Supramolecular assembly of tetronic-adamantane and poly(β-cyclodextrin) as injectable shear-thinning hydrogels

Injectable biomaterials have been widely utilized for biomedical applications because their implantation into the human body is minimally invasive and the therapeutic agents can be delivered locally. Shear-thinning hydrogels are notable because of their unique properties, whereby the viscosity decreases (solution) under shear stress and recovers (gel) after the removal of the shear stress. However, as most shear-thinning hydrogels are formed by physical crosslinking, their mechanical properties are often poor. To overcome this issue, additional secondary cross-linkages, via UV-crosslinking, thiol-ene reactions, and oxidative crosslinking, are usually applied. In this study, we developed a new shear-thinning hydrogel with improved mechanical strength, through host-guest interactions and thermo-gelling at 37 1C. Tetronic-adamantane (Tet-Ada) and b-cyclodextrin polymers (poly[ b-CD]), which can dissolve in aqueous environments, were successfully synthesized. The chemical structures of the synthesized polymers were confirmed by proton nuclear magnetic resonance spectroscopy. The hydrogels rapidly started to form, via host-guest interactions between Ada and b-CD and self-assembly of the Tet micelles at 37 1C. The elastic modulus of the hydrogels was assessed by varying both the concentrations of the polymers and the temperature. Importantly, the Tet-Ada/poly(b-CD) hydrogels showed shear-thinning behaviors, rapid recovery properties, pH-responsive properties, and long-term release of the hydrophobic drug, doxorubicin (DOX). In addition, we demonstrated the biocompatibility of the hydrogels and the anticancer effect of DOX released from the hydrogels. In conclusion, we suggest the potential usage of the Tet-Ada/poly(b-CD) hydrogels as injectable materials for various biomedical applications, including drug delivery systems.