New York: Plastic, heal thyself. In the latest efforts to design more resilient materials, scientists at UCLA have developed a transparent, yellowish plastic that mends its cracks when heated

Plastic is generally resilient, but when it breaks, it is hard to repair. Glue is often not as strong and a scar remains. Melting plastic to bond broken pieces together warps their space.

The new plastic is simple to fix. "If you break a piece of this plastic, you can put the two broken pieces together and warm it gently with a hair dryer, and it grows back together, literally," said Mr Fred Wudl, director of UCLA’s Exotic Materials Institute and leader of the research team.

The plastic, similar in texture and strength o epoxy resin, could be useful for electronic components where repeated heating and cooling can cause plastic to become battle and crack. "This stuff would be ideal," Mr Wudl said.

The material, which the researchers call Automend, is built of two small molecular building blocks that interlock with each other into a vast three-dimensional network. "They link up together to form one giant molecule," Mr Wudl said. Usually, a piece of metal or plastic breaks, the broken chemical bonds at the jagged edge quickly react with oxygen or other molecules in the air, and the surface is permanently altered.

With Automend, the two molecular building blocks are designed to bond easily only to each other. Holding the broken pieces next to each other and heating the plastic to about 250 degrees restores the chemical bonds to almost pristine condition with about 60 per cent of the strength of the original.

In tests where the plastic was partially cracked but not entirely broken in two, the heat repaired the crack, leaving no visible scars. That allows repairs to be made with-out glue. The heat also does not melt the plastic. Mr Wudl suggested the plastic could be used for large lenses where tiny wires embedded inside could be heated to fix cracks.

Mr Wudl and his collings in the current issue of the journal Science. "I think it’s pretty exciting," said Mr lames A. Moore, a professor of chemistry at the Rensselaer Polytechnic Institute in Troy. New York "You look at it and say, ‘Wow, why didn’t I think of that?"

A year ago, Mr Scott R. White, a professor of aeronautical and engineering at the University of Illinois, took a different approach to the problem, essentially embedding the repair materials within the plastic. "We get our inspiration from looking at biological systems," Mr White said.

When the plastic cracks, it breaks tiny capsules in the plastic, releasing a liquid healing agent, like blood flowing into a cut. The healing agent flows into contact with a catalyst, also embedded in the plastic, that causes it to solidify like a clot.

"That effectively bonds the crack closed." Mr White said. Unlike Automend, White’s plastic heals without heat, and it retains more of its strength. On the other hand, repeated cracking would eventually deplete the healing agent, and the material is more complicated to manufacture.

Mr White said he was developing composite materials with carbon or glass fibres running through the plastic- the type of material found in cellphones, computer circuit boards, tennis rackets and fibreglass boats.