Shu Yang University of Pennsylvania
Fiona Meldrum University of Leeds
Nicholas Kotov University of Michigan
Christopher Li Drexel University
MM1: Bioinspired Synthesis and Assembly
Tuesday PM, April 14, 2009
Room 3020 (Moscone West)
9:00 AM - **MM1.1
Patchy Micelles and Liposomal Systems: Modular Assembly for Drug and Gene Delivery
Paula Hammond 1 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
The ability to manipulate micellar structures to achieve optimal biomaterials properties has been one of the primary goals in the design of biomimetic and bioinspired materials systems. Natural systems often present molecular recognition sites on the surfaces of cell walls in clusters or predetermined groupings based on multivalent binding sites. Although it has been shown that binding avidity can be greatly influenced by the presence of multivalent ligands, there is little known about the impact of the nature of presentation of ligand. Cluster presentation has been shown to be of critical importance in cellular functions such as adhesion and mobility. Here we explore the role of cluster presentation of ligand on patchy micelles generated by the self-assembly of linear dendritic block copolymers. Key to the approach is the synthesis of new amphiphilic linear peptide-dendritic block copolymers that self-assemble in the solution state to generate stable micelles with highly branched, dense dendritic groups in the exterior shell. Due to the unique nature of the dendritic outer block, these micelles act as vessels with a highly tunable 3D presentation of ligand, enabling the creation of delivery nanoparticles with homo- or heterogeneous surfaces that enable cluster presentation of ligand. Biological studies of cellular interactions with ligands indicate that not only the valency but spatial and geometric factors such as branching mode and the localized clustering of groups are important in influencing binding, intracellular uptake and downstream signaling processes. In vitro and in vivo studies indicate that these factors have significant influence on uptake. Additional studies on the general self-assembly behavior of these peptide-dendritic systems, and the resulting formation of liposomal and other colloidal structures will also be discussed.
9:30 AM - **MM1.2
The Molecular Structure of Helical Supramolecular Dendrimers
Virgil Percec 1 Show Abstract
1 Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Helical secondary structures represent one of the most fundamental architecture encountered in biological macromolecules. Our laboratory is using self-assembling dendrons as a model to mimic and understand the principles via which helical structures are assembled. In this presentation the molecular structure of helical supramolecular dendrimers generated from self-assembling dendrons and dendrimers and from self-organizable dendronized polymers was elucidated by the simulation of the x-ray diffraction patterns of their oriented fibers by using the helical diffraction theory applied to simplified atomic helical models and Cerius2 calculations based on complete molecular helical structures. Hundreds of samples were screened until a library containing fourteen supramolecular dendrimers and dendronized polymers provided a sufficient number of helical features in their oriented fibers. These techniques provided examples of single-92 and -113 helices, triple-61, -81, -91 and -121 helices and an octa-321 helix that were assembled from crown-like dendrimers, hollow and non-hollow supramolecular crown-like dendrimers, hollow and non-hollow supramolecular disc-like dendrimers, hollow and non-hollow supramolecular and macromolecular helicene-like architectures. The method elaborated here was transplanted from structural biology and will be applicable to other classes of synthetic helical assemblies. These experiments demonstrated that self-assembling dendrons, dendrimers and self-organizable dendronized polymers have a simpler primary structure and more complex topology but exhibit a richer architectural diversity of their secondary structure than proteins, nucleic acids and carbohydrates. The elaboration of new functions based on helical assemblies will be discussed.
10:00 AM - MM1.3
Bio-inspired Use of Ionically Crosslinked Polyamines in Hollow Sphere Synthesis
Shyam Kadali 1 , Hitesh Bagaria 1 , Michael Wong 1 2 Show Abstract
1 Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas, United States, 2 Department of Chemistry, Rice University, Houston, Texas, United States
In nature, it is shown that polyamines behave in unusual ways in solution due to their charged nature and some times generate specific assemblies [1-2]. Studies have revealed that, in biosilification, naturally-occurring polyamines adopt particular conformations depending on their concentration and salts present, and cause aggregation of silica species [2-3]. To take advantage of this behavior, we developed a materials synthesis technique in which synthetic polyamines such as polyallylamine and polylysine are crosslinked with multivalent anions like citrate to form polymer-salt aggregates, that then serve as templates for the deposition of nanoparticles to form micron-sized hollow spheres or "nanoparticle-assembled capsules (NACs)" [4-5]. This electrostatically-driven route is attractive for encapsulation and scale-up because encapsulation and materials formation occur in water, at mild pH values, and at room temperature.NACs can potentially find wide-ranging applications in pharmaceutical, food, and consumer industries by serving as miniature containers to store, deliver, and release substances. One of the most encouraging aspects of NACs is the flexibility in design of materials to tailor them for specific applications. Although synthesis of NACs is well understood [4-5], less attention has been paid to their structural properties and stability. It is of crucial importance to address this aspect of NACs in view of their use and applicability. While most applications may require that NACs not disassemble or deform under shear stress, some may require triggered release under specific conditions to release the encapsulated material (e.g., enzymes or drugs). In this presentation, the stability of NACs is studied under varying pH, ionic strength, and osmotic pressure conditions.As an illustration, capsules can be made either polymer filled or water filled by changing pH between 3 and 10. On the other hand, outside this pH range, NACs can be dissembled. Osmotic pressure studies  carried out using poly(styrenesulfonate sodium salt) solutions suggests that the polymer-salt aggregates that reside inside the capsules provide structural reinforcement of the capsules. Understanding the sensitivity of NACs towards various conditions would help in better understanding and perhaps tailoring their properties for drug delivery and controlled release. Keywords: Microcapsule, hollow, nanoparticle, NACs, pH, ionic strength, osmotic pressureReferences: S. V. Patwardhan et al., Silicon Chemistry 1: 47–55, 2002. S. K. Tripathy et al.,Handbook of Polyelectrolytes and Their Applications, ed., American Scientific Publisher, California, 2002 S. V. Patwardhan et al., Chem Comm 1113-1121, 2005 R. K. Rana et al., Adv. Mater. 17, 1145-1150 (2005)  S. B. Kadali et al., Topic. Catal, 49, (3-4) ,251-258 (2008) C. Gao, et. al., Eur. Phys., V5, 21(2001)
10:15 AM - MM1.4
Supramolecular Assembly of the Dps-like Cage Protein from the Hyperthermophile Sulfolobus Solfataricus.
Chris Broomell 1 , Mark Young 1 , Trevor Douglas 1 Show Abstract
1 Center for Bioinspired Nanomaterials, Montana State University, Bozeman, Montana, United States
Metal organic frameworks (MOFs) have garnered much attention in the past several years for the relative facility of their synthesis and potential benefit in diverse applications such as energy storage, drug delivery and as novel polymeric materials. MOFs generally comprise metal ions or clusters coordinated by rigid or semi-rigid organic building blocks. To date there have been relatively few reports of MOF assembly from peptide-based precursors. However, there are numerous examples in nature whereby coordination polymerization directs macromolecular assembly and critically influences material properties. MOFs generated from biomolecules offer several potential advantages over their synthetic counterparts including extensive structural diversity, intrinsic chirality and the capacity for introduction of catalytic or similar biological functionalities.Protein cages represent an intriguing platform for construction of metal-organic assemblies. The cages are themselves supramolecular assemblies of limited numbers of protein subunits that spontaneously self-assemble into spherical structures with monodisperse size distributions. Cage surfaces are readily modifiable via genetic and chemical methods, thereby permitting the highly symmetrical and spatially controlled multi-valent display of metal coordinating ligands. Cage interiors are ideal for incorporation of additional functionality, for example, as nano-templates for mineralization or the controlled synthesis of functional bio-materials or as containers for drug encapsulation. Together, these features underscore the potential for protein cages as building blocks for MOF development, including the generation of heterogeneous materials with tunable properties and hybrid functionalities.Current focus will be recent generation and characterization of supramolecular assemblies using the dodecameric Dps-like protein from the hyperthermophile Sulfolobus solfataricus as a tecton and a combination of metal-chelate and organic click-based coordination connectivity.
10:30 AM - MM1.5
Theoretical Model for the Self-assembly of Clathrin into Targeted Nanoscale Assemblies.
Shafigh Mehraeen 1 , Alia Schoen 2 , Sung Yeon Hwang 2 , Sarah Heilshorn 2 , Andrew Spakowitz 3 Show Abstract
1 Mechanical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 Chemical Engineering, Stanford University, Stanford, California, United States
Clathrin is a cytoplasmic protein that plays a critical role in endocytosis by forming the basket-like cages on the cell membrane that seed the formation of the endosome pits that transport cargo into the cell. A single clathrin complex adopts a pinwheel configuration. The aggregation of many clathrin pinwheels on a membrane or interface leads to lattice-like assemblies with a mixture of 5-, 6-, and 7-member rings. In vitro assembly of clathrin within a solution results in closed, nanoscale assemblies with various shapes and sizes. Our goal in this research is to develop a fundamental theoretical model for the thermodynamics and kinetics of clathrin assembly in 2 and 3 dimensions in order to guide experiments toward the assembly of targeted nanoscale assemblies. Towards this goal, we have developed a theoretical model for clathrin assembly that can address the assembly dynamics in 2 and 3 dimensions. The clathrin are modeled as effective pinwheels that form leg-leg associations and resist elastic bending deformation; thus, the pinwheels are capable of forming the range of ring structures that are observed experimentally. Our theoretical model combines Brownian dynamics simulations with dynamic mean field theory in order to track the motion of hundreds of clathrin pinwheels at sufficiently long time scales to achieve complete assembly. With this theoretical model, we predict the phase diagram for clathrin assembly and perform dynamic simulations for a range of quenches into the phase diagram. The resulting dynamics exhibit the hallmark behavior of spinodal decomposition with subsequent coarsening of ordered domains. The defect structures in the final configurations result in large-scale elastic stresses in the lattice network; these stresses will be discussed in the context of the biological function of clathrin and in terms of controlling the resulting assembled structures.
10:45 AM - MM1.6
Artificial Polymers Mimic Bacteriophage Capsid Proteins and Encapsulate Nucleic Acids.
David Robinson 1 , George Buffleben 1 , Ronald Zuckermann 2 Show Abstract
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
The filamentous bacteriophage m13 and related viruses encapsulate DNA with protein, forming a relatively rigid organic nanowire about 1 micrometer long and less then 10 nanometers wide. The length of the wire is formed from many copies of a single protein, which is a single alpha helix formed from about 50 amino acids. It can be viewed as a very sophisticated surfactant, with hydrophilic regions that interact with the DNA and form the outer surface, and hydrophobic regions that pack against each other. We have implemented these design principles in peptoids (sequence-specific N-functional glycine oligomers) and have found that they form well-defined assemblies with DNA. We are applying these peptoids to branched DNA duplexes in efforts to create rigid three-dimensional organic structures that assemble in precisely defined ways.
11:15 AM - **MM1.7
Bio-inspired Polymer Brushes for Hierarchical Soft and Hybrid Materials.
Christopher Ober 1 , Abhinav Rastogi 1 2 , Rong Dong 1 2 , Marvin Paik 1 , Manabu Tanaka 1 , Grace Berrios 1 , Suddhasattwa Nad 2 , Norah Smith 2 3 , Lisa Blum 4 , Yelena Bisharyan 3 , Yi Liu 2 , Khajak Berberian 5 , Theodore Clark 3 , Judith Appleton 4 , Barbara Baird 2 , Manfred Lindau 5 , Hector Abruna 2 Show Abstract
1 Materials Science & Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, 3 Microbiology and Immunology, Cornell University, Ithaca, New York, United States, 4 James A. Baker Institute of Animal Health, Cornell University, Ithaca, New York, United States, 5 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States
Topological and chemical groups at the surface have been shown to affect biological response. Significant work has gone into studying protein adsorption and non-specific adsorption resistance on material surfaces. Self assembled monolayers (SAMs) have been used as model surface coatings to study biological interactions. However, polymer brushes present an attractive alternative to SAMs. Polymer brushes are an assembly of polymer chains that are tethered at one end to a surface or interface. This tethering is sufficiently dense that the polymer chains are crowded and are forced to stretch away from the surface or interface to avoid overlapping. They can be made using several different methods, giving the ability to tailor and design surface properties through functionalization of side-groups, and can be grown much thicker offering a higher density of surface reactive sites. Our group has invested much effort to study the use of polymer brushes in controlling the interaction between material surface properties and bio-matter. We have grown poly(acrylic acid) (PAA) brushes for use in two different electrochemical applications through surface modification of the polymer brush.
11:45 AM - **MM1.8
Orthogonal Approaches to Functionalized, Well-defined Nanostructures.
Craig Hawker 1 Show Abstract
1 Materials Research Laboratory, UCSB, Santa Barbara, California, United States
In designing polymeric materials for use in nanotechnology it rapidly becomes apparent that control over all aspects of polymer structure (molecular weight, polydispersity, number and position of functional groups, architecture, etc.) is required if these materials are to be used successfully to create nanostructures in the sub-50 nm size regime. Equally important to the rapid introduction and incorporation of these materials into devices is the development of robust and simple techniques for their synthesis. This last feature will allow a wide range of materials to be prepared efficiently while also permitting non-experts to prepare well-defined materials. The most promising approach to this is a ‘bottoms-up’ approach relying on chemistry, and recent developments in nanoparticles, shape persistent 3-dimensional macromolecules, 'living' free radical procedures and Click chemistry have allowed the construction of tailor-made polymer molecules and nanoparticles that facilitate this strategy. The design and application of these materials in the design of bio-inspired hierarchical soft and hybridmaterials will be described with examples including novel diagnostic and therapeutic agents for the treatment of cardiovascular disease, sub-20nm patterning strategies for advanced microelectronics and composite structures for controlling cell growth and proliferation. Further examples will demonstrate that these new synthetic techniques may also have application in other areas such as bio-sensors, DNA chips, delivery devices and high modulus hydrogels.
12:15 PM - MM1.9
The Self-organization of 2D Ordered Spines into 3D Mesoscale Hierarchical, Helical Assemblies.
Boaz Pokroy 1 , Sung Hoon Kang 1 , L. Mahadevan 1 , Joanna Aizenberg 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
In this talk we will show an interesting phenomenon of how spontaneous helicity may be induced in an athermal mesoscopic system, where neither the assembling elements nor the field are chiral. In our approach, capillarity-driven bending and subsequent optimization of the adhesive contact in a rationally-designed array of nanopillars result in the generation of highly-ordered helical clusters with unique structural hierarchy. This phenomenon arises from the sequential assembly of self-similar chiral building blocks over multiple length scales. While complex, chiral movement of the pillars and their significant mechanical interlocking at the sub-micron scale are expected to be widely applicable. In this presentation we will demonstrate their function in the context of self-assembly into new structures with uniform, periodic patterns and controlled chirality, and as an efficient particle-trapping and adhesive system.
12:30 PM - MM1.10
Designing Molecular-Recognition Hydrogels for Cell Encapsulation.
Cheryl Wong Po Foo 1 , Sarah Heilshorn 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Cell transplantation has emerged as a promising therapy for a variety of diseases, including Parkinson’s, Huntington’s, and stroke. However, cell survival after transplantation is poor and unpredictable; and enhanced cell survival is directly correlated to functional recovery. Cell encapsulation within a physical hydrogel has been found to increase cell survival during transplantation; however, current physical hydrogels require a change in environmental conditions, such as pH, temperature, or ionic strength, to initiate the sol to gel phase transition during cell encapsulation. These conditions are detrimental to cell survival and consequently can negate any positive effects of the hydrogel. In response, we have designed, synthesized, and characterized a family of molecular-recognition hydrogels that do not require environmental triggers for gelation to occur. Instead, the hydrogels are composed of two components that undergo a sol-gel phase transition upon mixing due to specific molecular-recognition interactions through hydrogen bonds. The design of the two components is based on simple polymer physics considerations and utilizes bio-mimimcry to create modular engineered proteins. Precise variations in the molecular-level design of the two components, created using recombinant protein techniques, are used to predictably tune the hydrogel viscoelasticity. Adult neural progenitor cells are encapsulated within these gels with high viability at constant physiological conditions. The gels promote the growth and differentiation of these neural progenitors into both glial and neuronal phenotypes, which adopt a well-spread and branched morphology in these 3D cultures.
12:45 PM - MM1.11
A Biocompatible Bottom-Up Route for Preparation of Hierarchical Hybrid and Bio-Hybrid Materials.
Francisco del Monte 1 , Maria C. Gutierrez 1 , Maria L. Ferrer 1 Show Abstract
1 , ICMM-CSIC, Madrid Spain
Structurally organized inorganic materials are attracting much attention for emerging applications (e.g., catalysis, storage and controlled release systems, smart fillers and biotechnologies) since they offer a desirable combination of high internal reactive surface along narrow nanopores with facile molecular transport through broad “highways” leading to and from these pores. The incorporation of biomolecules within such organized materials with a full preservation of their native structure would result in the achievement of functional materials with increased levels of space organization; e.g. hierarchically organized functional materials. In this work, we have applied the ISISA (ice-segregation induced self-assembly) process for the preparation of hierarchical hybrid and bio-hybrid materials exhibiting a very sophisticated structure with up to six levels of space organization. The ISISA process consists on the unidirectional freezing (at -196 degrees C) of the hydrogel nanocomposites. Upon freezing, the ice formation causes every solute originally dispersed in the hydrogel to be segregated from the ice phase. After freeze-drying, the resulting hierarchical structures consists on well aligned micrometer-sized pores in the freezing direction corresponding to the empty areas where ice crystals originally resided, being the macrostructure supported by the matter accumulated between adjacent ice crystals.
MM2: Biopolymer Mediated Synthesis and Assembly
Tuesday PM, April 14, 2009
Room 3020 (Moscone West)
2:30 PM - **MM2.1
Biohesion – Coupling Materials and Biological Entities using Engineered Solid Binding Peptides.
Mehmet Sarikaya 1 2 , Ersin Oren 1 2 3 , Ram Samudrala 1 2 , Beth Traxler 1 2 , John Evans 1 4 , Candan Tamerler 1 2 5 Show Abstract
1 Genetically Engineered Materials Science and Engineering Center, Universityof Washington, Seattle, Washington, United States, 2 Materials Science and Engineering, Universityof Washington, Seattle, Washington, United States, 3 Microbiology, University of Washington, Seattle, Washington, United States, 4 Chemistry, New York University, New York, New York, United States, 5 Molecular Biology and Genetics, Istanbul Technical University, Istanbul Turkey
In biology, molecular recognition is the basis of all interactions including those between antigen-antibody, anyzme-substrate, and protein-lipid membrane, in which proteins play the central role. As being molecular and ionic transporters, functional scaffolds, cell signalers, and transcription factors regulating genes, proteins are the workhorses of life. With the recent developments of nanoscale engineering in physical sciences and the advances in molecular biology, we are combining genetic tools with synthetic nanoscale constructs in creating a hybrid methodology, molecular biomimetics. Here, using biology as a guide and adapting bioschemes including combinatorial mutagenesis, bioinformatics, and recombinant DNA technologies, we select, design and tailor short peptides (7-60 amino acids) with specific binding to and assembly on functional solid materials and use them a building blocks in technology and medicine. Based on the fundamental principles of genome-based design, molecular recognition, and self-assembly, we can now engineer peptides with specific sequences to control adhesion of biological entities to solids (biohesion) and use them as nucleators, catalyzers, growth modifiers, molecular linkers and erector sets, simply as fundamental utilities for nano- and bionano-technology. We will review the recent developments in our collaborative research groups in this rapidly developing polydisciplinary field, focusing on the utility of solid-binding peptides in: i. Functional biomaterialization for nanotechnology (nanoparticles and thin films) and regenerative medicine (scaffolds towards tissue regeneration), ii. Bi-functional genetic fusion constructs (enzymes and cell signalers); iii. Molecular erectors for directed and targeted self assembly of biomolecular/nanoparticle multicomponent entities towards imaging and sensing for nanophotonics and diagnostics. The research is supported mainly, by, NSF-MRSEC, and also by NSF-BioMat, NSF-IRES, and NIH programs.
3:00 PM - **MM2.2
Reversible Structural Transition of a DNA-Lipid Film.
Matthew Tirrell 1 , Surekha Gajria 1 , Thorsten Neumann 1 , Luc Jaeger 1 Show Abstract
1 Materials Research Laboratory, University of California, Santa Barbara, Santa Barbara, California, United States
Naturally derived polyanions such as nucleic acids (RNA and DNA) can self-assemble with cationic lipids via electrostatic complexation, driven thermodynamically by the release of counterions. The structure of these complexes dispersed in water have been studied extensively by groups such as Safinya et al. and have been recognized as potentially useful in the field of gene delivery . The structure of films in water is dominated by the nature of the lipid e.g. cylindrical lipids like DDAB or DOPC and their nucleic acid complexes form lamellar structures. Within these lamellar complexes in aqueous solution the lipid assumes a bilayer formation and the DNA is a double helix. However amphiphilic lipids like DOPC and DOPE and their nucleic acid complexes are water soluble while cationic lipids like DDAB tend to form more water insoluble complexes, depending on the length of the carbon chain tail. These cationic complexes are only soluble in organic solvents like ethanol, isopropanol or chloroform. It is possible to obtain nucleic acid-lipid films when the dissolved cationic lipid complex of DDAB and nucleic acid is cast on a solid material such as Teflon or glass. These self-standing films have been characterized macroscopically by tensile properties and nucleic acid intercalation experiments. It has been reported that the DNA strands within these films can be aligned as the film is stretched, which has led to their application as a new type of anisotropically conductive material . The tensile properties of these films are adjustable with molecular weight or by mixing different kinds of nucleic acid, like DNA and RNA for the complex with DDAB. It was expected that these films would have the same characteristic structure as these complexes in water. The state of the DNA within similar films generated by Langmuir-Blodgett (LB) as well as layer-by-layer (LbL) deposition is a subject of controversy, as few papers have been able to propose a consistent structure (e.g. A-, B-, or C-form DNA. Although some papers have suggested the DNA in such films is single stranded, the evidence is very thin; often no structure is given to satisfactorily explain the state of the lipid . We focused in our work on the structure of DNA-DDAB films and found an intriguing model that is able to fully describe the behavior of the DNA and the lipid in the film.Our overall picture shows that the film undergoes a transition from double stranded helical DNA complexed with a bilayer of DDAB in the wet state, while in the dry state we observed a repetition unit of single stranded DNA complexed with a monolayer of DDAB.
3:30 PM - MM2.3
Biomediated Assembly of Complex and Dynamic Nanostructures.
Erik Spoerke 1 , Judy Hendricks 1 , Adrienne Greene 1 , Haiqing Liu 1 , George Bachand 1 , Elena Bekyarova 2 , Robert Haddon 2 , Bruce Bunker 1 Show Abstract
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , University of California at Riverside, Riverside, California, United States
Microtubules (MTs) and motor proteins (MPs) are remarkable biological tools that mediate sophisticated intracellular organization, assembly, and transport. Capable of regulating intracellular cargo transport, cytoskeletal organization, and even elements of cell division, these cooperative active biomolecules are attractive targets for integration into emerging nanotechnologies. We have learned to incorporate these biomolecular tools into in vitro materials assembly schemes that enable us to create dynamic, nanoscale architectures in two and three dimensions. We have demonstrated the use of MTs and MPs in the formation of dynamic templates for the formation of structures such as “erasable” arrays of interconnects formed from carbon nanotubes or three dimensional composite asters. We have also explored how interactions between the MTs, MPs, and synthetic supramolecular assemblies, such as hydrogels or liquid crystals, enable us to create complex, dynamic composite structures in three dimensions. This talk will focus on a description of these biomediated assemblies and discussion of some of the underlying interactions responsible for the dynamic, non-equilibrium structures created. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
3:45 PM - MM2.4
Protein-Polymer Biohybrid Amphiphiles.
Jeroen Cornelissen 1 , Irene Reynhout 1 , Ton Dirks 1 , Guillaume Delaittre 1 , Ho-Cheol Kim 2 , Roeland Nolte 1 Show Abstract
1 Institute for Molecules and Materials, Radboud University, Nijmegen Netherlands, 2 , IBM Almaden Research Center, San Jose, California, United States
Amphiphilic molecules (also termed surfactants or soaps) consist of both a hydrophilic and a hydrophobic segment and have been widely studied because of their self-assembling properties in aqueous media. For a long time these studies have mainly focused on low molecular weight amphiphiles, such as phospholipids and their synthetic counterparts (e.g., dioctadecyldimethylammonium chloride), and consequently the self-assembly behavior of these compounds is now well understood. In fact, the type of aggregates that phospholipids form in water (e.g., micelles, rod-like structures, bilayers, and vesicles) can accurately be predicted by established models, which are based on the shape of the molecules. Besides the traditional type of surfactants, also various amphiphilic block copolymers have recently beenshown to exhibit interesting self-assembling properties. Such block copolymers (also referred to as ‘‘super amphiphiles’’) often aggregate in a remarkably similar way as their low molecular weight counterparts. Compared to traditional surfactants, amphiphilic block copolymers, however, form more robust assemblies, rendering them ideal for the construction of nanoreactors and drug delivery vehicles. Following this line of development, our group has recently designed novel types of macromolecular amphiphiles that contain a biopolymer, e.g., a beta-sheet helical peptide or even a complete protein as the hydrophilic block. It was envisioned that the site-specific linking of a hydrophobic polymer to a protein would result in a biohybrid amphiphile, a so-called giant amphiphile, which shows great structural analogy with traditional surfactants even though it is considerably larger. Owing to their typical molecular structure, the giant amphiphiles were expected to show a similar hierarchical self-assembly behavior as the conventional surfactants .Here we will report on the formation of defined assemblies using these polymer-protein biohybrid building blocks. Increasingly complex architectures are formed when going from diblock copolymer to triblock copolymer based amphiphiles . On a surface, the phase segregation of these segmented macromolecules can be used to create proteins patterns. In dispersion, on the other hand, a variety of aggregate structures can be obtained. The properties of these materials are dictated by a combination of amphiphilicity and the function of the biomacromolecular component. Recent progress includes, among others, the formation of large vesicle-like structures that contain active enzyme of which the activity depends on the type and molecular weight of the hydrophibic polymer.. A.J. Dirks, R.J.M. Nolte, J.J.L.M. Cornelissen Adv. Mater. (2008) 20, 3953.. I.C. Reynhout, J.J.L.M. Cornelissen, R.J.M. Nolte J. Am. Chem. Soc. (2007) 129, 2327.
4:00 PM - MM2.5
Peptide-Mediated Deposition of Nanostructured TiO2 into the Periodic Structure of Diatom Biosilica and its Integration into the Fabrication of a Dye-Sensitized Solar Cell Device.
Clayton Jeffryes 1 , Tim Gutu 2 , Haiyan Li 2 , Jun Jiao 2 , Gregory Rorrer 1 Show Abstract
1 Chemical Engineering, Oregon State University, Corvallis, Oregon, United States, 2 Physics, Portland State University, Portland, Oregon, United States
Diatoms are single-celled algae that make silica shells called frustules that possess periodic structures ordered at the micro- and nanoscale. Nanostructured TiO2 was deposited onto the frustule biosilica of the diatom Pinnularia sp. Poly-L-lysine (PLL) conformally adsorbed onto surface of the frustule biosilica. The condensation of soluble Ti-BALDH to TiO2 by PLL-adsorbed diatom biosilica deposited 1.32 ± 0.17 g TiO2/g SiO2 onto the frustule. The periodic pore array of the diatom frustule served as a template for the deposition of the TiO¬2 nanoparticles, which completely filled the 200 nm frustule pores and also coated the frustule outer surface. Thermal annealing at 680 oC converted the as-deposited TiO2 to its anatase form with an average nanocrystal size of 19 nm, as verified by XRD, electron diffraction, and SEM/TEM. This material was then integrated into a dye-sensitized solar cell device. Specifically, a single layer of diatom-TiO2 frustules was deposited to surface density of 15 microgram TiO2/cm2 on top of an anatase TiO2 nanoparticle layer deposited to surface density of 2.5 mg/cm2 on conductive ITO glass. The composite structure was thermally annealed at 400 C, followed by addition of N719 dye, I3 electrolyte, and Pt back electrode. A relative increase in short-circuit current of nearly 50% was observed after deposition of the diatom-TiO2 layer. The difference was not due to the increase in the amount of TiO2 in the device, because the amount of diatom-TiO2 was small (<1%) relative to the anatase TiO2 base layer. Instead, the periodic structure of the intact frustule pores may have helped to improve photon capture. This is the first reported study of directing the peptide-mediated deposition of TiO2 into a hierarchical nanostructure using a biologically fabricated template. This study also illustrates how these materials can be integrated into device structures.
4:30 PM - **MM2.6
Synthesis and Characterization of Elastin Mimetic Hybrid Polymers with Alternating Molecular Architecture and Elastomeric Properties.
Xinqiao Jia 1 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States
We are interested in developing elastin mimetic hybrid polymers (EMHPs) that capture the multiblock molecular architecture of tropoelastin and the remarkable elasticity of mature elastin. In this study, multiblock EMHPs containing flexible synthetic segments based on poly(ethylene glycol) (PEG) alternating with alanine-rich, lysine-containing peptides were synthesized by step growth polymerization using telechelic azido-PEG and alkyne-terminated KA3K peptide, employing orthogonal click chemistry. The resulting EMHPs contain an estimated 5 repeats of PEG and KA3K, and have an average molecular weight of 34 KDa. Covalent cross-linking of EMHPs with hexamethylene diisocyanate (HMDI) through the lysine residue in the peptide domain afforded an elastomeric hydrogel (xEMHP) with a compressive modulus of 0.12 MPa when hydrated. The mechanical properties of xEMHP are comparable to a commercial polyurethane elastomer (TecoflexTM SG80A) under the same conditions. In vitro toxicity studies showed that although the soluble multiblock copolymers exhibited some toxicity at high concentrations, due partially to the presence of high charge density, the cross-linked hybrid elastomer did not leach out any toxic reagents and allowed primary porcine vocal fold fibroblasts (PVFFs) to grow and proliferate. These materials are promising candidates for applications as tissue engineering scaffolds in vocal folds as well as other mechanically active tissues.
5:00 PM - MM2.7
Using Double-Stranded DNA Probes to Assemble and Disassemble Colloidal Satellite Structures at Room Temperature.
Bryan Baker 1 , Valeria Milam 1 2 3 Show Abstract
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia, United States
DNA-mediated assembly of particles has been a widely popular area of study in the past decade. Owing to the specific recognition between complementary DNA sequences, particles can be directed to assemble into defined structures based on DNA hybridization events between complementary surfaces. The current study continues to explore this bio-inspired area of research using DNA hybridization to generate colloidal satellite structures consisting of large microspheres surrounded by a monolayer of nanoparticles. By varying the sequence length and affinity of each DNA duplex linkage or double-stranded probe on the nano-scale, we can tune the degree of microsphere-nanoparticle attraction within these micro-scale satellite structures to be weakly stable at room temperature. Upon incubation with a specific DNA target sequence under ambient conditions, the satellite structures disassemble due to competitive hybridization events in which the original immobilized partner strand is replaced by the soluble target sequence. We have found that the kinetics of these competitive hybridization events depends on the differences in base-length and fidelity in base-pair matches between the original partner strand and the soluble targets. Thus, by tuning the affinity of the double-stranded probes bridging the particles, we have been able to generate weakly stable satellite assemblies while controlling the kinetics of competitive hybridization that underlies disassembly.
5:15 PM - MM2.8
DNA-based Polymers and Liquid-like Hydrogel by Target-driven Polymerization.
Jong Bum Lee 1 , Young Hoon Roh 1 , Dan Luo 1 Show Abstract
1 Biological Eng., Cornell Univ., Ithaca, New York, United States
DNA, with its outstanding specificity and intrinsic biocompatibility, has been utilized as a new building block in the construction of polymers and hydrogels. Here we report DNA-based soft materials from micro- (DNA-based polymers) to macroscale (liquid-like DNA hydrogels) by target-driven polymerization. The polymers were generated only in the presence of a specific DNA by assembling a single photo-responsive moiety on a DNA monomer with nanoscale precision and then introducing the system to UV light. This precision allows for specific and sensitive pathogen sensing. In the macroscale, liquid-like DNA hydrogel was enzymatically created in the presence of specific target DNA used as a template deriving elongated DNA via polymerase. A gelling process was based on the physical interactions of long DNA strands as opposed to base pairing. These biocompatible DNA hydrogels were almost fluidic-like but still held gel properties. They were easily able to be transformed back and forth to any shape depending on the mold. Inspired by these characteristics of liquid-like DNA hydrogels, we have developed an injectable extracellular matrix for tissue engineering.
5:30 PM - MM2.9
Enzyme-Assisted Self-Assembly of Defined Peptide Nanostructures
Apurba Das 1 , Rein Ulijn 1 Show Abstract
1 Department of Pure & Applied Chemistry, The University of Strathclyde, Glasgow United Kingdom
Design and construction of various nanostructured materials using molecular self-assembly is a very active area in current research for biological and non-biological applications. It is a major challenge to control the self-assembly process (nucleation and growth of nanostructures) and to avoid kinetically entrapped aggregates under physiological conditions. Enzymes have recently emerged as tools to achieve this by converting non-assembling precursors into self-assembly building blocks in a space/time controlled fashion. Enzyme-controlled hydrogelation is particularly attractive for biomedical applications of hydrogels in drug delivery, 3D cell culture and diagnostics and supramolecular electronics.Peptide-based biomaterials are attracting interest due to their programmable and biodegradable nature. A number of Fmoc (fluorenyl-9-methoxycarbonyl) based amino acids and dipeptides form excellent supramolecular hydrogelators due to their hydrogen bonding and pi-pi interactions. We explore the use of hydrolytic enzymes to direct self-assembly of nanostructures based on aromatic short peptide derivatives. Two complementary approaches were followed (i) esterase-directed self-assembly via hydrolysis of N-(fluorenyl-9-methoxycarbonyl) (Fmoc)-peptide esters, (ii) thermolysin assisted self-assembly of nanofibrous hydrogels based on Fmoc-peptide-esters formed via a process known as reversed hydrolysis.1 Different types of nanostructures including tubes, fibers and twisted sheets were obtained depended both on the route of self-assembly and the chemical nature of the building blocks, highlighting the versatility of using aromatic short peptide derivatives in self-assembly. Interestingly, the first method allows the consequent formation of nanotubular structures with tunable diameter for different Fmoc-peptide building blocks. In each case, the self-assembly of Fmoc-peptides was driven by hydrogen bonding interactions forming β-sheet structures combined with pi-pi interactions of the aromatic fluorenyl groups as confirmed by FT-IR and fluorescence spectroscopy respectively. These self-assembled pi-conjugated peptide nanostructures can serve as a tool to find for supramolecular electronics.Reference:1. A. K. Das, R. Collins and R. V. Ulijn, Small, 2008, 4, 279.
5:45 PM - MM2.10
Self-assembly of π-conjugated Oligomers onto ssDNA Templates via Hydrogen-bonding.
Mathieu Surin 1 , Pim Janssen 2 , Roberto Lazzaroni 1 , Philippe Leclere 1 , Bert Meijer 2 , Albert Schenning 2 Show Abstract
1 Laboratory for Chemistry of Novel Materials, University of Mons-Hainaut, Mons Belgium, 2 Laboratory for Macromolecular and Organic Chemistry, Eindhoven University of Technology , Eindhoven Netherlands
Pi-conjugated oligomers and polymers are the central ingredients in the field of ‘organic electronics’ and offer new opportunities for devices such as solar cells and field-effect transistors, with the advantage of easy-processability and mechanical flexibility of organic materials. For tailoring the optical and electronic properties of those materials, the control over the assembly of conjugated molecules at the nm-scale is of major importance. An elegant way to direct the supramolecular order of conjugated molecules is to make use of a well-defined template. In this view, DNA is a remarkable building block to construct well-defined nano-objects because of the control in the design of its architecture and the high specificity of the base recognition process. Furthermore, the base-by-base synthesis of oligonucleotides makes it possible to control both their length and their sequence from a few to more than one hundred bases. In this study, we propose to fabricate π-conjugated molecular stacks for which the size, the shape, and the intermolecular interactions are controlled by a self-assembly process guided by a well-defined single-stranded oligonucleotide template. This is realized by mixing in aqueous solution a defined single-stranded DNA (ssDNA) with a hydrophilic pi-conjugated oligomer (e.g., an oligo(phenylene vinylene)) bearing a complementary H-bonding moiety. This bottom-up approach leads to hybrid, fully-bound structures for which the size is controlled by the length of the oligonucleotide. We characterize these supramolecular structures via a joint theoretical and experimental approach: atomistic modeling based on Molecular Dynamics is carried out to propose structural models that can be related to Circular Dichroism spectroscopy and Tapping-Mode Atomic Force Microscopy measurements. By modifying the nature of the conjugated oligomers that self-assemble onto the ssDNA, we obtain hybrid structures that differ in terms of the helical pitch of the strand, the amplitude of the intermolecular interactions, the assembly on surfaces, etc. [3,4] This is essential for exploiting these functional structures into optoelectronic devices and for the future design of hybrid systems with different chromophores (e.g., conjugated electron donors and acceptors) fine-positioned along the DNA strand.  a) N.C. Seeman, Nature 2003, 421, 427 ; b) F.A. Aldaye, A.L. Palmer, H.F. Sleiman, Science 2008, 321, 7195. P.G.A. Janssen, J. Vandenbergh, J.L.J. van Dongen, E.W. Meijer, A.P.H.J. Schenning, J. Am. Chem. Soc. 2007, 129, 6078-6079. G.P. Spada, S. Lena, S. Masiero, S. Pieraccini, M. Surin, P. Samorì, Adv. Mater. 2008, 20, 2433. M. Surin, P.G.A. Janssen, R. Lazzaroni, Ph. Leclère, E.W. Meijer, A.P.H.J. Schenning, Adv. Mater. 2008, in press (DOI: adma.200801701).
MM3: Poster Session: Synthesis of Bio-inspired Hierarchical Soft and Hybrid Materials
Tuesday PM, April 14, 2009
Exhibition Hall (Moscone West)
6:00 PM - MM3.1
Physicochemical and Dielectric studies of the Hydration Mechanism in Proteins (Casein and Lysozyme).
Kalliopi Vartzelis-Nikaki 1 , Sotiria Krypotou 1 , Amalia Konsta 1 Show Abstract
1 , National Technical University of Athens, Athens Greece
The hydration and proton transport mechanisms in casein and lysozyme powders are studied by means of physicochemical and dielectric spectroscopy methods, using: a) Equilibrium and dynamic water sorption isotherms, b) Differential scanning calorimetry (DSC), c) Thermally stimulated depolarization currents (TSDC) techniques in the temperature range from 77 to 300 K and d) Dielectric relaxation spectroscopy (DRS) in the frequency range 10-106Hz. The water content of the samples varied between 0.07 and 0.61 w/w.The experimental results of equilibrium water sorption were analyzed on the basis of the GAB equation and the tightly bound water percentage was approximately evaluated from the analysis. From dynamic water sorption isotherm the diffusion coefficients of water during sorption and desorption in our samples were determined.A detailed analysis of the peaks obtained by TSDC and DRS techniques permitted us to determine the hydration content corresponding to water irrotationally bound to the protein macromolecule, as well as the level as which percolative proton transfer along threads of hydrogen-bonded water molecules in the surface of protein macromolecules sets on, depending on the protein nature. A peak attributed to localized short range hopping of protons through the bulk sample has also been detected. Using special dielectric techniques, Arrhenius plots have been recorded and activation energies for the various processes, as a function of water content, have been determined. The role of glass transition temperature, as detected by DSC, on the onset of proton transport is emphasized and the behaviour of dc-conductivity, as well as its role on the biological function of living organisms, is further discussed.
6:00 PM - MM3.10
Perspective of Using the Biopolymers for Management Nanostructure and Functional Properties Fat-containing Food Products.
Tamara Rashevskaya 1 , Anatoliy Ukraines 1 Show Abstract
1 Department of products from milk, NUFT(National University of Food Technologies), Kyiv Ukraine
One of most actual social problems of our time is creation of technologies of foodstuff of functional purpose which are directed for protection and preservation of health of the population. The special attention is paid at the use of food additives from vegetative raw material. We create kinds of a butter with biopolymers pectin and inylin, which are received from vegetative raw material. By the results of clinical tests the kinds of butter are recommended by Ministry of Health of Ukraine in the treatment-and-prophylactic purposes and an improving in health feed. Complex researches have shown, that weedsakhared pectin and inylin in butter`s heterosystem are surface-active substances. Micro-and nanostructure of butter consists of crystal aggregates, nanoblocks and nanograins, which are formed during its self-organization.The mechanism of nanostructure`s self-organization is based on phase transformations and fractionating of glycereds. The hierarchy of self-organizing of nanostructure of butter is offered. The crystal fatty phase`s initial stage of formation is formation of crystals embryos made from highly melting glycered. During the growth of nanograins, nanoblocks and aggregates occurs fractionating of glycerids on temperatures of hardening, conformation and polimorphism to forms,Identical glycered are packed in lamelle;uncrystaled glycered and a water phase with the biopolymers dissolved in it make a start on periphery. Crystal nanograins d=5-10 nm form lamelle, the adsorptionis layers of biopolymers and a water phase are formed on the lamelles interface. Nanostructure of crystal aggregates and nanoblocks consists of alternating lamelles of nanograins and layers of water phase.The polysugated amorphous-crystal lipid layer is formed on the surface of aggregates and nanoblocks. It is established, that adding such polysugareds pectin and inylina leads to crushing the structural elements of butter at 5-25 × the most part of them are in nanosize range of 1-100 nm.Thus the quantity of a water phase, disparhyriesed on nanolevel increases for 60 %, that brakes microbiological and oxidizing processes of a product`s damage and accordingly raises its biological interface.Thus increasing of the butter`s biological value butter (with pectin and inylin) is connected with functional properties of these biopolymers, and with features nanostructure`s of these kinds of butter. The above-stated testifies to perspectivity of using of the biopolymers for butter`s and other fat-containing food products management of nanostructure and functional properties and also creation of the butter`s and food product`s interface nanotechnologies.
6:00 PM - MM3.11
Nanostructure Interfaces of Phases and Nanoelements Multicomponent Lipid System.
Tamara Rashevskaya 1 Show Abstract
1 Department of products from milk, NUFT(National University of Food Technologies), Kyiv Ukraine
The formation of the lipid systems' nanostructure multicomponent is investigated by the example of butter. On the result of complex researches it is established, that in the process of butter formation ,the formation of butter's nanostructure occurs on a method "from down to up". Nanostructure of a continuous fatty phase of a fresh-made aggregates consists of crystal glycered layers and set of layered many-sided crystal aggregates in size 1000 - 2600 nm. The crystal glycered layers and layers of aggregates consist from monomolecular glycered layers;their thickness is 5 nm; their surface has a lamelle structure.Lamelle are generated from mono - and biolayers of glycered. By electrono - positrono method angilation there were found out nanoporu r ~ 0,22-0,56 nm in dairy-fat structure. The most probable and steady radius of nanoporu is 0,35 nm; it is specified that nanoporu have fylerenosimilas structure.There are indentificate nanoparts waters on electrono - microscopic pictures nanostructure, are formed by the centers of their nanoporu. They are formed from nanoporu paralele crystal layers.On nanocapitals nanostructure's the product difindates continuous water phase. The borders of the amorphous and crystal layers nanogreins' and phases' aggregates of fat have rough with ledges surface; ther are formed nanodrops of moisture adsorptionis connection of moisture's films. During the storage of butter the self the organization nanostructure on a method "from down to up" occurs where crystal units are brocken into nanoblocks, size 40-800 nm. The formation of layered aggrgats and nanoblocks is based on glycered's fractionis. More fusible glycered make a start front cristalisation. On a surface of aggregats and nanoblocks amorphously - a crystal layer is formed, and on the surface of their crystal layers nanoparts water phase form, d ~ 3-50 nm; their size decreases with easilyfusibility glycered increasing; they are forming a surface. Adding the vegetative food additives the size of nanoelements decreases by 5 - 25 times, changes nanostructure crystal layers which architecture is influenced by the nature of the additive. So surfaces of crystal layers of aggregats and fatty globul (with the additive food inylina) have butter dentred nanostructure: an external surface - convex and inside of - concave which are connected by a principle, a ledge to a hollow. During the formation of the butter's nanostructure occurs fractionis inylina. The crystal nanoblocks include nanolayers with a various phase condition: crystal, amorphously crystal, amorphous and liquid crystal with structure smektives phases. They have various structure: dentred, string - like, fibrilarated, globularated. In nanostructure of butter with pectin superficial pectino - lipid layers of nanoblocks and fatty globul aggegates consist of cambers, many-sided nanocristal and cells,there size is up to 100 nm with nanoparticle and films of water phase on surfaces of borders of the aggregates.The results of researches have shown that the nanostructure surfaces of nanoelements and their borders of the aggregates are influenced by the nature brought additives storage period of the product that allows to operate the architecture and interactions surfaces nanoelements and also the physical and chemical properties of the materials.
6:00 PM - MM3.12
Nanodiamond-Embedded Hydrogels as Therapeutic Sequestering Matrices for Localized and Sustained Bioactivity.
Robert Lam 1 , Mark Chen 1 , Eiji Osawa 2 , Dean Ho 1 3 Show Abstract
1 Biomedical Engineering and Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 2 , NanoCarbon Research Institute, Nagano Japan, 3 Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, Illinois, United States
In this work, we describe a novel material consisting of embedded doxorubicin hydrochloride (DOX)-nanodiamond (ND) conjugates in poly(ethylene glycol) diarylate (PEGDA)-based hydrogels. NDs have recently been examined for biomedical applications due to their unique combination of size, aspect ratio and surface properties. NDs have been previously bound to numerous biological agents. In particular, we have previously attached 2-8 nm NDs with DOX, a well known chemotherapeutic ideal for drug release assays studies due to its innate UV-vis spectra absorbance. The polymer matrix we have chosen is PEGDA, due to the innate water solubility, versatility and ease of modifying density, pore sizes and functional attachment groups. The interplay between the components can be adjusted to obtain eventual desired sequestration or release kinetics. The hydrogels are formed via UV photopolymerization, thereby creating a matrix potentially applicable towards a variety of biomedical applications, including chemotherapy, regenerative medicine, and wound treatment. ND-PEGDA hydrogels were demonstrated to sequester drug extremely well in comparison to ND deficient hydrogels. Release assays consisted of immersion of hydrogels of different compositions with and without NDs in PBS and water at physiological conditions in triplicate. Standard hydrogels were shown to elute the majority of their payload within the first couple days in a seemingly diffusion based manner while hybrid gels that contained NDs showed a controlled and constant release for up to two weeks that avoided an initial “burst” release profile. In fact, ND-deficient hydrogels were shown to release 20 times more drug than ND containing hydrogels. After two weeks, the majority of the DOX still remained in ND embedded hydrogels, demonstrating the powerful drug entrapment abilities of the ND surface. Current studies are underway to explore the driving drug-ND surface binding mechanisms and exploiting these factors for desired release triggers and rates.Characterization via Environmental Scanning Electron Microscopy (ESEM) showed uniform dispersion of nanoparticle features within the hydrogel matrix upon UV polymerization. This was due to the fact that DOX-ND conjugates were mixed with a PEGDA precursor solution prior to photopolymerization. In addition, the process is facile, requires little time and can be accomplished on a benchtop. Photopolymerized hydrogels have particularly exciting implications in in vivo applications, since gels can be formed in situ into complex shapes. Since NDs have the capacity to be bound with several therapeutic and imaging agents, we postulate potential applications with these hydrogels in adjuvant therapy that require imaging or localized and slow drug release capabilities.
6:00 PM - MM3.13
Morphology and crystallization of the poly(3-hydroxybutyric acid) /Tannic acid blends
Chean Su 1 Show Abstract
1 Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung Taiwan
Miscibility and crystallization in blends of poly(3-hydroxyalkanoates) (PHAs) with tannic acid (TA) were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy ( SEM) and wide-angle X-ray diffraction (WAXD). The result of thermal analyzing revealed that the PHB/TA.PHB8V/TA and PHB12V/TA exhibited a homogenous phase and a composition-dependent glass transition temperature (Tg), indicating the blends are miscible. The dependence of the Tg on the composition of these blends were fitted by the Fox equation, Gordon-Taylor equation and Kwei equation. The q value of Kwei equation of these system are negative, showing an interaction existed. The k value of kwei equation is PHB12V/TA (B=-45.62 cal/cm3),PHB8V/TA (B=-40.12 cal/cm3) and PHB/TA (B=-23.4 cal/cm3), respectively. Furthermore, SEM showed that the morphology of these blends are homogenous phase. The results of SEM are equal to the results of DSC in these blends. To confirm the behavior of the specific interaction, FT-IR showed that there is a new absorbance peak at the wavenumber 1703 cm-1 regard as the feature of hydrogen bond. From a thermodynamic viewpoint, the strength of the specific interaction in a blend can be described by its interaction energy density parameter (B) which can be obtained from the depression in the equilibrium melting based on the Nish-Wang equation. On the morphology observation of PHAs/TA, PHB/TA, PHB8V/TA and PHB12V/TA have Malt-cross and ring-banded feature using POM. Twist and irregular feature increases with increasing crystallization temperature and blending proportion of TA. On the crystalline kinetics, the relative magnitudes of growth rate of spherulite is in order of PHB>PHB8V>PHB12V because PHV content of PHB-co-PHV increase steric hindrance. In the PHAs/TA blends, the hydrogen-bonding interactions between PHAs and TA, which resulted the growth rate of spherulite of the blends decreased quickly as TA content added.
6:00 PM - MM3.14
Selection of specific ZrO2-interacting Peptides using Phage Display
Dirk Rothenstein 1 , Joachim Bill 2 Show Abstract
1 Materials Synthesis and Microstructure Design, Max-Planck-Institute for Metals Research, Stuttgart Germany, 2 Institute of Non-Metallic Inorganic Materials, University of Stuttgart, Stuttgart Germany
Zirconium-based oxide ceramics are commonly applied as key active component in a broad field of technical applications, e. g. as ion conductors in sensing devices and fuel cells or scaffolding parts of dental implants. Conventional ceramic processing is connected with energy-intensive reaction conditions and the use of elaborated technical equipment. Contrasting man-made oxide ceramics the biomineralization of elaborate mineral structures by various living organisms is achieved under ambient conditions. Such mineralized hard tissues, consisting of carbonate, phosphate, or silicate compounds are composite materials of a mineral and an organic phase. Generally, the organic phase consists of one or more protein species which functions as scaffold and controlling substance presumably through boundary layer interactions. Up to the present, zirconium dioxide (ZrO2) was not detected in biominerals. Therefore, a straight forward approach to isolate naturally occurring proteins, which influence the mineralization of ZrO2 is not possible.By means of industrial biotechnology we aim to benefit the advantages of biomineralization processes in technical oxide ceramic synthesis. A phage display system was adapted to identify peptides, which specifically interact with defined crystal planes of single crystals als well as with powders made of ZrO2. Isolated peptides were analysed by bioinformatics and experimentally scrutinized to influence the mineralization from zirconium salt solutions under mild reaction conditions. The resultant materials were analysed using electron microscopy and diffraction methods.
6:00 PM - MM3.15
Fluorescent Organic Nanotubes for Biosensory Platform
Chiyoung Park 1 , Jeong Hun Lee 1 , Hyehyeon Kim 1 , Chulhee Kim 1 Show Abstract
1 Department of Polymer Science and Engineering, Inha University, Incheon Korea (the Republic of)
A self-assembly approach using suitable building blocks is a powerful strategy not only to construct nano-architectures but also to control materials properties through bottom up approach. Here, we report on the facile methodology to construct nanotubes with tunable surface functionalities derived from self-assembly of dendrons and cyclodextrins (CDs). In addition, we demonstrate that this type of fluorescent organic nanotubes with functionally controllable surface can be utilized as a useful tool for the construction of nanotube-nanoparticle hybrid, supramolecular biological assembly, and bioensory vehicle. As a primary building block, the amphiphilic amide dendron with the focal pyrene unit formed a vesicular structure in an aqueous phase. The assembly process can be regulated by various factors such as hydrophobic effect, hydrogen bonding, and host-guest interaction. The inclusion of the focal pyrene moiety into CDs with various C-6 functional groups at the narrower rim induces self-assembled functional nanotubes of which the surface is covered with CDs, therefore the surface can be functionalized with C-6 moieties of CD building blocks. The nanotubes with amine or carboxyl surface functionalities were effectively utilized as the nanotemplate for the orientation and direct nucleation of metal nanoparticles. The programmed assembly and fluorescence characteristics of the functional CD-covered dendron nanotubes enabled us to utilize this new type of nanotube as a platform for protein sensing.
6:00 PM - MM3.16
Self-assembly Formation of Multiple Tethered Lipid Bilayers.
Seyed Ruhollah Tabaei Aghda 1 , Magnus Branden 1 , Fredrik Hook 1 Show Abstract
1 Applied physics, Chalmers university, Göteborg Sweden
Tethered lipid bilayers have been proven powerful as experimental models in studies of membrane-spanning proteins, which are currently the most important targets in drug discovery. Tethering of planar lipid membranes reduces the influence from the solid support on the lateral mobility of the membrane constituents and provides a sufficiently large solvent reservoir underneath the membrane for studying molecular transport events. Inspired by cell-cell junctions, where membrane residing proteins control the separation between two or more membranes without interfering with their integrity, we developed a new self-assembly route for formation of multiple macroscopically homogenous and highly fluid tethered lipid bilayers (lipid diffusivity~5 μm2/s) with compartmentalized inter-membrane volumes geometrically confined by membrane-anchored DNA duplexes. The formation of multiple macroscopically homogeneous planar membrane-membrane junctions with sealed inter-membrane liquid reservoirs was accomplished using so called bicelles, which is a versatile class of model membranes generally composed of a mixture of the long-chained dimyristoyl phosphatidylcholine (DMPC) and the short-chained dihexanoyl PC. Quartz crystal microbalance with dissipation (QCM-D) was used to monitor the formation of such architectures and to study of their ion permeability.
6:00 PM - MM3.18
Electrochemically Active Vesicles.
Hoon Kim 1 , Ji-Woong Park 1 Show Abstract
1 , gist, Gwangju Korea (the Republic of)
We report the formation of electrochemically active vesicles by the rod-coil polymers consisting of a tetraaniline (TANI) block and a polyethylene glycol (PEG) block. Two diblock polymers of TANI-b-PEG550 and TANI-b-PEG2000 with respective molecular weights (MW) of PEG blocks, 550 and 2000, and a triblock polymer, TANI-b-PEG-b-TANI with the MW of its PEG block, 600, were synthesized by coupling of TANI and polyethylene glycol monocarboxylic acid. All three rod-coils were characterized in their aqueous solution with concentration of 0.001~0.005 wt%. Dynamic light scattering (DLS) data of their solutions indicated the presence of large particles with diameter ranging from several hundred nanometers to a few micrometers. Optical microscopy of the solution also gave clear images of the vesicles. Transmission electron microscopy (TEM) of rapidly evaporated sample on carbon coated TEM grids exhibited the images of collapsed vesicles with size of 1~2μm. We studied morphological transition of the vesicles by addition of oxidizing or reducing agents to the vesicular solutions. Detailed characterization of electrochemical properties as well as the solution behaviors of the vesicles will be presented. This work was supported by the Program for Integrated Molecular Systems (PIMS) at Gwangju Institute of Science and Technology and the Korea Research Foundation Grant funded by the Korean Government (Grant KRF-2005-205-D00035).
6:00 PM - MM3.2
Supramolecular Assembly of Peptide Fibers Through Metal Coordination.
Madhumita Mukherjee 1 , Michael Ogawa 1 Show Abstract
1 Chemistry, Bowling Green State University, Bowling Green, Ohio, United States
Peptide-based nanostructures play important roles in many areas of nanoscience and nanotechnology. Considerable effort is thus being devoted to better understand how the morphologies of such structures can be both predictively determined and rationally-controlled. Towards this end, our group has been exploring the use of transition metal chemistry to help direct the assembly of peptide structures in ways that may add to, and perhaps complement, the formation of native-like conformations (Biomacromol. 2007, 8, 3908).Reported here is the design, synthesis, and characterization of a new type of metal-peptide assembly prepared through the non-covalent self-association of amphipathic polypeptides that are coordinated to the axial positions of either Fe(III) or Co(III) protoporphyrin IX. The binding of the pyridine-containing peptide (AQ-Pal14) to the metalloporphyrin is monitored by UV-Vis spectroscopy which shows that the porphyrin Soret band loses intensity and undergoes a small, but distinct, red-shift upon the addition of peptide. This behaviour is accompanied by the appearance of an induced circular dichroism signal at 423 nm to indicate that the porphyrin ring is in close communication with the chiral peptide environment.Scanning Electron Microscopy (SEM) analysis of evaporated samples the peptide-porphyrin complex shows that these species form extended arrays of fiber bundles having having lengths that exceed several hundred microns. A closer examination reveals that these materials exist as bundles of smaller fibers which have diameters on the order of ca. 2 microns. The results show how metal coordination can be used to construct new types of peptide-based materials.
6:00 PM - MM3.20
Synthesis and Self-Assembly of Poly(diethylhexyloxy-p-phenylenevinylene)-b-poly(methyl methacrylate) Rod-Coil Block Copolymers.
Chun-Chih Ho 1 , Yi-Huan Lee 2 , Chi-An Dai 2 , Rachel Segalman 3 4 , Wei-Fang Su 1 Show Abstract
1 Materials Science and Engineering, National Taiwan University , Taipei Taiwan, 2 Polymer Science and Engineering, National Taiwan University, Taipei Taiwan, 3 Chemical Engineering, University of California, Berkeley, Berkeley, California, United States, 4 Materials Sciences Division, Lawrence Berkeley National Laboratories, Berkeley, California, United States
A series of monodisperse poly(diethylhexyloxy-p-phenylenevinylene-b-methyl methacrylate) (DEH-PPV-b-PMMA) polymers were synthesized using Siegrist polycondensation and anionic polymerizations followed by “click” chemistry. Alkyne-terminated DEH-PPV and azide-terminated PMMA were synthesized first, and then the two functionalized polymers underwent 1, 3-cycloaddition reaction to obtain copolymers. Both the conversion of the end-functionalization of the homopolymers and the yield of the “click” reaction were higher than 98% as determined by 1H nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). Transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) studies reveal the details of copolymer morphology. In previous studies of weakly segregated rod-coil copolymers, the rod-rod interaction dominated the phase behavior. The DEH-PPV-b-PMMA system presented here has higher block segregation strength and therefore offers new insight into the competition between rod-rod and rod-coil interactions that occurs in these systems. This competition results in new phase behavior. The DEH-PPV rods are organized as a monolayer that is inclined with the lamellar normal (smectic C) for the copolymers containing low volume fraction of PMMA coil (<54%). However, the DEH-PPV rods are organized as a strip and pack into hexagonal lattice with the coil for high coil fraction copolymers (>66%). The phase behaviors of the copolymers were studied using differential scanning calorimetry (DSC), polarized optical microscopy (POM) with heating stage, temperature varied wide angle X-ray scattering (WAXS), and temperature varied small angle X-ray scattering (SAXS). Upon heating the low coil fraction copolymers exhibit a series of clear transitions of smectic-lamellar to amorphous-lamellar to disordered structure. Whereas for the high coil fraction copolymers, two transitions of smectic-hexagonal to amorphous-hexagonal and smectic-hexagonal to disorder structure cannot be clearly differentiated. The order-to-disorder temperature (ODT) decreases slowly with increasing coil fraction while the smectic-to-isotropic transition (SI) temperature stays relatively unchanged. The steady SI temperature suggests the strong rod-rod interaction keeps the liquid crystalline behavior of DEH-PPV rod segment in the nanodomain structure regardless of the amount of coil segment in the copolymers. A complete phase diagram of this copolymer has been established basis on the theoretical results of phase behavior studies: Landau expansion theory and two-dimension self-consistent-field theory (2D-SCFT).
6:00 PM - MM3.21
Engineered Phage for Aligned Tissue Regenerating Materials.
Anna Merzlyak 1 2 , Seung Wuk Lee 1 3 4 Show Abstract
1 Bioengineering, UC Berkeley, Berkeley, California, United States, 2 Bioengineering, UCSF, San Francisco, California, United States, 3 Physical Bioscience Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 4 , Berkeley Nanoscience and Nanotechnology Institute, Berkeley, California, United States
In this study we have demonstrated that genetically engineered M13 bacteriophage can be utilized to construct a novel tissue engineering material that is able to both support and influence cell growth. M13 bacteriophage (phage) are naturally occurring nanofiber-like viruses, which can self-assemble into directionally organized liquid crystalline structures due to their long-rod shape and monodispersity. Multifunctionality can be imparted on the phage by genetically engineering them to display a high density of peptides and therapeutic molecules on their major and minor coat proteins. We have engineered M13 phage to display cell-signaling peptides RGD and IKVAV as well as their nonspecific controls (RGE and IQVAV) on its major coat proteins. We then used the engineered phage as a building block for the construction of aligned nanofiber tissue regenerating materials. Through viability assays and microscopy studies we have verified that three- dimensional fibers spun from the engineered viruses can support cellular growth, proliferation and differentiation. With immunostaining studies we have demonstrated the specificity of interaction of the RGD- and IKVAV modified phage to the cells. Furthermore with the aid of SEM and bright-field microscopy we have demonstrated that the fabricated phage matrices self assembled into directionally organized structures, which in turn dictated the alignment and direction of cell growth. Finally we have begun expanding the functionality of the phage by simultaneously engineering its minor and major coat proteins, to allow for future delivery of therapeutic particles. Such multifunctional and structurally aligned phage matrices offer promising opportunities for therapies that address challenging medical problems, such as the regeneration of nerve tissue after spinal cord injuries, or as in vitro model systems for studying complicated cell signaling environments.
6:00 PM - MM3.23
Enzymatic Synthesis of Amorphous Calcium Phosphate-Chitosan Nanocomposites and its Processing into Hierarchical Structures.
Francisco del Monte 1 , Maria C. Gutierrez 1 , Matias Jobbagy 1 , Maria L. Ferrer 1 Show Abstract
1 , ICMM-CSIC, Madrid Spain
Biomineralization offers the opportunity to produce highly organized nanocomposite structures, controlling specific architectures over extended length scales for a wide range of inorganic materials. Enzymatically assisted routes also offer the possibility to synthesize a number of materials with excellent control on the structural organization. In particular, HA precursors and different calcium carbonate precipitates could be obtained in solutions by enzyme-catalyzed decomposition of urea by urease. Furthermore, the gradual generation of base provided by urea hydrolysis has recently been used for the preparation of monolithic and homogeneous chitosan hydrogels. The homogeneous pH modulation besides the low temperature used for urea hydrolysis allow for the achievement of CHI hydrogels with a homogeneous 3D network structure with superior biotechnological performance than chitosan solutions gelled by neutralization with alkaline solutions, gaseous NH3 or dialysis. Here in, we applied the urease assisted hydrolysis of urea for the preparation of nanocomposites (of turbid appearance) based on calcium phosphate precipitates and CHI hydrogel (see Scheme I in downloaded file). The base generated by urea hydrolysis promoted both CHI gelation and calcium phosphate precipitation at biological temperatures (~37 degrees C). Otherwise (e.g., urea hydrolysis by thermal decomposition at 90 degrees C), CHI would undergo partial decomposition. Macroporous scaffolds (e.g.;, hierarchically organized) were obtained by a cryogenic process (named ISISA, ice segregation induced self-assembly) that simply consist on the unidirectional freezing (at -196 degrees C) of the hydrogel nanocomposites. Upon freezing, the ice formation (hexagonal form) causes every solute originally dispersed in the hydrogel to be segregated from the ice phase. After freeze-drying, the resulting hierarchical structures consists on well aligned micrometer-sized pores in the freezing direction corresponding to the empty areas where ice crystals originally resided, being the macrostructure supported by the matter (e.g., calcium phosphate nanoparticles dispersed within CHI matrix) accumulated between adjacent ice crystals. The excellent control on ice crystals formation, ice segregation matter and matter self-assembly between adjacent ice crystals allows ISISA for unique tailoring of the final macrostructural features of the resulting scaffolds. Thus, figure 1 (see at downloaded file) shows the porous channels of up to 90 microns that can be simply obtained by using different freezing rates in the application of the ISISA process to the hybrid hydrogel. The calcium phosphate nanoparticles entrapped within the CHI scaffold are identified as amorphous calcium phosphate as revealed by TEM, XRD and NMR experiments (see figure 1, right, at downloaded file).
6:00 PM - MM3.24
Fabrication of Nanoengineered Plasmonic Hybrid Systems for Bio-nanotechnology.
Kirsty Leong 1 , Melvin Zin 2 , Hong Ma 2 , Memet Sarikaya 2 , Alex K.-Y. Jen 2 1 Show Abstract
1 Chemistry, University of Washington, Seattle, Washington, United States, 2 Materials Science and Engineering, University of Washington, Seattle, Washington, United States
Using a protein enabling strategy and biomolecular recognition, surface plasmon enhanced tunable quantum dot (QD) nanoarrays are fabricated where a 25-fold and 40-fold increase in the QDs photoluminescence is observed. This is accomplished by spectrally tuning the localized surface plasmon resonance of gold nanopillars and exploiting their unique optical properties to modify their surrounding environment. Nine different unique geometric arrangements of gold nanopillars are arranged where the diameter is varied from 50 nm, 100 nm, and 200 nm with a tip-to-top distance spacing of 50, 100, 150, and 200 nm. Protein functionalized QDs are self-assembled onto the nanopillars in a step-wise fashion with a concomitant incremental increase in separation from the metal surface using gold binding polypeptides as a fusion partner and biotin-steptavidin spacer units. The highest QD emission intensity is observed at a QD-metal distance of ~17.50 nm when attached onto smaller gold nanopillars. The stronger near-field coupling interactions between neighboring nanopillars spaced at a tip-to-tip distance of 50 and 100 nm gives rise to higher emission intensity. At larger tip-to-tip distances, the nanopillars interact through far-field dipolar interactions thus behaving independently rather than collectively. The QDs emission intensity is further enhanced by sandwiching the QDs in between the local electromagnetic fields of two metal nanoparticles at equal QD-metal distances. In addition to enhancing the QD emission intensity, QD-dye hybrid assemblies are fabricated using these surface plasmon enhanced QD nanoarrays to demonstrate surface plasmon assisted Förster resonance energy transfer (FRET). The QDs-dye hybrid system exhibits an 80% increase in energy transfer rates from a donor (QD) to an acceptor (dye) compared to nonmetal QD-dye systems. The overall approach allows for a comprehensive control both laterally (lithographically defined nanostructures) and vertically (QD-metal distance) of the collectively behaving QD-nanostructure assemblies. Thus the use of metal nanostructures can enhance the photoluminescence of nearby fluorophores and FRET between a donor and acceptor chromophore in order to create optimally integrated systems for a variety of applications in bio-nanotechnology.
6:00 PM - MM3.25
Harnessing Mechanical Nanopatterning of Microenvironments by Cells with Matrix Compliance.
Nathaniel Huebsch 1 2 , Praveen Arany 1 , Angelo Mao 1 , Jose Rivera-Feliciano 1 , David Mooney 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Division of Health Sciences and Technology, Harvard-MIT, Cambridge, Massachusetts, United States
Functional complexity is a critical requirement for tissue engineering scaffolds, as such materials must function as local micro-environments which provide programming cues to host or transplanted cells. One approach to this goal is the design of complex, synthetic analogs of the natural extracellular matrix (ECM). Both the specific composition of receptor-binding adhesion epitopes presented by such materials and the nanoscale heterogeneity in their presentation, have demonstrated effects on cell behavior. In a seemingly unrelated observation, a variety of cell types, including mesenchymal stem cells (MSCs), change their behavior in response to the mechanics of their micro-environment. While mechanisms for cell responses to specific molecular adhesion epitopes are well established, the biophysical means through which cells sense and ultimately respond to the mechanical properties of the ECM are incompletely understood. We hypothesized that matrix mechanics might affect cell fate partially by controlling the formation of receptor-adhesion ligand bonds. To test this hypothesis, we assessed formation of bonds between MSCs and biomimmetic RGD-peptides grafted to 3D alginate hydrogels using a FRET-based technique. Strikingly, the number of RGD-integrin bonds indeed depended on matrix compliance, but in a biphasic manner that was independent of the specific type of alginate polymer or crosslinking molecule. Further analysis revealed that enhanced binding to RGD correlated not with microscale changes in MSC morphology but rather with their ability to exert traction forces to reorganize RGD peptides on the nanoscale. This suggests that stem cells can nanopattern their microenvironment in a mechanically regulated fashion. Consistent with that hypothesis, bond formation, along with matrix reorganization, was decoupled from ECM mechanics with drugs that inhibit cell traction.We speculated that this mechanical nanopatterning, by increasing the structural complexity of the ECM, would engender the micro-environment with functional complexity. Thus, we examined the effects of ECM elastic modulus on the specific receptors MSC used to bind RGD and on their lineage specification. Consistent with historical data, the α5-integrin could not act as an RGD receptor in 2D – however, in 3D matrices, this receptor bound RGD in a mechanically-dependent manner. MSCs’ ability to form α5-integrin-RGD bonds had important consequences on their fate, as their differentiation to osteoblast-like phenotype correlated with the α5-integrin-RGD bond formation, whereas differentiation toward adipocyte-like cells was optimal in softer matrices. This work highlights a role for stem cells, not only in terms of their ability to respond to complex biomaterials, but also in terms of their ability to transform simple template materials into information-rich, structurally complex materials in-situ.
6:00 PM - MM3.26
Reversible Alginate Sponge for 3D Cell Culture.
Zhensheng Li 1 Show Abstract
1 , Invitrogen Corporation, Frederick , Maryland, United States
AlgiMatrix is a product designed in Invitrogen as a tool to guide the formation of 3D spheroids or interconnected aggregates, which can be used for tissue engineering, drug screening, bioproduction and tumor metastasis research. Alginate, a defined polysaccharide extract from brown seaweed, is the main chemical component. With a modified lyophilization technology, it was made as porous sponge like structure and manipulated by two providing buffers. One buffer maintains the sponge structure, while the other one can dissolve oe soften sponge in medium. Both buffers works at neutral physiological conditions and reverse each other to control the sponge compliance and transparency, which makes the sponge very unique and flexible for 3D cell culture. This product is animal origin free, completely biocompatible and biodegradable. It can be used for RUO (research use only), IVD (in vitro diagnostic) and even clinic later on. It is going to lead the market of 3D cell culture to a new level.
6:00 PM - MM3.27
Patterned Biomineralization on Polydiacetylene Arrarys of Various Functional Groups
Won-doc Lee 1 , Gil-Sun Lee 1 , Dong-june Ahn 1 Show Abstract
1 Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of)
Biological organisms have unique abilities to nucleate, grow and organize biominerals which are being used as the essential body parts for their survivals. These abilities which are known as the biomineralization processes are usually achieved by the creation of proper organic matrices and the precipitation onto the matrices by the chemical interactions at the inorganic/organic interfaces. The in-vitro biomimetic synthesis of organic-inorganic composites produced by nature is a subject of much attention still being researched throughout these days.The most abundantly produced biominerals are calcite, aragonite and vaterite. These three biominerals classified by different crystal structures and possess distinctive properties. These biominerals consist of organic-inorganic hybride complex and shows the potential to be used as new material with high quality and performance that can be used in many fields of engineering. However, the discovery of specific optimal growing condition for biomineralization is still not cleared. In experiments, we made hollow tubes with the height and diameter of 5 mm and assembled them into close-packed pattern arrays. Then, the array water interface formed in each hole that is filled two-thirds with DI-water is deposited by solution coating with different polydiacetylenes(PDAs). Polymerization was performed in situ by UV (254 nm) irradiation. This results in two-dimensional polymer crystalline domains that are spanned by the linear polymer chains. We deposited patterned PDAs on the octadecyltrichloro-silane(OTS) coated slides by raising the height of the DI-water for the contact with the sample and the substrate. Then, growth for crystallization of calcium carbonate on the surfaces of patterned PDAs was carried out. From this experiment, we demonstrate for the first time that systematic combinational biomineralization becomes possible for farther understanding of crystal growth
6:00 PM - MM3.28
Single-Particle Tracking and Ca2+ -Triggered Fusion of Lipid Vesicles Tethered to a Fluid Supported Lipid Bilayer using DNA hybridization.
Lisa Simonsson 1 , Gudrun Stengel 1 , Peter Jonsson 2 , Fredrik Hook 1 Show Abstract
1 Applied Physics, Chalmers University of Technology, Gothenburg Sweden, 2 Solid State Physics, University of Lund, Lund Sweden
The diffusive dynamics and fusion of vesicles tethered to supported lipid bilayers (SLB) are key features in understanding the natural exocytosis process and for delivery of membrane constituents to real cell membranes or mimics thereof. We recently demonstrated efficient fusion of lipid vesicles induced by cholesterol-modified DNA zippers(1,2), which in a reductionist way mimics the natural protein-based fusion machinery. It was previously shown by us and others that lipid vesicles tethered to SLBs via DNA hybridization display lateral diffusion. In this paper we show that by tethering vesicles to an SLB in a zipper-like manner, vesicle fusion with the underlying bilayer can be induced upon addition of Ca2+. The tethered lipid vesicles (Ø~100 nm) and the fusion process were visualized using total internal reflectance fluorescence (TIRF) microscopy and single-particle tracking was used to investigate the influence of the number of DNA tethers on the diffusive behaviour of vesicles tethered, using either fusogenic DNA zippers or non-fusogenic binding DNA. It was found that the average diffusion coefficient increases non-linearly with decreasing number of DNA strands per vesicle. Interestingly, at a critical number of DNA per vesicle, Ca2+ can be used to induce fusion of vesicles already tethered to a SLB. Combined with TIRF microscopy of the same region prior to and after addition of Ca2+, we currently explore the correlation between the lateral mobility and the on set of fusion, including its kinetics. Taken together, DNA-mediated fusion emerges as a promising tool for retroactive functionalization of artificial and biological membranes and may help to dissect the func