Evaluation of modified hyaluronic acid in terms of rheology, enzymatic degradation and mucoadhesion

This study aimed to investigate the properties of modified hyaluronic acid in terms of rheological properties, enzymatic degradation and mucoadhesiveness.Hyaluronic acid (HA) was chemically modified with sulfhydryl ligand cysteine ethyl ester (C) in order to immobilize sulfhydryl groups on the polymeric backbone. MTT assay was performed to evaluate the safety of hyaluronic acid-cysteine ethyl ester (HAC). Rheological and enzymatic degradation studies were accomplished by preparing hydrogels of HA and HAC, respectively. HA served as control. Enzymes such as lysozyme, amylase and hyaluronidase were chosen to perform degradation studies. To study mucoadhesiveness, hydrogels of HA and HAC, respectively, were mixed with mucus and evaluated by rheology.MTT assay indicated no toxicity at all. The rheological assay showed 2.2-fold increase in gelling properties in case of HAC in comparison to HA. Furthermore, it could be shown that HAC was degraded by amylase to a lesser extent of 11.5-fold than HA. After 2 h, HA showed a higher degradation by lysozyme with 67.97% than HAC. Adhesion studies exhibited a 2.17-fold higher mucoadhesion of HAC with mucus compared to HA.These results will open the door for high efficient drug delivery systems based on hydrogels for mucosal application.