Takeaki Miyamoto

Bonelike apatite formation on ethylene-vinyl alcohol copolymer modified with silane coupling agent and calcium silicate solutions

An ethylene-vinyl alcohol copolymer (EVOH) was treated with a silane coupling agent and calcium silicate solutions, and then soaked in a simulated body fluid (SBF) with ion concentrations approximately equal to those of human blood plasma. A smooth and uniform bonelike apatite layer was successfully formed on both the EVOH plate and the EVOH-knitted fibers in SBF within 2 days. Part of the structure of the resulting apatite-EVOH fiber composite was similar to that of natural bone. If this kind of composite can be fabricated into a three-dimensional structure similar to natural bone, the resultant composite is expected to exhibit both mechanical properties analogous to those of natural bone and bone-bonding ability. Hence, it has great potential as a bone substitute.

Nitroxide-controlled free radical polymerization of a sugar-carrying acryloyl monomer

Controlled free radical polymerization of a sugar-carrying acrylate, 3-O-acryloyl-1,2: 5,6-di-O-isopropylidene-a-D-glucofuranoside (AIpGlc), was achieved in p-xylene at 100°C by using a di-tert-butyl nitroxide (DBN)-based alkoxyamine as an initiator and dicumyl peroxide (DCP) as an accelerator. The polymerization gave low-polydispersity (1.2 < M w /M n < 1.6) polymers with predicted molecular weights. The same approach with a DBN-capped polystyrene (PS-DBN) as an initiator afforded block copolymers of the type PS-b-PAIpGlc. The acidolysis of the homopolymers and block copolymers gave well-defined glucose-carrying polymers PAGlc and PS-b-PAGlc, respectively. These amphiphilic PS-b-PAGlc block copolymers were observed to exhibit microdomain surface morphologies that differ for different copolymer compositions. This success opens up a new, simple route to the synthesis of well-defined sugar-carrying polymers of various architectures.

Controlled synthesis of glycopolymers with pendant D-glucosamine residues by living cationic polymerization

D-Glucosamine-containing glycopolymers with well-controlled structure were synthesized by living cationic polymerization. To this end, D-glucosamine-containing vinyl ether(VE) of the type [CH 2 =CH(OCH 2 CH 2 OR)] was prepared, where R denotes a 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimide-β-D-glucopyranoside, i.e., the hydroxyl and amino groups in D-glucosamine residues are protected by acetyl and phthaloyl groups, respectively. It was found that (1) the efficient living cationic polymerization of VE monomer is achieved by a combination of ethylaluminum dichloride (EtAlC1 2 ) with an adduct of trifluoroacetic acid (TFA) and isobutyl VE (IBVE) [CH 3 CH(OiBu)OCOCF 3 ] (i.e., TFA/EtAlC1 2 initiating system); and (2) the polymerization in toluene at the elevated temperature (0°C ) is most suitable to proceed the homogeneous polymerization over the whole conversion range. The molecular weight distribution of the resulting polymers was very narrow (M ω /M n ∼1.1). Quantitative deprotection of the resulting precursor polymers was successfully achieved with hydrazine monohydrate to afford the corresponding water-soluble polymers with pendant D-glucosamine residues.

Controlled synthesis of amphiphilic block copolymers with pendant glucose residues by living cationic polymerization

Amphiphilic block copolymers of vinyl ethers (VEs) of the type —[CH2CH(OCH2CH2OR)]m—[CH2CH(OiBu)]n—were synthesized by living cationic polymerization, where R is a D-glucose residue, and m and n are the degrees of polymerization (m = 20–50; n = 11–89). To obtain them, sequential living block copolymerization of isobutyl vinyl ether (IBVE) and the vinyl ether carrying 1,2:5,6-diisopropylidene-D-glucose residue was conducted by using the HCl adduct of IBVE, CH3CH(OiBu)Cl, as initiator in conjunction with zinc iodide. These precursor block copolymers had a narrow molecular weight distribution (Mw/Mn ∼ 1.1) and a controlled composition. Treatment of them with a trifluoroacetic acid/water mixture led to the target amphiphiles. The solubility of the amphiphilic block copolymers in various solvents depended strongly on composition or the m/n ratio. Their solvent-cast thin films were observed, under a transmission electron microscope, to exhibit various microphase-separated surface morphologies such as spheres, cylinders, and lamellae, depending on composition.

Relationships between antithrombogenicity and surface free energy of regenerated silk fibroin films

Silk fibroin (SF) was dissolved in calcium chloride/ethanol/water mixture (1/2/8 in mole ratio) at 70°C for 4 h. The dissolved silk fibroin was regenerated by casting the dialyzed solution into the films. The films were treated with 50% aqueous solution of methanol for different times, and their antithrombogenicity was evaluated byin vitro andin vivo tests.In vivo blood tests were made by a method of peripheral vein indwelling suture. It was found that the silk fibroin had a good anti-thrombogenicity and an absorbability even though the polymer showed foreign body reaction. Finally, the blood compatibilty of silk fibroin films which were subjected to structural change by the methanol treatment, was examined in connection with their interfacial surface energy, and a correlation between these properties was found to be present.

Thermotropic cellulose derivatives with flexible substituents IV. Columnar liquid crystals from ester-type derivatives of cellulose

Abstract Cellulose tri-n-alkanoates, fully substituted ester-type derivatives of cellulose, having acyl groups with n carbon atoms (3 form a novel thermotropic mesophase, characterized by a low birefringence and an extremely high viscosity compared with those of cholesteric mesophases of ether-type derivatives. Photomicroscopic, differential scanning calorimetry, and X-ray diffraction studies indicate that the mesophase formed by the cellulose tri-n-alkanoates is of a hexagonal columnar type in which two polymer chains are included in one hexagonal lattice. Two possible packing structures, resembling direct and inverse hexagonal phases of amphiphilic molecular systems, are proposed and discussed in relation to the chemical structure of the polymer.

Biomimetic apatite formation on polyethylene photografted with vinyltrimethoxysilane and hydrolyzed

A photografting technique to produce functional groups of silanol able to induce apatite nucleation was attempted on polyethylene substrate for biomimetic formation of bone-mineral-like apatite layer on its surface. The polyethylene surface was subjected to vapor-phase photografting of vinyltrimethoxysilane and subsequently to hydrolysis. The photografting formed methoxysilyl groups on the polyethylene substrate, which was changed into silanol groups successively by the hydrolysis in a hydrochloric solution. The polyethylene modified in this way formed a dense and homogeneous bone-mineral-like apatite layer in a solution with ion concentrations 1.5 times that of human blood plasma. This result indicates that the biomimetic process in combination with a polymeric grafting technique might provide a homogeneous bone-mineral-like apatite coating even on polymer fibers to be woven into an apatite-polymer composite with three-dimensional structure analogous to that of natural bone.

Thermotropic cellulose derivatives with flexible substituents. III. Temperature dependence of cholesteric pitches exhibiting a cholesteric sense inversion

Abstract For the thermotropic cholesteric mesophase of tri-o-(β-methoxyethoxy)ethyl cellulose (DP = 11), cholesteric pitches larger than 2 μm were precisely determined by microscopic observation and their temperature dependence was examined in the temperature range from 80°C to 140°C. In the initial temperature region of 80°C to 106°C, the pitch increases with increasing temperature. After the pitch diverges at 106°C, it decreases as temperature is raised further. This anomalous temperature dependence of pitch was associated with a thermally-induced inversion from right- to left-handed helicoidal structure which was first observed in this kind of cellulose derivatives.

States of Water Sorbed on Wool as Studied by Differential Scanning Calorimetry

The states of water sorbed on Merino wool fibers, their histological components, and chemically modified wool fibers were investigated by differential scanning calo rimetry (DSC) in order to elucidate the amount of bound water on wool fibers, the differences between the histological components of wool fibers, and the effect of polar groups on the states of water sorbed on wool fibers. For the sake of comparison, the states of water sorbed on cotton and silk were also examined. There may exist three different kinds of water sorbed on wool fibers, i.e., free water, freezing bound water, and nonfreezing bound water. The amount of bound water on wool fibers is larger than that on cotton yam and silk. The amount of bound water on cortical cells is about two times higher than that on cuticular cells. The amount of bound water on nonkeratinous cell components is about three times higher than that on keratinous cell components. The cell membrane complex plays an important role in water pen etrating to wool fibers, but its contribution to the amount of bound water is negligible. The contribution of polar groups in wool fibers to the amount of bound water is not specific at high water contents, indicating that the peptide groups of the main chain play a significant role as water binding sites at high water contents.

Columnar liquid crystals in oligosaccharide derivatives. II. Two types of discotic columnar liquid-crystalline phase of cellobiose alkanoates

Abstract A series of cellobiose octaalkanoates, Cel-II-n (n is the carbon number of the alkyl chain), with n = 7–14 were prepared and their mesogenic properties examined by differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction. All of these compounds form enantiotropic discotic columnar phases, in which the columns are built up by a regular stacking of the cellobiose moieties and are packed in a two dimensional lattice. Homologues with n = 9–14 form the Dho phase only whilst the compound with n = 7 forms the Dro phase. The n = 8 compound forms the Dho phase at higher temperatures and the Dro phase at lower temperatures. Structural parameters obtained from X-ray diffraction studies are presented for both phases.