Preparation and properties investigation on a kind of pseudopolyrotaxane hydrogel with high intensity

As an important member of supramolecular hydrogel, pseudopolyrotaxane (PPR) hydrogel has attracted tremendous attention in recent years due to its good biocompatibility. Compared with conventional approaches reported, a new method was developed for PPR hydrogel preparation in this study, which can increase the strength of the hydrogel more efficiently. First, monoaccharide group-functionalized methoxypolyethylene glycols (MPEG) (MPEG-Glc, MPEG-Man and MPEG-Gal) were synthesized by click chemistry. After that, a series of PPR hydrogels (Glc-PPR, Man-PPR and Gal-PPR) with high stability and strength were successfully prepared via the "host-guest" interactions between -CD and monoaccharide group-functionalized MPEG (MPEG-Glc, MPEG-Man and MPEG-Gal, respectively). However, similar hydrogel cannot be obtained using -CD and MPEG without monoaccharide modification. The properties of Glc-PPR, Man-PPR and Gal-PPR were characterized by rheometer test, X-ray diffraction (XRD) and scan electron microscopy (SEM). Surprisingly, rheometer test results indicated that the elasticity modulus of Glc-PPR, Man-PPR and Gal-PPR could be up to 1.0 × 10⁵ Pa, which was much higher than that of the clay-enhanced hydrogel in the previous reports. As for this phenomenon, we propose that new sugar cross-linking agents from "carbohydrate-carbohydate interaction" have constructed among monoaccharide terminals of MPEG, so that the strength of Glc-PPR, Man-PPR and Gal-PPR could be improved efficiently. Furthermore, in order to demonstrate the mechanism of the strength enhancement of PPR hydrogel, phenylboronic acid cyclic monoester (PNIPAM-co-PBOB) and concanavalin A (Con A) were added into Glc-PPR, Man-PPR and Gal-PPR, respectively to eliminate the sugar cross-linking agents, which led to a significant decrease in the strength of Glc-PPR, Man-PPR and Gal-PPR. SEM and XRD results showed that the microstructures of Glc-PPR, Man-PPR and Gal-PPR were basically identical with PPR hydrogel reported in the references, which further confirmed that the PPR hydrogel was prepared successfully. Given its many merits of high intensity, non-toxicity and excellent biocompatibility of the obtained PPR hydrogel, it is expected that the PPR as prepared here will play an important role in drug delivery and biomedical engineering.