Escape route: The laser‐initiated release of fluorescently labeled polymers from polyelectrolyte‐multilayer microcapsules is demonstrated inside living cancer cells. A polymer is incorporated in capsules with metal nanoparticles in their walls, which serve as light‐absorbing centers. The capsules are internalized by cells and near‐infrared light ruptures the walls of the capsules, thus releasing the content into the cells.

The Matryoshka theory: This unique type of shell‐in‐shell microcapsule facilitates the stable spatial separation of biopolymers (enzymes) within distinct compartments of a single capsule entity. Architecture and wall properties of this system allow for the concerted action of enzymes from separate capsule compartments by metabolite diffusion across a semipermeable, intersecting polyelectrolyte membrane.

In this paper we review the recent contributions of polyelectrolyte microcapsules in the biomedical field, comprising in vitro and in vivo drug delivery as well as their applications as biosensors

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We describe recent developments with multifunctional nanoengineered polymer capsules. In addition to their obvious use as a delivery system, multifunctional nanocontainers find wide application in enzymatic catalysis, controlled release, and directed drug delivery in medicine. The multifunctionality is provided by the following components: 1) Luminescent semiconductor nanocrystals (quantum dots) that facilitate imaging and identification of different capsules, 2) superparamagnetic nanoparticles that allow manipulation of the capsules in a magnetic field, 3) surface coatings, which target the capsules to desired cells, 4) metallic nanoparticles in the capsule wall that act as an absorbing antenna for electromagnetic fields and provide heat for controlled release, and 5) enzymes and pharmaceutical agents that allow specific reactions. The unique advantage of multifunctional microcapsules in comparison to other systems is that they can be simultaneously loaded/functionalized with the above components, allowing for the combination of their properties in a single object.