Zoran Novak

Removal of BTEX vapours from waste gas streams using silica aerogels of different hydrophobicity

Silica aerogels are alternative adsorbents to activated carbon (AC) for the removal and the recovery of organic vapours from gas streams. The adsorption capacity measurements of different silica aerogels were done by mini-column method. Continuous adsorption measurements show that silica aerogels are excellent adsorbents of BTEX vapours from waste gas stream. Compared to the most used adsorbents, such as AC and silica gel, aerogels exhibit capacities which enormously exceed that of both commonly used adsorbents. By increasing the degree of hydrophobicity, aerogels become less effective, but they do not adsorb water vapour from gas stream. Silica monolith aerogels with different degrees of hydrophobicity by incorporating methyltrimethoxysilane (MTMS) or trimethylethoxysilane (TMES) in standard sol-gel synthesis were prepared. Excellent properties of aerogels, obtained with the sol-gel synthesis, were preserved with supercritical drying with CO(2). The degree of hydrophobicity of the aerogels was tested by measuring the contact angle (theta) of a water droplet with the aerogel surface. The aerogels were also characterised by FTIR, nitrogen sorption and DSC/TG measurements.

Diffusion of methanol–liquid CO2 and methanol–supercritical CO2 in silica aerogels

Drying of alcogel is the most critical step in production of transparent and monolithic silica aerogel. If alcohol extraction with liquid or supercritical carbon dioxide is used, diffusion of alcohol through the alcogel to the CO2 plays an important role. Dependent on the diffusion times, the quality and shape of aerogel samples vary from cracked (short diffusion times) to transparent crack-free aerogels (long diffusion times). At medium diffusion times, the non-transparent area was observed inside the aerogel samples. Diffusion coefficients of methanol in the liquid CO2 at two different temperatures and the diffusion coefficient of methanol in supercritical CO2 inside the silica aerogel were determined from the dependence of the width of the non-transparent damage area on diffusion times.

Supercritical impregnation of drugs and supercritical fluid deposition of metals into aerogels

The presented review covers the latest research on supercritical impregnation into organic and inorganic aerogels by investigating those factors that influence the impregnation. Supercritical impregnation is a promising method for incorporating drugs within porous carriers including for water insoluble drugs. An additional step (reduction from metallic precursor to metal) is required for the supercritical impregnation of metallic precursors. Hence, this expanded method is preferably termed as supercritical fluid deposition or adsorption. Supercritical impregnation of drugs, as well as metals, are mostly influenced by interactions between the compound and aerogel matrix, supercritical impregnation conditions, and the characteristics of a compound within a supercritical fluid.

Synthesis and Use of Organic Biodegradable Aerogels as Drug Carriers

Aerogels of natural polysaccharides possess both biocharacteristics of polysaccharides, such as good biological compatibility and cell or enzyme-controlled degradability, and aerogel characteristics, such as very high porosity and specific surface areas that makes them highly attractive in drug delivery. Biodegradable alginate aerogels were synthesized via a sol–gel process. In the present work two methods of ionic cross-linking were used to prepare alginate hydrogels as monoliths and spheres, which can be further easily converted to high surface area aerogels. The aerogels obtained were further used as drug carriers. We investigated the effect of process parameters, such as starting concentration and viscosity of alginate solution, on synthesis products and on model drug (nicotinic acid) release. The results indicate that by using the internal setting cross-linking method for obtaining monolithic aerogels nicotinic acid was released in a more controlled manner. The aerogels thus obtained also exhibited smaller volume shrinkage than the ones described in other publications. However, with increasing alginate concentration in both types of synthesis more compact and cross-linked aerogels were formed.

Rosemary extracts improve flow-mediated dilatation of the brachial artery and plasma PAI-1 activity in healthy young volunteers.

Polyphenol antioxidants decrease the risk of atherosclerosis. The study aimed to evaluate prospectively in healthy young participants the effect of oral rosemary extracts (RE), consisting of diphenols, upon endothelial dysfunction (ED), preceding structural atherosclerosis. Nineteen healthy young volunteers were studied prospectively, who received oral RE (77.7 mg) for 21 days, consisting of active substances carnosol (0.97 mg), carnosic (8.60 mg) and rosmarinic acid (10.30 mg). Before and after RE treatment, the study evaluated fasting serum levels of plasminogen‐activator‐inhibitor‐1 (PAI‐1), vascular cell adhesion molecule 1 (VCAM‐1), inter‐cellular adhesion molecule 1 (ICAM‐1), superoxide dismutase (SOD), glutathione peroxidase (GPX), fibrinogen, high‐sensitivity capsular reactive protein (hs‐CRP), tumor‐necrosis factor α (TNF‐α), the lipid profile and ED, characterized as flow‐mediated dilatation (FMD) in the brachial artery of <4.5%, estimated by ultrasound measurements. After 21 days, any side effects were registered, the mean FMD increased nonsignificantly (6.51 ± 5.96% vs 7.78 ± 4.56%, p = 0.546) and ED decreased significantly (66.6% vs 16.6%, p = 0.040). Among the serum markers, only the mean PAI‐1 level decreased significantly (4.25 ± 1.46 U/mL vs 3.0 ± 0.61 U/mL, p = 0.012) after 21‐day RE supplementation. It is concluded that oral RE supplementation has the potential to improve serum PAI‐1 activity and ED in young and healthy individuals. Copyright

Formation of polysaccharide aerogels in ethanol

Aerogels are outstanding materials, obtained by the sol–gel process. The production of polysaccharide aerogels is however time-consuming and their use for life-science applications is limited. To accelerate the production time, ethanol was used to induce the gelation of pectin, alginate, xanthan and guar gum. Polysaccharide aerogels were produced by dissolution in water, gelation in ethanol and supercritical drying. Only ethanol was used for the gelation without the use of any other cross-linking agent. In addition there was no solvent-exchange step prior to supercritical drying since the gelation occurred directly in ethanol. Differential scanning calorimetry was used to analyze the decompositions of the samples and also to measure their thermal conductivities. SEM and rheological analyses were performed in order to characterize the new materials. The prepared dry materials were highly porous and possessed some outstanding properties, namely, the low-methoxyl and high-methoxyl pectin monolithic aerogels possessed the highest surface areas yet reported, 510 m2 g−1 and 390 m2 g−1, respectively. To our knowledge this is the first known report regarding synthesis and characterization of pure xanthan and guar aerogels. Their surface areas were also high, 370 m2 g−1 and 110 m2 g−1, respectively. Very low thermal conductivity was observed for pectin aerogels, 0.021 W m−1 K−1.

Comparison of ionic and non-ionic drug release from multi-membrane spherical aerogels

The presented research was oriented towards the preparation of dry biodegradable alginate aerogels with multi-membranes using a multi-step sol-gel process with potential applications as carriers during oral drug delivery. First alginate spherical hydrogels were formed in CaCl2 or BaCl2 solutions by ionic cross-linking. These cores were further immersed into alginate sodium solution, filtered through a sieve, and dropped into the salt solution again. Multi-membrane hydrogels were obtained by repeating the above process. They were further converted into aerogels by supercritical drying. The effect of the number of membranes was investigated regarding the loading and release of the model drugs nicotinic acid and theophylline. Moreover, the efficiencies of Ba(2+) and Ca(2+) metal ions for forming tridimensional networks that retain and extend drug release were also investigated. Nicotinic acid release was prolonged by adding membranes around the core and using Ca(2+) for cross-linking. However, retarded theophylline release was only obtained by using Ba(2+) for cross-linking. Namely, by increasing the number of membranes and BaCl2 concentration drug release became linear versus time in all studied cases. In the case of nicotinic acid loading increased by adding membranes around the core, however, for theophylline the opposite results were obtained due to the different nature of the model drugs.

Novel ethanol-induced pectin–xanthan aerogel coatings for orthopedic applications

In this study, we developed a novel high methoxyl pectin-xanthan aerogel coating on medical-grade stainless steel, prepared by ethanol-induced gelation and subsequent supercritical drying. Two non-steroidal anti-inflammatory drugs, i.e. diclofenac sodium and indomethacin, were incorporated into the aerogel coating. Electrochemical analyses were performed on the coated samples using electrochemical impedance spectroscopy and cyclic polarization techniques. The results showed that all passivated samples were highly resistant to general corrosion. The release of both non-steroidal anti-inflammatory drugs was complete after 24h, as confirmed by the plateau in the drug release profiles as well as by IR spectroscopy after the final release point. The potential of samples for use in orthopedic applications was evaluated on a human bone-derived osteoblast cell and all samples were shown to be biocompatible. The increased viability of some samples indicates the high potential of the developed approach for future evaluation of possible clinical use.

Preparation of BaTiO3 powders using supercritical CO2 drying of gels

Abstract Two different drying methods, conventional drying of gels in air at 90°C and supercritical CO2 (SC-CO2) drying, were used to prepare BaTiO3 powders from sol–gel derived gels. The results reveal that powders prepared by supercritical drying with CO2 are less contaminated with the organic disintegration products which are formed during drying. As a result, the sintering of a sample prepared from the CO2-dried powder leads to a homogeneous and fine-grained microstructure.