Resorbable, porous glass scaffolds by a salt sintering process

Resorbable, porous glass scaffolds for tissue engineering were prepared by sintering borate glass with salt (sodium chloride). Subsequently, the sodium chloride was dissolved in water resulting in a highly porous material. By modifying the process parameters including salt particle size, salt volume percentage, sintering temperature and sintering time, sintered matrix structures were optimized. Analysis of the structure data indicates that the 50 vol% glass—50 vol% salt with particle sizes from 250–315 μm sintered at a temperature of 520°C for 10 min resulted in an optimum structure with 76.5% porosity and 29.3 N/cm² compressive strength. The process of HAP formation on the scaffolds in 0.25 M K₂HPO₄ solutions with pH 9.0 at 37°C was evaluated. The structural changes were analyzed by X-ray diffraction and scanning electron microscopy. An amorphous phosphate was formed on the surface of the scaffolds within 1d and crystalline hydroxyapatite (HA) within 10d.     

Fluoride removal performance of glass derived hydroxyapatite

A novel sodium calcium borate glass derived hydroxyapatite (G-HAP) with different ranges of particle size was prepared by immersion sodium calcium borate glass in 0.1 M K₂HPO₄ solution by the ratio of 50 g L⁻¹ for 7 days. The unique advantage of G-HAP for the adsorption of fluoride ions in solutions was studied. The effects of size and quantity of particles, pH value and adsorption time on adsorption performance were investigated. The maximum adsorption capacity was 17.34 mg g⁻¹ if 5 g L⁻¹, <100 μm G-HAP was added to a solution with an initial pH value of 6.72 and the adsorption time was 12 h. The results showed that the micro-G-HAP could immobilize F⁻ in solution more effectively than commercial nano-HAP, which makes potential application of the G-HAP in removing the fluoride ions from wastewater. The adsorption kinetics and isotherms for F⁻ could be well fitted by a second order kinetic model and Freundlich isotherm model respectively, which could be used to describe the adsorption behavior. The mechanism of G-HAP in immobilizing F⁻ from aqueous solutions was investigated by the X-ray diffraction (XRD), infrared spectra (IR) and scanning electron microscopy (SEM).     

Electrochemical fabrication of complex copper oxide nanoarchitectures via copper anodization in aqueous and non-aqueous electrolytes

Described is the synthesis of various copper oxide nanostructured thin films by anodization of Cu foil in aqueous and ethylene glycol electrolytes containing hydroxide, chloride and/or fluoride ions at room temperature. The nanostructure topology was found to depend on the pH of the anodization electrolyte, KOH concentration, applied voltage and the presence of chloride and fluoride ions. Our results demonstrate the opportunity to grow complex copper oxide nanostructured films possessing sub-micron thick layers by a simple and straightforward electrochemical route. Although no film was observed on the Cu surface when the anodization was carried out at 10 V in KOH solutions with pH ≤ 10, various nanoarchitectures were formed upon increasing the electrolyte pH in the presence of chloride ions. Replacing chloride ions with fluoride ions resulted in the formation of highly porous nanoarchitectures. A simple mechanism for the formation of such porous structures is proposed. Anodizing in ethylene glycol-based electrolytes resulted in the formation of leaf-like nanoarchitectures up to 500 nm in thickness. XPS analysis was performed to study the composition of the formed nanoarchitectures. Vacuum annealing of the material at 280 °C resulted in the formation of porous Cu₂O nanoarchitectures.     

Processing of bovine hydroxyapatite (HA) powders and synthesis of calcium phosphate silicate glass ceramics using DC thermal plasma torch

In the present work, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) was prepared from bovine bones with calcination method (up to 850 °C).The calcinated hydroxyapatite was powdered (30-40 μm) using a mechanical grinder; the particles were highly irregular in shape with sharp edges, angular, rounded, circular, dentric, porous and fragmented morphologies. The irregular shaped calcinated hydroxyapatite was plasma processed to produce spherical powders for thermal spray coating applications. More over; calcium phosphate silicate glass ceramics was produced by plasma melting of ball milled hydroxyapatite-borosilicate glass (50 wt.%) mixture. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and energy dispersive X-ray analysis (EDX). The morphology was determined using scanning electron (SEM) and optical microscopy (OM). The microhardness, density and porosity measurements for the synthesized samples were made.     

Innovative fabrication of ZrO2-HAp-TiO2 nano/micro-structured composites through MAO/EPD combined method

ZrO₂-HAp-TiO₂ porous layers were fabricated by micro arc oxidation/electrophoretic deposition hybrid processes in the electrolytes consisted of β-glycerophosphate, calcium acetate, sodium phosphate, and yttria-stabilized zirconia within short times and only in one step. The layers had a porous structure with a pores size of 50-750 nm. They contained anatase, hydroxyapatite, monoclinic ZrO₂, tetragonal ZrO₂, and some minor phases with a varying fraction depending on time. Increasing the time, the tetragonal ZrO₂ transformed to monoclinic ZrO₂. Moreover, hydroxyapatite relative content decreased with time. The nanosized zirconia particles (d = 20-40 nm) were dispersed on the surface and in the layers depth.     

Synthesis, characterization and mechanical properties of nano alumina particulate reinforced magnesium based bulk metallic glass composites

Mg₆₇Zn₂₈Ca₅ bulk metallic glass reinforced with 0.66-1.5 vol% of nano alumina particulates were successfully synthesized using disintegrated melt deposition technique. Microstructural characterization revealed reasonably uniform distribution of alumina particulates in a metallic glass matrix. The reinforced particles have no significant effect on the glass forming ability of the monolithic glass matrix. Mechanical characterization under compressive loading showed improved micro hardness, fracture strength and failure strain with increase in nano alumina particulate reinforcement. The best combination of strength, hardness and ductility was observed in Mg/1.5 vol% alumina composite with fracture strength of 780 MPa and 2.6% failure strain.     

Preparation of hollow hydroxyapatite microspheres by the conversion of borate glass at near room temperature

Hollow hydroxyapatite microspheres, consisting of a hollow core and a porous shell, were prepared by converting Li₂O-CaO-B₂O₃ glass microspheres in dilute phosphate solution at 37 °C. The results confirmed that Li₂O-CaO-B₂O₃ glass was transformed to hydroxyapatite without changing the external shape and dimension of the original glass object. Scanning electron microscopy images showed the shell wall of the microsphere was built from hydroxyapatite particles, and these particles spontaneously align with one another to form a porous sphere with an interior cavity. Increase in phosphate concentration resulted in an increase in the reaction rate, which in turn had an effect on shell wall structure of the hollow hydroxyapatite microsphere. For the Li₂O-CaO-B₂O₃ glass microspheres reacted in low-concentration K₂HPO₄ solution, lower reaction rate and a multilayered microstructure were observed. On the other hand, the glass microspheres reacted in higher phosphate solution converted more rapidly and produced a single hydroxyapatite layer. Furthermore, the mechanism of forming hydroxyapatite hollow microsphere was described.     

In vitro biocompatibility study of calcium phosphate glass ceramic scaffolds with different trace element doping

Porous calcium phosphate based glass ceramics (CaO-P₂O₅-Na₂O) containing different trace elements (2.0 mol% Mg, Sr and Zn respectively) were prepared by coating polyurethane foams with sol-gel derived glass slurry. After heat treatment at suitable temperatures, main phase catena hexaphosphate (Ca₄P₆O₁₉) and minor phase calcium pyrophosphate (β-Ca₂P₂O₇) crystallized from the glass matrix. These scaffolds were soaked in simulated body fluid (SBF) to determine the solubility and apatite formation, and mouse MC3T3-E1 cells were used to investigate the bioactivity and biocompatibility. The Sr doped scaffold showed a higher degradability than those samples containing Zn or Mg, inducing the formation of an apatite layer with a high (Sr + Ca)/P molar ratio of 1.64, whereas only some discontinuous CaP layers and spare apatite agglomerates were found on the scaffolds doped with Mg ((Mg + Ca)/P = 1.12) and Zn ((Zn + Ca)/P = 1.55) respectively. In vitro cell culture, a high degree of cell adhesion and spreading was achieved on the samples containing Sr or Zn, while only a few cells adhered to the Mg doped sample. These results implied that the bioactivity and biocompatibility of the scaffolds were not only strongly associated with the apatite forming ability, but also related with the Ca/P molar ratios of the deposits.     

Synthesis and luminescence properties of YVO4:Eu nanocrystals grown in nanoporous glass

We report on a feasible method to synthesize luminescence nanocrystals in porous glass in this paper. Well dispersed YVO₄:Eu nanocrystals were proved being grown in nanoporous glass by XRD, micro-Raman spectra and HRTEM equipped with EDS. The YVO₄:Eu³⁺ nanocrystal grown in porous glass herein shows very different luminescence properties compared with single Eu-doped sample. By this method, intense red emission from high silica glass due to energy transfers VO₄³⁻ → Eu³⁺ was obtained. The results show that the reduction from Eu³⁺ to Eu²⁺ in porous glass impregnated with Eu³⁺ ions was avoided effectively.     

Preparation and characterization of zeolite framework stabilized cuprous oxide nanoparticles

Zeolite framework stabilized copper(I) oxide nanoparticles (4.8 ± 2.6 nm) were prepared for the first time by using a four step procedure: the ion exchange of Cu²⁺ ions with the extra framework Na⁺ ions in Zeolite-Y, the reduction of the Cu²⁺ ions within the cavities of zeolite with sodium borohydride in aqueous solution, the dehydration of Zeolite-Y with the copper(0) nanoclusters, and the oxidation of intrazeolite copper(0) nanoclusters by O₂ at room temperature. Zeolite stabilized copper(I) oxide nanoparticles were thoroughly characterized by ICP-OES, XRD, HR-TEM, Raman, XPS, UV-vis spectroscopy and N₂ adsorption-desorption technique.     

Structural and magnetic properties of glass-ceramics containing silver and iron oxide

Glass-ceramics with a nominal composition of 25SiO₂–(50 − x)CaO–15P₂O₅–8Fe₂O₃–2ZnO–xAg (where x = 0, 2 and 4 mol%) have been prepared. Structural features of glass-ceramics have been investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Magnetic properties were studied using vibrating sample magnetometer and Mössbauer spectroscopy. Ca₃(PO₄)₂, hematite and magnetite are formed as major crystalline phases. The microstructure reveals the formation of 25–30 nm size particles. Mössbauer spectroscopy has shown the relaxation of magnetic particles. Saturation magnetization value is increased with an increase of Ag content up to 4 mol%, which has been attributed to the formation of magnetically ordered particles. The antibacterial response was found to depend on Ag ions concentration in the glass matrix and samples with 4 mol% Ag in glass matrix have shown effective antibacterial activity against Escherichia coli.     

Properties of lead zirconate-alumina ‘nanocomposites’

Microstructures, Vickers hardness and dielectric properties of PbZrO₃ ceramics with co-additions of 0.5-5 vol% Al₂O₃ nanoparticles have been investigated. The additive inhibited grain growth, with average grain size decreasing from ∼13 μm for PbZrO₃ to ∼1 μm for the nanocomposites. The mode of fracture also changed, from predominantly inter-granular in PbZrO₃ to a mixed-mode of intra- and inter-granular fracture in the composite samples. Vickers hardness values increased from 2.9 GPa for PbZrO₃ to 4.1 GPa for the sample with 1 vol% Al₂O₃, but there was a more gradual increase for higher Al₂O₃ contents. Plots of relative permittivity versus temperature indicated subtle differences which were attributed to a chemical reaction between the additive and matrix during sintering. X-ray powder diffraction showed that lead aluminium oxides were the principal products of this reaction.     

Fabrication and properties of titanium–hydroxyapatite nanocomposites

Titanium–hydroxyapatite nanocomposites with different HA contents (3, 10, 20 vol%) were produced by the combination of mechanical alloying (MA) and powder metallurgical process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vickers microhardness as high as 1030 and 1500 HV_0.2, which is more than 4–6 times higher than that of a conventional microcrystalline titanium. Titanium nanocomposite with 10 vol% of HA was more corrosion resistant (i_C = 1.19 × 10⁻⁷ A cm⁻², E_C = −0.41 V vs. SCE) than microcrystalline titanium (i_C = 1.31 × 10⁻⁵ A cm⁻², E_C = −0.36 V vs. SCE). Additionally, the electrochemical treatment in phosphoric acid electrolyte results in porous surface, attractive for tissue fixing and growth. Mechanical alloying and powder metallurgy process for the fabrication of titanium–ceramic nanocomposites with a unique microstructure are developed.     

Self-forming AlOx layer as Cu diffusion barrier on porous low-k film

The copper diffusion barrier properties of an ultrathin self-forming AlO_x layer on a porous low-k film have been investigated. Cu-3 at.% Al alloy films were directly deposited onto porous low-k films by co-sputtering, followed by annealing at various temperatures. Transmission electron microscopy micrographs showed that a ∼ 5 nm layer self-formed at the interface after annealing. X-ray photoelectron spectroscopy analysis showed that this self-formed layer was Al₂O₃. Sharp declines of the Cu and Si concentrations at the interface indicated a lack of interdiffusion between Cu and the porous low-k film for annealing up to 600 °C for 30 min. The leakage currents from Cu(Al)/porous low-k/Si structures were similar to as-deposited films even after a 700 °C, 5 min anneal while a Cu sample without Al doping failed at lower temperatures. Adding small amounts of Al to bulk Cu is an effective way to self-form copper diffusion layer for advanced copper interconnects.     

Highly porous polycaprolactone-45S5 Bioglass® scaffolds for bone tissue engineering

Highly porous biocompatible composites made of polycaprolactone (PCL) and 45S5 Bioglass® (BG) were prepared by a solid–liquid phase separation method (SLPS). The composites were obtained with BG weight contents varying in the range 0–50%, using either dimethylcarbonate (DMC) or dioxane (DIOX) as solvent, and ethanol as extracting medium. The porosity of the scaffolds was estimated to be about 88–92%. Mechanical properties showed a dependence on the amount of BG in the composites, but also on the kind of solvent used for preparation, composites prepared with DIOX showing enhanced stress at deformation with respect to composites prepared with DMC (stress at 60% of deformation being as high as 214 ± 17 kPa for DIOX-prepared composites and 98 ± 24 kPa for DMC-prepared ones, with 50 wt/wt_PCL% of glass), as well as higher elastic modulus (whose value was 251 ± 32 kPa for DIOX-prepared scaffolds and 156 ± 36 kPa for DMC-prepared ones, always with 50 wt/wt_PCL% of glass). The ability of the composites to induce precipitation of hydroxyapatite was positively evaluated by means of immersion in simulated body fluid and the best results were achieved with high glass amounts (50 wt/wt_PCL%). In vitro tests of cytotoxicity and osteoblast proliferation showed that, even if the scaffolds are to be considered non-cytotoxic, cells suffer from the scarce wettability of the composites.     

Towards modeling gadolinium-lead-borate glasses

Infrared spectra of gadolinium-lead-borate glasses of the xGd₂O₃·(100 − x)[3B₂O₃·PbO] system, where x = 0, 5, 10, 15, 25, 35 and 50 mol.%, have been recorded to explore the role of content of gadolinium ions behaving as glass modifier.The FTIR spectroscopy data for the xGd₂O₃·(1 − x)[3B₂O₃·PbO] glasses show the structural role of lead ions as a network-formers and of the gadolinium ions network modifiers. Adding of the rare earth ion up to 35 mol.% into the glass matrix, the IR bands characteristic to the studied glasses become sharper and more pronounced.Structural changes, as recognized by analyzing band shapes of IR spectra, revealed that Gd₂O₃ causes a change from the continuous borate network to the continuous lead-borate network interconnected through Pb-O-B and B-O-B bridges and the transformation of some tetrahedral [BO₄] units into trigonal [BO₃] units. Then, gadolinium ions have affinity towards [BO₃] structural units which contain non-bridging oxygens necessary for the charge compensation because the more electronegative [BO₃] structural units were implied in the formation of B-O-Gd bonds and the transformation of glass network into a glass ceramic.We propose a possible structural model of building blocks for the formation of continuous random 3B₂O₃·PbO network glass used by density functional theory (DFT) calculations.DFT calculations show that lead atoms occupy three different sites in the proposed model. The first is coordinated with six oxygen atoms forming distorted octahedral geometries. The second lead atom has an octahedral oxygen environment and the five longer Pb-O bonds are considered as participating in the metal coordination scheme. The third lead atom has ionic character. In agreement with the results offered by the experimental FTIR data, the theoretical IR data confirm that our proposed structure is highly possible.     

One-step synthesis of petal-like apatite/titania composite coating on a titanium by micro-arc oxidation

Petal-like apatite/titania (TiO₂) coating was prepared on commercially pure titanium (Ti) by micro-arc oxidation in electrolyte containing calcium and phosphate for the first time. The surface morphology, crystalline structure, chemical composition and binding state of the apatite/TiO₂ composite coating were characterized. The coating consists of a double-layer (apatite layer and TiO₂ layer) structure. The average thickness of the inner TiO₂ layer and the outer apatite layer is about 6 μm and 16 μm respectively. The outer apatite layer is porous and exhibits petal-like pattern. The apatite layer consists of hydroxyapatite (HA) and carbonate-apatite and the inner TiO₂ layer consists of anatase and rutile.     

Porous β-NaCaPO4 containing borate glass-ceramic scaffolds

A novel β-NaCaPO₄ containing borate glass-ceramic is prepared. Two porous glass-ceramic scaffolds are prepared by binding particles with the size of 200–300 μm by 5 wt.% sodium silicate solution and 2 wt.% chitosan solutions, respectively. The reaction of the scaffolds in the SBF solution is characterized by weight loss analysis, XRD, FTIR, and SEM. The same is done to the 45S5 glass scaffolds as comparison. XRD and FTIR indicate that the carbonate hydroxyapatite has formed more rapidly on the borate glass-ceramic scaffolds. The carbonated hydroxyapatite depositing on chitosan binding scaffolds has lower crystallization degree than that on sodium silicate binding scaffolds and is similar to that of the human bone, which makes the chitosan binding scaffolds a good potential prospect in the field of tissue engineering.     

Retention of fluoride ions from aqueous solution using porous hydroxyapatite. Structure and conduction properties

Synthetic porous calcium hydroxyapatite (noted p-HAp) treated with different fluoride concentrations at room temperature in the presence of carbonate, sodium chloride and phosphate-rich media was investigated. The fluoridation rate of the porous calcium hydroxyapatite was 89% using 1 mol/L [F(-)] solution compared with 30% for crystalline hydroxyapatite (c-HAp). The high specific surface area of p-HAp (235 m(2)g(-1)) compared with c-HAp sample (47 m(2)g(-1)) has an important effect on the removal of fluoride ions from aqueous solution, when p-HAp was treated with high fluoride concentration to produce calcium fluorohydroxyapatite materials. Fluoride adsorption on porous hydroxyapatites (p-HAp) modified their structural and conduction properties.     

Stripping voltammetric behavior of nitrogen-doped tetrahedral amorphous carbon thin film electrodes in NaCl solutions

Conductive nitrogen-doped tetrahedral amorphous carbon (ta-C:N) thin films fabricated with a filtered cathodic vacuum arc technique were investigated for their ability to detect multiple trace heavy metals such as mercury, copper and lead by linear sweep anodic stripping voltammetry in sodium chloride aqueous solutions. The ta-C:N film electrodes exhibited a significant stripping response for determination of individual elements (Pb²⁺ and Hg²⁺) and multiple elements (Pb²⁺ + Hg²⁺ and Cu²⁺ + Hg²⁺), indicating that these electrodes have a great potential for simultaneously tracing multiple heavy metals in aqueous solutions.