Supramolecular hydrogels formed by beta-cyclodextrin self-association and host-guest inclusion complexes

Supramolecular hydrogels are highly interesting for drug delivery and tissue engineering applications, especially those systems that display a combination of tunable properties, high mechanical strength and easy preparation from well-available and biocompatible building blocks. In the present paper, we show that the combination of free beta-cyclodextrin (beta CD) and 8-arm or linear cholesterol-derivatized poly(ethylene glycol) (PEG-chol) in aqueous solution resulted in the formation of almost fully elastic gels with storage moduli in the range of 10-500 kPa. X-Ray diffraction measurements demonstrated the presence of crystalline beta CD domains in the hydrogel networks. Rheological experiments further proved that hydrogel formation is based on inclusion complex formation between these beta CD clusters and cholesterol coupled to the terminal end of PEG. The observation that the gels were weakened by addition of the competitive beta CD-guest molecule adamantanecarboxylic acid (ACA) supported the proposed gelation mechanism. The gel mechanical properties were dependent on temperature, concentration of cholesterol-derivatized PEG and/or beta CD, PEG's molecular weight and its architecture. This hydrogel system can be considered as an excellent candidate for future applications in the biomedical and pharmaceutical fields.