Most substances that effectively absorb vibration are soft, so they do not make efficient structural components as chassis, beams or motherboards. For inspiration on how to prepare hard substances that survive repeated shocks, the scientists considered the nature.
“Artificial enamel is better than solid experimental and commercial materials that are aimed at the same vibration damping,” says Nicholas Kotov, the Joseph B. and Florence V. Cejka Lecturer of Chemical Engineering. “It’s lighter, more efficient and cost-effective.” He and his group did not settle on enamel instantly. They analysed numerous structures in animals that had to go through vibrations and shocks, shells, bones, teeth and carapaces. Such living structures altered from species to species and over the eons.
Evolution had hit on a pattern that worked for pretty much everyone with teeth. And unlike bone that can be repaired, enamel had to last the lifetime of the both – decades, years or longer still. It must withstand recurrent stresses and general vibrations without cracking. Enamel is made of columns of ceramic crystals infiltrated with a matrix of proteins, set into a hard protective layering. This layer is sometimes repeated, prepared of thicker in the teeth that have to be strong.
The reason why such structure is effectual at absorbing vibration, Kotov explained, is that stiff nanoscale column bending under stress from above result in a lot of friction with the softer polymer surrounding them within the enamel. The big product area between the protein and ceramic components further enhances the dissipation of energy that may otherwise damage it.
BongjunYeom, a postdoctoral scientist in Kotov’s lab, recreated the structure of enamel by expanding zinc oxide nanowires on a chip. Then he layered two polymers over the nanowires, spinning the chip to spread out the liquid and baking it to cure the plastic between coats. It took almost 40 layers to build up a singular micrometre, or one thousandth of a millimetre, of enamel like structure. Then they laid down another layer of zinc oxide nanowires and filled it in with 40 layers of polymer, repeating the entire process up to 20 times.
Kotov’s team illustrated that their synthetic tooth enamel approaches the potential of real tooth enamel to defend itself from damage due to vibrations. From the inception of project as a challenge from the Defense Advanced Research Projects Agency, Kotov worked with fellow substances heavyweights Anthony Waas, the Felix Pawlowski, Collegiate Lecturer Emeritus and Ellen Arruda, U-M lecturer of mechanical engineering.
Kotov expects to witness the synthetic enamel deployed in airplanes and other environment in which vibrations are inescapable, protecting structures and electrical devices. The challenge, he said, will be automating the production of the substance.
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