Thiolated cyclodextrins: New perspectives for old excipients

•Thiolated cyclodextrins (CDS) are obtained by covalent attachment of thiol groups.•Inclusion complexes formed with thiolated CDs enhance drug solubility.•Thiolated CDs are mucoadhesive due to disulfide bond formation with mucus.•Thiolated CDs have in-situ gelling and permeation enhancing properties.•These unique properties make thiolated CDs a useful tool for drug delivery systems. Thiolated cyclodextrins (CDs) are obtained by covalent attachment of thiol moieties on the oligomeric backbone of different types of CDs. First, thiolated CDs were introduced in the field of drug delivery as mucoadhesive oligomers forming disulfide bonds with cysteine-rich substructures of mucus glycoproteins providing a prolonged mucosal residence time. In the following, their in-situ gelling and permeation enhancing properties were shown. Furthermore, inclusion complexes formed with thiolated CDs can enhance drug solubility and provide a sustained release. These in combination unique properties make thiolated CDs a useful tool for different drug delivery systems and regenerative medicine. Within this review article, an overview of the synthesis of thiolated CDs and their key properties is provided. Moreover, the potential of thiolated CDs for different applications in drug delivery is shown.