Yuichi Ohya

Aggregation phenomenon of PEG-grafted chitosan in aqueous solution

Chitosan (deacetylated chitin), which is a naturally occurring polysaccharide having primary amino groups, is known to be insoluble in water because of its strong intermolecular hydrogen bonds. We prepared water-soluble poly(ethylene glycol) grafted chitosan (PEG-g-chitosan) through the chemical modification of chitosan and investigated its aggregation phenomenon in aqueous solutions. The solution properties of PEG-g-chitosans differ depending on the degree of introduction of PEG in aqueous solution, and were studied by measuring transmittance and light scattering. The PEG-g-chitosans could form aggregates spontaneously by means of their intermolecular hydrogen bonds in the aqueous solution. The PEG-g-chitosan aggregates could also uptake N-phenyl-1-naphthylamine (PNA) as a hydrophobic substance in neutral conditions and this PNA could be released from the aggregates in acidic conditions.

Possibility of application of quaternary chitosan having pendant galactose residues as gene delivery tool

Since chitosan is a cationic natural polysaccharide having the formation ability of a polyelectrolyte complex with DNA, it is expected to be used as a carrier of DNA in gene delivery systems. So, in order to achieve an efficient gene delivery via receptor-mediated endocytosis, the synthesis of a novel polycationic polysaccharide derivative having recognizable saccharide residues, N,N,N-trimethyl(TM)-chitosan/galactose conjugate, was performed. The formation of a polyelectrolyte complex with DNA and the cellular recognition ability of TM-chitosan/galactose conjugate were tested, and then the possibility of its application as a gene delivery tool was investigated.

Biodegradable Shape-Memory Polymers Exhibiting Sharp Thermal Transitions and Controlled Drug Release

Biodegradable shape-memory polymer networks prepared by cross-linking star shape branched oligo(ε-caprolactone) (bOCL) with hexamethylene diisocyanate are introduced. The thermal and mechanical properties of these networks were investigated using differential scanning calorimetry and tensile testing, respectively, and the morphology of the phase structure was characterized by polarized optical microscopy. The shape-memory properties of the networks were quantified using thermomechanical tensile experiments and showed strain fixity rates R(f) higher than 97% and strain recovery rates R(r) as high as 100%. Of note, networks of OCL segments with a lower degree of polymerization (DP; 10) exhibited significantly improved temperature-sensitive shape recovery: 90% of the permanent shape was recovered upon heating to within a 2 °C range (37-39 °C). The networks exhibited complete shape recovery to the permanent shape within 10 s at 42 °C. Theophylline-loaded (10 and 20 wt %) shape-memory materials, prepared by cross-linking bOCL with hexamethylene diisocyanate in the presence of theophylline, are also described as a model for a controlled drug release device. The 10 wt % loaded material was sufficiently soft and flexible for complex shape transformation and also showed high R(f) (98%) and R(r) (99%). Sustained release of loaded theophylline was achieved over 1 month without initial burst-release in a phosphate buffer solution (PBS; pH 7.4) at 37 °C.

Release behaviour of 5-fluorouracil from chitosan-gel microspheres immobilizing 5-fluorouracil derivative coated with polysaccharides and their cell specific recognition

In order to provide a device releasing drugs in a controlled manner and having targetability to specific organs or cells, chitosan-gel microspheres, CMS, crosslinked with glutaraldehyde, immobilizing 1-[N-(5-aminopentyl) carbamoyl]-5-fluorouracil, 1, coated with anionic polysaccharides, such as 6-O-carboxymethyl-N-acetyl-alpha-1,4-polygalactosamine (CM-NAPGA), 6-O-carboxymethyl-chitin, alginic acid and heparin, by polyelectrolyte complex membrane formation were prepared. When chitosan was crosslinked with glutaraldehyde, 1 was simultaneously immobilized into CMS by Schiffs base formation. Average diameter of CMS obtained was estimated to be about 0.5-1.0 micron by SEM observation. In physiological saline media, only free 5-FU was released from the CMS but 1 and any 5-FU derivative was not. Release rate of 5-FU from the CMS was reduced by coating with polyelectrolyte complex membrane of cationic chitosan and anionic polysaccharides. CMS coated with CM-NAPGA showed a lectin-mediated specific aggregation phenomenon by addition of Abrus precatorius agglutinin. Moreover, the CMS immobilizing 1 coated with CM-NAPGA showed higher growth-inhibitory effect against SK-Hep-1 (human hepatoma) cells in vitro than the CMS coated with other polysaccharides.

Release Behavior of 5-Fluorouracil from Chitosan-Gel Nanospheres Immobilizing 5-Fluorouracil Coated with Polysaccharides and Their Cell Specific Cytotoxicity

Abstract Small-sized chitosan-gel nanospheres, CNSs (average diameter 250 nm), containing 5-fluorouracil (5FU) or immobilizing 5FU derivatives (aminopentyl-carbamoyl-5FU or aminopentyl-ester-methylene-5FU) were prepared by the glutaraldehyde crosslinking technique and the emulsion method. When chitosan was crosslinked with glutaraldehyde, these 5FU derivatives were simultaneously immobilized to CNSs by means of Schiffs base formation. The CNSs were coated with anionic polysaccharides, such as 6-O-carboxymethyl-N-acetyl-α-l,4-polygalactosamine/Na (CM-NAPGA/Na), 6-O-carboxymethyl-chitin/Na (CM-chitin/Na), and sodium hyaluronate, through formation of a polyelectrolyte complex membrane to give CNS/polyanion, i.e., CNS/G, CNS/C, and CNS/H, respectively. The polyelectrolyte complex of polysaccharide was employed to achieve the controlled release and effective targeting of 5FU by the CNSs. The release rate of 5FU from the CNSs could be controlled by immobilization of 5FU, degree of deacetylation of chitosan use...

Design of quaternary chitosan conjugate having antennary galactose residues as a gene delivery tool

Abstract It is well-known that some kinds of saccharide play the important roles in biological recognition on cellular surface. So, they are expected to be applied for cellular recognition devices. Recently, it was reported that cluster glycosides were effective in the specific interaction between oligosaccharide chains and receptors. Since chitosan is a cationic natural polysaccharide, having formation ability of polyelectrolyte complex with DNA, it is expected to be used as a carrier of DNA in gene delivery systems. So, in order to achieve an efficient gene delivery via receptor-mediated endocytosis, the synthesis of novel polycationic polysaccharide derivative having recognizable branched saccharide residues, N,N,N-trimethyl(TM)-chitosan/tetragalactose antenna conjugate (TC-Gal4A20), was carried out. The cellular recognition ability of TC-Gal4A20 conjugate were tested, and then the possibility of its application as a gene delivery tool was investigated. TC-Gal4A20 conjugate showed high affinity to RCA120 lectin and its polycation-DNA complex had the ability of specific gene delivery to hepatocyte.

Synthesis and enzymatic hydrolysis of lactic acid–depsipeptide copolymers with functionalized pendant groups

Since poly(lactic acid) is the biodegradable polyester having low immunogenicity and good biocompatibility, it is utilized as a medical material. However, poly(lactic acid) is a water-insoluble crystalline polymer having no reactive side-chain group. Thus, the use of poly(lactic acid) is limited. To modify the properties of poly(lactic acid) and to introduce the functionalized pendant groups to poly(lactic acid), we synthesized two kinds of lactic acid-depsipeptide copolymers with reactive pendant groups, namely poly[LA-(Glc-Lys)] and poly[LA-(Glc-Asp)]. This was done through ring-opening copolymerizations of L-lactide with the corresponding protected cyclodepsipeptides, cyclo[Glc-Lys(Z)] and cyclo[Glc-Asp(OBzl)], and subsequent deprotection of benzyloxycarbonyl and benzyl groups, respectively. By changing the mole fraction of the corresponding depsipeptide units, the solubility, thermal transition and degradation behavior of the modified poly(lactic acid) could be varied.

Modification of polylactide upon physical properties by solution-cast blends from polylactide and polylactide-grafted dextran

Polylactide (PLA)-grafted polysaccharides with various lengths and numbers of graft chains were synthesized using a trimethylsilyl protection method. The properties of the cast films prepared from graft-copolymers were investigated through thermal and dynamic mechanical analyses. The graft-copolymer films exhibited a lower glass transition temperature (Tg), melting temperature, and crystallinity, and higher viscosity properties compared to PLA films. Moreover, the usefulness of graft-copolymer as a plasticizer was investigated with 1:4 blend films prepared from the graft-copolymers and PLA. The blend films showed lower Tg and crystallinity, and higher viscosity properties compared to PLA films.

Biodegradable Polymeric Assemblies for Biomedical Materials

Recently, self-assembled systems using biodegradable polymers at the nanometer scale, such as microspheres, nanospheres, polymer micelles, nanogels, and polymersomes, have attracted much attention especially in biomedical fields. To construct such self-assembled systems, it is extremely important to have precise control of intermolecular noncovalent interactions, such as hydrophobic interactions based on their amphiphilic molecular structures. Biodegradable polymers, especially aliphatic polyesters such as polylactide, polyglycolide, poly(e-caplolactone) and their copolymers, have been used as biomedical materials for a long time. This chapter is mainly focused on aliphatic polyesters and related polymers, and reviews the synthetic methods for amphiphilic biodegradable polymers containing aliphatic polyesters as components. Moreover, the application of various types of self-assembly systems using amphiphilic biodegradable copolymers such as micro- or nanosized particles (microspheres, nanospheres, polymer micelles, nanogels, polymersomes), supramolecular physically interlocked systems, and stimuli-responsive systems for biomedical use such as drug delivery systems are also reviewed.

One‐Pot Synthesis of Novel Branched Polylactide Through the Copolymerization of Lactide with Mevalonolactone

Polylactide, which is a biodegradable and bio-absorbable polymer having low immunogenicity and good biocompatibility, has been mainly studied for biomedical applications. Branched polymers have different rheological and mechanical properties compared with their linear counterparts owing to their molecular architectures. We synthesized novel biodegradable polylactide having a branched structure composed of metabolically degradable and/or absorbable materials only. The branched polylactide was obtained from a one-pot copolymerization of L-lactide using metabolic intermediate dl-mevalonolactone as a bifunctional comonomer having both lactone ring and pendant hydroxy group. The glass transition point, melting point and crystallinity of the branched polylactide are lower than those of linear polylactide.