新型穹顶状珍珠层板片的三维形貌、纳米结构演化及形成机理

Nacre is a model biomineral material consisting of >95 wt% tabular aragonite crystals (platelets) embedded in an organic matrix. For a long time, these platelets are considered, explicitly or implicitly, to be always flat by nearly all authors, which results in that our current knowledge on nacre is mainly based on the investigation of the flat platelets. However, in 2011, we discovered that the nacre in Perna viridis shell contains dome-shaped platelets (DSPs) with a dynamic morphology and nanostructure, which have never been described so far except by our group. Therefore, in this program, we intend in sequence to: 1) investigate the variations of DSP's morphology and nanostructure with its growing stages and shell's positions, using methods such as FESEM and HRTEM; 2) analyze biochemically the organic matrix that is closely related to the DSP's growth, which is then used as an organic additive for biomimetic mineralization of CaCO3,so as to understand how this organic matrix may influence the DSP's formation. Through above experiments, we expect to establish the evolutionary models of DSP's morphology and nanostructure and to analyze the DSP's formation mechanism. In summary, we aim to produce new knowledge about DSP-based nacre, which may provide new insights for further understanding the biomineralization mechanism and biomimetically fabricating the nacre-like material with high performance.

珍珠层是一种典型的生物矿物材料，由95 wt% 以上的板片状文石晶体(简称板片)和少量有机质组成。长期以来，几乎所有作者均承认或默认"珍珠层板片为平板状"，导致目前关于珍珠层的知识是建立在研究平板状板片基础上的。2011年我们首次发现翡翠贻贝珍珠层中存在穹顶状板片，它的形貌及纳米结构均是动态的。至今关于这类板片的研究除了我们小组外国内外均未见报道。因此，本项目拟以珍珠层穹顶状板片为研究对象，首先采用场发射扫描电镜、高分辨透射电镜等为研究手段，对穹顶状板片的三维形貌及纳米结构演化（随其生长阶段及生长位置的变化）进行详细研究。然后通过与板片形成有关的有机质的生物化学分析及仿生矿化实验，了解有机质对穹顶状板片形成的控制作用。以期建立穹顶状板片形貌和纳米结构演化模型，并分析其形成机理。最终产生以穹顶状板片为基础的珍珠层新知识，为深入剖析生物矿化机理及仿生合成高性能的类珍珠层材料提供新思路。

贝壳长期以来就作为仿生矿化和仿生材料合成的经典研究对象，尤其是珍珠层。本项目中，我们主要采用场发射扫描电镜、高分辨率透射电镜、X-射线衍射以及傅里叶红外光谱等对翡翠贻贝的总体结构、珍珠层板片的三维形貌及演化、空间排列、纳米结构、成核与生长等进行了研究。结果如下：1）翡翠贻贝由表壳层、棱柱层和珍珠层构成；2）穹顶状板片和平板状板片在贝壳中共存，并呈梯度排列；3）穹顶状板片的生长会经历一个从锥到截顶椎体最终到穹顶帽状棱柱的形貌转变；4）未成熟的穹顶状板片是无序文石纳米颗粒的集合体，而成熟穹顶状板片和平板状板片为单晶；5）板片呈同心生长模型生长，新生板片初始成核于核-环结构的环表面上；6）层间膜与底层板片定向一致，并通过超晶格区域与后者相连接；7）腹侧表壳层有三层结构，外层和内层由蛋白质组成，而中层是矿化层，由非晶质纳米球体组成；8）介于表壳层和棱柱层之间的一层独特的乳状突起层取代表壳层充当初始矿化基底。这些研究结果将会加速我们对贝壳生物矿化过程的认识，以及为仿生合成出具有优越力学性能的类珍珠层材料提供进一步指导。