Fabrication of pH-sensitive graphene oxide-drug supramolecular hydrogels as controlled release systems

A novel graphene oxide (GO)-based hydrogel with drug molecules as crosslinking agents was fabricated. Metformin hydrochloride (MFH), which has no aromatic groups, but only has N-containing functionalities, was chosen as a model drug. When a very small amount of MFH was introduced into a GO solution, a supramolecular assembled hydrogel was rapidly formed without any polymers or chemical additives. The gelation process can be influenced by the weight ratio of MFH to GO. The driving forces were hydrogen bonding and electrostatic attraction. Both air-dried and freezedried samples of GO-MFH hydrogels were utilized for controlled drug release in water (pH = 7) and hydrochloric acid (pH = 1, 3 and 5). The release mechanism of capsulated MFH was Fickian diffusion according to the fitted results. Both the freeze-dried and air-dried samples released around 74% of the MFH in a strongly acidic medium after 70 h, but only 50% in a neutral solution. This pH-sensitivity makes it a potential candidate for the controlled release of drugs in the acidic environment of the stomach.