DAYS 1, 2
SUNDAY, MONDAY, August 15-16, 2010
Cancún is located in Mexico's easternmost state of Quintana Roo on the Yucatán Peninsula. The XIX International Materials Research Congress 2010 (IMRC 2010) is being held from August 15 through the 20th in Cancún at the J.W. Marriott and the Marriott Casa Magna hotels. The inaugural session was held on Sunday evening. This was followed by the first plenary lecture by Prof. Michele Parinello (ETH Zurich). A welcome reception was held after the plenary. The conference started in earnest on Monday with most symposia holding sessions. Other events on Monday included the poster session in the evening, funding agency seminars in the afternoon and the first day of the exhibit.
Ab Initio Molecular Dynamics Progress and Challenges - Michele Parrinello
Michele Parrinello is a trailblazer in the field of molecular dynamics. He is currently a full professor at ETH Zurich, Department of Chemistry and Applied Biosciences, and has held the position of Director of Solid State Research at the Max Planck Institute in Stuttgart, Germany. Parrinello’s groundbreaking work on the Ab Initio, Car-Parrinello, and the Parrinello-Rahman molecular dynamics methods has expanded the use of computational methods into several branches of materials science. His publication list is extensive and highly cited in a range of disciplines. Through his distinguished career, he has received numerous accolades and awards such as the Rahman prize of the American Physical Society in 1995, the American Chemical Society Award in Theoretical Chemistry in 2001, and most recently the Dirac Medal in 2009.
On the first night of the conference, Parrinello commenced the scientific program with a rousing talk on the current state of Ab Initio Molecular Dynamics in materials science (AIMD). Classic molecular dynamics (MD) is a computational method of determining the movement of atoms using the particles' potential energy. AIMD uses quantum mechanics, specifically Density Functional Theory (DFT) to approximate interactions. Parrinello noted that while AIMD is an ideal simulation method that is especially suitable for complex chemical reactions, it has significant disadvantages in dealing with mixed systems such as nanoparticles embedded in solid matrices. He stated that the challenges for the future are to produce, “Bigger, Better, and Longer” simulation methods. Because real-life problems require higher accuracy, more computing power, and longer time scales. To meet this challenge, he introduced the concept of metadynamics, a method that he and his group have developed to analyze molecular systems. This sampling method explores the surface free energy of the system. It provides enhanced sampling and minimizes convergence and overfilling issues. The model would provide significant benefits in simulating protein and lipid transitions.
Engineered Biotic/Abiotic Materials and interfaces for understanding and controlling biology - C. Jeffrey Brinker
The second plenary talk of the congress was presented by Prof. Jeffrey Brinker, Distinguished Regent's Professor of Chemical and Nuclear Engineering at the University of New Mexico and Fellow at Sandia National Laboratories. Brinker also holds faculty appointments in Molecular Genetics and Microbiology and the UNM Cancer Research and Treatment Center. Brinker has earned international recognition for his work in sol-gel processing and its application to self-assembly of nanostructures, and more recently to novel biotic/abiotic materials. His wide-ranging research has spanned a broad swath of areas. The primary motivations of his work are (1) to emulate proven biological designs in robust, processable engineering materials, in other words, improve upon Nature by nanostructuring, (2) to establish general, efficient self-assembly procedures/processing rules to create, integrate, and understand complex (organic/inorganic) functional nanostructures such as by evaporation-Induced Self-Assembly (EISA), and (3) direct assembly of engineered bio-nano interfaces to achieve biocompatibility, direct cellular behavior, and enable development of targeted nanoparticle delivery strategies, such as through cell-directed assembly, multi-photon protein lithography, and protocells. Brinker described specific examples of some of these areas in his presentation.
As one example of direct assembly of engineered bio-nano interfaces, Brinker described his latest work with silica nanoparticle-supported lipid bilayers called protocells. These cell-like structures synergistically combine advantages of porous inorganic nanoparticles and liposomes and represent a model nanomedicine platform. Key properties of protocells include enhanced cargo capacity, long-term stability, tunability of release rate and circulation time, and low inherent toxicity and immunogenicity. Protocells bearing the SP94 peptide were found to have a high specific affinity for human hepatocellular carcinoma and minimal interaction with healthy hepatocytes and other tissue. Brinker stated that SP94-modified protocells combine drastically enhanced capacity for chemotherapeutic agent cocktails, high specificity at low peptide densities, and long-term stability that is independent of the type of lipid in the supported bilayer. One protocell is sufficient to kill a cancer cell, a killing efficiency 105 greater than current liposome delivery agents
A fascinating aspect of Brinker's work is the integration of living cells within an inorganic framework. Cells can build ‘living’ nanostructures from exogenous components. Cells can serve as active colloids by creating localized chemical potential gradients that can redirect self-assembly and self-catalyze silica condensation. Cell-built nanostructures can symbiotically or diabolically influence cellular behavior. Chemical and mechanical ‘signaling’ reinforced by cellular integration and confinement within engineered synthetic envionments provides a new means to control and understand biology with materials science, which is important for applications including sensors, biofuel cells and cancer treatment.
Symposium 2: Theory and Computer Simulation of Materials
Hybrid Quantum Simulations of Biomolecules: The Role of Copper in Neurodegenerative DiseasesJerry Bernholc, of North Carolina State University, USA, reviewed molecular simulation methods used in biological applications and highlighted how the use of these quantum simulations can play a role in understanding protein based disease states. Biomolecules require models that take into account interactions between the molecule and a solvent. Bernholc indicated that this could be done using either an implicit model, an efficient method that treats the solvent as a continuum; or the more accurate explicit model which requires the calculations of more molecules. However, a hybrid model using both quantum mechanics and molecular mechanics is most suitable. His research group has developed their own hybrid model combining two density function theories (DFT), which merge the Kohn-Sham DFT with the frozen-density orbital free DFT. This method was used to study the interactions of the copper II ion with proteins, such as the α-synuclein found in neural tissue and the prion protein that causes Creutzfeld-Jacob disease. Bernholc’s research indicated that Cu (II)-protein binding results in the generation of a misfolded protein structure, which is intrinsic of both neurodegenerative diseases. With their hybrid model, they were able to analyze various binding geometries and suggest a mechanism for the misfolding of the protein.
Advanced Computing Technologies and U.S. National Open Science Cyberinfrastructure – Now and Soon
The Texas Advanced Computing Center (TACC) is a world-renowned leader in advanced computing support for visualizations. TACC Director Jay Boisseau presented an overview of TACC’s goals for increasing computational support to the scientific community, the current petascale cyberinfrastructure, and the future of high-speed computing. One of their chief concerns is increasing access of this computing power to a broader range of disciplines such as materials science, which has been underrepresented in the use of the systems at their facility relative to other disciplines. To help achieve this goal they have partnered with the NSF TeraGrid network which would create a hub at the Texas center and connect it to a nexus of 10 other resource providers throughout the United States. Over the years their facility has acquired several high performing computers, one of them being the Ranger, among the fastest computers in the world. Currently these technologies employ a petascale cyberinfrastructure which can have a computing performance greater than one petaflop, very useful for simulations using advanced computations. But Boisseau indicated that the future may be in exascale computing and that science will drive the need for faster and more powerful computers. The progression from petascale computing to exascale computing would be a thousand-fold increase in computing capabilities. But the biggest obstacle in this progression is the immense amounts of power needed, at least one gigawatt. Boisseau believes that the technology for his type of computing is several years away.
Symposium 4: Advanced Structural Materials
Quantitative 3-D Imaging of Single/Double Sheet Graphene
Graphene is being intensively investigated by numerous researchers. Since graphene is a 2-D layer of carbon atoms, it has been sunjected to TEM investigations, particularly high resolution TEM, to image the structure including defects. Researchers have used spherical aberration correction in TEM and STEM modes. However, no quantitative analysis of the electron dose has thus far been carried out even though the dose is critical. H. A. Calderon (USFN-IPN, Mexico City) gave a presentation on behalf of J. R. Jinschek (FEI Company, Eindhoven, The Netherlands) on using exit wave reconstruction and a 80 kV accelerating voltage to successfully quantitatively image the structure of graphene. 80 kV was used to minimize damage and maximize contrast of light elements. In a FEI Titan G2 TEM, focal series reconstruction (FSR) was used wherein 20 images at exposure time interval of 0.1 s were obtained, and the images formed a complex exit wave image. This still included residual aberration and is not directly interpretable. This residual aberration was then corrected using software yielding a corrected phase image that was directly interpretable and could be analyzed quantitatively.
This method was used to resolve and image a double layer of graphene, as confirmed using simulations. The difference between a single carbon atom position and a double carbon atom position, and an upper and lower layer single carbon atom could be distinguished, indicating that an atomic 3D structure was resolved. In fact the contrast difference between the upper and lower layer carbon atoms matched a focus change of 0.3 nm which is equivalent to the distance between two carbon sheets. The results suggest that graphene sheets can be quantitatively imaged in 3-D using FSR and exit wave reconstruction in the TEM. This method will be very valuable to investigate the structure of graphene and defects.
Symposium 6: Biomaterials
How does Surface Topography of Biomaterials Influence Cell Response?
Karine Anselme (Universite de Haute-Alsace) discussed how interest in cell-material interfaces is focused on the millimeter scale, but that this behavior is determined by interactions at micron and nanometer scales. It is therefore important to know how cells respond to the micro and nanotopology of surfaces. Specifically, Anselme showed the response of osteoblasts to a host of different surfaces: 5 different processes, 3 different metal alloys with each surface treated in 2 ways. It was determined that short term adhesion (24 hours) was dependent more on surface chemistry while long term adhesion (21 days) was determined more by surface topology, with isotropic roughness being more beneficial for adhesion. The best process, electro-erosion, was used to generate different surface roughness amplitudes from 1 to 21 microns while maintaining the same surface morphology, isotropic peaks and valleys. There is an apparent “sweet spot” for low adhesion of cells when surface roughness is about the same size scale as the cells. This provides an important length scale to keep in mind when designing materials for in vivo applications.
Symposium 7: Ecomaterials and Climate Change
Environmentally-Friendly Removal of Metallic Impurities in Rice Husks
Barbara Moreno-Murguía (Universidad Nacional Autonoma de Mexico) presented a poster on eco-friendly alternatives for the purification of silica extracted from rice husks. These agricultural by-products are a significant source of silica (~15-20% silica); however the husks typically contain 0.8-1.0% metallic impurities which must be removed to obtain silica of high purity which is of great industrial interest. Strong inorganic acids such as HCl, HNO3, and H2SO4 have been used to leach high purity silica from rice husks but these acids are hazardous to the humans and the environment and require special handling of wastes. Moreno-Murguía reported that the organic citric acid can be used to purify silica via a chelation reaction between carboxylic acid groups and the metal impurities. Citric acid leaching efficiency was quantified by Energy Dispersive X-ray Spectroscopy (EDS) as a function of concentration and was found to be a viable alternative for purification of silica from rice husks.
Symposium 9: Advances in Semiconducting Materials
Nanocomposites Polymer Latex – Carbon Nanotubes with Photonic Effect and Conductive Properties
In this poster presentation, L. Farias Cepeda, of the Universidad Autónoma De Coahuila, Mexico, demonstrated how a novel composite of carbon nanotubes (CNTs) and polymer latex nanoparticles can produce a material with optical and electrical properties suitable for use in the semiconductor, aeronautic, and medical industries. Core-shell particles, particles made with a polystyrene core surrounded by a poly (methylmethacrylate)-co-butylacrylate shell, were used to form the polymer latex. The composite was made by mixing an aqueous solution of those particles with CNTs functionalized with -COOH to increase hydrophilicity. After casting a thin film, material properties were examined by microscopic methods and FTIR. SEM images revealed strong interphase adhesion between the two particles due to similarities in functional groups. The images also revealed that the CNTs induced order into the particle system, by stimulating the formation of colloid crystals. The measured volumetric conductivity was found to be between 2.47 X 10-6 and 4.76 X 10-7 S/cm, values consistent with materials used in semiconductor applications. Cepeda concluded that due to the good electrical conductivity and multifunctionality of this new material, it would find use in a broad range of applications.
Symposium 17: Domain Engineering in Ferroic Systems
Domain Boundary Engineering
Domains in ferroic and other magnetic materials have been investigated for tailoring properties for applications such as memory devices. In his presentation, Ekhard Salje (University of Cambridge and Los Alamos National Lab.) made the case that domain boundaries can also be engineered to yield useful properties. For iinstance, enhanced conductivity has been observed in multiferroic domain walls of BiFeO3. This is because twin boundaries that forms the walls act as fast diffusion tracks for ions. The structure of domains walls is becoming clearer recently after several years of investigations. The domain wall itself has been shown to have a specific thickness. Salje showed how the wall can be described in terms of two coupled order parameters. He demonstrated how the twin wall in CaTiO3 could be described using these primary and secondary order parameters.
An interesting aspect is the modification of domain boundaries by defects for instance which modifies their properties. How can we tell whether a boundary has been modified? The answer according to Salje is to measure the movement of the interface and the pinning force. The interface always moves faster that any defects within. An interesting example he gave was SnTe, a phase change materials which contains no twin boundaries. However, by placing nucleation centers, Cr in the example, the material behaves more classically, as a magnetic material. In the case of CuAlBe, by introducing defects and nucleating dislocations, a factor of increase of up to 20 in the elastic modulus was obtained. All of these results suggest that domain wall engineering could be a very useful technique for various applications.
Symposium 20: Materials and Devices for Flexible Electronics
Thin Film Transistors Based on CdS Chalcogenide for Flexible Electronics
Ana L. Salas Villasenor of the University of Texas at Dallas, USA, described the synthesis of thin film transistors (TFTs) based on CdS n-type semiconductor as the active layer. The objectives of this work were to find the best gate dielectric material and thickness while developing a TFT suitable for flexible electronic applications. CdS was deposited onto SiO2 and HfO2 gate dielectrics via chemical bath deposition. Aluminum top contact was deposited using e-beam evaporation using shadow mask. The common gate metal was also aluminum. Villasenor reported significantly higher effective mobility of TFTs when HfO2 was used compared to SiO2, with no annealing performed before or after CdS deposition. Better performance of HfO2 was explained using XRD and XPS. XRD revealed that CdS films were more polycrystalline when grown on SiO2 resulting in more grain boundaries and therefore higher carrier scattering. Also, formation of Cd(OH)2 from hydroxyl groups on the HfO2 surface resulted in enhanced nucleation of CdS film compared to SiO2. Effective mobility of ~25 cm2/ Vs and threshold voltage of 2V were obtained for devices with 90 nm HfO2 gate dielectric. These values are the best reported for CdS TFTs to date.
Symposium 21: Nanomaterials for Biomedical Applications
Microengineered Hydrogels for Stem Cell Bioengineering and Tissue Regeneration
Stem cells are an attractive systemfor use in tissue engineering because of their ability to differentiate down numerous developmental pathways. One major challenge in this area of research is teasing apart how the cell’s physical environment affects how it behaves. As Prof. Ali Khademhosseini (Harvard-MIT) puts it, it is important to understand “what a cell sees determines what a cell does” because cells in vivo see a much different environment than researchers are currently able to replicate in an in vitro culture. Khademhosseini outlined different ways by which soft lithography microfabrication techniques have proven useful to address this question.
Methods to differentiate stem cells often begin with forming cell aggregates called embryoid bodies (EBs). By using microfabricated wells of poly(ethylene glycol) in sizes ranging from 150 to 450 microns in diameter, the size of the EBs was controlled before further steps were taken for differentiation. It was shown that larger EBs were better suited for cardiac differentiation while smaller EBs exhibited better performance when differentiated down endothelial lineages. Interestingly, non-canonical Wnt signaling was distinct in different sized EBs, with Wnt11 being abundant in large EBs while Wnt5a was more highly expressed in smaller EBs. By siRNA inhibition of Wnt5a in smaller EBs, performance in endothelial differentiation assays was diminished. More investigations into understanding these early signals and how they are affected by EB size are underway.
The next section of the talk described work aimed at replicating the complex 3-D environment that cells “see” within an organ. As a bottom-up approach, cells were encapsulated into microgels; small pieces of hydrogel of various shapes were created through stamping, molding, or stop-flow lithography techniques. These microgels were used as building blocks for self assembly of more complex structures using surface tension in a two-phase solution system or at an air-water interface. From the top-down perspective, channels were ablated inside hydrogels containing cells to mimic a vascular network. Cell viability was found to be higher nearer to the channels, presumably because access to diffusing nutrients was higher. This is an important design parameter to keep in mind moving forward with this idea. On the horizon are network structures built with the viability length scale in mind and seeding the channels with endothelial cells to encourage actual vascular growth within the “gel organ”.
Anticancer Effectiveness of Polymeric Prodrug micelles on HT-29 Human Colon Cancer Cells
Colorectal cancer is among the leading types of cancer in industrialized countries, and chemotherapy is currently the main treatment for metastatic forms. 5-FU is a common chemotherapeutic used, but it exhibits a poor serum half life and low selectivity for tumor cells which leads to high toxicity away from target areas. Ching-An Peng of Michigan Technological University, USA, described using micelles made of 5-DFUR, a hydrophobic prodrug form of 5-FU, grafted to chitosan, which is hydrophilic, to create an amphiphilic subunit that self-assembles into “prodrug micelles”. The prodrug can be transformed into the active drug through activity of the enzyme thymidine phosphorylase (TP). These micelles are endocytosed by the cells and processed into active drug by the cell’s own protein. Data showed that generating a stable cell line of HT-29 colon cancer cells that overexpressed TP increased the ability of the prodrug micelles to kill the cells, though unmodified HT-29 cells do have some TP which can make the drug active. Peng also showed preliminary data suggesting that delivering TP plasmid along with the prodrug micelles is also a feasible approach to enhancing the cell production of TP and therefore prodrug activation. This strategy of combining gene-dependent drug activation and gene delivery in one step is another step towards making chemotherapy drugs that are locally active and systemically less toxic.
Symposium 23: Nanostructure Applications in Crossover Scientific and Technology Fields
Integrated Nanobiosensors and Devices for Sensitive Electrical Detection of DNA Molecules
In a talk Monday afternoon, Rashid Bashir (University of Illinois at Urbana-Champaign, USA) spoke of an integrated microfluidic device his lab is developing for point-of-use detection of DNA molecules. This work is directed at food-borne pathogens, but could easily be expanded to include any type of DNA-based signatures as long as the target sequence is known. The device is an on-chip polymerase chain reaction (PCR) system that can detect small amounts of label-free DNA by amplifying a target sequence and sensing an increase in DNA concentration through electrical impedance measurements. PCR is performed on the device, which has microfluidic channels for reagents, temperature cycling capabilities, as well as sensors for the electrical measurements which take place as the reactions are running for in situ detection.
Data was shown to prove that the impedance detection approach works in low ionic strength solutions, for maximum effect, but also works well in standard PCR buffers containing moderate concentrations of ions. The PCR-based method is very sensitive, and the device is also highly specific. Whole cell lysate was tested, as well as a mixture of DNA from different pathogen species, and the target sequence was found each time. This system provides sensitive, accurate, label-free detection of DNA and represents a truly interdisciplinary effort.
Scanning the Conference
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