Unavoidable vibrations, such as those on airplanes, cause rigid structures to age and crack, but researchers have found that if you design them more like tooth enamel, it could lead to more resilient structures such as flight computers. Most materials that absorb vibration are soft and don’t make good structural components such as beams, chassis or motherboards. Artificial enamel is better than solid commercial and experimental materials that are aimed at the same vibration damping, as it’s lighter, more effective and less expensive.
Researchers from the University of Michigan examined many structures in animals that had to withstand shocks and vibrations: bones, shells, carapaces and teeth. These living structures changed from species to species and over the eons. Tooth enamel told a different story. Under an electron microscope, it shared a similar structure whether it came from a Tyrannosaurus, a walrus, a sea urchin or a human.
Enamel evolved to last the lifetime of the tooth which could be many years, decades or even longer. Enamel must withstand repeated stresses and general vibrations without cracking. Enamel is made of columns of ceramic crystals infiltrated with a matrix of proteins and set into a hard protective coating. This layer is sometimes repeated and is thicker in certain teeth .
The reason why enamel’s structure is effective at absorbing vibrations, is that the stiff nanoscale columns bending under stress from above create a lot of friction with the softer polymer surrounding them within the enamel. The large contact area between the ceramic and protein components further increases the dissipation of energy that might otherwise damage it.
The enamel structure was recreated in a lab by growing zinc oxide nanowires on a chip. Then layering two polymers over the nanowires, spinning the chip to spread out the liquid and baking it to cure the plastic between coats. It took 40 layers to build up a single micrometer, or one thousandth of a millimeter, of enamel-like structure. Then, another layer of zinc oxide nanowires and filled it in with 40 layers of polymer, repeating the whole process up to 20 times.
The synthetic tooth enamel approached the ability of real tooth enamel to defend itself from vibration damage. Computer modeling of the synthetic enamel was performed by researchers at Michigan Technological University and the Illinois Applied Research Institute. They confirmed the structure diffused the forces from vibrations through the interaction between the polymer and columns. The synthetic enamel one day might be deployed in airplanes and other environments in which vibrations are inescapable which can help protect structures and electronics.
Bongjun Yeom, Trisha Sain, Naida Lacevic, Daria Bukharina, Sang-Ho Cha, Anthony M. Waas, Ellen M. Arruda, Nicholas A. Kotov. Abiotic tooth enamel. Nature, 2017; 543 (7643): 95.