1. Langer, R. New methods of drug delivery. Science 249, 1527–1533 (1990).
2. Ishihara, K., Muramoto, N. & Shinohara, I. Controlled release of organic substances using polymer membrane with responsive function for amino compounds. J. Appl. Polym. Sci. 29, 211–217 (1984).
3. Thomas, J. L., You, H. & Tirrel, D. A. Tuning the response of a pH-sensitive membrane switch. J. Am. Chem. Soc. 117, 2949–2950 (1995).
4. Kwon, I. C., Bae, Y. H. & Kim, S. W. Electrically erodible polymer gel for controlled release of drugs. Nature 354, 291–293 (1991).
5. Bae, Y. H., Okano, T., Hsu, R. & Kim, S. W. Thermo-sensitive polymers as on-off switches for drug release. Makromol. Chem. Rapid Commun. 8, 481–485 (1987).