Abiotic tooth enamel

Nanometre-scale columnar structures in tooth enamel inspire novel nanocomposites containing layers of vertically aligned nanowires, produced by layer-by-layer fabrication and combining high values of both storage modulus and energy dissipation. A tough material inspired by tooth enamel (Kotov 21410, Physics Letter, Ros Daw) Biomimetic composite materials often take the form of nacre-like structures in which platelets are arranged in layers. Here Nicholas Kotov and colleagues take inspiration from the nanoscale columnar structures found in tooth enamel and other biocomposites, and use a layer-by-layer fabrication process to generate novel nanocomposites containing layers of vertically aligned nanowires. The columnar architecture combines both hardness and high energy dissipation (toughness). The resulting materials are light and stiff with impressive damping capabilities—a useful combination of properties for load-bearing applications. Tooth enamel comprises parallel microscale and nanoscale ceramic columns or prisms interlaced with a soft protein matrix 1 , 2 , 3 . This structural motif is unusually consistent across all species from all geological eras 4 , 5 , 6 . Such invariability—especially when juxtaposed with the diversity of other tissues—suggests the existence of a functional basis. Here we performed ex vivo replication of enamel-inspired columnar nanocomposites by sequential growth of zinc oxide nanowire carpets followed by layer-by-layer deposition of a polymeric matrix around these. We show that the mechanical properties of these nanocomposites, including hardness, are comparable to those of enamel despite the nanocomposites having a smaller hard-phase content. Our abiotic enamels have viscoelastic figures of merit (VFOM) and weight-adjusted VFOM that are similar to, or higher than, those of natural tooth enamels—we achieve values that exceed the traditional materials limits of 0.6 and 0.8, respectively. VFOM values describe resistance to vibrational damage, and our columnar composites demonstrate that light-weight materials of unusually high resistance to structural damage from shocks, environmental vibrations and oscillatory stress can be made using biomimetic design. The previously inaccessible combinations of high stiffness, damping and light weight that we achieve in these layer-by-layer composites are attributed to efficient energy dissipation in the interfacial portion of the organic phase. The in vivo contribution of this interfacial por