El Briak-BenAbdeslam Hassane, Mochales Carolina, Ginebra Maria Pau, Nurit Josiane, Planell Josep A, Boudeville Philippe
Laboratoire de Chimie Générale et Minérale, Faculté de Pharmacie, 15 Av. Charles Flahault, BP 14 491, 34093 Montpellier Cedex 5, France.
J Biomed Mater Res A. 2003 Dec 1;67(3):927-37. doi: 10.1002/jbm.a.10025.
Calcium phosphate ceramics have been used successfully as synthetic bone substitutes in orthopedics, dentistry, and maxillofacial surgery. One way of preparing these ceramics is the sintering of a calcium-deficient hydroxyapatite (CDHA), which can be obtained in different ways. Mechanochemistry is one possible means of synthesizing CDHA, with an expected molar calcium-to-phosphate (Ca/P) ratio +/- 0.005. The grinding can be carried out under dry or wet conditions. To optimize the experimental conditions of CDHA preparation by dry mechanosynthesis and for a better understanding of the DCPD/CaO mechanochemical reaction, we performed a kinetic study in which some of the experimental parameters were varied. Carried out with two different vertical rotating ball mills, this kinetic study showed that (1) experiments are reproducible and give as a final product a hydroxyapatite powder, formed of nano-sized crystals of around 20 nm, with a controlled Ca/P ratio; (2) the time for complete disappearance of DCPD and the time for complete reaction are in direct proportion to the mass of the ground powder; but (3) the time for complete disappearance of DCPD is independent of the Ca/P ratio while the time for complete reaction increases exponentially with the Ca/P ratio; and (4) the time for complete disappearance of DCPD corresponds to the time for complete reaction solely for Ca/P = 1.5. These observations suggest a reaction mechanism in two well differentiated stages: (First stage) CaO reacts with DCPD to give first an amorphous calcium phosphate (ACP) with a low Ca/P ratio that transforms into CDHA when its Ca/P ratio reaches 1.5. At the same time, CaO is hydrated into Ca(OH)(2) by the water produced by the reaction. (Second stage) If the Ca/P > 1.5 in the initial mixture, the excess Ca(OH)(2) is added to CDHA 1.5 by reacting with the HPO(4) group of CDHA until its Ca/P ratio reaches the expected value. The slower the reaction, the higher the Ca/P in the initial mixture.
磷酸钙陶瓷已成功用作骨科、牙科和颌面外科的人工骨替代物。制备这些陶瓷的一种方法是烧结缺钙羟基磷灰石（CDHA），其可通过不同方式获得。机械化学是合成CDHA的一种可能方法，预期的钙磷摩尔比（Ca/P）为±0.005。研磨可在干法或湿法条件下进行。为了优化通过干机械合成制备CDHA的实验条件，并更好地理解DCPD/CaO机械化学反应，我们进行了一项动力学研究，其中一些实验参数有所变化。通过两台不同的垂直旋转球磨机进行的这项动力学研究表明：（1）实验具有可重复性，最终产物为羟基磷灰石粉末，由约20nm的纳米级晶体组成，Ca/P比可控；（2）DCPD完全消失的时间和完全反应的时间与研磨粉末的质量成正比；但（3）DCPD完全消失的时间与Ca/P比无关，而完全反应的时间随Ca/P比呈指数增加；并且（4）仅当Ca/P = 1.5时，DCPD完全消失的时间才与完全反应的时间相对应。这些观察结果表明了一个分为两个明显不同阶段的反应机制：（第一阶段）CaO与DCPD反应首先生成低Ca/P比的无定形磷酸钙（ACP），当其Ca/P比达到1.5时转变为CDHA。同时，CaO被反应产生的水合成为Ca(OH)₂。（第二阶段）如果初始混合物中的Ca/P > 1.5，则过量的Ca(OH)₂通过与CDHA的HPO₄基团反应添加到CDHA 1.5中，直至其Ca/P比达到预期值。反应越慢，初始混合物中的Ca/P越高。
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