Surface-conductive and pH-sensitive hydrogels based on 4-O-methylglucuronoxylan/chitosan reinforced with graphene oxide

Abstract

Multifunctional hydrogels based on natural polyelectrolyte complexes (PECs) of 4-O-methyglucuronoxylan (MGX) and chitosan (Ch) were prepared. The polyelectrolytes were combined at a mass ratio of 70 wt% MGX/30 wt% Ch, in the absence or presence of graphene oxide (GO: 0, 2.0 wt%). The release behavior of metformin (MF: 0.2, 0.4 wt%) in different pH media (1.7, 5.0, and 7.4) was studied. The starting materials, colloidal suspensions, and hydrogels were characterized using different analytical techniques (Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy, potential titration, elemental analysis, zeta potential and particle size, scanning electron microscopy, and X-ray diffraction) and the mechanical properties of hydrogels were determined. All hydrogels showed high swelling capacity (higher than 280%, 4h), maintaining their integrity over time. The presence of GO mainly improved the elongation at break and surface electrical conductivity of hydrogels. These properties were also enhanced in the presence of MF. Particularly, the electrical conductivity increased by 270% (from 20.1 to 74.1 μS/cm) when 2 wt% GO and 0.4 wt% MF were used, highlighting their application as biosensors. Furthermore, the release behavior of MF at different pH values showed that hydrogels also exhibited a pH-sensitive response, preventing an immediate release, especially under acidic conditions (pH 1.7).