Polymers with Tunable Rigidity Enable Thermal Stiffening Peptide Hydrogels and Ultra‐Tough Polyvinyl Alcohol Membranes

Rigidity is a fundamental attribute of linear polymers that determines their functions and applications, and the modulation of polymer rigidity is thus attractive. However, tuning the rigidity of polymers after their formation without changing their chemical composition is challenging. Herein, pH-responsive rigid homodimeric peptide coiled-coils are used as transformable linkers to polymerize with rigid peptide bundles to yield rigid polymers, which can transform into a distinct semi-flexible state upon the in situ unfolding of rigid dimeric linkers into flexible monomeric chains. The resultant semi-flexible polymers exhibit unique thermally driven self-crosslinking capabilities, enabling the spontaneous hydrogelation of highly concentrated polymer solutions. Elevated temperatures accelerate the gelation kinetics and enhance the hydrogel stiffness, demonstrating a rare thermal stiffening phenomenon in the peptide hydrogel. Additionally, semi-flexible polymers promote cell proliferation and migration at certain concentrations. The thermally self-crosslinkable semi-flexible polymers can ideally synergize with thermoresponsive polyvinyl alcohol (PVA), facilitating the facile fabrication of a robust PVA membrane with an ultrahigh toughness of 303.6 MJ m^-3 and enhancing swelling resistance. Peptide-based semi-flexible polymers may offer a universal, effective, and biocompatible toughening strategy for biomedical applications.