Initial Dissolution Research Articles

Impact of iron and sulfur cycling on the bioavailability of cadmium and arsenic in co-contaminated paddy soil

The biogeochemical cycling of iron (Fe) or sulfur (S) in paddy soil influences the cadmium (Cd) and arsenic (As) migration. However, the influence of coupled reduction effects and reaction precedence of Fe and S on the bioavailability of Cd and As is still not fully understood. This study aimed to reveal the influence of Fe and S reduction on soil Cd and As mobility under various pe + pH conditions and to elucidate the related mechanism in subtropical China. According to the findings, higher adsorption from Fe reduction caused high-crystalline goethite (pe + pH > 2.80) to become amorphous ferrihydrite, which in turn caused water-soluble Cd (62.0%) to first decrease. Cd was further decreased by 72.7% as a result of the transformation of SO42- to HS-/S2- via sulfate reduction and the formation of CdS and FeS. As release (an increase of 8.1 times) was consequently caused by the initial reduction and dissolution of iron oxide (pe + pH > 2.80). FeS had a lesser impact on the immobilization of As than sulfate-mediated As (V) reduction in the latter stages of the reduction process (pe + pH < 2.80). pe + pH values between 3 and 3.5 should be maintained to minimize the bioavailability of As and Cd in moderate to mildly polluted soil without adding iron oxides and sulfate amendments. The practical remediation of severely co-contaminated paddy soil can be effectively achieved by using Fe and S additions at different pe + pH conditions. This technique shows promise in reducing the bioavailability of Cd and As.

Development of Fast Disintegrating Tablets Containing Loxoprofen Sodium by HYDROFLASH Manufacturing Method.

In order to create and offer superior pharmaceuticals for consumers who wish to be relieved of headache and fever as soon as possible, we established HYDROFLASH manufacturing method that enables us to offer fast disintegration tablets containing loxoprofen sodium (LX), which are difficult to disintegrate. As a result of screening excipients, tablets using mannitol showed the fastest disintegration time, about 2 min. From the result of viscosity measurement, we found that LX produced higher viscosity when dissolved in water. This suggests that tablets containing LX disintegrate slower by inhibiting the penetration of water into the tablet due to the viscosity caused of LX. Therefore, we created a manufacturing method to make it easy for water to penetrate the tablet. It is possible to achieve fastest disintegration in about 30 s for tablets containing LX by granulating in a fluidized-bed with spraying of the dispersion of light anhydrous silicic acid (LASA). LX-containing tablets manufactured by the HYDROFLASH method disintegrated immediately after contact with water. Furthermore, it was observed that LASA was uniformly dotted on the surface of tablets by HYDROFLASH method, compared with other manufacturing methods. We considered that by fluidized-bed granulation with LASA dispersion (HYDROFLASH manufacturing method), water permeates through LASA on the tablet surface regardless of viscosity of LX. Futhermore, LX-containing tablets by the HYDROFLASH method showed that the dissolution rate of LX was nearly 100% at 5 min after starting the test. We considered that the initial dissolution became faster because of the fast disintegration.

Mechanistic insights into the co-recovery of nickel and iron via integrated carbon mineralization of serpentinized peridotite by harnessing organic ligands.

The rising need to produce a decarbonized supply chain of energy critical metals with inherent carbon mineralization motivates advances in accelerating novel chemical pathways in a mechanistically-informed manner. In this study, the mechanisms underlying co-recovery of energy critical metals and carbon mineralization by harnessing organic ligands are uncovered by investigating the influence of chemical and mineral heterogeneity, along with the morphological transformations of minerals during carbon mineralization. Serpentinized peridotite is selected as the feedstock, and disodium EDTA dihydrate (Na2H2EDTA·2H2O) is used as the organic ligand for metal recovery. Nickel extraction efficiency of ∼80% and carbon mineralization efficiency of ∼73% is achieved at a partial pressure of CO2 of 50 bars, reaction temperature of 185 °C, and 10 hours of reaction time in 2 M NaHCO3 and 0.1 M Na2H2EDTA·2H2O. Extensive magnesite formation is evidence of the carbon mineralization of serpentine and olivine. An in-depth investigation of the chemo-morphological evolution of the CO2-fluid-mineral system during carbon mineralization reveals several critical stages. These stages encompass the initial incongruent dissolution of serpentine resulting in a Si-rich amorphous layer acting as a diffusion barrier for Mg2+ ions, subsequent exfoliation of the silica layer to expose unreacted olivine, and the concurrent formation of magnesite. Organic ligands such as Na2H2EDTA·2H2O aid the dissolution and formation of magnesite crystals. The organic ligand exhibits higher stability for Ni-complex ions than the corresponding divalent metal carbonate. The buffered environment also facilitates concurrent mineral dissolution and carbonate formation. These two factors contribute to the efficient co-recovery of nickel with inherent carbon mineralization to produce magnesium carbonate. These studies provide fundamental insights into the mechanisms underlying the co-recovery of energy critical metals with inherent carbon mineralization which unlocks the value of earth abundant silicate resources for the sustainable recovery of energy critical metals and carbon management.

Development of an Al-Zn-Bi alloy sacrificial anode for the protection of steel in artificial seawater: an electrochemical analysis

The Al-Zn sacrificial anodes are widely used for cathodic protection in marine steel structures. This study evaluates the impact of bismuth addition on the electrochemical properties of the Al-Zn sacrificial anode in artificial seawater. The microstructure analysis confirms the presence of uniformly distributed intermetallic β-AlFeSi and spherical Bi within the α-Al matrix. The open circuit potential (OCP) comparison between Al-Zn-Bi and carbon steel reveals a potential difference of approximately 400 mV, indicating sufficient cathodic protection for the steel. Electrochemical impedance measurements indicate the initial hindered dissolution of the anode due to surface film formation, which later dissociates due to the aggressive attack of Cl− species in the electrolyte. The sufficiently negative surface potential (−0.875 Vvs. Ag/AgCl) observed at 10 mA cm−2 demonstrates the suitability of anode for fulfilling the cathodic protection criteria of steel structures.

Anodic Dissolution of Aluminum in Sodium-Ion Batteries: A Comparison of Electrolyte and Solvent Composition

The anodic dissolution behavior of aluminum was studied in various sodium-based electrolyte solutions using cyclic voltammetry and chronoamperometry. The aim was to investigate how different electrolyte and solvent compositions affect the dissolution process. The electrolyte solutions tested included 0.284 m NaBOB in TEP, 1.00 m NaPF6 in TEP, 1.00 m NaPF6 in EC:DEC, 1.00 m NaPF6 in diglyme, 1.00 m NaFSI in PC, and 1.00 m NaFSI in TEP. SEM imaging was also performed to analyze the morphological changes of the aluminum surface during the dissolution process.To emphasize any dissolution process, relatively large volumes (3-5 ml) of electrolyte solution was used in polytetrafluoroethylene beaker cells. A three-electrode configuration was used to obtain the desired accuracy in the electrochemical tests.Severe anodic aluminum dissolution was not observed below 5.3 V vs. Na+/Na in electrolyte solutions containing NaBOB in TEP, NaPF6 in TEP, NaPF6 in EC:DEC, or NaPF6 in diglyme. Anodic dissolution was, however, detected in electrolyte solutions containing NaFSI in PC and NaFSI in TEP, affirming that caution should be exercised when using FSI-anions with aluminum current collectors.1,2 Yet, the choice of solvent used with NaFSI appeared to influenced the anodic dissolution behavior of aluminum. Here, TEP seemed to suppress the initial dissolution, compared to PC.In summary, this study provides insights into the anodic dissolution behavior of aluminum in sodium-ion batteries, and highlights the significance of selecting appropriate solution compositions to mitigate potential anodic dissolution issues. The findings contribute to the understanding of the electrochemical behavior of aluminum in the context of sodium-ion batteries, and provides a foundation for further studies.The authors acknowledge The Swedish Energy Agency via project no. 50177-1, VINNOVA via projects no. 2022-01465 and 2019-00064 (Batteries Sweden), and H2020 research and innovation programme under Grant agreements No 958174 and 963542 for financial support.1. L. Otaegui, E. Goikolea, F. Aguesse, M. Armand, T. Rojo and G. Singh, J. Power Sources, 2015, 297, 168–173.2. A. Bitner-Michalska, A. Krztoń-Maziopa, G. Żukowska, T. Trzeciak, W. Wieczorek and M. Marcinek, Electrochim. Acta, 2016, 222, 108–115. Figure 1

Effect of Various Acid Solutions on the CO2 Dissolution Rate, Morphology, and Particle Size of Precipitated Calcium Carbonate Synthesized Using Seashells.

In this study, the influence of acid solutions on the production of precipitated calcium carbonate (PCC) using seashells was investigated. In terms of the Ca dissolution efficiency and atmosphere for dissolving CO32-, the results indicate that HCl, HNO3, CH3COOH, and HCOOH at 1.0 M were the most ideal among the acid solutions. The use of weak acids resulted in the low degree of dissolution of Al and Fe. These impurities could be mostly removed through the pH adjustment process, leading to PCC with a purity of 99% or more. Further, CH3COOH and HCOOH exhibited low CaCO3 carbonation efficiency owing to the hydrogen bonding of the carboxyl group and its hindering effect on the growth of CaCO3 particles. In addition, in the presence of the carboxyl group, the morphology tended to be oval, and the particle size was small. Particularly, when CH3COOH was used, the combined effect of the low initial Ca ion concentration and slow CO2 dissolution rate resulted in minimal changes during the carbonation time and the smallest particle size. However, variations in the degree of Ca concentration with a change in the acid solution concentration influenced the dominance of nucleation and particle growth, leading to variations in the particle size. The results of this study revealed that when manufacturing PCC using seashells, the appropriate acid solution must be selected to obtain the required PCC properties.

Fundamental Understanding and Quantification of Capacity Losses Involving the Negative Electrode in Sodium-Ion Batteries.

Knowledge about capacity losses related to the solid electrolyte interphase (SEI) in sodium-ion batteries (SIBs) is still limited. One major challenge in SIBs is that the solubility of SEI species in liquid electrolytes is comparatively higher than the corresponding species formed in Li-ion batteries. This study sheds new light on the associated capacity losses due to initial SEI formation, SEI dissolution and subsequent SEI reformation, charge leakage via SEI and subsequent SEI growth, and diffusion-controlled sodium trapping in electrode particles. By using a variety of electrochemical cycling protocols, synchrotron-based X-ray photoelectron spectroscopy (XPS), gas chromatography coupled with mass spectrometry (GC-MS), and proton nuclear magnetic resonance (1 H-NMR) spectroscopy, capacity losses due to changes in the SEI layer during different open circuit pause times are investigated in nine different electrolyte solutions. It is shown that the amount of capacity lost depends on the interplay between the electrolyte chemistry and the thickness and stability of the SEI layer. The highest capacity loss is measured in NaPF6 in ethylene carboante mixed with diethylene carbonate electrolyte(i.e., 5 µAhh-1/2 pause or 2.78 mAhg·h-1/2 pause ) while the lowest value is found in NaTFSI in ethylene carbonate mixed with dimethoxyethance electrolyte (i.e., 1.3 µAhh-1/2 pause or 0.72 mAhg·h-1/2 pause ).

Cure-All cannabidiol? The cannabidiol content of commercial products

BackgroundThe recent easing of regulations around the world regarding Cannabis sativa and its main active compounds, such as cannabidiol (CBD), led to an explosion in the number of over-the-counter consumer products. The number of product types is surpassed by the vast quantity of products of each type, but even this is exceeded by the associated health claims which range from the benign, such as ‘fighting inflammation’, to the completely asinine such as ‘fighting the tyranny of the urgent’ or ‘shedding light on your inner darkness’. Any health claim should in the first instance be supported by the product containing the correct actives at the correct dosage. PurposeThe purpose of this study was to test a diverse range of commercially available product types including soft drinks, honey, coffee, oils, gummy bears, chocolate, etc. that claim to contain CBD and compare the results to their label claims. Study designForty commercially available products were extracted and quantitatively analyzed. MethodsExtraction efficiency for all product types was conducted over a 1 h period using acetonitrile and ultrasonication. Samples were taken every five min and analyzed using a validated HPLC method. All products were then extracted in triplicate using the applicable extraction time and quantitatively analyzed. ResultsFifteen min of sonication was found to be adequate for the oils and drinks samples. The honey, chocolate and gummies samples required initial dissolution in water followed by extraction with acetonitrile. The remaining products required sonication of 45 min. It was found that only three products (7.5 %) contained CBD levels within 90–110 % of their label claim. Two products had trace amounts of delta-9-tetrahydrocannabinol and some of the products were completely devoid of CBD. ConclusionMislabeling is of serious concern and this study shows that the problem not only includes problems with the content of CBD, but also regarding the chemical properties such as containing “water-soluble CBD” while it is insoluble in water, and the diverse number of health claims that in some cases have no foundation in reality. This highlights not only the lax attitude of producers but also of the regulatory authorities in ensuring the consistent quality of these products.

Atomic-scale identification of defects in alite

Crystallographic defects play a crucial role in cement hydration, with initial dissolution being dominated by the formation of etch pits that rely on the intersection of defects on surfaces. However, the defects present in cement particles have remained a mystery due to the lack of detailed direct observation at the atomic scale. In this study, we used scanning transmission electron microscopy to unravel the defects in alite particles at the single-atom level. Our observations identified different types of defects, including vacancies, doping, dislocations, rough surfaces, and grain boundaries. Atomic ordering in the alite crystal was further examined based on our single-atom recognition method. Our findings indicate that defects in cement particles may serve as reactive sites during the early hydration stage, facilitating the initial dissolution and providing nucleation sites for hydration products. This work provides insights into cement defect formation at the single-atom level and offers new opportunities in tuning the hydration process through defect engineering of cement particles.

Surface Passivation by Embedment of Polyphosphate Inhibits the Aragonite-to-Calcite Thermodynamic Pump.

We monitored the conversion of aragonite to calcite in water by comparing single and mixed polymorph suspensions. We demonstrate that the enhanced aragonite-to-calcite conversion in mixed polymorph suspensions is dramatically inhibited by adding polyphosphate (sodium hexametaphosphate). 13C and 31P solid-state magic angle spinning (MAS) NMR and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra allow us to follow quantitatively these effects as imparted by the dissolution-recrystallization processes. 31P{13C} and 13C{31P} rotational echo double resonance (REDOR)NMR experiments reveal coprecipitated phosphate that is embedded only within the surfaces of both polymorphs during the initial dissolution and recrystallization processes, causing passivation that arrests phase conversion.

Isomerization of proline-46 in the N-terminal tail of galectin-3 enhances T cell apoptosis via the ROS-ERK pathway

Galectin-3 (Gal-3) is unique in the galectin family, due to the presence of a long N-terminal tail (NT) arising from its conserved carbohydrate recognition domain (CRD). Although functional significance of the NT has remained elusive, our previous studies demonstrated the importance of NT prolines to Gal-3 function. Here, we show that during the time Gal-3 stands in solution for three or more days, Gal-3 NT undergoes a slow, intra-molecular, time-dependent conformational/dynamical change associated with proline cis-trans isomerization. From initial dissolution of Gal-3 in buffer to three days in solution, Gal-3-mediated T cell apoptosis is enhanced from 23 % to 37 %. Western blotting and flow cytometry show that the enhancement occurs via the ROS-ERK pathway, and not by the PKC-ERK pathway. To assess which proline(s) is (are) responsible for this effect, we individually mutated all 14 NT prolines within the first 68 residues to alanines, and assessed their effect on ROS production. Our study shows that isomerization of P46 alone is responsible for the upregulation of ROS and T cell apoptosis. NMR studies show that this unique effect is mediated by a change in dynamic interactions between the NT and CRD F-face, which in turn leads to this change in Gal-3 function.

Rates and Mechanism of Vivianite Dissolution under Anoxic Conditions.

The iron phosphate mineral vivianite Fe(II)3(PO4)2·8H2O has emerged as a potential renewable P source. Although the importance of vivianite as a potential P sink in the global P cycle had previously been recognized, a mechanistic understanding of vivianite dissolution at the molecular level, critical to its potential application, is still elusive. The potential of vivianite as a P sink or source in natural or engineered systems is directly dependent on its dissolution kinetics under environmentally relevant conditions. To understand the thermodynamic and kinetic controls on bioavailability, the oxidation and dissolution processes of vivianite must be disentangled. In this study, we conducted controlled batch and flow-through experiments to quantitatively determine the dissolution rates and mechanisms of vivianite under anoxic conditions as a function of pH and temperature. Our results demonstrate that vivianite solubility and dissolution rates strongly decreased with increasing solution pH. Dissolution was nonstoichiometric at alkaline pH (>7). The rapid initial dissolution rate of vivianite is related to the solution saturation state, indicating a thermodynamic rather than a kinetic control. A defect-driven dissolution mechanism is proposed. Dissolution kinetics over pH 5-9 could be described with a rate law with a single rate constant and a reaction order of 0.61 with respect to {H+}: The activation energy of vivianite dissolution proved low (Ea = 20.3 kJ mol-1), suggesting hydrogen bridge dissociation as the rate-determining step.

Effects of some polymeric additives on the cocrystallization of naproxen and nicotinamide via freeze drying

Crystallization of active pharmaceutical ingredients (APIs) has important implications for their bioavailability. Their dissolution behavior is affected by the phase, size, and dispersion of the crystal particles. Polymeric additives have served as effective modifiers of the API crystallization, and we tested their effects during the crystallization via freeze drying. Poly(vinylpyrrolidone), poly(vinylpyrrolidone-co-vinyl acetate), and poly(acrylic acid) were investigated for their effects on the cocrystallization of naproxen (API) and nicotinamide (coformer). We aimed to establish the types and concentrations of the polymers that modulated the size and dispersion of the particles without affecting the cocrystal phase. Poly(vinylpyrrolidone) (Mw 40000) and poly(vinylpyrrolidone-co-vinyl acetate) (Mw 45000–70000) at the concentration level of 3–5% were effective in this regard in increasing the initial and overall API dissolution, which was correlated with the microstructure of the freeze-dried solids. This study is intended to contribute to foundations for further research to apply crystal-modulating additives to the process of freeze drying.

Composition‐dependent leaching behavior in ion‐irradiated borosilicate glasses: A corrosion mechanism study

AbstractEvaluating the corrosion behavior of borosilicate glass after irradiation holds vital importance for the safe geological disposal of high‐level radioactive waste. This study examined the leaching properties of three kinds of sodium‐borosilicate (RNa2O‒B2O3‒KSiO2, denoted as “NBS”) glasses with the same R but varying K under 5 MeV Xe‐ion radiation to decipher the correlation between the corrosion mechanism and glass composition. After Xe‐ion radiation, an increase in [BO3] units was observed, indicative of the glass network depolymerization. Irradiated glasses exhibited a more significant change in [BO3] units over the leaching time compared to their pristine counterparts. There is a strong correlation between the initial dissolution rates of pristine glasses, the K value, and the proportion of Na. Additionally, the initial Si dissolution rate of the NBS glasses has been accelerated by heavy ion irradiation. For the same R value over the glass series, the initial Si dissolution rates in ternary borosilicate glasses change at similar rates after irradiation. This study concluded that the variation trend in the initial dissolution rate of Si and Na differs under ion radiation.

Spontaneous hierarchical surface engineering of minerals through coupled dissolution‐precipitation chemistry

AbstractPeculiar hierarchical microstructures in creatures inspire modern material design with distinct functionalities. Creatures can effortlessly construct sophisticated yet long‐range ordered microstructure across bio‐membrane through ion secretion and precipitation. However, microstructure biomimicry in current technology generally requires elaborate, point‐by‐point fabrication. Herein, a spontaneous yet controllable strategy is developed to achieve surface microstructure engineering through a natural surface phenomenon similar to ion secretion‐precipitation, that is, coupled dissolution‐precipitation. A series of hierarchical microstructures on mineral surfaces in fluids with tunable morphology, orientation, dimension, and spatial distribution are achieved by simply controlling initial dissolution and fluid chemistry. In seawater, long‐range ordered film of vertically aligned brucite flakes forms through interfacial dissolution, nucleation, and confinement‐induced orientation of flakes with vertically grown {110} plane, on the edge of which, fusiform aragonite epitaxially precipitates. With negligible initial surface dissolution, prismatic aragonite epitaxially grows on a calcite polyhedron‐packed surface. By tuning fluid chemistry, closely packed calcite polyhedron and loosely packed calcite micro‐pillars are engineered through rapid and retarded precipitation, respectively. Surprisingly, the spontaneously grown microstructures resemble those deliberately created by human or found in nature, and tremendously modulate surface functionality. These findings open new possibilities for facile and customizable engineering of microstructural surfaces, hierarchical heterostructures, and biomimetic materials.

Characterization of enteric-coated erythromycin tablets by Raman mapping and its pharmaceutical evaluation.

Enteric tablet coating thickness is a critical quality attribute of the coating process that can affect dissolution behavior in vitro as well as release in vivo. Raman mapping offers unique advantages in analyzing the distribution of active pharmaceutical ingredients and excipients in formulations. In this study, Raman mapping was used to characterize the coating of enteric-coated erythromycin tablets coated by two different processes and compare the differences in their coating formulation, thickness, and uniformity. Furthermore, we aimed to select the appropriate pH of the dissolution medium at which the coating slowly cracks to release the drug and determine the dissolution profile. The differences in the coating thickness and uniformity of the two products resulted in differences in dissolution behavior. Although there are differences in the coating processes for the two types of enteric-coated erythromycin tablets, the thickness of the outer coating on the side is a critical quality attribute in both processes. The outer coating of product A is relatively thick, and the thickness of the outer coating on the side affects the dissolution amount. The outer coating of product B is relatively thin, resulting in a short cracking time and large variation and a significant difference in the initial dissolution amounts between tablets. Raman mapping can be used to analyze the differences in coating formulations and for process evaluation.

Initial dissolution of Mg-containing phase and corrosion product formation in cut-edge corrosion of Zn-11%Al-3%Mg-0.2%Si coated steel

Simulated cut-edge specimens of Zn-11%Al-3%Mg-0.2%Si coated steel were fabricated, and their corrosion behaviors were assessed using salt spray test (SST). The Mg-containing phases in the coating near the simulated cut-edge dissolved during early corrosion, leading to the formation of protective corrosion products on the steel surface. The corrosion products suppressed the oxygen reduction reaction on the steel. Additionally, the anodic dissolution rate of the coating layer decreased after the SST. Consequently, the cut-edge corrosion rate of the Zn-Al-Mg coating after the deposition of the corrosion products decreased compared with that of a conventional Zn coating.

Chitosan Dissolution in [BMIM]Cl Ionic Liquid: An Optimisation and Bacterial Ecotoxicity Study

Chitosan is formed from chitin deacetylation, but its insolubility remains challenging for industrial applications. An alternative would be employing Ionic Liquids (ILs) as a potential green solvent to dissolve chitosan. Hence, this research aims to study the optimum conditions of chitosan-[BMIM]Cl dissolution using Response Surface Methodology (RSM) and evaluate the ecotoxicity of chitosan-[BMIM]Cl mixture against Gram-positive and Gram-negative bacteria. Chitosan was obtained from heterogenous N-deacetylation of chitin using 50% sodium hydroxide solution at 100°C for 2.5 h. Chitosan dissolution in [BMIM]Cl was optimised using Central Composite Design (CCD) via RSM based on three independent factors: temperature, initial chitosan loading and dissolution time. Ecotoxicity of chitosan-[BMIM]Cl was evaluated using broth microdilution test against Escherichia coli and Staphylococcus aureus. Chitosan with a degree of deacetylation (DD) of 83.42% was obtained after three successive alkali treatments. Fourier Transform Infrared Spectroscopy (FTIR) revealed the presence of free hydroxyl groups, additional amino groups, and reduced C=O and C-H stretch intensity, indicating successful chitin deacetylation. The regression model for chitosan dissolution in [BMIM]Cl was significant (p &lt; 0.05) with a non-significant lack of fit (p &gt; 0.05). The optimised conditions to dissolve chitosan in [BMIM]Cl was 130°C, 1 wt. % and 72 h with a mean relative error of 1.78% and RMSE of 5.0496 wt. %. The toxicity of 10 wt. % chitosan-[BMIM]Cl mixture was “relatively harmless” (EC50 &gt; 1000 mg/L) with an EC50 value of 3.1 wt. % for Escherichia coli and 3.2 wt. % for Staphylococcus aureus.

Nanostructured Porous Silicon for Bone Tissue Engineering: Kinetics of Particle Degradation and Si-Controlled Release.

Nanostructured porous silicon (pSi) is a synthetic silicon-based material. Its biocompatibility and bioresorbability in body fluids make pSi an appealing biomaterial for tissue engineering, with surfaces characteristics facilitating human cell adhesion and differentiation. The resorption kinetics of such porous biomaterials is crucial for in vivo bone regeneration, in order to adapt biomaterial resorption to tissue formation, and to control the release of loaded bioactive molecules. We investigated pSi as a bioactive scaffold for bone tissue engineering, with an emphasis on kinetics of pSi resorption and silicon release. PSi particles and chips were fabricated from crystalline silicon, and functionalized by oxidation and chemical grafting of amine groups to mimic biological structures. Materials resorption over time was investigated with Raman spectroscopy, infrared spectroscopy, and Scanning Electron Microscopy. Silicon release was followed by mass spectrometry. Particle degradation and inclusion in newly formed bone were studied in vivo. The in vitro experiments revealed that non-oxidized pSi had an accelerated initial dissolution in ddH2O and an inhibition of initial Si release in SBF. This high reactivity also led to transformation towards amorphous non-resorbable silica when incubated in SBF. PSi resorption started immediately with a maximal dissolution in the first 24 h. Later, the dissolution rate decreased over time. In comparison, the resorption process of oxidized pSi seemed delayed, but more continuous. This delayed dissolution increased the bioactivity and stability, leading to enhanced bone formation in vivo. Delayed pSi degradation provided a constant surge of silicic acid over time and promoted bone regeneration, demonstrating the high potential of pSi for bone tissue engineering: Oxidized pSi were almost completely resorbed after 2 months of healing, with remaining partially dissolved particles surrounded by newly formed bone. On the contrary, non-oxidized particles were still obviously present after 2 months with limited bone regeneration. This delayed resorption is consistent with the in vitro observations in SBF, and particles' transformation towards silica.

The presence of silicate melt may enhance rates of cation diffusion in olivine

Olivine is commonly used as a ‘crystal clock’ to extract timescales relevant to pre-eruptive perturbations within mafic magmatic systems. Diffusion chronometry applications require accurate calibrations for the rates at which Fe-Mg or other commonly measured elements like Ni, Mn, and Ca diffuse through the crystal lattice. In the past, these rates have been mainly characterized using solid-solid diffusion couple experiments involving olivine single crystals, thin films, or powder sources. Despite the presence of melt surrounding olivine in natural magmatic systems, very few experiments involving magma have been performed, largely because controlling interface reactions is difficult. For this study, we carried out olivine-melt diffusion experiments as a test of the diffusion chronometry method, and to determine whether the presence of melt influences the calculated timescales. To approximate a natural system, we incorporated small natural Kīlauea and San Carlos olivine seeds within a natural Kīlauea basalt and tracked diffusive re-equilibration through time. To better control interface reactions, after some equilibration period at an initial superliquidus temperature of 1290°C, the runs were rapidly cooled to form a rim and left to dwell at various final temperatures (1200, 1220, 1240, 1255°C) for 6–84 h. Concentration gradients for Fe-Mg, Mn, Ni, Ca were measured, and the step-wise nature of the core-rim transition was ascertained using slow diffusing elements like P or Al. When these gradients are modeled using published diffusivities, the timescales retrieved are typically 10 times longer than the actual experiment durations. Thus, measured diffusivities are an order of magnitude faster than those previously obtained in olivine-solid source experiments, but they are in excellent agreement with the only two other melt-olivine datasets. We explore reasons for why melt-bearing olivine diffusion experiments tend to yield faster rates. The possible effects of (1) growth during diffusion, (2) diffusion during any initial dissolution step, and (3) extended tube or planar defects at the interface on calculated diffusivities are all considered but found to be inconsequential. Instead, we argue that additional point defects (vacancies) are likely created at the interface by higher concentrations in elements like Al or H in the basalt melt compared to other solid couple diffusant sources. Future applications of diffusion chronometry in olivine may require a complete re-evaluation of published diffusivities using melt-bearing experimental configurations.