stiffness, which have thus evolved as promising experimental platform in cell biology and cell-free biotechnology. However, to process macromolecular building blocks into well-defined polymer materials with feature sizes from 1 to 100 µm, and spatial control over physicochemical / mechanical properties on the same length scale requires innovative fabrication strategies. On this account, we utilize two methods: droplet microfluidics to fabricate polymer microgels swollen in water, and 3D-printing based on micro-stereolithography to fabricate polymer materials with micron-scale precision in bulk. Focusing on applications in cell-free biotechnology, we combine these methods to design experimental platforms that reflect key aspects of cellular life, and allow for controlling biochemical reactions in a tailored microenvironment with reduced energy consumption and undesired side reactions.
Keywords: microfluidics, micro-stereolithography, cell-free protein synthesis

45. Wan, Hao; Maria Santore

UMass Amherst
"The Interplay of Tension, Curvature, and Morphology in Lipid Membranes Containing Coexisting Fluid and Solid Domains "
Cell membranes, which are made of delicate structure of lipid bilayer with embedded protein, are vital to the life of the cell. Artificial lipid bilayer made of phospholipids is an ideal model to study the behavior of biological membranes. Here, we study the complicated phase separation behavior of lipid membranes. GUVs that contain coexisting solid and fluid membrane domains at ambient temperature, are used as the model membrane system. We will study how processing parameter such as thermal history would influence domain formation and domain morphology. A better understanding of the principles of the morphology development of those multi-component lipid membranes would be potentially useful in life science related areas such as drug delivery, tissue scaffolding applications or energy application.
Keywords: Lipid membranes, Phase seperate pattern, Tension

46. Wang, Xun; Karen Kasza

Columbia University
"The role of cell-cell adhesion in tissue mechanics and morphogenesis"
During development, simple epithelia reorganize and remodel into functional tissues. In Drosophila, the embryonic epithelium doubles in length to elongate the embryo body axis in just 30 minutes. Cell-cell adhesion and contractile tension are thought to be key parameters in controlling tissue mechanics. However, it remains unclear how the balance between adhesion and tension determines the structure and mechanics of tissues. To gain insight, we systematically modulate cell-cell adhesion in Drosophila embryos. We find that modulating cell-cell adhesion influences cell shapes before the onset of axis elongation as well as cell rearrangement during elongation. Our studies of tissue mechanics are an essential step for building models of morphogenesis.
Keywords: morphogenesis, E-cadherin, tissue mechanics, cell-cell adhesion

47. Werner, Joerg; Guanming Lao, David Weitz

SEAS, Harvard University
"Double emulsion drops in electric fields"
Electro-coalescence of water drops dispersed in oil, so-called water-in-oil (W/O) emulsions, is a well known phenomena that is employed in de-emulsification processes on the industrial scale. Complex, multiple emulsions, however, such as oil-in-water-in-oil (O/W/O) double emulsion drops resist de-emulsification and complete phase separation during electro-coalescence. We set out to study the behavior of double emulsion drops in electric fields under controlled conditions in droplet microfluidc devices. Droplet microfluidics enable the production of homogeneous complex emulsion drops with control over size, oil-to-water ratio, electric field strength, and residence time.
Keywords: Microfluidics, complex emulsions, electro-coalescence

48. Xiao, Gao; Junling Guo,Yongchen Wang

Harvard University
"Biomass - inspired Multifunctional Materials"
Nature excels in the design and synthesis of complex and hierarchical hybrid (organic/inorganic) materials for various functional purposes. Such hybrid biomass like bone, collagen fiber and plant polyphenols with unique physicochemical and biological properties have inspired researchers to mimic their structure and function for various applications. A library of functional biomass based metal-phenolic network (MPN) nanostructured porous fibers, membranes,biohybrids and anticancer drug was prepared from the coordination between a phenolic ligand and a range of metal ions. Furthermore, the biomass-based polyphenolic particle functionalization was discoved to generate a highly versatile and effective methodology to prepare a large variety superstructures assembled from a wide range of building blocks. The generic nature of this method led to a large family of modularly assembled superstructures including core-satellite, hollow, hierarchically organized supraparticles and inorganic-biological hybrids. In functional aspects, the biomss-based polyphenolic materials were tailored for catalysis, seawater uranium extraction, biosythesis, advanced drug delivery, positron emission tomography (PET), magnetic resonance imaging (MRI), etc.
Keywords: Polyphenols, Biomass, Metal-Phenolic Networks

49. Xiao, Gao; Junling Guo,Xuepin Liao, Bi Shi, Wei Luo, Ke Li, Neel S. Joshi, Daniel G. Nocera, David A. Weitz

Weitz Lab, Harvard University
"Biomass - inspired Multifunctional Materials"
Nature excels in the design and synthesis of complex and hierarchical hybrid (organic/inorganic) materials for various functional purposes. Such hybrid biomass like bone, collagen fiber and plant polyphenols with unique physicochemical and biological properties have inspired researchers to mimic their structure and function for various applications. A library of functional biomass based metal-phenolic network (MPN) nanostructured porous fibers, membranes,biohybrids and anticancer drug was prepared from the coordination between a phenolic ligand and a range of metal ions. Furthermore, the biomass-based phenolic particle functionalization was discoved to generate a highly versatile and effective methodology to prepare a large variety superstructures assembled from a wide range of building blocks. The generic nature of this method led to a large family of modularly assembled superstructures including core-satellite, hollow, hierarchically organized supraparticles and inorganic-biological hybrids. In functional aspects, the biomss-based phenolic materials were tailored for catalysis, seawater uranium extraction, biosythesis, advanced drug delivery, positron emission tomography (PET), magnetic resonance imaging (MRI), etc.
Keywords: polyphenols, biomass, inorganic-biological hybrids, hierarchically superstructures, metal-phenolic networks,

50. Xie, Zhaoyu; Timothy J. Atherton

Tufts University
"Exploiting percolation transition in Thomson problem"
Thomson problem and its generalization can help us understand the crystallography of particles constrained on a sphere with repulsive interaction. Classical Thomson problem studies the lowest energy structure of congruent particles distributed on a sphere under Coulomb potential. Previous research shows that for small number of particles there exists 12 five-fold disclinations locating at the corners of an icosahedron while for large number of particles excess dislocations appear and form grain boundaries to reduce the elastic energy. This can also be applied to the generalized Thomson problem where the charges interact through other repulsive potential. In this research, we focus on particles interacting through Coulomb potential but change the charge of half of the particles instead of congruent ones. As the charge ratio increase, we find out that more defects appear and tend to form one whole network. We verify that this growth of defect network can be explained by percolation theory in 2D flat space.
Keywords: Thomson problem, percolation

51. Xin, Weiyue; Maria Santore

UMass Amherst
"The impact of curvature on solid domains in multicomponent phospholipid vesicles."
Multicomponent phospholipid membranes have long held scientific interest as an ideal model to study the complex phase behavior of biological membranes and their utility as drug delivery agents. The control of molecular organization is important because solid type and the domain shape will determine the ability of membrane diffusion, affect transportation along the membrane, also curvature at domain edges can influence biochemical reaction. Here I am using curvature to pattern patch-shaped membrane-integral solid domains on multicomponent phospholipid vesicles.
Keywords: Membranes, Vesicles phase separation

52. Yamani, Sami; Gareth McKinley; Irmgard Bischofberger

Massachusetts Institute of Technology
"Submerged turbulent jets of polymer solutions"
Dilute synthetic polymer solutions have been shown to reduce turbulent drag in pipelines and around marine vehicles. Water-soluble biopolymers such as flax seed mucilage extracts have the potential to serve as cheap and environmentally friendly alternatives to synthetic polymers. In this work, we employ Schlieren imaging to unveil the mixing dynamics and recirculating regions that develop in turbulent jets of dilute aqueous polymer solutions in quiescent water. At the interface of the viscoelastic jet and water, a free shear boundary layer develops leading to momentum transfer between the two fluids. We demonstrate the impact of viscoelasticity on this momentum transfer and evaluate the performance of both synthetic polymers and biopolymers in dampening turbulent vortical structures.
Keywords: Schlieren imaging, Dilute polymer solutions, mixing, turbulence, biopolymers

53. Yang, Xiaoyu; Xiaochen Ma, Ganggang Chang, Ge Tian

SEAS, Harvard University
"Strong host-guest interaction induced supported amorphous/ crystalline hetero-phase Pd nanoclusters for highly efficient performance in tandem catalysis"
The tandem reaction processes that incorporate several reactions to give the final product in one operation have recently emerged as a promising field for advancing modern and sustainable chemistry due to the avoidance of separation, purification, and transfer processes of costly intermediates produced in each step. Acid, base and noble metal sites have been widely used as the catalytic active sites in one-pot tandem catalysis, however, the integration of different active site in to a single catalyst has been a great challenge considering the maximum usage of each active sites. Especially, for noble metal sites, the size, shape, composition, interaction with support/reactants and so on, can significantly affect its catalytic performance. In the present work, a strong host-guest interaction strategy has been employed to synthesis an ultrafine supported Pd nanoclusters, which showed an interesting amorphous/crystalline hetero-phase structure, and was first observed in sole metal nanoparticles as far as we know. When applied our catalyst in one-pot Knoevenagel condensation-hydrogenation reactions, our material showed excellent catalytic activities both in conversion and selectivity in terms of its ultralow Pd loading (0.14 wt%) and mild reaction conditions (atmospheric temperature and pressure), which was ascribed to the amorphous/crystalline hetero-phase structure induced by strong interaction between host and Pd nanoclusters. More importantly, a significantly higher structure and performance stability of our materials was also presented, and a unique restored property of amorphous/crystalline hetero-phase structure during H2 reducing was discovered. The successful fabrication of high performance bifunctional catalyst pave the way to new opportunities on design and preparation of highly stable metal supported composite materials, especially for advanced catalysis applications carried out under mild and green conditions.
Keywords: MOFs, tandem catalysis, amorphous nanoclusters, host-guest interaction

54. Yuan, Yuan; Jing Xia, Brouchon Julie, John Heyman, David Weitz

Harvard University
"Droplet-based assay for activated immune cell detection and sorting"
Immune system is a defense system of our body to fight against cancer or infections. In our blood, there is a huge number of immune cells, about 7 billion immune cells per liter blood, while only a small fraction of cells would be activated when pathogen comes. Insufficient activation usually accounts for severe diseases like cancer and viral infections, so we really need a good way to detect and sort activated immune cells to take full advantage of the immune system. Based on our microfluidic droplet technique, we developed a quick assay by co-encapsulating individual immune cells and target cells into one drop. On one hand, immune cells are coat with a bispecific antibody, which can be coated on the surface of immune cells and thus the secreted cytokines could be captured and enriched on the surface of the exact activated 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

55. Zhang, Liyuan; Giridhar Anand,Sharad Ramanathan, David Mooney, David Weitz

Harvard University
"Explore embryogenesis using microcapsules"
Stem cell encapsulation holds tremendous promise either as an in-vitro model recapitulating an early embryonic development or a renewable source of therapeutic useful cells. The current way to study embryonic development is randomly culturing stem cell on the premise that they self-assemble and grow into a blastula with holly core-shell structure. However, the cell to cell variation is missing, and the efficiency of forming blastula is low, in most case forming a cell cluster. Here, we develop a new method to encapsulate single stem cell in alginate microcapsules. The single stem cell can proliferate inside to form a blastula-like structure after culturing for a few days. The shell can further be incorporated with interesting protein that mimics of zona pellucida covring the embryo in vivo offers the chance to study the early embryo development stage.
Keywords: embryogenesis, droplet microfluidc, alginate capsules.

56. Zhang, Weixia; Weixia Zhang, Liangliang Qu, Hao Pei, Jonathan Didier, David Weitz

Harvard SEAS
"Controllable Fabrication of Inhomogeneous Microcapsules for Triggered Release by Osmotic Pressure"
In this study, microcapsules with inhomogeneous shell thickness are controllably fabricated to encapsulate various cargo using a microfluidic approach, which can be triggered to release cargo at a low critical osmotic pressure. Using a glass capillary microfluidic device, monodisperse water-in-oil-in-water double emulsion droplets are produced with cargo in the core and an inhomogeneous middle oil layer containing photo-curable monomers that can be crosslinked under UV exposure. The inhomogeneity of shell thickness in these microcapsules can be controlled by tuning the flow rate ratio of the middle oil phase to the inner aqueous phase. It is demonstrated that the swelling of these inhomogeneous microcapsules begins at the thinnest part of shell and eventually leading to rupture at the weak spot with a low osmotic pressure. Moreover, systematic studies indicate the rupture fraction of these inhomogeneous microcapsules increases with the increasing internal osmotic pressure and the inhomogeneity. Finally, the inhomogeneous microcapsules are demonstrated to be impermeable to small probe molecules, which enables long-term storage, and to release enzyme triggered by osmotic pressure without impairing its biological activity. Our study provides a new approach to design effective carriers to protect and release biomolecules on-demand upon applying osmotic shock.

57. Zhang, Xingcai; J. Heyman, D. Weitz, E. Appel

Harvard University;
"Multifunctional Drugs/Vaccines Delivery System"
My project is to generate a transformational strategy for vaccination/drugs in a single injection. 1.5 million children die each year from vaccine-preventable diseases. According to the World Health Organization, 40% of those children had received the first dose of the vaccine but were unable to complete the 3-dose series. 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.4 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 multifunctional vaccines/drugs single-administration technology would reduce the number of required interventions, thereby preventing the unnecessary spreading of infectious disease, especially amongst rural populations, 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. I am developing a single administration vaccination platform using advanced micro/nanotechnology along with a novel hydrogel excipient to create tunable, pulsatile release of vaccines.
Keywords: Multifunction; Drugs; Vaccines; Delivery System

58. Zheng, Wenshan; Huidan Zhang, David Weitz

Harvard University
"Massively Parallel Single Bacterium Whole Genome Sequencing in Drop Based Microfluidics"
Genome of each and every bacterium is the key information to study a bacterial community. Single bacterium whole genome sequencing offers the opportunity to acquire this information. However, with current microplate based methods, this is practically impossible because a bacterial community often contains millions of bacteria and hundreds of species if not more. We use drop-based microfluidics to solve this problem. Millions of bacteria can be isolated and encapsulated in small drops within an hour. Inside drops, we can further add reagents to lyse bacteria, amplify their genomes and label each genome with a barcoded bead. With these procedures, tens of thousands of single bacterial genomes can be acquired within one week. We anticipate this method to vastly facilitate the study of bacterial communities.
Keywords: single cell sequencing, bacterial genome, microfluidics

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