One-step preparation of hydrogel based on different molecular weights of chitosan with citric acid

Chitosan-based hydrogels have been prepared previously by a two-step protocol in which chitosan was first dissolved in dilute acetic acid and then crosslinked by glutaraldehyde or genipin. This was a time-consuming method, which had the disadvantages of high costs and biological safety problems.

Scanning electron microscopy (SEM) results verified the successful preparation of hydrogels based on high, medium, and low molecular-weight chitosan (HCS, MCS, and LCS), respectively. The hydrogels prepared with HCS, MCS, and LCS were formed through the accumulation of different-sized crystals. The framework density of the hydrogel was enhanced by an increase in the chitosan molecular weight and exhibited a crack pore pattern composed of flake particles. Medium molecular-weight chitosan-based hydrogel exhibited the highest specific surface area and total pore volume, with values of 3.81 m² g^-1 and 0.0109 cm³ g^-1 , respectively. The water absorption rate of the chitosan based hydrogels was influenced by its molecular weights at the sequence of LCS > HCS > MCS, while the maximum compression stress was affected at the sequence of HCS > MCS > LCS. The network structure was enhanced with an increase in the chitosan molecular weight and reached maximum stress levels of 4.50, 1.50 and 0.75 MPa for HCS-, MCS-, and LCS-based hydrogels, respectively.

Citric acid was shown to be an effective dissolving and crosslinking agent in the preparation of MCS- and HCS-based hydrogels. The physiochemical properties of the hydrogels were enhanced as the molecular weight of the chitosan increased. © 2021 Society of Chemical Industry.