Synthesis And Properties Of A Biomimetic Tooth Replicate,That Is Hard,Damage-Tolerant And Self-Healable

Hard materials typically lack the mechanism of energy dissipation and cannot selfheal.Nature addresses this challenge by creating multiscale interfaces between highcontrast materials,namely minerals and biopolymers.Inspired by the enamel-dentin junction in nature,a novel biomimetic bilayer tooth replicate was successfully synthesized by using layer-by-layer assembly,which uses β-Fe OOH nanorods as the top enamel-like crown and flexible and self-healing polymer as the bottom dentin-like structure.The hardness and modulus of the synthesized material are about 6.4 GPa and94 GPa,which are equivalent to human teeth and higher than other enamel mimetics.Tooth enamel experiences repetitive contact deformation during daily chewing,which is simulated by cyclic nanoindentation in this work.The iron oxide top layer has exceptionally high modulus and hardness,which is more resistant to cyclic deformation than the bottom layer.The latter however provides an additional pathway for viscous and plastic energy dissipation.Compared with a single polymer substrate,it can withstand repeated contact loads,reflecting the advantages of a bilayer structure.However,despite high modulus and hardness,the indentations with deep penetration under nanoindentation and after 100 cycles of cyclic nanoindendation are all free of cracks.Picture-frame crack patterns were observed under large loading conditions using microindentation,which is superior to a radial crack as it may avoid catastrophic failure by localizing the damage.Layer-by-layer assembly was futher used to finely tune the constituent thickness to optimize the bending properties.The bending properties can be optimized by varying the thickness of the bottom layer.The calculation of the normalized top surface strain in three cases is consistent with our observation,showing that when the bottom layer is 30 polymer bilayers,the smallest strain is achieved closer to the optimal position,which is no crack on the surface.The crack induced by bending can be effectively captured at the interface without any delamination,which is very similar to enamel-dentin interface that can effectively arrest the crack to avoid further damage to the dentin.The biomimetic tooth replicate is highly adhesive to a ceramic surface and shows an obvious inhibition effect against Streptococcus mutans,a significant contributor to tooth decay.The bottom layer that contains reversible hydrogen bond network enables self-healing by allowing upward polymer diffusion to seal the damage.Combined with ultralow thermal diffusivity,this has great potential as dental material.Learning from nature,our work thus provides a powerful pathway to broadening the scope of synthetic materials for dental replicates and this work also provides an effective strategy for designing multifunctional materials with high rigidity,high hardness,energy dissipation and self-healing ability.