Scientists draw inspiration from giant panda teeth
SHENYANG/HEFEI/LANZHOU, China/BERKELEY, Calif., US: Tooth enamel protects teeth over the lifetime of an organism by providing a hard surface resistant to wear and tear and by withstanding impacts without breaking. According to researchers, the giant panda has particularly resistant tooth enamel, which can recover its structure and geometry to counteract the early stages of damage.
The team which investigated the tooth structure of the panda was made up of researchers from the Institute of Metal Research of the Chinese Academy of Sciences in Shenyang, the University of Science and Technology of China in Hefei, Lanzhou University of Technology in Lanzhou and the University of California, Berkeley in the US. They believe their observations could be replicated in the tooth enamel of all vertebrates, including humans, and inspire the design of artificial durable ceramics.
“Tooth enamel possesses an exceptional durability and plays a critical role in the function of teeth, however, [it] exhibits a remarkably low resistance to the initiation of large-scale cracks comparable to geological minerals,” said Prof. Robert O. Ritchie, who led the study.
The ingenious design of the panda’s tooth enamel, which has to withstand a daily diet of bamboo—a material of remarkable strength and toughness—comprises parallel micro-scale prisms made up of vertically aligned nanoscale fibres of the mineral hydroxyapatite embedded in an organic-rich matrix. When there is an impact on the enamel, a variety of different deformation mechanisms take place to mitigate the growth of small cracks and prevent the formation of large cracks.
“The tooth enamel is capable of partially recovering its geometry and structure at nano- to micro-scale dimensions autonomously after deformation to counteract the early stage of damage,” explained first author Zengqian Liu. “[This] property results from the unique architecture of tooth enamel, specifically the vertical alignment of nanoscale mineral fibres and micro-scale prisms within a water-responsive organic-rich matrix.”
Hydration plays a key role in the process. The viscoelasticity of the organic-rich matrix surrounding the mineral prisms and fibres facilitates self-recovery, while the presence of water decreases the width of any cracks that do form, with only a minor cost in terms of hardness.
“Our findings identify a novel means by which the tooth enamel of vertebrates develops an exceptional durability to accomplish its functionality,” added Liu. “The self-recovery process represents a new source of durability that differs markedly from the conventional protocol of fracture mechanics.”
As the architecture of the panda’s tooth enamel is essentially similar to that of other vertebrates, the researchers believe that this self-recovery behaviour is likely to occur in tooth enamel in general. “Our findings also offer inspiration for the development of artificial, durable, self-recoverable ceramic materials,” said Ritchie. The team is hoping to develop tooth enamel-inspired self-recoverable durable materials by introducing shape memory polymers at the interface of ceramics.
The study, titled “Hydration-induced nano- to micro-scale self-recovery of the tooth enamel of the giant panda”, was published in the November 2018 issue of Acta Biomaterialia.