In this work, we developed a simple, novel method for constructing gold nanocomposite supramolecular hybrid hydrogels for drug delivery, in which gold nanocrystals were utilized as building blocks. First, methoxypoly(ethylene glycol) thiol (mPEG-SH, molecular weight (MW)=5 K) capped gold nanocrystals (nanospheres and nanorods) were prepared via a facile one-step ligand-exchange procedure. Then, the homogeneous supramolecular hybrid hydrogels were formed, after adding α-cyclodextrin (α-CD) into PEG-modified gold nanocrystal solutions, due to the host-guest inclusion. Both gold nanoparticles and inclusion complexes formed between α-CD and PEG chain provided the supra-cross-links, which are beneficial to the gelation formation. The resulting hybrid hydrogels were fully characterized by a combination of techniques including X-ray diffraction, rheology studies, and scanning electron microscopy. Meanwhile, the hybrid hydrogel systems demonstrated unique reversible gel-sol transition properties at a certain temperature caused by the temperature-responsive reversible supramolecular assembly. The drug delivery applications of such hybrid hydrogels were further investigated in which doxorubicin was selected as a model drug for in vitro release, cytotoxicity, and intracellular release studies. We believe that the development of such hybrid hydrogels will provide new and therapeutically useful means for medical applications.

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Taking advantage of the strong hydrophobicity of the anticancer drug camptothecin (CPT), the CPT molecule was conjugated to a class of low-molecular-weight (MW) poly(ethylene glycol) (PEG) chains (MW = 500, 1000, and 2000), forming an amphiphilic prodrug. The CPT-PEG prodrug formed stable hydrogels based on a combination of the partial inclusion complexation between one end of the PEG blocks and α-CD and the hydrophobic aggregation of CPT groups. Meanwhile, the formed hydrogels could be loaded with water-soluble drug 5-fluorouracil (5-FU), which is always combined with CPT drugs to enhance their anticancer activity. Moreover, the hydrogel systems demonstrate unique structure-related reversible gel-sol transition properties at a certain temperature due to the reversible supramolecular assembly, and the gel-sol transition temperature could be modulated by varying the length of the PEG chain and the concentrations of α-CD, demonstrating the possibility of achieving on-demand gel-sol transitions. The structure-related reversible gel-sol transition properties were proved by rheological property, XRD, DSC, and SEM measurements. The different controlled release profiles of two different anticancer drugs showed significant temperature-dependent properties. This easily prepared supramolecular hydrogel with excellent biocompatibility and tunable temperature responsiveness has significant potential for controlled drug release applications.