Electroactive hybrid hydrogel: Toward a smart coating for neural electrodes

Electroactive hybrid hydrogels, composed of single-walled carbon nanotubes, polypyrrole, and poly(ethylene glycol) diacrylate–polyacrylamide, were synthesized on titanium-mesh electrodes via interfacial polymerization. The modified electrodes can be used as controlled drug delivery system by applying an external electrical stimulation of cyclic voltammetry. Investigations revealed that single-walled carbon nanotubes acted as nucleators in the hybrid hydrogel and facilitated the formation of a continuous and uniform polypyrrole coating. Simultaneous incorporation of single-walled carbon nanotubes and polypyrrole improved not only the electrochemical performance but also the drug loading capacity of the hydrogel. Study of dexamethasone release triggered by cyclic voltammetry indicated that the hybrid hydrogel exhibited good electrochemical stability, a high drug loading capacity, and a linear and sustaining drug release profile, making the modified electrode a novel high-performance drug delivery device. Moreover, in vitro experiments demonstrated that dexamethasone released from the modified electrodes well retained its bioactivity, having the same effect on reducing lipopolysaccharide-induced macrophage activation as the intact commercially available dexamethasone. More important, the obtained modified electrodes possessed good biocompatibility with neural cells, demonstrated by in vitro cell culture.