In this work, a steroidal gelator containing an imine bond was synthesized, and its gelation behavior as well as a sensitivity of its gels towards acids was investigated. It was shown that the gels were acid-responsive, and that the gelator molecules could be prepared either by a conventional synthesis or directly in situ during the gel forming process. The gels prepared by both methods were studied and it was found that they had very similar macro- and microscopic properties. Furthermore, the possibility to use the gels as carriers for aromatic drugs such as 5-chloro-8-hydroxyquinoline, pyrazinecarboxamide, and antipyrine was investigated and the prepared two-component gels were studied with regard to their potential applications in drug delivery, particularly in a pH-controlled drug release.
We report the new development of fire extinguishing agents employing the latest technology of fighting and preventing fires. The in situ technology of fighting fires and explosions involves using large-scale ultrafast-gelated foams, which possess new properties and unique characteristics, in particular, exceptional thermal stability, mechanical durability and full biocompatibility. We provide a detailed description of the physico-chemical processes of silica foam formation at the molecular level and functional comparison with current fire extinguishing and fighting agents. The new method allows to produce controllable gelation silica hybrid foams in the range from 2 to 30 seconds up to 100 Pa·s viscosity. Chemical structure and hierarchical morphology obtained by SEM and TEM images develop thermal insulation capabilities of the foams, reaching a specific heat value of more than 2.5 kJ/(kg·°С). The produced foam consists of organized silica nanoparticles as determined by XPS and X-Ray diffraction analysis with a narrow particle size distribution of about 10-20 nm. As a result of fire extinguishing tests, it is shown that the extinguishing efficiency exhibited by silica-based sol-gel foams is almost 50 times higher than that for ordinary water and 15 times better than that for state-of-the-art firefighting agent AFFF(aqueous film forming foam). The biodegradation index determined by the time of the induction period was only 3 days, while even for conventional foaming agents this index is several times higher.
The use of ethylcellulose (EC) polymers as a means to structure edible oils for fat replacement is beginning to show great promise and the use of these ‘oleogels’ has recently been shown to be feasible in food products. These gels are very versatile, as the mechanical properties can be tailored by altering either the fatty acid profile of the oil component, or the viscosity or concentration of the polymer component. Here we report the observation that certain formulation of EC oleogels tend to separate into two distinct phases; a soft interior core surrounded by a firm exterior sheath. It was found that the extent of this effect depends on EC viscosity, and can also be induced through the addition of certain surfactants, such as sorbitan monostearate and sorbitan monooleate, though not by glycerol monooleate. Although the two visually distinct regions were shown to be chemically indistinct, the cooling rate during gel setting was found to play a large role; rapid setting of the gels reduces the fractionation effect, while slow cooling produced a completely homogeneous structure. In addition, by reheating only the soft region of the gel, a firm and soft fractionated gel could again be produced. Finally, it was observed that oleogels prepared with castor oil or mineral oil have the ability to remove or induce the gel separation, respectively. Taken together, these results indicate chemical interactions may incite the separation into two distinct phases, but the process also seems to be driven by the cooling conditions during gel setting. These findings lend insight into the EC-oleogel gelation process and should provide a stepping stone for future research into the manufacturing of these products.
In situ forming systems including thermoreversible hydrogels, which undergo sol-gel transition upon an increase in temperature have been used for various biomedical applications. Heparins are the standard of anticoagulation in the prophylaxis and treatment of deep vein thrombosis and pulmonary embolism. Both conditions require long-lasting treatment with frequent subcutaneous administrations of heparin. The objective of this study was to prepare and evaluate in situ forming gel systems designed by combination of two poloxamers (P407 and P188) and hydroxypropylmethylcellulose (HPMC) for prolonged release of heparin. Thermoreversible hydrogels were prepared with heparin solution and dispersion of heparin/chitosan nanocomplexes. Nanocomplexes formed by self-assembly of heparin with chitosan at various mass ratios were thoroughly characterized. A heparin/chitosan mass ratio of 1:1 with pH 5.20 was the most appropriate for preparation of small, homogenous and stable nanocomplexes (mean diameter 123 nm; polydispersity index 0.22 and zeta potential +35.5 mV). Thermoreversible hydrogels were evaluated by gelation temperature, viscosity over the temperature range 20 to 40°C, rate of hydrogel dissolution, and heparin release in vitro. The addition of P188 to P407 gel formulations resulted in an increase in gelation temperature, decrease in viscosity at room temperature and faster gel dissolution. The opposite effects were observed with formulations containing HPMC which demonstrated 18-day-long gel dissolution and complete heparin release in 9 days from gels containing heparin solution. Considerable prolongation of heparin release was achieved with incorporation of heparin/chitosan nanocomplexes into the gelling systems. It may be concluded that with poloxamer mixtures at specific concentrations, addition of HPMC and use of heparin/chitosan nanocomplexes dispersions, thermoreversible formulations for prolonged subcutaneous release of heparin are feasible.
In this study, a new thermo-sensitive polymer, glycol chitin, was synthesized by controlled N-acetylation of glycol chitosan and evaluated as a thermogelling system. The physico-chemical properties of glycol chitins with different degrees of acetylation (DA) were investigated in terms of degradation, cytotoxicity, rheological properties, and in vitro and in vivo gel formation. Aqueous solutions of glycol chitins were flowable freely at room temperature but quickly became a durable gel at body temperature. Thermo-reversible sol-gel transition properties were observed with fast gelation kinetics. Glycol chitins with higher DA showed faster degradation in the presence of lysozyme. They exhibited no significant biological toxicity against human cell lines. An anti-cancer drug, doxorubicin, could be incorporated into the hydrogel by a simple mixing process and released in a sustained pattern over 13 days. Our findings suggest that glycol chitins could be useful as a new thermogelling biomaterial for drug delivery and injectable tissue engineering.
Understanding the role of kinetics in fiber network microstructure formation is of considerable importance in engineering gel materials to achieve their optimized performances/functionalities. In this work, we present a new approach for kinetic-structure analysis for fibrous gel materials. In this method, kinetic data is acquired using a rheology technique and is analyzed in terms of an extended Dickinson model in which the scaling behaviors of dynamic rheological properties in the gelation process are taken into account. It enables us to extract the structural parameter, i.e. the fractal dimension, of a fibrous gel from the dynamic rheological measurement of the gelation process, and to establish the kinetic-structure relationship suitable for both dilute and concentrated gelling systems. In comparison to the fractal analysis method reported in a previous study, our method is advantageous due to its general validity for a wide range of fractal structures of fibrous gels, from a highly compact network of the spherulitic domains to an open fibrous network structure. With such a kinetic-structure analysis, we can gain a quantitative understanding of the role of kinetic control in engineering the microstructure of the fiber network in gel materials.
Physicochemical and acid gelation properties of UHT-treated commercial soy, oat, quinoa, rice and lactose-free bovine milks were studied. The separation profiles were determined using a LUMiSizer dispersion analyser. Soy, rice and quinoa milks formed both cream and sediment layers, while oat milk sedimented but did not cream. Bovine milk was very stable to separation while all plant milks separated at varying rates; rice and oat milks being the most unstable products. Particle sizes in plant-based milk substitutes, expressed as volume mean diameters (d4.3), ranged from 0.55μm (soy) to 2.08μm (quinoa) while the average size in bovine milk was 0.52μm. Particles of plant-based milk substitutes were significantly more polydisperse compared to those of bovine milk. Upon acidification with glucono-δ-lactone (GDL), bovine, soy and quinoa milks formed structured gels with maximum storage moduli of 262, 187 and 105Pa, respectively while oat and rice milks did not gel. In addition to soy products currently on the market, quinoa may have potential in dairy-type food applications.
Microalgae represent a promising source of renewable biomass for the production of biofuels and valuable chemicals. However, energy efficient cultivation and harvesting technologies are necessary to improve economic viability. A Tris-Acetate-Phosphate-Pluronic (TAPP) medium that undergoes a thermoreversible sol-gel transition is developed to efficiently culture and harvest microalgae without affecting the productivity as compared to that in traditional culture in a well-mixed suspension. After seeding microalgae in the TAPP medium in a solution phase at 15 °C, the temperature is increased by 7 °C to induce gelation. Within the gel, microalgae are observed to grow in large clusters rather than as isolated cells. The settling velocity of the microalgal clusters is approximately ten times larger than that of individual cells cultured in typical solution media. Such clusters are easily harvested gravimetrically by decreasing the temperature to bring the medium to a solution phase.
We report the synthesis of ion-exchangeable molyb-denum-sulfide chalcogel through an oxidative coupling process, using (NH4)2MoS4 and iodine. After supercritical drying the MoSx amorphous aerogel, appears spongy and shows large surface areas up to 370 m(2)/g, with broad range of pore sizes. X-ray photoelectron spectroscopic and pair distribution function analyses reveal that Mo(6+) species undergo reduction during network assembly, to produce Mo(4+) containing species where the chalcogel network consists of [Mo3S13] building blocks comprising triangular Mo metal clusters and S2(2-) units. The band gap of the brown-black chalcogel is ~1.36 eV. The ammonium sites present in the molybdenum-sulfide chalcogel network are ion-exchangeable with K(+) and Cs(+) ions. The molybdenum-sulfide aerogel exhibits high adsorption selectivities for CO2 and C2H6 over H2, and CH4. The aerogel also possess high affinities for iodine and mercury.
Thin films of molecular gels formed in a confined space have potential applications in transdermal delivery, artificial skin, molecular electronics, etc. The microstructures and properties of thin gel films can be significantly different from those of their bulk counterparts. However, so far a comprehensive understanding of the effects of spatial confinement on the molecular gelation kinetics, fiber network structure and related mechanical properties is still lacking. In this work, using rheological techniques, we investigated the effect of one-dimensional confinement on the formation kinetics of fiber networks in the molecular gelation process. Fractal analyses of the kinetic information in terms of an extended Dickinson model enabled us to describe quantitatively the distinct kinetic signature of molecular gelation. The structural features derived from gelation kinetics support well the fractal patterns of the fiber networks acquired by optical and electron microscopy. With the kinetics-structure correlation, we can gain an in-depth understanding of the confinement-induced differences in the structure and consequently the mechanical properties of a model molecular gelling system. Particularly, the confinement induced structural transition, from a three-dimensional, dense and compact spherulitic network composed of highly branched fibers to a quasi-two-dimensional sparse spherulitic network composed of less branched fibers and entangled fibrils at the boundary areas, renders a gel film to become less stiff but more ductile. Our study suggests here a new strategy of engineering the fiber network microstructure to achieve functional gel films with unusual but useful properties.