Study On The Composition And Structure Of Seawater Cultured Pearls And In Vitro Mineralization Based On Pearl Layer

Pearl is a very precious organic gem,crystal clear and bright,loved by much people.Pearl not only has a very high value of gemology,but also has a powerful mechanical properties and good biocompatibility,is a typical biocomposite materials,synthetic materials can not match its advantages.Pearl have become a hotspot in the development and application of biomimetic composites.In this paper,the organic and inorganic chemical constituents and microstructures of seawater cultured pearls were studied.The relationship between organic matter and inorganic mineral in pearls was discussed.On this basis,the mechanism of pearl formation was deduced.At the same time,the in vitro mineralization experiment of calcium carbonate crystals was carried out on the basis of pearl layer,and the nucleation process of calcium carbonate crystals in pearls was explored.The effects of six different amino acids on the crystal morphology were discussed.It is hoped that the growth rule of the crystal in the process of pearl formation can be found,and the understanding of pearl biomineralization theory can be extensived,which will provide the theoretical basis for the bionic composites similar to the pearl layer.The results are summarized below:(1)The organic matter,amino acid and metal elements of the pearls were analyzed by gas chromatography-mass spectrometry,amino acid analyzer and inductively coupled plasma mass spectrometer.The results showed that : seawater culture pearl dichloromethane extract of the highest content of organic compounds is diethyl phthalate,followed by terephthalic acid,isovaleric acid and 3-amino-1,2-benzisothiazole,the total amount of fatty acids accounted for more than 10% of organic components;Amino acid analysis showed that the highest content was glycine and alanine,followed by aspartic acid,the lowest content was histidine and methionine;The results of elemental analysis show that the elements with high content are Ca,Na,Fe,Sr,Mg and Cr,the content of Li,Al,Ti,V,Mo,Pb is less than 5mg / kg.(2)The pearl layer of seawater culture pearls is composed by pearl layer,prism layer and transition layer.The pearl layer is mainly aragonite type calcium carbonate.The aragonite sheet is formed by intertwining of nanometer aragonite microcrystallineparticles and organic matter particles.The growth rate of aragonite microcrystals in the c-axis direction is faster than that in the horizontal direction,that make the aragonite grains looks like bread.The calcite type calcium carbonate and aragonite calcium carbonate are present in the prism layer.The transition layer consists of organic matter and small amount of calcium carbonate,and is connected to the prism layer and the pearl layer by organic matter.(3)The results of in vitro mineralization of calcium carbonate basis on pearl layer showed that the crystal was originally deposited in the form of amorphous calcium carbonate,and then nucleated on the surface of the substrate.The diameter of nuclei was about 50 nm.Due to the regulation of the organic matter of the substrate,the new crystals at the edge of the aragonite sheet are more closely aligned with the crystal arrangement in the center of the plate,and the new crystals are stacked vertically by the small chips;After some time,the surface of the substrate almost completely covered by tapered crystals,tapered crystal regularly arranged,are the same size and orientation;After 10 hours of deposition,the new crystal showed a discontinuous lamellar structure.The experiment on the glass plate did not show the above phenomenon,which indicated that the unique growth pattern of the crystal was determined by the pearl substrate.The crystals deposited in the glutamic acid and aspartic acid mineralization solution completely cover the nacre layer,and the distribution of the new crystals in the aspartic acid mineralization solution is consistent with the hexagonal network structure on the pearl substrate;In lysine and arginine mineralization solution,the crystal growth is more scattered,most of the new crystal may be suspended in the solution;The crystal morphology in glycine and serine mineralization solution was not significantly different from that in the control group,which had little effect on the crystal morphology of calcium carbonate.