Systems for stimuli-controlled release: Materials and applications

The design and development of delivery controlled systems of molecules of interest has attracted great interest over the last years. pH variation, light irradiation, temperature increasing, variation of the redox potential and the application of a magnetic field are among the most widely used stimuli that can be used to induce the release of an active molecule in a medium. The dominance of pH and photo-controlled release is clearly highlighted by the numerous articles published in these fields as well as all the related applications. In the case of pH-controlled release, two main parameters govern the release: the solubility of the active molecule in the releasing medium and the stability of the carrier materials. In the photo-controlled release, the carrier needs to contain a photo-sensible functionality; this stimulus can be successfully applied in the medical field when red light, that is able to penetrate the human tissues, is used. A large panel of applications of controlled release can be identified in the pharmaceuticals, agriculture, cosmetics, chemistry and dyes industry fields. More recently, biological, enzymatic, and mechanical (ultrasounds, stretching, shear stress) stimuli have been developed for target applications, in particular for drugs and hormones release. Consequently, many types of materials (polymers, silica, oxides, MOF...) can be used as carrier in relation to their compatibility with the active molecule and the type of releasing medium. This review aims to gives a useful overview on the materials, applications and mechanisms implied in stimuli-controlled release.