Stimuli-induced gel-sol transition of supramolecular hydrogels based on β-cyclodextrin polymer/ferrocene-containing triblock copolymer inclusion complexes

A novel kind of host-guest hydrogel possessing gel-sol phase transformation in response to temperature, oxidizing agent and glucose was prepared by ferrocene (Fc)-containing pluronic F127 and β-cyclodextrin (β-CD) linear polymer, which was synthesized in aqueous alkali by using native β-CD and epichlorohydrin in the presence of toluene. Because of the reversible association-dissociation of Fc-β-CD inclusions and F127 micelles, the gel-sol transition was easily observed. Two-dimension nuclear overhauser effect spectroscopy (2D NOESY), nuclear magnetic resonance (NMR), TEM (transmission electron microscopy) and TGA (thermogravimetric analysis) measurements were used to clarify the inclusion complexes of Fc-β-CD. The results showed that the formation of inclusion complexes affected the micelle size and stabilized the hydrogels. The rheological properties of solution and hydrogels were measured. The viscosity of hydrogel was enhanced markedly, to about 90 times higher than that of Fc-F127-Fc solution at the same concentration. Due to the coactions of PPO aggregation and Fc-β-CD inclusion, the gelation temperature of hydrogel was lower than that of Fc-F127-Fc solution. The reversible gel-sol transition and multi-sensitive supramolecular hydrogels may potentially be used in injectable hydrogel for drug delivery.