Visualising the evolution of crystallisation and mineralisation of bioactive glasses
Biomaterials
Synthesis and Properties of Functional Materials
Final Report Abstract
This project was focused on the characterization of bioactive glasses and glass-ceramics. The role of crystallization in bioactivity is still very controversial. Crystallization was studied in 45S5 BG (melt-derived and sol-gel), 13-93 BG and a series of 6 glasses with variying phosphate/silicate ratio. We showed that the nature of the crystalline phases (silicate of phosphate) can be tuned with the composition (from 45S5 to 13-93, and phosphate/silicate glasses), with the sinthesis method (melting or sol-gel) and with the heat treatement, but also the crystal size and crystalline fraction can be optimized. Besides thermal and structural characterization, the focus was the use of imaging techniques. For the first time X-ray microscopy was employed to characterize the internal volumen of bioactive glasses and glass-ceramics, including bulk and powder samples, in amorphous state and crystallized, and before and after immersion in biological solutions. XRM samples were prepared by a dedicated laser-micromachining tool, which represents a further novelty in this project. XRM completes the TEM results, showing the morphology and volumen distribution of large particles in 3D. The combination of all the employed microscopies allowed us to visualize changes in microstructure f rom near-nucleation to almost full crystallization in a broad spectrum of glass compositions. The visualization of combeite spheres in the melt-derived 45S5 glass-ceramic would not be possible without XRM, and its ability to provide 3D inf ormation. In general the 45S5 melt-derived samples exhibit a low contrast in XRM, due to the solely crystallization of combeite, whose composition is similar to the residual glassy phase. By contrast, sol-gel materials present a higher inhomogeneity and thus, an improved contrast of different phases is achieved. New insights of the distribution of elements (e.g. Cu) and crystalline phases in the volumen of the samples, as well as their morphology were achieved. A very complete crystallization study was carried out in glasses with variying phosphate to silicate ratio, including thermal and structural characterization. The nano- and microstructural changes were evaluated as a f unction of composition, and af ter the immersion in Tris buffer. It is possible to tune the crystallization degree of two of the most important phases in the f ield of bioactive glasses, wollastonite and f luorapatite, by variying the phosphate/silicate ratio and the temperature-time protocol. Crystallization mechanisms were determined by DSC studies. Additionally two pionering workflows were carried out with dedicated XRM sample design: (1) quasi-insitu study, by alternating heat treatment and XRM scanning of the 45S5 (meltderived), and (2) direct correlation of XRM with EDX to get chemical information of regions of interest observed in sol-gel 45S5. Besides crystallization, sintering studies reveal that crystallization does not inhibit densification neither in all the investigated glasses with different phosphate to silicate ratio, nor in the boron-doped 45S5 glass. Scaffolds were prepared from melt-derived and sol-gel 13-93 glass. The cytocompatibility of the prepared bioactive glasses having different silicate/phosphate ratios was determined via an indirect cell culture approach using ST-2 cell line for three days. The aliquots of BGs showed dose-dependent cell viability. More specifically, crystalline glasses exhibited higher cell viability when compared with amorphous glasses for each tested parameter (incubation time and particle size). This behaviour could be due to the higher release of ions from amorphous samples as compared to their crystallized counterpart. The fluorescence microscopy images showed the spreading and proliferation of the cells. The results are interesting and promising for the design of amorphous-crystalline systems with different compositions, where the crystallinity represents a new variable that can be tuned to affect the biological activity.
Publications
- „New insights into the crystallization process of sol-gel–derived 45S5 bioactive glass“ Journal of the American Ceramic Society (2020), 103 (8), pp. 4234-4247
Q. Nawaz, A. de Pablos-Martín, J. Martins de Souza e Silva, K. Hurle, A.T. Contreras Jaimes, D.S. Brauer, A.R. Boccaccini
(See online at https://doi.org/10.1111/jace.17124) - “Deepening our understanding of bioactive glass crystallization using TEM and 3D nano-CT”, Journal of the European Ceramic Society (2021) 41 (9), pp. 4958-4969
A.T Contreras Jaimes, A. de Pablos-Martín, K. Hurle, J. Martins de Souza e Silva, L. Berthold, T. Kittel, A.R. Boccaccini, D.S Brauer
(See online at https://doi.org/10.1016/j.jeurceramsoc.2021.02.051) - “Fluorine loss determination in bioactive glasses by laser-induced breakdown spectroscopy (LIBS)” International Journal of Applied Glass Science (2021), 12 (2), pp. 213-221
A. de Pablos-Martín, A.T Contreras Jaimes, S. Wahl, S. Meyer, D.S. Brauer
(See online at https://doi.org/10.1111/ijag.15867) - „Crystallization study of sol–gel derived 13-93 bioactive glass powder“, Journal of the European Ceramic Society (2021), 41 (2), pp. 1695-1706
Q. Nawaz, A. de Pablos-Martín, J. Martins de Souza e Silva, L. Berthold, K. Hurle, A.T. Contreras Jaimes, M. Sitarz, D.S. Brauer, A.R. Boccaccini
(See online at https://doi.org/10.1016/j.jeurceramsoc.2020.09.052)
