Minoru Morimoto

Preparation and characterization of water-soluble chitin and chitosan derivatives

Chitosan was modified with poly(ethylene glycol)-aldehyde (PEG-aldehyde) of various molecular weights under the various molar ratios of PEG-aldehyde to chitosan. Then the prepared chitosan-PEG hybrid was converted to chitin-PEG hybrid by the acetylation with acetic anhydride. The solubility of various derivatives was investigated in three buffers of various pH. Some of these derivatives were soluble in 0.01 M phosphate buffer saline (PBS, pH = 7.2). The solubility in PBS was dependent on the degree of PEG substitution, the degree of acetylation, the molecular weight of PEG, and the weight ratio of PEG in chitin/chitosan-PEG hybrid.

Preparation of Chitin Nanofibers with a Uniform Width as α-Chitin from Crab Shells

Chitin nanofibers were prepared from dried crab shells by a simple grinding treatment in a never-dried state under an acidic condition after the removal of proteins and minerals. The obtained nanofibers were observed by FE-SEM and found to have a uniform width of approximately 10-20 nm and high aspect ratio; both these findings were similar to those for nanofibers from prawns. Furthermore, it was confirmed that the nanofibers were extracted from the natural chitin/protein/mineral composites of crab shell in their original state. That is, the N-acetyl group was not removed and the alpha-chitin crystal structure was maintained, as confirmed by elemental analysis data, FT-IR spectra, and X-ray diffraction profiles.

Synthesis of Silver Nanoparticles Templated by TEMPO-Mediated Oxidized Bacterial Cellulose Nanofibers

We have prepared silver nanoparticles on the surface of bacterial cellulose (BC) nanofibers. The synthesis of silver nanoparticles incorporates 2,2,6,6-tetramethylpiperidine-1-oxyradical (TEMPO)-mediated oxidation to introduce carboxylate groups on the surface of BC nanofibers. An ion exchange of the sodium to the silver salt was performed in AgNO(3) solution, followed by thermal reduction. By using oxidized BC nanofibers as a reaction template, we have prepared stable silver nanoparticles with a narrow size distribution and high density through strong ion interactions between host carboxylate groups and guest silver cations, which have been investigated by scanning electron microscopy, UV-visible spectroscopy, and a small-angle X-ray scattering method.

Chitin, Chitosan, and Its Derivatives for Wound Healing: Old and New Materials

Chitin (β-(1-4)-poly-N-acetyl-d-glucosamine) is widely distributed in nature and is the second most abundant polysaccharide after cellulose. It is often converted to its more deacetylated derivative, chitosan. Previously, many reports have indicated the accelerating effects of chitin, chitosan, and its derivatives on wound healing. More recently, chemically modified or nano-fibrous chitin and chitosan have been developed, and their effects on wound healing have been evaluated. In this review, the studies on the wound-healing effects of chitin, chitosan, and its derivatives are summarized. Moreover, the development of adhesive-based chitin and chitosan are also described. The evidence indicates that chitin, chitosan, and its derivatives are beneficial for the wound healing process. More recently, it is also indicate that some nano-based materials from chitin and chitosan are beneficial than chitin and chitosan for wound healing. Clinical applications of nano-based chitin and chitosan are also expected.

Effects of chitin/chitosan and their oligomers/monomers on migrations of fibroblasts and vascular endothelium

Effects of chitin/chitosan and their oligomers/monomers on migrations of fibroblasts (3T6) and vascular endothelial cells (human umbilical vascular endothelial cell: HUVEC) were evaluated in vitro. In direct migratory assay using the blind well chamber method, migratory activity of 3T6 was seen to be reduced by chitin, chitosan and the chitosan monomer (GlcN). Migratory activity of HUVECs was enhanced by chitin, chitosan and the chitin monomer (GlcNAc), and was reduced by chitosan oligomers and GlcN. Supernatant of 3T6 preincubated with chitin or chitosan reduced migratory activity of 3T6 cells. Supernatant of HUVECs preincubated with chitosan also reduced migratory activity of HUVECs, but supernatant preincubated with chitin had no effect on them. In a proliferation (MTT reduction) assay, none of the samples affected proliferation of either type of cell.

Preparation of Chitin Nanofibers from Mushrooms

Chitin nanofibers were isolated from the cell walls of five different types of mushrooms by the removal of glucans, minerals, and proteins, followed by a simple grinding treatment under acidic conditions. The Chitin nanofibers thus obtained have a uniform structure and a long fiber length. The width of the nanofibers depended on the type of mushrooms and varied in the range 20 to 28 nm. The Chitin nanofibers were characterized by elemental analyses, FT-IR spectra, and X-ray diffraction profiles. The results showed that the α-chitin crystal structure was maintained and glucans remained on the nanofiber surface.

Analgesic effects of chitin and chitosan

The analgesic effects of chitin and chitosan on inflammatory pain were evaluated using the acetic-acid-induced writhing test in mice. When chitin and chitosan suspensions were mixed with the 0.5% acetic acid solution (chitin-AC and chitosan-AC, respectively) and administered intraperitoneally in mice, both agents induced a dose-dependent decrease in the number of the abnormal behaviors (writhing) due to pain, including extension of the hind legs, abdominal rigidity, and abdominal torsion. This effect was greater in the animals administered the chitosan-AC than in those administered the chitin-AC. In vitro study indicated that addition of the chitin or chitosan suspension increased the pH of the AC, and that this effect was greater in the chitosan than the chitin. Furthermore, the level of bradykinin in the peritoneal lavage fluid in the animals administered the chitin-AC was lower than in the animals administered the chitosan-AC. In vitro study showed that the chitin particles absorbed bradykinin more extensively than the chitosan particles. These results suggest that the main analgesic effect of chitosan is the absorption of proton ions released in the inflammatory site, while that of chitin is the absorption of bradykinin.

Acetylation of chitin nanofibers and their transparent nanocomposite films.

Chitin nanofibers were acetylated to modify the fiber surface and were characterized in detail. The acetyl DS could be controlled from 0.99 to 2.96 by changing the reaction time. FT-IR spectra indicate that chitin nanofibers were acetylated completely after 50 min reaction time. X-ray diffraction profiles and TGA curves show that the chitin nanofibers were acetylated heterogeneously from the surface to the core. SEM images show that fiber shape was maintained even in the high-DS sample and that the thickness of the nanofibers increased with the introduction of bulky acetyl groups. Acetylated chitin nanofiber composites were fabricated with acrylic resin with the fiber content of approximately 25 wt %. Due to the size effect, all nanocomposites had high transparency, despite the variety of acetyl DS, and the transparency of the chitin nanofiber composite was less sensitive to acetylation. By only 1 min acetylation, the moisture absorption of the nanocomposite drastically decreased from 4.0 to 2.2%. Although the coefficient of thermal expansion (CTE) of the tricyclodecane dimethanol dimethacrylate (TCDDMA) resin was 6.4 x 10(-5) degrees C(-1), the CTE of the chitin nanofiber/TCDDMA composite decreased to 2.3 x 10(-5) degrees C(-1) by the reinforcement effect of the chitin nanofibers with low thermal expansion.

Gene transfer by DNA/mannosylated chitosan complexes into mouse peritoneal macrophages.

Chitosan is a biodegradable and biocompatible polymer and is useful as a non-viral vector for gene delivery. In order to deliver pDNA/chitosan complex into macrophages expressing a mannose receptor, mannose-modified chitosan (man-chitosan) was employed. The cellular uptake of pDNA/man-chitosan complexes through mannose recognition was then observed. The pDNA/man-chitosan complexes showed no significant cytotoxicity in mouse peritoneal macrophages, while pDNA/man-PEI complexes showed strong cytotoxicity. The pDNA/man-chitosan complexes showed much higher transfection efficiency than pDNA/chitosan complexes in mouse peritoneal macrophages. Observation with a confocal laser microscope suggested differences in the cellular uptake mechanism between pDNA/chitosan complexes and pDNA/man-chitosan complexes. Mannose receptor-mediated gene transfer thus enhances the transfection efficiency of pDNA/chitosan complexes.

Preparation and characterization of optically transparent chitin nanofiber/(meth)acrylic resin composites

Optically transparent chitin nanofiber composites were fabricated with 11 different types of (meth)acrylic resins. Chitin nanofibers significantly increased the Youngs moduli and the tensile strengths, and decreased the thermal expansion of all (meth)acrylic resins due to the reinforcement effect of chitin nanofibers having an extended crystal structure.