Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ UK.
Biomed Mater. 2013 Apr;8(2):025003. doi: 10.1088/1748-6041/8/2/025003. Epub 2013 Jan 23.
Substituted hydroxyapatites have been investigated for use as bone grafts and have been investigated for many years. Zinc is of interest due to its potential to reduce bone resorption and antibacterial properties. However, it has proven problematic to substitute biologically significant levels of zinc into the crystal structure through wet chemical routes, whilst retaining the high temperature phase stability required for processing. The aim of this study is to investigate two different precipitation routes used to synthesize zinc substituted hydroxyapatite and to explore the effects of ammonia used in the reactions on the levels of zinc substituted into the crystal lattice. It was found that considerable amounts of ammonia are required to maintain a pH sufficiently high for the production of stoichiometric hydroxyapatite using a reaction between calcium nitrate, zinc nitrate and ammonium phosphate. X-ray fluorescence analysis showed that a significant proportion of the zinc added did not substitute into the hydroxyapatite lattice. Fourier transform infrared spectroscopy revealed the existence of a zinc-ammonia complex that, it is proposed, inhibits zinc substitution for calcium. It was found that by reacting orthophosphoric acid with calcium nitrate and zinc nitrate, the volume of ammonia required in the reaction was reduced and higher levels of zinc substitution were achieved, with up to 0.58 wt% incorporated into the hydroxyapatite lattice. The resulting products were found to be stoichiometric hydroxyapatite and did not appear to contain any extraneous calcium phosphate phases after heat treatment up to 1100 °C. X-ray diffraction and Rietveld analysis revealed that the effect of substituting zinc into the HA lattice was to decrease the a-lattice parameter whilst increasing the c-lattice. Transmission electron microscopy also showed that the incorporation of zinc reduced both the length and width of the precipitated crystals.
已研究了取代羟磷灰石作为骨移植物的用途，并对其进行了多年的研究。锌因其具有减少骨吸收和抗菌特性的潜力而引起关注。然而，通过湿化学途径将生物学上有意义水平的锌替代到晶体结构中，同时保持加工所需的高温相稳定性，这被证明是有问题的。本研究旨在研究两种不同的沉淀途径，用于合成锌取代羟磷灰石，并探索反应中使用的氨对晶体晶格中锌取代程度的影响。结果发现，使用硝酸钙、硝酸锌和磷酸铵之间的反应来生产化学计量的羟磷灰石时，需要相当大量的氨来维持足够高的 pH 值。X 射线荧光分析表明，添加的锌中有很大一部分没有取代到羟磷灰石晶格中。傅里叶变换红外光谱显示存在锌-氨络合物，据推测，该络合物会抑制锌对钙的取代。结果发现，通过使正磷酸与硝酸钙和硝酸锌反应，可以减少反应中所需的氨量，并实现更高水平的锌取代，最多可将 0.58wt%的锌掺入羟磷灰石晶格中。发现所得产物为化学计量的羟磷灰石，并且在热处理至 1100°C 之前，似乎不含有任何外来的磷酸钙相。X 射线衍射和 Rietveld 分析表明，锌取代 HA 晶格的作用是减小 a 晶格参数，同时增大 c 晶格参数。透射电子显微镜还表明，锌的掺入减小了沉淀晶体的长度和宽度。
