Using the biomimetic method, we prepared hydrogel-hydroxyapatite (HAp) composites and polyurethane (PU) -HAp composite. The hydrogel-HAp composites were studied as model systems of calcification. PU-HAp composites were used as implantable materials for studying soft-tissue compatibility of HAp. HAp layers were formed on/in certain types of nonionic hydrogels that have hydroxyl groups on their side chains. The hydrogels used were poly (vinyl alcohol) (PVA), poly (2-hydroxyethyl methacrylate) (PHEMA), poly (glucosyloxyethyl methacrylate) (PGEMA), and agarose. Under an optical microscope, one could observe the formation of thin and continuous HAp layers on the top surface of the PVA, PHEMA, and PGEMA gels. On the other hand, intermittent HAp layers were observed on the surface of the agarose gel. The swelling ratio and the bound water content of these hydrogels were measured as an essential character in HAp formation. There were relations among the HAp formation, the swelling ratios, and the bound water content. PU-HAp composites were implanted subcutaneously into rats. HAp which formed on the PU could exhibit good tissue regeneration activity. The effect of HAp was comparable to that of fibronectin, collagen and RGD peptide. HAppolymer composites will become novel biomaterials in the near future.

View full abstract

The copper (II) complexes of ^L/D-arginine (^L/D-Arg), one of the essential amino acids, have been revealed to form various selforganized structures, such as right- and left-handed double helical and single helical and sheet structures, according to the structural requirements for hydrogen bonds with the key counteranions. The reflectance and solid state ESR spectra for these systems reflected the coordination environments around the metal atoms and their crystal structures, respectively. The self-organization process in solution leading to the double helical structure of [Cu (^L-Arg) ₂] (isophthalate) in solid state has been followed by CD and NMR spectra by use of the corresponding [Pd (^L-Arg) ₂] ²⁺-(isophthalate) system. The structure-determining factors in the self-organizing system are discussed in detail.

View full abstract

Recently, organic-inorganic hybrid materials have been widely investigated. However, there are few reports concerning hybrid materials using engineering plastics which can be expected to be high in function and performance. We synthesized a new material by a sol-gel reaction of a bisphenol-A type polycarbonate (PC) oligomer, which is well-known as an engineering plastic, having a triethoxysilyl group at both end-sites. The obtained film had a higher T_g and a wider temperature width of T_g than PC film. The storage elastic modulus of the film decreased gradually with an increase in temperature over T_g, whereas PC film has a very rapid decrease. In addition, its surface hardness and mechanical strength were superior to those of PC film. These results led us to the conclusion that the new material was an organic-inorganic hybrid material in which PC segments directly bound to silica.

View full abstract

The hydrogen bond, which is one of the non-covalent interactions, plays an important role as well as covalent- and coordinatebonds for controlling supramolecular synthesis through metal-induced self-assembly of organic compounds. The 1: 1 adducts of the octahedral Co (III) complexes containing biguanidato (bg) and violurato (va) ligands, [Co (bg) ₃ ] and [Co (va) ₃ ], which enable formation of the DAD-ADA type hydrogen-bonding system (D: proton donor and A: proton acceptor), revealed the formation of a three-dimensional network structure constructed with triple hydrogen-bonding interaction and the porosity capturing water molecules. They were characterized by IR and ¹H NMR spectra and elemental, thermogravimetry (TG), and Defferential Scanning Calorimetry (DSC) analyses. Moreover, the 1: 1 reaction of square planar [Cu (va) ₂ ] and octahedral [Mn (enbg) (OH) (H₂O)] complexes (enbg=ethylenebis-biguanidato) demonstrated an interesting electron transfer reaction, Cu (II) +Mn (III) -Cu (I) +Mn (IV), which were examined by use of UV-Vis and ESR spectra and cyclic voltammetry. This oxidation of Mn (III) to Mn (IV) by Cu (II) has proceeded through Mn-O-Cu bond formed between the linear tape structures with an infinite triple hydrogen-bond networks between the va and enbg complexes, which may have been induced by the proton transfer in the DAD-ADA system.

View full abstract

Polymer hybrids were prepared by radical polymerization of vinyltrimethoxysilane with t-butyl peroxide (DTBP) as an initiator followed by acid-catalyzed hydrolytic polycondensation to investigate the relationship between the structure of hybrids and the properties of the films. Radical polymerization of vinyltrimethoxysilane (VTS) with various molar ratios of DTBP to VTS provided polyvinyltrimethoxysilanes with different degrees of polymerization (DP=46-74) which were hydrolyzed to prepare polyvinylpolysilsesquioxanes (PVPS) with various molecular weights (M_w=5000-170000) and degrees of condensation of siloxane linkage (DC=7-13%). Transparent, colorless and flexible free-standing films (thickness: 0.04-0.07mm) were prepared by casting PVPS on the polymethylpentene shale followed by heating at 80r for 10 days. Homogeneous, colorless and transparent coating films (thickness: 0.39-0.56μm) were prepared by dipping the several organic, metal and ceramic substrates into 20 wt% acetonemethanol solution of PVPS. Mechanical properties of the free-standing films were measured and surface hardness and adhesion to the substrates of coating films were evaluated by pencil scratch test and cross-cut tape test, respectively, according to JIS K5400. In the same way, the radical polymerization of methacryloxypropyltrimethoxysilane (MAS) followed by hydrolytic polycondensation provided transparent and colorless free-standing films (thickness: 0.02-0.15mm) and coating films (thickness: 1.23-2.45pm) of polymethacryloxypropylpolysilsesquioxane (PMPS).

View full abstract

A novel self-organized organic/inorganic hybrid compound was synthesized by means of dilauryldimethylammonium bromide and lead bromide as organic cation and metal halide, respectively. The synthesized compound was characterized by X-ray diffraction and optical measurements. The powder X-ray diffraction patterns indicated that the synthesized compound had a two dimensional layered structure. Spin-coated films were easily prepared from chloroform solutions of the compounds. After the film preparation, a polycrystalline structure that showed the same X-ray diffraction pattern as that of a powder sample, is observed to form by selforganization. The spin-coated film had an absorption band at around 352.5 nm that corresponded to self-organized inorganic region. The fluorescence measurement for the powder sample showed a fluorescence band that was assigned to the inorganic structure. These structural and optical measurements suggested that a novel quantum confined structure was constructed with the compound.

View full abstract

A new intercalation compound was obtained by the reaction of Zn (OH) ₂ with isonicotinic acid, in which the formation of COO-Zn bond was confirmed by IR spectra. Interlayer spacing of the organic-inorganic hybrid was 10.7Å, indicating the existence of monolayer structure of isonicotinic acid between the layers. After the treatment of nanohybrid with difunctional compounds such as aliphatic dicarboxylic acids, preparation of bundle structure was confirmed by SEM images.

View full abstract

Organic-inorganic hybrids containing various amounts of silica were synthesized from epoxy resin and several silanealkoxides by utilizing a sol-gel process. The obtained epoxy/silica hybrids were studied with regard to phase structure and thermal and mechanical properties. In the hybrids with γ-glycidoxypropyltrimethoxysilane, transmission electron microscope (TEM) observation revealed that fine silica particles about 10 nm in size are uniformly dispersed throughout the epoxy matrix. The storage modulus in the rubbery region increased and the peak area of the tanδ curve at glass transition region decreased with the hybrization of small amounts of silica. This may result from the suppression of epoxy network moiety due to the incorporation of silica network. Thermal stability was remarkably improved and toughness of hybrids was slightly decreased by the hybrization with small amounts of silica.

View full abstract

Strontium carbonate was crystallized in the presence of poly (1-carboxylic acid-3-n-butylaminocarbonyl-teramethylene) derived from poly (acrylic acid) as models of biominerallization. The novel composite of polymer ligand-inorganic crystals has a strong Ca-COO^- bond due to the formation of NH…O hydrogen bond between the coordinating oxygen and the neighboring amide NH, as established by the ^13CC CP/MAS NMR spectra. It exhibits organized aggregates with microcrystals, as observed by the SEM image.

View full abstract

Copper (Cu) migration at the interface of (polyimide (PI) /Cu) bilayers prepared from various precursors was investigated on the basis of dynamic secondary ion mass spectroscopic (D-SIMS) analysis. The Cu migration into the PI phase at the (PI/Cu) in terface was clearly detected from the D-SIMS profiles. The Cu migration state depended on the presence of carboxyl groups of PI precursor during the interface formation and on the properties of solvents. On the basis of the D-SIMS profiles, a model of the Cu migration state at the (PI/Cu) interface was proposed. The model consisted of an interfacial region formed by the interpercolation of each component and a diffusional region formed by the diffusion of precursor molecules complexed with Cu. The degree of gradual decrease of Cu secondary-ion intensity from the (PI/Cu) interface to the PI surface ((PI/air) interface) depended on the polarity of solvents. The interfacial region as well as the diffusional one was formed for the specimen prepared from the precursor solutions of aprotic polar solvent. On the other hand, only the interfacial region was formed for the specimen prepared from the precursor solutions of protic solvent. Therefore, it was concluded that the Cu migration state mainly depends on the complex formation with Cu and the diffusion capability of the PI precursor, while the contribution of the solvent was very small.

View full abstract

Preparation of monodisperse hybrid silica particles with polymer electrolyte was achieved via two-step modification and controls of ζ-potential were investigated. The silica composite particles were prepared through the initial modification with poly- (maleic anhydride-styrene) and successive attachment of amino-terminated, triphenylphosphonium- or triethylammonium- grafted polyester to anhydride moieties on the surface. The two-step modification made ζ-potential of the composite particles controllable in the range from -110 mV to + 72 mV. The addition of ammonium chloride to the suspension of the composite particles in ethanol unexpectedly gave the maximum ζ-potential at the concentration of 10^-3-10^-4M. The phenomenon was explained by the additional effects of an increase of surface charge density coming from shrinking of polymer electrolyte and a decrease of Debye length due to the salt addition.

View full abstract

We have prepared a novel organic-inorganic hybrid vesicle “Cerasome”, which has a silica-like structure on its vesicular surface. A newly synthesized compound bearing a triethoxysilyl head and a dialkyl tail were dispersed in water under various pH conditions. The cerasome was obtained most efficiently at pH 3, where a gradual and stepwise process of hydrolysis on the triethoxysilyl head did not disturb vesicle formation. In a dried sample, TEM observation revealed formation of a multivesicular assembly.

View full abstract