Reframing Chitosan through the Source–Conversion–Value Chain: A Mechanistic Framework for Sustainable Materials Design

Chitosan has evolved from a waste-derived biopolymer into a strategic platform for sustainable materials design. This Review integrates chitosan research into the Source–Conversion–Value Chain (SCVC) framework, providing a mechanistic connection among biological origin, matrix-imposed processing constraints, molecular architecture, and functional performance. Comparative analysis of crustacean, fungal, and insect sources demonstrates how matrix composition governs processing severity and constrains the achievable degree of acetylation, molecular weight, and acetylation pattern. Conventional acid–alkali workflows are critically compared with enzymatic, fermentation-based, and deep eutectic solvent (DES) routes, revealing how greener technologies preserve structural fidelity while reducing environmental impact. By integrating SOURCE, PROCESSING, and STRUCTURE, the SCVC framework resolves long-standing ambiguities in structure–property relationships and explains the variability that has limited reproducibility and scalability. This framework positions chitosan as a rationally engineerable material platform and defines the design principles required for its scalable deployment in circular bioeconomy-driven technologies.