Highly Mechanical Double Network Hydrogel By Dual Physically Hydrophobic Association And Ionic Crosslinking

Hydrogel is a three-dimensional network polymer containing a large amount of water.As a soft and wet material,hydrogel can be widely used in tissue engineering,cartilage repair,and wearable devices.However,the applications of traditional hydrogels were greatly limited by their weak mechanical property and poor recoverability.Although many strategies have been promised,the preparation of hydrogels with self-healing and excellent mechanical properties is still the most cutting-edge.Although traditional double-network hydrogels increase the mechanical properties of hydrogels,there are many limitations of hydrogels because of the two chemically cross-linked asymmetric networks.When the stress was applied to DN hydrogels,the first network acted as sacrificial bonds and dissipated energy effectively,the second network was used to retain the network elasticity and sustain larger stress.However,the conventional DN hydrogels suffered from internal network fracture and irreversible deformation,resulting in poor recoverability and fatigue resistance.In this investigation,we synthesized a double physically cross-linked networks hydrogel(HPAAm/Alginate-Ca²⁺DN hydrogel)demonstrating excellent mechanical properties,self-recovery,notch-insensitivity and fatigue resistance properties.HPAAm/Alginate-Ca²⁺DN hydrogels consist of hydrophobic association and ionic crosslinking.On the one hand,the hydrophobic micelles in polyacrylamide network were acted as crosslinking points.On the other hand,?-L-guluronic acids?G?residues of alginate could form ionic crosslinking with divalent metal ions Ca²⁺.We measured the mechanical properties,hysteresis energy properties and rheological properties of HPAAm hydrogels,HPAAm/Alginate hydrogels and HPAAm/Alginate-Ca²⁺DN hydrogels,in order to determine the toughening mechanism of the hydrogels.The internal structure of the hydrogel was also characterized by scanning electron microscopy.As a result,the HPAAm/Alginate-Ca²⁺DN hydrogel exhibits excellent mechanical properties with the fracture stress of 1.16 MPa?3.0 and 1.7 times higher than that of HPAAm hydrogel and HPAAm/Alginate hydrogel,respectively?,fracture strain of 2604%,elastic modulus of71.79 kPa,and toughness of 14.20 MJ m^-3.HPAAm/Alginate-Ca²⁺DN hydrogels also demonstrate self-recovery,notch-insensitivity and fatigue resistance properties without any external stimuli at room temperature through reversible physical bonds consisting of hydrophobic association and ionic crosslinking.