Dispersed Gel Research Articles

Rheological characterization of amaranth protein gels

Gel forming properties of amaranth proteins at different thermal conditions and protein concentration were studied. Gel point ( G′ and G″ crossover) and gelation kinetics ( G′ vs. time) were analyzed. The type of gel formed from the rheological point of view was studied analyzing the rheograms obtained from frequency sweeps. Texture properties of cold-set gels were analyzed by TPA assays. Minimum conditions for gelation were 7%, w/v and 70 °C. Elasticity of heated dispersions and gels increased with the increase of protein concentration. A high value of the network structure index was observed. This behavior could be related to the great proportion of disulfide bonds formed during amaranth protein gelation. At temperatures above 70 °C (80, 90 and 95 °C), gelation of dispersions (15%, w/v) took place at times less than 5 min. A first order kinetic gelation process with reaction rate specific constant values that increased with the increase of heating temperature was observed. A rapid denaturation of globulins followed by sulfhydryl/disulfide interchange reactions between protein molecules conduced to a gelation phenomenon enhanced by protein aggregation. Gels prepared over critical conditions ( T>70 °C, protein concentration >7%, w/v) presented a strong gel-like behavior. These type of gels were elastic in nature (tan δ<0.1), of high hardness, fracturability and cohesiveness, although presented low adhesiveness. Depending on protein and thermal conditions, amaranth proteins were able to form self-supporting gels that could be applied in different gel-like foods.

Formulation and characterization of bupivacaine lipospheres

Bupivacaine lipospheres were prepared as a parenteral sustained-release system for post-operative pain management. Bupivacaine free base was incorporated into micron-sized triglyceride solid particles coated with phospholipids, which were formed via a hot emulsification and cold resolidification process. The bupivacaine liposphere dispersions were characterized with respect to drug loading, particle-size distribution, and morphology. Gelation of the fluid liposphere dispersions was observed at different time intervals upon storage. The type of phospholipids used in the formulation was found to have a major impact on the gelation of the dispersion. The use of synthetic phospholipids instead of the natural phospholipids in the formulation yielded bupivacaine liposphere dispersions exhibiting prolonged gelation time. The addition of a hydrophilic cellulosic polymer can further improve the physical stability of the dispersion.

Self‐Assembly Fractal Microstructures of HPAM/Chromium Acetate and HPAM/Phenolic Aldehyde Colloidal Dispersion Gel

HPAM (partially hydrolyzed polyacrylamide)/chromium acetate and HPAM/phenolic aldehyde colloidal dispersion gels (CDGs) were investigated microscopically using atomic force microscope. The results show that the colloidal dispersion gels eventually form self‐assembly branch‐like fractal structures over a scanning range of micrometers. The fractal aggregates of single twigs formed by compact assembly of nanometer particles were observed over a smaller scanning range regardless of the concentration of HPAM and the crosslinking reagent. This indicated an HPAM‐dependence for the formation of the fractal structure and the crosslinking reagent independence of the geometrical morphology of the gel. Also, the results demonstrated that the elastic modulus (G′) of the fractal structure formed by the smaller (nanometer‐sized) colloidal particles was one order of magnitude higher than obtained for the micrometer‐sized particles. The elastic modulus (G′) and the dynamic stability of the gels increased with decreasing particle diameter.

Novel preparation of BIMEVOX materials assisting in elementary step resolved investigations of the oxygen transfer at the surface

A novel preparation method of BIMEVOX materials involving the decomposition of a well dispersed cation gel is described, allowing a simple, rapid manufacturing of bismuth-vanadium oxide based membranes. A detailed investigation of the required oxidative decomposition and the sintering procedure was performed, indicating the conditions for a complete removal of carbon containing compounds and the formation of dense samples. Differently doped BIMEVOX materials were prepared and investigations on the interaction of gas-phase oxygen with the membrane material were carried out. For the first time, the oxygen transfer from the gas phase to the bulk was studied directly by the highly time resolved TAP transient technique.

Gelation of Shark Meat under Mild Acidic Conditions: Physicochemical and Rheological Characterization of the Gel

ABSTRACT:Homogenate of washed shark meat in water was converted into a gel by lowering its pH to 3.5 by acetic acid. Unlike unacidified homogenate, water was strongly bound to the gel. The strength of the gel increased with increasing moisture content, while expressible water content was not affected. Gelation was associated with reduction in myosin heavy chain and sulfhydryl groups. Dynamic rheological measurements indicated viscoelastic nature of the gel. The storage modulus increased with increased temperature. The shear stress sweep of the gel dispersions as a function of temperature suggested pseudoplastic behavior.

Nanosized cationic hydrogels for drug delivery: preparation, properties and interactions with cells

A new family of nanoscale materials on the basis of dispersed networks of cross-linked ionic and nonionic hydrophilic polymers is being developed. One example is the nanosized cationic network of cross-linked poly(ethylene oxide) (PEO) and polyethyleneimine (PEI), PEO-cl-PEI nanogel. Interaction of anionic amphiphilic molecules or oligonucleotides with PEO-cl-PEI results in formation of nanocomposite materials in which the hydrophobic regions from polyion-complexes are joined by the hydrophilic PEO chains. Formation of polyion-complexes leads to the collapse of the dispersed gel particles. However, the complexes form stable aqueous dispersions due to the stabilizing effect of the PEO chain. These systems allow for immobilization of negatively charged biologically active compounds such as retinoic acid, indomethacin and oligonucleotides (bound to polycation chains) or hydrophobic molecules (incorporated into nonpolar regions of polyion–surfactant complexes). The nanogel particles carrying biological active compounds have been modified with polypeptide ligands to enhance receptor-mediated delivery. Efficient cellular uptake and intracellular release of oligonucleotides immobilized in PEO-cl-PEI nanogel have been demonstrated. Antisense activity of an oligonucleotide in a cell model was elevated as a result of formulation of oligonucleotide with the nanogel. This delivery system has a potential of enhancing oral and brain bioavailability of oligonucleotides as demonstrated using polarized epithelial and brain microvessel endothelial cell monolayers.

Sol-gel transition of biopolymer dispersions

Sol-gel transition of dispersions of biopolymers, which are used widely in food, cosmetics, biomedical and related industries, is classified by the temperature dependence of storage shear modulus. Sol-gel transition of gellan gum solution is described well by a criterion of Winter-Chambon. Too fast gelation of dispersions of konjac glucomannan in the presence of excessive amount of alkaline coagulant and/or at higher temperatures leads to a formation of gels with lower modulus. A solution of xyloglucan from which a certain amount of galactose residues is removed forms a gel on heating and reverts into a solution on further heating. The lower temperature transition of this xyloglucan solution is induced by hydrophobic interaction.

Liquid Crystal Formulations

Chral-Nematic Dispersions and Encapsulations were investigated for different mixture concentrations of the nematic liquid crystal E7 and E48 and the cholesteric liquid crystals TM74A and TM75A in the Infrared and Visible regime. Liquid crystal (E7:TM74A) dispersions as stand alone systems and as polymer dispersed materials were found to be bistable in the near IR region.‡ Chiral-nematic dispersion of E48:TM74A displayed different bright colors in the 400-760 visible range and exhibited thermochromic properties at room temperature. The PVA encapsulated E48:TM74A mixture (60:40) also showed thermochromicity between 30°C to 43°C. A ternary system was formulated from TM74A:TM75A:E48. Mixtures with high cholesteric concentration exhibited thermochromicity whereas systems with low cholesteric concentration showed electro-optic properties. Gel dispersion was done on mixtures with low cholesteric concentration using a liquid crystal polymer cinnamate. The polymer network effected stabilization on the liquid crystal molecules. Electro-optic tests showed that threshold voltage increases as the cholesteric amount increases in the different LC mixtures. Polymer and gel dispersions also increased the threshold voltages.

Dry pressing boehmite gels for the fabrication of monolithic α-Al2O3

It is demonstrated that dense alpha alumina can be fabricated by pressing ethanol-dispersed, α-Al2O3 seeded boehmite. Green bodies were formed by uniaxially pressing either water or ethanol dispersed gel powder and then isostatically pressing the compacts at 280 MPa. Green microstructure and alumina densification are correlated with gel agglomerate size and dispersing medium. The ethanol-dispersed specimens showed better sinterability than the water-dispersed specimens, and sintered to more than 99% theoretical density at 1300°C. It is shown that softer gel agglomerates were obtained by alcohol dispersion and resulted in better green microstructure and higher sintered density.

Rheological properties of alumina‐polyacrylate gel dispersions

AbstractRheological properties of aqueous alumina‐polyacrylate gel dispersions have been investigated with a controlled stress rheometer as functions of both cross‐linked polyacrylate and alumina concentrations at pH 13. These studies were conducted to understand the role of alumina‐polyacrylate interactions in building the rheology of complex liquids that contain surfactants, sodium hypochlorite, alkali, and inorganic salts. Viscosity and viscoelasticity of polyacrylate gel dispersions can be enhanced by the addition of colloidal alumina. The trends in viscosity and viscoelasticity are explained on the basis of changes in the conformation of polyacrylate and repulsive interactions of negatively charged polyacrylate and alumina particles.

Gradient flattening of sodium dodecyl sulfate (SDS) and isoelectric focusing (IEF) gels.

In addition to our previously reported versatile methods for sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis [1] and isoelectric focusing (IEF)-gel [2], I have achieved molecular weight gradient flattening of the SDS-polyacrylamide gel and pH gradient flattening of the IEF gel at any segment using the same electrophoresis system. Any crowded gel segment where congregated components are not separated well can easily be widened for good separation and any dispersed gel segment where components are too far apart can easily be narrowed. Therefore, every gel segment can be used effectively and meaningfully because the gradient curve can be adjusted to any distribution of the components. In the crowded area, any small spots of components which could not be detected previously because of nearby heavy staining or strong radioactivity of an abundant component can be sufficiently separated from the nearby spots in a small gel without sacrificing other areas.

Effects of sucrose on the rheological behavior of wheat starch pastes

AbstractThe rheological properties of starch–water–sucrose pastes have been determined under steady and oscillatory shear conditions. The results show that the effect of sucrose at concentrations of less than about 20% w/w is to increase the apparent viscosity, yield stress, dynamic viscosity, and dynamic rigidity. At higher surose concentrations the yield stress and dynamic rigidity tend to zero while values of the dynamic viscosity and apparent viscosity are reduced compared with controls. Sucrose causes the dispersed gel particles in pastes to change volume, and it is suggested that this is one of the factors responsible for the observed effects of sucrose on rheological behavior.

Chromatographic techniques for rapid measurement of gel in elastomers

AbstractTechniques for measuring gel contents of elastomers by liquid exclusion chromatography are described. Chromatographic methods are based on solubilizing aqueous latex in a water‐miscible elastomer solvent. The resulting mixture of solubilized elastomer and dispersed gel particles is separated and analyzed by liquid chromatography, columns packed with porous glass particles and a differential refractometer detector being used. Applicability of these techniques is illustrated with results for typical nitrile elastomers in methyl ethyl ketone. Chromatographically measured gel contents in the range 30–80% gel were in good agreement with those measured by a classical, 3‐day static method. Repeatability of chromatographic measurement was ±1.35% gel. The entire analysis, including solution preparation, required less than 1 hr and can be as short as 10–20 min.

Method for the Extraction of Extraneous Materials from Ground Cinnamon

Abstract A new method has been developed for the extraction of extraneous materials from ground cinnamon. In the method, hydrochloric acid is used to disperse gel formations, wet sieving is used to eliminate the dispersed gel, and a percolator replaces a trap flask to separate the extraneous material from cinnamon tissue. Collaborative results were good, and the method is recommended for adoption as official, first action.