Gelation of hydrophobized pullulan

Gelation of hydrophobized polysaccharides such as cholesterol-bearing pullulan (CHP) and long alkyl chain-bearing pullulan (C12P, C16P, C20P) was investigated. In dilute aqueous solution, the hydrophobized polysaccharides intermolecularly self-aggregate to form nanoparticles. The size and the density of the nanoparticles are controlled by changing the chemical structure and the substitution degree of the hydrophobic groups. CHP and C16P formed gels at the concetration above 3.5 wt% and 5.5 wt%, respectively. TEM image showed that CHP provides a gel in which the CHP nanoparticles link together, while C16P gel was fibrous. Structure and rheological behavior of the gels were dependent on the structure of the hydrophobic group conjugated to the polysaccharide. The addition of a surfactant such as SDS induced gelation of CHP and C16P. The oscillatory shear measurements of the gels showed trends of a typical Maxwellian fluid. The self-aggregate of CHP dissociated by complexation with beta-cyclodextrin (beta-CD) to yield a dis-aggregated CHP-CD complex, in which the cholesteryl group was a suitable guest for beta-CD. The monodisperse nanoparticles were regenerated by addition of 1-adamantancarboxylic acid, which is a better guest molecule for beta-CD than cholesterol.