基于贝壳棱柱-珍珠层界面区的特征探讨珍珠层的生物矿化机理

Nacre exhibits beautiful iridescence, considerable economic value, and unusual mechanical properties. Therefore, it has become one of the typical research objects in the field of biomineralization and biomimetic materials science. Importantly, in mollusk shells, nacre is always deposited on the substrate formed by the prismatic layer. More precisely, the existence of the prismatic layer is necessary for nacre deposition. For this reason, the prism-nacre interfacial region contains key information about nacre biomineralization. Therefore, in this program, we aim to investigate the nacre-bearing shells and use FESEM and HRTEM as the main tools. In particular, we aim to investigate the characteristics of different types of prism-nacre interfacial region, which include the chemical composition, morphology, structure, crystallographic orientation, and hydrophilicity/hydrophobicity of the interfacial components. Moreover, we hope to understand the orientation mechanism of the first layer of nacreous tablets (i.e. those closest to the prismatic layer), and the effect of the primary organic membrane on the structural transition from the prismatic to nacre layer. After that, we intend to establish detailed structural models for the different types of prism-nacre interfacial region. Finally, we aim to explore the factors and mechanisms responsible for the structural transition from the prismatic to nacre layer. We expect that this program will provide a theoretical basis for further understanding the biomineralization mechanism of nacre and for designing and synthesizing biomimetic materials.

珍珠层具有美丽的彩虹色光泽、重要的经济价值、以及不同寻常的力学性能，因而一直生物矿化及仿生材料领域的典型研究对象之一。重要的是，在贝壳中，珍珠层总是沉积在棱柱层基底上，更准确地说，棱柱层是珍珠层沉积的必要条件之一，故棱柱-珍珠层界面区包含了珍珠层矿化机理的关键信息。据此，本项目拟以含珍珠层的贝壳为研究对象，以场发射扫描电镜和高分辨透射电镜等为主要研究手段，研究不同类型的棱柱-珍珠层界面区的特征，包括界面区各组成要素的化学组成、形貌、结构、晶体取向、及亲/疏水特征等。重点了解离棱柱层最近的第一层珍珠层板片的结晶学取向的控制机理，及初始有机膜在棱柱-珍珠层结构转换中的作用。然后建立不同类型棱柱-珍珠层界面的详细结构模型，进而探讨棱柱-珍珠层结构转换的控制因素及控制机理，为深入了解珍珠层的生物矿化机理及仿生材料的设计和合成提供理论基础。

珍珠层由文石板片层和层间有机膜层交替排列而成。长期以来，珍珠层一直是生物矿化及仿生材料领域的典型研究对象之一。然而关于珍珠层与其沉积基底即棱柱层的界面区的特征仍未完全清楚。本项目以我国产9种含珍珠层的双壳纲贝壳为研究对象，以FE-SEM和TEM等为主要研究手段，对贝壳棱柱-珍珠层界面区的各组成要素，尤其是界面区附近初生珍珠层板片的形貌演化及结晶机理进行了系统的研究。同时还利用水接触角测量技术对珍珠层内表面的亲疏水性进行了分析。取得的主要结果如下：(1) 棱柱-珍珠层层界面区结构复杂多样，与生物种类有关；(2) 虽然紧邻棱柱层的第一层珍珠层板片的形貌及粒径等特点与生物种类有关，但它们厚度及直径通常比正常珍珠层板片大数倍，说明在贝壳由棱柱向珍珠层过渡时，贝壳生长动力学起了关键作用；(3) 不同种类的珍珠层层间有机膜普遍具疏水性，同时正在生长的板片与层间有机膜的接触角普遍大于90度，两者相互印证了碳酸钙材料不能润湿层间有机膜表面；(4)下层板片边缘的结晶度和弹性应变等因素引起了新生板片的边缘成核；(5) 珍珠层板片的生长模式类似薄膜材料的岛状生长模式，其矿化过程受多种因素的影响，如文石结晶学及层间膜的疏水性等。本项目的研究结果，尤其是首次发现层间有机膜的疏水性对珍珠层生物矿化有重要影响，不仅加深了人们对珍珠层形成机理的认识，同时为仿生材料合成提供了新思路。