Amphiphilic chitosan nanosphere: studies on formation, toxicity, and guest molecule incorporation

Amphiphilic chitosan developed by conjugating hydrophobic phthalimido groups and hydrophilic poly (ethylene glycol) chains gives a well-dispersed colloidal solution in polar solvents and shows a regular nano-sized spherical structure ( approximately 200 nm) with negatively charged surface (-31.24+/-4.85 mV). An in vivo acute oral toxicity test confirms the non-toxicity of the chitosan nanosphere with LD(50) higher than 2000 mg/kg body weight. A success of incorporating amine molecules into the nanosphere declares that the heterogeneous incorporation system is more effective than the homogeneous ones. The study on guest molecule incorporation using alkylamines and carboxylic acid as models suggests requirements that the guest be hydrophobic and positively charged. TGA study clarifies that the weight loss at 250-300 degrees C relating to the amount of guest incorporation via heterogeneous system is as high as 42.3%, whereas those of homogeneous systems are about 16.86-28.27%. The nanosphere size is significantly changed after guest incorporation, that is, from 200 nm to approximately 500-1000 nm.     

One-pot synthesis in aqueous system for water-soluble chitosan-graft-poly(ethylene glycol) methyl ether

Chitosan is functionalized with poly(ethylene glycol) methyl ether (mPEG) at the amino and hydroxyl groups via a single step reaction in a homogeneous aqueous system. A chitosan aqueous solution obtained from the mixture of chitosan and hydroxybenzotriazole (HOBt) in water is a key factor in providing mild conditions to conjugate mPEG by using a carbodiimide conjugating agent. The reaction at ambient temperature for 24 h gives chitosan-g-mPEG with water solubility with mPEG content as high as 42%. This work demonstrates that a water-soluble chitosan-HOBt complex is an effective system for the preparation of chitosan derivatives via the aqueous system without the use of acids or organic solvents.     

A novel soft and cotton-like chitosan-sugar nanoscaffold

A novel type of chitosan nanoscaffold with a soft and cotton-like appearance is proposed. The key to success is based on two points: (i) the change in morphology of chitin whisker to chitosan nanoscaffold and (ii) the surface modification of the nanoscaffold chitosan with a sugar unit. Simple deacetylation of chitin whisker gives a colloidal solution of chitosan, of which the chitosan is in a nanoscaled scaffold. Surface functionalization of the chitosan nanoscaffold with lactose or maltose via a heterogeneous system in water at room temperature results in a soft and cotton-like chitosan containing mesopores. As all steps are organic solvent free, this chitosan-sugar nanoscaffold might be a promising material for biopolymer-supported tissue engineering.     

Controlled hydrophobic/hydrophilicity of chitosan for spheres without specific processing technique

Chitosan is functionalized with phthalic anhydride at the amino group and poly(ethylene glycol) methyl ether at the hydroxyl group via homogeneous reaction. The product regenerated forms particles in either aqueous solution or organic solvents. The particles are spheres with the size of few micrometers as observed from scanning electronmicroscopy. The present work demonstrates that by simply adjusting the hydrophilicity and hydrophobicity, we can directly obtain spheres without a specific processing technique.     

Optimal gamma-ray dose and irradiation conditions for producing low-molecular-weight chitosan that retains its chemical structure

This study focuses on the optimal conditions for gamma irradiation to reduce the molecular weight of chitosan but still retain its chemical structure. Chitosan was irradiated under various conditions, i.e. flake solid state (condition 1), flake dispersed in water (condition 2), flake dispersed in 0.05, 0.1, 1 and 2% aqueous K(2)S(2)O(8) solution (conditions 3a, 3b, 3c and 3d, respectively), flake dispersed in 0.5, 1 and 2% aqueous H(2)O(2) solution (conditions 4a, 4b and 4c, respectively), and chitosan acetic acid solution (condition 5). Comparative studies were done using three types of chitosans with molecular weights of the order of 10(5) Da with degrees of deacetylation of 0.80, 0.85 and 0.90%. For all conditions, after irradiation, there were two regions of molecular weight reduction. A severe degradation occurred in the first region with decreases in the molecular weight of 80% for radiation doses up to 50 kGy for conditions 1, 2 and 3 (3a-3c) and 20 kGy for condition 4. In the second region, a slow degradation occurred, which resembled a plateau stage. The results for conditions 3d and 5 were the most dramatic, since the primary structure of chitosan was changed after the irradiation. The degradation of chitosan by gamma rays was found to be most effective for the amorphous structure. The retention of the structure of chitosan after gamma irradiation makes it possible to produce a low-molecular-weight chitosan that retains its functionality, as demonstrated by its activity in the coupling reaction with N,N'-carbonyldiimidazole.     

Microwave technique for efficient deacetylation of chitin nanowhiskers to a chitosan nanoscaffold

A chitosan nanoscaffold in the form of a colloidal solution was obtained from the deacetylation of chitin whiskers under alkaline conditions by using a microwave technique in only 1/7 of the treatment time of the conventional method. Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H NMR) techniques confirm the degree of deacetylation to be above 90% within 3 h. The wide-angle X-ray diffraction (WAXD) pattern clearly shows that the highly crystalline chitin whiskers are changed to amorphous chitosan. SEM micrographs show the aggregation of branched nanofibers, whereas the TEM micrographs reveal the scaffold morphology.