Controlled enzymatic hydrolysis and synthesis of lignin cross-linked chitosan functional hydrogels

This study presents a novel fully enzymatic process for the controlled depolymerisation of fungal and shrimp chitosan, and their subsequent use in the synthesis of lignin cross-linked chitosan (CTS) hydrogels. Cellobiosehydrolase (CBH) was used to depolymerize CTS resulting in decrease in average molecular weight (Mw) of shrimp CTS from 140 kDa and degree of deacetylation (DD %) from 91.3% to an average MW of 15 kDa and 16% DD. Similarly, fungal chitosan average molecular weight decreased from 92 kDa and the degree of deacetylation (DD) of 48.3% to 12 kDa and a DD of 13%. The depolymerized CTS were completely soluble in water and miscible with lignosulfonates without encountering the usual problem of formation of flocs. Introduction of laccase into a lignosulfonate-chitosan mixture resulted in the oxidation and generation of lignin reactive phenoxyl radicals that cross-linked with CTS-NH₂ reactive groups resulting in the increase of Mw from 20 kDa to >500 kDa and viscosity from 20 mPa to >500 mPa. This resulted in the formation of stable lignin-cross-linked hydrogels with elongation at break of 111% and tensile strength of 7 mPa. The produced functional hydrogels have potential application in food and biomedical industries as e.g. as oxygen barriers in packaging or as functional wound dressing or tissue engineering platforms.