“On demand” triggered crystallization of CaCO3 from solute precursor species stabilized by the water-in-oil microemulsion

Can we control the crystallization of solid CaCO3 from supersaturated aqueous solutions and thus mimic a natural process predicted to occur in living organisms that produce biominerals? Here we show how we achieved this by confining the reaction between Ca2+ and CO32- ions to the environment of nanosized water cores of water-in-oil microemulsions, in which the reaction between the ions is controlled by the intermicellar exchange processes. Using a combination of in situ small-angle X-ray scattering, high-energy X-ray diffraction, and low-dose liquid-cell scanning transmission electron microscopy, we elucidate how the presence of micellar interfaces leads to the formation of a solute CaCO3 phase/species that can be stabilized for extended periods of time inside micellar water nano-droplets. The nucleation and growth of any solid CaCO3 polymorph, including the amorphous phase, from such nano-droplets is prevented despite the fact that the water cores in the used microemulsion are highly supersaturated with respect to all known calcium carbonate solid phases. On the other hand the presence of the solute CaCO3 phase inside of the water cores decreases the rigidity of the micellar surfactant/water interface, which promotes the aggregation of micelles and the formation of large (>2 μm in diameter) globules. The actual precipitation and crystallization of solid CaCO3 could be triggered “on-demand” through the targeted removal of the organic-inorganic interface and hence the destabilization of globules carrying the CaCO3 solute

Formulating injectable pastes of porous calcium phosphate glass microspheres for bone regeneration applications

Current trends in regenerative medicine treatments for bone repair applications focus on cell-based therapies. These aim to deliver the treatment via a minimally invasive injection to reduce patient trauma and to improve efficacy. This paper describes the injectability of porous calcium phosphate glass microspheres to be used for bone repair based on their formulation, rheology and flow behavior. The use of excipients (xanthan gum, methyl cellulose and carboxyl methyl cellulose) were investigated to improve flow performance. Based on our results, the flow characteristics of the glass microsphere pastes vary according to particle size, surface area, and solid to liquid ratio, as well as the concentration of viscosity modifiers used. The optimal flow characteristics of calcium phosphate glass microsphere pastes was found to contain 40 mg/mL of xanthan gum which increased viscosity whilst providing elastic properties (∼29,000 Pa) at shear rates that mirror the injection process and the resting period post injection, preventing the glass microspheres from both damage and dispersion. It was established that a base formulation must contain 1 g of glass microspheres (60–125 μm in size) per 1 mL of cell culture media, or 0.48 g of glass microspheres of sizes between 125 and 200 μm. Furthermore, the glass microsphere formulations with xanthan gum were readily injectable via a syringe-needle system (3–20 mL, 18G and 14G needles), and have the potential to be utilized as a cell (or other biologics) delivery vehicle for bone regeneration applications.</p

Formulating injectable pastes of porous calcium phosphate glass microspheres for bone regeneration applications

Current trends in regenerative medicine treatments for bone repair applications focus on cell-based therapies. These aim to deliver the treatment via a minimally invasive injection to reduce patient trauma and to improve efficacy. This paper describes the injectability of porous calcium phosphate glass microspheres to be used for bone repair based on their formulation, rheology and flow behavior. The use of excipients (xanthan gum, methyl cellulose and carboxyl methyl cellulose) were investigated to improve flow performance. Based on our results, the flow characteristics of the glass microsphere pastes vary according to particle size, surface area, and solid to liquid ratio, as well as the concentration of viscosity modifiers used. The optimal flow characteristics of calcium phosphate glass microsphere pastes was found to contain 40 mg/mL of xanthan gum which increased viscosity whilst providing elastic properties (∼29,000 Pa) at shear rates that mirror the injection process and the resting period post injection, preventing the glass microspheres from both damage and dispersion. It was established that a base formulation must contain 1 g of glass microspheres (60–125 μm in size) per 1 mL of cell culture media, or 0.48 g of glass microspheres of sizes between 125 and 200 μm. Furthermore, the glass microsphere formulations with xanthan gum were readily injectable via a syringe-needle system (3–20 mL, 18G and 14G needles), and have the potential to be utilized as a cell (or other biologics) delivery vehicle for bone regeneration applications

Inorganic pathways controlling selenium mobility in natural environments

The variation in geographical distribution of selenium (Se) in environmental settings and the food chain can cause serious human health deficiencies, or poisoning and fatal death. Although Se toxicity is usually inferred as caused by local geology or human activities, the current food trade practices raise Se concerns to a global level, as the Se contained in agricultural products is often unknown. In most natural settings, the prime -. source of Se are shale rocks. Yet, Se weathering pathways and release mechanisms are poorly understood because the locus and the distribution of Se in shales are unknown. Therefore, this thesis assessed the geochemical environment surrounding Se in shales and identified the main inorganic and organic host phases and elucidated the Se speciation and the way this may affect the Se mobilization pathways. This was done by combining simple and complex geochemical, mineralogical and spectroscopic techniques -that were statistically validated to analyse shale samples from the UK, Colombia and China that were representative for typical (1 - 10 ug/g) and extreme (>1 %) Se concentrations. The first important result was the identification of pyrite and organic matter as the two main Se host phases. Additionally, the data showed that in typical shales (e.g. with <6% organic C and 1-2% reduced inorganic S) Se was preferentially associated to pyrite, while in low pyrite shales the association between Se and organic matter was favoured. Interestingly, the data also revealed that depending on the formation pathways pyrite morphology also differentially bound Se with euhedrals concentrating more Se than framboids. Finally, the spectroscopic data showed that Se was not substituting S in pyrite, instead Se was present as an independent FeSex species in close association with both euhedral and framboidal pyrite. Conversely, in the organic matrix, nanosized elemental Se and organo-Se species (Se=C, Se-Se and Se-C bonds) were the main Se carriers.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Nanoparticle Assembly Leads to Mackinawite Formation

Iron sufides are important mineral phases in natural environments where they control global elemental cycles. Fe–S phases have been suggested to form through the transformation of several possible precursors to finally reach stable crystalline structures. Mackinawite is a metastable intermediate, of which a full chemical and structural characteristization of various possible intermediate stages in its formation pathways, or the chemical conditions that affect the transformations to the metastable mackinawite, are well understood. Here we report, the various steps of mackinawite formation via oriented aggregation (OA) from a nanoparticulate precursor. During OA, the formation of aggregates is a crucial stage for self-assembly of primary particles to reach stable structures. The formation occurs in five steps: (1) homogeneous nucleation of primary FeSnano particles; (2 and 3) formation of mass fractal-like aggregates from the FeSnano as precursor toward the transformation to mackinawite; (4) oriented alignment and self-assembly of these mackinawite-like aggregates; and (5) transformation to a still metastable but typical layered mackinawite structure

Facile Synthesis of Perovskite-Structured Powders Using Barite–Celestite Ore under Hydrothermal Alkaline Conditions

Barite–celestite (BC) crystals were treated in highly concentrated alkaline hydrothermal fluid (5 M KOH) coexisting with a Ti(OH)₄·4.5H₂O gel to produce SrTiO₃ particles between 150 and 250 °C for several intervals between 6 h and 96 h. The BC transformation was initiated at a lower temperature (150 °C) and the total precursors consumption was completed at 250 °C for 96 h, resulting only in the crystallization of SrTiO₃ particles. Different temperatures of reaction (≤200 °C) lead to variations in morphology and particle size of the SrTiO₃ . The crystal growth of faceted cubic agglomerates was achieved at 250 °C, and it is provoked by the Oswald ripening mechanism. The release of barium to the hydrothermal fluid from the precursor occurred simultaneously with the transformation process. A low value of activation energy required for the single-step transformation of the BC plates into SrTiO₃ particles was observed (26.33 kJ mol‾¹), under static hydrothermal conditions

Selenium Speciation in Framboidal and Euhedral Pyrites in Shales

The release of Se from shales is poorly understood because its occurrence, distribution, and speciation in the various components of shale are unknown. To address this gap we combined bulk characterization, sequential extractions, and spatially resolved μ-focus spectroscopic analyses and investigated the occurrence and distribution of Se and other associated elements (Fe, As, Cr, Ni, and Zn) and determined the Se speciation at the μ-scale in typical, low bulk Se containing shales. Our results revealed Se primarily correlated with the pyrite fraction with exact Se speciation highly dependent on pyrite morphology. In euhedral pyrites, we found Se­(-II) substitutes for S in the mineral structure. However, we also demonstrate that Se is associated with framboidal pyrite grains as a discrete, independent FeSe_<i>x</i> phase. The presence of this FeSe_<i>x</i> species has major implications for Se release, because FeSe_<i>x</i> species oxidize much faster than Se substituted in the euhedral pyrite lattice. Thus, such an FeSe_<i>x</i> species will enhance and control the dynamics of Se weathering and release into the aqueous environment

Data associated with 'An effective surrogate tracer technique for S. aureus bioaerosols in a mechanically ventilated hospital room replica using dilute aqueous lithium chloride'

Raw data associated with 'An effective surrogate tracer technique for S. aureus bioaerosols in a mechanically ventilated hospital room replica using dilute aqueous lithium chloride

An Effective Surrogate Tracer Technique for S. aureus Bioaerosols in a Mechanically Ventilated Hospital Room Replica Using Dilute Aqueous Lithium Chloride

Finding a non-pathogenic surrogate aerosol that represents the deposition of typical bioaerosols in healthcare settings is beneficial from the perspective of hospital facility testing, general infection control and outbreak analysis. This study considers aerosolization of dilute aqueous lithium chloride (LiCl) and sodium chloride (NaCl) solutions as surrogate tracers capable of representing Staphylococcus aureus bioaerosol deposition on surfaces in mechanically ventilated rooms. Tests were conducted in a biological test chamber set up as a replica hospital single patient room. Petri dishes on surfaces were used to collect the Li, Na and S. aureus aerosols separately after release. Biological samples were analyzed using cultivation techniques on solid media, and flame atomic absorption spectroscopy was used to measure Li and Na atom concentrations. Spatial deposition distribution of Li tracer correlated well with S. aureus aerosols (96% of pairs within a 95% confidence interval). In the patient hospital room replica, results show that the most contaminated areas were on surfaces 2 m away from the source. This indicates that the room’s airflow patterns play a significant role in bioaerosol transport. NaCl proved not to be sensitive to spatial deposition patterns. LiCl as a surrogate tracer for bioaerosol deposition was most reliable as it was robust to outliers, sensitive to spatial heterogeneity and found to require less replicates than the S. aureus counterpart to be in good spatial agreement with biological results

Universality of hair as a nucleant: exploring the effects of surface chemistry and topography

The ability to control crystal nucleation through the simple addition of a nucleating agent (nucleant) is desirable for a huge range of applications. However, effective nucleating agents are known for only a small number of systems, and many questions remain about the mechanisms by which they operate. Here, we explore the features that make an effective nucleant and demonstrate that the biological material hair─which naturally possesses a chemically and topographically complex surface structure─has excellent potential as an effective nucleating agent. Crystallization of poorly soluble compounds in the presence of hairs from a range of mammals shows that nucleation preferentially occurs at the cuticle step edges, while a novel microdroplet-based methodology was used to quantify the nucleating activities of different hairs. This showed that the activities of the hairs can be tuned over a wide range using chemical treatments. Analysis of the hair structure and composition using atomic force microscopy, scanning ion conductance microscopy, and X-ray photoelectron spectroscopy demonstrates that surface chemistry, surface topography, and surface charge all act in combination to create effective nucleation sites. This work therefore contributes to our understanding of heterogeneous nucleating agents and shows that surface topography as well as surface chemistry can be used in the design or selection of universal nucleating agents.</p