Masatsugu Shimomura

Mesoscopic patterns of molecular aggregates on solid substrates

Abstract A two-dimensional micron-sized honeycomb structure was formed when a chloroform solution of an amphiphilic polymer was cast on solid surfaces at high atmospheric humidity. This simple method is widely applicable for patterning of molecular aggregates on solid surfaces. Mesoscopic patterns are demonstrated to be formed spontaneously from a variety of amphiphilic polyion complexes, amphiphilic covalent polymers, and organic–inorganic hybrid materials. Size and structure of the patterns can be regulated by concentration, atmospheric humidity, etc.

Bottom-up strategy of materials fabrication: a new trend in nanotechnology of soft materials

Recent progresses in nanometer-scale molecular self-organization and mesoscopic pattern formation are reviewed from the view point of nanotechnology of bottom-up materials fabrication. Nanometer-scale layer-by-layer self-assemblies on nanoparticles will provide wide applications in many fields. The micro-contact printing technique is effectively used for up-sizing the nanostructured molecular assemblies as submicrometer- and micrometer-scale patterns. Dissipative structures formed in non-equilibrium systems as self-organized spatio-temporal structures are newly employed for the mesoscopic patterning of the nanostructured molecular assemblies.

Honeycomb-patterned thin films of amphiphilic polymers as cell culture substrates

Abstract Recently, we have found honeycomb patterns with sub-micron line width that form during the non-equilibrium process of cast film formation. The honeycomb-patterned films were fabricated using four macromolecular compounds (amphiphilic copolymers containing lactose units or carboxyl groups as side-chains and polyion complexes composed of anionic polysaccharides). The specific binding of lactose by lectin confirmed that the lactose moieties contained in the honeycomb films work as biologically active ligands. Bovine serum albumin (BSA) labeled with fluorescein was covalently attached to the honeycomb films using water-soluble carbodiimide (WSC) as an activator. Using fluorescence imaging of the modified film, we could show that the proteins are immobilized on the honeycomb patterns. Adhesion of bovine aorta endothelial cells (ECs) to the honeycomb films indicates that the honeycomb structure works as an adhesive site for the cells.

Mesoscopic pattern formation of nanostructured polymer assemblies

Abstract Hierarchical mesoscopic structures of the nanoscopic supramolecular assemblies, which consist of polyelectrolytes and bilayer-forming amphiphiles, are prepared by a simple and new solvent-casting method. Submicron scale 2-D structures, e.g. regular dots, stripes, and networks, are formed when highly diluted organic solutions of polymer assemblies are cast on solid surfaces. Dynamic mesoscopic regular structures, the so-called ‘dissipative structures’, formed in the non-equilibrium processes of solvent-casting are fixed as hierarchically structured polymer assemblies.

Formation of ordered mesoscopic patterns in polymer cast films by dewetting

Abstract Ordered arrays of polymer aggregates can be prepared by a simple process: rinsing of smooth hydrophilic surfaces with a dilute solution of a hydrophobic polymer. The patterns consist of submicron-size polymer aggregates which can form superlattices over several tens of micrometers, thus self-assembling several hundred aggregates in an orderly fashion. Atomic force microscopy shows that the structures consist of isolated `polymer islands, separated by the bare substrate. The ordering of the aggregates can be explained by the formation of regular, dissipative structures caused by convection during the evaporation of the solvent, followed by dewetting of the hydrophobic polymer solution from the smooth hydrophilic surface.

Construction of two-dimensional DNA-mimetics: supramolecular architecture with highly stacked base-pairs of amphiphilic adenine and thymine at the air–water interface

Abstract In order to construct two dimensional DNA-mimetics, nucleo base monolayers, composed of amphiphilic adenine and thymine derivatives, were prepared at the air–water interface. The monolayer were characterized by pressure–area isotherm measurements, UV-Vis absorption and FT-IR reflection-absorption spectroscopy (RAS), and fluorescence spectroscopy and microscopy. A 1:1 mixture of octadecyladenine (C18-Ade) and octadecylthymine (C18-Thy) formed the most condensed monolayer on a pure water subphase in the three combinations of the equimolar mixtures of C18-Ade, C18-Thy, and octadecylcytosine (C18-Cyt). A FT-IR RAS spectrum of the transferred monolayer suggests the base-pairing with Watson–Crick type hydrogen bonds in the C18-Ade/C18-Thy monolayer. An in situ observation of fluorescence image and spectrum at the air–water interface indicates that the Watson–Crick type monolayer can incorporate an amphiphilic intercalator, octadecylacridineorange (C18-AO), as well as DNA.

DNA monolayers complexed with amphiphilic intercalator at the air-water interface

Abstract The interaction of a newly synthesized cationic intercalator amphiphile C18AO into double-stranded DNAs at the air-water interface was investigated. Polyion complex monolayers consisting of DNAs and cationic amphiphiles were prepared. Pressure-area isotherms, fluorescence measurements, Fourier transform infrared-reflection-absorption spectroscopy and quartz crystal microbalance measurements suggest that C18AO molecules can be intercalated into base-pairs of DNAs to form densely packed two-dimensional DNA arrays at the air-water interface.

Stabilization of Micropatterned Polymer Films as Artificial Extracellular Matrices for Tissue Engineering

Abstract Honeycomb-patterned polymer films are formed upon self-organization of water microspheres stabilized by amphiphilic polymers. The honeycomb films can work as cell culture substrates. The films composed of heparin-cationic lipid complex, however, gradually lost the honeycomb structure when immersed in culture medium. Crosslinking of the films was carried to stabilize the honeycomb pattern. A bisazido derivative was used as a crosslinker connecting the constituent polymer of the honeycomb films. Morphological study of the immersed films revealed that the crosslinked films maintained the honeycomb structure in the phosphate buffer solution.

Tailored charge transfer complex based on two-dimensional molecular assemblies

Abstract For tailoring charge transfer (CT) complexes in bilayer membranes, single-chain bilayer-forming amphiphiles, having a hydrophilic viologen head and a hydrophobic aromatic segment, such as an azobenzene or a biphenyl group, were prepared. Bilayer membranes with a titled molecular orientation were formed when the amphiphiles which had five carbon atoms in the spacer methylene chain between the viologen head and the aromatic segment were dissolved in water. A visible absorption band at 460 nm, which was attributed to the CT interaction between the viologen head and the biphenyl segment of the adjacent molecule in the two-dimensional molecular array, was newly observed in the bilayer membrane.

Mesoscopic Patterns of Polythiophenes for Electronic Applications

Abstract Ordered arrays of micron-size (i.e. mesoscopic) lines of conducting polymers can be deposited from solution by a simple casting process. The arrays were characterized by optical microscopy and AFM and the darkconductivity and photoconductivity of single poly(3-hexylthiophene) lines was measured by using microelectrodes. Doping with iodine leads to an increase of the darkcurrent.