If the aircraft you're traveling in suddenly experiences some kind of damage while in mid flight, you're pretty much toast. Still, air travel is one of the safest means to get around. In theory airplanes could become even safer if they were built out of materials that regenerate themselves even while in flight, similar to the healing process of animal tissue in nature. A missed crack during inspection could be easily repaired as resin flows from tubes embedded in the material. Not only that, but these materials could make the vehicle lighter, allowing it to become more fuel efficient.

"At oil approaching $130 a barrel, if you can strip weight off, you could save money", said researcher Ian Bond from the University of Bristol. A great deal of money is also used for damage resistant materials, since the day-to-day use of the aircraft is sure to produce some kind of damage at some point in time.

"You would be surprised how often trucks drive into aircraft when parked at airports. And then you have tools dropped on planes at maintenance hangers, or hailstones when flying through storms. Very subtle damage, little dings and cracks and bangs that, if left undetected, could grow into something serious. At aircraft hangers, a lot of time is spent trying to find these defects", said Bond.

"The idea is that you'd want what structure you'd have left after damage to be able to sustain all the loads you'd be likely to see. This ends up adding weight, which as you can imagine is at a premium with aircraft. Self-repairing materials would definitely help with safety, and by not worrying as much about damage, there could be huge savings in weight. The human body repairs itself all the time, sometimes after quite severe damage. Why can't we make structures do the same sort of thing?", Bond added.

The basic concept involves a material containing a set of hollow fibers filled with resin and hardener. For example, when a crack appears, the fiber would break and start bleeding resin, which would seal the crack and prevent it from further widening. The repaired structure could retain as much as 80 to 90 percent of the original strength, allowing the airplane to function properly without causing any worries.

Furthermore, the resin could be mixed with a dye so that later inspection would show the damage sustained by the respective part and how it managed to heal itself. "It would complement rather than replace conventional inspection and maintenance routines, which can readily pick up larger-scale damage, caused by a bird strike, for example", Bond said.

An alternative to the self repairing method thought up by Bond would take out the use of individual resin containing fiber in favor of a system circulating resin through a network of fibers, similar to the circulatory system in animals.

"Such a system could have its healing agent refilled or replaced and could repeatedly heal a structure throughout its lifetime. Furthermore, it offers potential for developing other biological-type functions in man-made structures, such as controlling temperature or distributing energy sources", he said.

Since the system is not working with conventional resin, the research team is now trying to improve it for this specific use. "Current epoxy systems have to be mixed in precise ratios, such as two parts of one ingredient with one part of another. We'd need the resin to be much more tolerant of different mix ratios, because we can't control the situation in the air. And we'd need it to be low viscosity, and fairly stable - it needs to last a long time. It could be sitting in an aircraft's structure for quite long periods of time, maybe years, and still needs to be reactive when called upon", Bond said.

Resin flow rates and hardening time would have to be precisely tuned so that it could repair any damage even while in flight, low temperatures and low atmospheric pressure. Nevertheless, Bond believes that the task can be achieved, even though nobody has ever tried it before. If it works, we'll find out in five years' time, Bond concluded.