Showing papers by "Yoshiharu Kimura published in 2015"
TL;DR: These are the first successful demonstrations of short-term patency at clinically applicable sizes of tissue-engineered small-caliber long-bypass grafts measuring 20-30 cm in length and having a 2-mm inner diameter.
112 citations
TL;DR: These sol–gel systems producing strengthened gels are versatile for use as injectable scaffolds in the tissue engineering, and were thought to be controlled by the dual cross-linking mechanisms for the gel formation.
30 citations
18 citations
TL;DR: The enantiomeric block copolymer system can be applicable as a novel thermoplastic elastomer that is environmentally friendly in terms of its biobased nature and the use of carbon dioxide as feedstock.
Abstract: ABA triblock copolymers of polylactides (PLA: A) and aliphatic polycarbonates (APC: B) were prepared by ring-opening polymerization of d- and l-lactides with poly(hexamethylene carbonate) diol and poly(hexamethylene/pentamethylene carbonate) diol (PHPC) as macro-initiators. The enantiomeric copolymers with similar block sequences (PLLA-APC-PLLA and PDLA-APC-PDLA) were mixed in a 1:1 weight ratio to form a stereocomplex of PLA blocks. The resultant stereo mixtures were found to be more thermally stable (up to 200 °C) than the single block copolymers. Polymer films of the stereo mixtures PLLA-PHPC-PLLA/PDLA-PHPC-PDLA exhibited higher elongation and lower modulus. It was therefore evident that the present enantiomeric block copolymer system can be applicable as a novel thermoplastic elastomer that is environmentally friendly in terms of its biobased nature and the use of carbon dioxide as feedstock. © 2014 Society of Chemical Industry
16 citations
TL;DR: In this paper, the authors reported the synthesis of a hyperbranched supramolecular polymer composed of continuum of amylose-poly( l -lactide) (PLLA) inclusion complexes by phosphorylase-catalyzed enzymatic polymerization using a branched maltoheptaose-pLLA conjugate according vine-twining polymerization.
16 citations
TL;DR: 4,6-dimethoxy-1,3,5-triazin-2-yl glycosides, glycosyl donors prepared in one step from free saccharides without protection of the hydroxy groups, were stereoselectively and equivalently converted t...
Abstract: 4,6-Dimethoxy-1,3,5-triazin-2-yl glycosides, glycosyl donors prepared in one step from free saccharides without protection of the hydroxy groups, were stereoselectively and equivalently converted t...
13 citations
TL;DR: A high-molecular-weight ABA tri-block copolymer, synthesized by ring-opening polymerization of [RS]-β-butyrolactone in the presence of PEG and 1,3-dichlorotetrabutyldistannoxane (DTD) as the catalyst, evaluated cell adhesion with 3T3 fibroblast cells.
11 citations
9 citations
TL;DR: In this article, a two-step ring-opening polymerization of poly(oxyethylene) (PEG), poly( d -lactide) (PDLA), and poly( l -lactic acid) (PLA) was successfully performed by using triblock copolymers.
9 citations
TL;DR: Results indicate that a multiblock structure is useful for controlling micelle size without changing the PLA/PEG composition or PEG molecular weight, which strongly influences other micelle features.
Abstract: The ability to control the micelle size of poly(lactic acid) and poly(ethylene glycol) (PLA–PEG) block copolymers is important for controlling their circulation in blood cell recognition, drug release and therapeutic effects. We successfully controlled the micelle size by changing the block number of copolymers (multiblock index). PLA–PEG multiblock copolymers with multiblock indexes ranging from 1.35 to 2.78 were synthesized by direct polycondensation with tin chloride/p-toluenesulfonic acid binary catalysts, using PEG with a molecular weight (Mw) of 3200 Da. The Mw of PLA–PEG copolymers increased with an increase in the multiblock index, while micelle size, measured by dynamic light scattering, decreased greatly from 349 to 28 nm. In addition, the X-ray diffraction peak of the PLA crystal disappeared when the multiblock index was increased. These results indicate that a multiblock structure is useful for controlling micelle size without changing the PLA/PEG composition or PEG molecular weight, which strongly influences other micelle features.
TL;DR: In this article, a mixture of poly(l-lactide) and poly(d-lactic acid) oligomers was used to synthesize a hyperbranched polymers having particulate morphology.
Abstract: Silyl-terminated oligomers of poly(l-lactide) (mSi-PLLA) and poly(d-lactide) (mSi-PDLA) were synthesized by hydrosilylation of allyl-terminated derivatives. They were readily hydrolyzed into hyper-branched polymers having particulate morphology. When a mSi-PDLA oligomer was blended with a PLLA sample (52.5 kDa) in 1–10 wt.-% by solution casting, small cross-linked particles with stereocomplex form were generated and distributed homogenously in the PLLA matrix, and by which the homo-chiral crystallization of PLLA was efficiently suppressed. When another mSi-PLLA oligomer was blended with PLLA, the cross-linked particles formed from mSi-PLLA were amorphous and distributed inhomogeneously. It was, therefore, indicated that the hydrolytic polycondensation of mSi-PDLA and mSi-PLLA was induced during the film casting, changing the inner structure and properties of the blend films with PLLA.
TL;DR: In this article, the authors used amorphous poly(hexamethylene carbonate) (PHMC) diol as the macro-initiator to obtain similar polycarbonate block copolymers, and for which the elastomeric properties are evaluated.
Abstract: Aliphatic polycarbonates (APC) are a class of biodegradable polymers that are attracting great interest of materials engineers because of their good biocompatibility and degradation to less acidic products. There are many types of APC consisting of different alkanediol units. Those consisting of diols of middle carbon-chain length (C5 C8) are used as soft segments having low Tg, while those consisting of alicyclic building blocks can be applied as hard segments. The commercially available poly(hexamethylene carbonate) (PHMC) diol and poly(hexamethylene/ pentamethylene carbonate) (PHPC) diol, having low molecular weight and bis-hydroxyl terminals, are used as soft segments of polyurethane. Recently their environmental friendliness is highlighted because they are synthesized from ethylene carbonate (EC) manufactured by the use of carbon dioxide as feedstock. With this nature in mind, we have demonstrated that PHMC diol can be used as a macroinitiator of the ring-opening polymerization (ROP) of Llactide to prepare tri-block copolymers comprising polyL-lactide (PLLA) and PHMC (PLLA-PHMC-PLLA) that have both biobased and CO2-originated characters. Since PHMC is crystalline at ambient temperature, the properties of the PLLA-PHMC-PLLA copolymers may be significantly influenced by the temperature change. In the present study, therefore, we use amorphous PHPC diol as the macro-initiator to obtain similar PLLA-APC block copolymers, and for which the elastomeric properties are evaluated. Here, we first analyze the microstructure of the PHPC oligomer that is industrially produced by the reaction of an alkanediol mixture and EC. Since the synthetic procedure using EC as the starting carbonate source is different from the ordinary polycondensation of diphenyl carbonate (DPC) and diols, the resultant polycarbonate is known to involve minor units different from the diol units. The well-characterized PHPC oligomer is then chain-extended with DPC as chain extender to obtain high molecular weight polymers, and which were used as the macroinitiators of the ROP of Llactide to prepare PLLA-PHPC-PLLA tri-block copolymers (Scheme 1). The PLLA-PHPC-PLLA block copolymers obtained are finally characterized in detail to Preparation of Chain-Extended Poly(hexamethylene/pentamethylene carbonate)s and Their Block Copolymerization with Poly-L-lactide into Partly Biobased Thermoplastic Elastomers
TL;DR: In this paper, triethoxysilyl-terminated poly(d-lactide)s (eSi-PDLA) were successfully prepared by hydrosilylation of allylterminated PDLAs.
Abstract: Triethoxysilyl-terminated poly(d-lactide)s (eSi-PDLA) were successfully prepared by hydrosilylation of allyl-terminated PDLAs (A-PDLA-ac) which were readily prepared by ring-opening polymerization of d-lactide and the following terminal protection by acetylation. Their acid-catalyzed hydrolysis produced hyper-conjugated PDLAs with terminal silanol coupling. Blend PLLA films containing eSi-PDLA (Mn = 2.1 kDa) in 5-25 wt.% were successfully prepared by the solution casting method. The blend films were found to take a nano-porous or micro-phase separation structure, being different from that of the blend PLLA films containing trimethoxysilyl-terminated poly(d-lactide) (mSi-PDLA) which exhibited particle distribution structure. This difference was reasonably attributed to the different rate of hydrolytic polycondensation of the trimethoxy- and triethoxy-silyl terminals. These results revealed that the competing sterecomplexation/ hyper-conjugation/phase separation can afford specific morphologies, allowing fine control of properties.
TL;DR: 4,6-dimethoxy-1,3,5-triazin-2-yl glycosides, glycosyl donors prepared in one step from free saccharides without protection of the hydroxy groups, were stereoselectively and equivalently converted t...
Abstract: 4,6-Dimethoxy-1,3,5-triazin-2-yl glycosides, glycosyl donors prepared in one step from free saccharides without protection of the hydroxy groups, were stereoselectively and equivalently converted t...