Moneesh Upmanyu Colorado School of Mines
L. Mahadevan Harvard University
Cait MacPhee Cambridge University
Jonathan V. Selinger Kent State University
G1: Carbon Nanotubes and Other Inorganic Nanofibers
Wednesday AM, November 29, 2006
Room 309 (Hynes)
9:30 AM - **G1.1
Novel Approaches for the Prediction of Atomic Structure of Quasi-1D Nanostructures.
Cristian Ciobanu 1 Show Abstract
1 Division of Engineering, Colorado School of Mines, GOlden, Colorado, United States
10:00 AM - *G1.2
Biomimetic Nanofibers Produced by a Solution-Precursor-Solid (SPS) Mechanism
Matthew Olszta 1 2 , Sara Jensen 1 , Laurie Gower 1 Show Abstract
1 Materials Science & Engineering, University of Florida, Gainesville, Florida, United States, 2 Materials Science & Engineering, Penn State University, State College, Pennsylvania, United States
Wednesday 11/29Presentation Time Extended to 30 minutes*G1.29:00 - 9:30 amBiomimetic Nanofibers Produced by a Solution-Precursor-Solid (SPS) Mechanism. Laurie B. Gower
10:30 AM - **G1.4
Solid-State Assembly of Carbon Nanotube Sheets
Mei Zhang 1 , Shaoli Fang 1 , Anvar Zakhidov 1 , Sergey Lee 1 , Ali Aliev 1 , Christopher Williams 1 , Ken Atkinson 2 , Ray Baughman 1 Show Abstract
1 Nanotech Institute, University of Texas at Dallas, Richardson, Texas, United States, 2 , CSIRO Textile & Fibre Technology, Belmont, Victoria, Australia
Individual carbon nanotubes (CNTs) are like minute bits of string, and many trillions of these invisible strings must be assembled to make useful macroscopic articles. Though major advances have been made on the fabrication of nanotube sheets and yarns, no one is yet able to assemble carbon nanotubes into sheets and yarns that retain the spectacular properties of the individual nanotubes. For fabricating sheets and yarns having close to single nanotube properties, we have developed a process to assemble CNTs by solid-state fabrication. The production processes involve growth of CNT forests by chemical vapor deposition (CVD) and then drawing CNTs from the forest. During CVD process, CNTs form small bundles of a few nanotubes each in the forest, with individual nanotubes moving in and out of different bundles. During drawing process, the nanotubes in the forest transition from the highly ordered forest state to a rather disordered intermediate state immediately in front of the forest sidewall, and then to the highly oriented aerogel state. Bundled nanotubes are simultaneously pulled from different elevations in the forest sidewall, so that they join with bundled nanotubes that have reached the top and bottom of the forest, thereby minimizing breaks in the resulting fibrils (containing many bundled CNTs). We have demonstrated the assembly at rates about 7 m/min by cooperatively flipping carbon nanotubes in vertically-oriented nanotube arrays (forests) and made five-centimeter-wide, meter-long transparent sheets. These self-supporting nanotube sheets, having fundamentally unlimited width and length, comprise a novel state of matter: a highly anisotropic electronically conducting aerogel with a density of about 0.0015 g/cm3 that can be densified into exceptionally strong sheets that are as thin as 50 nm. Experimental results suggest applications for transparent, highly elastomeric electrodes; low-noise electronic devices; planar sources of polarized broad-band radiation; two-dimensionally reinforced composites; welding agents for microwave bonding of plastics; conducting appliqués; and hole injecting electrodes for flexible organic light-emitting diodes.
11:30 AM - **G1.5
Engineering Carbon Nanotube Architectures for Applications
Pulickel Ajayan 1 Show Abstract
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
The talk will focus on the fabrication of carbon nanotube based architectures tailored for various applications. Various organized architectures of multiwalled and singlewalled carbon nanotubes can be fabricated using relatively simple vapor deposition processes and the work in attaining control on the directed assembly of nanotubes will be highlighted. We have pursued several novel applications for these structures, for example, as gas breakdown sensors, electrical interconnects, unique filters for separation technologies, thermal management systems, multifunctional brushes, and polymer infiltrated thin film composites. Some of these promising applications of carbon nanotubes and composites will be discussed.
12:00 PM - G1.6
Self-assembled Multi Wall Carbon Nanotubes Forming Macroporous 3D Architectures.
Francisco del Monte 1 , Maria Gutierrez 1 , Maria Hortigüela 1 , Zaira Garcia-Carvajal 1 , Ilida Ortega 1 , Matias Jobbagy 1 , Maria Ferrer 1 Show Abstract
1 , Institute for Materials Science at Madrid (ICMM), Spanish Research Council (CSIC), Madrid Spain
12:15 PM - G1.7
High Performance Carbon Nanotube Fibres Directly Spun from the CVD Reaction Zone.
Marcelo Motta 1 , Anna Moisala 1 , Krzysztof Koziol 1 , Juan Vilatela 1 , Ian Kinloch 1 , Alan Windle 1 Show Abstract
1 Dept. of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
We have developed a process for continuously spinning high performance carbon nanotube fibres directly from the catalytic vapour deposition zone in which the nanotubes are produced [Li et al. Science 304, 2004, 276-278]. In our process, a solution containing catalyst precursor (ferrocene), promoter (thiophene) and hydrocarbon feedstock (ethanol or hexane) is injected into a hot hydrogen atmosphere, where the ferrocene decomposes to form iron particles from which the nanotubes grow. The nanotubes then entangle into an aerogel which can be collected directly as a fibre or tape, depending on the spindle geometry. This paper studies the reaction chemistry of the process, explaining how either single, double or multi-walled nanotubes are produced depending on the growth parameters. The role of sulphur is also studied by using high resolution EELs, with elemental mapping finding a layer of sulphur on the surface of the iron. Previous results (Motta et al., Nano Letters, 2005, 5, 1529-1533) have shown that the nanotube fibres have promising fracture strength (up to 0.7 N/tex), with the best properties coming from the fibres containing predominantly thinner nanotubes (e.g. single-walled and double walled nanotubes). The latest mechanical values will be presented and related to the microstructure of the fibres.
12:30 PM - G1.8
Interactions Between Carbon Nanotubes and Bacteria
Pavan Raja 1 , Anurag Sharma 2 , Pulickel Ajayan 3 , Omkaram Nalamasu 3 4 5 Show Abstract
1 Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 4 Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, New York, United States, 5 Center for Integrated Electronics, Rensselaer Polytechnic Institute, Troy, New York, United States
While carbon nanotubes (CNTs) possess diverse application potential ranging from polymer nanocomposites to nanostructured therapeutic devices, their environmental implications are still not well understood. In this study, we conducted experiments to monitor changes in bacterial physiology as a consequence of interactions with the CNTs. Our experiments included a common anaerobe, Escherichia coli, in an SWNT system as a model for understanding the environmental implications of CNTs. Observations over several weeks indicated that the bacteria in the presence of SWNTs showed significant morphological changes, that included elongation. It is interesting to note that similar morphological changes have been reported in response to extreme temperature and pressure, chemical agents, and quantum dots. In this presentation, the authors will present further physiological evidence, such as bacterial growth and substrate consumption rates, towards defining a possible bacteria-CNT interaction model consistent with these experimental observations, and will discuss the overall environmental implications.
12:45 PM - G1.9
Effect of Aggregation on the Rheological Properties of Carbon Nanotube Dispersions
Sameer Rahatekar 1 2 , Jeffrey Gilman 2 , K. Koziol 1 , J. Elliott 1 , M. Shaffer 3 , S. Butler 4 , M. Mackley 4 , A. Windle 1 Show Abstract
1 Materials Sceince and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Fire Research Division, National Institue of Standards and Technology, Gaithersburg, Maryland, United States, 3 Department of Chemistry, Imperial College, London United Kingdom, 4 Department of Chemical Engineering, University of Cambridge, Cambridge United Kingdom
We report the rheological properties and corresponding microstructure of multiwall carbon nanotubes (MWCNTs) suspended in epoxy resin. Even with efficient dispersion, agglomeration of the MWCNTs appeared to be a key microstructural feature at high loading fraction of MWCNTs. Addition of just 0.5 wt% of MWCNT in epoxy resin resulted in 70 fold increase in the low shear viscosity of the MWCNT suspension as compared to the viscosity of base epoxy resin. For the sample containing very low MWCNTs concentration no significant viscosity enhancement was observed and isolated clusters of MWCNTs agglomerates were seen. Above the critical concentration threshold, there was a progressive increase in the low shear viscosity with increase in the MWCNTs concentration. The increase in the suspension viscosity was attributed to the formation of interconnected network of agglomerates of MWCNTs in the base epoxy resin. During steady state shear test, shear thinning of the suspension was observed with the viscosity asymptotically approaching that of the pure resin, at high shear rates. Optical microscopic observations indicated that the shear thinning behaviour could be due to a “de-flocculation” of the MWCNT agglomerates rather than shear-induced alignment of the MWCNTs. At high shear rates MWCNTs showed de-flocculation. However, when the de-flocculated sample was subjected to low shear, the “shear-induced agglomeration” was observed. The effect of increase in the temperature on the viscosity of MWCNTs suspension was also studied. With increase in the temperature, at high shear rates, the shear thinning behaviour was enhanced. The pure epoxy resin was found to show pure viscous behaviour (viscous modulus G” dominated system), whereas the 0.35 wt % MWCNTs sample showed solid-like behaviour at low shear rates (G’ dominated) and liquid like behaviour (G” dominated) at high shear rates. We also plan to extend our current approach to study microstructure and rheological behavior of dispersion of nanoparticles/nanoclay in low molecular weight dispersion medium. Such a study will be useful for general understanding processing behaviour of nanotube/nanoparticle aggregates.
G2: Amyloid Fibrils and Other Helical Fibrillar Aggregates
Wednesday PM, November 29, 2006
Room 303 (Hynes)
2:30 PM - G2.1
Aggregating Proteins as Building Blocks for Molecular Devices
Wojciech Dzwolak 1 , Urszula Narkiewicz 2 , Witold Lojkowski 1 Show Abstract
1 Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw Poland, 2 Institute of Chemical and Environment Engineering, Szczecin University of Technology, Szczecin Poland
Protein misfolding and spontaneous aggregation have profound medical implications, as they lead to a number of fatal disorders such Alzheimer, Parkinson, or the ‘prion’-associated Creutzfeldt - Jakob Diseases. Because formation of linearly-ordered aggregates, the so-called amyloids, reflects a common, generic in proteins feature, it can be also induced in benign proteins. Here we show how topologies, configurational variability, and dynamics of aggregating proteins may inspire novel strategies in engineering of molecular devices. One case concerns the amyloidogenic stacking of insulin molecules, which is tunable under high hydrostatic or osmotic pressure leading to formation of either straight nanopipes, or regular nanorings [1,2]. At the same time, the high specificity of the docking interactions between incoming protein monomers and the fibril’s end (during elongation of an amyloid fibril) suggests plausibility of employing fibrils as selective molecular receptors. As growth of amyloid may be triggered by seeding, and the conformational pattern of the template easily overrides environmental biases, it is now possible to obtain highly homogenous (in terms of morphology) samples of amyloid fibrils [3,4]. Another example of employing aggregation-prone biomolecules in nanoscience concerns pH-controllable ‘molecular Velcro’ system devised from a pair sequenceless polypeptides . Bionanomaterials manufactured through a spontaneous self-assembly of proteins may constitute a new generation of biocompatible scaffolds with programmable nanomechanical and biochemical properties, or, as the ‘Velcro’ system  Dzwolak W, Grudzielanek S, Smirnovas V, Ravindra R, Nicolini C, Jansen R, Loksztejn A, Porowski S, Winter R “Ethanol-Perturbed Amyloidogenic Self-Assembly of Insulin: Looking for Origins of Amyloid Strains” Biochemistry, 44 (2005) 8948, Jansen R, Grudzielanek S, Dzwolak W, Winter R, “High Pressure Promotes Circularly Shaped Insulin Amyloid” Journal of Molecular Biology, 338 (2004) 203, Dzwolak W, Jansen R, Smirnovas V, Loksztejn A, Porowski S, Winter R “Template-controlled conformational patterns of insulin fibrillar self-assembly reflect history of solvation of the amyloid nuclei” Physical Chemistry Chemical Physics 7 (2005) 1349, Dzwolak W, Smirnovas V, Jansen R, Winter R, “Insulin Forms Amyloid in a Strain-Dependent Manner: an FT-IR Spectroscopic Study” Protein Science, 13 (2004) 1927 Dzwolak W, Marszalek PE, “Zipper-like properties of [poly(L-lysine) + poly(L-glutamic acid)] beta-pleated molecular self-assembly” Chemical Communications 44 (2005) 5557
2:45 PM - G2.2
Poly(Glu) and Poly(Glu:Ala) Fibril Formation and CaCO3 Templating Ability.
Martin Colaco 1 , Jun Park 1 , Harvey Blanch 1 Show Abstract
1 Chemical Engineering, UC-Berkeley, Berkeley, California, United States
Amyloid fibrils are misfolded proteins that form ordered aggregates characterized by extensive β-sheet structure. Natural amyloids are most often found linked to diseases such as Alzheimer’s and Parkinson’s. Once formed, these fibril structures are usually temperature and pH stabilized over the native peptide conformation. In vitro studies have shown that amyloid-like fibrils can be formed from many different protein and polypeptide sequences with the appropriate solution conditions, indicating that fibril formation could be a general property of the peptide backbone. Due to their stability and sequence variety leading to different chemical functionality and fibril morphology, amyloid-like fibrils have potential nanotechnological applications. Our research here focuses on characterizing polyglutamic acid (PE) and a random polyglutamic acid/polyalanine (PEA) copolymer fibril formation, morphology, and surface chemistry through Thioflavin-T binding, AFM, and TEM. Additionally, we have studied the effect of seeding with both homo and heteropolymers on the morphology and kinetics of fibril formation. Finally, we have examined the ability of these fibrils to template CaCO3 formation and have analyzed the resulting composites through light microscopy and SEM.
3:00 PM - G2.3
Amyloid Fibrils for Alignment and Assembly of Conjugated Polyelectrolytes into Nanowire Geometries
Anna Herland 1 , Per Björk 1 , K Peter R Nilsson 1 , Ralph Hania 2 , Ivan G Scheblykin 2 , Per Hammarström 3 , Olle Inganäs 1 Show Abstract
1 Biomolecular and Organic Electronics, IFM, Linkoping Sweden, 2 , Chemical Physics, Lund Sweden, 3 Chemistry, IFM, Linkoping Sweden
The development of self-assembled nanoscopic materials for controlled bottom-up fabrication of electronic devices is of current interest. In this regard, the self-assembly and the well-ordered structures of biomolecules could be used as construction tools for the assembly of electronic devices. Among the geometries needed, wires are ubiquitous, either carrying current to devices, or formed into integrated devices.Amyloid fibrils have earlier been used to create metal nanowires, where metals were associated post-self-assembly of the fibrils. We have taken two different routes to combine conjugated polymers with amyloid fibrils into electroactive luminescent nanowires with ~10 nm width and lengths up to 10 µm. First, based on the affinity between the amyloid fibril structure and conjugated polyelectrolytes (CPE)[1,2] we have complexed amyloid fibrils with a CPE, poly(thiophene acetic acid) PTAA. Individual CPE decorated fibrils can be aligned through molecular combing (MC) on hydrophobic surfaces or through MC on patterned PDMS stamps and transferred to hydrophilic surfaces. The aligned fibrils have been studied with single molecule spectroscopy (SMS) to evaluate the fluorescence from single objects. Through measurements of the anisotropy of the emitted light from the fibrillar complexes we can conclude that the PTAA is highly oriented on the fibrils. The molecular axis of the CPE chain is preferentially aligned along the fibrillar axis.The second approach is a co-assembly of the amyloid fibril protein and conjugated oligoelectrolytes (COE) with a thiophene backbone. The luminescent oligomers were integrated into the fibril, which was evident from intensity and spectral distribution of the fluorescence and from the supramolecular structures in the form of bundled nanowires. The electro-optical properties of the wires are demonstrated with reversible electrochemical doping induced fluorescence quenching, demonstrating both electrical transport and electro activity. We suggest that this self-assembly method can be used for several types of electroactive organic materials. The possibility to design amyloid forming peptides can be used in the formation of wires or devices. The peptides can further be designed with address functions for anchoring of the wire to electrodes or other wires. Furthermore, changes in optical properties of the CPE or COE can be used to probe amyloid fibril formation. The conformation changes of the protein result in alterations in the geometry and the electronic structure of the conjugated chains, which have been monitored with absorption and emission spectroscopy. A development towards more complex samples is that we have shown selective staining of amyloid with CPE in tissue samples. 1) Nilsson KPR, et al., BIOCHEMISTRY 44 3718-3724 2005 2) Herland A, et al. JACS 127 2317-2323 2005 3) Herland A., et al submitted 4) Herland A, et al. ADV MAT 17 1466-1471 2005 5) Nilsson KPR, et al. CHEMBIOCHEM 2006
3:15 PM - G2.4
Assembly of β-Sheet Fibrils with Desired Morphology via Designed Peptides.
Matthew Lamm 1 , Karthikan Rajagopal 2 , Ronak Rughani 2 , Joel Schneider 2 , Darrin Pochan 1 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Chemistry and Biochemistry, University of Delaware, Newark, Delaware, United States
Synthetic peptides have been de novo designed to self-assemble into nanoscale, β-sheet rich fibrils of varying morphology. A unique, nontwisted, laminated morphology has been observed in peptides containing a central diproline sequence, resulting in self-assembly in 2-dimensions. The role of peptide sequence, diproline placement, solution conditions and kinetics is explored in the context of understanding the mechanism of self-assembly and the resulting morphology. In addition, fibrils have been used as templates for two-dimensional ordering and structuring of inorganic materials such as oxides and metals where fibril morphology is transferred to the resulting peptide-inorganic hybrid material. Characterization techniques include electron microscopy, atomic force microscopy, FT-IR, circular dichroism spectroscopy and x-ray diffraction.
4:00 PM - G2.5
Nanostructure and Nanomechanical Studies of Peptide Glucagon Fibrils by Atomic Force Microscopy.
Mingdong Dong 1 2 , Daniel Otzen 1 3 , Flemming Besenbacher 1 2 Show Abstract
1 Interdisciplinary Nanoscience Center , University of Aarhus, Aarhus Denmark, 2 Department of Physics and Astronomy, University of Aarhus, Aarhus Denmark, 3 Department of Life Sciences, Aalborg University, Aalborg Denmark
Glucagon is a 29 residue peptide amphiphatic hormone, involved in the regulation of blood glucose levels in conjunction with insulin. In concentrated aqueous solutions of glucagon, peptides spontaneously aggregate to form amyloid fibrils, limiting the stability of hormone. It is an important issue to study the structure and mechanical properties of glucagons fibrils in order to understand the mechanism of fibril formation. In this work, we have used Atomic Force Microscopy (AFM) to study in detail the in vitro genesis and structure of glucagon fibrils at pH 2.0 to reveal fibrillogenesis pathway. AFM-based single molecule force spectroscopy (SMFS)provides the stretching experiments to reveal an overstretching transition of single glucagons fibril. Thus AFM is able to assist understanding the relation between structure, function, and mechanical properties of glucagons fibrils.
4:15 PM - G2.6
Shape Selection in Self-Assembled Chiral Membranes: New Mechanism Based on the Flexoelectric Effect.
Zhao Lu 1 , Robin Selinger 1 , Jonathan Selinger 1 Show Abstract
1 Liquid Crystal Institute, Kent State University, Kent, Ohio, United States
Many amphiphilic molecules self-assemble into cylindrical tubules, helical ribbons, and other twisted microstructures in solution. These structures have been studied extensively in diacetylenic lipid systems. They also occur in a wide range of other materials, including chiral diblock copolymers, charged achiral surfactants with chiral counterions, naturally occurring bile, and synthetic analogues of bile.Several investigators have proposed theories to explain the formation of tubules and related twisted microstructures based on chirality of the membrane. In particular, a continuum elastic theory shows that chirality can lead both to cylindrical curvature and to a helical modulation in the molecular orientation. This theory can explain many aspects of tubule formation, including (1) the observation of helical ribbons, as well as helical stripes winding around most tubules, (2) the correlation between the observed helical sense of the tubules and the chirality of the constituent molecules, in most experiments, and (3) the observation of very high circular dichroism in the tubule phase of lipids.However, the theory still leaves some open questions about tubule formation: Why do certain experiments show tubules with the "wrong" helical sense, compared with the chirality of the molecules? Why do certain achiral molecules form tubules with a random helical sense?To address these questions, we suggest a new mechanism for tubule formation based on the flexoelectric effect. The basic physical concept is that whenever a bend distortion is imposed on a liquid-crystalline phase, the molecules develop order in their transverse orientation, perpendicular to the director. Conversely, whenever there is order in the transverse axis of the molecules, there should be a favored bend in the director. If the molecules are in a membrane, the favored bend should lead to a curvature of the membrane. This is a new mechanism to induce curvature, different from the favored twist associated with chirality, or the favored splay (spontaneous curvature) associated with asymmetry between the two sides of the bilayer.We investigate this concept, using analytic calculations and numerical simulations. Our results show that this mechanism leads to both the formation of curved microstructures and a spontaneous chiral symmetry-breaking transition, even if molecular chirality is absent. If molecular chirality is present, it should bias the sense of the symmetry-breaking transition.This model is promising because it suggests that tubule formation is caused by orientational ordering of the transverse axis of the molecules. This seems plausible in terms of the chemistry: The most distinctive feature of tubule-forming molecules is the kink in the molecular tails, which may well provide transverse order. It seems reasonable to associate this transverse axis with the distinctive tubule formation in these lipids.
4:30 PM - G2.7
Charged Helical Patterns on the Surface Nanofibers and the Salt-induced Melting of the Nanopatterns.
Kevin Kohlstedt 1 , Francisco Solis 1 , Graziano Vernizzi 1 , Monica Olvera de la Cruz 1 Show Abstract
1 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Co-assembled molecules of opposite charge, which have a degree of intermolecular incompatibility, lead to surface charge heterogeneities. Similar heterogeneities can result in the adsorption of cationic amphiphilic molecules such as binding protein ligands along anionic fibers. The stability of incompatible mixtures of cationic and anionic amphiphiles, co-assembled into micelles, is determined by the surface charge heterogeneities, in which charged ligands can bind to the surface of the micelles. The competition between electrostatic interaction, favoring ionic structures, and the net incompatibility of the co-assembled species, favoring macroscopic segregation, leads to local segregation and the formation of regular patterns along the surface of the aggregates.We analyze the symmetry and size of the surface patterns on the surface of cylindrical structures. Striped patterns are arranged into helical structures along the cylinder breaking the chiral symmetry of the fiber. At high salt concentrations the surface domain size jumps discontinuously to an infinite value, resulting in macroscopic phase segregation of the components. The critical amount of salt concentration depends on the angle (pitch) of the stripe with the fiber axis suggesting a physical way to separate fibers with patterns with different pitches.
4:45 PM - G2.8
Liquid-crystalline Collagen Phase Leading to Dense Ordered Matrices.
Frederic Gobeaux 1 2 , Emmanuel Belamie 1 , Gervaise Mosser 1 , Patrick Davidson 2 , Pierre Panine 3 , Marie-Madeleine Giraud-Guille 1 Show Abstract
1 Chimie de la Matière Condensée UMR 7574, CNRS-UPMC-EPHE, Paris France, 2 Laboratoire de Physique du Solide UMR 8502, CNRS-UPS XI, Orsay France, 3 High Brilliance Beamline ID2, European Synchrotron Radiation Facility, Grenoble France
Dense ordered collagen matrices can be obtained by fine tuning the electrostatic interactionsin highly concentrated solutions of type I collagen . Such biomimetic fibrillar materialshave a high application potential in the field of tissue engineering , owing to their structuralidentity with major biological tissues like cornea, tendon, skin and bone. It is thereforeimportant to understand extensively the guided-and self-assembly properties of the precursorliquid-crystalline (LC) collagen phase.Concentrated solutions of acid-soluble collagen spontaneously form a cholesteric (chiralnematic) phase because of excluded volume effects. Uniaxially oriented LC solutions areproduced by applying a moderate shear-stress. We characterized the positional order acrossthe isotropic/anisotropic (I/N*) phase transition and showed for the first time that interparticlescattering between collagen triple helices gives rise to an interference peak recorded by SAXS(Small Angle X-ray Scattering). The average distance between triple helices dave is thusestimated and shown to decrease linearly as a function of Φ-1/2 from 14.2 ±1.2 nm (20 mg/mL)to 5 ±0.6 nm (160 mg/mL). The I/N* coexistence concentrations and the order parameter ofthe nematic phase agree well with theoretical predictions for semiflexible macromolecules.Electrostatic attractive forces overcome repulsive forces over a rather wide pH range (6-13),around the isoelectric point (9,3). In those conditions we have obtained the famous 67 nm-striatedfibrils in extremely dense collagen matrices, while maintaining the long-range orderinherited from the LC phase. The axial periodicity of the fibrils and their macroscopicalignment have been assessed by SAXS and TEM imaging. In particular, we were able torecord, in reassembled dense matrices, the typical Bragg reflexions corresponding to the 67nm-period characteristic of collagen fibrils in biological tissues.Most biological systems benefit from a long process of evolutive design that selected thecompositions and structures best suited for their functional properties. Bone for instancecombines (i) a dense collagen matrix with the same helical structure as in a cholesteric LC,(ii) hydroxyapatite nanocrystals and (iii) specialized cells responsible for tissue remodeling(osteoclasts and osteoblasts). The results presented here are therefore very promising fortissue-engineering applications, in particular for bone reconstruction, since these matrices canbe mineralized, and used to host and carry osteoblastic cells. G. Mosser, A. Anglo, C. Helary, Y. Bouligand and M.-M. Giraud-Guille “Dense tissue-like collagen matricesformed in cell-free conditions” Matrix Biology, 25, 1 (2006) 3-13 C. Helary, A. Foucault-Bertaud, G. Godeau, B. Coulomb and M.-M. Giraud Guille“Fibroblast populated dense collagen matrices: cell migration, cell density and metalloproteinases expression”Biomaterials, 26, 13 (2005) 1533-1543
G3: Poster Session: Fibrillar Materials
Wednesday PM, November 29, 2006
Exhibition Hall D (Hynes)
9:00 PM - G3.1
Fabrication of Nanotapes by Solution-based Nanocoating Process (III)-Silver Nanotapes Prepared by Electroless Plating.
Kentaro Miyoshi 1 , Shigenori Fujikawa 1 , Toyoki Kunitake 1 Show Abstract
1 Innovative Nanopatterning Laboratory, RIKEN, Saitama Japan
9:00 PM - G3.2
Fabrication of Nanotapes by Solution-based Nanocoating Process (I)-Metal Oxide Nanotapes with the Binary Compositions of SiO2 and TiO2.
Rie Takaki 1 , Shigenori Fujikawa 1 , Toyoki Kunitake 1 Show Abstract
1 Innovative Nanopatterning Laboratory, RIKEN, Wako Japan
9:00 PM - G3.3
Fabrication of Nanotapes by Solution-based Nanocoating Process (II)-Nanotapes with the Compositions of Polymers and Metal Oxides.
Shigenori Fujikawa 1 , Rie Takaki 1 , Toyoki Kunitake 1 Show Abstract
1 Topochemical Design Lab./Innovative Nanopatterning Lab, RIKEN, Wako, Saitama, Japan
9:00 PM - G3.4
Preparation of Long Monocrystalline Silicon Carbide Fibers by Sol-Gel Process.
Bettina Friedel 1 , Siegmund Greulich-Weber 1 Show Abstract
1 Department of Physics, University of Paderborn, Paderborn Germany
Ceramic fibers of silicon carbide are a commonly used for composite materials. Usually these fibers cannot take full advantage of the extraordinary properties of SiC, because the fibers are either amorphous or polycrystalline. We show a method for the easy and cost-effective synthesis of long monocrystalline silicon carbide fibers using a sol-gel process, followed by carbothermal reduction, in which tetraethoxysilane was used as silicon and saccharose as carbon source. Diameters of as-grown fibers varied depending on process parameters from several tens to several hundreds nanometers, whereas the length of the fibers even was located in the millimetre region. Silicon carbide fibers were synthesized pure without the presence of any carbon or silica residues, by careful controlling the atomic ratio of Si / C. Their consistence supports preparation of silicon carbide textiles, felts or papers. Silicon carbide is a very hard material, stable against most chemicals and heat resistant. Such tissues are therefore usable for many applications such as for fireproof clothing, high temperature or chemical filters and for composite materials. Additionally the silicon carbide fibers were easily doped during sol-gel synthesis, to achieve p- or n-conduction within, guiding to new applications in the field of wide bandgap semiconductors. The structure of 3C-SiC fibers was determined using scanning electron microscopy, X-ray diffraction, nuclear magnetic resonance and fourier transform infrared spectroscopy. The electronic properties were studied using electron paramagnetic resonance spectroscopy and current-voltage measurements.
9:00 PM - G3.5
Characterization of Repetitive and Block-Copolymerized Polypeptides.
Seiichiro Higashiya 1 , Natalya Topilina 1 , John Welch 1 Show Abstract
1 Chemistry, University at Albany, Albany, New York, United States
9:00 PM - G3.6
Kinetics and Morphology of Carbon Nanotube Aggregation from Charged Supramolecular Complexes.
Harsh Chaturvedi 2 , Andrea Giordano 1 , Ryan Phillips 1 , Thomas Younts 1 , Jordan Poler 1 2 Show Abstract
2 Center for Optoelectronics and Optical Communications, UNC Charlotte, Charlotte, North Carolina, United States, 1 Chemistry, UNC Charlotte, Charlotte, North Carolina, United States
9:00 PM - G3.7
Electrochemical Synthesis of Superhydrophobic Conducting Polyaniline Films Consisting of Helical Sub-Micron Fibers
Lianbin Xu 1 , Zhongwei Chen 1 , Wilfred Chen 1 , Ashok Mulchandani 1 , Yushan Yan 1 Show Abstract
1 Department of Chemical and Environmental Engineering, University of California at Riverside, Riverside, California, United States
Superhydrophobic conducting polyaniline films are electrochemically deposited in acetonitrile-water electrolyte containing aniline monomer and perfluorooctanesulfonic (PFOS) acid. The polyaniline films exhibit extended network structure composed of helical polyaniline sub-micron fibers. The surface of the PFOS-doped polyaniline films shows a water contact angle of 153 degrees. Details on the preparation and characterization of the helical fibrous conducting polyaniline films are presented including scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), UV-Vis spectroscopy, cyclic voltammetry (CV), contact angle, and conductivity measurements.
Moneesh Upmanyu Colorado School of Mines
L. Mahadevan Harvard University
Cait MacPhee Cambridge University
Jonathan V. Selinger Kent State University
G4: Protein Fibrillar Networks and Other Organic Fibers
Thursday AM, November 30, 2006
Room 303 (Hynes)
9:30 AM - G4.1
Self-Assembled Peptide Structures: from Fibers to Hydrogels.
Antonios Konstantopolous 1 , Amran Mohammed 2 , Alberto Saiani 1 2 , Aline Miller 1 Show Abstract
1 School of Chemical Engineering and Analytical Science, University of Manchester, Manchester United Kingdom, 2 School of Materials, University of Manchester, Manchester United Kingdom
Molecular self-assembly is a powerful tool for the preparation of molecular materials with a wide variety of properties. This is illustrated by the abundance of self-assembled proteins and polysaccharides encountered in nature. Peptides are particularly promising as building blocks for a number of reasons. The natural amino acid pool consists of 20 members with different physical properties including polar, non-polar, acid, basic and aromatic groups. In addition, an infinite number of unnatural amino acids can be designed in the laboratory. Amino acids can be combined in endless different ways leading to a vast number of building blocks with different physical properties. However, the understanding of the molecular interactions and self assembly rules in these materials is still limited; consequently, the fundamental link between building block structure, mesoscopic structure and material properties has yet to be elucidated. To address this we have focused our work on an evolutionary series of so-called ionic- complementary peptides. Here we discuss our results for a systematic series of octo-peptides synthesized in our laboratory with different hydrophobicities, size and alternating charges based on the following amino acids: alanine (A), glutamic acid (E), lysine (K), phenylalanine (F) and aspartic acid (D). The following peptides have been synthesised:AEAEAKAK, FEFEFKFK, FDFDFKFK, FDFDFRFRAEAKAEAK, FEFKFEFK, FDFKFDFK, FDFRFDFR. Peptide solutions were prepared by dissolving the desired quantity of peptide in distilled water at 90 oC and the resulting pH was always between 6 and 7. The solutions were subsequently cooled at room temperature. We found all peptides were capable of forming fibrillar structures. Despite alanine based peptide molecules forming fibers they did not form hydrogels in the concentration range investigated (1 to 80 mg ml-1), while all phenylalanine based peptides formed hydrogels upon cooling. Fiber dimension and the critical gelation concentration were both found to be a function of the type of amino acids used as well as the charge distribution along the peptide sequence. Structure-property relationships across the length scales have been elucidated for these peptide systems by relating structural information, including secondary structure, hydrogen bonding (infra red spectroscopy), fibril dimension (AFM and TEM) and network morphology (cryo-SEM and SANS) to their rheological properties (oscillatory rheology). In this paper we will discuss in detail these results as a function of concentration, pH and ionic strength of the media, and also propose a generalized gelation mechanism.
9:45 AM - G4.2
Thermo-Reversible Protein Fibrillar Hydrogels as Cell Scaffolds
Hui Yan 1 , Julie Gough 2 , Alberto Saiani 2 , Aline Miller 1 Show Abstract
1 School of Chemical Engineering and Analytical Science, University of Manchester, Manchester United Kingdom, 2 School of Materials, University of Manchester, Manchester United Kingdom
Hydrogels have recently attracted much interest in the biomaterials sector because of their ability to entrap large quantities of water or biological fluids. This high water content mimics the natural living environment which gives them excellent biocompatibility. Moreover, their porous microstructure gives them good permeability while the 3-dimensional network provides mechanical support. Over the past few decades many synthetic hydrogels have been developed and used extensively in biomedical applications. Recent research has focused on creating hydrogels from natural materials including peptides and proteins. However, the fundamental understanding of how these building blocks self-assemble has yet to be fully elucidated.Here we will focus on the self-assembly, gelation behavior and application potential of the model protein hen egg white lysozyme (HEWL) under physiological conditions. Hydrogels have been prepared by dissolving 2 - 5 mM of protein in either a 20 or 50 mM DTT/water mixture, heating to 85 °C and cooling at room temperature. No gels were observed below the critical concentration of 2 mM of protein or for the equivalent sample without DTT. The elastic nature of the gel formed were confirmed by rheology and the storage moduli of our gels were found to be of the same order of magnitude as other cross linked biopolymers. Micro differential scanning calorimetry (microDSC) experiments confirmed that the hydrogels were thermally reversible and that gelation and melting occurs through a solid-liquid like 1st order transition. Congo red assay and transmission electron microscopy studies of very dilute samples revealed the presence of beta-sheet rich fibrils that were ~ 4 – 6 nanometers in diameter and 1 micron in length. These fibrils are thought to self-assemble along their long axes to form larger fibers that become physically entangled to form the 3-dimensional network observed in both cryoSEM and small angle neutron scattering studies. The potential of our hydrogels to be used as tissue engineering scaffolds has also been explored by culturing our gels with 3T3 fibroblasts. In this paper we will discuss in detail the results obtained for lysozyme under reductive conditions and propose a gelation mechanism. Additional results for lysozyme hydrogels formed at various pH’s will also be presented and similarities and differences highlighted.
10:00 AM - G4.3
Collagen and Fibrin Microthreads in a Discrete Thread Model of in Vitro ACL Scaffold Regeneration.
Kevin Cornwell 1 2 , George Pins 1 Show Abstract
1 Biomedical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts, United States, 2 , University of Massachusetts Medical School, Worcester, Massachusetts, United States
10:15 AM - G4.4
Design and Fabrication of a Multiphase Osteochondral Scaffold.
Brendan Harley 1 , Andrew Lynn 2 , Zachary Wissner-Gross 1 , William Bonfield 2 , Ioannis Yannas 1 , Lorna Gibson 3 Show Abstract
1 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, 2 , Cambridge University, Cambridge United Kingdom, 3 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
11:00 AM - G4.5
Enzyme-Triggered Self-Assembly of Peptide Hydrogels.
Rein Ulijn 1 , Andrew Smith 1 , Richard Williams 1 Show Abstract
1 School of Materials, University of Manchester, Manchester United Kingdom
Self-assembly of macroscopic materials from small-molecule building blocks provides a route to designed molecular biomaterials. The ability to control the assembly of these structures on demand by application of an external stimulus is of value, especially in biomedical contexts. For example, in minimal invasive surgery for tissue repair, a liquid precursor is mixed with cells and injected into the body to form a gel scaffold in situ for tissue regrowth. Stimuli that have been used to trigger self-assembly include a variety of chemical and physical means, such as changes in ionic strength, pH, and temperature, and addition of certain chemical entities. An alternative approach is to exploit enzyme catalyzed reactions as selective biological stimuli to trigger hydrogel assembly. This approach has a number of advantages because enzymes highly selective, work under mild conditions (aqueous, pH 5-8, 37 °C) and play key roles as selective catalysts in cell pathways and disease states.We recently described a conceptually novel approach by using proteases, enzymes that normally hydrolyze peptide bonds in aqueous medium, to perform the reverse reaction (i.e., peptide synthesis or reversed hydrolysis) to produce amphiphilic peptide hydrogelators that self-assemble to form nanofibrous structures (Toledano et al, JACS, 2006). The self-assembly mechanism that is exploited builds on recent reports by us and others that demonstrated that a number of N-(fluorenylmethoxycarbonyl) (Fmoc)-modified di- and tri-peptides self-assemble into nanofibrous structures driven by pi-stacking of the conjugated fluorenyl group further stabilized by hydrogen bonding. We used IR, Fluorescence and CD spectroscopies combined with Cryo-scanning electron microscopy to verify the formation of nano-scale fibrillar structures with time. We believe that enzyme triggered formation of fibrillar gels may have applications in minimal invasive surgery for tissue repair.
11:15 AM - G4.6
Structural Polymorphism of the Actin-espin System: A Prototypical System of Filaments and Linkers in Stereocilia.
Kirstin Purdy 1 , James Bartles 2 , Gerard Wong 1 Show Abstract
1 Materials Science and Engineering, University of Illinois at Urbana Champaign, Urbana, Illinois, United States, 2 Department of Cell and Molecular Biology, Northwestern University, Feinberg School of Medicine, Chicago, Illinois, United States
11:30 AM - G4.7
Effects of Fabrication Parameters on the Mechanical Strength of Cellulose Nanocrystal-Polymer Composite Thin Films.
Lang Sui 1 , Paul Podsiadlo 2 , Nicholas Kotov 3 2 1 , John Kieffer 1 Show Abstract
1 Material Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Cellulose nanocrystals can be derived from many natural materials such as wood, cotton, and tunicate. The strength of a single crystal is one-seventh that of carbon nanotube (~1 TPa). Fabrication of thin films using the layer-by-layer (LBL) method creates films with very high loading of cellulose nanocrystals, as well as high deposition rates. This results in a polymer/nanocrystal film with exceptional strength. Additionally, the low cost of raw material, ease of dispersion, and adsorption quality may allow for more efficient mass production of layer-by-layer composite films using either dipping or spraying methods.In this study, thin films were fabricated via LBL using polyvinyl alcohol (PVA) solutions containing short (~200 nm) cellulose nanocrystals derived from the hydrolysis of cotton or long (~2 μm) ones derived from tunicate. For the LBL method thin multilayered films were created from the alternating deposition of oppositely charged PVA and cellulose nanocrystals onto Si wafers. The thicknesses of PVA layers were adjusted by varying the pH and salt content of PVA solutions. The films were then treated with glutaraldehyde and heated to promote cross-linking. The elastic moduli of the films were determined using Brillouin light scattering, which measures the inelastic scattering of light from its interactions with acoustic phonons. For PVA/nanocrystal films with total thickness of ~1 μm, higher elastic moduli was found by creating films with thicker individual layers, longer crystals length, and cross-linking using glutaraldehyde.
11:45 AM - G4.8
Coaxial Electrospinning of Nanofibers with Phase Change Properties
Jesse McCann 1 , Manuel Marquez 2 , Younan Xia 1 Show Abstract
1 Department of Chemistry, University of Washington, Seattle, Washington, United States, 2 INEST, PMUSA, Richmond, Virginia, United States
We have developed a coaxial electrospinning method for fabricating phase change nanofibers composed of long-chain paraffin cores and composite sheaths. This method combines melt electrospinning with a coaxial spinneret, and allows for nonpolar solids such as paraffins to be encapsulated and electrospun in one step. Shape-stabilized phase change fibers have many potential applications as they are able to absorb, hold, and emit large amounts of thermal energy over a certain temperature range by taking advantage of the large heat of fusion of long-chain alkanes. Compounds with melting points near room temperature and body temperature were chosen for our studies as these temperature ranges are the most useful. We have created thermally-stable phase change materials up to 45 wt% loading, as measured by differential scanning calorimetry. In addition, the resultant fibers display novel segmented core morphologies due to the rapid solidification of the alkanes driven by evaporative cooling of the carrier solution. Aside from the fabrication of phase change fibers, the melt coaxial method is promising for applications involving encapsulation and controlled release.
12:00 PM - G4.9
Electrochemical Organic Transistors Integrated on 3D Mirco Thread Networks.
Mahiar Hamedi 1 , Robert Forchheimer 2 , Olle Inganas 1 Show Abstract
1 Biomolecular and Organic Electronics, IFM, Linkoping Sweden, 2 , ISY, Linkoping Sweden