Chitosan bio-inspiration material: a controlled structure at molecular level by balancing of hydrophobicity and hydrophilicity

Abstract

The present dissertation proposes (i) the use of y-ray irradiation to molecular weight of chitosan in the range as desired and (ii) the chang of chitosan flake tonanosphere by simple reaction without specific processing technique. In the case of (i), at 20 kG of y-ray dose, the molecular weight of chitosan decreases for 50% in dry solid and aqueous wet state, for 55% in aqueous with 0.05-1% K2S2O8, and for 85% in aqueous with 0.5-2% H2O2. For chitosan acetic acid solution, chitosan loses its primary structure after the exposure to y-ray at 20 kGy. Radicals initiate mainly chain-scission rather than cross-linking. The model reaction with N,N'-carbonyldiimidazole (CDI) clarifies the increase in the reactivity of irradiated chitosan. In the case of (ii), the modification of irradiated chitosan flake with hydrophobic phthalimido group and hydrophilic poly(ethylene glycol) methyl ether (mPEG) chain gives colloidal phenomena in both protic and aprotic solvents to form nanospheres at the sizes of 80-500 nm as as observed by transmission electron microscope (TEM). The sizes are dependent on the chain length and content of mPEG conjugated on chitosan chain. The nanospheres perform effective drug incorporation by simply mixing with drug solution as demonstrated by stearylamine model molecule.