The Growth Mechanism Of Two Kinds Of Self-organized Hard Tissue Structures

The biological hard tissues are composites self-organized by nano crystals of apatite or Calcium Carbonate(CC) and organics. The highly ordered hierarchical structures in hard tissues endowed them with outstanding physical properties. Many experiments in vivo/vitro have been performed to study the self-organize growth mechanism of hard tissues and to mimicking fabricate the structures. However, the detailed mechanisms of hard tissue formation such as the formation of enamel prism structures are still unclear due to their complicity. Studying the self-organization growth mechanism of hard tissues structures therefore is still attracting intensive attention.In this work, we developed a solution-air interface growth method to self-organize hard tissue structures and we successfully synthesized large scale translucent hydroxyapatite(HAP) and chondroitin sulfate(CHS) composite enamel-like material. We found that trace fluoride could improve the crystallinity and orientation of HAP crystals in the material; CHS prone to absorb on HAP crystals and bind to Ca2+, subsequently promoted the nucleation and self-templated growth of HAP. Based on the experiment results, we demonstrated that the material is composed by self-organized HAP spherulites formed at solution air interface. The spherulites are restricted by solution air interface as well as the interfaces between spherulites and grow toward the solution, with the orientation increases. Finally the prism-like structures are formed. The growth model could excellently explain the formation and orientation development of enamel prism structure as well as other self-organized ordered nano-arrays such as ZnO and TiO2. The synthesis method we used also provided a simple and efficient method to fabricate tissue like self-organized structure.Besides, we self-organized a kind of vaterite spherulites with nacre like lamellar morphology using diffusion method. The spheulites are hexagonal symmetrically grown. We studied its components, microstructure and growth process through methods including in-situ observation, then we explained the formation of the hexagonal symmetrtic structure using spherulitic growth model. The work is beneficial for a better understanding the self-organization growth mechanism of vaterite spherulite and nacre structures.