Evolution of Cyclodextrin Nanosponges

Cyclodextrin-based nanosponges (CD-NSs) are insoluble, highly cross-linked 3D network polymers used in several scientific and technological fields, the main area of investigation concerns the pharmaceutical applications, in which CD-NSs have been mostly employed as drug delivery systems. CD-NSs can be generally grouped into four consecutive generations, taking into account their chemical composition and properties. The 1st generation of NSs are plain nanosponges, subdivided into four main types: urethane, carbonate, ester and ether NSs, depending on the chemical nature of the functional group connecting the CD to the cross-linker. The 2nd generation of NSs are modified nanosponges characterized by specific properties, such as fluorescence and electric charge. The 3rd generation of NSs is represented by stimuli-responsive CD polymers, which are able to modulate their behavior according to external variations in the environment, such as pH and temperature gradients, oxidative/reducing conditions, and finally the 4th generation of NSs, a new family of molecularly imprinted CD polymers (MIPs), exhibiting a high selectivity towards specific molecules. The following review focuses on the evolution of cyclodextrin nanosponges, listing some examples of each generation.