Designing pH-Responsive Biodegradable Polymer Coatings for Controlled Drug Release via Vapor-Based Route
We present the design of a novel pH-responsive drug release system that is achieved by solventless encapsulation of drugs within a microporous membrane using a thin capping layer of biodegradable polymethacrylic anhydride (PMAH) coating. The coating was synthesized via a mild vapor polymerization process, namely initiated chemical vapor deposition (iCVD), which allowed perfect retention of the anhydride groups during deposition. The synthesized polyanhydride underwent degradation upon exposure to aqueous buffers, resulting in soluble polymethacrylic acid (PMAA). The degradation behavior of PMAH is highly pH-dependent, and the degradation rate under pH 10 is 15 times faster than that under pH 1. The release profile of a model drug rifampicin clearly exhibited two stages: the initial stage that the coatings were being degraded but the drugs were well stored, and the second stage that drugs were gradually exposed to the medium and being released. The drug release also showed strong pH-responsiveness where the duration of the initial stage under pH 1 was more than 7 and 3 times longer than that of pH 10 and 7.4, respectively, and the release rates at pH 7.4 and 10 were significantly faster than that at pH 1. The pH-dependent degradation of encapsulant thus enabled good preservation of drugs under low pH environment, but high drug release efficiency under neutral and alkaline environment, suggesting potential applications in site-specific drug delivery systems.