Structure and dissolution of silicophosphate glass.

P2O5-SiO2-Na2O-CaO glasses are promising therapeutic ion-releasing materials. Herein, we investigated the state of silicon (Si) in P2O5-SiO2-Na2O-CaO glass using a model with a composition of 55.0P2O5-21.3SiO2-23.7Na2O (mol%), incorporating a six-fold-coordinated silicon structure ([6]Si). The model was constructed using a classical molecular dynamics method and relaxed using the first-principles method. Further, we experimentally prepared glasses, substituting Na2O for CaO, to investigate the dissolution of glass with varying [6]Si and PO4 tetrahedra (Q P n ) distributions (n = number of bridging oxygens (BOs) to neighboring tetrahedra). [6]Si in the glass model preferentially coordinated with Q P 3. When Si was surrounded by phosphate groups, phosphorus (P) induced the formation of [6]Si by elongating the Si-O distance, and [6]Si acted like a glass network former (NWF). Na+ coordinated with [6]Si-O-P bonds via electrostatic interactions with BO. 31P and 29Si magic-angle-spinning-nuclear-magnetic-resonance spectra of three experimental glass samples with the compositions of 55.0P2O5-21.3SiO2-xCaO-(23.7 - x)Na2O (mol%, x = 0, 12.4, and 23.7) showed that Q P 3 and [6]Si increased with increasing Na2O. When each glass powder was immersed in a tris-HCl buffer solution at 37 °C, the dissolution of NWF ions and network modifier (NWM) ions increased almost monotonically with time for all samples, indicating that the solubility of the samples was suppressed by the coexistence of CaO and Na2O, attributed to the delocalization of the electron distribution of P in the [6]Si-coordinated Q P 3 units compared to that in the P- or [4]Si-coordinated Q P 3 units, which reduces hydrolysis.

Core-shell fibremats comprising a poly(AM/DAAM)/ADH nanofibre core and nylon6 shell layer are an attractive immobilization platform for constructing immobilised enzymes.

Core-shell fibremats, comprising poly(acrylamide)-co-poly(diacetone-acrylamide)/adipic dihydrazide [poly(AM/DAAM)/ADH] core-nanofibres and hydrophobic polymer shell layers, are a new class of platforms for constructing various immobilised enzymes. In this study, to elucidate the impacts of the shell-layer material on fibremat properties and enzymatic activities, we synthesised core-shell fibremats with shell layers comprising nylon6 or acetyl cellulose (AcCel) instead of poly(ε-caprolactone) (PCL), as in our previous study. Transmission and scanning electron microscopy images revealed that the lactase-encapsulated poly(AM/DAAM)/ADH-nylon6 and -AcCel fibremats were both constructed like the poly(AM/DAAM)/ADH-PCL one. Leakage measurements of the beforehand loaded molecules inside the core-nanofibres revealed that both fibremats exhibited efficient permeability for low-molecular-weight molecules and stable retention of enzyme molecules inside the core-nanofibres. Meanwhile, the fibremats' mechanical properties considerably depended on the choice of shell-layer material. The thermal analyses of the lactase-encapsulated fibremats revealed residual water inside the core nanofibres. The core-shell fibremats fabricated with a nylon6 or PCL shell exhibited excellent enzymatic activities (102 and 114%, respectively, compared to that of free lactase), superior to that of the same amount of free enzyme in a buffer. Furthermore, both core-shell fibremats retained over 95% of their initial enzymatic activities, even after they were re-used 10 times.

Silver-doped calcium silicate sol-gel glasses with a cotton-wool-like structure for wound healing.

Skin has excellent capacity to regenerate, however, in the event of a large injury or burn skin grafts are required to aid wound healing. The regenerative capacity further declines with increasing age and can be further exacerbated with bacterial infection leading to a chronic wound. Engineered skin substitutes can be used to provide a temporary template for the damaged tissue, to prevent/combat bacterial infection and promote healing. In this study, the sol-gel process and electrospinning were combined to fabricate 3D cotton-wool-like sol-gel bioactive glass fibers that mimic the fibrous architecture of skin extracellular matrix (ECM) and deliver metal ions for antibacterial (silver) and therapeutic (calcium and silica species) actions for successful healing of wounds. This study investigated the effects of synthesis and process parameters, in particular sintering temperature on the fiber morphology, the incorporation and distribution of silver and the degradation rate of fibers. Silver nitrate was found to decompose into silver nanoparticles within the glass fibers upon calcination. Furthermore, with increasing calcination temperature the nanoparticles increased in size from 3 nm at 600 °C to ~25 nm at 800 °C. The antibacterial ability of the Ag-doped glass fibers decreased as a function of the glass calcination temperature. The degradation products from the Ag-doped 3D non-woven sol-gel glass fibers were also found to promote fibroblast proliferation thus demonstrating their potential for use in skin regeneration.

Exfoliation Resistance, Microstructure, and Oxide Formation Mechanisms of the White Oxide Layer on CP Ti and Ti-Nb-Ta-Zr Alloys.

We found that specific biomedical Ti and its alloys, such as CP Ti, Ti-29Nb-13Ta-4.6Zr, and Ti-36Nb-2Ta-3Zr-0.3O, form a bright white oxide layer after a particular oxidation heat treatment. In this paper, the interfacial microstructure of the oxide layer on Ti-29Nb-13Ta-4.6Zr and the exfoliation resistance of commercially pure (CP) Ti, Ti-29Nb-13Ta-4.6Zr, and Ti-36Nb-2Ta-3Zr-0.3O were investigated. The alloys investigated were oxidized at 1273 or 1323 K for 0.3-3.6 ks in an air furnace. The exfoliation stress of the oxide layer was high in Ti-29Nb-13Ta-4.6Zr and Ti-36Nb-2Ta-3Zr-0.3O, and the maximum exfoliation stress was as high as 70 MPa, which is almost the same as the stress exhibited by epoxy adhesives, whereas the exfoliation stress of the oxide layer on CP Ti was less than 7 MPa, regardless of duration time. The nanoindentation hardness and frictional coefficients of the oxide layer on Ti-29Nb-13Ta-4.6Zr suggested that the oxide layer was hard and robust enough for artificial tooth coating. The cross-sectional transmission electron microscopic observations of the microstructure of oxidized Ti-29Nb-13Ta-4.6Zr revealed that a continuous oxide layer formed on the surface of the alloys. The Au marker method revealed that both in- and out-diffusion occur during oxidation in Ti-29Nb-13Ta-4.6Zr and Ti-36Nb-2Ta-3Zr-0.3O, whereas only out-diffusion governs oxidation in CP Ti. The obtained results indicate that the high exfoliation resistance of the oxide layer on Ti-29Nb-13Ta-4.6Zr and Ti-36Nb-2Ta-3Zr-0.3O are attributed to their dense microstructures composing of fine particles, and a composition-graded interfacial microstructure. On the basis of the results of our microstructural observations, the oxide formation mechanism of the Ti-Nb-Ta-Zr alloy is discussed.

Diffusion of protons and sodium ions in silicophosphate glasses: insight based on first-principles molecular dynamic simulations.

We propose a microscopic diffusion mechanism of protons and Na+ ions in phosphate glasses using first-principles molecular dynamic simulations. Protons hop and are chemisorbed onto non-bridging oxygen (NBO) of nearby PO4 tetrahedra through hydrogen bonds. The subsequent behavior depends on the morphology of the PO4 tetrahedra (QnP values). When a proton is adsorbed onto the NBO of a Q3P unit, it is desorbed on a short time scale of within 10 fs and re-adsorbed onto the NBO that was previously adsorbed. However, when a proton is adsorbed onto the NBO of a Q2P unit, another proton coordinated before adsorption is desorbed in a chain, resulting in the diffusion of protons. When a Na+ ion is present in the vicinity, the adsorption of a proton onto a Q2P unit leads to a decrease in the electrostatic interaction between Na+ and O- ions and induces the diffusion of Na+ ions. We conclude that the difference in the morphology of PO4 tetrahedra greatly affects the diffusion of protons and Na+ ions.

Regulating size of silver nanoparticles on calcium carbonate via ultrasonic spray for effective antibacterial efficacy and sustained release.

Calcium carbonate is used as bone-filling material due to its good biocompatibility, bioactivity, and bioabsorbability, but the prevalence of infectious complications associated with calcium carbonate has created a persisting challenge in the treatment of bone defect. Therefore, this greatly necessitate the need to endow calcium carbonate with antibacterial properties. In this study, calcium carbonate powders loaded with silver nanoparticles (Ag-CaCO3) were prepared in attempt to serve as a novel antibacterial inorganic filler material. This objective was achieved using ultrasonic spray-pyrolysis (USSP) route to produce Ag-CaCO3 with 1, 5 and 10 mol% silver. The size of silver nanoparticles on CaCO3 microspheres could be regulated by adjusting silver concentration to facilitate effective release of Ag+ ions. This was demonstrated in Ag-CaCO3 (1), where the lowest silver content at 1 mol% achieved the highest Ag+ ions release over 28 days. This in turn gave rise to effective antibacterial efficiency against Staphylococcus aureus and Escherichia coli. Furthermore, CaCO3 (1) could also support osteoblast-like cells (MG-63) at a cell viability of 80%. Overall, this work extends the capabilities in employing USSP to produce inorganic filler materials with sustained antibacterial properties, bringing one step closer to the development of antibacterial products.

Structures and Dissolution Behaviors of Quaternary CaO-SrO-P2O5-TiO2 Glasses.

Calcium phosphate glasses have a high potential for use as biomaterials because their composition is similar to that of the mineral phase of bone. Phosphate glasses can dissolve completely in aqueous solution and can contain various elements owing to their acidity. Thus, the glass can be a candidate for therapeutic ion carriers. Recently, we focused on the effect of strontium ions for bone formation, which exhibited dual effects of stimulating bone formation and inhibiting bone resorption. However, large amounts of strontium ions may induce a cytotoxic effect, and there is a need to control their releasing amount. This work reports fundamental data for designing quaternary CaO-SrO-P2O5-TiO2 glasses with pyro- and meta-phosphate compositions to control strontium ion-releasing behavior. The glasses were prepared by substituting CaO by SrO using the melt-quenching method. The SrO/CaO mixed composition exhibited a mixed cation effect on the glassification degree and ion-releasing behavior, which showed non-linear properties with mixed cation compositions of the glasses. Sr2+ ions have smaller field strength than Ca2+ ions, and the glass network structure may be weakened by the substitution of CaO by SrO. However, glassification degree and chemical durability of pyro- and meta-phosphate glasses increased with substituted all CaO by SrO. This is because titanium groups in the glasses are closely related to their glass network structure by SrO substitution. The P-O-Ti bonds in pyrophosphate glass series and TiO4 tetrahedra in metaphosphate glass series increased with substitution by SrO. The titanium groups in the glasses were crosslink and/or coordinate phosphate groups to improve glassification degree and chemical durability. Sr2+ ion releasing amount of pyrophosphate glasses with >83% SrO substitution was larger than 0.1 mM at day seven, an amount that reported enhanced bone formation by stimulation of osteogenic markers.

Unravelling the dissolution mechanism of polyphosphate glasses by 31P NMR spectroscopy: ligand competition and reactivity of intermediate complexes.

Phosphate glass dissolution can be tailored via compositional and subsequent structural changes, which is of interest for biomedical applications such as therapeutic ion delivery. Here, solid-state 31P nuclear magnetic resonance characterisation of 45P2O5-xCaO - (55 -x)Na2O glasses was correlated with dissolution studies using time-dependent liquid 31P NMR spectroscopy and quantitative chemical analysis. Glasses dissolved congruently in aqueous media, and the first dissolution stage was the hydration of phosphate chains. In deionised water and Tris buffer (pH0 7.4 or 7.9), trimetaphosphate rings and orthophosphates were the predominant species in solution, indicating relatively fast degradation. By contrast, long phosphate chains were identified in EDTA (pH0 10.0). Besides pH differences, coordination of phosphate species by metal cations appears to play a catalytic role in the hydrolysis mechanism via turning phosphorus atoms into suitable electrophiles for the subsequent nucleophilic attack by water. Hydrolysis rates were proportional to phosphate complex stability, with stronger complexes for chains than for rings. A competition between solvent and phosphate species for the metal ion occurred in the order EDTA > Tris > deionised water.

Development of orthophosphosilicate glass/poly(lactic acid) composite anisotropic scaffolds for simultaneous reconstruction of bone quality and quantity.

Reconstruction of organ-specific architecture is necessary to recover the original organ function. The anisotropic structure of bone tissue is strongly related to the collagen fibril alignment and bone apatite crystal direction. Bone regeneration indicates following two main process; first, restoration of bone mineral density (BMD; bone quantity), and second, restoring bone apatite c-axis orientation (bone quality). In addition to BMD, bone quality is the most important factor among bone mechanical properties. Recovery of the original bone function requires development of novel scaffolds with simultaneous reconstruction of bone quality and quantity. Herein, novel orthophosphosilicate glass (PSG)/poly(lactic acid) composite anisotropic scaffolds were developed to control cell alignment and enhance bone formation, which are important for the simultaneous reconstruction of bone quality and quantity. The strategy to control cell alignment and bone formation involved designing anisotropic scaffolds in combination with the release of therapeutic ions by PSGs. The morphology of fibrous scaffolds containing PSGs was quantitatively designed using electrospinning. This successfully modulated cell alignment and subsequent bone apatite c-axis orientation along the fiber-oriented direction. The released silicate and Mg2+ ions from PSGs in scaffolds improved cell adhesion, proliferation, and calcification. To best of our knowledge, this is the first report demonstrating that the anisotropic scaffolds containing bioactive glasses regenerate bone tissues with simultaneous reconstruction of bone quality and quantity via stimulating osteoblasts by inorganic ions and designing morphology of scaffolds.

First-Principles Density Functional Theory Calculations for Formic Acid Adsorption onto Hydro-Garnet Compounds.

Efficient and large-scale removal of humic acid (HA) from aqueous environments is required since HA causes human health and esthetic issues. Hydro-garnet compounds, Ca3Al2(SiO4)3-x (OH)4x , have recently been suggested as HA adsorbents not only due to their superior adsorption behaviors but also because they are ubiquitous element-derived compounds. In this study, the adsorption behavior of formic acid to hydro-garnets was investigated by means of first-principles density functional theory (DFT) computations. Formic acid was chosen owing to its reasonable computational cost and inclusion of carboxylic acid as HA. Comparisons of adsorption energies for formic acid among various compounds (including platinum and kaolinite) indicate that hydro-garnet compounds are promising due to their lower (more stable) adsorption energies. Also, the optimization of composition x enables selective adsorption of formic acid against solvent water molecules. Relationships between surface electronic/atomistic structures and adsorption properties are discussed.

Water wettability dependence on surface structure of a snail shell.

There are many reports on the special wettability of hierarchical surface structures in nature. Snail shells with three types of roughness of 10, 100, and 500 µm have a unique wetting behavior. In the present study, we investigate the influence of the surface structure on the water wettability using snail shells with different surface roughness. The wettability of a water droplet on the samples was evaluated. The three types of roughness on the surface structure of snail shell had higher water droplet spreading properties than the two types of roughness 500 µm and, 10 or 100 µm. Surface structures of snail shells with different surface roughness were simulated using epoxy resins to clarify the mechanism for the dynamics wetting behavior. The contact angle with a hydrophobic nature, of the epoxy resin with the three types of roughness decreased with increasing time, indicating a hydrophilic nature. The base diameter of the epoxy resins with the three types of roughness increased with increasing time. This was larger than that for a flat epoxy resin with hydrophilicity. Other epoxy resins with shell texture containing 100 and 500 or 10 and 500 µm roughness showed almost no change in the contact angle and diameter of the droplet base. The three types of roughness on the sample surface contributed to development of the water droplet spreading. The 10 µm roughness of the sample surface influenced the dynamic contact angles.

Heat transfer properties of Morpho butterfly wings and the dependence of these properties on the wing surface structure.

The heat transfer properties of a material strongly rely on its surface structure. The wings of the Morpho butterfly have a unique surface structure with features of order and disorder. In this work, the surface temperature and radiative heat flux of Morpho butterfly wings with structural colour when a ceramic heater attached to the opposite surface of the wings was heated to 250 °C were evaluated in terms of their heat transfer properties. Morpho menelaus butterfly (MM) wings and Cithaerias (CE) wings with no periodic structure on their surface, were used as samples. The MM wings had higher surface temperature and radiative heat flux than the CE wings, which is the first report of heat transfer properties of the wings. The surface structure of the MM wings was changed by heat treatment in order to investigate the effect of the surface structural change on their heat transfer properties. The treatment changed the colour of the wings to red and brown, distorting the periodic structure. The radiative heat flux increased due to the change in the structure on their surface. XPS spectra revealed that the treatment leads to a slight change in the chemical structure of the wings. The spectral analyses results showed there was no obvious change in the mid-infrared absorbance. The heat radiative properties of the MM wings were strongly influenced by the surface structural changes due to the heat treatment.

Electrospinning 3D bioactive glasses for wound healing.

An electrospinning technique was used to produce three-dimensional (3D) bioactive glass fibrous scaffolds, in the SiO2-CaO sol-gel system, for wound healing applications. Previously, it was thought that 3D cotton wool-like structures could only be produced from sol-gel when the sol contained calcium nitrate, implying that the Ca2+ and its electronic charge had a significant effect on the structure produced. Here, fibres with a 3D appearance were also electrospun from compositions containing only silica. A polymer binding agent was added to inorganic sol-gel solutions, enabling electrospinning prior to bioactive glass network formation and the polymer was removed by calcination. While the addition of Ca2+ contributes to the 3D morphology, here we show that other factors, such as relative humidity, play an important role in producing the 3D cotton-wool-like macrostructure of the fibres. A human dermal fibroblast cell line (CD-18CO) was exposed to dissolution products of the samples. Cell proliferation and metabolic activity tests were carried out and a VEGF ELISA showed a significant increase in VEGF production in cells exposed to the bioactive glass samples compared to control in DMEM. A novel SiO2-CaO nanofibrous scaffold was created that showed tailorable physical and dissolution properties, the control and composition of these release products are important for directing desirable wound healing interactions.

Tuning of ion-release capability from bio-ceramic-polymer composites for enhancing cellular activity.

In our previous study, we investigated the synergetic effects of inorganic ions, such as silicate, Mg2+ and Ca2+ ions on the osteoblast-like cell behaviour. Mg2+ ions play an important role in cell adhesion. In the present study, we designed a new composite that releases a high concentration of Mg2+ ions during the early stage of the bone-forming process, and silicate and Ca2+ ions continuously throughout this process. Here, 40SiO2-40MgO-20Na2O glass (G) with high solubility and vaterite-based calcium carbonate (V) were selected as the source of silicate and Mg2+ and Ca2+ ions, respectively. These particles were mixed with poly(lactic-co-glycolic acid) (PLGA) using a kneading method at 110°C to prepare the composite (G-V/PLGA, G/V/PLGA = 4/56/40 (in weight ratio)). Most of the Mg2+ ions were released within 3 days of immersion at an important stage for cell adhesion, and silicate and Ca2+ ions were released continuously at rates of 70-80 and 180 ppm d-1, respectively, throughout the experiment (until day 7). Mouse-derived osteoblast-like MC3T3-E1 proliferated more vigorously on G-V/PLGA in comparison with V-containing PLGA without G particles; it is possible to control the ion-release behaviour by incorporating a small amount of glass particles.

Enhancing Wettability of Radio Frequency Magnetron-Sputtered Glass Films by Exploiting Structural Defects.

Silica-based films were prepared by radio-frequency magnetron sputtering to investigate the influence of the chemical compositions of the target glass on the structure and wettability of the sputtered films. The sputtered films were more hydrophilic than the untreated glasses. Oxygen defects formed in the silica units of the sputtered films and resulted in the formation of hydroxyl groups, regardless of the chemical composition of the glass. The three-phase contact lines were distorted by chemical heterogeneities on the surfaces of the sputtered films.

Wettability and dynamics of water droplet on a snail shell.

HYPOTHESIS: There are many natural surfaces with special wettabilities. Snail shells have unique rough structures, which indicates a specific wettability. In this study, the surface of a snail shell was simulated using epoxy resins, and water droplet dynamics on original and simulated snail shells were investigated to understand its special wettability. EXPERIMENTS: The shell of the Euhadra sandai species of snails was used. The surface structure of the snail shell was simulated using epoxy resins. The surface of this EP resin was treated with UV-O3 for different periods of time. Wettabilities and dynamics of water droplet on the samples were characterized. FINDINGS: The surface of the snail shell with a water contact angle of approximately 85° caused the droplet to spread, which is the first report of water droplet dynamics on the shell surface. The behavior of a water droplet on the shell transformed from the Cassie state into the Wenzel state. Changes in the contact angle and diameter of the droplet base on the snail shell were larger than those on the epoxy resins. The surface roughness and chemical heterogeneity of the snail shell led to distortion of the three-phase contact line and enhancement of the spreading of the water droplet.

Correction to: 'Adsorption behaviour of hydrogarnet for humic acid'.

[This corrects the article DOI: 10.1098/rsos.172023.].

Combinatorial effects of inorganic ions on adhesion and proliferation of osteoblast-like cells.

Combinatorial effects of three ions, namely silicate (Si), calcium (Ca), and magnesium (Mg) ions, on the adhesion and proliferation of MC3T3-E1 mouse osteoblast-like cells were evaluated. The cells were cultured in single-, dual-, or triple-ion-conditioned culture media with systematically changed ion concentrations. The ranges of Si, Ca, and Mg ion concentrations were set as 10-70, 80-400, and 25-500 ppm, respectively. The numbers of adherent live cells were measured after culturing for 3 h and for 1, 3, and 5 days to examine cell adhesion and proliferation, respectively. Mg ions predominantly enhanced cell adhesion in both the dual-ion (xSi-zMg and yCa-zMg) and triple-ion (xSi-yCa-zMg) systems but had no effect when they acted individually in the single-ion system. Conversely, Si ions predominantly enhanced cell proliferation in most single- and triple-ion-conditioned media. Evaluation of the combinatorial effects of the three ions on cell adhesion and proliferation revealed that the dual- and triple-ion-conditioned media mainly conferred synergistic effects on adhesion but antagonistic effects on proliferation. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1042-1051, 2019.

Development of bifunctional oriented bioactive glass/poly(lactic acid) composite scaffolds to control osteoblast alignment and proliferation.

During the bone regeneration process, the anisotropic microstructure of bone tissue (bone quality) recovers much later than bone mass (bone quantity), resulting in severe mechanical dysfunction in the bone. Hence, restoration of bone microstructure in parallel with bone mass is necessary for ideal bone tissue regeneration; for this, development of advanced bifunctional biomaterials, which control both the quality and quantity in regenerated bone, is required. We developed novel oriented bioactive glass/poly(lactic acid) composite scaffolds by introducing an effective methodology for controlling cell alignment and proliferation, which play important roles for achieving bone anisotropy and bone mass, respectively. Our strategy is to manipulate the cell alignment and proliferation by the morphological control of the scaffolds in combination with controlled ion release from bioactive glasses. We quantitatively controlled the morphology of fibermats containing bioactive glasses by electrospinning, which successfully induced cell alignment along the fibermats. Also, the substitution of CaO in Bioglass®(45S5) with MgO and SrO improved osteoblast proliferation, indicating that dissolved Mg2+ and Sr2+ ions promoted cell adhesion and proliferation. Our results indicate that the fibermats developed in this work are candidates for the scaffolds to bone tissue regeneration that enable recovery of both bone quality and bone quantity. © 2019 The Authors. journal Of Biomedical Materials Research Part A Published By Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1031-1041, 2019.

Adsorption behaviour of hydrogarnet for humic acid.

Discharge of humic acid (HA) in aqueous environments is a key health and aesthetic issue. The present work investigates the use of hydrogarnet as a novel adsorbent for HA. Hydrogarnet was hydrothermally synthesized with different solvents to control the chemical composition. Hydrogarnet with three types of chemical compositions had better adsorption properties for HA than hydrogarnet with a single chemical composition. Controlling the chemical composition of hydrogarnet increased the number of hydroxyl groups and the overall binding energy of the system, leading to changes in the zeta potential. The enhancement of these adsorption properties is related to the increased numbers of hydroxyl groups on the surface and their diverse binding energies.