Temperature- and pH-controlled hydrogelation of poly(ethylene glycol)-grafted hyaluronic acid by inclusion complexation with α-cyclodextrin

A series of poly(ethylene glycol) (PEG)-grafted hyaluronic acid (HA) was prepared by condensation reaction with hydrazide-terminated PEG using water soluble carbodiimide. PEG-grafted HA (PgH) solutions exhibited hydrogelation on adding alpha-cyclodextrin (alpha-CD). The solid-state C-13 CP/MAS NMR spectroscopic and powder X-Ray diffraction measurements revealed the formation of inclusion complex between the PEG grafts and alpha-CD. The gel-melting temperature increased with increasing the degree of substitution of the PEG grafts and decreasing pH of aqueous medium. These results indicate that PgH hydrogels were constructed by inclusion complexation between the PEG grafts and alpha-CD, and the gel-melting temperature could be controlled by both the degree of substitution of the PEG grafts and pH.