Bridge Heal Thyself

For the last sixty years, science fiction has promised materials that, when broken, torn or otherwise damaged by use and stress simply repair themselves.  Crumbling infrastructure across much of the United States and Europe testifies to the social good of self-repairing infrastructure like roads, bridges and dams.  Or the safety of vehicles that no longer groan as stress is placed upon steel and plastic.

But science fiction promises what science cannot often deliver.

That is until engineers at the University of Southern Mississippi and the University of Illinois started to look for inspiration to living things.  In Mississippi, engineers have developed a coating which will heal itself based on the shells of crabs.  Farther north in Illinois, they have mimicked tiny blood vessels to repair stress cracks and fractures in materials.

Professor Marek Urban, the director of Southern Mississippi’s research into polymers and high-performance materials used molecules from chitosan, derived from the shells of crabs and other crustaceans and then joined them with oxetane molecules and added the pair to a mix of polyurethane, a popular plastic material used in clothing and coatings.

When the polyurethane was scratched or damaged it would split rings of oxetane which, when exposed to sunlight would join with the chitosan.

Professor Urban found coatings could heal themselves within 30 minutes when exposed to sunlight.

If researchers at the University of Illinois in the United States are to be believed, infrastructure projects like bridges, damns and roads may someday be able to repair themselves as they crack.

According to results published in the Journal of the Royal Society Interface, self-healing materials have taken a leap forward by mimicking an animal’s vascular systems.

Professor Nancy Sottos of the University of Urbana-Champaign, have successfully impregnated plastics with fine networks of channels that can be filled with liquid resin.  Prior to her teams’ work, the rub with self-healing materials was always that embedding capsules of healing agents in various composites, metals or plastics weakened the material and made failure more likely.  But Professor Sottos’ tubes, less than 100 millionths of a metre in diameter and mimicking capillaries, seem fine enough to provide potential strength without ensuring weakness.  And they can already heal cracks in materials of a millimeter in width which is 50 or 100 times larger than the current technology.

When a crack appears in a material, reservoirs of fluids rush through the capillaries, solidify, and deal the new rifts.  At this point the reservoirs are external to the materials and use pressure to impregnate the microscopic tubes, but when the technology is used outside of the laboratory, the team would want to incorporate the reservoirs into the material and drive it through the cracks with pressure or magnets.

Hydraulic systems are already in place in most bridges, dams, airplanes and spacecraft.