Peptide-Crosslinked, Highly Entangled Hydrogels with Excellent Mechanical Properties but Ultra-Low Solid Content

Low solid content is the ultimate reason for the brittleness and weakness of ordinary hydrogels. Here, hydrogels with ultra-low solid content but good mechanical properties are successfully synthesized using high monomer concentrations and low cross-linker/monomer ratios to obtain highly entangled structure and poly(l-lysine)-based cross-linker to introduce peptide chains. Compared with hydrogel cross-linked with N,N'-methylenebisacrylamide (BIS), the peptide-crosslinked one has a larger swelling degree in water, leading to fully swollen gel with ultra-low solid content (5.8%). However, it still exhibits excellent mechanical properties, including high stretchability (440%), high tensile strength (220 KPa), superb resilience (99%), high fracture toughness (2100 J m^-2 ), excellent fatigue resistance (720 J m^-2 ), low friction (0.0059), and high wear resistance. These properties are comparable to or even better than the BIS-crosslinked hydrogel, although the former has much lower solid content. The excellent mechanical properties of the peptide-crosslinked gel are attributed to its highly entangled structure and also to the introduction of a novel mechanism for energy dissipation, that is, energy dissipation via breakage of intramolecular hydrogen bonds stabilizing the helical structure of the peptide.