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，可以并入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）或抗菌作用。尽管生物活性玻璃具有良好的生物相容性和生物活性，但仍存在一些问题，这些问题尚未完全了解并限制了生物活性玻璃的临床应用。一个关键问题是它们的结晶行为。一般来说，玻璃材料可以很容易地通过烧结成形，形成涂层或复杂的3D结构，如多孔支架。然而，典型的生物活性玻璃有一个特殊的缺点，那就是它们在高温下会快速结晶。众所周知，这抑制了最常用的组合物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性能，需要回答的最重要的问题是：结晶和形成的晶相类型如何影响烧结？这是如何变化的成分和玻璃结构？结晶对体外生物活性和细胞相容性有何影响？众所周知，生物活性玻璃的结晶本身并不是一件坏事。然而，我们需要更深入地了解发生的过程，以控制结晶和获得生物活性玻璃系统，这允许在烧结过程中致密化，并创造机械上更稳定的支架，具有高度的生物活性。因此，该项目的主要目的是研究生物活性玻璃和玻璃陶瓷的结晶过程，通过不同的合成途径（熔融淬火vs溶胶凝胶）和不同的组成。为了实现这一目标，这项研究的新颖性在于使用x射线显微镜（XRM）以及传统的表征技术，如电子显微镜（SEM和TEM）和x射线衍射。相比之下，XRM提供了重要的优势，主要是关于非破坏性样品制备和以纳米分辨率获得样品的3D体可视化的可能性。这使我们能够在热处理的不同阶段观察同一试样结晶过程中的变化。从初始成核步骤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。因此，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、烧结和高温处理以及它们对体外生物活性的影响有关的开放性问题。

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.