Naotsugu Nagasawa

Synthesis of antibacterial PVA/CM-chitosan blend hydrogels with electron beam irradiation

A series of excellent hydrogels were prepared from poly(vinyl alcohol) (PVA) and carboxymethylated chitosan (CM-chitosan) with electron beam irradiation (EB) at room temperature. Electron spectroscopy analysis of the blend hydrogels revealed that good miscibility was sustained between CM-chitosan and PVA. The properties of the prepared hydrogels, such as the mechanical properties, gel fraction and swelling behavior were investigated. The mechanical properties and equilibrium degree of swelling improved obviously after adding CM-chitosan into PVA hydrogels. The gel fraction determined gravimetrically showed that a part of CM-chitosan was immobilized onto PVA hydrogel. The further analyses of FTIR and DSC spectra of the prepared gels after extracting sol manifested that there was a grafting interaction between PVA and CM-chitosan molecules under irradiation. The antibacterial activity of the hydrogels against Escherichia coli was also measured via optical density method. The blend hydrogels exhibited satisfying antibacterial activity against E. coli, even when the CM-chitosan concentration was only 3 wt%.

Hydrogels of polysaccharide derivatives crosslinked with irradiation at paste-like condition

Abstract Polysaccharides such as cellulose, starch, chitin/chitosan and their water-soluble derivatives have been known as degradable type polymers under action of ionizing radiation. Recently, we found that water-soluble polysaccharides derivatives such as carboxymethylcellulose (CMC), carboxymethylstarch (CMS) and carboxymethylchitin (CMCT), carboxymethylchitosan (CMCTS) lead to radiation crosslinking at high concentrated aqueous solution (more than 10%, paste-like state). It was proved that the crosslinking was remarkably affected by their concentration. It was assumed that radiation formation of hydrogels of these polysaccharides derivatives were mainly due to the mobility of side chains. Side-chains radicals were formed mostly via indirect effects, by the abstraction of H atoms by the intermediate products of water radiolysis. Some important characteristics of these novel hydrogels were also investigated. These hydrogels exhibited good swelling in water and possess satisfying biodegradability. In addition, the antibacterial activity against E.coli was also found in CMCTS hydrogel.

Utilization of carbohydrates by radiation processing

Abstract Upgrading and utilization of carbohydrates such as chitosan, sodium alginate, carrageenan, cellulose, pectin have been investigated for recycling these bio-resources and reducing the environmental pollution. These carbohydrates were easily degraded by irradiation and various kinds of biological activities such as anti-microbial activity, promotion of plant growth, suppression of heavy metal stress, phytoalexins induction, etc. were induced. On the other hand, some carbohydrate derivatives, carboxymethylcellulose and carboxymethylstarch, could be crosslinked under certain radiation condition and produce the biodegradable hydrogel for medical and agricultural use.

Radiation crosslinking of carboxymethylcellulose of various degree of substitution at high concentration in aqueous solutions of natural pH

AbstractCarboxymethylcellulose(CMC)hydrogelformedbyionizingradiationathighlyconcentratedaqueoussolutionswasfoundtoundergoswellingdependingonthepHoftheswellingmedia.SwellingincreasesatneutralandbasicpHduetoionizationofcarboxymethylgroupsonsidechains.Thepresenceofchargesdevelopsrepulsiveforcesbetweenpolymerchainsofthenetworkcausingitsexpansion.Hydrogelinrelaxedstateaswellasdriedgelrevealsgoodmechanicalproperties.Itwasconsideredthatintermolecularcrosslinkingreactionsoccurbyaradicalroute.RadicalsplacedonanhydroglucoserepeatingunitaswellasonsidechainsweredistinguishedfromESRspectraofCMC.Astabledoubletsignal with 2.0mT splitting constant belongs to a radical placed on the a-carbon atom of the substituent group,R–O– d CH–COO – .Itwasassumedthatthisspeciesparticipatesinintermolecularcrosslinking.r 2003ElsevierLtd.Allrightsreserved. Keywords: Carboxymethylcellulose;Hydrogels;Crosslinking;Ionizingradiation;Radicals 1. IntroductionBasicrequirementsforpolymericabsorbentsarelargefluid uptake and high mechanical strength. These twodemandsareclearlyconflicting,andasuitablecompro-mise needs to be found. A high degree of swelling inaqueous systems can be achieved by using polyelec-trolytesbecauseofmobilecounterions presentinsuchgels develop a large swelling pressure (Florry, 1953).Thus,carboxymethylcellulose(CMC),whichisthemostpopularandthecheapestcelluloseethercanbeusedforthis purpose. It is an anionic linear polymer in whichoriginal H atoms of cellulose hydroxyl groups arereplaced by carboxymethyl substituent, –CH

Radiation crosslinking of methylcellulose and hydroxyethylcellulose in concentrated aqueous solutions

Abstract The effects of ionizing radiation on aqueous solutions of cellulose ethers, methylcellulose (MC) and hydroxyethylcellulose (HEC) were investigated. The well-established knowledge states that cellulose and its derivatives belong to degrading type of polymers. However, in our study intermolecular crosslinking initiated by gamma rays or electron beam leaded to the formation of insoluble gel. This is an opposite effect of irradiation to the degradation. Paste-like form of the initial specimen, i.e. concentration 20–30%, when water plasticizes the bulk of polymer; and a high dose rate were favorable for hydrogel formation. Gel fraction up to 60% and 70% was obtained from solutions of HEC and MC, respectively. Produced hydrogels swell markedly in aqueous media by imbibing and holding the solvent. Radiation parameters of irradiation, such as yields of degradation and crosslinking and the gelation dose, were evaluated by sol–gel analysis on the basis of Charlesby–Rosiak equation. Despite of the crosslinked structure, obtained hydrogels can be included into the group of biodegradable materials. They undergo decomposition by the action of cellulase enzyme or microorganisms from compost.

Biological effect of radiation‐degraded alginate on flower plants in tissue culture

Alginate with a weight‐average molecular mass (Mw) of approx. 9.04×105 Da was irradiated at 10–200 kGy in 4% (w/v) aqueous solution. The degraded alginate product was used to study its effectiveness as a growth promoter for plants in tissue culture. Alginate irradiated at 75 kGy with an Mw of approx. 1.43×104 Da had the highest positive effect in the growth of flower plants, namely limonium, lisianthus and chrysanthemum. Treatment of plants with irradiated alginate at concentrations of 30–200 mg/l increased the shoot multiplication rate from 17.5 to 40.5% compared with control. In plantlet culture, 100 mg/l irradiated alginate supplementation enhanced shoot height (9.7–23.2%), root length (9.7–39.4%) and fresh biomass (8.1–19.4%) of chrysanthemum, lisianthus and limonium compared with that of the untreated control. The survival ratios of the transferred flower plantlets treated with irradiated alginate were almost the same as the control value under greenhouse conditions. However, better growth was attained for the treated plantlets.

Reagent-free crosslinking of aqueous gelatin: manufacture and characteristics of gelatin gels irradiated with gamma-ray and electron beam.

In order to obtain a gelatin hydrogel crosslinked by a reagent-free method, gamma-ray and electron beam radiation was applied to porcine, bovine and fish gelatin gels and the products were characterized by measuring the gel fraction, the swelling ratio and the enzymatic degradability. On increasing the radiation dose, the gel fraction increased and both the swelling ratio and the enzymatic degradability decreased. The transition temperature from gel to sol of the hydrogel containing more than 5% mammal gelatins increased up to more than 90°C when gamma-ray or electron beam were irradiated by more than 10 kGy. The results show that the degree of crosslinking of irradiated gelatin hydrogels increases with increasing irradiation dose and with decreasing concentration. It is suggested that the radiation crosslinking occurs around the physical crosslinking point or multiple helix structure of gelatin gel.

Biological effect of irradiated chitosan on plants in vitro.

For degradation of chitosan, chitosan with an 80% degree of deacetylation and a weight‐average molecular mass (Mw) of approx. 48 kDa was irradiated with γ‐rays at doses up to 200 kGy in a 10% (w/v) solution. The Mw of chitosan was reduced from 48 to 9.1 kDa by irradiation. The characteristics of irradiated chitosan were analysed by using Fourier‐transform IR spectroscopy and an elemental analyser. The amino group was found to be stable, whereas the C‐O‐C group decreased with increase in the dose. The product of chitosan irradiated at 100 kGy with an Mw of approx. 16 kDa showed the strongest growth promotion effect on plants in vitro. For shoot culture, supplementation with irradiated chitosan increased the fresh biomass of shoot clusters (7.2–17.0%) as well as the shoot multiplication rate (17.9–69.0%) for Chrysanthemum morifolium (florists chrysanthemum), Limonium latifolium (limonium or sea‐lavender), Eustoma grandiflorum (lisianthus, tulip gentian or Texas bluebell) and Fragaria ananassa (modern garden strawberry). The optimum concentrations of irradiated chitosan were found to be approx. 70–100 mg/l for chrysanthemum, 50–100 mg/l for lisianthus and 30–100 mg/l for limonium. For the plantlet culture, the optimum concentrations were found to be approx. 100 mg/l for chrysanthemum, 30 mg/l for lisianthus, 40 mg/l for limonium and 50 mg/l for strawberry. Supplementation with optimum concentrations of irradiated chitosan resulted in a significant increase in the fresh biomass (68.1% for chrysanthemum, 48.5% for lisianthus, 53.6% for limonium and 26.4% for strawberry), shoot height (19.4% for chrysanthemum, 16.5% for lisianthus, 33.9% for limonium and 25.9% for strawberry) and root length (40.6% for chrysanthemum, 66.9% for lisianthus, 23.4% for limonium and 22.6% for strawberry). In addition, treatment with irradiated chitosan enhanced the activity of chitosanase in treated plants and also improved the survival ratio and growth of the transferred plantlets acclimatized for 10–30 days under greenhouse conditions.

Modification of biodegradable polymers by radiation crosslinking technique with polyfunctional monomers

Poly(e-caprolactone) (PCL) and poly(butylene succinate-co-adipate) (PBSA) were electron beam-irradiated in the presence of five different polyfunctional monomers at ambient temperature. Trimethallyl isocyanurate (TMAIC) has been found to greatly enhance the radiation crosslinking of PCL and PBSA. It was pointed out that the optimum yield of gel fraction can be achieved when the polymers were irradiated at a dose of 50 kGy in the presence of 1% TMAIC. High gel fraction largely improves heat stability of PBSA, while biodegradability evaluated by soil burial test of the crosslinked polymers is slightly retarded, however they are effectively destroyed with a slightly smaller rate.

Effect of radiation and fungal treatment on lignocelluloses and their biological activity

Abstract Effects of high-dose irradiation and fungal treatment on some kinds of lignocellulosic material were investigated in order to assess the potential effects of bioactive substances on plants. Each treatment and combination of treatments significantly altered the components of lignocellulosic materials. Irradiation strongly affected all plant materials, causing a series of changes in physico-chemical parameters such as solubilization during solvent extraction and losses of fibre components. By these degradations, certain biologically active substances formed and acted as antagonists of auxin-induced growth.