Ni Ming, Ratner Buddy D
Department of Chemical Engineering, University of Washington Engineered Biomaterials (UWEB), RM 484 Bagley Hall, 4th Floor, Box 351720, Seattle, WA 98195-1720, USA.
Biomaterials. 2003 Oct;24(23):4323-31. doi: 10.1016/s0142-9612(03)00236-9.
Nacre, also known as mother-of-pearl, constitutes the inner layer of mollusc shells. Nacre is a natural composite material consisting mostly of calcium carbonate in the aragonite crystal form and some organic matter. Previous studies have shown that geological aragonite, coral and nacre can convert hydrothermally to hydroxyapatite (HAP) in phosphate solution by a solid-state topotactic ion-exchange reaction. This conversion typically occurs within the range of 140-260 degrees C, although higher temperatures are possible. In this work, we have found that nacre can transform to HAP in a phosphate buffer solution at room temperature via a surface reaction. The morphology of the nacre-transformed HAP surface was investigated by scanning electron microscopy (SEM). The HAP surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). A layer covered with packed particles was found in contrast to the tablet structure typical of nacre surfaces. XPS and SIMS indicated that the mineral phase of the nacre surface had converted from an aragonite phase to an HAP phase. Fourier transform infrared spectroscopy (FTIR) showed that phosphate (PO(4)) bands appeared after nacre was soaked in a phosphate buffer and the intensity of the PO(4) bands increased with exposure time. The FTIR was consistent with XPS and SIMS results. We suggest that this surface reaction occurs by a dissolution-precipitation mechanism. Calcium ions are released from the nacre surface, react with phosphate ions in the buffer solution, and then precipitate as HAP on the nacre surface.
珍珠层，又称珍珠母，构成了软体动物贝壳的内层。珍珠层是一种天然复合材料，主要由文石晶体形式的碳酸钙和一些有机物组成。先前的研究表明，地质文石、珊瑚和珍珠层在磷酸盐溶液中可通过固态拓扑离子交换反应水热转化为羟基磷灰石（HAP）。这种转化通常发生在140 - 260摄氏度的范围内，不过更高的温度也是可能的。在这项工作中，我们发现珍珠层在室温下的磷酸盐缓冲溶液中可通过表面反应转化为HAP。通过扫描电子显微镜（SEM）研究了珍珠层转化后的HAP表面形态。利用X射线光电子能谱（XPS）和二次离子质谱（SIMS）对HAP表面进行了表征。与珍珠层表面典型的片状结构不同，发现了一层覆盖着紧密堆积颗粒的结构。XPS和SIMS表明珍珠层表面的矿物相已从文石相转化为HAP相。傅里叶变换红外光谱（FTIR）显示，珍珠层浸泡在磷酸盐缓冲液后出现了磷酸盐（PO(4)）谱带，且PO(4)谱带的强度随暴露时间增加。FTIR结果与XPS和SIMS结果一致。我们认为这种表面反应是通过溶解 - 沉淀机制发生的。钙离子从珍珠层表面释放出来，与缓冲溶液中的磷酸根离子反应，然后以HAP的形式沉淀在珍珠层表面。
