Biomimicry: Self Healing Materials

 The development of self-healing materials has surged forward as scientists have taken inspiration from biological systems. Researchers at the University of Illinois in the US have found a way to pump healing fluids around a material like the circulation of animal's blood. Materials that could repair themselves as they crack would have uses in civil engineering and construction.


Different approaches have been taken to creating such materials, depending on the kind of material that needs to be repaired: metals, plastics, or carbon composites. These methods include creating materials which have micro-capsules containing a healing agent embedded within them, which are broken open when the material is damaged, releasing the healing fluid that hardens and fills the crack. While effective, this method and others are limited by the small amount of healing agent that can be contained within the material without weakening it.
New developments in self-healing technology have come along involving the impregnation of plastics with a fine network of channels, each less than 100 millionths of a metre in diameter, that can be filled with liquid resins. These "micro-vascular" networks penetrate the material like an animal's circulation system, supplying healing agent to all areas, ready to be released whenever and wherever a crack appears.
Limitations still blight this technology however, as the healing process relies on the slow wicking action and diffusion of the healing agent into a crack. The researchers have therefore taken another lesson from biology to improve on the self-healing material's performance. 
"In a biological system, fluids are pumping and flowing," said Prof Sottos, so they have devised a way to actively pump fluids into their micro-vascular networks.
Syringes on the outside of the material put healing fluids under pressure so that when a crack appears, a constant pressure drives the fluid into the cracks.
In the experiments that Prof Sottos' team carried out, two parallel channels are created in a plastic and pumped with a liquid resin and a hardening chemical that triggers the resin to solidify. The micro-vascular healing system is inspired by the circulation of blood in animals.

The researchers experimented with pumping the liquids in pulses so that first the resin was pushed into the crack, and then the hardener, in repeating cycles.This, they found, was the most efficient way of filling large cracks and ensuring the widest spread of the healing agents.


"Micro-capsule technology will enable damaged openings around 50-100 [millionths of a metre] to be filled, whereas pumping healing agents through a micro-vascular network can fill major cracks up to a millimetre across," said Prof Sottos.