Drug release kinetics of pH-responsive microgels of different glass-transition temperatures

The pH-responsive microgels (MGs) consisting of methacrylic acid-ethyl acrylate (MAA-EA), methacrylic acid-butyl methacrylate (MAA-BMA) or methacrylic acid-methyl methacrylate (MAA-MMA) crosslinked with di-allyl phthalate (DAP) were synthesized via emulsion polymerization. It was found that the energy required to extract a proton from MGs with higher glass-transition temperature (T-g) was greater than at a lower T-g. Procaine hydrochloride (PrHy) was used to study the release of a model hydrophobic drug from MGs with different T(g)s. A drug selective electrode (DSE) was used to monitor the release as a function of pHs and T(g)s. With increasing pH or decreasing T-g, the swelling of MGs was enhanced, leading to greater release of the drug. From the Berens and Hopfenberg model, the contributions of chain relaxation and diffusion processes during a release process were determined. The drug release from lower T-g MGs and at high pH is dominated by diffusion rather than chain relaxation. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47284.