Abstract
Glasses are a remarkable class of materials with a rich history and a wide range of applications. Traditionally, inert silicate glass compositions have been used in applications such as tableware and window glass panes. Today, the category of amorphous materials has expanded to include various types, from metallic glasses to optical glass fibers. Bioactive glasses are specific types of glasses that react at measurable rates in aqueous solutions. These reactions can lead to chemical bonding with bone apatite and the promotion of new bone regeneration, making bioactive glasses suitable for bone healing applications. When a bioactive glass implant gradually dissolves, it forms a hydroxyapatite layer on its surface through a series of chemical reactions. The ions released during this process are known to induce angiogenesis and promote osteogenesis. Since the ion release rate depends on various parameters, such as the implantation site, glass composition, and implant surface area, understanding the long-term dissolution of bioactive glass-based products is important.
This thesis studied the long-term dissolution of different types of bioactive glass scaffolds and particles in order to gain insight and enable predictions about their dissolution behavior over time. The in vitro studies were conducted using a dynamic flow-through set-up for up to 21 days for glasses 45S5, S53P4, and S59. During the thermal treatments needed for the scaffold manufacture,
these glasses exhibit different crystallization behaviors, which affects the longterm dissolution of scaffolds sintered from them. Dissolution of partially crystallized S53P4 and amorphous S59 scaffolds was also studied in vivo for up to 56 days, and the results were compared to the in vitro findings.
The long-term in vivo dissolution behavior was better mimicked with the dynamic flow-through set-up when compared to results from traditional static dissolution studies. For partially crystallized glass S53P4 scaffolds, the cumulative silicon release from dynamic in vitro study was over 40% of the total silicon during 14 days of immersion, while in static tests, only 4.4% of silicon dissolved. The estimates from the in vivo analyses of the scaffolds suggested that approximately 60% of the silicon had dissolved after 14 days.
Analyzing the partially crystallized scaffolds after the dissolution suggested that their outer dimensions stayed almost constant, while most of the calcium phosphate precipitated inside the crystallized layer and not on the outer surfaces. Thus, the dissolution did not decrease the outer dimensions of the scaffold but hollowed the granules in them. This behavior enabled the numerical approximations for the in vivo dissolution. After 56 days, 68% of silicon and 90% of sodium had dissolved from the original sintered scaffolds, suggesting that all sodium would be exhausted after three months (87 days) and all silicon after eight months (240 days). No similar approximations on
long-term dissolution have been reported on bioactive glasses, which underlines the results' significance.
In contrast to earlier reports, this thesis showed that through careful optimization of the thermal treatment parameters, glass S53P4 could be sintered into amorphous scaffolds with compressive strength comparable to cancellous bone (5 MPa). This result was significant, as glass S53P4 is one of only a few compositions approved for clinical bone implantation applications. Earlier, its sintering window was considered too narrow to achieve strong scaffolds for implantation purposes.
The results obtained in this thesis give valuable information and approximation tools for the bioactive glass research community and pave the way for potential future clinical applications for hot-worked S53P4 glass. The estimates regarding long-term dissolution help predict the optimal duration during which the dissolving dose benefits biological processes. Improvements in the accuracy and relevance of in vitro studies reduce the need for in vivo experiments.
This thesis studied the long-term dissolution of different types of bioactive glass scaffolds and particles in order to gain insight and enable predictions about their dissolution behavior over time. The in vitro studies were conducted using a dynamic flow-through set-up for up to 21 days for glasses 45S5, S53P4, and S59. During the thermal treatments needed for the scaffold manufacture,
these glasses exhibit different crystallization behaviors, which affects the longterm dissolution of scaffolds sintered from them. Dissolution of partially crystallized S53P4 and amorphous S59 scaffolds was also studied in vivo for up to 56 days, and the results were compared to the in vitro findings.
The long-term in vivo dissolution behavior was better mimicked with the dynamic flow-through set-up when compared to results from traditional static dissolution studies. For partially crystallized glass S53P4 scaffolds, the cumulative silicon release from dynamic in vitro study was over 40% of the total silicon during 14 days of immersion, while in static tests, only 4.4% of silicon dissolved. The estimates from the in vivo analyses of the scaffolds suggested that approximately 60% of the silicon had dissolved after 14 days.
Analyzing the partially crystallized scaffolds after the dissolution suggested that their outer dimensions stayed almost constant, while most of the calcium phosphate precipitated inside the crystallized layer and not on the outer surfaces. Thus, the dissolution did not decrease the outer dimensions of the scaffold but hollowed the granules in them. This behavior enabled the numerical approximations for the in vivo dissolution. After 56 days, 68% of silicon and 90% of sodium had dissolved from the original sintered scaffolds, suggesting that all sodium would be exhausted after three months (87 days) and all silicon after eight months (240 days). No similar approximations on
long-term dissolution have been reported on bioactive glasses, which underlines the results' significance.
In contrast to earlier reports, this thesis showed that through careful optimization of the thermal treatment parameters, glass S53P4 could be sintered into amorphous scaffolds with compressive strength comparable to cancellous bone (5 MPa). This result was significant, as glass S53P4 is one of only a few compositions approved for clinical bone implantation applications. Earlier, its sintering window was considered too narrow to achieve strong scaffolds for implantation purposes.
The results obtained in this thesis give valuable information and approximation tools for the bioactive glass research community and pave the way for potential future clinical applications for hot-worked S53P4 glass. The estimates regarding long-term dissolution help predict the optimal duration during which the dissolving dose benefits biological processes. Improvements in the accuracy and relevance of in vitro studies reduce the need for in vivo experiments.
| Original language | English |
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| Place of Publication | Åbo |
| Publisher | |
| Print ISBNs | 978-952-12-4507-7 |
| Electronic ISBNs | 978-952-12-4508-4 |
| Publication status | Published - 2025 |
| MoE publication type | G5 Doctoral dissertation (article) |