Rapid conversion of highly porous borate glass microspheres into hydroxyapatite

This paper reports on the rapid development of porous hydroxyapatite (HA) microspheres with large external pores and fully interconnected porosity. These porous microspheres were produced by converting borates glasses (namely 45B5, B53P4 and 13-93B) into HA by immersing them in potassium phosphate media and simulated body fluid (SBF). Solid (SGMS) non-porous and highly porous (PGMS) microspheres were prepared from borate glasses via a novel flame spheroidisation process and their physicochemical properties including in vitro biological response were investigated. Morphological and physical characterisation of the PGMS showed interconnected porosity (up to 75 ± 5%) with average external pore sizes of 50 ± 5 μm. Mass loss, ion release, X-ray diffraction (XRD) and Scanning electron microscopy (SEM) analysis confirmed complete conversion to HA in 0.02 M K2HPO4 solution for the PGMS (with exception of 13-93B glass) and at significantly faster rates compared to their SGMS counterparts. However, 13-93B microspheres only converted to HA in Na2HPO4 solution. The in vitro SBF bioactivity studies for all the borate compositions showed HA formation and much earlier for PGMS compared to SGMS. Direct cell culture studies using hMSCs revealed that the converted porous HA microspheres showed enhanced pro-osteogenic properties compared to their unconverted counterparts and such are considered as highly promising candidate materials for bone repair (and orthobiological) applications

Effect of varying the Mg with Ca content in highly porous phosphate-based glass microspheres

Natural ventilation is a low energy strategy used in many building types. Design approaches are mature but are dependent on variables with high uncertainty, such as the aerodynamic behaviour of purpose provided openings (PPOs), which need improved characterisation. An analytical framework is used to define different types of flow through openings based on the balance of environmental forces that drive flow, and the different flow structures they create. This allows a comprehensive literature review to be made, where different studies and descriptive equations can be compared on a like-for-like basis, and from which clear gaps in knowledge, technical standards, and design data are identified. Phenomena whose understanding could be improved by analysis of existing data are identified and explored. A Statistical Effective Area Model (SEAM) is developed from academic data to estimate the performance of butt hinged openings during the design stage, that accounts for the impact of aspect ratio and opening angle. Its predictions are compared against available empirical data and are found to have a standard error of 1.2%, which is substantially lower than the 15–25% prediction errors of free area models commonly used in practice. An analytical model is made based on entrainment theory to explain the increase in flow rate that occurs through two aligned openings. This model defines characteristic design parameters and predicts a detrimental impact on the ventilation of the wider space. Finally, an analytical model is created to explain the reduction in discharge coefficient that occurs when a large temperature difference exists across an opening. This model defines novel dimensionless parameters that characterise the flow, and predicts empirical data well, suggesting that it should be integrated into design equations

Development and Characterisation of Phosphate-Based Glass Coatings via Suspension High Velocity Oxy-Fuel (SHVOF) Thermal Spray Process

Phosphate based glasses (PBGs) are promising materials for biomedical applications due to their biocompatible and fully resorbable characteristics in aqueous environments. These glasses can be coated on to metal substrate via the technique of suspension high velocity oxy-fuel (SHVOF) thermal spraying to produce nano structured coatings with improved physical and mechanical properties. PBGs coatings were produced using SHVOF thermal spray process at 50 and 75 kW flame power. The 75 kW coating was rougher (R a = 3.6 ± 0.1 µm) than the 50 kW coating (R a = 2.7 ± 0.1 µm), whereas the 50 kW coating was much thicker (24.6 ± 2.3 µm) than the 75 kW coating (16.0 ± 3.4 µm). Due to the rougher surface, the 75 kW coating showed high degradation and ion release rates. Moreover, structural changes were observed by Raman analysis, the initial glass formulation contained Q 1 (phosphate tetrahedra with one bridging oxygen) and Q 2 (phosphate tetrahedra with two bridging oxygen) species. However, the coatings showed a reduction of Q 2 species and higher concentrations of Q 1 and Q 0 (phosphate tetrahedra with no-bridging-oxygen) species, which led to lower degradation rates and reduced ion release profiles in the glass coating compared to the initial glass

Process parameter optimisation for manufacturing porous bioactive silicate glass microspheres via flame spheroidisation: The goldilocks effect

This study investigated the influence of flame spheroidisation process parameters for successfully manufacturing solid (dense) and highly porous microspheres from Food and Drug Administration approved bioactive 45S5 glass and 45S5 with addition of viscosity modifiers (i.e. 2 and 5 mol% borax and V2O5), compared against successfully processed phosphate glass microspheres (termed P40). Characterisation studies performed included thermal analysis (SDT), glass viscosity measurements using high temperature rotational viscometry and hot stage microscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. This study revealed that aside from intrinsic material properties (i.e. melt temperature and viscosity profiles), process parameters including starting glass particle size, cooling rate and gas flow rates were important factors in achieving the desired porous glass microsphere morphology. Considering the above influential factors, a processing model has been proposed for the manufacture of highly porous microspheres from bioactive silicate glasses

Flame spheroidisation of dense and porous Ca2Fe2O5 microspheres

Compositionally uniform magnetic Ca2Fe2O5 (srebrodolskite) microspheres created via a rapid, single-stage flame spheroidisation (FS) process using magnetite and carbonate based porogen (1:1 Fe3O4:CaCO3) feedstock powders, are described. Two types of Ca2Fe2O5 microsphere are produced: dense (35 - 80 µm), and porous (125 - 180 µm). Scanning electron microscopy (SEM) based techniques are used to image and quantify these. Complementary high-temperature X-ray diffraction (HT-XRD) measurements and thermogravimetric analysis (TGA) provide insights into the initial process of porogen feedstock decomposition, prior to the coalescence of molten droplets and spheroidisation, driven by surface tension. Evolution of CO2 gas (from porogen decomposition) is attributed to the development of interconnected porosity within the porous microspheres. This occurs during Ca2Fe2O5 rapid cooling and solidification. The facile FS-processing route provides a method for the rapid production of both dense and porous magnetic microspheres, with high levels of compositional uniformity and excellent opportunity for size control. The controllability of these factors make the FS production method useful for a range of healthcare, energy and environmental remediation applications

Production of nano hydroxyapatite and Mg-Whitlockite from biowaste-derived products via continuous flow hydrothermal synthesis : a step towards circular economy

Biowastes from agriculture, sewage, household wastes, and industries comprise promising resources to produce biomaterials while reducing adverse environmental effects. This study focused on utilising waste-derived materials (i.e., eggshells as a calcium source, struvite as a phosphate source, and CH3COOH as dissolution media) to produce value-added products (i.e., calcium phosphates (CaPs) derived from biomaterials) using a continuous flow hydrothermal synthesis route. The prepared materials were characterised via XRD, FEG-SEM, EDX, FTIR, and TEM analysis. Magnesium whitlockite (Mg-WH) and hydroxyapatite (HA) were produced by single-phase or biphasic CaPs by reacting struvite with either calcium nitrate tetrahydrate or an eggshell solution at 200 °C and 350 °C. Rhombohedral-shaped Mg-WH (23–720 nm) along with tube (50–290 nm diameter, 20–71 nm thickness) and/or ellipsoidal morphologies of HA (273–522 nm width) were observed at 350 °C using HNO3 or CH3COOH to prepare the eggshell and struvite solutions, and NH4OH was used as the pH buffer. The Ca/P (atomic%) ratios obtained ranged between 1.3 and 1.7, indicating the formation of Mg-WH and HA. This study showed that eggshells and struvite usage, along with CH3COOH, are promising resources as potential sustainable precursors and dissolution media, respectively, to produce CaPs with varying morphologies

Thermal and crystallization kinetics of yttrium-doped phosphate-based glasses

© 2019 The American Ceramic Society and Wiley Periodicals, Inc Yttrium-doped glasses have been utilized for biomedical applications such as radiotherapy, especially for liver cancer treatment. In this paper, the crystallization behavior of phosphate-based glasses doped with yttrium (in the system 45P2O5–(30 − x) Na2O–25CaO–xY2O3—where x = 0, 1, 3 and 5) have been investigated via Differential Scanning Calorimetry (DSC) using nonisothermal technique at different heating rates (5°C, 10°C, 15°C and 20°C/min). The glass compositions were characterized via EDX, XRD, Density and Molar volume analysis. The Moynihan and Kissinger methods were used for the determination of glass transition activation energy (Eg) which decreased from 192 to 118 kJ/mol (Moynihan) and 183 to 113 kJ/mol (Kissinger) with increasing yttrium oxide content. Incorporation of 0 to 5 mol% Y2O3 revealed an approximate decrease of 71 kJ/mol (Ozawa and Augis) for onset crystallization (Ex) and 26 kJ/mol (Kissinger) for crystallization peak activation energies (Ec). Avrami index (n) value analyzed via Matusita–Sakka equation suggested a one-dimensional crystal growth for the glasses investigated. SEM analysis explored the crystalline morphologies and revealed one-dimensional needle-like crystals. Overall, it was found that these glass formulations remained amorphous with up to 5 mol% Y2O3 addition with further increases in Y2O3 content resulting in significant crystallization

Production of Nano Hydroxyapatite and Mg-Whitlockite from Biowaste-Derived Products via Continuous Flow Hydrothermal Synthesis: A Step towards Circular Economy

Biowastes from agriculture, sewage, household wastes, and industries comprise promising resources to produce biomaterials while reducing adverse environmental effects. This study focused on utilising waste-derived materials (i.e., eggshells as a calcium source, struvite as a phosphate source, and CH3COOH as dissolution media) to produce value-added products (i.e., calcium phosphates (CaPs) derived from biomaterials) using a continuous flow hydrothermal synthesis route. The prepared materials were characterised via XRD, FEG-SEM, EDX, FTIR, and TEM analysis. Magnesium whitlockite (Mg-WH) and hydroxyapatite (HA) were produced by single-phase or biphasic CaPs by reacting struvite with either calcium nitrate tetrahydrate or an eggshell solution at 200 °C and 350 °C. Rhombohedral-shaped Mg-WH (23–720 nm) along with tube (50–290 nm diameter, 20–71 nm thickness) and/or ellipsoidal morphologies of HA (273–522 nm width) were observed at 350 °C using HNO3 or CH3COOH to prepare the eggshell and struvite solutions, and NH4OH was used as the pH buffer. The Ca/P (atomic%) ratios obtained ranged between 1.3 and 1.7, indicating the formation of Mg-WH and HA. This study showed that eggshells and struvite usage, along with CH3COOH, are promising resources as potential sustainable precursors and dissolution media, respectively, to produce CaPs with varying morphologies

Rapid synthesis of magnetic microspheres and the development of new macro–micro hierarchically porous magnetic framework composites †

Magnetic framework composites (MFCs) are a highly interesting group of materials that contain both metal–organic frameworks (MOFs) and magnetic materials. Combining the unique benefits of MOFs (tuneable natures, high surface areas) with the advantages of magnetism (ease of separation and detection, release of guests by induction heating), MFCs have become an attractive area of research with many promising applications. This work describes the rapid, scalable synthesis of highly porous magnetic microspheres via a flame-spheroidisation method, producing spheres with particle and pore diameters of 206 ± 38 μm and 12.4 ± 13.4 μm, respectively, with a very high intraparticle porosity of 95%. The MFCs produced contained three main iron/calcium oxide crystal phases and showed strong magnetisation (Ms: 25 emu g−1) and induction heating capabilities (≈80 °C rise over 30 s at 120 W). The microspheres were subsequently surface functionalised with molecular and polymeric coatings (0.7–1.2 wt% loading) to provide a platform for the growth of MOFs HKUST-1 and SIFSIX-3-Cu (10–11 wt% loading, 36–61 wt% surface coverage), producing macro–micro hierarchically porous MFCs (pores > 1 μm and <10 nm). To the best of our knowledge, these are the first example of MFCs using a single-material porous magnetic scaffold. The adaptability of our synthetic approach to novel MFCs is applicable to a variety of different MOFs, providing a route to a wide range of possible MOF–microsphere combinations with diverse properties and subsequent applications