Chemistry and Biological Activities of Marine Polysaccharides: Chitin, Chitosan, Chitooligosaccharide, and Their Derivatives

Chitin, mainly derived from marine organisms, is the second-most abundant natural polysaccharide. Notably, marine sponge-derived chitin has recently emerged as a highly promising resource due to its unique naturally pre-organized three-dimensional nanofibrous network and high purity, offering unparalleled advantages for modern biomedical engineering and advanced materials science. Generally, chitin and its derivatives have shown great application potential in the fields of biomedicine and agriculture due to their excellent biocompatibility and diverse biological activities such as antibacterial, anti-inflammatory, immunomodulatory, and antitumor properties. However, the poor solubility and structural inertia of natural chitin limit its development and utilization to a certain extent. In this review, we systemically summarized the biological activities and structural functionalization strategies of chitin, chitosan, chitooligosaccharide and their derivatives from 2020 to 2025. Then, their mechanisms of action and structure–activity relationships (SARs) were concluded. Moreover, the applications of these marine-derived biopolymers in future therapeutics and sustainable smart materials were prospected. Finally, we analyzed the current scientific challenges from laboratory research and development to large-scale application. Hopefully, we enthusiastically anticipate that this review will offer readers valuable insights and proposals on developing chitin-based effective agents in the future.