Biaxially constrained drying strategy for fabricating strong and tough quasi-isotropic alginate hydrogels

The application of hydrogels in flexible electronics and strain sensors devices is severely constrained by their intrinsic mechanical weaknesses. Conventional uniaxial orientation strategies enhance strength along one direction but inevitably result in mechanical anisotropy within the plane, making them susceptible to failure under complex loads. This study presents a "Cooperative Ordered Arrangement" strategy to fabricate sodium alginate/polyacrylamide (SA/PAM) hydrogels with exceptional and uniform in-plane mechanical properties due to the alignment of SA parallel to the plane. The obtained hydrogel exhibits outstanding comprehensive properties with quasi-isotropic and uniformly reinforced in-plane performance. It delivers a tensile strength of 6.06 ± 0.15 MPa, a Young's modulus of 24.79 ± 0.86 MPa, a fracture toughness of 10.20 ± 0.55 MJ m^-3, and a fracture strain of 226.88 ± 10.71%, consistently achieved along all in-plane directions. Meanwhile, the hydrogel also shows direction-insensitive strain-sensing behavior, exhibiting a high conductivity of 81.18 ± 1.91mS m^-1 and nearly identical relative resistance change (ΔR/R₀) trend under deformation regardless of the loading directions. This work provides an efficient manufacturing strategy for developing high-performance hydrogels with uniform in-plane characteristics, demonstrating their significant potential for use in demanding mechanical and sensing applications.