Seiichi Tokura

Chitosan-Alginate Multilayer Beads for Gastric Passage and Controlled Intestinal Release of Protein

Abstract Chitosan-alginate beads loaded with a model protein, bovine serum albumin (BSA) were investigated to explore the temporary protection of protein against acidic and enzymatic degradation during gastric passage. Optimum conditions were established for preparation of homogenous, spherical, and smooth chitosan-alginate beads loaded with BSA. Multilayer beads were prepared by additional treatment with either chitosan or alginate or both. The presence of chitosan in the coagulation bath during bead preparation resulted in increased entrapment of BSA. During incubation in simulated gastric fluid (SGF pH 1.2), the beads showed swelling and started to float but did not show any sign of erosion. Inclusion of pepsin in the gastric fluid did not show a further effect on the properties of the beads. Release studies were done in simulated gastric fluid (SGF pH 1.2) and subsequently in simulated intestinal fluid (SIF pH 7.5) to mimic the physiological gastrointestinal conditions. After transfer to intestinal fluid, the beads were found to erode, burst, and release the protein. Microscopic and macroscopic observations confirmed that the release of protein was brought about by the burst of beads. Chitosan-reinforced calcium-alginate beads showed delay in the release of BSA. The multilayer beads disintegrated very slowly. The enzymes pepsin and pancreatin did not change the characteristics of BSA-loaded chitosan-alginate beads. Single layer chitosan-alginate beads released 80–90% of the model protein within 12 h while multilayer beads released only 40–50% in the same period of time. The release from chitosan-alginate beads and multilayer beads in SIF was further delayed without prior incubation in SGF. It is concluded that alginate beads reinforced with chitosan offer an excellent perspective for controlled gastrointestinal passage of protein drugs.

Chitosan coated cotton fiber : preparation and physical properties

Abstract A new cotton fiber with a chitosan coating (CCCF) was prepared by the oxidation of a cotton thread with potassium periodate at 60°C in water and subsequent treatment with a solution of chitosan in aqueous acetic acid. Infrared spectra of the CCCF suggested the formation of Schiffs base between the chitosan and the oxidized cellulose. Kjeldahl nitrogen analysis of the CCCF showed that the maximum percentage of chitosan introduced into the cotton fiber was 1.58% (w/w). Treatment of the fiber with 2′,7′-difluoro fluorescein (an amino group-specific probe) followed by fluorescent microscopic analysis revealed that the modification with chitosan occurred on the surface of the cotton fiber. Scanning electron microscopy (SEM) photographs showed that the surface of the CCCF was slightly changed after the series reaction. However, the mechanical strength of the cotton thread, which was oxidized by the potassium periodide solution at a concentration of less than 2.0xa0mg/ml, was found to be almost the same as the original cotton thread. Furthermore, a model experiment for the controlled release of the drug was preformed using shikonin, a component of a Chinese medicine, suggested potential usefulness of the CCCF as a supporter for the controlled release of drugs.

Preparative methods of phosphorylated chitin and chitosan—An overview

Biomaterials such as chitin, chitosan and their derivatives have a significant and rapid development in recent years. Chitin and chitosan have become cynosure of all party because of an unusual combination of biological activities plus mechanical and physical properties. However, the applications of chitin and chitosan are limited due to its insolubility in most of the solvents. The chemical modification of chitin and chitosan are keen interest because of these modifications would not change the fundamental skeleton of chitin and chitosan but would keep the original physicochemical and biochemical properties. They would also bring new or improved properties. The chemical modification of chitin and chitosan by phosphorylation is expected to be biocompatible and is able to promote tissue regeneration. In view of rapidly growing interest in chitin and chitosan and their chemical modified derivatives, we are here focusing the recent developments on preparation of phosphorylated chitin and chitosan in different methods.

Surface modification of nonporous glass beads with chitosan and their adsorption property for transition metal ions

Abstract A new hybrid material that adsorbs transition metal ions was prepared by immobilizing chitosan on the surface of nonporous glass beads. The glass beads, prepared by etching in aqueous NaOH at 100°C, were first reacted with γ-aminopropyltriethoxysilane (APES) to introduce amino groups on the surface. Subsequently, the resulting aminated beads were treated with glutaraldehyde at 25°C to change the amino groups into aldehyde groups. Finally, chitosan of average molecular weight 40,000 was introduced via the aldehyde groups through a Schiffs reaction. After complete acid-hydrolysis of the immobilized chitosan, the Svennerholm method for glucosamine analysis showed that 0.3% (w/w) chitosan had been successfully introduced on the glass beads. Atomic absorption spectroscopic analysis of eluants of a column of the chitosan-modified glass beads showed that metal ions such as Cu 2+ , Ag + , Pb 2+ , Fe 3+ , and Cd 2+ were more than 90% entrapped on a column of beads prepared in this manner.

Preparation of chitosan-coated alginate filament

The coating of alginate filament was achieved simply by the addition of chitosan to the first coagulation bath for alginate filament. The smooth and uniform chitosan coatings were confirmed both by the microscopic picture of ninhydrin-treated filament and the brightness of filament. The enhancement of tensile strength was also observed by the coating of alginate filament by chitosan through ionic interaction. There was significant molecular weight dependency on the tensile strength of chitosan-coated alginate filament especially in wet properties, suggesting the tight interaction of chitosan to alginate filament.

A method for direct harvest of bacterial cellulose filaments during continuous cultivation of Acetobacter xylinum

Abstract Continuous filamentation of bacterial cellulose (BC) was successfully achieved by using shallow pan for the incubation to regulate thickness of the BC gel produced by Acetobacter xylinum . The BC filament was harvested and prepared directly by picking up BC pellicles, the thin BC gel, and winding slowly from the surface of the culture medium passed through a preliminary bactericidal washing bath. The X-ray diffraction analysis and scanning electron microscopic observation of the BC filament thus obtained showed that the filament was smooth and the fairly good orientation of BC molecules. The average tensile strength was 4.4 g denier −1 for the filament prepared by hot alkaline treatment and subsequent washing with distilled water and dried under tension (Filament W): 3.4 g denier −1 for washing with 10% aqueous ethylene glycol after alkaline treatment followed by drying under tension (Filament E) and 2.4 g denier −1 for the treatment with 10% ethylene glycol after normal water-washing followed by drying under tension.

Novel synthesis of a water-soluble cyclodextrin-polymer having a chitosan skeleton

Formation of Schiffs base between 2-O-(formylmethyl)-β-cyclodextrin and chitosan with an average molecular weight of 40 000 in acetate buffer at pH 4.4, followed by reduction with sodium cyanoborohydride produced a β-cyclodextrin-linked chitosan in a one-pot reaction. The product, which had a degree of substitution of 37%, was soluble in water at neutral and alkaline conditions. UV-visible and circular dichroism spectroscopic examinations revealed that the product had the ability to form a host-guest complex with p-nitrophenolate.

Chitosan beads with pendant α-cyclodextrin: preparation and inclusion property to nitrophenolates

Highly porous beads having an ability to form inclusion complexes with specific substrates have been synthesized and preliminary experiments for the application to adsorbent for affinity column chromatography and controlled release were carried out. Water-insoluble chitosan beads were synthesized by adding an aqueous acetic acid solution of chitosan into ethanolic aqueous sodium hydroxide and subsequent crosslinking with hexamethylene diisocyanate in N, N-dimethylformamide. The resulting beads were further treated with 2-O-formylmethyl-α-cyclodextrin in the presence of sodium cyanoborohydride in acetate buffer at pH 4.4, giving the cyclodextrin-linked chitosan beads. Their inclusion ability was examined by the use of p-nitrophenol and its analogue as model compounds.

A novel method for immobilization of chitosan onto nonporous glass beads through a 1,3-thiazolidine linker

Abstract A new method for the surface modification of nonporous glass beads (average diameter, 6xa0μm), which characterized by formation of a 1,3-thiazolidine ring between l -cysteine linkers on the glass bead and reducing ends of chitosan, has been developed. γ-Aminopropyltriethoxysilane (APES)-treated glass bead was first subjected to condensation with an l -cysteine derivative, l -4-carboxy-3-formyl-2,2-dimethylthiazolidine (CFMT), in the presence of water-soluble carbodiimide hydrochloride (WSC) and HOBt. After deprotection by diluted hydrochloric acid, the glass beads with activated cysteine linkers on the surface were treated with reducing chitosan in aqueous acetic acid solution at room temperature. The maximum content of chitosan immobilized on the glass beads estimated by acid-hydrolysis and subsequent glucosamine analysis by Svennerholm method after was 0.73% (w/w). This was obtained by using chitosan having an average molecular weight of 14xa0kD. Model reactions of the cysteine derivatives with reducing chitosan were also performed and the product was examined by IR and NMR spectroscopy to verify the linkage between cysteine and chitosan.

Biosynthesis of hetero-polysaccharides by Acetobacter xylinum - Synthesis and characterization of metal-ion adsorptive properties of partially carboxymethylated cellulose

Abstract Biological reconstruction of water-soluble carboxymethylated cellulose (CMC; D.S. =0.47) has been achieved by culturing Acetobacter xylinum in medium containing CMC and d -glucose to give a novel hetero-polysaccharide having a carboxymethyl function. The novel extracellular polysaccharide, carboxymethylated-bacterial cellulose (CM-BC), had an ion exchange ability with enhanced specific adsorption for lead and uranyl ions compared to the original CMC and bacterial cellulose. The contribution of the hydroxy group at C-2 was confirmed by applying carboxymethylated chitin, which possesses acetamido group at C-2 of the glucose residue, as the carbon source of the incubation.