Design and construction of high strength double network hydrogel with flow-induced orientation

The design and construction of high strength hydrogels is a widely discussed topic in hydrogel research. In this study, we combined three toughening strategies, including dual network, oriented structure construction and nanophase doping, to develop an alginate/polyacrylamide (PAM)/modified titanium dioxide fiber (TiO₂ NF@PAM) dual network composite hydrogel prepared via syringe. The effects of different preparation methods, AM/Alginate ratios, inorganic doping phases and TiO₂ NF@PAM/AM ratios on the mechanical properties of composite hydrogels were investigated. The study found that the alginate hydrogel prepared by syringe exhibited superior axial orientation and achieved a tensile strength of (1091 ± 46) kPa. And the composite hydrogel doped with 0.2 wt% TiO₂ NF@PAM had a tensile strength of (1006 ± 64) kPa, which was higher than that of the composite hydrogel doped with 0.2 wt% TiO₂ nanoparticles (976 ± 66) kPa. The highest tensile strength (1120 ± 67) kPa and elongation at break (182 ± 8) % were achieved when the ratio of TiO₂ NF@PAM/AM was 0.6 wt%. The force applied to the gel solution in the syringe affects the orientation of the polymer chains and TiO₂ NF@PAM within the gel, which subsequently impacts the mechanical properties of the hydrogel. Therefore, we further investigated the mechanical properties of composite hydrogels under varying propulsion speeds, syringe diameters, and syringe lengths. It was observed that the gel solution's shear strength increased as the syringe diameter decreased. The resulting composite hydrogels were better oriented and had improved mechanical properties. The composite hydrogels' tensile strength peaked at (1117 ± 47) kPa when the syringe advance rate was between 1-7 mL/min. The mechanical properties of the hydrogels were optimal when the syringe length was 30 mm, with a maximum tensile strength of (1131 ± 67) kPa and a tensile ratio of (166 ± 5) %. This study demonstrates the viability of integrating three distinct strengthening methodologies to generate hydrogels of considerable strength. Furthermore, the Alginate/PAM/TiO₂ NF@PAM composite hydrogels possess remarkable potential as adaptable, wearable sensors due to their exemplary mechanical properties, knittability, and conductivity.