Moldable Crystalline α‑Chitin Hydrogel with Toughness and Transparency toward Ocular Applications

A N-acetylated chitosan hydrogel was investigated for ocular applications. One of the drawbacks in the original hydrogel protocol, poor moldability, was circumvented by optimizing the addition of the acetylating agent, acetic acid anhydride (Ac₂O), at −10 °C. This simple but significant optimization realized the preparation of N-acetylated chitosan hydrogels with a wider variety of parameters such as higher chitosan concentration and molecular weight, the use of a more benign solvent (ethanol replaced methanol), and the arbitral shapes ranging from microbeads and contact lenses to bulky blocks that could be gripped. The prepared N-acetylated chitosan hydrogels exhibited high transparency and integrity given the nanofibrous network made of highly crystalline α-chitin. Furthermore, the gel retained a regenerable character: an oven-dried gel was reswollen by emersion in an acid bath. These previously unnoticed advantages and the innate high biocompatibility of chitosan and chitin elevate N-acetylated chitosan hydrogel as a next-generation bio-derived soft material for ocular applications such as contact lenses, artificial corneas, and drug delivery vehicles.