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Silica is extensively deposited by plants, however, only little is known about the molecular control over this process. Siliplant1 is the only known plant protein to precipitate biosilica. The protein contains seven repeats made of three domains. One of the domains exhibits a conserved sequence, which catalyzes silica precipitation in vitro. Here, silica was synthesized by the activity of a peptide carrying this conserved sequence. Infrared spectroscopy and thermal gravimetric analyses showed that the peptide was bound to the mineral. Scanning electron microscopy showed that silica-peptide particles of 22 ± 4 nm aggregated to spherical structures of 200-300 nm when the ratio of silicic acid to the peptide was below 183:1 molecules. When the ratio was about 183:1, similar particles aggregated into irregular structures, and silica gel formed at higher ratios. Solid-state NMR spectra indicated that the irregular aggregates were richer in Si-O-Si bonds as well as disordered peptide. Our results suggest that the peptide catalyzed the condensation of silicic acid and the formation of ∼20 nm particles, which aggregated into spheres. Excess of the peptide stabilized surface Si-OH groups that prevented spontaneous Si-O-Si bonding between aggregates. Under Si concentrations relevant to plant sap, the peptide and possibly Siliplant1, could catalyze nucleation of silica particles that aggregate into spherical aggregates., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Rivka Elbaum reports financial support was provided by Israel Science Foundation. Sabrina Diehn reports financial support was provided by Minerva Foundation. Vincent Otieno Ayieko reports financial support was provided by RH Smith Foundation., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Background: Silicon and aluminium oxides make the bulk of agricultural soils. Plants absorb dissolved silicon as silicic acid into their bodies through their roots. The silicic acid moves with transpiration to target tissues in the plant body, where it polymerizes into biogenic silica. Mostly, the mineral forms on a matrix of cell wall polymers to create a composite material. Historically, silica deposition (silicification) was supposed to occur once water evaporated from the plant surface, leaving behind an increased concentration of silicic acid within plant tissues. However, recent publications indicate that certain cell wall polymers and proteins initiate and control the extent of plant silicification., Scope: Here we review recent publications on the polymers that scaffold the formation of biogenic plant silica, and propose a paradigm shift from spontaneous polymerization of silicic acid to dedicated active metabolic processes that control both the location and the extent of the mineralization., Conclusion: Protein activity concentrates silicic acid beyond its saturation level. Polymeric structures at the cell wall stabilize the supersaturated silicic acid and allow its flow with the transpiration stream, or bind it and allow its initial condensation. Silica nucleation and further polymerization are enabled on a polymeric scaffold, which is embedded within the mineral. Deposition is terminated once free silicic acid is consumed or the chemical moieties for its binding are saturated., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Diatoms are an important group of algae that can produce intricate silicified cell walls (frustules). The complex process of silicification involves a set of enigmatic integral membrane proteins that are thought to actively transport the soluble precursor of biosilica, dissolved silicic acid. Full-length silicic acid transporters are found widely across the diatoms while homologous shorter proteins have now been identified in a range of other organisms. It has been suggested that modern silicic acid transporters arose from the union of such partial sequences. Here, we present a computational study of the silicic acid transporters and related transporter-like sequences to help understand the structure, function and evolution of this class of membrane protein. The AlphaFold software predicts that all of the protein sequences studied here share a common fold in the membrane domain which is entirely different from the predicted folds of non-homologous silicic acid transporters from plants. Substrate docking reveals how conserved polar residues could interact with silicic acid at a central solvent-accessible binding site, consistent with an alternating access mechanism of transport. The structural conservation between these proteins supports a model where modern silicon transporters evolved from smaller ancestral proteins by gene fusion., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

Molecular simulation was performed to study the interaction between PAMAM(DETA as the core) with different generations and silicic acid molecules, and discussed the inhibition effect mechanism against silica scale through gyration radius and radial distribution function et al. The results showed that adsorption interactions between silicic acid molecules and the PAMAM with -NH 2 terminated groups molecule (G1.0 and G2.0) were stronger than those and the PAMAM with -COOH terminated groups molecule (G0.5 and G1.5). The adsorption interactions were primarily divided into electrostatic interactions, vdW interactions as well as H-bond interactions, where electrostatic interaction was dominant. Molecular simulation results were consistent with our experimental results., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Mesoporous silica has attracted significant attention in the drug delivery area; however, impurities can be a source of toxicity. The current study used commercial microparticles produced at large scale in a well-controlled environment. Micrometer sized mesoporous silica particles were acquired through a commercial vendor and pore structures were characterized by SEM. The three silica particle formulations had a diameter of 15 micrometers and three different pore sizes of 10 nm, 30 nm, and 100 nm. The fourth formulation had particle size of 20-40 micrometers with 50 nm pores. Before in vivo tests, an in vitro cytotoxicity test was conducted with silicic acid, derived from the sol-gel particles, on EA.hy926 cells. Low concentration (2.5 µg/mL) of silicic acid showed no cytotoxicity; however, high concentration (25 µg/mL) was cytotoxic. In vivo intravitreal injection demonstrated that 15 um silica particles with 10 nm pore were safe in both rabbit and guinea pig eyes and the particles lasted in the vitreous for longer than two months. Formulations of with larger pores demonstrated variable localized vitreous cloudiness around the sol-gel particle depot and mild inflammatory cells in the aqueous humor. The incidence of reaction trended higher with larger pores (10 nm: 0%, 30 nm: 29%, 50 nm: 71%, 100 nm: 100%, p  < .0001, Cochran Armitage Trend Test). Sol-gel mesoporous silica particles have uniform particle sizes and well-defined pores, which is an advantage for implantation via a fine needle. Selected formulations may be used as an intraocular drug delivery system with proper loading and encapsulation.

This paper concerns simultaneous removal of fluoride and hydrated silica from groundwater (4.08 mg L -1 fluoride, 90 mg L -1 hydrated silica, 50 mg L -1 sulfate, 0.23 mg L -1 phosphate, pH 7.38 and 450 μS cm -1 conductivity) by electrocoagulation (EC), using an up-flow EC reactor, with a six-cell stack in a serpentine array, opened at the top of the cell to favor gas release. Aluminum plates were used as sacrificial electrodes. The effect of current density (4 ≤ j ≤ 7 mA cm -2 ) and mean linear flow rate (1.2 ≤ u ≤ 4.8 cm s -1 ), applied to the EC reactor, on the elimination of fluoride and hydrated silica was analyzed. The removal of fluoride followed the WHO guideline (<1.5 mg L -1 ), while the hydrated silica was abated at 7 mA cm -2 and 1.2 cm s -1 , with energy consumption of 2.48 kWh m -3 and an overall operational cost of 0.441 USD m -3 . Spectroscopic analyses of the flocs by XRD, XRF-EDS, SEM-EDS, and FTIR indicated that hydrated silica reacted with the coagulant forming aluminosilicates, and fluoride replaced a hydroxide from aluminum aggregates, while sulfates and phosphates were removed by adsorption process onto the flocs. The well-engineered EC reactor allowed the simultaneous removal of fluoride and hydrated silica., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest regarding the publication of this paper., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Crystallite aluminosilicates are inorganic microporous materials with well-defined pore-size and pore-structures, and have important industrial applications, including gas adsorption and separation, catalysis, etc. Crystallite aluminosilicates are commonly synthesized via hydrothermal processes, where the oligomerization of silicic acids is crucial. The mechanisms for the oligomerization of poly-silicic acids in neutral aqueous solution were systematically investigated by extensive first-principles-based calculations. We showed that oligomerization of poly-silicic acid molecules proceeds through the lateral attacking and simultaneously proton transfer from the approaching molecule for the formation of a 5-coordinated Si species as the transition state, resulting in the ejection of a water molecule from the formed poly-silicic acid. The barriers for this mechanism are in general more plausible than the conventional direct attacking of poly-silicic acid with reaction barriers in the range of 150-160 kJ/mol. The formation of linear or branched poly-silicic acids by intermolecular oligomerization is only slightly more plausible than the formation of cyclic poly-silicic acids via intramolecular oligomerization according to the reaction barriers (124.2-133.0 vs. 130.6-144.9 kJ/mol). The potential contributions of oligomer structures, such as the length of the linear oligomers, ring distortions and neighboring linear branches, etc., to the oligomerization were also investigated but found negligible. According to the small differences among the reaction barriers, we proposed that kinetic selectivity of the poly-silicic acids condensation would be weak in neutral aqueous solution and the formation of zeolite-like structures would be thermodynamics driven.

The cell wall polymer callose catalyses the formation of silica in vitro and is heavily implicated in biological silicification in Equisetum (horsetail) and Arabidopsis (thale cress) in vivo Callose, a β-1,3-glucan, is an ideal partner for silicification, because its amorphous structure and ephemeral nature provide suitable microenvironments to support the condensation of silicic acid into silica. Herein, using scanning electron microscopy, immunohistochemistry and fluorescence, we provide further evidence of the cooperative nature of callose and silica in biological silicification in rice, an important crop plant and known silica accumulator. These new data along with recently published research enable us to propose a model to describe the intracellular events that together determine callose-driven biological silicification., (© 2018 The Authors.)

The silicon transport and use inside cells are key processes for understanding how diatoms metabolize this element in the silica biogenic cycle in the ocean. A spin-probe electron paramagnetic resonance (EPR) study over time helped to investigate the interacting properties and the internalization mechanisms of silicic acid from different silicon sources into the cells. Diatom cells were grown in media containing biogenic amorphous substrates, such as diatomaceous earth and sponge spicules, and crystalline sodium metasilicate. It was found that the amorphous biogenic silicon slowed down the internalization process probably due to formation of colloidal particles at the cell surface after silicic acid condensation. Weaker interactions occurred with sponge spicules silicon source if compared to the other sources. The EPR results were explained by analyzing transcript level changes of silicon transporters (SITs) and silaffins (SILs) in synchronized Thalassiosira pseudonana cultures over time. The results indicated that the transport role of SITs is minor for silicic acid from both biogenic and crystalline substrates, and the role of SIT3 is linked to the transport of silicon inside the cells, mainly in the presence of sponge spicules. SIL3 transcripts were expressed in the presence of all silicon sources, while SIL1 transcripts only with sponge spicules. The data suggest that the transport of silicic acid from various silicon sources in diatoms is based on different physico-chemical interactions with the cell surface., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Easy-to-prepare drug delivery systems, based on smart, silica gels have been synthesized, characterized, and studied as hosts in the controlled release of bisphosphonates. They exhibit variable release rates and final % release, depending on the nature of bisphosphonate (side-chain length, hydro-philicity/-phobicity, water-solubility), cations present, pH and temperature. These gels are robust, injectable, re-loadable and re-usable.

There is good evidence that certain silicon-containing materials promote would healing and their common feature is the delivery of orthosilicic acid (Si(OH) 4 ) either directly or following metabolism. In this respect, amorphous silica nanoparticles (NP), which dissolve in aqueous environments releasing up to 2mM orthosilicic acid, may be appropriate 'slow release' vehicles for bioactive silicon. Here we studied the impact of silica NP suspensions (primary particles∼10nm) in undersaturated conditions (below 2mM Si) with differing degrees of surface charge and dissolution rate on human dermal fibroblasts (CCD-25SK cells) viability, proliferation and migration in a cellular wound model. Silica was shown to be non-toxic for all forms and concentrations tested and whilst the anticipated stimulatory effect of orthosilicic acid was observed, the silica NPs also stimulated fibroblast proliferation and migration. In particular, the amine-functionalized particles promoted wound closure more rapidly than soluble orthosilicic acid alone. We suggest that this effect is related to easy cellular internalization of these particles followed by their intracellular dissolution releasing silicic acid at a faster rate than its direct uptake from the medium. Our findings indicate that amorphous silica-based NPs may favour the delivery and release of bioactive silicic acid to cells, promoting wound healing., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Diopside (DIOP) was introduced into polyetheretherketone/polyglycolicacid (PEEK/PGA) scaffolds fabricated via selective laser sintering to improve bioactivity. The DIOP surface was then modified using a silane coupling agent, 3-glycidoxypropyltrimethoxysilane (KH570), to reinforce interfacial adhesion. The results showed that the tensile properties and thermal stability of the scaffolds were significantly enhanced. It could be explained that, on the one hand, the hydrophilic group of KH570 formed an organic covalent bond with the hydroxy group on DIOP surface. On the other hand, there existed relatively high compatibility between its hydrophobic group and the biopolymer matrix. Thus, the ameliorated interface interaction led to a homogeneous state of DIOP dispersion in the matrix. More importantly, an in vitro bioactivity study demonstrated that the scaffolds with KH570-modified DIOP (KDIOP) exhibited the capability of forming a layer of apatite. In addition, cell culture experiments revealed that they had good biocompatibility compared to the scaffolds without KDIOP. It indicated that the scaffolds with KDIOP possess potential application in tissue engineering.

Magnesium is a trace element in the human body, known to have important effects on cell differentiation and the mineralisation of calcified tissues. This study aimed to synthesise highly porous Ca-Mg silicate foamed scaffolds from preceramic polymers, with analysis of their biological response. Akermanite (Ak) and wollastonite-diopside (WD) ceramic foams were obtained from the pyrolysis of a liquid silicone mixed with reactive fillers. The porous structure was obtained by controlled water release from selected fillers (magnesium hydroxide and borax) at 350°C. The homogeneous distribution of open pores, with interconnects of modal diameters of 160-180μm was obtained and maintained after firing at 1100°C. Foams, with porosity exceeding 80%, exhibited compressive strength values of 1-2MPa. In vitro studies were conducted by immersion in SBF for 21days, showing suitable dissolution rates, pH and ionic concentrations. Cytotoxicity analysis performed in accordance with ISO10993-5 and ISO10993-12 standards confirmed excellent biocompatibility of both Ak and WD foams. In addition, MC3T3-E1 cells cultured on the Mg-containing scaffolds demonstrated enhanced osteogenic differentiation and the expression of osteogenic markers including Collagen Type I, Osteopontin and Osteocalcin, in comparison to Mg-free counterparts. The results suggest that the addition of magnesium can further enhance the bioactivity and the potential for bone regeneration applications of Ca-silicate materials., Statements of Significance: Here, we show that the incorporation of Mg in Ca-silicates plays a significant role in the enhancement of the osteogenic differentiation and matrix formation of MC3T3-E1 cells, cultured on polymer-derived highly porous scaffolds. Reduced degradation rates and improved mechanical properties are also observed, compared to Mg-free counterparts, suggesting the great potential of Ca-Mg silicates as bone tissue engineering materials. Excellent biocompatibility of the new materials, in accordance to the ISO10993-5 and ISO10993-12 standard guidelines, confirms the preceramic polymer route as an efficient synthesis methodology for bone scaffolds. The use of hydrated fillers as porogens is an additional novelty feature presented in the manuscript., (Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

The immunomodulatory functions of monocytes are increasingly being recognized. Silicified collagen scaffolds (SCSs), produced by infiltrating collagen matrices with intrafibrillar amorphous silica, exhibit osteogenic and angiogenic potential and are promising candidates in tissue engineering. Here, we demonstrate that SCS promotes in situ bone regeneration and angiogenesis via monocyte immunomodulation. Increased numbers of TRAP-positive monocytes, nestin-positive bone marrow stromal cells (BMSCs) and CD31-positive and endomucin-positive new vessels can be identified from new bone formation regions in a murine calvarial defect model. In addition, sustained release of silicic acid by SCS stimulates differentiation of blood-derived monocytes into TRAP-positive cells, with increased expressions of SDF-1α, TGF-β1, VEGFa and PDGF-BB. These cytokines further promote homing of BMSCs and endothelial progenitor cells as well as neovascularization. Taken together, these novel findings indicate that SCSs possess the ability to enhance recruitment of progenitor cells and promote osteogenesis and angiogenesis by immunomodulation of monocytes., (Published by Elsevier Ltd.)

The contamination of agricultural areas by heavy metals has a negative influence on food quality and human health. Various remediation techniques have been developed for the removal and/or immobilization of heavy metals (HM) in contaminated soils. Phytoremediation is innovative technology, which has advantages (low cost, easy monitoring, high selectivity) and limitations, including long time for procedure and negative impact of contaminants on used plants. Greenhouse investigations have shown that monosilicic acid can be used for regulation of the HM (Cd, Cr, Pb and Zn) mobility in the soil-plant system. If the concentration of monosilicic acid in soil was increased from 0 to 20 mg L(-1) of Si in soil solution, the HM bioavailability was increased by 30-150%. However, the negative influence on the barley by HM was reduced under monosilicic acid application. If the concentration of monosilicic acid was increased more than 20 mg L(-1), the HM mobility in the soil was decreased by 40-300% and heavy metal uptake by plants was reduced 2-3 times. The using of the monosilicic acid may increase the phytoremediation efficiency. However the technique adaptation will be necessary for phytoremediation on certain areas., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Bioactive mesoporous diopside (m-DP) and poly(L-lactide) (PLLA) composite scaffolds with mesoporous/macroporous structure were prepared by the solution-casting and particulate-leaching method. The results demonstrated that the degradability and bioactivity of the mesoporous/macroporous scaffolds were significantly improved by incorporating m-DP into PLLA, and that the improvement was m-DP content-dependent. In addition, the scaffolds containing m-DP showed the ability to neutralize acidic degradation products and prevent the pH from dropping in the solution during the soaking period. Moreover, the scaffolds containing m-DP enhanced attachment, proliferation and alkaline phosphatase activity of MC3T3-E1 cells, which were also m-DP content-dependent. Furthermore, the histological and immunohistochemical analysis results showed that the scaffolds with m-DP significantly promoted new bone formation and improved the materials degraded in vivo, indicating good biocompatibility. The results suggested that the mesoporous/macroporous scaffolds of the m-DP/PLLA composite with osteogenesis had a potential for bone regeneration., (© 2015 The Author(s).)

In low dimensional cesium silicate LDS-1 (monoclinic phase of CsHSi2O5), anomalous infrared absorption bands observed at 93, 155, 1210, and 1220 cm(-1) are assigned to the vibrational mode of protons, which contribute to the strong hydrogen bonding between terminal oxygen atoms of silicate chain (O-O distance = 2.45 Å). The integrated absorbance (oscillator strength) for those modes is drastically enhanced at low temperatures. The analysis of integrated absorbance employing two different anharmonic double-minimum potentials makes clear that proton tunneling through the potential barrier yields an energy splitting of the ground state. The absorption bands at 93 and 155 cm(-1), which correspond to the different vibrational modes of protons, are attributed to the optical transition between the splitting levels (excitation from the ground state (n = 0) to the first excited state (n = 1)). Moreover, the absorption bands at 1210 and 1220 cm(-1) are identified as the optical transition from the ground state (n = 0) to the third excited state (n = 3). Weak Coulomb interactions in between the adjacent protons generate two types of vibrational modes: symmetric mode (93 and 1210 cm(-1)) and asymmetric mode (155 and 1220 cm(-1)). The broad absorption at 100-600 cm(-1) reveals an emergence of collective mode due to the vibration of silicate chain coupled not only with the local oscillation of Cs(+) but also with the proton oscillation relevant to the second excited state (n = 2).

Marine diatoms are silica-precipitating microalgae that account for over half of organic carbon burial in marine sediments and thus they play a key role in the global carbon cycle. Their evolutionary expansion during the Cenozoic era (66 Ma to present) has been associated with a superior competitive ability for silicic acid relative to other siliceous plankton such as radiolarians, which evolved by reducing the weight of their silica test. Here we use a mathematical model in which diatoms and radiolarians compete for silicic acid to show that the observed reduction in the weight of radiolarian tests is insufficient to explain the rise of diatoms. Using the lithium isotope record of seawater as a proxy of silicate rock weathering and erosion, we calculate changes in the input flux of silicic acid to the oceans. Our results indicate that the long-term massive erosion of continental silicates was critical to the subsequent success of diatoms in marine ecosystems over the last 40 My and suggest an increase in the strength and efficiency of the oceanic biological pump over this period.

The present work is an amalgamation of computation and experimental approach to gain an insight into composition-structure-bioactivity relationships of alkali-free bioactive glasses in the CaO-MgO-SiO2-P2O5 system. The glasses have been designed in the diopside (CaO·MgO·2SiO2; Di)-tricalcium phosphate (3CaO·P2O5; TCP) binary join by varying the Di/TCP ratio. The melt-quenched glasses have been investigated for their structure by molecular dynamic (MD) simulations as well as by nuclear magnetic resonance spectroscopy (NMR). In all the investigated glasses silicate and phosphate components are dominated by Q(2) (Si) and Q(0) (P) species, respectively. The apatite forming ability of the glasses was investigated using X-ray diffraction (XRD), infrared spectroscopy after immersion of glass powders in simulated body fluid (SBF) for time durations varying between 1 h and 14 days, while their chemical degradation has been studied in Tris-HCl in accordance with ISO 10993-14. All the investigated glasses showed good bioactivity without any substantial variation. A significant statistical increase in metabolic activity of human mesenchymal stem cells (hMSCs) when compared to the control was observed for Di-60 and Di-70 glass compositions under both basal and osteogenic conditions., (Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Carbon nanotubes are ideal candidates for the mechanical reinforcement of ceramic due to their excellent mechanical properties, high aspect ratio and nanometer scale diameter. In this study, the effects of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of diopside (Di) scaffolds fabricated by selective laser sintering were investigated. Results showed that compressive strength and fracture toughness improved significantly with increasing MWCNTs from 0.5 to 2 wt %, and then declined with increasing MWCNTs to 5 wt %. Compressive strength and fracture toughness were enhanced by 106% and 21%, respectively. The reinforcing mechanisms were identified as crack deflection, MWCNTs crack bridging and pull-out. Further, the scaffolds exhibited good apatite-formation ability and supported adhesion and proliferation of cells in vitro.

The growing field of silicon solar cells requires a substantial reduction in the cost of semiconductor grade silicon, which has been mainly produced by the rod-based Siemens method. Because silicon can react with almost all of the elements and form a number of alloys at high temperatures, it is highly desired to obtain high purity crystalline silicon at relatively low temperatures through low cost process. Here we report a fast, complete and inexpensive reduction method for converting sodium hexafluorosilicate into silicon at a relatively low reaction temperature (∼ 200 °C). This temperature could be further decreased to less than 180 °C in combination with an electrochemical approach. The residue sodium fluoride is dissolved away by pure water and hydrochloric acid solution in later purifying processes below 15 °C. High purity silicon in particle form can be obtained. The relative simplicity of this method might lead to a low cost process in producing high purity silicon.

Controlled synthesis of silicon is a major challenge in nanotechnology and material science. Diatoms, the unicellular algae, are an inspiring example of silica biosynthesis, producing complex and delicate nano-structures. This happens in several cell compartments, including cytoplasm and silica deposition vesicle (SDV). Considering the low concentration of silicic acid in oceans, cells have developed silicon transporter proteins (SIT). Moreover, cells change the level of active SITs during one cell cycle, likely as a response to the level of external nutrients and internal deposition rates. Despite this topic being of fundamental interest, the intracellular dynamics of nutrients and cell regulation strategies remain poorly understood. One reason is the difficulties in measurements and manipulation of these mechanisms at such small scales, and even when possible, data often contain large errors. Therefore, using computational techniques seems inevitable. We have constructed a mathematical model for silicon dynamics in the diatom Thalassiosira pseudonana in four compartments: external environment, cytoplasm, SDV and deposited silica. The model builds on mass conservation and Michaelis-Menten kinetics as mass transport equations. In order to find the free parameters of the model from sparse, noisy experimental data, an optimization technique (global and local search), together with enzyme related penalty terms, has been applied. We have connected population-level data to individual-cell-level quantities including the effect of early division of non-synchronized cells. Our model is robust, proven by sensitivity and perturbation analysis, and predicts dynamics of intracellular nutrients and enzymes in different compartments. The model produces different uptake regimes, previously recognized as surge, externally-controlled and internally-controlled uptakes. Finally, we imposed a flux of SITs to the model and compared it with previous classical kinetics. The model introduced can be generalized in order to analyze different biomineralizing organisms and to test different chemical pathways only by switching the system of mass transport equations.

Background: Fluoride additives contain metal contaminants that must be diluted to meet drinking water regulations. However, each raw additive batch supplied to water facilities does not come labeled with concentrations per contaminant. This omission distorts exposure profiles and the risks associated with accidents and routine use., Objectives: This study provides an independent determination of the metal content of raw fluoride products., Methods: Metal concentrations were analyzed in three hydrofluorosilicic acid (HFS) and four sodium fluoride (NaF) samples using inductively coupled plasma-atomic emission spectrometry. Arsenic levels were confirmed using graphite furnace atomic absorption analysis., Results: Results show that metal content varies with batch, and all HFS samples contained arsenic (4·9-56·0 ppm) or arsenic in addition to lead (10·3 ppm). Two NaF samples contained barium (13·3-18·0 ppm) instead. All HFS (212-415 ppm) and NaF (3312-3630 ppm) additives contained a surprising amount of aluminum., Conclusions: Such contaminant content creates a regulatory blind spot that jeopardizes any safe use of fluoride additives.

Chitosan-coated calcium silicate hydrate (CSH/chitosan) mesoporous microspheres formed by self-assembly of nanosheets have been synthesized in aqueous solution under ambient conditions without using any toxic surfactant or organic solvent. The method reported herein has advantages of simplicity, low cost and being environmentally friendly. The BET specific surface area of CSH/chitosan mesoporous microspheres is measured to be as high as ~356 m(2) g(-1), which is considerably high among calcium silicate materials. The as-prepared CSH/chitosan mesoporous microspheres are promising adsorbent and exhibit a quick and highly efficient adsorption behavior toward heavy metal ions of Ni(2+), Zn(2+), Cr(3+), Pb(2+) Cu(2+) and Cd(2+) in aqueous solution. The adsorption kinetics can be well fitted by the pseudo second-order model. The maximum adsorption amounts of Ni(2+), Zn(2+), Pb(2+), Cu(2+) and Cd(2+) on CSH/chitosan mesoporous microspheres are extremely high, which are 406.6, 400, 796, 425 and 578 mg/g, respectively. The CSH/chitosan adsorbent exhibits the highest affinity for Pb(2+) ions among five heavy metal ions. The adsorption capacities of the CSH/chitosan adsorbent toward heavy metal ions are relatively high compared with those reported in the literature., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Purpose: To compare the ability of two active ingredients - sodium fluoride (NaF) and stannous fluoride (SnF2 ) - to inhibit hydroxyapatite (HAP) dissolution in buffered acidic media., Methods: Two in vitro studies were conducted. HAP powder, which is representative of tooth mineral, was pretreated with: test solutions of NaF or SnF2 , 10 g solution per 300 mg HAP powder (Study 1); or NaF or SnF2 dentifrice slurry supernatants, 20 g supernate per 200 mg HAP powder for 1 minute followed by three washes with water, then dried (Study 2). About 50 mg of pretreated HAP was exposed to 25 ml of acid dissolution media adjusted to and maintained at pH 4.5 in a Metrohn Titrino reaction cell. Exposure of HAP to the media results in dissolution and release of hydroxide ion, increasing the pH of the solution. The increase in pH is compensated for by automatic additions of acid to maintain the original pH (4.5) of the reaction cell. Total volume of titrant added after 30 minutes was used to calculate the percentage reduction in dissolution versus non-treated HAP control., Results: Both F sources provided protection against acid dissolution; however, in each study, SnF2 -treated HAP was significantly more acid-resistant than the NaF treated mineral. In study 1, at 280 ppm F, representing concentrations of F found in the mouth after in vivo dentifrice use, the reduction in HAP dissolution was 47.7% for NaF and 75.7% for the SnF2 -treated apatite (extrapolated). In study 2, the reduction in HAP dissolution was 61.3% for NaF and 92.8% for SnF2 -treated samples. Differences in percentage reduction were statistically significant (Paired-t test)., Conclusions: Results of these studies demonstrate that both of the fluoride sources tested enhance the acid resistance of tooth mineral and that resistance is significantly greater after treatment with SnF2 compared with treatment of tooth mineral with NaF., (© 2014 FDI World Dental Federation.)

The interaction of nanoparticles (NPs) with lipid membranes is an integral step in the interaction of NPs and living cells. During particle uptake, the membrane has to bend. Due to the nature of their phase diagram, the modulus of compression of these membranes can vary by more than one order of magnitude, and thus both the thermodynamic and mechanical aspects of the membrane have to be considered simultaneously. We demonstrate that silica NPs have at least two independent effects on the phase transition of phospholipid membranes: 1), a chemical effect resulting from the finite instability of the NPs in water; and 2), a mechanical effect that originates from a bending of the lipid membrane around the NPs. Here, we report on recent experiments that allowed us to clearly distinguish both effects, and present a thermodynamic model that includes the elastic energy of the membranes and correctly predicts our findings both quantitatively and qualitatively., (Copyright © 2012 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

Moxifloxacin and lomefloxacin are fluoroquinolone antibiotics used in treating urinary and respiratory tract infections. Fluoroquinolones are known to have interactions with drugs that are active in gastro intestinal tract. Being moxifloxacin and lomefloxacin fluoroquinolones the interaction study of was carried out with sucralfate, gelusil, erythromycin and multi minerals. The interaction was studied at neutral, acidic and basic conditions both at room temperature and 37°C. The effect of dissolution medium simulating various body environments with response to pH has been examined in order to elucidate the interactions. The response of moxifloxacin and lomefloxacin after interaction with co-administered drugs at different conditions and temperature were noted using a Shimadzu HPLC system with PDA detector. It was seen that interaction of these fluoroquinolones was more at 37°C than at room temperature. Moxifloxacin and Lomefloxacin reacts faster with sucralfate and gelusil in acidic media whereas with erythromycin in basic media and multi-minerals in neutral media. The study ensures the interaction of fluoroquinolones with selected class of drugs. In order to achieve the effective therapeutic effect appropriate time intervals between administrations of drugs is essential.

The instant thin-layer chromatographic method of determining the radiochemical purity of (99m)Tc-tetrofosmin recommended by the manufacturer uses a mixture of acetone and dichloromethane (35:65 v/v) as the solvent and a silica gel (SG) strip as the solid phase. Currently, SG strips are not available commercially and an alternative solid phase is needed. The present study reports that silicic acid strips are an appropriate substitute for SG strips for the chromatographic method using the same solvent mixture but mixed in a reverse ratio (65:35 v/v). The 2 methods yielded similar values (within 1 SD) of radiochemical purity for (99m)Tc-tetrofosmin.

Silicic acid (H(4)SiO(4)) adsorbs at the ferrihydrite-water interface as monomeric or oligomeric surface silicate complexes.ATR-IR spectra were used to determine the proportions of monomeric and oligomeric surface silicate as a function of pH and Si surface concentrations (Γ(Si)) for H(4)SiO(4) in ferrihydrite suspensions.At each pH the proportion of adsorbed silicate present as monomers decreased as Γ(Si) increased while at a given Γ(Si) the proportion of adsorbed silicate present as monomers was higher at higher pH. ATR-IR spectra for ferrihydrite suspensions in combination with the adsorption isotherm data were used to calibrate the Diffuse Layer Model (DLM) to describe H(4)SiO(4) adsorption as monomers and oligomers on ferrihydrite surface sites (≡FeOH). Using a set of reactions that were consistent with the ATR-IR spectra the DLM could accurately describe the H(4)SiO(4) adsorption isotherms, the distribution of surface monomeric and oligomeric silicates, and the decrease in surface potential with Γ(Si).The reactions included the formation of monomeric complexes (≡FeH((3-n))SiO(4)((-n))) and trimeric silicate complexes formed between two surface sites(≡Fe(2)H((6-n))Si(3)O(10)((-n))). This oligomer stoichiometry is consistent with previous studies suggesting the surface silicate oligomer is formed by a solution H(4)SiO(4) bridging two adjacent adsorbed monomers to form a linear trimer. This study also showed that carbonate can enhance H(4)SiO(4) adsorption between pH 9 and 11. The data were consistent with formation of an outer-sphere complex between a solution H(3)SiO(4)(-) and a protonated adsorbed carbonate species which is analogous to the mechanism by which carbonate enhances the goethite adsorption of sulfate., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Glass-ceramics in the diopside (CaMgSi2O6)-fluorapatite (Ca5(PO4)3F)-wollastonite (CaSiO3) system are potential candidates for restorative dental and bone implant materials. The present study describes the influence of varying SiO2/CaO and CaF2/P2O5 molar ratio on the structure and thermal behavior of glass compositions in the CaO-MgO-SiO2-P2O5-Na2O-CaF2 system. The structural features and properties of the glasses were investigated by nuclear magnetic resonance (NMR), infrared spectroscopy, density measurements and dilatometry. Sintering and crystallization behavior of the glass powders were studied by hot-stage microscopy and differential thermal analysis, respectively. The microstructure and crystalline phase assemblage in the sintered glass powder compacts were studied under non-isothermal heating conditions at 825 °C. X-ray diffraction studies combined with the Rietveld-reference intensity ratio (R.I.R) method were employed to quantify the amount of amorphous and crystalline phases in the glass-ceramics, while scanning electron microscopy was used to shed some light on the microstructure of resultant glass-ceramics. An increase in CaO/SiO2 ratio degraded the sinterability of the glass powder compacts, resulting in the formation of akermanite as the major crystalline phase. On the other hand, an increase in P2O5/CaF2 ratio improved the sintering behavior of the glass-ceramics, while varying the amount of crystalline phases, i.e. diopside, fluorapatite and wollastonite., (Copyright © 2010. Published by Elsevier Ltd.)

Diopside (CaMgSi(2)O(6)) powders and dense ceramics have been shown to be bioactive biomaterials for bone repair. The aim of this study is to prepare bioactive diopside scaffolds and examine their physicochemical and biological properties. X-ray diffraction, scanning electron microscopy (SEM), micro-computerized tomography and energy-dispersive spectrometry were used to analyse the composition, microstructure, pore size and interconnectivity of the diopside scaffolds. The mechanical strength and stability as well as the degradation of the scaffolds were investigated by testing the compressive strength, modulus and silicon ions released, respectively. Results showed that highly porous diopside scaffolds with varying porosity and high interconnectivity of 97% were successfully prepared with improved compressive strength and mechanical stability, compared to the bioglass and CaSiO(3) scaffolds. The bioactivity of the diopside scaffolds was assessed using apatite-forming ability in simulated body fluids (SBF) and by their support for human osteoblastic-like cell (HOB) attachment, proliferation and differentiation using SEM, and MTS and alkaline phosphatase activity assays, respectively. Results showed that diopside scaffolds possessed apatite-forming ability in SBF and supported HOB attachment proliferation and differentiation. Bioactive diopside scaffolds were prepared with excellent pore/structure art, and improved mechanical strength and mechanical stability, suggesting their possible applications for bone tissue engineering regeneration., (Copyright 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Ideal bioceramic microspheres for bone regeneration need to be bioactive and degradable, but at the same time possess a controlled drug-release ability. The main disadvantage of the currently available microspheres is their failure to combine these properties. The aim of this study is to develop bioactive ceramic microspheres with optimal properties for use in bone-tissue regeneration. In this study, we utilize diopside (CaMgSi(2)O(6), DP) with proven excellent bioactivity and degradation ability to develop microspheres by controlling their porosity and size, and further modify their surface with polymer to enhance and control their drug-loading/release ability. The phase composition, surface and inner microstructure, and porosity of DP microspheres were tested. Results indicate that carbon powders as porogens with various contents determined the porosity of the porous DP microspheres. The drug-loading and release ability of dexamethazone (DEX) from porous DP microspheres was regulated by their porosity and size. Poly(lactide-co-glycolide) modification forms a film on the surface of DP microspheres and resulted in an enhanced DEX-loading and release ability of the microspheres. Results presented here indicate that the developed DP microspheres have the potential to be used as bioactive filling materials for bone-tissue regeneration., (Copyright 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Frequently metal implants undergo detachment from the host tissue due to inadequate biocompatibility and poor osteointegration. In view of this, bioactive porous apatite-wollastonite/chitosan nanocomposite coating was prepared using electrophoretic deposition (EPD) technique in the present work. The effect of coating duration and current density on surface characteristics of the nanocomposite coating was assessed using optical microscope and scanning electron microscope. EPD led to the formation of thick and homogeneous coating. Adhesion of the composite coating on titanium substrate was evaluated using tape test and bioactivity of the coatings was studied by immersing in simulated body fluid (SBF). The coating with higher current density and longer coating duration was found to be suitable with improved adhesion and bioactivity for intended metal implants.

Competition between selenium (IV) and silicic acid for the hematite (alpha-Fe(2)O(3)) surface has been studied during this work. Single batch experiments have been performed to study separately the sorption of selenium (IV) and silicic acid as a function of the pH. With the help of the 2-pK surface complexation model, experimental data have been fitted using the FITEQL 4.0 program. Two monodentate inner-sphere surface complexes have been used to fit selenite ions retention, triple bond FeSeO(3)(-) and triple bond FeHSeO(3). In order to fit sorption of silicic acid, the two following surface complexes, namely triple bond FeH(3)SiO(4), and triple bond FeH(2)SiO(4)(-), have been used. Using the surface complexation constants coming from these two binary systems, prediction curves of the effect of silicic acid on the retention of selenium (IV) onto hematite have been obtained. Finally, performed experiments showed a competition between selenium (IV) and silicic acid for the surface sites of hematite. Experimental data matched DDLM predictions, confirming the ability of the surface complexation model to predict quantitatively and qualitatively the ternary system selenium (IV)/H(4)SiO(4)/hematite.

A novel method via a semibatch process in the absence of surfactant has been adopted to prepare pH- and temperature-sensitive nanogels. The shape, charge distribution, temperature, and pH-induced volume phase transition behavior of the latexes were investigated by scanning electronic microscopy, zeta potentials, dynamic laser light scattering, and UV/vis spectroscopy. It was found that, in the absence of surfactant, with increasing the amount of AAc from 5 to 20 mol% of N-isopropylacrylamide (NIPAM), the hydrodynamic diameters (D(H)) decrease from 230 to 60 nm. With increasing pH value from 3 to 11, the D(H) values increase slightly, which is different than the dramatic increase seen when using a conventional batch method with a range from 680 to 1700 nm. However, at pH 3, the turbidity curves of these kinds of particles increase dramatically at temperatures between 33 and 37 degrees C, while remaining constant at first and then increasing directly at pH 11. Furthermore, the distribution of carboxylic groups located not only on the interior but also on the exterior of colloidal particles as a result of adoption of the semibatch method, other than simple surface distribution of poly(NIPAM-co-AAc) latexes via the batch method.

Mono-phase ceramics of monticellite (CaMgSiO4) were successfully synthesized by sintering sol-gel-derived monticellite powder compacts at 1,480 degrees C for 6 h. The mechanical properties and the coefficient of thermal expansion (CTE) of the monticellite ceramics were tested. In addition, the bioactivity in vitro of the monticellite ceramics was evaluated by investigating their bone-like apatite-formation ability in simulated body fluid (SBF), and the biocompatibility in vitro was detected by osteoblast adhesion and proliferation assay. The results showed that the bending strength, fracture toughness and Young's modulus of the monticellite ceramics were about 159.7 MPa, 1.63 MPa m1/2 and 51 GPa, respectively. The CTE was 10.76x10(-6) degrees C(-1) and close to that of Ti-6Al-4V alloy (10.03x10(-6) degrees C(-1)). Furthermore, the monticellite ceramics possessed bone-like apatite-formation ability in SBF and could release soluble ionic products to significantly stimulate cell growth and proliferation. In addition, osteoblasts adhered and spread well on the monticellite ceramics, which indicated good bioactivity and biocompatibility.

Background: The incorporation of silica within the plant cell wall has been well documented by botanists and materials scientists; however, the means by which plants are able to transport silicon and control its polymerization, together with the roles of silica in situ, are not fully understood., Recent Progress: Recent studies into the mechanisms by which silicification proceeds have identified the following: an energy-dependent Si transporter; Si as a biologically active element triggering natural defence mechanisms; and the means by which abiotic toxicities are alleviated by silica. A full understanding of silica formation in vivo still requires an elucidation of the role played by the environment in which silica formation occurs. Results from in-vitro studies of the effects of cell-wall components associated with polymerized silica on mineral formation illustrate the interactions occurring between the biomolecules and silica, and the effects their presence has on the mineralized structures so formed., Scope: This Botanical Briefing describes the uptake, storage and function of Si, and discusses the role biomolecules play when incorporated into model systems of silica polymerization as well as future directions for research in this field.

In bis(2-carboxypyridinium) hexafluorosilicate, 2C(6)H(6)NO(2)+.SiF6(2-), (I), and bis(2-carboxyquinolinium) hexafluorosilicate dihydrate, 2C(10)H(8)NO(2)+.SiF6(2-).2H2O, (II), the Si atoms of the anions reside on crystallographic centres of inversion. Primary inter-ion interactions in (I) occur via strong N-H...F and O-H...F hydrogen bonds, generating corrugated layers incorporating [SiF6](2-) anions as four-connected net nodes and organic cations as simple links in between. In (II), a set of strong N-H...F, O-H...O and O-H...F hydrogen bonds, involving water molecules, gives a three-dimensional heterocoordinated rutile-like framework that integrates [SiF6](2-) anions as six-connected and water molecules as three-connected nodes. The carboxyl groups of the cation are hydrogen bonded to the water molecule [O...O = 2.5533 (13) A], while the N-H group supports direct bonding to the anion [N...F = 2.7061 (12) A].

To understand the roles of hydroxyl-containing biomolecules in biosilicification, theoretical and experimental studies of silica formation utilizing biological and model organic additives have been undertaken. However, the role of hydroxyl functionalized biomolecules in silica formation is still not fully understood. To address this problem, we performed a systematic in vitro study of silica formation in the presence of two proteins rich in hydroxyl-containing amino acids (native sericin proteins extracted from Bombyx mori and a recombinant sericin precursor peptide) and a range of small alkanediols. The data obtained suggest the following hypotheses for the role of hydroxyl-containing organic molecules in silica formation. In the first case, hydroxyl-containing organic molecules are not at all involved chemically in the formation of silica. Instead, they may be only assisting in rendering stability and solubility to the organic molecules found occluded in silica. The second possibility is that if we assume that hydroxyl-containing organic molecules affect silica formation, then the environments of silicic acid polymerization could be highly deficient in water to increase the effects of hydroxyl functional groups of proteins in silica formation. These results and their implications are discussed in the context of biosilicification and biomineralization.

The structure of the interface generated by a spread layer of beta-casein on an aqueous colloidal poly(silicic) acid subphase is described. The results are compared with data for the protein alone spread at the air/water interface and the silicate solution. Films develop at the air-solution interface and a strong pH dependence of the interaction causing this is demonstrated. Reflectometry with X-rays and neutrons was used to probe the interaction as a function of subphase pH and film compression. Film thickness, tau/A, scattering length density, rho/A(-2), water volume fraction, phi(w), and surface coverage, Gamma/mg m(-2), were used to quantify the interfacial structure. Where possible, the X-ray and neutron data sets were co-refined enabling phi(w) to be evaluated without assumption regarding the protein density. At pH 5-7, strong protein-silicate interaction occurred, the interface comprising three regions: a discrete protein upper layer on top of a 15 +/- 2 A layer of silicated material followed by a diffuse layer that extended into the subphase.

Alginate-based reflux suppressant preparations provide symptom relief by forming a physical barrier on top of the stomach contents in the form of a neutral floating gel or raft. This study investigated whether reduced acidity in the stomach brought about by omeprazole pre-treatment affected the formation and gastric residence time of alginate rafts. It was a balanced, cross-over study in 12 healthy non-patient volunteers following a single dose of two indium-111-labelled alginate tablets in the presence or absence of 3 days' pre-treatment with omeprazole. Raft formation and gastric residence, in the presence of a technetium-99m-labelled meal, were assessed by gamma scintigraphy for 3 h after alginate tablet administration. The relative raft-forming ability of alginate tablets after omeprazole compared with alginate tablets alone was 0.950 with 95% confidence intervals of 0.882 and 1.018. Pre-treatment and co-administration with omeprazole has no significant effect on the raft-forming ability of alginate tablets.

We investigated a method to quantitatively determine amorphous nicardipine hydrochloride (NIC) in the NIC-long acting formula (LA) model formulas prepared using NIC, light anhydrous silicic acid (LASA) and carboxymethylethylcellulose (CMEC). Consequently, since the quantity of total NIC in the formula can be determined by means of HPLC and crystal NIC can be determined by the differential scanning calorimetry (DSC) method because the heat of fusion (85.08 J/g) of NIC is constant and unaffected by excipients, we developed the HPLC-DSC method by which the quantity of amorphous NIC is calculated as the difference between the quantity of total NIC determined by HPLC and the quantity of crystal NIC determined by DSC. This practical HPLC-DSC method was confirmed to have good accuracy and reproducibility.

The behavior of porous apatite- and wollastonite-containing glass-ceramic (AW) in the bone marrow cavity was investigated. Cylinders of porous AW (4 mm in diameter and 20 mm long, mean porosity of 70% and mean pore diameter of 200 microm) were implanted into the bone marrow cavity of rabbit femurs, and analyzed by chronological radiograms and by scanning electron microscopy one, three, six, and 12 months later. The pores of porous AW are interconnected and homogeneously distributed, and its compressive strength is nearly equal to that of human cancellous bone. Bone formed in the pores at the center of the material by one month and bonded to the material directly. The volume of newly formed bone in the material pores reached a peak at three months, and decreased gradually after six months. The trabecular structures of AW were gradually remodeled by newly formed bone, while AW-bone bonding was maintained during bone remodeling and material absorption. AW was absorbed continuously, and at six and 12 months the residual material corresponded to about 64 and 30% of the starting material, respectively. Porous AW may therefore be useful as an absorbable bone substitute.

Silicon is, besides oxygen, the most abundant element on earth. Only two taxa use this element as a major constituent of their skeleton, namely sponges (phylum Porifera) and unicellular diatoms. Results from combined cytobiological and molecularbiological techniques suggest that, in the demosponge Suberites domuncula, silicic acid is taken up by a transporter. Incubation of cells with the fluorescent silica tracer PDMPO [2-(4-pyridyl)-5-[[4-(2-dimethylaminoethylaminocarbamoyl)methoxy]phenyl]-oxazole] showed a response to silicic acid by an increase in fluorescence; this process is temperature-dependent and can be blocked by DIDS (4,4-di-isothiocyanatostilbene-2,2-disulphonic acid). The putative NBC (Na+/HCO3-) transporter was identified, cloned and analysed. The deduced protein comprises all signatures characteristic of those molecules, and phylogenetic analysis also classifies it to the NBC transporter family. This cDNA was used to demonstrate that the expression of the gene is strongly up-regulated after treatment of cells with silicic acid. In situ hybridization demonstrated that the expression of the sponge transporter occurs in those cells that are located adjacent to the spicules (the skeletal element of the animal) or in areas in which spicule formation occurs. We conclude that this transporter is involved in silica uptake and have therefore termed it the NBCSA [Na+/HCO3-[Si(OH)4]] co-transporter.

Glass-ceramic apatite-wollastonite (A-W)/high-density polyethylene composite (AWPEX) materials have been designed to match the mechanical strength of human cortical bone and to provide favourable bioactivity, with potential use in many orthopaedic applications. To better understand AWPEX properties, the effects of surface finish and ceramic filler size and content on osteoblast-like cell attachment, proliferation, and differentiation were examined. Glass-ceramic content was tested at 30 and 50 vol% and median particle size at 4.5 and 7.7 microm. Samples were prepared as 1 x 10 x 10 mm(3) tiles with polished or rough surfaces, sterilized by gamma irradiation (2.5 Mrad), and characterized by scanning electron microscopy (SEM) and surface profilometry. Saos-2 human osteoblast-like cells were cultured on each surface at an initial concentration of 4500 cells/cm(2) for 1, 3, or 7 days. At each time point, adenosine triphosphate and alkaline phosphatase levels were measured to assess cell number and osteoblast differentiation. SEM imaging of cells on the composite surfaces showed preferential cell attachment to filler particles within the polymer matrix. Significant biochemical assay differences were found at 7 days, confirmed by ANOVA post-hoc testing using Bonferroni's correction. Overall, increased exposure of the glass-ceramic A-W phase in AWPEX through surface polishing, higher volume fraction and/or larger particle size was found to lead to an improved cell response.

The formation mechanism of apatite on the surface of wollastonite coating was examined. Plasma-sprayed wollastonite coatings were soaked in a lactic acid solution (pH=2.4) to result in the dissolution of calcium from the coating to form silanol (triple bond Si-OH) on the surface. Some calcium-drained samples were soaked in a trimethanol aminomethane solution (pH=10) for 24h to create a negatively charged surface with the functional group (triple bond Si-O(-)). These samples before and after treatment in a trimethanol aminomethane solution were immersed in simulated body fluids (SBF) to investigate the precipitation of apatite on the coating surface. The results indicate that the increase of calcium in the SBF solution is not the critical factor affecting the precipitation of apatite on the surface of the wollastonite coating and the apatite can only form on a negatively charged surface with the functional group (triple bond Si-O(-)). The mechanism of apatite formation on the wollastonite coating is proposed. After the wollastonite coatings are immersed into the SBF, calcium ions initially exchange with H(+) leading to the formation of silanol (triple bond Si-OH) on the surface of the layer and increase in the pH value at the coating-SBF interface. Consequently, a negatively charged surface with the functional group (triple bond Si-O(-)) forms on the surface. Due to the negatively charged surface, Ca(2+) ions in the SBF solution are attracted to the interface between the coating and solution, thereby increasing the ionic activity of the apatite at the interface to the extent that apatite precipitates on the coating surface.

Sintering behavior and bioactivity of diopside, CaMgSi(2)O(6), prepared by a coprecipitation process were examined for its biomedical applicability. As-prepared powder was synthesized by adding aqueous ammonia to an ethanol solution containing Ca(NO(3))(2).4H(2)O, Mg(NO(3))(2).6H(2)O, and Si(OC(2)H(5))(4) and characterized by means of TG-DTA, XRD, and TG-MS. The dried powder was X-ray amorphous and crystallized into diopside at 845.5 degrees C. The glass network formation by SiO(4) tetrahedra was almost completed below 800 degrees C. The bioactivity of the diopside prepared by sintering the compressed powder at 1100 degrees C for 2h was evaluated by immersion of the sintered body in a simulated body fluid (SBF) at 36.5 degrees C. Leaf-like apatite particles were found to be formed on the surface of the sintered body and grew with passage of soaking time. This apatite-forming behavior in the SBF is related to the dissolution of Ca(II) ions from the sintered body in the early stage of immersion. Thus, diopside prepared by the coprecipitation process using the metal alkoxide and the metal salts was found to have an apatite-forming ability.

Composites which comprise a bioactive filler and ductile polymer matrix are desirable as implant materials since both their biological and mechanical properties can be tailored for a given application. In the present study three-point bending was used to characterise biomedical materials composed of glass-ceramic apatite-wollastonite (A-W) particulate reinforced polyethylene (PE) (denoted as AWPEX). The effects of filler volume fraction, varied from 10 to 50 vol%, and average particle size, 4.4 and 6.7 microm, on the bending strength, yield strength, mode of fracture, Young's modulus and strain to failure were investigated. HAPEX, a commercially used composite of hydroxyapatite and polyethylene, with a 40 vol% filler content, was used for comparison. Increasing the filler content caused an increase in Young's modulus, yield strength and bending strength, and a decreased strain to failure. When filler particle size was increased, the Young's modulus, yield and bending strengths were found to be slightly reduced. A transition in fracture behaviour from ductile to brittle behaviour was observed in samples containing between 30 and 40 vol% filler.