Takayuki Narita, Saga University, Japan, and colleagues have developed membranous polymer microcapsules that expand and contract, or self-pulse, under certain conditions, such as change in pH. Such capsules might be loaded with a pharmaceutical agent and portions released at regular intervals by the pulsing behavior as it opens up the “membrane” of the capsule and allows material to diffuse out from within the capsule.

Previous pulsing systems have been based only on the likes of the Belousov–Zhabotinsky reaction which utilizes toxic ingredients and so would be inappropriate for a drug-delivery system. Narita’s team made their microcapsules from poly(L-lysine-alt-terephthalic acid), PPL, and demonstrated dramatic volume changes in the structure accompanied by similarly dramatic permeability changes as the capsules oscillate from one form to the other.

• Self-Pulsation Observed in pH-Sensitive Microcapsules,
  Takayuki Narita, Hirokazu Takakura, Naoko Ogata, Hidetaka Kawakita, Yushi Oishi,
  Chem. Commun. 2012.
  DOI: 10.1039/C2CC36026H