Dual thermoresponsive mPEG-b-poly(O-benzyl-l-threonine acid) hydrogel based on β-sheet nano-structural disassembly and PEG dehydration

It is a challenging work to design novel responsive materials by controlling the secondary structure of polypeptide , especially β-sheet. We designed and synthesized a novel dual responsive diblock copolymer of methyl poly (ethylene glycol)- b -poly (O-benzyl- l -threonine) (mPEG- b -PBnLT). The copolymer solutions exhibited unusual and reversible gel-to-sol-to-gel transition behavior with temperature, and the transition temperature window could be easily adjusted by changing copolymer concentration or PBnLT block length . It was confirmed that low temperature gel-to-sol transition was due to the disassembly of the preliminary β-sheet layered nano-assemblies that induced the transformation of self-organized morphology from nanosized fibrils to spherical aggregates, while the high temperature sol-to-gel transition was ascribed to the dehydration of PEG segments. The disassembly of β-sheet structures was caused by the change in the polarity of the pendant benzyl ether bond of PBnLT block in water with temperature. This stimuli-responsiveness of secondary self-assembled nanostructures and the corresponding change in macroscopic phase transition inspires a brand-new strategy for structural design and functional control of polypeptide materials.