Gellan–thioglycolic acid conjugate: Synthesis, characterization and evaluation as mucoadhesive polymer

Gellan–thioglycollic acid conjugate was synthesized with the objective to improve its mucoadhesive properties. Synthesis of conjugate was confirmed by –SH stretch in the Fourier-transform infrared spectra at 2571 cm−1. It was found to contain 13.92 mM of thiol groups/g of the conjugate. Thiolation of gellan gum was found to slightly increase its degree of crystallinity and decrease its sensitivity to Ca2+-induced gelation. On screening of gellan–thioglycollic acid conjugate for ex-vivo ocular tolerance using henʹs egg chorio-allantoic membrane test and for biocompatibility by resazurin assay on Vero-cells, it was found to be non-irritant and biocompatible. Metronidazole gels formulated using gellan thioglycollic acid conjugate as bioadhesive agent showed 1.82-fold higher mucoadhesive strength than the gels formulated using gellan gum. Further, the metronidazole gels containing gellan and gellan–thioglycollic conjugate released the drug following first-order and Higuchiʹs square-root release kinetics. In conclusion, gellan–thioglycollic acid conjugate is a promising bioadhesive excipient.