Injectable and thermosensitive poly(2-ethyl-2-oxazoline)-poly(L-alanine) hydrogel with enhanced mechanical...

Thermosensitive hydrogels derived from thermogelling polymers have garnered growing interest as injectable biomaterials. However, conventional thermosensitive hydrogels often suffer from inadequate mechanical robustness and limited in vivo persistence. To address these issues, a series of amphiphilic poly(2-ethyl-2-oxazoline)-poly(L-alanine) (PEOz-PAla) copolymers are synthesized, and an injectable thermosensitive hydrogel based on thermogelling PEOz-PAla polymers is developed. By controlling the PEOz/PAla block ratio and polymer concentration, the sol-gel transition temperature and mechanical strength of the resulting hydrogel can be conveniently regulated. Multi-technique analyses indicate that the gelation mechanism involves thermally induced micelle aggregation, while the PAla domains possess pre-existing β-sheet-rich structures that substantially boost the hydrogel's mechanical performance. UV irradiation effectively sterilizes the PEOz-PAla powder, and pre-filled hydrogels display good storage stability at ambient temperature for more than three months. Non-invasive fluorescence imaging combined with traditional anatomical observation reveals that the PEOz-PAla hydrogel degrades stably and gradually at the subcutaneous injection site over 100 days, with biocompatibility confirmed by in vitro cytocompatibility and in vivo histological assessments. Furthermore, real-time fluorescence tracking verifies the sustained release of encapsulated macromolecular drugs for over 35 days. These results establish the PEOz-PAla hydrogel as a promising platform for sustained drug delivery and tissue engineering applications. STATEMENT OF SIGNIFICANCE: In this study, we developed a new thermosensitive and injectable hydrogel using rationally engineered poly(2-ethyl-2-oxazoline)-poly(L-alanine) (PEOz-PAla) copolymers. Compared with previously reported thermosensitive hydrogels, this hydrogel system simultaneously achieves enhanced mechanical properties and prolonged in vivo retention (> 100 days). Meanwhile, by systematically tuning the block lengths of PEOz and PAla, as well as the polymer concentration, a structure-property relationship is also established for thermogelling PEOz-PAla copolymers. Overall, this study introduces a design strategy for the development of new thermogelling polymers.