Winter 2005-2006 Schedule
Grace Under Pressure: Mechanics of the Actin Cytoskeleton
March 17, 2006; 3:30pm
Presented by:
Prof. Daniel A. Fletcher
Department of Bioengineering
University of California, Berkeley
The actin cytoskeleton, a complex network of nanometer-scale protein filaments, provides eukaryotic cells with mechanical stability and generates forces for shape change and cell movement. One example of this is crawling motility in which single cells use protrusion, adhesion, and contraction to translate across a surface, a behavior exhibited by human neutrophils and other cells of the immune system. The forces and mechanical rigidity necessary for protrusion of the cell membrane during crawling motility are generated by growing actin filaments that are organized by actin-binding proteins into branched and cross-linked filament networks. In this talk, I will present recent work investigating the mechanics of growing actin networks using an atomic force microscope modified to make differential measurements. Our results reveal that growing actin networks exhibit non-linear elasticity under increasing forces and grow at rates that are dependent on loading history rather than instantaneous load. These results are only partially explained by existing models of actin networks and pose new challenges for theoretical prediction of actin network mechanics and dynamics.
Biomaterials
March 10, 2006; 3:30pm
Presented by:
Prof. Kevin Healy
Department of Bioengineering and Materials Science
and Engineering
University of California, Berkeley
Prof. Kevin Healy's Biomaterials Group at UC Berkeley is currently investigating the design and synthesis of biomimetic materials that actively direct the behavior of mammalian cells to facilitate regeneration of tissue and organs.
Traditionally, biomaterials encompass synthetic alternatives to the native materials found in our body. A central limitation in the performance of traditional materials used in the medical device, biotechnological, and pharmaceutical industries is that they lack the ability to integrate with biological systems through either a molecular or cellular pathway, which has relegated biomaterials to a passive role dictated by the constituents of a particular environment, leading to unfavorable outcomes and device failure. The design and synthesis of materials that circumvent their passive behavior in complex mammalian cells is the focus of the work conducted at Berkeley.
The group's work encompasses three main areas of research. Three-dimensional hydrogel scaffolds for tissue engineering are being created that incorporate biomimetic motifs, such as cell binding sequences, proteolytically degrable crosslinks, and regulatory protein analogs. Surface coatings tuned to resist non-specific protein and cell adsorption are being explored, which can then be tethered to cell binding and regularory protein sequences to study basic cell biology and tissue engineering. Polymer-based drug delivery systems for gene therapy are being developed as well, which incorporate a variety of strategies for protection, targeting, and delivery of the systems content.
Self-Organized Nanostructures and Guided Self-Assembly
March 3, 2006; 3:30pm
Presented by:
Prof. Wei Lu
Mechanical Engineering Department
University of Michigan, Ann Arbor
Advancing technologies demand solid structures of ever-decreasing length scales. During fabrication and use of these structures, atoms are mobile by diffusion or other mass transport processes. The structures may change configurations over time. Experimental evidence has accumulated in recent years that nanoscale structures can self-assemble, leading to ordered nanophase patterns in polymers and other materials. In a structure, collective actions of photons, electrons and ions contribute to the free energy. When the configuration of the structure changes, the free energy also changes. This free energy change defines a thermodynamic force which, in its turn, motivates the configuration change of the structure. The effects of such forces may be negligible in macrostructures, but significant in nanostructures. Insight into these forces becomes increasingly valuable as the structures of technological interest miniaturize. This talk presents some of our recent work on self-organized nanostructures and guided self-assembly. Examples include self-organized nanophase patterns on solid surfaces, guided assembly by surface chemistry and strain field, organized nanovoids and nanobubbles in a solid, patterning multilayer of molecules via dipole interaction, electric field induced ordered polymer nanostructures and tuning of nanoparticles in polymer nanocomposites. We have developed a thermodynamic framework to study the remarkable phenomena. Large-scale simulations have been developed to simulate the process of formation and evolution of nanostructures. The simulations reveal remarkably rich dynamics and suggest a significant degree of experimental control in growing ordered nanoscale structures.
Commercializing the Promise of Nanotechnology
February 24, 2006; 3:30pm
Presented by:
Dr. Calvin Chow
Chief Executive Officer
Nanosys, Inc.
Palo Alto, CA
Chemo-Mechanical Interactions and Implications for Micro-Device Design
February 17, 2006; 3:30pm
Presented by:
Prof. Matthew R. Begley
Department of Civil Engineering & Materials
Science and Engineering
University of Virginia
This talk will describe efforts to develop microfluidic devices for biomolecular sensing, characterization and actuation, based on the chemo-mechanical coupling generated by surface adsorption. The first part of the talk will outline a multiscale modeling framework that relates molecular characteristics (such as adsorption spacing/distribution, persistence length, interaction potential, etc.) to continuum variables. This approach will be illustrated by quantifying the mechanical driving forces that can be generated from adsorption of DNA and C60 fullerenes. The use of polyelectrolytes such as DNA is particularly attractive, since surface forces driving deformation can be tuned over a very wide range by varying grafting density and chemical environment. The translation of molecular behavior to continuum variables enables an evaluation of the performance of any adsorption-driven microdevice in terms of nanoscale parameters. Examples include cantilevers, valves (including adsorption-induced buckling), torsional pendulums, etc.
The second part of the talk will use the above framework to evaluate the performance of elastomer microdevices, for three applications:
- Bio-molecular detectors can be developed whose large deflections enable optical or electronic transduction of chemical binding events. This will be illustrated using experiments involving biotin-avidin binding and PDMS cantilevers.
- New approaches to quantifying inter- and intramolecular behavior are possible; e.g., the use of PDMS cantilevers creates the possibility to quantify the persistence length in DNA using self-assembled monolayers.
- It is possible to construct chemically-activated valves for microfluidic devices (i.e. micro-Total Analysis Systems), with deflections on the order of 100 microns.
Hierarchically Ordered Inorganic-Organic Materials
February 10, 2006; 3:30pm
Presented by:
Prof. Brad F. Chmelka
Department of Chemical Engineering
University of California, Santa Barbara
Substantial recent progress has occurred in the development of ordered inorganic/organic composites, nanocrystals, and porous inorganic materials with versatile properties for a wide variety of applications. Such materials can be prepared by using self-assembling organic agents, such as low-molecular-weight surfactants, block copolymers, emulsions, or biomolecules, that allow control to be exercised over material compositions, structures, and morphologies with length scales ranging from molecular to macroscopic dimensions. This includes the use of multiple ‘templating’ agents, the incorporation of guest species, and/or post-synthetic surface modifications, which provide versatility over the location and distribution of functional species within the materials, the extents of local site ordering, structural periodicities, and macroscopic morphologies (e.g., nanocrystals, powders, membranes, fibers, or monoliths.) NMR spectroscopy, in particular multidimensional methods, yield detailed molecular and interfacial information that can be correlated with Xray diffraction, electron microscopy, and bulk measurements to explain many meso- and macroscale material properties. Recent results will be presented on self-assembled inorganic-organic materials with ordering on multiple discrete length scales, crystal-like frameworks, and/or long-range orientational order, and their correspondingly different functional properties. Such materials show promise for an increasingly diverse range of applications in catalysis, separations, micro- and opto-electronics, etc., several of which will be highlighted.
Materials and Processes for MEMS: Some New Research Opportunities
February 3, 2006; 3:30pm
Presented by:
Prof. Roger T. Howe
Department of Electrical Engineering
Stanford University
This talk outline trends in selected MEMS technologies and applications extrapolated over the next two decades*. One important development over the next decade is the absorption of micro and nano-mechanical signal-processing, memory, and logic devices into "mainstream" electronics technologies. Looking further down the road, there are opportunities for NEMS in ultra-high frequency signal processing, in ultra-low power untethered sensor nodes, and in quantum-limited nano-instruments and quantum computing.
The material requirements for these new applications will move MEMS away from its roots in group IV of the periodic table. Metals, dielectrics, electrets, pyroelectrics, and piezoelectric materials will play major roles. Surfaces have been a major factor in MEMS and promise to have an even more critical role in the future. Finally, there are major materials challenges in the further extension of parallel assembly technologies to include high quality electromechanical interconnects between micro or nano components.
* Some of this material was presented at the DARPA Microsystems 2025 Workshop in Dec. 2005.
In Situ High Resolution Electron Microscopy of Materials
January 27, 2006; 3:30pm
Presented by:
Prof. Robert Sinclair
Chair
Department of Materials Science and Engineering
Stanford University
Nanoscale Composition Mapping in the Transmission Electron Microscope by EELS and EFTEM
January 20, 2006; 3:30pm
Presented by:
Dr. Jim Bentley
Metal and Ceramics Division
Oak Ridge National Laboratory, TN
In order to be able to make structure-property-processing correlations that are the core of traditional materials science, the “structural” input often involves composition information, sometimes implied but many times necessarily measured directly by spectroscopy. Although atomic resolution with single atom sensitivity has been demonstrated for special cases, well-established analytical electron microscopy methods that provide quantitative compositions at a resolution of 1 nm are more generally applicable to broad classes of materials. There are two main techniques: energy-filtered transmission electron microscopy (EFTEM) and spectrum imaging in the scanning transmission electron microscopy (STEM) mode. Both electron energy-loss spectrometry (EELS) and energy-dispersive X-ray spectroscopy (EDS) can be used in STEM spectrum imaging, whereas EFTEM is purely an EELS technique. Examples from recent research at the ORNL SHaRE User Facility will illustrate the techniques and will include aspects of work on intergranular segregation in thin-film CoCr(PtTa) magnetic recording media for computer hard disks, SiC/SiO2 interfacial compositions, nano-clusters in mechanically alloyed oxide-dispersion-strengthened ferritic steels, reaction ball-milled Y-Ni-O nanostructures, precipitation and segregation profiles in V-4%Cr-4%Ti, and reduced surfaces on ceria abrasive particles.
Biological Large Scale Integration
January 13, 2006; 3:30pm
Presented by:
Prof. Stephen Quake
Department of Bioengineering
Stanford University
The integrated circuit revolution changed our lives by automating computational tasks on a grand scale. My group has been asking whether a similar revolution could be enabled by automating biological tasks. To that end, we have developed a method of fabricating very small plumbing devices chips with small channels and valves that manipulate fluids containing biological molecules and cells, instead of the more familiar chips with wires and transistors that manipulate electrons. Using this technology, we have fabricated chips that have thousands of valves in an area of one square inch. We are using these chips in applications ranging from screening to structural genomics to ultrasensitive genetic analysis. However, there is also a substantial amount of basic physics to explore with these systems the properties of fluids change dramatically as the working volume is scaled from milliliters to nanoliters!