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This paper describes the characteristics of akermanite-gehlenite and diopside bioceramics derived from the CaO-MgO-Al2O3-SiO2 system as a potential bone substitute material. The akermanite-gehlenite and diopside bioceramics were synthesised for 4 h at 500 rpm via the wet mechanochemical process. The resultant powder was sintered at 1050 and 1150 °C for 1 h to obtain the akermanite-gehlenite and diopside bioceramics. The bioceramic's microstructural, physical, and mechanical properties were investigated comparatively. XRD diffraction, FTIR and scanning electron microscopy, with energy dispersive spectroscopy (SEM-EDS) analysis, were conducted to characterise the samples. The bioceramic samples' linear shrinkage, density, porosity, and water contact angle were analysed to determine their physical properties. The mechanical properties of the samples were determined using compressive tests before and after undergoing in vitro bioactivity. The in vitro bioactivity of the bioceramic was investigated by analysing its apatite-forming ability in a simulated body fluid (SBF) at 37 °C. XRD patterns, SEM micrographs, and FTIR spectra for pellets sintered at 1050 °C indicated the presence of apatite particles on their surfaces. The pellets' compressive strength before being immersed in SBF ranged between 24.42 ± 1.5 and 24.93 ± 1.7 MPa. The compressive strength of the pellets noticeably decreased to 34.4% and 40.7% after 14 days of immersion in SBF. In conclusion, the akermanite-gehlenite bioceramic prepared using the wet mechanochemical method can potentially become a bone substitute. [ABSTRACT FROM AUTHOR]

Maghemite (γ-Fe2O3) nanoparticles were synthesised using the coprecipitation method, with different concentrations (5 M, 10 M, 11 M, 12 M and 13.4 M) of sodium hydroxide (NaOH) as the precipitation agent. The resulting powder was characterised using x-ray diffraction (XRD), vibrating sample magnetometer (VSM), and transmission electron microscope (TEM). All characterisations were performed at room temperature. The XRD results showed that the γ-Fe2O3 powder was in a single phase for samples synthesised using 11 M, 12 M and 13.4 M NaOH and the crystallite size ranged between 5.74 nm-6.42 nm. TEM observations and analysis showed that the particles were in a cubo-spheroidal shape and the mean physical size of the nanoparticles was between 8.52 nm and 8.59 nm. Hysteresis loop indicated that γ-Fe2O3 nanoparticles have superparamagnetic properties with an acceptable range of saturation magnetisation of 31.08 emu/g-48.88 emu/g and negligible coercivity value. MTT assay demonstrated that the γ-Fe2O3 nanoparticles exhibited biocompatibility with V79-4 cells at different dosages (1000 µg/mL-50 µg/mL) for 48 h. The results suggested that maghemite can be a valuable low-cost biomagnetic material in biomedical applications. [ABSTRACT FROM AUTHOR]

This work aims to investigate the effects of isothermal treatment on the structural, microstructure, and physio-mechanical properties of Li2O-Al2O3-SiO2 (lithium aluminosilicate (LAS)) glass–ceramics. The different sintering temperatures affected the final crystalline phase formation leading to a variation of LAS glass–ceramic properties. This work also aims to achieve the most stable crystalline phase at high temperature in LAS glass–ceramics which is β-spodumene (LiAlSi2O6) with improved density, lower porosity, and higher flexural strength. The LAS was isothermally sintered at elevated temperatures of 900 to 1200 °C for 30 min. The X-ray diffraction (XRD) results showed the complete transformation of β-spodumene from β-quartz occurred at 1000 °C. However, the sintering temperature did not change the crystalline phase when sintered above 1000 °C, but the lattice parameter of the crystal structure was slightly altered. It was observed that the LAS glass–ceramic grain size, density, and flexural strength increased with temperature. The smallest mean grain size of 0.61 µm for LAS glass–ceramic sintered at 1100 °C implied the increased flexural strength of LAS glass–ceramic at 146.25 MPa which is also influenced by the full densification at 2.46 g/cm3 with less porosity. The isothermal treatment indicated that sintering at 1100 °C provided a denser, less porous, smaller mean grain size and higher flexural strength LAS glass–ceramics which is preferred for thermal shock resistance applications. [ABSTRACT FROM AUTHOR]

In order to determine the correlation of flexural strength and thermal shock resistance properties, the sintering behavior of Li2O-Al2O3-SiO2 (LAS) glass-ceramics at different sintering treatment times and the effect of thermal shock cycles on LAS glass-ceramics were investigated. The LAS glass-ceramics were isothermally treated at 1100°C from 1.5 to 4.5 h. Phase transformation of major crystalline of β-spodumene and minor crystalline of ZrTiO4 revealed unchanged as sintering treatment time increased. The physical properties of LAS glass-ceramics that were sintered for 3.5 h demonstrated an increased density (2.45 g/cm3) and less porosity percentage (0.62%). The prolonged sintering treatment affected the microstructure whereby the mean grain size increased from 0.55 to 0.67 µm which also demonstrated the increase of microhardness in the range between 3.90 and 5.47 GPa. The flexural strength of LAS glass-ceramics revealed an enhancement of 158 MPa when sintered for 3.5 h. The thermal shock resistance properties were assessed at 500°C from one to seven cycles via thermal shock tests. After four thermal shock cycles, LAS glass-ceramics showed an improvement of 82% of residual strength from its original strength, due to a decrease in the formation of pores and an increase in the crystallinity and percentage of β-spodumene. [ABSTRACT FROM AUTHOR]

This study aims to characterise β-wollastonite that was derived from rice straw ash and limestone and also its bioactivity by soaking in SBF for 1, 3, 5, 7, 14, and 21 days. Rice straw was fired to obtain SiO2 and CaO from calcined limestone. The ratio of CaO:SiO2 was set at 55:45. The precursor mixture was then autoclaved for 8 h at 135 °C and sintered for 3 h at 950 °C. The chemical composition of the raw materials was obtained using XRF, which was approximately 79.0 wt.% SiO2 and 97.2 wt.% CaO for rice straw ash and limestone respectively. From the phase identification, the rice straw ash has a cristobalite phase, while the limestone has a CaO phase. The β-wollastonite phase was obtained after both autoclaving and sintering were performed. Chemical analysis for soaked β-wollastonite showed that the Ca/P molar ratio was 1.66, which is close to that of "calcium deficient" hydroxyapatite (CDHA). FTIR has indicated the occurrence of rapid adsorption during exposure of β-wollastonite sample to the SBF, which is apparent from the peak of phosphate after one day of soaking. SEM has revealed the formation of hydroxyapatite microstructures on the surface of the immersed β-wollastonite sample. For heavy metal elemental evaluation, metal panel that included As, Cd, Hg and Pb were selected and both precursor and β-wollastonite had fulfilled the requirement of ASTM F1538-03 standard specification. In conclusion, β-wollastonite produced from rice straw ash and limestone has a characteristic of bioactive properties, and is suitable for implant purposes. [ABSTRACT FROM AUTHOR]