Preparation and characterization of poly(ethylene glycol) hydrogels cross-linked by hydrolyzable polyrotaxane

PEG hydrogels cross-linked by a hydrolyzable polyrotaxane were prepared and their hydrolytic erosion characterized in terms of supramolecular dissociation of the polyrotaxane. The hydrolyzable polyrotaxane, in which many alpha-cyclodextrins (alpha-CDs) are threaded onto a poly(ethylene glycol) (PEG) chain capped with L-phenylalanine via ester linkages, was used as a multifunctional cross-linker: the PEG network was covalently bound to hydroxyl groups of alpha-CDs in the polyrotaxane. The contact angle and water content of the hydrogels were varied with the polyrotaxane content in the feed. In vitro hydrolysis study revealed that the time to reach complete gel erosion was shortened by increasing the polyrotaxane content in the feed in relation to the decreased number of chemical cross-links between PEG and alpha-CDs in the polyrotaxane. The hydrogel degradation in a physiological condition was found to be followed by bulk mechanism. These findings suggest that changing the preparative conditions such as polyrotaxane content will make it possible to control programmed gel erosion for tissue engineering.