Calendar of MRSEC Events

2018 Events
November 30, 2018 77th New England Complex Fluids Workshop at Harvard University
September 21, 2018 76th New England Complex Fluids Workshop at Brandeis University
September 19, 2018 Squishy Physics Seminar
Wei Zhang, University of Massachusetts Boston

6 - 7pm | Pearce Hall, Room 209

Development of small molecule inhibitors & probes for druggable targets

This presentation highlights our recent effort on the development of green and highly efficient methods for drug-like molecule synthesis and asymmetric catalysis. A series of technologies including fluorous technologies, multicomponent reactions, and organocatalysis are integrated to maximize reaction and separation efficiency in the synthesis of diverse heterocyclic scaffolds with substitution, skeleton, and stereochemistry variations. Through the collaboration with Harvard and other medical schools in US and Europe, our compounds have been integrated to a number of drug discovery programs. Several lead compounds have been developed for druggable targets such bromodomains (BET, CBP), kinases (PLK1), MDM2, PARP1&2, HIV-1, and RORgt targets which are related cancer, immune, inflammation, and other diseases.
September 12, 2018 Squishy Physics Seminar
Jiawei Yang, Harvard University

6 - 7pm | Pearce Hall, Room 209

Hydrogel Adhesion

Hydrogel adhesion, integrating hydrogels with a variety of materials—from soft, living tissues to hard, rigid metals—has sparked unprecedented capabilities and advanced many emerging technologies in designing functional materials, biomedical applications, soft ionotronics and electronics, and robots. However, achieving strong hydrogel adhesion is fundamentally challenging. This talk presents the chemistry, mechanics and topology for strong hydrogel adhesion. I will highlight several our recently developed bonding methods, including molecular stitching, bridging and bonding, to strongly bond any type of hydrogel with other materials, and retain a soft and stretchable interface. Unlike traditional adhesion, our adhesion is programmable, and can be designed as permanent adhesion, transient adhesion, and triggerable de-adhesion. This method further inspires many diverse applications, ranging from strong tissue adhesives, wearable devices, to underwater adhesion.
September 5, 2018 Squishy Physics Seminar
Gilad Yossifon, Israel Institute of Technology

6 - 7pm | Pearce Hall, Room 209

Active Particles as Mobile Microelectrodes for Unified Label-Free Selective Cargo Transport

Utilization of active particles to transport both biological and inorganic cargo has been widely examined in the context of applications ranging from targeted drug delivery to sample analysis. Generally, carriers are customized to load one specific target via a mechanism distinct from that driving the transport. Here, we unify these tasks and extend loading capabilities to include on-demand selection of multiple nano/micro sized targets without the need for pre-labelling or surface functionalization. An externally applied electric field is singularly used to drive the active cargo carrier and transform it into a mobile floating electrode that can attract or repel specific targets from its surface by dielectrophoresis; enabling dynamic control of target selection, loading and rate of transport via the electric field parameters. Adding directed motion via magnetic stirring enables to develop these active particles into in-vitro assays with single cell precision and building blocks for bottom-up fabrication.
August 22, 2018 Squishy Physics Seminar
Nadir Kaplan, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Theoretical design of hard and soft biomimetic materials

Realizing next-generation materials with intricate shapes or complex signal processing abilities to perform adaptive functions greatly benefits inspiration from biological systems. In the first part of this talk, I will present a geometrical theory that explains the growth and form of carbonate-silica precipitates, which exemplify biomineralization-inspired formation of inorganic brittle microarchitectures. The theory predicts new assembly pathways of arbitrarily complex morphologies and thereby guides the synthesis of light-guiding optical structures. The second part will concern a soft matter analog of information storage and differentiation in living organisms, which constantly process dynamic environmental signals. Specifically, I will introduce a continuum framework of a hydrogel system that utilizes unique cascades of mechanical responses, transport and complexation of chemical stimuli to expand the sensing repertoire beyond standard hydrogels that rapidly equilibrate to their surroundings. Altogether, the confluence of theory and experiment enables the design of optimized hard or soft biomimetic materials for applications ranging from bottom-up manufacturing to soft robotics to data encoding.
August 15, 2018 Squishy Physics Seminar
Andrew Wong, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Advances in Aqueous Organic Redox Flow Batteries

Rising demand for utility-grid and micro-grid energy storage has spurred rapid advancements in electrochemical energy storage systems. Aqueous organic redox flow batteries (AORFB) are among the technologies poised to catch this wave of innovation and discovery. This talk will include the historical progression of AORFB chemistries from acid, to alkaline, to neutral pH conditions. Advancements of these novel chemistries through enhancements in polymer ion exchange membranes, porous carbon electrodes, and fluid flow distribution will also be discussed. Finally, unique insights into AORFB enabled by optical techniques will shed light on future improvements waiting to be designed.
August 11, 2018 2018 Research Experiences for Undergraduates (REU)
move out
August 8, 2018 Squishy Physics Seminar
Luhan Ye, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Thick and flexible electrode design for advanced lithium-ion batteries

The power and energy density of a battery cell is quickly diminished by the inclusion of excess inactive materials. Given that the amount of inactive materials is directly determined by the number of battery layers, as each layer requires a separator and current collector, minimizing the number of layers is critical in optimizing the performance of a battery. It is shown here that ionic polymers can be utilized to drastically improve the thickness of each battery layer and, by extension, reduce the number of layers needed for a given total capacity. This is achieved by the ionic polymer enabling both improved ion conductivity and flexibility, the key limitations faced when maximizing electrode thickness.
August 1, 2018 Squishy Physics Seminar
Apoorva Sarode, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Biologically Inspired Approaches for Effective Drug Delivery

Over eons of evolution, biological systems have reached an unparalleled sophistication in their performance. The wide array of nano- and microscale entities in nature, from spiral-shaped bacteria to biconcave red blood cells, hints at the importance of shape in biology. Furthermore, the distinct features like size and rigidity of these cells are very crucial to carry out their native functions. Inspired by these cues, we are developing various polymer-based biomimetic carriers for targeted drug delivery. This talk will shed light on our lab’s contribution in understanding the effect of physico-mechanical parameters of polymeric particles in drug delivery (uptake, circulation, targeting, etc.). The discussion will also focus on application of these fundamental findings for the treatment of cancer and cardiovascular disorders.
July 25, 2018 Squishy Physics Seminar
Frans Spaepen, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Live 3D modeling with colloids: a retrospective

Colloidal particles, being large and slow and hence trackable in the confocal microscope, can be used to gain insight into complex problems in materials science on the particle (i.e., atomic) level. This talk will be an informal survey of the many projects in our long-standing collaboration with the Weitz group to exploit this technique: the deformation of amorphous materials, the motion of dislocations, the kinetics of solidification, the observation of crystal nucleation, the dynamics and stiffness of the solid-liquid interface, the structure and dynamics of grain boundaries,... With lots of pictures and movies.
July 18, 2018 Squishy Physics Seminar
Felix Wong, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Mechanics and dynamics of translocating filaments on curved membranes

Protein filaments that bind to curved membranes and translocate in directions determined by principal membrane curvatures exhibit rich behavior, as suggested by prior studies on bacterial filament systems. Here we model the direct binding of protein filaments to membranes and show that it is energetically favorable for filaments to orient in a manner compatible with their intrinsic curvatures. We then model the curvature-based translocation of an ensemble of filaments and show that their macroscopic properties, such as localization, can vary significantly depending on membrane geometry. Finally, we discuss the implications of our study to bacterial morphogenesis and regulation of rod shape by the bacterial actin homolog MreB. Our work introduces general methods likely to be of interest to both biologists and physicists.

This work is carried out in collaboration with Ethan Garner (MCB).
July 11, 2018 Squishy Physics Seminar
Rees Garmann, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Watching viral capsids self-assemble

The formation of a viral capsid—the highly-ordered protein shell that surrounds the genome of a virus—is the classic example of self-assembly in biology. As far back as the 1950s and 1960s, researchers have been reconstituting viral capsids in the laboratory simply by mixing together the viral coat proteins and genome molecules. The high yields of proper capsids that assemble in such experiments is remarkable, given the complexity of the structures.In this talk, I will describe our ongoing efforts to understand the kinetics of viral capsid assembly by monitoring the formation individual capsids. In our experiments, we inject a solution of viral coat proteins over a glass coverslip on which viral RNA strands are tethered to the surface. Using an optical technique called interferometric scattering microscopy, we measure how many proteins bind to each RNA as a function of time. Our measurements reveal some new features of the assembly process—such as an initial nucleation step, and the possibility of subsequent nucleation steps—that may help us understand how viruses regulate the assembly of correct capsids, and also how assembly can go awry.
June 27, 2018 Squishy Physics Seminar
David Nelson, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

On Growth and Form of Microorganisms on Liquid Substrates

The interplay between fluid flows and living organisms plays a major role in the competition and organization of microbial populations in liquid environments. Hydrodynamic transport leads to the dispersion, segregation or clustering of biological organisms in a wide variety of settings. To explore such questions, we have created microbial range expansions in the laboratory by inoculating two identical strains of S. cerevisiae (Baker’s yeast) with different fluorescent labels on a nutrient-rich fluid 10^4 to10^5 times more viscous than water. The yeast metabolism generates intense flow in the underlying fluid substrate several times larger than the unperturbed colony expansion speed. These flows dramatically impact colony morphology and genetic demixing, triggering in some circumstances a fingering instability that allows these organism to spread across an entire Petri dish within two days. We argue that yeast colonies create fluid flow by consuming nutrients from the surrounding fluid, decreasing the density of the substrate fluid, and ultimately triggering a baroclinic instability when the fluid’s pressure and density contours are no longer parallel. Our results suggest that microbial range expansions on viscous fluids will provide rich opportunities to study the interplay between advection and spatial population genetics.

Work carried out in collaboration with Severine Atis, Bryan Weinstein and Andrew Murray
June 20, 2018 Squishy Physics Seminar
Berna Özkale Edelmann, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Dynamic single cell mechanotransduction with optically responsive extracellular matrices

The interactions between cells and the surrounding extracellular matrix (ECM) help guide key processes such as cell spreading, proliferation, and differentiation. The mechanochemical communication between cells and their microenvironment is highly dynamic and complex. For organs such as the lung and the heart, strain and its frequency are crucial parameters for tissue function. Understanding the dynamic relationship between a single cell and its microenvironment is key to deciphering tissue level complexity. Our understanding of mechanotransduction so far has mainly relied on static models which are insufficient in fully recreating the dynamic microenvironment. Recent studies involving dynamic models have shown that externally applied forces can actively guide cellular processes. However, the influence of frequency and magnitude of applied forces on cellular mechanoresponses and their downstream effects are not well understood. In this talk, I will present a dynamic approach to studying mechanotransduction at the single cell level. I will first introduce an optically responsive artificial ECM which contracts under near-infrared (NIR) light and relaxes rapidly when the light is turned off. This approach allows for precisely confined actuation of the optically responsive ECM around a single cell. I will then discuss how locally applied cyclic stretching affects two cellular mechanoresponses, namely the nuclear translocation of a mechanoresponsive transcriptional regulator and the triggering of stretch activated ion channels.
June 15, 2018 75th New England Complex Fluids Workshop at MIT
June 13, 2018 Squishy Physics Seminar
Katia Bertoldi, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Soft robots: where robotics meets mechanics

Soft robots comprising several inflatable actuators made of compliant materials have drawn significant attention over the past few years because of their ability to produce complex motions through nonlinear deformation. Their design simplicity, ease of fabrication and low cost sparked the emergence of soft robots capable of performing many tasks, including walking, crawling, camouflaging and assisting humans in grasping, suggesting new paths for space exploration, biomimimetics, medical surgery and rehabilitation. However, to achieve a particular function existing fluidic soft robots typically require multiple input lines, since each actuator must be inflated and deflated independently according to a specific preprogrammed sequence.

An interesting avenue to reduce the number of required input signals is the direct exploitation of the highly nonlinear behavior of the system without the introduction of additional stiff elements. In this talk I will present three different strategies that we have recently explored to achieve this. First, I will show that a segmented soft actuator reinforced locally with optimally oriented fibers can achieve complex configurations upon inflation with a single input source. Then, I will demonstrate that the non-linear properties of flexible two-dimensional metamaterials are also effective in reducing the complexity of the required input signal. Finally, through a combination of evolutionary optimization and experiments I will show that fluid viscosity in the tubes can be harnessed to design fluidic soft robots capable of achieving a wide variety of target responses through a single input.
June 6, 2018 Squishy Physics Seminar
Shima Parsa, Harvard University

5:30 - 7pm | Pearce Hall, Room 209

Origin of polymer enhanced oil recovery

Polymer flooding is one of the most economically viable methods for enhanced oil recovery. By flowing a small volume of polymer solution into the reservoir, after an initial recovery by water, a considerable additional amount of oil is recovered. However, the commonly accepted mechanisms for the enhanced recovery based on viscoelastic properties of the polymer solution are inadequate to explain the enhanced recovery observed in all different conditions. We use confocal microscopy to investigate the origin of polymer enhanced oil recovery by measuring the velocities of the displacing fluid around trapped oil in a 3D micromodel of porous media. A completely different mechanism for improved recovery is observed. Polymer retention in the pore space results in highly heterogeneous changes in the velocities of the displacing fluid and in some pores provides large enough viscous pressure to mobilize the trapped oil ganglia. Our pore level measurements provide new insights into the origin of polymer enhanced recovery.
June 4, 2018 2018 Research Experiences for Undergraduates (REU)
move in
May 30, 2018 Squishy Physics Seminar
Mark Skylar-Scott, Harvard University

5:30pm | Pearce Hall, Room 209

Multimaterial Multinozzle Arrays for Rapid 3D Printing

Knots occur naturally in biological DNA, a phenomenon relevant for cellular genome organization Direct ink writing (DIW) can be used to deposit viscoelastic inks into three-dimensional multimaterial architectures. Using inks that range from ceramics to biological tissues, DIW is uniquely capable of driving technological development in 3D printing from ‘printed form’, towards ‘printed function’. However, the exploration of potential architectures is critically limited by the low throughput of DIW; for a constant filament diameter and print speed, the print time increases with the cube of the size of the printed part. Here, we use stereolithography to manufacture multimaterial multinozzle 3D (MM3D) printheads that enable the rapid construction of multimaterial architectures. We demonstrate 1D and 2D arrays of multimaterial nozzles, each capable of generating continuous filaments that switch materials at up to 50 Hz. We derive and experimentally validate an analytical model to predict the print parameter space in which MM3D nozzles can operate. Using these MM3D printheads, we generate a Miura origami fold using patterns of stiff and soft epoxy inks which vary in stiffness by almost four orders of magnitude. This MM3D system promises to enhance the scalability of multimaterial DIW, particularly for inks with limited pot-lives.
May 17, 2018 Squishy Physics Seminar
Matan Yah Ben Zion, NYU - Center for Soft Matter Research

2:00pm | Cruft Hall, Room 309

Colloidal Self Assembly - from Synthesis to Function

Although stereochemistry has been a central focus of the molecular sciences since Pasteur, its province has previously been restricted to the nanometric scale. I will present our approach of combining DNA nanotechnology with colloidal science to program the self-assembly of micron-sized clusters with structural information stemming from a nanometric arrangement. We bridged the functional flexibility of DNA origami on the molecular scale, with the structural rigidity of colloidal particles on the micron scale, by tuning the mechanical properties of a DNA origami complex. We demonstrate the parallel self-assembly of three-dimensional micro-constructs, evincing highly specific geometry that includes control over position, dihedral angles, and cluster chirality. I will end my talk describing two recent projects where we used these techniques to synthesize and study active systems: light driven fluid micro-particles, and sedimenting irregular clusters.
May 16, 2018 Squishy Physics Seminar
Alex Klotz, MIT

5:30pm | Pearce Hall, Room 209

Dynamics of knotted DNA and knots in DNA

Knots occur naturally in biological DNA, a phenomenon relevant for cellular genome organization as well as genetic sequencing technology. Knotted DNA molecules serve as a model experimental system for polymer entanglement, where fluorescent microscopy can be used to study polymer dynamics on the individual chain level. To study the dynamics of knots in DNA, we induce knotting in viral DNA using an electrohydrodynamic instability and stretch the molecules with a divergent electric field in a microfluidic channel, analogous to elongational flow. I will discuss some recent results from our experiments and simulations, including the effect of knots on the entropic elasticity of a stretched molecule, the motion of knots along elongated molecules, and the process by which knots untie as they reach the end of the molecule.
May 2, 2018 Squishy Physics Seminar
John Hart, MIT

5:30pm | Pearce Hall, Room 209
April 11, 2018 Squishy Physics Seminar
Martin Lenz, CNRS (Paris, France)
The Laboratory of Theoretical Physics and Statistical Models

5:30pm | Pearce Hall, Room 209

Slimming down through frustration

Controlling the self-assembly of supramolecular structures is vital for living cells, and a central challenge for engineering at the nano- and microscales. Nevertheless, even particles without optimized shapes can robustly form well-defined morphologies. This is the case in numerous medical conditions where normally soluble proteins aggregate into fibers. Beyond the diversity of molecular mechanisms involved, we propose that fibers generically arise from the aggregation of irregular particles with short-range interactions. Using minimal models of frustrated aggregating particles, we demonstrate robust fiber formation for a variety of particle shapes and aggregation conditions. Geometrical frustration plays a crucial role in this process, and accounts for the range of parameters in which fibers form as well as for their metastable, yet long-lived character.
April 4, 2018 Squishy Physics Seminar
Prof. Jia Niu, Department of Chemistry, Boston College

5:30pm | Pearce Hall, Room 209

Biocompatible Controlled Radical Polymerization: at the Interface of Polymer Science and Biology

Synthetic polymers as biomaterials have attracted significant research and development efforts in the recent years. Compared to the biological counterparts, synthetic polymers can provide improved physical, chemical, or mechanical properties as well as the capability to actively manipulate biological functions. However, traditional synthetic polymer biomaterials are still primarily used as crosslinked matrices, limited by the lack of defined polymer structures and low polymer grafting efficiency. The overall goal of our research is to expand the controlled polymerization techniques towards improved biocompatibility and the mimicry of biopolymers. In this seminar, two examples will be presented. First, a rapid controlled radical polymerization technique is described. In situ NMR monitoring confirmed the kinetics of this reaction and its spatiotemporal control over polymerization by light. Using this technique, synthetic polymers with narrow polydispersity (PDI < 1.3) were generated in aqueous solution at room temperature. The rapid reaction kinetics of this CRP enabled direct cytocompatible polymerization from chain transfer agents (CTAs) immobilized on the surfaces of live yeast and mammalian cells, as shown in the second example. High (>90%) cell viability and non-impaired cell functions, including cell propagation and signaling transduction, were observed for polymer-modified cells. Incorporation of various functional groups in the cell surface-initiated synthetic polymers was shown to enable post-polymerization functionalization of cell surface and mediate cell-cell interaction. These preliminary results serve as the initiators for our efforts towards applying synthetic polymeric system in various biotechnological applications, such as live cell-based sensing or catalytic systems, programmable cell assembly, and engineering cell surface with molecular or nano-scale structures.
March 30, 2018 74th New England Complex Fluids Workshop at Yale University
March 30, 2018 MCB Harvard Seminar
M. Lisa Manning, Ph.D., Associate Professor of Physics, Department of Physics and Soft and Living Matter Program, Syracuse University

1:0pm | Biological Labs 1080, 16 Divinity Avenue, Cambridge

Modeling Physical Forces at Large Scales to Discover Molecular Mechanisms in Cell Biology

March 28, 2018 Squishy Physics Seminar
Dr. María L. Jiménez, Department of Applied Physics, University of Granada (Spain)

5:30pm | Pearce Hall, Room 209

Biocompatible Controlled Radical Polymerization: at the Interface of Polymer Science and Biology

In the last decades, a great effort has been devoted to control the size, geometry and internal morphology of nanoparticles. In many practical situations, such systems are suspended in aqueous media. If this is the case, nanoparticles usually acquire surface charge, and this also determines their behavior. Both size and charge in aqueous media are usually characterized by scattering techniques. While these methods are well established, there are multiple situations in which they provide limited information. For instance, the size is not well measured when the particles are highly non-spherical. With respect to the electric properties, scattering methods provide a single characteristic quantity, the zeta potential. Hence, they cannot characterize the behavior of more complex systems, such as soft particles, soft coated particles, non homogeneous surface charge, etc. Finally, only dilute suspensions can be measured with these techniques, which is not always the desired situation.

In this talk I will show a different approach: the measurement of the electric permittivity and electric birefringence spectra of suspensions. These quantities are directly related to the polarization of the particles: under the action of electric fields, particles polarize by different mechanisms that manifest in separated frequency regimes, depending on the particle size, geometry and the electric properties of the interface particle/solution. We will show that the electric permittivity spectra provide the particle size, aggregation state and surface charge in the case of concentrated suspensions. On the other hand, the electric birefringence is very sensitive to the particle geometry and charge distribution as compared to standard techniques based on the light scattered by the particles. In particular, we will show that it is an excellent tool to obtain the size distribution in the case of non spherical particles.
March 21, 2018 Squishy Physics Seminar
Dr. Lukas Zeininger, Department of Chemistry, MIT

5:30pm | Pearce Hall, Room 209

Rapid Detection of Foodborne Pathogens using Directional Emission from Dynamic Complex Emulsions

Multiphase complex emulsions formed from two or more immiscible solvents offer a unique platform as new materials for chemical sensor applications. The temperature controlled miscibility of fluorocarbons (F) and hydrocarbons (H) enables a temperature induced phase-separation, leading to structured emulsion droplets of H and F in water (W), which can be alternated between encapsulated (F in H, and H in F), and Janus configurations by varying the interfacial tensions using surfactants. These complex emulsion droplets can selectively invert morphology in response to external stimuli such as the presence of specific analytes, small pH changes, light or high energy irradiation, and the presence of an electric or magnetic field. This, in combination with the unique optical properties of our emulsion droplets enables the application of our complex emulsions as a new transduction material for chemo- and bio-sensing applications. Here, we will show how the addition of stimuli-responsive surfactants to the complex emulsions provides a method to induce a morphology change or droplet reconfiguration as a response to the presence of specific chemical or biological analytes. In order to create a ratiometric optical read-out of small changes in the droplet morphology, emissive dyes were added to one of the two immiscible phases of the complex emulsions. The potential of these micro-colloids to manipulate light in form of waveguides led to the development of several optical transduction methods, where an adjustment of the refractive indices of the solvents results in a new unprecedented control of light propagation inside the emulsion droplets. We will demonstrate that having control over the total internal reflection of light from outside and inside the emulsion droplets results in new sensory schemes for the rapid and sensitive detection of various chemical and biological analytes, including common foodborne pathogens such as Salmonella and E.coli bacteria.
March 14, 2018 Squishy Physics Seminar
Craig Maloney, Department of Mechanical and Industrial Engineering, Northeastern University

5:30pm | Pearce Hall, Room 209

Models for sheared amorphous solids: from the particle scale to the meso-scale

Many solid-like materials lack any underlying crystalline order. Examples include soft glasses (emulsions, foams, pastes, colloidal glasses), granular packings, amorphous alloys, and glassy polymers. Over the past few decades, local shear transformations have been identified as the particle-scale processes which accommodate imposed shear and allow for yielding and flow. In this talk we will discuss coarse-grained, meso-scale models based on this notion of local shear transformations, and will quantitatively reconcile the coarse-grained approaches with particle-scale simulations and experimental data. In particular, we will discuss how the diffusion and rheology are governed by cascades of shear transformations and will show how the yield point can be thought of as a dynamical critical point with associated scaling relations with some exponents being universal, and other depending on microscopic details of the model.
March 7, 2018 Squishy Physics Seminar
Prof. Arturo Moncho Jorda, Departamento de Física Aplicada, Universidad de Granada

5:30pm | Pearce Hall, Room 209

Cosolute Partitioning in Hydrogel Particles

Hydrogels are formed by cross-linked polymer chains dispersed in water, with the ability to reversibly swell and in response to various stimuli, such as temperature, salt concentration, and pH. They can be designed to be biocompatible, biodegradable, and allow the incorporation of biomacromolecules with relatively small changes in its biological activity. Because of these features, hydrogels have been proposed as excellent candidates for transport and delivery systems of different types of cosolutes, such as biomacromolecules, drugs and chemical reactants in controlled catalysis. However, the interactions involved in the cosolute absortion and the swelling response of the hydrogel in the presence of the cosolutes are not totally understood under a theoretical point of view.

This talk will address these two problems. In the first part of the talk, the absorption of charged globular inside charged hydrogels is studied by calculating the effective interaction between the hydrogel network and the protein. Different sorption states are identified, from complete exclusion of the protein to its full absorption, passing through metastable and stable surface adsorption. The results indicate that proteins with a large dipole moment tend to be adsorbed at the external surface of the hydrogel, even if like-charged, whereas uniformly charged biomolecules tend to partition toward the internal core of an oppositely charged hydrogel. In the part of the talk, the effect that neutral hydrophobic cosolutes has on the hydrogel swelling/deswelling is studied using coarse-grained simulations and mean-field theory. The results show the existence of "cosolute-induced" collapsed states, where strongly attractive cosolutes bridge network monomers albeit the latter interact mutually repulsive.
February 28, 2018 Squishy Physics Seminar
Prof. Carlos Hidrovo, Mechanical and Industrial Engineering Department, Northeastern University

5:30pm | Pearce Hall, Room 209

Gas-Liquid Droplet Microfluidics: Fundamentals and Applications

Over the past two decades microfluidics has quickly morphed from an emerging field to a mature technology that is widely used in biotechnology and healthcare. One specific field that has thrived extensively in its adoption and development has been droplet microfluidics. The ability to compartmentalize reactions and processes into multiple individual droplets has made these systems extremely attractive in multiple and varied applications. However, most of the focus has centered on liquid-liquid systems, where dispersed droplets of a liquid are formed on another continuous, immiscible one.

This talk will focus on the relatively untapped field of gas-liquid droplet microfluidics, where liquid droplets are formed in a continuous, gaseous flow. The fundamentals of droplet formation and transport will be explored. Due to the lower viscosity of the carrier fluid, these systems tend to operate at much higher Re than those encountered in typical microfluidic systems. As such, the role of inertial forces on the dynamics of these systems will be addressed. Applications geared towards the creation of monodisperse aerosols and the sampling of gaseous targets will be discussed. A specific example on the sampling and detection of gaseous ammonia will be presented. The talk will finish with an outlook on the future of these systems.
February 21, 2018 Squishy Physics Seminar
Lisa Tran, Department of Physics, University of Pennsylvania

5:20pm | Pearce Hall, Room 209

A change in stripes for liquid crystal shells — controlling elasticity to order nanomaterials

Liquid crystals are ubiquitous in modern society. Whenever we text, use a calculator, or check our emails, we are interacting with LCDs — liquid crystal displays. These materials are the basis of the modern display industry because of their unique properties. They can be manipulated with electric fields and can alter light. They are also deformable because they are elastic: their rod-like molecules tend to align with one another. These properties allow for liquid crystals to be engineered into a pixel. Despite these advances in their technological applications so far, the structures that liquid crystals can form are yet to be completely understood. Current research aims to elucidate these structures to develop liquid crystals as biological sensors and as blue prints for assembling nanomaterials in energy applications.

Since liquid crystal molecules tend to order with one another, they can respond to geometrical confinement. Geometrical constraints can create patterned molecular structures and defects — localized, "melted" areas of disorder that can lower the distortion in the system and that can drive the assembly of objects. I will present recent work in which defects are controlled by using microfluidics to create liquid crystal double emulsion droplets — confining the liquid crystal into spherical shells. Molecular configurations are controlled by the topology and geometry of the system and by varying the concentration of surfactants. Defect structures are examined through experiments and simulations, and the surfactant concentration is altered to transition between different defect types. I will then present ongoing experiments where nanoparticles are used in place of traditional surfactants to pattern them at the liquid crystal-water interface. This work has the potential to dynamically template nanomaterials for the enhancement of liquid crystal-based optical devices and sensors.
February 14, 2018 Squishy Physics Seminar
Prof. Thomas C. Pochapsky, Department of Chemistry, Brandeis University

5:20pm | Pearce Hall, Room 209

Some surprising implications of NMR-directed simulations of substrate recognition and binding by cytochromes P450

Cytochromes P450 are a superfamily of heme-containing monooxygenases that typically catalyze the oxidation of unactivated C-H and C=C bonds by molecular oxygen, often with high regio- and stereospecificity. Over 450,000 members of the superfamily have been tentatively identified, from all genera of life, suggesting a vast range of possible substrates and even larger one of potential products. However, little is yet known about the relationship between sequence, structure and substrate/product specificity in P450s. Residual dipolar couplings (RDCs) measured for backbone amide 1H-15N correlations in substrate-free and bound forms of two P450s, the camphor 5-exo hydroxylase CYP101A1 and macrolide antibiotic biosynthetic MycG were used as restraints in soft annealing molecular dynamics (MD) simulations in order to identify average conformations of these enzymes with and without substrate bound. Multiple substrate-dependent conformational changes remote from the enzyme active site were identified in both enzymes. Perturbation response scanning (PRS) and umbrella sampling MD of the RDC-derived CYP101A1 structures are used to probe the roles of remote structural features in enforcing the regio- and stereospecific nature of the hydroxylation reaction catalyzed by CYP101A1. An improper dihedral angle Ψ was used to maintain substrate orientation in the CYP101A1 active site, and it different values of Ψ result in different PRS response maps. Umbrella sampling methods show that the free energy of the system is sensitive to Ψ, and bound substrate forms an important mechanical link in the transmission of mechanical coupling through the enzyme structure. Finally, a qualitative approach to interpreting PRS maps in terms of the roles of secondary structural features is proposed.
February 7, 2018 Squishy Physics Seminar
Prof. Yujun Song, Department of Physics, University of Science and Technology Beijing

5:20pm | Pearce Hall, Room 301

Microfluidic Synthesis of Nanomaterials and their Application for Tumor Diagnosis and Therapy

Great progresses in the coupling of nanomaterials and biomedicines have been achieved in the disease diagnosis and therapy, leading to the brand-new field in nanomedicines by conjugating nanoparticles with bio-molecules in the past decades. However, the controlled synthesis of varieties of nanoparticles and their surface modification and conjugation with desired medicines (particularly small organics with inorganic nanoparticles) are still much challenging. Here we developed a programmed microfluidic process in the controlled synthesis of varieties of hybrid nanoparticles and versatile surface modification and functionalization processes based on comprehensive coupling reactions, fulfilling these issues. Thus, surfaces of noble metal, metal@metal-oxide or ceramic nanoparticles can be conveniently modified and conjugated with biomolecules with –NHx, -COOH or –OH ligands. Using breast cancer and hepatocellular carcinoma as disease model, and noble metal and magnetic-metal@metal-oxide as nanoparticle model, several nanomedicines have been successfully synthesized based on the invented conjugation process. Their applications as molecule imaging enhancers (MRI or CT), targeting nanoprobes and anti-tumor nanomedicines were evaluated, showing excellent clinical potentials.
February 1, 2018 2018 Research Experiences for Undergraduates (REU)
application deadline

Prior Events