Sintering, crystallisation and biodegradation behaviour of Bioglass®-derived glass–ceramics

Abstract

Sintering and crystallisation phenomena in powders of a typical bioactive glass composition (45S5 Bioglass) have been investigated in order to gain further understanding of the processes involved in the fabrication of Bioglass, based glass-ceramic scaffolds for tissue engineering applications. In situ experiments in an environmental scanning electron microscope with a heating stage were carried out to follow the morphology of Bioglass particles during sintering and crystallisation. Optimal processing parameters for the manufacture of Bioglass based glass-ceramic scaffolds by the foam-replica technique were determined. To assess the in vitro performance and bioreactivity of Bioglass -derived glass-ceramic scaffolds, the biodegradation of samples in simulated body fluid (SBF) was investigated using various techniques, including SEM, TEM, XRD and EDX. The mechanism of interaction of the glass-ceramic surface with SBF was determined, which involves (i) preferential dissolution at glass/crystal interfaces, (ii) break-down of crystalline particles into very fine grains through preferential dissolution at crystal structural defects, and (iii) amorphisation of the crystalline structure by introduction of point defects produced during ion exchange. The present report thus offers for the first time a complete assessment of the processing parameters, microstructure, and in vitro performance of Bioglass derived glass-ceramic scaffolds intended for bone tissue engineering.

Processing and in vitro bioactivity of high-strength 45S5 glass-ceramic scaffolds for bone regeneration

“…It has been mentioned in the literature that 45S5 tends to crystallize during heat treatments due to the relatively low percentage of silica and the high content of network modifiers. Additionally, it has been noted that crystallization during sintering has adverse effects on the bioactivity of the scaffolds and can even suppress it [4]. However, as shown in the present results, crystallization only slowed down the bioactivity.…”

“…This discovery has stimulated research on the use of bioactive glasses as scaffolds for tissue engineering. It has been demonstrated that bioactive glass 45S5, also known as Bioglass®, has the greatest potential to be used as a threedimensional matrix (regenerative scaffold) in a large number of human bone components; although it crystallizes during sintering, its bioactivity slows down but it is not eliminated [2][3][4]. Recent studies have shown that the ability to regenerate human tissue through the formation of a hydroxyapatite surface layer depends on the porosity of the 3D bioactive glass structure, given that the scaffold has greater capacity when it is more porous [5][6][7][8].…”

Bioactive glass and glass-ceramic scaffolds for bone tissue engineering

“…Recent developments related to bone TE try to bridge this gap and overcome this problem by architectures and components carefully designed from comprehensive levels, i.e., from the macro-, meso-, micrometer down to the nanometer scale [101], including both multifunctional bioactive glass composite structures (see §3.2) and advanced bioactive glass-ceramic scaffolds exhibiting oriented microstructures, controlled porosity and directional mechanical properties [99,[102][103][104][105], as discussed in the following paragraphs. Most studies have investigated mainly the mechanical properties, in vitro and cell biological behavior of glass-ceramic scaffolds [13][14][15]30,43,52,94,95,97,99,, as summarized in Table 1, and scaffolds with compressive strength [99,102] and elastic modulus values [99,105] in magnitudes far above that of cancellous bone and close to the lower limit of cortical bone have been realized. Fu et al [99] fabricated bioactive glass (13-93) scaffolds with oriented (i.e., columnar and lamellar) microstructures and found that at an equivalent porosity of 55-60%, the columnar scaffolds had a compressive strength of 25 ± 3 MPa, compressive modulus of 1.2 GPa, and pore width of 90-110 µm, compared to values of 10 ± 2 MPa, 0.4 GPa, and 20-30 μm, respectively, for the lamellar scaffolds.…”

“…Glass-ceramics are partially crystallized glasses produced by heating the parent bioactive glass above its crystallization temperature, usually at about 610-630 °C [33,44,96,97]. In the case of glass-ceramics obtained by a sintering process, during the occurrence of crystallization and densification, the microstructure of the parent glass shrinks, porosity is reduced and the solid structure gains mechanical strength [70].…”

Production and Characterization of Glass-Ceramic Materials for Potential Use in Dental Applications: Thermal and Mechanical Properties, Microstructure, and In Vitro Bioactivity

“…As regards the crystalline phases of TT-CEL2, Na 2 Ca 2 Si 3 O 9 is the same crystalline phase that develops in 45S5 Bioglass ® when thermally-treated above 600 • C [42][43][44]-This commercial bioactive glass has been implanted since the early 1990s in millions of patients to regenerate bone [45]-And Ca 2 Mg(Si 2 O 7 ) was proved effective to promote new bone tissue formation in vivo, too [46,47]. FA, found in TT-FaGC, is a natural component of tooth enamel [48]; canasite is biocompatible, although its use for bone repair requires caution due to its tendency to fast resorption in vivo [49].…”