Dual physically crosslinked double network hydrogels with high toughness and self-healing properties

Toughness and self-healing properties are desirable characteristics in engineered hydrogels used for many practical applications. However, it is still challenging to develop hydrogels exhibiting both of these attractive properties in a single material. In this work, we present the fabrication of fully physically-linked Agar/PAAc-Fe³⁺ DN gels. These hydrogels exhibited dual physical crosslinking through a hydrogen bonded crosslinked agar network firstly, and a physically linked PAAc-Fe³⁺ network via Fe³⁺ coordination interactions secondly. Due to this dual physical crosslinking, the fabricated Agar/PAAc-Fe³⁺ DN gels exhibited very favorable mechanical properties (tensile strength 320.7 kPa, work of extension 1520.2 kJ m^-3, elongation at break 1130%), fast self-recovery properties in Fe³⁺ solution (100% recovery within 30 min), in 50 °C conditions (100% recovery within 15 min), and under ambient conditions (100% recovery of the initial properties within 60 min), as well as impressive self-healing properties under ambient conditions. All of the data indicate that both the hydrogen bonds in the first network and the ionic coordination interactions in the second network act as reversible sacrificial bonds to dissipate energy, thus conferring high mechanical and recovery properties to the prepared Agar/PAAc-Fe³⁺ DN gels.