Hydrophilic and hydrophobic payloads can be encapsulated in polymer shell either in processes involving a polymerization in emulsion or a polymerization [1] and then an emulsification of the synthesized polymer [2]. Furthermore, polymer capsules with a very large combination of core and shell can be produced [3]. Very well-defined inorganic shells such as silica can be also synthesized in dispersed phase instead of a polymer shell [4]. The payloads that can be encapsulated are drugs, fertilizers, enzymes, nucleotides, monomers, catalysts, initiators, solvents, inorganic nanoparticles, and corrosion inhibitors. We have shown recently that the use of osmotic pressure by the co-encapsulation of simple salts is an inexpensive and efficient way to control the release profile of encapsulated payloads [5] (Figure 1).

Figure 1. Schematic illustration of the release of the dye from nanocapsules induced by osmotic pressure. Left: The osmotic pressure between the inner core and the release medium is equalized with the flux of water through the shell. Middle: Swelling of nanocapsules leads to an increase in the dye and the salt release. Right: Payload release results in a decrease of the osmotic pressure inside the core and the subsequent deswelling of nanocapsules. From reference [5].

The polymer or the inorganic shell can be synthesized to display stimuli-responsive properties. These properties can be used to control the permeability of payloads through the shell. Thus, the release of self-healing agents and corrosion inhibitors could be triggered by oxidation and reduction [3-4], the addition of carbon dioxide [5], or a change in the pH value of the surrounding medium [6]. The control over release profiles can be reinforced by combining the stimuli that can be applied to the nanocontainers. Hence, different payloads encapsulated in the same nanocontainers could be selectively released upon reduction or change of pH value [7]. Finally, a cascade release was achieved by synthesizing polymer shell with cleavable side-chains that can liberate a drug or a corrosion inhibitor upon chemical reduction (Figure 2). The first release can induce a second release of another payload that is entrapped in the core of the nanocontainers [8-9]. The syntheses are performed in mild conditions and therefore the capsules can be used for biomedical applications either for imaging [10] or for the delivery of drugs [11].



Figure 2. Schematics showing the cascade release of a corrosion inhibitor followed by the release of a dye from a nanocontainer. In a first step, the corrosion inhibitor that is initially encoded in the chemical structure of the polymer forming the shell of the nanocontainer is released upon a redox-stimulus. In a second step, the shell is disrupted and therefore the dye entrapped in the core of the nanocontainers is also released. From reference [9]. The concept is general and can be applied to any payloads and for a wide variety of chemistry.