Professor Guo Lin from the School of Chemistry in Beihang University and his collaborators have made important progress in the research of enamel-like composite materials. Their research paper, titled “Multiscale engineered artificial tooth enamel”, was published online in the journal Science on February 4, 2022.
Associate Professor Zhao Hewei from the School of Chemistry is the first author; doctoral student Liu Shaojia, Professor Wei Yan from Peking University Stomatological Hospital and Professor Yue Yonghai from the School of Chemistry at Beihang are the co-first authors; Professor Guo Lin is the corresponding author; Professor Deng Xuliang from Peking University Stomatological Hospital and Professor Nicholas A. Kotov from the University of Michigan is the co-corresponding authors. Beihang University is the first completion unit.
As the hardest and strongest tissue in the human body, tooth enamel exhibits excellent resistance to deformational and vibrational damage during chewing, which realizes various contradictory mechanical properties such as high hardness, high elasticity, high strength and high toughness. Tooth enamel is mainly composed of hydroxyapatite nanowires arranged in regular parallel sequence and combined with a small number of biological proteins. Further research has found that hydroxyapatite nanowires also have the inorganic amorphous interstitial layer, which is the key to the excellent mechanical properties of tooth enamel.
Due to the lack of macro-size controllable assembly methods of one-dimensional nanowires, and the technical bottlenecks in the preparation and morphology control of inorganic amorphous nanomaterials, it is a great challenge to simulate the hierarchical structure of enamel at multiple scales to achieve or even exceed the excellent mechanical performance of enamel in artificial engineering materials. In particular, the introduction of an amorphous interstitial layer that plays a key role in mechanical properties has not been reported yet.
Professor Guo Lin’s research team designed a multi-scale assembly pathway based on “macro synthesis and controllable assembly of nano-structural units”, and realized the controllable preparation of artificial tooth enamel (ATE) with the most similar structure to tooth enamel so far. They engineered an enamel analog with the essential hierarchical structure at multiple scales through assembly of amorphous intergranular phase (AIP)–coated hydroxyapatite nanowires intertwined with polyvinyl alcohol.
Fig.1 Tooth enamel and synthesis of artificial tooth enamel (ATE)
The prepared multi-level enamel-like composite materials have high stiffness (105GPa), high hardness (5.9GPa), high viscoelasticity (VFOM, 5.5GPa), high strength (143MPa), and high toughness (7.4MPa m1/2 ), superior to previously reported enamel-like composite materials and biological materials such as enamel and bone, which fully reflects the importance of material microstructure design in improving material performance. In particular, the mechanical properties of multi-level enamel-like composites can be adjusted by changing their components, and then composite materials with properties close to natural teeth can be prepared. The composite material with similar structure and properties to natural tooth enamel is expected to become a new generation of dental restorative materials.
Fig. 2 Mechanical properties of ATE
The mechanical behaviors such as strong support, interface enhancement, structural confinement and stress dissipation caused by the multi-level enamel-like structure of the material are important factors for realizing its excellent mechanical properties. This research provides a theoretical reference and design basis for the synthesis of next-generation dental restoration materials with matched biomechanical properties and engineering materials with better comprehensive mechanical properties.
Fig. 3 Polymer confinement in ATE
The work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, etc.
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Reported by Wei Qian
Reviewed by Li Hongjie
Edited by Jia Aiping
Translated by Zang Mingming