Deepening our understanding of bioactive glass crystallization using TEM and 3D nano-CT
Deepening our understanding of bioactive glass crystallization using TEM and 3D nano-CT
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DOI：
10.1016/j.jeurceramsoc.2021.02.051
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发表时间：
2021-04-14
影响因子：
5.7
通讯作者：
Brauer, Delia S.
中科院分区：
文献类型：
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作者：
Contreras Jaimes, Altair T.;de Pablos-Martin, Araceli;Brauer, Delia S.
影响生物玻璃45 S5在组织工程中更广泛应用的一个关键问题是其固有的结晶倾向，严重限制了3D多孔支架的机械强度。尽管进行了大量研究，但生物玻璃45 S5结晶尚未完全了解所涉及的机制或晶相形成的形态。在这里，我们展示了两种尖端的成像技术，最先进的透射电子显微镜（TEM）与图像校正，包括能量色散X射线光谱和X射线纳米计算机断层扫描（nano-CT），使我们能够可视化从近成核到几乎完全结晶的散装生物玻璃45 S5的微观结构的变化。在660 ℃热处理的早期？观察到在玻璃基质内形成相分离的纳米液滴。后来，除了表面结晶，体结晶的Combeite球占主导地位。通过原位高温光学显微镜视频记录了第一个Combeite球体的形成，它们随时间的粗化以及最后它们在接近完全结晶时的合并。纳米CT证实了这些球体的3D性质，而TEM显示其内部结构由亚微米颗粒组成。在早期时间点的X射线衍射分析显示，与粉末样品相比，散装样品中的结晶分数高得多，突出了加工和样品形态的影响。这些结果表明，使用互补技术的重要性，以深入了解结晶过程中的体积。此外，我们表明，TEM和纳米CT是合适的表征技术，可视化的结晶，即使在快速结晶系统，如生物活性玻璃。
One key issue influencing a broader application of Bioglass 45S5 in tissue engineering is its inherent crystallization tendency, severely limiting the mechanical strength of 3D porous scaffolds. Despite numerous studies, Bioglass 45S5 crystallization is not yet fully understood with regard to the mechanisms involved or morphology of the crystal phases forming. Here we show how two cutting-edge imaging techniques, state-of-the-art transmission electron microscopy (TEM) with image correction including energy dispersive X-ray spectroscopy and Xray nano-computed tomography (nano-CT), allowed us to visualize changes in microstructure from nearnucleation to almost full crystallization in bulk Bioglass 45S5. At early times of heat treatment at 660 ?C the formation of phase-separated nano-droplets within the glassy matrix was observed. Later, besides surface crystallization, bulk crystallization of combeite spheres was predominant. The formation of the first combeite spheres, their coarsening with time and finally their merging at near full crystallization were recorded by in situ high-temperature optical microscopy videos. The 3D nature of these spheres was confirmed by nano-CT, while TEM showed that their internal structure was composed of sub-micron grains. X-ray diffraction analysis at early time points showed a much higher crystalline fraction in bulk samples compared to powder samples, highlighting the influence of processing and sample morphology. These results show the importance of using complementary techniques for gaining insight into the crystallization process in the volume. In addition, we show that TEM and nano-CT are suitable characterization techniques to visualize the crystallization even in fast crystallizing systems, such as bioactive glasses.