A review of sodium silicate solutions: Structure, gelation, and syneresis.

Sodium silicate solutions, also known as waterglass, have been found to have remarkable utility in a variety of applications. The cumulative weight of evidence from 70 years of varied analysis indicates that silicate solutions consist of a wide range of species, from monomers through oligomers, up to colloids. Moreover, the structure and distribution of these species are greatly dependent upon many parameters, such as solute concentrations, silica to alkali ratio, pH, and temperature. The most interesting and characteristic property of silicate solutions is their ability to form silica gels. Overall, despite extensive research using different spectroscopic and scattering techniques, many questions related to sodium silicate's dynamic structure, stability, polymerization, and gelation remain difficult to answer. The multitude of simultaneous reactions which restructure the silicate species at the atomic scale in response to variation in solution and environmental parameters, makes it difficult to investigate the individual events using only experimental data. Molecular modelling provides an alternative way to study the unknown areas in the aqueous silicate and silica gel systems, generating key insights into the chemical reactions at microscopic length scales. However, sufficient sampling remains a challenge for the practical use of molecular simulation for these systems. Based on both experimental and modelling studies, this review provides a detailed discussion over the structure and speciation of sodium silicate solutions, their gelation mechanism and kinetics, and the syneresis phenomenon. The goal is not only to review the current level of understanding of sodium silicate solutions, silica gels and characterization techniques suitable for studying them, but also to identify the gaps in the literature and open up opportunities for advancing knowledge about these complex systems. We believe that the future direction of research should be toward correlating atomistic, molecular, and meso-scale level details of interactions and reactions in silicate solution and establishing a fundamental understanding of its gelation mechanism and kinetics. We believe that this knowledge could eliminate the "trial and error" approach in manufacturing, and improve structural control in the synthesis of important materials derived from these solutions, such as silica gels and zeolites.

Bone 'spackling' paste: Mechanical properties and in vitro response of a porous ceramic composite bone tissue scaffold.

Bone defects are treated with bone grafts, replacing damaged or diseased bone tissue with either natural bone or bone substitutes. This study investigates the structure, mechanical properties, and in vitro response of an all-ceramic composite designed for use as a bone 'spackling' paste: a formable synthetic bone graft paste used to repair bone defects in place, reacting with CO2 gas in ambient conditions to become a void-filling, rigid scaffold. The composite is comprised of bioactive glass frit and a soluble liquid silicate precursor combined to form an air-setting, open porous scaffold with compressive strength within the low range for trabecular bone (1.3-4.4 MPa). Characterization of scaffolds, with varying amounts of binder, was executed in accordance with established design criteria of porosity, load-bearing capacity, and bioactivity. Bioactivity was assessed via morphological, structural, and chemical changes in surface mineralization that occurred during in vitro immersion in simulated body fluid. All phases of composite specimens were observed to form calcium phosphate minerals, indicating that a chemical change occurred between the bioactive glass and sodium silicate binder phase. Ion exchange between the two phases was likely, as sodium silicate (control) was not found to produce calcium phosphate in the absence of bioactive glass. Of the selected compositions, composites with 7.4 vol% sodium silicate binder were observed to possess the highest open porosity (44 vol%), highest rate of calcium phosphate mineralization, most uniform surface mineral distribution, and largest amount of hydroxycarbonate apatite formation. The structure, mechanical properties, and in vitro response of the composite scaffolds analyzed in this research signify their potential success as bone tissue scaffolds.

Measurement of grouped intracellular solute osmotic virial coefficients.

Models of cellular osmotic behaviour depend on thermodynamic solution theories to calculate chemical potentials in the solutions inside and outside the cell. These solutions are generally thermodynamically non-ideal under cryobiological conditions. The molality-based Elliott et al. form of the multi-solute osmotic virial equation is a solution theory which has been demonstrated to provide accurate predictions in cryobiological solutions, accounting for the non-ideality of these solutions using solute-specific thermodynamic parameters called osmotic virial coefficients. However, this solution theory requires as inputs the exact concentration of every solute in the solution being modeled, which poses a problem for the cytoplasm, where such detailed information is rarely available. This problem can be overcome by using a grouped solute approach for modeling the cytoplasm, where all the non-permeating intracellular solutes are treated as a single non-permeating "grouped" intracellular solute. We have recently shown (Zielinski et al., J Physical Chemistry B, 2017) that such a grouped solute approach is theoretically valid when used with the Elliott et al. model, and Ross-Rodriguez et al. (Biopreservation and Biobanking, 2012) have previously developed a method for measuring the cell type-specific osmotic virial coefficients of the grouped intracellular solute. However, the Ross-Rodriguez et al. method suffers from a lack of precision, which-as we demonstrate in this work-can severely impact the accuracy of osmotic model predictions under certain conditions. Thus, we herein develop a novel method for measuring grouped intracellular solute osmotic virial coefficients which yields more precise values than the existing method and then apply this new method to measure these coefficients for human umbilical vein endothelial cells.

Thermal expansion of substrate may affect adhesion of Chinese hamster fibroblasts to surfaces during freezing.

Despite success in cryopreservation of cells in suspension, cryopreservation of cells in monolayers is still challenging. One of the major problems is detachment of the cells from the substrate which occurs during cryopreservation. We hypothesized that this detachment may be due to a mismatch in the coefficient of linear thermal expansion αL between glass and the frozen cell layer which manifests as residual stress and stress relaxation. This mismatch results in a difference between the thermal expansion of ice and glass as they undergo temperature changes. Rinzl plastic coverslips were selected as a possible substitute for glass because Rinzl has an αL (60 × 10-6/K) similar to that of ice (51 × 10-6/K) whereas glass has a much lower αL (5 × 10-6/K). V79-4 Chinese hamster fibroblasts were cultured on both glass and Rinzl coverslips until confluent and the area of coverage was measured before and after freezing at -9 °C. The glass coverslips showed significant loss of cells (coverage = 77.9 ±â€¯8.0%) compared with Rinzl (coverage = 97.9 ±â€¯1.4%). We concluded that Rinzl coverslips may improve cell attachment in future monolayer cryopreservation experiments.

Comparison of the contact angle of water on set elastomeric impression materials.

PURPOSE: The hydrophilicity of some elastomeric impression materials has not been fully established. The purpose of this study was to measure and compare the advancing contact angle of water on the surface of several set elastomeric impression materials. MATERIALS AND METHODS: We tested various consistencies of vinyl polysiloxane (VPS; Imprint 4) and vinyl polyether silicone (VPES; EXA'lence) with a polyether (PE; Impregum Soft) control. Impression discs (25.07 mm) were made using a metal die and ring. Deionized ultra-filtered water was placed on each disc and contact-angle measurements were made at 0, 15, 30, 45 and 60 s using a video contact angle drop shape analysis machine. The data were analyzed using repeated ANOVA and a post-hoc test with Bonferroni correction. RESULTS: VPS contact angles reached a mean of 10.1° ± 0.2° at 60 s vs. 40.7° ± 0.1° for VPES. Overall, VPS contact angles were smaller than those for VPES at all measured times. However, heavy and super quick heavy VPS had much higher contact angles at 0 s compared with other VPS consistencies. There was a significant difference in contact angles between VPS and VPES (mean difference 33.9°, p < 0.05) and between VPS and PE (mean difference 32.8°, p < 0.05) but not between VPES and PE (P = 0.196). VPS heavy and super quick heavy were significantly different from other VPS materials (p < 0.05), but not from each other (p = 1.00). CONCLUSIONS: Set VPS is more hydrophilic than VPES. Contact-angle values of VPS indicated super hydrophilicity. VPES was hydrophilic, with measurements similar to the PE control. Thus, VPS impression materials may be excellent in terms of spreading and copying wet surfaces.

Nonideal Solute Chemical Potential Equation and the Validity of the Grouped Solute Approach for Intracellular Solution Thermodynamics.

The prediction of nonideal chemical potentials in aqueous solutions is important in fields such as cryobiology, where models of water and solute transport-that is, osmotic transport-are used to help develop cryopreservation protocols and where solutions contain many varied solutes and are generally highly concentrated and thus thermodynamically nonideal. In this work, we further the development of a nonideal multisolute solution theory that has found application across a broad range of aqueous systems. This theory is based on the osmotic virial equation and does not depend on multisolute data. Specifically, we derive herein a novel solute chemical potential equation that is thermodynamically consistent with the existing model, and we establish the validity of a grouped solute model for the intracellular space. With this updated solution theory, it is now possible to model cellular osmotic behavior in nonideal solutions containing multiple permeating solutes, such as those commonly encountered by cells during cryopreservation. In addition, because we show here that for the osmotic virial equation the grouped solute approach is mathematically equivalent to treating each solute separately, multisolute solutions in other applications with fixed solute mass ratios can now be treated rigorously with such a model, even when all of the solutes cannot be enumerated.

Improving the compatibility of an Y-TZP/porcelain system using a new composite interlayer composition.

The aim of this study was to evaluate the effects of different cooling procedures and a new composite interlayer composition on the flexural strength, and veneer delamination resistance, of an all-ceramic veneered translucent Y-TZP core. One hundred twenty bar-shaped specimens of a translucent Y-TZP ceramic were prepared and divided into three groups: (1) no composite interlayer; (2) a glass interlayer (silica-based glass); (3) a mixed composite interlayer of glass and porcelain veneer material. A veneering porcelain (with and without a composite interlayer) was applied on the specimen surface and sintered. Each core-veneer group was cooled using a rapid or a slow cooling rate. All specimens were tested in four-point bending. Data were statistically analyzed using two-way ANOVA, followed by Post-Hoc tests with Bonferroni correction (α=0.05) and Weibull analysis. The group with no interlayer using the rapid cooling technique exhibited the highest flexural strength. However, with low reliability and the greatest delaminated area of porcelain under tension. A glass interlayer between porcelain veneer and zirconia core presents as a good alternative for maintaining flexural strength and porcelain veneer delamination resistance in zirconia based restorations.

Sponge-Templated Macroporous Graphene Network for Piezoelectric ZnO Nanogenerator.

We report a simple approach to fabricate zinc oxide (ZnO) nanowire based electricity generators on three-dimensional (3D) graphene networks by utilizing a commercial polyurethane (PU) sponge as a structural template. Here, a 3D network of graphene oxide is deposited from solution on the template and then is chemically reduced. Following steps of ZnO nanowire growth, polydimethylsiloxane (PDMS) backfilling and electrode lamination completes the fabrication processes. When compared to conventional generators with 2D planar geometry, the sponge template provides a 3D structure that has a potential to increase power density per unit area. The modified one-pot ZnO synthesis method allows the whole process to be inexpensive and environmentally benign. The nanogenerator yields an open circuit voltage of ∼0.5 V and short circuit current density of ∼2 µA/cm(2), while the output was found to be consistent after ∼3000 cycles. Finite element analysis of stress distribution showed that external stress is concentrated to deform ZnO nanowires by orders of magnitude compared to surrounding PU and PDMS, in agreement with our experiment. It is shown that the backfilled PDMS plays a crucial role for the stress concentration, which leads to an efficient electricity generation.

The effect of air-abrasion and heat treatment on the fracture behavior of Y-TZP.

OBJECTIVES: This study evaluated how the flexural strength and fracture behavior of a zirconia-based ceramic (Y-TZP) were affected by pre- and post-sintering mechanical and thermal treatments. METHODS: Treatments included sandblasting with different particle size and type (30µm SiO2; 50 and 110µm Al2O3) and thermal conditioning. Two hundred bar-shaped specimens of pre-sintered Y-TZP ceramic (Lava Frame, 3M) were prepared (specimen dimensions: 25mm length×4mm width×0.7mm thickness) and divided into three groups (before sintering, after sintering and after sintering with heating treatment). The before sintering group specimens were airborne-particle abraded prior to dense sintering. Specimens from the after sintering group were airborne-particle abraded after sintering. The after sintering with heating treatment group specimens were submitted to a heating procedure after airborne-particle abrasion. The controls were the specimens that were sintered and not treated with any conditioning procedures. The specimens from all experimental conditions were analyzed by SEM, CLSM and XRD. All specimens were tested in four-point bending. Data were statistically analyzed using one-way ANOVA and Post Hoc tests (α=0.05). A Weibull analysis was used to analyze the strength reliability. RESULTS: Sandblasting pre-sintered zirconia before sintering significantly decreased the flexural strength, except when the smallest blasting particles were used (30µm SiO2). Phase transformation (t-m) was observed after sandblasting and reverse transformation (m-t) was observed after heating. SIGNIFICANCE: Sandblasting with 30µm SiO2 and 50µm Al2O3 allowed lower phase transformation. However, 30mm SiO2 presented better reliability.

Comment on "Determination of the quaternary phase diagram of the water-ethylene glycol-sucrose-NaCl system and a comparison between two theoretical methods for synthetic phase diagrams" Cryobiology 61 (2010) 52-57.

Recently, measurements of a considerable portion of the phase diagram for the quaternary system water-ethylene glycol-sucrose-NaCl were published (Han et al., 2010). In that article, the data were used to evaluate the accuracy of two non-ideal multi-solute solution theories: the Elliott et al. form of the multi-solute osmotic virial equation and the Kleinhans and Mazur freezing point summation model. Based on this evaluation, it was concluded that the freezing point summation model provides more accurate predictions for the water-ethylene glycol-sucrose-NaCl system than the multi-solute osmotic virial equation. However, this analysis suffered from a number of issues, notably including the use of inconsistent solute-specific coefficients for the multi-solute osmotic virial equation. Herein, we reanalyse the data using a recently-updated and consistent set of solute-specific coefficients (Zielinski et al., 2014). Our results indicate that the two models have very similar performance, and, in fact, the multi-solute osmotic virial equation can provide more accurate predictions than the freezing point summation model depending on the concentration units used.

In vitro fracture toughness of commercial Y-TZP ceramics: a systematic review.

PURPOSE: The aim of this review was to assess research methods used to determine the fracture toughness of Y-TZP ceramics in order to systematically evaluate the accuracy of each method with regard to potential influencing factors. MATERIALS AND METHODS: Six databases were searched for studies up to April 2013. The terms "tough*," "critical stress intensity factor," "zirconi*," "yttri*," "dent*," "zirconia," "zirconium," and "stress" were searched. Titles and abstracts were screened, and literature that fulfilled the inclusion criteria was selected for a full-text reading. Test conditions with potential influence on fracture toughness were extracted from each study. RESULTS: Ten laboratory studies met the inclusion criteria. There was a significant variation in relation to test method, ambient conditions, applied/indentation load, number of specimens, and geometry and dimension of the specimen. The results were incomparable due to high variability and missing information. Therefore, 10 parameters were listed to be followed to standardize future studies. CONCLUSIONS: A wide variation in research methods affected the fracture toughness reported for Y-TZP ceramics among the selected studies; single-edge-precracked beam and chevron-notched-beam seem to be the most recommended methods to determine Y-TZP fracture toughness; the indentation methods have several limitations. CLINICAL SIGNIFICANCE: The accurate calculation of toughness values is fundamental because overestimating toughness data in a clinical situation can negatively affect the lifetime of the restoration.

Comparison of non-ideal solution theories for multi-solute solutions in cryobiology and tabulation of required coefficients.

Thermodynamic solution theories allow the prediction of chemical potentials in solutions of known composition. In cryobiology, such models are a critical component of many mathematical models that are used to simulate the biophysical processes occurring in cells and tissues during cryopreservation. A number of solution theories, both thermodynamically ideal and non-ideal, have been proposed for use with cryobiological solutions. In this work, we have evaluated two non-ideal solution theories for predicting water chemical potential (i.e. osmolality) in multi-solute solutions relevant to cryobiology: the Elliott et al. form of the multi-solute osmotic virial equation, and the Kleinhans and Mazur freezing point summation model. These two solution theories require fitting to only single-solute data, although they can make predictions in multi-solute solutions. The predictions of these non-ideal solution theories were compared to predictions made using ideal dilute assumptions and to available literature multi-solute experimental osmometric data. A single, consistent set of literature single-solute solution data was used to fit for the required solute-specific coefficients for each of the non-ideal models. Our results indicate that the two non-ideal solution theories have similar overall performance, and both give more accurate predictions than ideal models. These results can be used to select between the non-ideal models for a specific multi-solute solution, and the updated coefficients provided in this work can be used to make the desired predictions.

In vitro wear behavior of zirconia opposing enamel: a systematic review.

PURPOSE: The aim of this systematic review was to assess enamel wear on teeth opposing zirconia restorations and to evaluate factors related to the wear of natural teeth opposing zirconia restorations. MATERIALS AND METHODS: Five electronic databases were searched through May 2013 without limitations. The terms "antagonist*," "enamel," "wear," and "zirconi*" were used. Titles and abstracts were initially screened, and those that fulfilled the inclusion criteria were selected for a full-text assessment. Studies that evaluated only the material wear were not included. RESULTS: The database search strategy retrieved 142 potentially eligible studies. After the duplicate studies were removed, 62 studies were obtained. Titles and abstracts that fulfilled the inclusion criteria were selected for a full-text assessment (25). Seven laboratory studies met the inclusion criteria. In addition, reference lists from the finally selected studies were also screened. CONCLUSIONS: There was a large variation in relation to wear test method quantification, applied force, lateral movement, number and frequency of cycles, number of specimens, and enamel specimen preparation. In all studies, enamel wear rates were lower against polished zirconia. Differences in the test methods did not allow for comparisons of wear rates among the studies. CLINICAL SIGNIFICANCE: Polishing the surface is recommended for a full-contour zirconia restoration because polished zirconia presents favorable wear behavior opposing natural teeth.

Bioactive glass 45S5 powders: effect of synthesis route and resultant surface chemistry and crystallinity on protein adsorption from human plasma.

Despite its medical applications, the mechanisms responsible for the osseointegration of bioactive glass (45S5) have yet to be fully understood. Evidence suggests that the strongest predictor for osseointegration of bioactive glasses, and ceramics, with bone tissue as the formation of an apatitic calcium phosphate layer atop the implanted material, with osteoblasts being the main mediator for new bone formation. Most have tried to understand the formation of this apatitic calcium phosphate layer, and other bioresponses between the host and bioactive glass 45S5 using Simulated Body Fluid; a solution containing ion concentrations similar to that found in human plasma without the presence of proteins. However, it is likely that cell attachment is probably largely mediated via the adsorbed protein layer. Plasma protein adsorption at the tissue bioactive glass interface has been largely overlooked. Herein, we compare crystalline and amorphous bioactive glass 45S5, in both melt-derived as well as sol-gel forms. Thus, allowing for a detailed understanding of both the role of crystallinity and powder morphology on surface ions, and plasma protein adsorption. It was found that sol-gel 45S5 powders, regardless of crystallinity, adsorbed 3-5 times as much protein as the crystalline melt-derived counterpart, as well as a greater variety of plasma proteins. The devitrification of melt-cast 45S5 resulted in only small differences in the amount and variety of the adsorbed proteome. Surface properties, and not material crystallinity, play a role in directing protein adsorption phenomena for bioactive glasses given the differences found between crystalline melt-cast 45S5 and sol-gel derived 45S5.

Wettability of biomimetic thermally grown aluminum oxide coatings.

In this paper, wettability behavior of a rough but intrinsically hydrophilic oxide ceramic, formed via simple thermal oxidation of a commercial metallic alloy in laboratory air, has been analyzed. Drop shape analysis (DSA) revealed static water contact angles for the rough ceramic surfaces up to 128° (greater than for Teflon™). We propose the high apparent contact angles to be a result of surface roughening via the morphological changes of the oxide scale with oxidation conditions. The surface morphological changes occurring during the growth of the oxide film resulted in the formation of vertical platelets that ably shifted the wetting behavior from a Wenzel to an unstable Cassie-Baxter state. The platelet morphology of the ceramic resembles the structure of epicuticular waxes on certain species of superhydrophobic leaves. Moreover, surface textures for very short oxidation times were also found to increase hydrophilicity in the scale and reduce the contact angle by imparting a Wenzel state. Various characterization techniques (XRD, XPS, and SEM) were performed in order to detect the crystallographic phases in the scales, analyze carbon content and determine the morphology of the oxide layer. Morphological features of the oxide platelets were quantified and platelet width, spacing and height were found to correlate well with the apparent contact angle trend as a function of oxidation time.

In vitro bioactivity of 45S5 bioactive glass as a function of indentation load.

Many fabrication routes used to process biomaterials result in residual stresses. The presence of residual stress can cause failure or even change the dissolution rates of many materials, in particular biomaterials that are designed to be resorbed. Stored strain energy can add extra thermodynamic driving force for dissolution and result in varied dissolution rates depending on the sign of the stress. This work describes in vitro testing in phosphate buffer solution after micro-indenting the surface of bioactive glass 45S5 discs with varying loads. Indentation and fracture characteristics of the bioactive glass are discussed. Local dissolution and morphology of mineral deposits at the surface were analyzed by scanning electron microscopy to determine the effects of local residual stresses on bioactivity. It was found that the compressive stress field surrounding indents (above a threshold indentation load) slowed the dissolution of the bioactive glass significantly.