  The full 2D analysis of roughness profiles of fracture surfaces resulting
from quasi-static crack propagation in gelatin gels reveals an original
behavior characterized by (i) strong anisotropy with maximum roughness at
$V$-independent symmetry-preserving angles, (ii) a sub-critical instability
leading, below a critical velocity, to a cross-hatched regime due to straight
macrosteps drifting at the same magic angles and nucleated on crack-pinning
network inhomogeneities. Step height values are determined by the width of the
strain-hardened zone, governed by the elastic crack blunting characteristic of
soft solids with breaking stresses much larger that low strain moduli.
