Deepening our understanding of bioactive glass crystallization using TEM and 3D nano-CT

One key issue influencing a broader application of Bioglass 45S5 in tissue engineering is its inherent crystallization tendency, severely limiting the mechanical strength of 3D porous scaffolds. Despite numerous studies, Bioglass 45S5 crystallization is not yet fully understood with regard to the mechanisms involved or morphology of the crystal phases forming. Here we show how two cutting-edge imaging techniques, state-of-the-art transmission electron microscopy (TEM) with image correction including energy dispersive X-ray spectroscopy and X-ray nano-computed tomography (nano-CT), allowed us to visualize changes in microstructure from near-nucleation to almost full crystallization in bulk Bioglass 45S5. At early times of heat treatment at 660 °C the formation of phase-separated nano-droplets within the glassy matrix was observed. Later, besides surface crystallization, bulk crystallization of combeite spheres was predominant. The formation of the first combeite spheres, their coarsening with time and finally their merging at near full crystallization were recorded by in situ high-temperature optical microscopy videos. The 3D nature of these spheres was confirmed by nano-CT, while TEM showed that their internal structure was composed of sub-micron grains. X-ray diffraction analysis at early time points showed a much higher crystalline fraction in bulk samples compared to powder samples, highlighting the influence of processing and sample morphology. These results show the importance of using complementary techniques for gaining insight into the crystallization process in the volume. In addition, we show that TEM and nano-CT are suitable characterization techniques to visualize the crystallization even in fast crystallizing systems, such as bioactive glasses.     

New insights into the crystallization process of sol-gel–derived 45S5 bioactive glass

In this work the influence of thermal treatment conditions on crystallization of a sol-gel-derived 45S5 bioactive glass was evaluated using DSC, XRD, TEM, EDX, and X-ray nanocomputed tomography (nano-CT). Temperature and time of the thermal treatment strongly influence the composition of the crystalline phases. At the onset of the glass transition temperature (600°C), combeite crystallizes as the main phase along with a calcium silicate-phosphate phase, which decomposes into rhenanite from 2 hours of thermal treatment at this temperature. At the crystallization temperature (700°C), combeite remains as the main crystalline phase. Additionally, Na₂Ca₂Si₂O₇ crystalline phase is formed. Our results provide a basic platform for tailoring the crystalline phases by controlling the nucleation and growth of crystalline phases via thermal treatments. Different morphologies (round particles, stacked layers, toothpick-like, and long features) were discerned by TEM as a function of temperature and time of treatment. It is the first time that bioactive glass is investigated by nano-CT at laboratory scale. This novel technique enables the 3D visualization of features in the nanometer range, giving clear information about the volumetric distribution of phases in the sample.     

Poly(vinyl alcohol) functionalization with aldehydes in organic solvents: Shining properties of poly(vinyl acetals)

Poly(vinyl alcohol) has been functionalized with aldehydes in tetrahydrofuran (THF) with a good control of the grafting. A wide library of poly(vinyl acetals) could be obtained in order to study some structure/property correlations. The influence of the aldehyde nature on the functionalization rates has been studied, in particular for optical properties by measurement of the shininess for further applications in the cosmetic field. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40677.     

Pea pod, broad bean pod and okara, potential sources of functional compounds

Disposal of by-products generated by plant food processing represent an important problem in the industry, but these by-products are also promising sources of compounds which may be used for their technological or nutritional properties, and today they are considered as a possible source of functional compounds. This work has contributed to the knowledge of three legume by-products, pea pod (Pisum sativum L.), broad bean pod (Vicia faba L.) and okara from soybean (Glycine max L.). These three by-products have in common that their major fraction is dietary fibre (pea pod: 58.6 g/100 g; okara: 54.3 g/100 g; broad bean pod: 40.1 g/100 g). Sucrose, glucose and fructose are the most important soluble sugars in both pods; however α-galactosides (stachyose and raffinose) are in greater concentration in okara. Protein is also a considerable component, although in higher amount in okara than in pods. Okara presents a large quantity of fat however both pods show similar low contents. Linoleic acid is the most important fatty acid; oleic acid is remarkable in okara and pea pod and linolenic acid in broad bean pod. Mineral amount is major in by-product pods than in okara, and the most important minerals are potassium, calcium and iron.     

Synthesis,characterization, photocatalytic evaluation,and toxicity studies of TiO2–Fe3+ nanocatalyst

Based on our previous work on the green preparation of Ag–TiO₂ photocatalyst with bactericidal activity under visible light, we extended our studies to the synthesis of TiO₂–Fe³⁺ materials with enhanced photocatalytic activity for the degradation of recalcitrant organic pollutants in water. TiO₂–Fe³⁺ nanopowders were synthesized using a robust, environmentally friendly procedure. Established amounts of Fe(NO₃)₃·9H₂O and titanium tetraisopropoxide (TTIP) were mixed using glacial acetic acid as solvent. Hydrolysis of TTIP–Fe³⁺ was accomplished using a 30 % (W/V) Arabic gum aqueous solution. TiO₂–Fe³⁺ nanopowders were obtained by thermal treatment at 400 °C. In order to elucidate the structure of these photocatalysts, microscopic and spectroscopic characterization techniques were applied. The high resolution transmission electron microscopy (HRTEM) analysis indicated the presence of uniformly distributed particles with average particle size of about 9 nm. According to the HRTEM lattice fringes, ring pattern, and selected area electron diffraction pattern, the crystalline part of the samples consists of anatase (PDF 01-086-1157 with the lattice constant of 3.7852, 9.5139 Å and 90°) as dominant phase. X-ray photoelectron spectroscopy (XPS) was applied to determine the oxidation state of iron. The XPS provides evidence for Fe³⁺ surface species in the TiO₂–Fe³⁺ composite. Complete degradation of aqueous solutions (20 ppm) of methylene blue and/or methyl orange was accomplished after 4 h of treatment using 150 mg of TiO₂–Fe³⁺/150 mL of dye solution. The in vitro toxicity of the materials was tested. The materials showed no toxicity against human red blood cells.     

Health-promoting effects in the gut and influence on lipid metabolism of Himanthalia elongata and Gigartina pistillata in hypercholesterolaemic Wistar rats

The intake of Himanthalia elongata and Gigartina pistillata from the Spanish Atlantic coasts was evaluated in Wistar rats. Both seaweed diets showed higher (p < 0.001) faecal excretion. Colonic fermentation increased (p < 0.001) total short-chain fatty acids (SCFAs) in Himanthalia-fed rats due to the higher (p < 0.001) levels of acetic, propionic and butyric acids. The intake of Gigartina increased (p < 0.001) propionic acid and decreased (p < 0.001) butyric acid. The apparent absorption and true retention of calcium and magnesium enhanced (p < 0.05) with Himanthalia diet, while Gigartina produced no significant effect. The serum concentration of HDL-C increased (p < 0.01), triglycerides (TGL) decreased (p < 0.001) and bile acids diminished (p < 0.001) in faeces of Himanthalia-fed rats. The Gigartina diet produced a decrease (p < 0.001) in TGL, total cholesterol (p < 0.01) and LDL-C (p < 0.05) in serum and reduced TGL in liver (p < 0.001). Thus, both seaweeds improved the lipid profile, and Himanthalia increased SCFA production and the absorption and retention of Ca and Mg as a result of the gut fermentation.     

Energy and economic assessment of soda and organosolv biorefinery processes

Lignocellulosic biomass, particularly agricultural and forestry residues, is becoming a potential renewable energy and products source. Lignocellulosic biomass processing technologies include a primary separation of its main constituents, cellulose, hemicelluloses and lignin, as well as further treatment and processing to obtain different platform chemicals to design consistently structured compounds as chemical building blocks. The economic competitiveness of the obtained products is highly dependent on the separation and purification technologies used and the process energetic efficiency. For this proposal, process simulation tools are very useful to design a competitive and effective biorefinery scheme. In the present work, the energetic and economical efficiencies of two biorefinery processes, soda and organosolv-ethanol systems, were analyzed using the simulation software Aspen Plus^®. The process design consisted of several units (reaction, solid fraction washing, products recovery and liquid fraction processing). Mass and energy balances were established and both systems were compared in terms of yield, solvents/reactants recovery and energy consumption. Aspen HX-Net software was used to analyze the process heat exchange network in order to improve energy consumptions. The development of rigorous simulations allowed to determine the economical feasibility of both biorefinery schemes, and to establish the most appropriate operation conditions for both processes.