Spontaneous chitosan hydrogel formation through carbonic acid modulation: A crosslinker-free, efficient preparation for dressings

Chitosan hydrogels are widely recognized as promising wound dressings. However, traditional preparation methods often rely on crosslinkers, which pose challenges in terms of biocompatibility and cost. This study introduces a new approach for the spontaneous formation of chitosan hydrogels via carbonic acid modulation, which is crosslinker-free, rapid, simple, and economical. By adding ammonium bicarbonate to acetic acid-solubilized chitosan, an unstable solution is formed. This solution spontaneously releases CO 2 and transforms into a gel within 30 min at 40 °C. Subsequent purification yields a pure chitosan hydrogel composed solely of chitosan and water. The   prepared hydrogel demonstrates excellent biocompatibility and significantly promotes wound healing, achieving over 90 % closure of a 1 cm diameter full-thickness skin defect within 10 days. Key performance metrics include a compressive strength of 55.26 kPa, a water retention capacity of 7880.5 %, and a water vapor transmission rate of 496.2 g/(cm 2 ·day). This methodology   not only circumvents   the limitations of crosslinker-dependent methods but also establishes new possibilities for the biomedical applications of chitosan hydrogels, particularly in advanced wound care and other therapeutic contexts.