  Tough adhesive hydrogels find broad applications in engineering and medicine.
Such hydrogels feature high resistance against both cohesion and adhesion
failure. The superior fracture properties may, however, deteriorate when the
hydrogels swell upon exposure of water. The underlying correlation between the
polymer fraction and fracture properties of tough adhesive hydrogels remains
largely unexplored. Here we study how the cohesion and adhesion energies of a
tough adhesive hydrogel evolve with the swelling process. The results reveal a
similar scaling law of the two quantities on the polymer fraction. Our scaling
analysis and computational study reveal that it stems from the scaling of shear
modulus. The study will promote the investigation of scaling of hydrogel
fracture and provide development guidelines for new tough adhesive hydrogels.
