Strong Tough Hydrogel with Regional Programmable Mechanical Properties via Universal Physical Directional Anneal‐Casting Strategy for Bioengineering

Engineering tissue‐like hydrogels with tailored mechanical properties and matching water contents is essential for biomimetic organ platforms in both ex vivo and in vivo biomedical applications. Achieving this goal is particularly challenging due to the need for a green, straightforward, and universally applicable approach to mimic various tissues with specific hydrogels. Herein, a universal physical one‐step directional anneal‐casting strategy for anisotropic water evaporation is presented to produce hierarchical anisotropic poly(vinyl alcohol) hydrogel with tunable Young's modulus (≈0.13–77.2 MPa) in a wide range. As a typical example, the ultimate stress, toughness, fracture energy, and fatigue threshold of strong tough poly(vinyl alcohol) hydrogels can be up to 31.8 MPa, 45.7 MJ m −3 , 568.6 kJ m −2 , and 407.8 J m −2 at ≈208% strain with controllable water content (≈20–80%) without compromising their toughness. Integral to our approach is the capability for localized control of mechanical properties within the same hydrogel unit, allowing for distinct functional characteristics in different regions of the hydrogel. Furthermore, the versatility of our strategy extends to various other hydrogel systems, such as polyacrylamide and alginate, broadening its applicability in the fields of bioelectronics and biomedical engineering, including the development of physiological signal acquisition devices and artificial implantable electronic ligaments.