A pH-responsive composite hydrogel based on konjac glucomannan and its oxidized derivatives: synthesis, characterization and swelling behavior

A novel pH-responsive hydrogel composed of oxidized konjac glucomannan (OKGM) and konjac glucomannan (KGM) was fabricated using sodium trimetaphosphate as a crosslinker for intestinal-targeted delivery applications. A series of OKGM samples with carboxyl contents ranging from 1.35% to 5.59% and degree of oxidation (DO) values from 0.49 to 2.01 was successfully prepared. The OKGM and the OKGM-KGM hydrogels were characterized by Fourier Transform Infrared Spectroscopy, thermogravimetric analysis, and small angle X-ray scattering. Congo red assays revealed that OKGM adopted a random-coil conformation under alkaline conditions. Rheological analysis showed that OKKH-1 exhibited the highest yield stress (948.8 Pa), indicating the strongest gel network, whereas increasing DO reduced structural strength and enhanced flexibility. The hydrogels showed pronounced pH responsiveness, with equilibrium swelling ratios of 5.12-12.27 g/g at pH 2.0 and 13.96-21.91 g/g at pH 7.2. Furthermore, in vitro release studies revealed that the release kinetics conformed well to the Korsmeyer-Peppas model with release exponent values greater than 0.89, implying that the release process was governed by a super case-II transport mechanism. These results demonstrate that the OKGM-KGM hydrogels possess tunable structure and performance, showing promise as biocompatible carriers for controlled intestinal delivery in food and pharmaceutical applications.