Abstract
AbstractThe sintering of bioactive glasses allows for the preparation of complex structures, such as three‐dimensional porous scaffolds. Such 3D constructs are particularly interesting for clinical applications of bioactive glasses in bone regeneration, as the scaffolds can act as a guide for in‐growing bone cells, allowing for good integration with existing and newly formed tissue while the scaffold slowly degrades. Owing to the pronounced tendency of many bioactive glasses to crystallize upon heat treatment, 3D scaffolds have not been much exploited commercially. Here, we investigate the influence of crystallization on the sintering behavior of several bioactive glasses. In a series of mixed‐alkali glasses an increased CaO/alkali metal oxide ratio improved sintering compared to Bioglass 45S5, where dense sintering was inhibited. Addition of small amounts of calcium fluoride helped to keep melting and sintering temperatures low. Unlike glass 13‐93, these new glasses crystallized during sintering but this did not prevent densification. Variation in bioactive glass particle size allowed for fine‐tuning the microporosity resulting from the sintering process.
Highlights
The reason for the clinical success of Bioglass 45S5,1 which has been used clinically since the mid‐1980s,2 is its ability to degrade in aqueous solution, release calcium and phosphate ions, form a surface layer of hydroxycarbonate apatite and allow for the formation of an intimate bond to bone.[1]
Sintered powder compacts were crushed with a steel mortar and milled twice for 30 seconds in an agate ball mill (KM1; Janetzki) for analysis by powder X‐ray diffraction (XRD; D8 Advance; Bruker AXS, Karlsruhe, Germany; Cu‐Kα radiation, scanning in 0.02° steps for 2 seconds in a 5 to 80°2θ range) and attenuated total reflection (ATR) Fourier‐transform infrared spectroscopy (FTIR; Nicolet Avatar 370DTGS with art Orbit addition; Thermo Electron Corporation; 525‐1700 cm−1)
Taken together our results show that while crystallization inhibits complete sintering of Bioglass 45S5 at temperatures around 600°C, crystallization does not necessarily prevent the dense sintering of bioactive glasses, depending on the glass composition
Summary
The reason for the clinical success of Bioglass 45S5,1 which has been used clinically since the mid‐1980s,2 is its ability to degrade in aqueous solution, release calcium and phosphate ions, form a surface layer of hydroxycarbonate apatite and allow for the formation of an intimate bond to bone.[1]. One reason is that Bioglass 45S5, which has a highly disrupted silicate structure consisting of Q2 chains mostly with only small amounts (10%‐15%) of Q3 branching units,[11,12] shows a pronounced tendency to undergo devitrification upon heat treatment This makes it challenging to process the glass without crystallization occurring.[13] For bioactive glass applications, in bone regeneration, the capacity to sinter complex, three‐dimensional porous structures, so‐called scaffolds, would be of great interest as this could broaden the field of clinical applications. |2 these applications, the porous scaffold acts as a 3D template, which ideally integrates well with existing tissue, allows for the ingrowth of cells, guides them to grow deep into the pores and stimulates them to form new bone and allows for the growth of new blood vessels into this structure For this reason, this paper investigates the sintering behavior of Bioglass 45S5 and other bioactive glasses, to analyze how crystallization affects sintering and the resulting microstructure of the materials
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