Active particles can form two-dimensional crystals that are different from those formed by passive particles in equilibrium, showing extreme spontaneous deformation at large scales without melting.

Depending on their fracture mode, materials are traditionally gathered into three distinct classes: (i) ductile materials that like metals deform plastically before their fracture (ii) quasi-brittle materials such as rock or concrete, where "non-visible" damage starts to accumulate through microcracking, up to coalescence that yields to catastrophic failure. (iii) brittle materials like oxide or polymer glasses... that deform elastically up to their fracture.