Thermoresponsive hydrogelation of N-acetyl chitohexaose: Gelation mechanism and application in controlled protein release.

Chitin is a polysaccharide composed of N-acetylglucosamine units that form highly crystalline structures in biological systems; however, the precise mechanism underlying its self-assembly in aqueous environments remains unclear. In this study, we demonstrated that N-acetyl chitohexaose (GN6), a chitin oligosaccharide with a degree of polymerization of six, uniquely undergoes thermally induced self-assembly into crystalline nanofibers and forms reversible hydrogels in water. Among chitin oligosaccharides ranging from monomer to hexamer, only GN6 exhibited gelation upon heating, which is attributed to its optimal molecular length and balanced hydrophilic-hydrophobic characteristics. Comprehensive structural analyses using solid-state nuclear magnetic resonance spectroscopy, small- and wide-angle X-ray scattering, transmission electron microscopy, atomic force microscopy, and microcrystal electron diffraction revealed that GN6 molecules align along the crystallographic β-axis and assemble into nanofibers with highly ordered α-chitin-type molecular packing. This directional organization is driven by cooperative hydrogen bonding and hydrophobic interactions. Furthermore, the hydrogels exhibited a sustained release of encapsulated proteins, including insulin, albumin, and immunoglobulin G, for more than four weeks under physiological conditions, without using chemical crosslinking agents. These findings highlight the potential of this oligosaccharide as a biocompatible, drug delivery material and as a minimalistic model system for studying polysaccharide self-assembly in aqueous environments.