HARVARD
Materials Research Science and Engineering Center
 
 
 
Calendar of MRSEC Events
2014 Events
December, 2014 61st New England Complex Fluids Workshop
September, 2014 60th New England Complex Fluids Workshop at Brandeis University
July 20-22, 2014 7th Annual Future Faculty Workshop
MIT (Co-sponsored by the NSF MRSECs at MIT (CMSE) and Harvard University)
June 27, 2014 59th New England Complex Fluids Workshop at Cabot Business & Technology Center, Billerica, MA
April 9, 2014 Squishy Physics Seminar
Jeffrey Guasto, Tufts University

Shear-induced unmixing in bacterial suspensions


Abstract: Motile bacteria play integral roles in biophysical processes ranging from biogeochemical cycling in the oceans to the spread of infections in the human body. Their ability to seek out nutrients and chemical signals for survival is conferred through swimming using long, thin, actuated flagella. However, these processes can be disrupted by the ubiquitously dynamic fluid environments in which they live. In this seminar, we will discuss microfluidic experiments using video microscopy to uncover transport mechanisms that lead to bacterial unmixing in flowing fluids. In particular, hydrodynamic shear produces striking spatial heterogeneity in suspensions of motile bacteria, characterized by up to 70% cell depletion from low-shear regions due to cell 'trapping' in high-shear regions. A Langevin model reveals that trapping arises from the competition between the alignment of elongated bacteria with the flow and the stochasticity in their swimming orientation. Finally, we show that shear-induced trapping directly impacts bacterial survival strategies, suppressing chemotaxis by hampering directional motility and more than doubling surface attachment by increasing the transport of bacteria towards surfaces.
April 3, 2014 Squishy Physics Seminar
Esther Amstad, Harvard SEAS

The microfluidic nebulator: Production of amorphous nanoparticles


Abstract: The usefulness of many hydrophobic substances is limited by their poor solubility in water; this restricts their applicability for example in the pharmaceutical, biomedical, and food industry. The dissolution kinetics can be increased if they are formulated as nanoparticles as it scales with the surface-to-volume ratio. The dissolution kinetics can be increased even more if these substances are formulated as amorphous nanoparticles as the amorphous phase has a higher solubility than the crystal; amorphous substances thus dissolve faster and in higher quantities. However, many materials have a high propensity to crystallize as this is the energetically most favorable state; it is thus difficult to make these materials amorphous. I will present a microfluidic spray drier, we call it a microfluidic nebulator that produces unprecedentedly small nanoparticles that are amorphous. Nanoparticles are produced in small drops that are formed inside the nebulator through the use of supersonic air. The nanoparticle size is determined by the number of solute molecules contained in the drop. The nanoparticle structure is determined by the probability for a crystalline nucleus to form as the drop evaporates; this probability is typically very high in supersaturated solutions as crystalline solids readily form under these conditions. However, the formation of a crystalline nucleus itself entails some time delay. We demonstrate that the nebulator can kinetically suppress the formation of crystalline nuclei; thereby, it produces amorphous nanoparticles from many different materials, even from materials that have a very high propensity to crystallize.
March 26, 2014 Squishy Physics Seminar
Igor Sokolov, Tufts

Squishing Molecules, Polymers, Cells, etc., with AFM


Abstract: Atomic Force Microscopy (AFM) is probably one of the major tools responsible for the emergence of what is now called Nanoscience and Nanotechnology. We observe a tremendous proliferation of AFM applications in the fields of soft condensed matter, materials science, chemistry, bioengineering, and nanotechnology. AFM has a particular advantage in dealing with biological objects, soft condensed matter in general, where the ability to image objects in their natural environment is paramount.

In this talk I will briefly overview the basic principles of the AFM work, and show examples of applications of this technique in soft condensed matter physics, from single molecules and polymers to cells (and if time permits, the study of small creatures, like beetles). Specifically, I will describe what information can be obtained when the AFM probes squiring soft objects, in the study of molecular self-assembly, immunorecognition, mechanics of cells, etc.

Biography: Igor Sokolov received his B.S. in Physics from St. Petersburg State University (Russian Harvard), Russia in 1984, and earned his Ph.D. from D.I. Mendeleev Institute for Metrology (similar to NIST), Russia in 1991. He is a professor and the Bernard M. Gordon Senior Faculty Fellow in the Departments of Mechanical, Biomedical Engineering, Physics of Tufts University. He has 135 refereed publications, more than 20 patents issued and pending, 100+ invited and 100+ contributed presentations. He serves as an editorial board member in a number of journals. Igor?s current research focuses on nanomechanics of soft materials, nanophotonics (fluorescence and sensing), nanocomposite materials, early detection of cancer, etc.
March 19, 2014 Squishy Physics Seminar
Susmita Bose, Washington State University

Calcium phosphate ceramics in bone tissue engineering and drug delivery


Abstract: There are an estimated one million bone grafting procedures performed annually in the U.S. and a few million worldwide to repair fractures, craniomaxillofacial defects, bone defects, tumors, as well as hip and knee replacements. Increase in the number of procedures is strongly tied to the increase in musculoskeletal disorder, aging population segment and sports related injuries. World dental implant and bone graft market could top $6 billion by 2014, and hip and knee implants market to reach $21 Billion by 2016. Calcium phosphate (CaP) ceramic being compositionally similar to the inorganic part of bone, show significant promise towards drug delivery and bone graft applications. We have used CaP scaffolds, fabricated using 3-D printing technology, for bone tissue engineering. Dopant chemistry in CaP plays a vital role in controlling their resorption or degradation kinetics as scaffolds, mechanical strength, and biological properties of resorbable CaPs. 3D interconnected channels in CaP scaffolds provide pathways for micronutrients, improved cell-material interactions, and increased surface area allows improved mechanical interlocking between scaffolds and surrounding bone. In vivo studies show improved osteogenesis and angiogenesis with these 3D printed scaffolds. These systems with controlled strength degradation and drug release, show promise for use in orthopedic and bone tissue engineering applications. Our study on doped CaP coated metal implants shows enhanced in vitro cell material interactions and improved osseointegration in vivo. We have used induction plasma spray system to coat metal implants to improve coating interfacial strength and antibacterial properties while showing effect of dopants on osteoblast and osteoclast cell performance. The presentation will include recent scientific and technological advances towards developing next generation ceramics, composites and scaffolds for bone implants and drug delivery.

Biography: Susmita Bose is a Professor in the School of Mechanical and Materials Engineering, an affiliate professor in the Department of Chemistry at Washington State University (WSU). Dr. Bose received the prestigious Presidential Early Career Award for Scientist and Engineers (PECASE, the highest honor given to a young scientist by the US President at the White House) award in 2004 from the National Science Foundation. Dr. Bose was named as a ?Kavli fellow? by the National Academy of the Sciences. In 2009, she received the prestigious Schwartzwalder-Professional Achievement in Ceramic Engineering (PACE) Award from the American Ceramic Society, which is an international award given to one scientist annually below the age of 41. Dr. Bose is an editorial board member for five different international journals including Acta Biomaterialia and Journal of the American Ceramic Society (Associate Editor). Dr. Bose has published over 200 technical papers with ~ 4400 citations, ?h? index 37. Dr. Bose is a fellow of the American Institute for Medical and Biological Engineering (AIMBE) and the American Ceramic Society (ACerS).
March 12, 2014 Squishy Physics Seminar
Qi Wen, WPI

Decoupling effects of substrate nanotopography and stiffness on tissue cells


Abstract: Tissue cells can sense and respond to both physical and biochemical signals. It has been demonstrated that mechanical stiffness and topographical features of the extra cellular matrix (ECM) can affect cellular function including migration, proliferation and gene expression. In a real tissue, the ECM mechanical properties are often coupled with its the micro- and nano structure and hence the nanotopography. I will discuss the synergistic effects of topography and mechanical stiffness on cytoskeletal stiffness and morphology of NIH 3T3 fibroblasts cultured on polydimethysloxane (PDMS) surfaces with different stiffness and surface roughness. By characterizing cell-ECM adhesions on the single molecular level, we try to elucidate how stiffness and nanotopography regulate cellular function. We hope this study on cell-ECM interactions will provide insights to guide the design of materials for tissue engineering and hopefully the mechanism of tumor formation and metastasis.
March 5, 2014 Squishy Physics Seminar
Andrejs Cebers, University of Latvia

Magnetotactic bacteria as self-propelling magnets


Abstract: Magnetotactic bacteria are microorganisms which use chains of magnetic nanoparticles (magnetosomes) to navigate in the magnetic field of the Earth. Their behavior in magnetic fields of different configurations will be described. As the simplest case the transition from a synchronous to a non-synchronous regime of a non-motile bacterium in a rotating field will be considered. Thermal fluctuations near the threshold of the non-synchronous regime cause the phase lag slips. Trajectories of motile magnetic bacteria under the action of a rotating magnetic field will be described. They are circles in the synchronous regime and complex curves in the non-synchronous. Experimental results of their study will be demonstrated. The random switching of rotary motors of a bacterium leads to peculiar diffusion process of curvature centers of its trajectory. The results of analytical and numerical calculations of the diffusion coefficient of this random process will be given and compared with experimental results. An interesting phenomenon noticed during the experiments in a rotating magnetic field is splitting of the chains of magnetosomes during division of bacterium now studied in detail by several groups. Magnetotactic bacteria are anaeorobic. This is illustrated by a band formation in a constant magnetic field along the axis of capillary where the oxygen gradient is created. The model of this phenomenon will be described. Finally some phenomena with flexible filaments of ferromagnetic particles which mimic the chains of magnetosomes are demonstrated behavior of flexible ferromagnetic filament at magnetic field inversion, its self-propulsion driven by an AC magnetic field and other.
February 28, 2014 58th New England Complex Fluids Workshop at MIT
February 26, 2014 SEED
Pierce 100f
February 19, 2014 IRG II
McKay 402
February 19, 2014 Squishy Physics Seminar
Justin Burton, Emory University

Iceberg capsize hydrodynamics and the source of glacial earthquakes


Abstract: Accelerated warming in the past few decades has led to an increase in dramatic, singular mass loss events from the Greenland and Antarctic ice sheets, such as the catastrophic collapse of ice shelves on the western antarctic peninsula, and the calving and subsequent capsize of cubic-kilometer scale icebergs in Greenland's outlet glaciers. The latter has been identified as the source of long-period seismic events classified as glacial earthquakes, which occur most frequently in Greenland's summer months. The ability to partially monitor polar mass loss through the Global Seismographic Network is quite attractive, yet this goal necessitates an accurate model of a source mechanism for glacial earthquakes. In addition, the detailed relationship between iceberg mass, geometry, and the measured seismic signal is complicated by inherent difficulties in collecting field data from remote, ice-choked fjords. To address this, we use a laboratory scale model to measure aspects of the post-fracture calving process not observable in nature. Our results show that the combination of mechanical contact forces and hydrodynamic pressure forces generated by the capsize of an iceberg adjacent to a glacier's terminus produces a dipolar strain which is reminiscent of a single couple seismic source.
February 13, 2014 IRG III
Pierce 100f
February 12, 2014 IRG I
Pierce 309
February 5, 2014 Squishy Physics Seminar
Alfredo Alexander-Katz, MIT

Blood Clotting-Inspired Polymer Physics


Abstract: Nature has devised creative and efficient ways of solving complex problems, and one of these problems is that of blood clotting in flowing conditions. In fact, nature has used a novel combination of polymer physics and chemistry that enhances the self-healing propensity of a vessel when strong flows are present while avoiding coagulation when the flow is diminished, a rather counter-intuitive phenomenon. Underlying this process is a globular biopolymer, the so-called von Willebrand Factor, whose function is strongly regulated by flow. In this talk I will present our work on this macromolecule starting from the single molecule approach and building up to the multi component system that more closely resembles blood. I will emphasize how new concepts have emerged from trying to understand such a complex system, in particular I will show how these polymers can display giant non-monotonic response to shear, as well as a very large propensity to form polymer-colloid composites in flow while being a stable dispersed suspension in quiescent conditions. In fact, the aggregation behavior is universal and can be explained with simple scaling arguments. These novel concepts and results are in principle not unique to blood clotting and can have important ramifications in other areas.
January 29, 2014 Squishy Physics Seminar
Maria Kilfoil, UMass Amherst

Seeing how biology feels: Nonthermal fluctuations in the cell nucleus


Abstract: In this talk I will present direct measurements of fluctuations in the nucleus of yeast cells. While prior work has shown these fluctuations to be active and non-thermal in character, their origin and time dependence are not understood. We show that nuclear fluctuations can be quantitatively understood by uncorrelated, active force fluctuations driving a nuclear medium that is dominated by an uncondensed DNA solution, for which we perform rheological measurements on an in vitro model system under similar conditions to what is expected in the nucleus. We conclude that the eukaryotic nucleus of living cells is a nonequilibrium soft material whose fluctuations are actively driven, and are far from thermal in their time dependence. I will also introduce a new in vitro system we developed to study active processes in the nuclear microenvironment.
January 22, 2014 Squishy Physics Seminar
Randall Erb, Harvard

Manufacturing Ordered Composites with Colloidal Assembly


Abstract: Recently, we have found an ultra-high magnetic response in stiff anisotropic particles by adsorbing nominal amounts of magnetite nanoparticles onto the surface of the particle [1]. This modification allows for the remote control of particle orientation and spatial positioning under magnetic fields only an order of magnitude larger than the Earth?s magnetic field. This level of control, among numerous exciting possibilities, can lead to the positioning of particle reinforcement in manmade materials that mimics the structures found in natural systems such as seashells or mammalian bone.

We have developed an energy model for these particle suspensions that explain this ultra-high response and suggest the key parameters essential in these systems. To help validate these parameters, we consider an idealized system and analyze the dynamic response of isolated platelets under magnetic fields. We find that using theoretical Perrin friction factors, originally developed to describe rotational drag for anisotropic molecules, we can precisely predict the interplay between magnetic, viscous and gravitational torques on these particles. We extend our model to describe the alignment of the platelets second major axis under rotating magnetic fields. We have found a relationship between the viscosity of the suspension and the critical frequency required to change from "rolling" to "fully-aligned" modes.

We use these techniques to create a family of advanced materials exhibiting 3-d reinforcements, spatial gradients, and various deliberate alignments. These composites exhibit the 3-D reinforced biological structures predicted to have enhanced material properties, such as higher stiffness and "wear-free" characteristics. This manipulation technique further enables fabrication of a diverse family of reinforced hydrogels. These systems have structures and anisotropic swelling that mimics natural systems [2]. These include hydrogels with the following: 1) in-plane reinforcement leading to swelling with high anisotropy (*plant stems*); 2) simple bilayer reinforcement leading to curled swelling (*pinecones*); 3) orientationally unique bilayers that swell into helical configurations (*orchid tree seed pods*). This work offers a way forward in recreating these defined reinforcement architectures within manufactured polymers.

[1] R. M. Erb, R. L. Libanori, N. Rothfuchs, A. R. Studart, *Science*, *335*, 199-204, 2012.

[2] R. M. Erb, J. Sanders, R. Grish, A. R. Studart, *Nature Communications*, *4*, 1712, 2013.
January 15, 2014 Squishy Physics Seminar
Andrej Kosmrlj, Harvard

Elasticity, Geometry, and Buckling


Abstract: In this talk I present how geometrical shape affects the mechanical properties of thin solid membranes and how buckling instabilities change the geometry of periodic microstructures in materials. Using methods rooted in statistical physics, we find that random shape fluctuations and thermal excitations of thin solid membranes significantly modify their mechanical properties. Such membranes are much harder to bend, but easier to stretch, compress and shear. Finally, I show how methods from solid state physics can help us deduce the geometry of buckled periodic microstructures. Buckling instabilities can change the microstructure symmetries, including a spontaneous chiral symmetry breaking, which drastically modifies the material properties.

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