Temperature and pH sensitive hydrogels: an approach towards smart semen-triggered vaginal microbicidal vehicles

Microbicides are drug delivery systems (DDSs) for the prevention of sexual transmission of HIV and other STDs. A topically applied vaginal microbicidal gel should provide uniform coating of vaginal tissue, retention of this gel layer prior to intercourse, and controlled release kinetics of antivirals to inactivate the viral load potentially introduced during sexual activity. Here, we describe the microbicide-oriented characterization of a DDS made with a dual pH sensitive and thermosensitive smart polymer gel composed of a random terpolymer of N-isopropyl acrylamide, butyl methacrylate, and acrylic acid. The system was engineered to coat vaginal tissue with a stable gel layer and to release entrapped model agents in a burst release profile in response to the presence of the infecting agent: semen. The gel rheology, layer erosion properties, model drug release kinetics, and cytocompatibility of the terpolymer system were studied. Negligible erosion of the gel in the presence of vaginal fluid simulant suggests prolonged retention. Burst release of molecular and macromolecular model compounds was observed when the system's pH changed from the vaginal pH to the pH of semen, and cytotoxicity studies showed that the terpolymer is equally cytocompatible as a commonly used polymeric vaginal carrier.