Visualising the evolution of crystallisation and mineralisation of bioactive glasses

生物活性玻璃被认为是骨再生和组织工程的优良材料。此外，某些离子，如铜或银离子，可以加入到生物活性玻璃组合物中，提供额外的治疗益处，如刺激血管生成(血管形成)或抗菌效果。尽管生物活性玻璃具有良好的生物相容性和生物活性，但仍有一些问题尚未完全了解，限制了生物活性玻璃的临床应用。其中一个关键问题是它们的结晶行为。一般来说，玻璃材料很容易通过烧结成型，形成涂层或复杂的3D结构，如多孔支架。然而，典型生物活性玻璃的一个特殊缺点是，它们在高温下快速结晶。众所周知，这会抑制最常用的组合物45S5的致密烧结，并导致其支架具有较差的机械性能。为了改善这些玻璃的烧结，需要回答的最重要的问题是：晶化和晶相形成的类型如何影响烧结？这会随着成分和玻璃结构的不同而变化吗？结晶化对体外生物活性和细胞相容性有什么影响？众所周知，生物活性玻璃的晶化本身并不是一件负面的事情。然而，我们需要更深入地了解所发生的过程，以便控制晶化和获得生物活性玻璃系统，该系统允许在烧结过程中致密，并创造出机械上更稳定的高度生物活性的支架。因此，本项目的主要目的是研究生物活性玻璃和微晶玻璃的晶化过程，这些玻璃和微晶玻璃是通过不同的合成路线(熔融-急冷和溶胶-凝胶)和不同的组成合成的。为了实现这一点，这项研究的新颖性在于除了使用传统的表征技术，如电子显微镜(扫描电子显微镜和电子显微镜)和X射线衍射之外，还使用了X射线显微镜(XRM)。相比之下，XRM提供了重要的优势，主要是在非破坏性样品制备和以纳米分辨率获得样品的3D整体可视化的可能性方面。这使我们能够观察同一样品在不同热处理阶段结晶过程中的变化。从初始成核阶段到最终结晶阶段的结晶过程的演变将通过上述组合技术进行监测。XRM结果将为这些材料的3D结构提供新的见解，并将有助于澄清与结晶、烧结和高温加工相关的悬而未决的问题及其对体外生物活性的影响。

Bioactive glasses are known to be excellent materials for bone regeneration and tissue engineering. Moreover, certain ions, like copper or silver ions, can be incorporated into the bioactive glass composition, providing additional therapeutic benefits, like stimulation of angiogenesis (blood vessel formation) or antibacterial effects. Despite their excellent biocompatibility and bioactivity, there are still several issues, which are not fully understood and limit bioactive glass clinical application.One key issue is their crystallisation behaviour. Generally, glassy materials can easily be shaped by sintering, to form coatings or complex 3D structures such as porous scaffolds. One special drawback of typical bioactive glasses, however, is their rapid crystallisation at elevated temperatures. This is known to inhibit dense sintering of the most commonly used composition, 45S5, and results in its scaffolds possessing poor mechanical properties. In order to improve sintering of these glasses, the most important questions to be answered are: How do crystallisation and the type of crystal phases forming affect sintering? How does this vary with composition and glass structure? And what is the influence of crystallisation on in vitro bioactivity and cell compatibility? It is known that the crystallisation of bioactive glasses is not per se a negative thing. However, we need a deeper understanding of the processes taking place in order to control crystallisation and obtain bioactive glass systems, which allow for densification during sintering, and create mechanically more stable scaffolds which are highly bioactive. Thus, the main aim of this project is to investigate the crystallisation processes in bioactive glasses and glass-ceramics, synthesised by different routes (melt-quench vs. sol-gel) and of varying composition. To achieve this, the novelty of this research lies in the use of X-ray microscopy (XRM) in addition to conventional characterisation techniques like electron microscopy (SEM and TEM) und X-ray diffraction. XRM offers important advantages in comparison, mainly with regard to non-destructive sample preparation and the possibility to get a 3D bulk visualisation of the sample with nanometre resolution. This allows us to observe changes during crystallisation on the same specimen at different stages of heat treatment. The evolution of crystallisation processes from the initial nucleation step to the final crystallisation stage will be monitored by the combined techniques mentioned above. XRM results will hereby provide new insight into the 3D structure of these materials and will help to clarify open questions related to crystallisation, sintering and high-temperature processing as well as their influence on in vitro bioactivity.