Scientists say they have created an "immune system" for composite materials that lets them repair themselves when damaged.

Tiny microcapsules repair cracks in the material as soon as they form and restore it to most of its original strength.

They can be used in a variety of applications ranging from microelectronics and biomedicine to aerospace, buildings and bridges.

"We have developed a material that behaves like the human body when it is damaged and hurt," Scott White of the University of Illinois at Urbana-Champaign said on Wednesday.

When a person is cut or bruised, this sets off a cascade of events in the body which send chemicals and healing agents to the injury to repair it.

"In these materials, wherever it is hurt there are tiny cracks, and those cracks actually break open a microcapsule that has the healing agent in it," White explained.

"The agent leaks out and fills these cracks, and there is a chemical reaction that hardens the healing agent and glues the crack closed."

Tiny cracks are the very beginnings of structural failure, so repairing them as soon as they occur will help the materials last longer.

Early tests, reported in the science journal Nature, show the self-repairing system restores the structure to 75 percent of its original strength.

"Filling the micro-cracks will also mitigate the harmful effects of environmentally assisted degradation such as moisture swelling and corrosion cracking," added White, a materials and aeronautical engineer.

　　MICRO AND MACRO

Although the microcapsules, which should be commercially available in three to five years, will be used initially in microelectronics, White and his colleagues said they could also be used in buildings, particularly in earthquake-prone areas.

If structural columns in buildings were made with the repair system, it could prevent the structure collapsing and give people more time to escape.

"Ideally, if you could achieve this sort of healing in a matter of a few seconds you could certainly buy time for people to exit, especially when you are talking about aftershocks," White added.

The hardest part of the project was determining the thickness of the shell for the healing agent. If the shell was too thick it would not break when a crack occurred, and if it was too thin it could be damaged during processing.

"This technology could increase the lifetime of structural components, perhaps by as much as two or three times," White said.

Richard Wool, of the University of Delaware, described the inbuilt healing material as ingenious.

"The concept of self-healing composites cuts against the grain of current material-design principles, but has far-reaching consequences for improving product safety and reliability," he said in a commentary in Nature.

The microcapsules could be particularly useful in components for satellites, rocket motors and prosthetic organs, or in space stations or bridges, Wool added.

(From ChinaDaily)