Materials That Fix Themselves

Nature already solved damage. Engineers are copying its answers:

• Skin sparked the idea: automatic wound healing showed it was possible.
• Microcapsules: hidden glue pockets burst at a crack and seal it.
• Bacteria: dormant microbes wake on contact with water and grow limestone in concrete.
• Bone: composites that bulk up where stress is highest.
• Vascular channels: built-in 'veins' carry repair fluid to the wound.