The Influence of Phase Separation on Bioactivity of Spray Pyrolyzed Bioactive Glass

Abstract

In this study, bioactive glass (BG) particles were synthesized directly using spray pyrolysis (SP). Since the bioactivity of glass particles is well correlated with their chemical composition, how to obtain homogenous bioactive glass becomes an important issue. For SP, the main reason for chemical inhomogeneity was considered to be caused by the difference in the precipitation speed of each precursor. So, two Si-containing precursors of BG, namely tetraethyl orthosilicate (TEOS) and silicon acetate (SiA), have been applied to prepare BG particles. The bioglasses were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy to examine their phase composition, and surface structures, inner morphologies and chemical compositions. It was observed that, under the calcination temperature of 700 degrees C, TEOS-derived powder contained Si-rich nanoparticles and Si-deficit submicron particles as inhomogeneity, whereas the SiA-derived powder was homogenous. The reason of inhomogeneity is that TEOS dissolves in "volatile" ethanol more readily than in water via the SP mechanism of "gas-to-particle-conversion" to form Si-rich nanoparticles. The presence of Si-rich nanoparticles causes Si-deficit "wollastonite submicron particles" to form, which impairs the bioactivity. Finally, BG particle formation mechanisms from different precursors have been proposed.

The Correlation of Surfactant Concentrations on the Properties of Mesoporous Bioactive Glass

“…So, the formation of amorphous SiO 2 nanoparticles inhibits the formation of HA. This result supports that the view that the addition of a surfactant stabilizes the Si precursor and avoids the formation of amorphous SiO 2 nanoparticles [31] that cause the gas-to-particle conversion for phase separation.…”

“…In a previous study, we used TEOS, CN, and TEP as precursors (Si, Ca, and P precursors, respectively) to prepare SP-derived BG at a high calcination temperature of 700 °C, and the nanoparticles of amorphous SiO 2 and the submicron particles of wollastonite-based glass were observed using TEM and X-ray energy-dispersive spectroscopy [31]. TEOS is insoluble with water because of its hydrolysis behavior, whereas CN and TEP are soluble in water, and the different precipitation behaviors of TEOS, CN, and TEP led to this inhomogeneity.…”

An Investigation of In Vitro Bioactivities and Cytotoxicities of Spray Pyrolyzed Apatite Wollastonite Glass-Ceramics

“…Since the crystallinity of our starting powder is weaker than that of AWGC prepared by Kitsugi et al [19], and the main reason is that the short calcination time of spray pyrolysis (~10 s) at the temperature of 700 • C [20], and AWGCs may not have enough time for crystal growth. For the SEM analysis (see Figure 1b), the starting powder has an average particle size of 0.92 ± 0.44 µm, and the powder exhibits the two typical shapes of a smooth sphere and rough sphere, which is similar to our previous spray pyrolysis study of bioglass [21]. Additionally, the XEDS measurement revealed that the as-prepared powder contained 36.00 ± 1.16 mol% Ca, 9.73 ± 0.02 mol% Mg, 22.09 ± 0.53 mol% P, 31.10 ± 2.17 mol% Si, and 1.08 ± 0.03 mol% F, which is close to the precursor composition.…”

The Correlation of Pore Size and Bioactivity of Spray-Pyrolyzed Mesoporous Bioactive Glasses

“…In the former, micron-sized droplets atomized by an ultrasonic nebulizer are directly converted into oxide particles. In the latter, nano-sized particles (<0.1 μm) condense from the gas phase [28]. Based on the SEM observations, all the surfactant-treated MBG powders had an average particle size of ~600 nm, indicating that all the MBG powders formed via the “one-particle-per-drop” mechanism [27].…”