A multinuclear solid state NMR spectroscopic study of the structural evolution of disordered calcium silicate sol-gel biomaterials.
A multinuclear solid state NMR spectroscopic study of the structural evolution of disordered calcium silicate sol-gel biomaterials.
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DOI：
10.1039/c4cp04492d
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发表时间：
2015-01
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通讯作者：
Zhongjie Lin;Julian R. Jones;J. Hanna;Mark E. Smith
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作者：
Zhongjie Lin;Julian R. Jones;J. Hanna;Mark E. Smith
无序溶胶-凝胶法制备的硅酸钙生物材料表现出显著的、成分依赖的与骨结合的能力。骨结合是由于浸入体液(或植入)后在玻璃表面快速形成羟基碳酸盐磷灰石(HCA)。(CaO)x(SiO)1-x(x=0.2，0.3和0.5)在热处理和随后在模拟体液(SBF)中溶解的原子尺度细节通过使用一维(17)O，(29)Si，(31)P和(1)H.本研究的中心是传统的静态和幻角旋转(MAS)和二维(2D)三量子(3Q)(17)O核磁共振实验的结合，这些实验可以容易地区分和定量硅酸盐网络中的桥(BOS)和非桥(NBOS)氧。尽管溶胶中存在可溶钙，但(17)O-核磁共振结果表明，在凝胶、老化和干燥(例如在120℃)后，溶胶-凝胶生成的网络结构最初是由BOS主导的，表明钙盐和以硅酸盐为主的网络结构是纳米级的混合物。只有当钙盐在高温下分解时，Ca(2+)离子才能分解BO。磷灰石在SBF中的形成能力强烈依赖于表面羟基和钙含量。钙的存在通过促进表面水化和Ca(2+)离子的可获得性来促进HCA的形成。(17)O-核磁共振显示，当NBO被浸出到SBF中时，它的电荷被钙平衡地迅速损失。通过~(31)P核磁共振可以检测到纳米晶偏序羟基磷灰石的形成。这一数据表明了实现BO/NBO的正确平衡对于优化生化反应和网络性能的重要性。
Disordered sol-gel prepared calcium silicate biomaterials show significant, composition dependent ability to bond with bone. Bone bonding is attributed to rapid hydroxycarbonate apatite (HCA) formation on the glass surface after immersion in body fluid (or implantation). Atomic scale details of the development of the structure of (CaO)x(SiO2)1-x (x = 0.2, 0.3 and 0.5) under heat treatment and subsequent dissolution in simulated body fluid (SBF) are revealed through a multinuclear solid state NMR approach using one-dimensional (17)O, (29)Si, (31)P and (1)H. Central to this study is the combination of conventional static and magic angle spinning (MAS) and two-dimensional (2D) triple quantum (3Q) (17)O NMR experiments that can readily distinguish and quantify the bridging (BOs) and non-bridging (NBOs) oxygens in the silicate network. Although soluble calcium is present in the sol, the (17)O NMR results reveal that the sol-gel produced network structure is initially dominated by BOs after gelation, aging and drying (e.g. at 120 °C), indicating a nanoscale mixture of the calcium salt and a predominantly silicate network. Only once the calcium salt is decomposed at elevated temperatures do the Ca(2+) ions become available to break BO. Apatite forming ability in SBF depends strongly on the surface OH and calcium content. The presence of calcium aids HCA formation via promotion of surface hydration and the ready availability of Ca(2+) ions. (17)O NMR shows the rapid loss of NBOs charge balanced by calcium as it is leached into the SBF. The formation of nanocrystalline, partially ordered HCA can be detected via(31)P NMR. This data indicates the importance of achieving the right balance of BO/NBO for optimal biochemical response and network properties.