Electroplating involves passing a current through an electrolyte solution containing positive metal ions. The object that needs to be coated is given a negative charge and immersed in the electrolyte. The positive ions are attracted to the negative surface, creating a thin layer of metal.

The Fraunhofer researchers make the nanocapsules separately before adding them to an electrolyte solution. But making capsules that survive the electroplating process was not easy--the harsh electrolytes can easily degrade the capsules, Holeczek says. Additionally, "the very tiny capsules tend to stick to each other once introduced in an aqueous medium." So the researchers had to add a proprietary mix of chemicals to the electrolyte solution, and to the capsules themselves, to prevent this from happening.

As a result, the nanocapsules can be integrated into the thin plating without affecting its hardness and other mechanical properties, Holeczek says. They are also distributed evenly through the metal layer, which means there's a better chance that the capsules will open even when damage is minor.

Paul Braun, a materials science and engineering professor at the University of Illinois at Urbana-Champaign, has made a microcapsule healing system that can be added to a wide range of paints and protective coatings and is now being marketed. He says that making the capsules too small could defeat the purpose: "If you have a 15-micrometer-wide scratch, then you can't release enough material to fill the crack plane."

However, once the researchers come up with the appropriate chemistries to show that the material can heal itself, Braun says, it could "open up a whole new opportunity space."