A stiff and tough triple-shape memory hydrogel triggered at body temperature by hydrophobic association and electrostatic interaction

While triple-shape memory hydrogels (TSMHs) are considered promising materials for intelligent medical devices, obtaining TSMHs triggered at the human body temperature with adequate mechanical performance remains challenging. Herein, a stiff and tough TSMH with a wide glass transition temperature (Tg) range at approximately 36 °C is constructed by copolymerizing hydrophobic 2-aminoethyl methacrylate isopropyl carbamate (IMA) with zwitterionic sulfobetaine methacrylate (SBMA). While the introduction of SBMA into the poly(2-aminoethyl methacrylate isopropyl carbamate) (PIMA) polymer chain weakens the ultra-strong hydrophobic association, it causes an electrostatic interaction, which increases the flexibility of the copolymer chains and the cross-linking density of the network. Based on these structural characteristics, the poly(2-aminoethyl methacrylate isopropyl carbamate-co- sulfobetaine methacrylate) [P(IMA-co-SBMA)] hydrogels show reasonable triple shape memory effect with wide Tg ranging from 22 °C to 46 °C, Young's modulus from 2.82 MPa to 22.15 MPa, and fracture strain from 43 % to 444 %. This study provides a novel strategy for balancing the mechanical properties and Tg of TSMHs as materials for intelligent medical devices.