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Layer-by-layer Assembly (layer-by-layer + assembly)
Selected AbstractsLayer-By-Layer Assembly of ,-Estradiol Loaded Mesoporous Silica Nanoparticles on Titanium Substrates and Its Implication for Bone HomeostasisADVANCED MATERIALS, Issue 37 2010Yan Hu Drug-loadingmesoporous silica nanoparticles that serve as a nanoreservoir-type drug-delivery system are successfully attached to titanium substrates via the layer-by-layer assembly technique (see scheme). The obtained structure demonstrates great potential for regulating the biological behaviors of osteoblasts/ steoclasts in order to maintain bone homeostasis. The approach we present here may have wide applications in implant technology, tissue engineering, and regenerative medicine. [source] Electrochemical Biosensors Based on Layer-by-Layer AssembliesELECTROANALYSIS, Issue 18 2006Wei Zhao Abstract Layer-by-layer (LBL) assemblies, which have undergone great progress in the past decades, have been used widely in the construction of electrochemical biosensors. The LBL assemblies provide a strategy to rationally design the properties of immobilized films and enhance the performance of biosensors. The following review focuses on the application of LBL assembly technique on electrochemical enzyme biosensors, immunosensors and DNA sensors. [source] Electrically Conductive Thin Films Prepared from Layer-by-Layer Assembly of Graphite PlateletsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Mubarak Alazemi Abstract Layer-by-layer (LBL) assembly of carbon nanoparticles for low electrical contact resistance thin film applications is demonstrated. The nanoparticles consist of irregularly shaped graphite platelets, with acrylamide/,, -methacryl-oxyethyl-trimethyl-ammonium copolymer as the cationic binder. Nanoparticle zeta (,,) potential and thereby electrostatic interactions are varied by altering the pH of graphite suspension as well as that of the binder suspension. Film thickness as a function of zeta potential, immersion time, and the number of layers deposited is obtained using Monte Carlo simulation of the energy dispersive spectroscopy measurements. Multilayer film surface morphology is visualized via field-emission scanning electron microscopy and atomic-force microscopy. Thin film electrical properties are characterized using electrical contact resistance measurements. Graphite nanoparticles are found to self-assemble onto gold substrates through two distinct yet overlapping mechanisms. The first mechanism is characterized by logarithmic carbon uptake with respect to the number of deposition cycles and slow clustering of nanoparticles on the gold surface. The second mechanism results from more rapid LBL nanoparticle assembly and is characterized by linear weight uptake with respect to the number of deposition cycles and a constant bilayer thickness of 15 to 21,nm. Thin-film electrical contact resistance is found to be proportional to the thickness after equilibration of the bilayer structure. Measured values range from 1.6,m,,cm,2 at 173,nm to 3.5,m,,cm,2 at 276,nm. Coating volume resistivity is reduced when electrostatic interactions are enhanced during LBL assembly. [source] Preparation of Protamine,Titania Microcapsules Through Synergy Between Layer-by-Layer Assembly and Biomimetic MineralizationADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Yanjun Jiang Abstract A novel approach combining layer-by-layer (LbL) assembly with biomimetic mineralization is proposed to prepare protamine,titiania hybrid microcapsules. More specifically, these microcapsules are fabricated by alternative deposition of positively charged protamine layers and negatively charged titania layers on the surface of CaCO3 microparticles, followed by dissolution of the CaCO3 microparticles using EDTA. During the deposition process, the protamine layer induces the hydrolysis and condensation of a titania precursor, to form the titania layer. Thereafter, the negatively charged titania layer allows a new cycle of deposition step of the protamine layer, which ensures a continuous LbL process. The morphology, structure, and chemical composition of the microcapsules are characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. Moreover, these protamine,titania hybrid microcapsules are first employed as the carrier for the immobilization of yeast alcohol dehydrogenase (YADH), and the encapsulated YADH displays enhanced recycling stability. This approach may open a facile, general, and efficient way to prepare organic,inorganic hybrid materials with different compositions and shapes. [source] Pseudobilayer Vesicle Formation via Layer-by-Layer Assembly of Hydrophobically Modified Polymers on Sacrificial Substrates,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2005J. Khopade Abstract A bilayer of a hydrophobically modified polyelectrolyte, octadecyl poly(acrylamide) (PAAm), sandwiched between the layers of a hydrophilic polyelectrolyte, poly(ethyleneimine) (PEI), is prepared by the sequential electrostatic,hydrophobic,electrostatic-interaction-driven self-assembly on planar and colloid substrates. This process results in a PEI/[PAAm]2/PEI-multilayer-coated substrate. The removal of a PAA/PEI/[PAAm]2/PEI-multilayer-coated decomposable colloidal template produces hollow capsules. Irregular hydrophobic domains of the [PAAm]2 bilayer in the PEI/[PAAm]2/PEI-multilayer capsule are infiltrated with a lipid to obtain a uniform, distinct hydrophobic layer, imparting the capsule with a pseudobilayer vesicle structure. [source] Layer-by-Layer Assembly of Reactive Ultrathin Films Mediated by Click-Type Reactions of Poly(2-Alkenyl Azlactone)s,ADVANCED MATERIALS, Issue 22 2007E. Buck Covalently crosslinked ultrathin films can be fabricated layer-by-layer by exploiting fast and efficient click-type reactions between polyamines and the ,spring-loaded' functionality of poly(2-alkenyl azlactone)s. The accessibility and reactivity of residual azlactone functionality in these ultrathin materials permits further functionalization post-fabrication, suggesting new approaches to the modification, passivation, or patterning of curved or topologically complex surfaces with chemical or biological functionality. [source] Biomedical Applications of Layer-by-Layer Assembly: From Biomimetics to Tissue Engineering,ADVANCED MATERIALS, Issue 24 2006Z. Tang Abstract The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific and engineering communities because of the broad application of these materials in the biomedical field. Among the available techniques, the layer-by-layer assembly method introduced by Decher and co-workers in 1992 has attracted extensive attention because it possesses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials' structure, and robustness of the products under ambient and physiological conditions. In this context, a systematic review of current research on biomedical applications of layer-by-layer assembly is presented. The structure and bioactivity of biomolecules in thin films fabricated by layer-by-layer assembly are introduced. The applications of layer-by-layer assembly in biomimetics, biosensors, drug delivery, protein and cell adhesion, mediation of cellular functions, and implantable materials are addressed. Future developments in the field of biomedical applications of layer-by-layer assembly are also discussed. [source] Multilayer Thin Films by Layer-by-Layer Assembly of Hole- and Electron-Transport Polyelectrolytes: Optical and Electrochemical PropertiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 20 2006Kyungsun Choi Abstract Summary: In this paper, we present the synthesis of a series of p-type and n-type semiconducting polyelectrolytes with triarylamine, oxadiazole, thiadiazole and triazine moieties. The synthesized polymeric hole and electron transport materials were examined optically and electrochemically using UV/Vis spectroscopy, PL spectroscopy and CV. Based on the optical and electrochemical data, each of the energy levels were calculated and all values suggested that they were promising hole- (p-type) or electron-transport (n-type) materials for devices. Moreover, the synthesized ionic polymers were suitable for LBL thin film deposition from dilute polymer solutions and the multilayers were fully characterized by UV/Vis, PL spectroscopy and CV. [source] Covalent Layer-by-Layer Assembly and Solvent Memory of Multilayer Films from Homobifunctional Poly(dimethylsiloxane),ANGEWANDTE CHEMIE, Issue 35 2010Rohama Gill Dr. Mit einer einfachen Prozedur gelingt der kovalente schichtweise Aufbau (Layer-by-Layer, LbL) von homodifunktionellem H2N-Poly(dimethoxysilan)-NH2 auf SiO2 -Oberflächen. Man erhält robuste LbL-Filme von optischer Qualität (siehe Bild, Photo links) trotz Verwendung nicht gereinigter kommerzieller Ausgangsmaterialien. Die Filme zeigen ein Solvensgedächtnis bezüglich ihres Quellverhaltens in den Lösungsmitteln der entsprechenden Polymere. [source] Multilayer Assemblies Consisting of Tri-Vanadium-Substituted Heteropolyanions and Its Electrocatalytic PropertiesELECTROANALYSIS, Issue 14 2003Shengyong Zhai Abstract We describe the controlled fabrication of ultrathin multilayer films consisting of tri-vanadium- substituted heteropolytungstate anions (denoted as P2W15V3) and a cationic polymer of quaternized poly (4-vinylpyridine) partially complexed with osmium bis(2,2,-bipyridine) (denoted as QPVP-Os) on the 4-aminobenzoic acid (4-ABA) modified glassy carbon electrode (GCE) surface based on layer-by-layer assembly. Cyclic voltammetry and UV-vis absorption spectrometry have been used to easily monitor the thickness and uniformity of thus-formed multilayer films. The V-centered redox reaction of P2W15V3 in the multilayer films can effectively catalyze the reduction of BrO and NO. The resulting P2W15V3/QPVP-Os multilayer film modified electrode behaves as a much promising electrochemical sensor because of the low overpotential for the catalytic reduction of BrO and NO, and the catalytic oxidation of ascorbic acid. [source] The Assembling of Semiconductor NanocrystalsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2005Alexey Shavel Abstract Recent accomplishments in arranging semiconductor nanoparticles in a desired manner are reviewed. Coupling mechanisms utilized for this purpose include electrostatic and covalent interactions, methods like layer-by-layer assembly, solvent-controlled precipitation and surface amination for covalent attachment of nanoparticles are employed. Dipole,dipole interactions are operative in nanocrystal solids and fast Förster energy transfer is observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] High-Nanofiller-Content Graphene Oxide,Polymer Nanocomposites via Vacuum-Assisted Self-AssemblyADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Karl W. Putz Abstract Highly ordered, homogeneous polymer nanocomposites of layered graphene oxide are prepared using a vacuum-assisted self-assembly (VASA) technique. In VASA, all components (nanofiller and polymer) are pre-mixed prior to assembly under a flow, making it compatible with either hydrophilic poly(vinyl alcohol) (PVA) or hydrophobic poly(methyl methacrylate) (PMMA) for the preparation of composites with over 50 wt% filler. This process is complimentary to layer-by-layer assembly, where the assembling components are required to interact strongly (e.g., via Coulombic attraction). The nanosheets within the VASA-assembled composites exhibit a high degree of order with tunable intersheet spacing, depending on the polymer content. Graphene oxide,PVA nanocomposites, prepared from water, exhibit greatly improved modulus values in comparison to films of either pure PVA or pure graphene oxide. Modulus values for graphene oxide,PMMA nanocomposites, prepared from dimethylformamide, are intermediate to those of the pure components. The differences in structure, modulus, and strength can be attributed to the gallery composition, specifically the hydrogen bonding ability of the intercalating species [source] Stable Inverted Polymer/Fullerene Solar Cells Using a Cationic Polythiophene Modified PEDOT:PSS Cathodic InterfaceADVANCED FUNCTIONAL MATERIALS, Issue 15 2010David A. Rider Abstract A cationic and water-soluble polythiophene [poly[3-(6-pyridiniumylhexyl)thiophene bromide] (P3PHT+Br,)] is synthesized and used in combination with anionic poly(3,4-ethylenedioxythiophene):poly(p -styrenesulfonate) (PEDOT:PSS), to produce hybrid coatings on indium tin oxide (ITO). Two coating strategies are established: i) electrostatic layer-by-layer assembly with colloidal suspensions of (PEDOT:PSS),, and ii) modification of an electrochemically prepared (PEDOT:PSS), film on ITO. The coatings are found to modify the work function of ITO such that it could act as a cathode in inverted 2,5-diyl-poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61 -butyric acid methyl ester (PCBM) polymer photovoltaic cells. The interfacial modifier created from the layer-by-layer assembly route is used to produce efficient inverted organic photovoltaic devices (power conversion efficiency ,2%) with significant long-term stability in excess of 500,h. [source] Flexible Silk,Inorganic Nanocomposites: From Transparent to Highly ReflectiveADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Eugenia Kharlampieva Abstract A novel type of all-natural, biocompatible, and very robust nanoscale free-standing biohybrids are reported. They are obtained by integrating a silk fibroin matrix with functional inorganic nanoplatelets using a spin-assisted layer-by-layer assembly. The organized assembly of the silk fibroin with clay (montmorillonite) nanosheets results in highly transparent nanoscale films with significantly enhanced mechanical properties, including strength, toughness, and elastic modulus, as compared to those for the pristine silk nanomaterials. Moreover, replacing clay nanoplatelets with a highly reflective Langmuir monolayer of densely packed silver nanoplates causes a similar enhancement of the mechanical properties, but in contrast to the materials above, highly reflective, mirror-like, nanoscale flexible films are created. This strategy offers a new perspective for the fabrication of robust all-natural flexible nanocomposites with exceptional mechanical properties important for biomedical applications, such as reinforced tissue engineering. On the other hand, the ability to convert silk-based nanoscale films into mirror-like biocompatible flexible films can be intriguing for prospective photonics and optical exploitation of these nanobiohybrids. [source] Encapsulation of Water-Insoluble Drugs in Polymer Capsules Prepared Using Mesoporous Silica Templates for Intracellular Drug DeliveryADVANCED MATERIALS, Issue 38 2010Yajun Wang Water-insoluble compounds were encapsulated in polymer capsules through mesoporous silica nanoparticle-mediated layer-by-layer assembly. The drug-loaded capsules exhibit excellent colloidal stability and high potency to colorectal cancer cells in vitro with similar cytotoxicity to the free drug dissolved in organic solvent. [source] Highly Reactive Multilayer-Assembled TiO2 Coating on Electrospun Polymer NanofibersADVANCED MATERIALS, Issue 12 2009Jung Ah Lee Highly efficient photocatalytically active TiO2 -coated polymer fibers are prepared using a facile and universal method involving layer-by-layer assembly of TiO2 nanoparticles and POSS molecules on various electrospun fibers. The TiO2 -coated fibers display excellent photocatalytic properties in degradation of allyl alcohol under UV illumination, without degradation of substrates. [source] Biomedical Applications of Layer-by-Layer Assembly: From Biomimetics to Tissue Engineering,ADVANCED MATERIALS, Issue 24 2006Z. Tang Abstract The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific and engineering communities because of the broad application of these materials in the biomedical field. Among the available techniques, the layer-by-layer assembly method introduced by Decher and co-workers in 1992 has attracted extensive attention because it possesses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials' structure, and robustness of the products under ambient and physiological conditions. In this context, a systematic review of current research on biomedical applications of layer-by-layer assembly is presented. The structure and bioactivity of biomolecules in thin films fabricated by layer-by-layer assembly are introduced. The applications of layer-by-layer assembly in biomimetics, biosensors, drug delivery, protein and cell adhesion, mediation of cellular functions, and implantable materials are addressed. Future developments in the field of biomedical applications of layer-by-layer assembly are also discussed. [source] Linear Assemblies of Silica-Coated Gold Nanoparticles Using Carbon Nanotubes as Templates,ADVANCED MATERIALS, Issue 23-24 2004A. Correa-Duarte Silica-coated gold nanoparticles were assembled on carbon nanotubes by polymer wrapping and layer-by-layer assembly (see Figure). The procedure was applied to ordered arrays of vertically aligned nanotubes, resulting in parallel nanotubes of compact nanoparticle monolayers for potential use in photonics. [source] Thermal stability of porous it -PMMA thin film obtained by the extraction of st -PMAA from it -PMMA/st -PMAA stereocomplex with layer-by-layer assembly on a substrateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2010Hiroharu Ajiro Abstract The functionality of porous isotactic (it) poly(methyl methacrylate) (PMMA) thin films, which were previously developed by the selective extraction of syndiotactic (st) poly(methacrylic acid) (PMAA) from the it -PMMA/st -PMAA stereocomplex thin film on a substrate using the layer-by-layer assembly method was investigated after thermal treatment (70, 80, and 90 °C) in water for 4 h. Quartz crystal microbalance analysis and infrared spectra measurements revealed that the st -PMAA incorporation ability of the porous it -PMMA thin film decreased in order at 80 and 90 °C, while there was no decrease observed at 70 °C. X-ray diffraction analysis also supported the thermal stability of the porosity at 70 °C, whereas two it -PMMA crystalline peaks (2, = 9° and 14°) were generated during heating at 90 °C. The loss of the functionality of the it -PMMA thin film was thus shown to be due to crystallization, which was caused by the increase in polymer-chain mobility during the heating process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3265,3270, 2010 [source] Layer-by-Layer Assembled Nanotubes as Biomimetic Nanoreactors for Calcium Carbonate DepositionMACROMOLECULAR RAPID COMMUNICATIONS, Issue 18 2009Qiang He Abstract Enzyme-loaded magnetic polyelectrolyte multilayer nanotubes prepared by layer-by-layer assembly combined with the porous template could be used as biomimetic nanoreactors. It is demonstrated that calcium carbonate can be biomimetically synthesized inside the cavities of the polyelectrolyte nanotubes by the catalysis of urease, and the size of the calcium carbonate precipitates was controlled by the cavity dimensions. The metastable structure of the calcium carbonate precipitates inside the nanotubes was protected by the outer shell of the polyelectrolyte multilayers. These features may allow polyelectrolyte nanotubes to be applied in the fields of nanomaterials synthesis, controlled release, and drug delivery. [source] Enhanced Biomacromolecule Encapsulation by Swelling and Shrinking ProceduresCHEMPHYSCHEM, Issue 1 2004Changyou Gao Prof. Dr. Reversible growth: Microcapsules were fabricated by layer-by-layer assembly of poly(diallyldimethyl ammonium chloride)/poly(styrene sulfonate) onto removable melamine formaldehyde particles. The capsules with swelling and shrinking features (see graphic) provide a novel route for microencapsulation. Loading of biomacromolecules such as dextran with ultrahigh molecular weight is achieved by spontaneously opening the capsule during core removal procedure, followed by closing the capsule in salt solution. [source] |