A nano composite of aluminum oxide and a polymer is as tough as metals but lighter. In their efforts to create strong yet light materials, chemists and materials scientists have long tried to mimic nanostructures found in nature. Shells, bones, and tooth enamel all consist of stiff ceramic platelets arranged in a polymer matrix like bricks in mortar. These hybrid materials combine the strength of ceramics and the stretchability of polymers. An added advantage of the hybrid material is that it is light. The material is half to a quarter as heavy as steel of the same strength. It would make a good substitute for fiberglass, which is commonly used in car parts. Because the material's strength comes from the platelets diffused through it will be strong in two directions and not only in one direction as in the case of fiber-reinforced material. Moreover, while the material is translucent now, its structure could be modified to render it transparent, making it suitable for dental material and transparent electronic circuits.

Researchers have dispersed tiny platelets of aluminum oxide in a polymer to make a material that is tough, stretchy, and lightweight. The material could lead to longer-lasting bone and dental implants and lighter, more fuel-efficient car and airplane parts. It could also be used to make bendable, transparent electronics.
In 2007, University of Michigan researchers engineered clay-reinforced polymers that were extremely strong but brittle: it takes a lot of energy to deform them, but when they do deform, they break abruptly. Researchers at MIT succeeded in making stiff but less brittle clay-polymer composites, which will tolerate some stretching before they break. The research team at the Swiss Federal Institute of Technology Zurich, says that the group's composite is better still. It's five times as strong as the material made at MIT, he says, yet it's still stretchy. A film of the composite is already as strong as aluminum foil, but if stretched, it can expand by up to 25% of its size; aluminum foil would break at 2%.
To assemble their material, the researchers disperse aluminum oxide platelets in ethanol and spread the mixture over water. The platelets arrange themselves into a single layer on the surface of the water. Then the researchers dip a glass plate into the solution, transferring the platelets to the glass. Finally, they deposit a layer of the biocompatible polymer on top of the platelets. The researchers repeat this process until the thickness of the final composite is a few tens of micrometers, and then they peel the material off the glass plate with a razor blade. The ratio between the length and thickness of the platelets has to be just right. If it is too high, the platelets break when the material is stretched. If it is too low, the material is not very stiff. The researchers chose to work with aluminum oxide platelets, which are five times as strong as the calcium carbonate platelets found in nature. They also made their platelets thinner--about 200 nanometers across, as opposed to the 500 to 1,000 nanometers of the naturally occurring platelets--to lower the likelihood of flaws in their structure. The best average length-to-thickness ratio is 40, so they made the platelets 5 to 10 micrometers long. Low concentrations are important because that means the composite has more polymer and has a lot of stretchability.

The material needs many improvements before it can be practically used. A better polymer would make the composite stronger. The researchers also need to find a way to get better bonding between the aluminum oxide and the polymer. But before the material can be used, the researchers will have to develop a faster way to make it in larger quantities.