Stimuli-responsive microgels for the loading and release of functional compounds: Fundamental concepts and applications

Stimuli-responsive microgels represent a highly interesting and unique class of materials since they exhibit exceptional properties which stem from the particular combination of their colloidal nature with their internal network structure. While this fascinating characteristic feature has been exploited in various different research fields and applications, the essential commonality for the successful development of all those diverse materials is a precise design of the respective microgels to adjust their functionality to a specific application. Regarding the delivery of functional compounds in particular, one of the main tasks is to combine an efficient loading process with a well defined release profile. A basic requirement to achieve this goal is a profound understanding of the underlying concepts of these material's features and the impact of these basic models on the design and preparation of such highly functional materials exhibiting tailor-made properties. Therefore, in this review we present some of the important fundamental examinations on the influence of (tunable) network characteristics on loading and release profiles, basic synthetic concepts to realize these concepts and highlight several examples of different approaches to stimuli-responsive microgels for loading and release applications. By this, we wish to give the reader a broad overview of the design criteria and practical methodologies to control the functionality of microgels in order to encourage further development of highly interesting concepts and materials in this area of materials science.