Synthesis And Properties Of Transparent Biomimetic Tooth Enamel

Transparent and hard materials such as glass lack impact resistance and are prone to catastrophic damage,while transparent polymer materials with excellent toughness are not resistant to scratching due to their soft texture.Some biological tissues in organisms,such as the outer shell of Placuna platenta and the teeth of deep-sea arowana,can simultaneously have ideal mechanical properties and optical transparency.Inspired by the multi-level structure of dental enamel,we prepared transparent bionic dental enamel by combining hydrothermal method with spin coating technology.This material combines excellent properties such as high transparency,low haze,high hardness,and high fracture toughness.By comparing with bionic enamel with a single stage structure,the mechanism of synergistic optimization of mechanical and optical properties of materials using multi-level structures was revealed.The main research results obtained in this paper are as follows:(1)Under hydrothermal conditions,highly oriented fluoroapatite nanorod arrays(as-FA)with single stage structure were synthesized on the surface of FTO conductive glass substrate.Fluoroapatite nanorod arrays(ab-FA)with multi-level structure were synthesized by changing the p H of the reaction system and using as-FA as the seed layer.Using spin coating technology,different polymers were poured into the nanorod gap to obtain a bionic enamel structure.(2)The optical properties of different bionic enamel structures were studied and it was found that the haze of both types of bionic enamel was lower than 1.5%,mainly due to the highly aligned structure limiting the scattering angle.When the refractive index of polymer and fluoroapatite is matched,the transmittance of biomimetic enamel(h-CNs)with multi-level structure is as high as 90%,which is much higher than that of biomimetic enamel(s-CNs)with only single-level structure.This is mainly due to the fact that multi-level structure has smaller size structural units,thereby reducing the scattering intensity.Both bionic enamel structures have birefringence characteristics.(3)Using nanoindentation to measure the hardness and modulus of bionic tooth enamel structures,it was found that the hardness and modulus of the two bionic tooth enamel structures were comparable and superior to natural tooth enamel and most dental enamel imitations.The fracture toughness was measured using a hardness tester,and the crack propagation was observed under a scanning electron microscope.The toughening mechanism of the multi-level structure was discussed.Due to the stress passivation mechanism at the multi-level interface,the fracture toughness of transparent bionic enamel with multi-level structure is 40% higher than that of bionic enamel with single-stage structure.Using cyclic nanoindentation testing,the ability of multi-level structures to improve energy dissipation under dynamic conditions was explored,and it was found that transparent bionic enamel with multi-level structures had a more effective plastic energy dissipation pathway.