Electrochemically stimulated drug release from dual stimuli responsive chitin hydrogel

A stimuli-sensitive chitin derivative with water solubility was used for electrochemically stimulated protein release. Chitin was homogeneously functionalized with acrylamide (AM) through Michael addition in NaOH/urea aqueous solution. The product was characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), ¹H nuclear magnetic resonance (¹H-NMR), gel permeation chromatography (GPC) and titration methods. The results show that the water solubility relates to two functional groups (i.e. acylamino and carboxyl groups) and the degree of substitution (DS) can be adjusted by changing the molar ratio of acrylamide to chitin. Importantly, the acrylamide-modified chitin (AMC) is pH-sensitive and cationic sensitive. Reversible sol-gel transition was conducted either by changing the pH or the presence of cationic metal ions in AMC solution. Furthermore, we demonstrate the protein entrapment and release on electrodes can be controlled by electrical signals. Specifically, an anodic signal imposed to the electrode induced a pH decrease that allows a sol-gel transition of AMC adjacent to the electrode and simultaneous protein entrapment. The release of protein from AMC hydrogel can be triggered by a cathodic potential induced pH increase. In the case of cationic ion crosslinked AMC hydrogel, the conversion of Fe²⁺/Fe³⁺ was controlled by electrical potentials and the corresponding protein entrapment and release can be achieved based on the fact that Fe³⁺ can crosslink with AMC to form a gel while Fe²⁺ lacks the ability to crosslink. The present result represents a facile and "green" method to functionalize chitin and the resulted stimuli-responsive water soluble derivative may have potential applications in controlled drug delivery activated by electrical signals.