Covalently cross-linked amphiphilic block copolymer micelles

Polymeric micelles constitute an important class of nanomaterials that are highly attractive for pharmaceutical applications. The hydrophobic core of the micelles can be loaded with poorly water soluble drugs, while the shell of the micelles provides colloidal stability in vitro and in vivo. In recent years, covalent cross-linking of micelles is attracting increasing attention, because in vitro data show that it can prevent the self-assembled micelles from dissociation, can modulate drug release and may provide tools for triggered release. This paper reviews the methods used to cross-link either the core or the shell of the micelles, and focuses on drug delivery applications of cross-linked micelles. Whereas non-cross-linked micelles generally do not improve pharmacokinetics of encapsulated drugs when compared to common drug formulations, recent in vivo data show that cross-linking provides dramatic improvements in both pharmacokinetics and biodistribution of the micelles, and that drugs can fully benefit from that when they are covalently linked to the micelles. Although the field is still in its infancy, the latest results promise a bright future of cross-linked micelles for drug delivery and/or diagnostic applications.