Coherent surface structure induces unique epitaxial overgrowth of metastable octacalcium phosphate on stable hydroxyapatite at critical fluoride concentration
Coherent surface structure induces unique epitaxial overgrowth of metastable octacalcium phosphate on stable hydroxyapatite at critical fluoride concentration
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在临界氟化物浓度下，一致的表面结构诱导亚稳态磷酸八钙在稳定的羟基磷灰石上独特的外延过度生长
DOI：
10.1016/j.actbio.2021.02.024
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发表时间：
2021
影响因子：
9.7
通讯作者：
Koichi Momma
中科院分区：
文献类型：
--
作者：
Kazuo Onuma;Mari M. Saito;Yasuo Yamakoshi;Mayumi Iijima;Yu Sogo;Koichi Momma
从可溶性磷酸钙到难溶羟基磷灰石(HAP)的相变是热力学上的自然途径。这一过程是不可逆转的，有效利用低活性羟基磷灰石修复没有细胞代谢的牙齿仍然具有挑战性。然而，这种热力学控制的转变显然可以通过亚稳相的快速形核和生长而逆转，导致反应性的HAP表面。在这里，组装的羟基磷灰石-纳米棒相被证明在含有0.8ppm氟化物的磷酸钙溶液中转变为亚稳定的磷酸八钙(OCP)相。生长的有机氯农药呈现平行的表面条纹，它们的110和00L(L：奇数)电子衍射点通常是看不到的。线条细长的OCP逐渐成长为具有平坦表面的大平板，显示出强烈的110光点。晶体结构模型表明，由于两种材料共用共格的{100}晶面，导致11、0和00l OCP斑点的明显消失，从而在HAP上发生了独特的OCP外延生长。对于OCP的生长，提出了一个可靠地解释这种消失的多合成孪生模型。这种明显的反向相变产生了由羟基磷灰石核心和高活性外层OCP组成的混合钙磷酸盐，有望用于牙本质龋齿的修复。这篇论文展示了关于磷酸钙的形成与其晶体结构的关系的重要而有趣的发现。我们首先证明，人类牙齿和骨骼的主要成分羟基磷灰石(HAP)可以反向转变为其前体磷酸八钙(OCP)，这与热力学稳定性规则相反。这种明显的逆相变是通过在控制氟浓度下共享两种材料的共格{100}面而发生的。两个晶体表面的纳米尺度相似性使得OCP能够在HAP上共享外延生长，这得益于OCP比HAP更快的生长速度。这种反应产生了由外层OCP和核心HAP组成的杂化晶体，这是以前未知的，能够应用于牙本质龋齿修复。
The phase transformation from soluble calcium phosphates to less-soluble hydroxyapatite (HAP) is a thermodynamically natural route. This process is irreversible, and effective use of poorly reactive HAP to repair teeth that have no cellular metabolism remains challenging. However, this thermodynamically controlled transformation may apparently be reversed through the fast nucleation and growth of metastable phases, leading to a reactive HAP surface. Here, the assembled HAP-nanorod phase is demonstrated to change into the metastable octacalcium phosphate (OCP) phase in a calcium phosphate solution containing 0.8 ppm fluoride. Grown OCPs display parallel surface streaks and their 1 1¯ 0 and 00l (l: odd) electron-diffraction spots are often not visible. The streaked, elongated OCP gradually grows into large plates with flat surfaces that exhibit an intense 1 1¯ 0 spot. Crystal-structure models reveal that the unique epitaxial overgrowth of OCP on HAP occurs since both materials share coherent {100} faces, resulting in the distinctive disappearance of 1 1¯ 0 and 00l OCP spots. A polysynthetic twin model that reliably explains this disappearance is proposed for the growth of OCP. This apparent reverse phase transformation produces hybrid calcium phosphates consisting of HAP cores and highly reactive outer OCP layers that are promising for the repair of dentin caries. Statement of significance This paper demonstrates important and interesting finding regarding formation of calcium phosphates in relation to their crystal structures. We first show that hydroxyapatite (HAP), the major constituent of human teeth and bone, can reversely change to its precursor, octacalcium phosphate (OCP), contrary to thermodynamic-stability rule. This apparent reverse phase transformation occurs through sharing the coherent {100} faces of both materials under controlled fluoride concentration. Nanoscale similarity of two crystal surfaces enables structurally shared epitaxial overgrowth of OCP on HAP aided by faster growth rate of OCP than that of HAP. This reaction produces hybrid crystal consisting of outer OCP and core HAP, that has not been known before and is able to be applied to dentin caries repair.