Microcapsules possessing a selective permeability are well-suited vessels for conducting cell studies or chemical reactions that require selective exchanges of reagents over a prolonged time. Most currently reported microcapsules are single-use delivery carriers since cargo is only released in significant amounts if their shells are damaged or the release relies on passive diffusion. Stable capsules possessing a selective, rapidly interchangeable permeability, which enables their repeated loading and unloading with selected reagents remain to be shown. Here, capsules are introduced that are composed of thin, viscoelastic, charge-selective shells made of surfactants that are functionalized with a chelator, 3-hydroxy-4-pyridinonone and crosslinked with appropriate nm-sized ion clusters, for example composed of Fe3+/Tris or Al3+/Tris ion clusters. The charge selectivity of the shell permeability can be conveniently tuned with the crosslinking ion clusters. It is demonstrated that these capsules can be repeatedly loaded and unloaded with well-defined substances. This feature enables their application as re-usable selectively permeable filters to remove certain pollutants from solutions. These capsules are envisaged to be well-suited for waste water treatment and as picoliter-sized reaction vessels to selectively conduct chemical reactions within capsule cores while continuously supplying new reagents.

The charge-selective permeability and the functionality of viscoelastic microcapsule shells can be tuned with the choice of ion/Tris clusters/nanoparticles used to crosslink 3-hydrox-4-pyridinone (HOPO)-functionalized surfactants.image