Atypical swelling gelation of chitin physical hydrogel and the tunable mechanical properties

Atypical swelling gelation of chitin physical hydrogels were investigated. Only by tuning the amount of N-acetylation reagent, the degree of acetylation varied and the moldable chitin hydrogels with a wide variety of gel concentration (0.21–6.4 wt%) were obtained. In response to the gel concentration, the mechanical properties ranged from swollen soft gels to shrunk rigid gels (compressive E = 4.22–310 kPa). Thus-prepared chitin hydrogels, which are made only of chitin and water, exhibited high transparency and integrity. The swelling gelation of chitin physical hydrogels was achieved owing both to the cationic charge of the amino groups inducing the osmotic pressure and the toughness of chitin hydrogels that endured the large volume change. These previously-unnoticed advantageous aspects of chitin have pioneered a novel region of swellable physical gels that has been exclusive to chemical gels.