TEMPO-oxidized nanochitin based hydrogels and inter-structure tunable cryogels prepared by sequential chemical and physical crosslinking.

Well dispersibility of 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO)-oxidized nanochitins under alkaline conditions supports the effective chemical crosslinking between nanochitin and epichlorohydrin. The storage modulus of nanochitin hydrogels can be promoted by approximately 10 times as the nanochitin-to-epichlorohydrin mass ratio changes from 4:1 (120 Pa) to 1:4 (1200 Pa). Besides the enhanced mechanical property of hydrogels, the inter-structure of resulting cryogels is found controllable. With increasing epichlorohydrin dosage, the inter-structure of cryogels transforms from a typical fiber-like to honeycomb-like texture. The balance between chemical crosslinking effect and electrostatic repulsion between nanochitins is believed to result this controllable inter-structure. Further immersing into acetic acid solution can greatly enhance the mechanical strength of nanochitin hydrogels due to the introduction of physical crosslinking domains by shielding the electrostatic repulsion, the storage modulus becomes two times higher after immersing in 50% (w/w) acetic acid solution, while the surface area of nanochitin cryogels decreases due to the denser structure.