Low modulus ultra-ductility ionic skin by highly entangled PAM-co-UPyMA hydrogel

•Highly entangled dynamic non-covalent bonds PAU ionic skin was constructed.•The extremely stretchable PAU ionic skin achieves the GF value as high as 16.14.•PAU sensor undergoes a significant change in the size of the cross-linking domain.•Microstructure change upon stretching is beneficial to improve the sensitivity. This work primarily discusses the construction of physically cross-linked polyacrylamide copolymer containing 2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate (PAM-co-UPyMA, short for PAU) hydrogels with topological entanglement by designing high concentrations of acrylamide (AM) monomers and introducing “bridging” flexible non-covalent bonds. This method overcomes the poor stretchable performance of chemically cross-linked hydrogels, as well as the limited improvement in mechanical properties due to the low dissipation energy of physically cross-linked hydrogel (non-covalent bonding) under an external force. This new hydrogel exhibits low modulus (0.12 MPa), a certain fracture strength (0.2 MPa), and high toughness with an elongation at a break of 5700 %, demonstrating excellent tensile strain sensitivity with a gauge factor (GF) of 16.14, capable of detecting tiny deformations of 0.2 %. It also exhibits fast strain response, long-term stability, and performs well in applications such as human joints and voice monitoring. Furthermore, this work elucidates the relationship between the microstructure of PAU hydrogels and sensing performance, proving that the rate of microstructure change serves as an essential mechanism. The less cross-linked and highly entangled PAU hydrogel strain sensor increases the cross-linked domain size under tensile load, leading to ion channel blockade with a rapid increase in resistance during deformation, thus resulting in an improved sensitivity.