Tuning chitosan's chemical structure for enhanced biological functions

Chitosan, an amino polysaccharide mostly derived from crustaceans, has been recently highlighted for its biological activities that depend on its molecular weight (MW), degree of deacetylation (DD), and acetylation pattern (AP). More importantly, for some advanced biomaterials, the homogeneity of the chitosan structure is an important factor in determining its biological activity. Here we review emerging enzymes and cell factories, respectively, for in vitro and in vivo preparation of chitosan oligosaccharides (COSs), focusing on advances in the analysis of the AP and structural modification of chitosan to tune its functions. By 'mapping' current knowledge on chitosan's in vitro and in vivo activity with its MW and AP, this work could pave the way for future studies in the field.