Patel U, Moss R M, Hossain K M Z, Kennedy A R, Barney E R, Ahmed I, Hannon A C
Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK.
Department of Medical Physics and Biomedical Engineering, University College London, London, UK.
Acta Biomater. 2017 Sep 15;60:109-127. doi: 10.1016/j.actbio.2017.07.002. Epub 2017 Jul 4.
Neutron diffraction, Na and P NMR, and FTIR spectroscopy have been used to investigate the structural effects of substituting CaO with SrO in a 40PO·(16-x)CaO·20NaO·24MgO·xSrO glass, where x is 0, 4, 8, 12 and 16mol%. The P solid-state NMR results showed similar amounts of Q and Q units for all of the multicomponent glasses investigated, showing that the substitution of Sr for Ca has no effect on the phosphate network. The M-O coordinations (M=Mg, Ca, Sr, Na) were determined for binary alkali and alkaline earth metaphosphates using neutron diffraction and broad asymmetric distributions of bond length were observed, with coordination numbers that were smaller and bond lengths that were shorter than in corresponding crystals. The Mg-O coordination number was determined most reliably as 5.0(2). The neutron diffraction results for the multicomponent glasses are consistent with a structural model in which the coordination of Ca, Sr and Na is the same as in the binary metaphosphate glass, whereas there is a definite shift of Mg-O bonds to longer distance. There is also a small but consistent increase in the Mg-O coordination number and the width of the distribution of Mg-O bond lengths, as Sr substitutes for Ca. Functional properties, including glass transition temperatures, thermal processing windows, dissolution rates and ion release profiles were also investigated. Dissolution studies showed a decrease in dissolution rate with initial addition of 4mol% SrO, but further addition of SrO showed little change. The ion release profiles followed a similar trend to the observed dissolution rates. The limited changes in structure and dissolution rates observed for substitution of Ca with Sr in these fixed 40mol% PO glasses were attributed to their similarities in terms of ionic size and charge.
Phosphate based glasses are extremely well suited for the delivery of therapeutic ions in biomedical applications, and in particular strontium plays an important role in the treatment of osteoporosis. We show firstly that the substitution of strontium for calcium in bioactive phosphate glasses can be used to control the dissolution rate of the glass, and hence the rate at which therapeutic ions are delivered. We then go on to examine in detail the influence of Sr/Ca substitution on the atomic sites in the glass, using advanced structural probes, especially neutron diffraction. The environments of most cations in the glass are unaffected by the substitution, with the exception of Mg, which becomes more disordered.
采用中子衍射、钠和磷核磁共振以及傅里叶变换红外光谱法，研究了在40PO·(16 - x)CaO·20NaO·24MgO·xSrO玻璃中用SrO替代CaO的结构效应，其中x为0、4、8、12和16mol%。磷固态核磁共振结果表明，在所研究的所有多组分玻璃中，Q和Q单元的含量相似，这表明用Sr替代Ca对磷酸盐网络没有影响。利用中子衍射确定了二元碱金属和碱土金属偏磷酸盐的M - O配位（M = Mg、Ca、Sr、Na），观察到键长呈宽不对称分布，其配位数比相应晶体中的小，键长比相应晶体中的短。Mg - O配位数最可靠地确定为5.0(2)。多组分玻璃的中子衍射结果与一种结构模型一致，在该模型中，Ca、Sr和Na的配位与二元偏磷酸盐玻璃中的相同，而Mg - O键有明显向更长距离的偏移。随着Sr替代Ca，Mg - O配位数和Mg - O键长分布宽度也有小但一致的增加。还研究了包括玻璃化转变温度、热加工窗口、溶解速率和离子释放曲线等功能特性。溶解研究表明，最初添加4mol% SrO时溶解速率降低，但进一步添加SrO变化不大。离子释放曲线与观察到的溶解速率趋势相似。在这些固定的40mol% PO玻璃中，用Sr替代Ca时观察到的结构和溶解速率的有限变化归因于它们在离子大小和电荷方面的相似性。
磷酸盐基玻璃非常适合在生物医学应用中输送治疗性离子，特别是锶在骨质疏松症治疗中起重要作用。我们首先表明，在生物活性磷酸盐玻璃中用锶替代钙可用于控制玻璃的溶解速率，从而控制治疗性离子的输送速率。然后，我们继续使用先进的结构探针，特别是中子衍射，详细研究Sr/Ca替代对玻璃中原子位置的影响。玻璃中大多数阳离子的环境不受替代影响，除了Mg，其变得更加无序。
