Citric acid crosslinked natural bi-polymer-based composite hydrogels : Effect of polymer ratio and beta-cyclodextrin on hydrogel microstructure

Composite hydrogels based on natural polymers arouse interest as sustainable matrices for the delivery of bioactive materials. This study investigates the possibility of achieving high thermally and hydrolytically stable, well-defined microstructure bi-polymer composite hydrogels using only natural materials at a low energy process. Firstly, citric acid (CA) crosslinked hybrid hydrogel matrices are developed by varying mole ratio of carboxymethyl cellulose (CMC) to chitosan (CSN) by 1:1, 1:2 and 2:1. Then, hydrolytic, thermal and structural properties of the matrices are studied to determine microstructure. Lastly, the matrices are functionalized with beta-cyclodextrin (β-CD), and the effect of β-CD on hydrogels’ microstructure and antibacterial activity is examined. Optimum microstructure is found at CMC:CSN = 1:1 for CMC~CA~CSN with a gel fraction of 63%, which increases to 82% when reinforced with β-CD. Interestingly, CMC~CA~2CSN exhibits a combination of good crosslinking, super-absorbency (1229.7% water absorbency and 2200% swelling) yet enhanced hydrolytic stability (84.7% gel fraction). Complexation with β-CD propagates the growth of Gram-positive bacterium, Corynebacterium glutamicum ATCC 13032. Overall, CMC~CA~CSN~β-CD is considered as a green, crystalline, thermally, and hydrolytically stable composite hydrogel matrix.