Kinetics Of Gel Formation Research Articles

Peculiarities of some Fmoc-dipeptides gelation in DMSO/water medium

The possibility of the gels formation with a high-water content of 90% v/v using Fmoc-dipeptides without mechanical actions or pH-switching was demonstrated. For the first time, the formation of a colloid gel based on Fmoc-LL dipeptide was discovered. The effect of side substituents in the amino acid residues of Fmoc-dipeptides in the range of GG, AA, LL, and FF on their ability to form gels in DMSO/water systems was thoroughly studied. Non-linear dependence of gel formation kinetics in dipeptide/DMSO/water systems, gel properties, and supramolecular organization in xerogels on the size of side substituents was observed. The results obtained give a new insight into the mechanism of gelation with low-molecular-weight gelators based on Fmoc-dipeptides and may be useful for the preparation of new supramolecular or colloidal gels.

Using detailed milk protein composition to explain variations in rennet gelation properties

Individual milk samples were used to investigate how much of the variation in rennet gelation properties that can be explained by variation in milk composition by linear regression using the ordinary least squares method so as to optimise cheese milk. Natural variation in casein (CN) content was shown to have a large effect on gel strength but did not affect gel formation kinetics. Ionic calcium concentration was more important for initial gel formation whereas total calcium content is a better predictor for the developed gel structure. Of the individual milk proteins, κ-CN had the largest effect on gelation explaining up to 20% of the variation in gel forming kinetics and gel strength, while post-translational modifications of κ-CN did not explain more variation than total κ-CN. However, the relative concentration of glycosylated κ-CN seems to be more important for gel-build-up kinetics and un-glycosylated κ-CN for the gel-structure.

Milk curd self-segmentation in cheesemaking tank

The purpose of this work is to describe and study the previously unknown phenomenon of self-segmentation of a milk curd in an open-type cheesemaking tank. Based on the analysis of the kinetics of gel formation, it has been determined that self-segmentation of the gel begins near the gel point, develops over several tens of seconds, and becomes stable as the gel condenses. The segments in the milk curd do not have a definite regular shape; their average size varies from 5 to 50 cm. The shape and size of the segments do not repeat and do not correlate with the type of cheese being produced. The displacement of the segments of the milk curd in the cheesemaking tank relative to each other in height is from 0.5 to 2 mm. The width of the boundary layer between the curd segments increases during the secondary phase of gelation from 3 to 10 mm. As a result of experimental studies, it has been shown that self-segmentation of milk gel is caused by thermogravitational convection, which forms Benard convection cells. A description of a possible mechanism of milk gel self-segmentation in open-type cheesemaking tanks is proposed. The effective role of fat globules in the mechanism of self-segmentation of the milk curd has been noted. It has been suggested that self-segmentation of the milk curd in the cheesemaking tank may cause some organoleptic defects in the finished cheese, in particular inhomogeneity of texture and color.

Saccharomyces cerevisiae improves rennet-induced gelation of ultra-high temperature milk

Heating milk at high temperatures impairs its renneting properties, but rennet-induced curds can be formed from ultra-high temperature (UHT) milk inoculated with Saccharomyces cerevisiae. Herein, we measured physicochemical indices of UHT milk inoculated with S. cerevisiae before rennet addition, monitored the kinetics of gel formation, and investigated the physicochemical properties and microstructure of rennet-induced curds to explore the mechanisms by which S. cerevisiae influenced rennet-induced gelation of UHT milk. Compared with untreated pasteurized cow milk and UHT milk, the ethanol content was increased, the pH was decreased, the particle size and ζ-potential were increased, the time points at which the elasticity index began to increase were advanced, and the maximum elasticity index was increased for UHT milk inoculated with S. cerevisiae. The number of S. cerevisiae cells affected the structure of rennet-induced curds; with few cells added, the protein network of curds was continuous and tight, the mean square displacement curves showed an asymptotic behavior, and the water retention capacity and curd yield were high; with more cells added, the loosely entangled proteins aggregated, the continuity of the network was destroyed, and the curd yield decreased. In summary, a low number of S. cerevisiae cells (<1.0 × 107 cfu/mL) can increase particle size, ζ-potential, and ethanol content, and decrease pH of S. cerevisiae-inoculated UHT milk, thereby accelerating the aggregation reactions after enzymatic reaction and improving the renneting properties.

Molecular design of amphiphiles for Microenvironment-Sensitive kinetically controlled gelation and their utility in probing alcohol contents

Pyrene-laced ‘fluorescent’ amphiphiles have been designed with a C4-alkyl chain as ‘hydrophobic spacer’ and sugar moiety as hydrophilic residue. The amphiphile containing acetylacetohydrazide as a bridging unit (1) showed gel formation both in water and ethanol medium, while no gelation was observed with compound (2) with acetohydrazide as bridging unit. Accordingly, the self-assembly behavior of 1 was thoroughly investigated both in water and EtOH medium (as well as in their mixtures) in addition to their physicochemical properties. Though the gel formation kinetics was slower in water medium, the hydrogel showed superior mechanical strength (and thixotropic behavior) and improved thermal stability compared to the ethanolic gel. In water, the percolating H-bonding network with high cohesive force restricts the dynamics of the probe molecules, leading to some extent limited intermolecular interactions. However, hydrophobic interactions in water medium can result in the formation of rather ‘compact’ nano-assembly (H-type aggregation) with prominent π-π stacking interactions. Such unique solvent-dependency of 1 was further utilized to screen commercially available beverages in terms of their alcohol contents and probe adulteration in beverages. Besides, the hydrogel also showed excellent stimuli responsiveness, a gel-to-sol transition, accompanied by fluorescence color change, was observed in the presence of insulin.

Stable nanocellulose gels prepared by crosslinking of surface charged cellulose nanofibrils with di- and triiodoalkanes

Nanocellulose gels were prepared by a new chemical crosslinking approach. Carboxy group containing cellulose nanofibrils, which were prepared by (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO) mediated oxidation, were reacted with two different diiodoalkanes and one triiodoalkane in DMSO/water dispersions at elevated temperatures. Mechanically stable gels were obtained that were characterized with respect to chemical and physical properties. It was confirmed by FTIR spectroscopy that crosslinking of TEMPO oxidized cellulose nanofibrils (TCNF) occurs by the formation of ester bonds. The kinetics of gel formation were evaluated by oscillatory rheology experiments. For long alkyl chain cross-linkers, namely 1,4-diiodobutane and 1,10-diiododecane, the initial gel was formed within a short time (gel point < 5 min) and further evolved upon time for about 0.5–2 h. For the short crosslinker triiodomethane, gel formation was slower and resulted in lower mechanical strength.

Thermokinetics and rheology of agarose gel applied to bioprinting technology

The paper presents new results on the study of thermokinetics of gel system based on agarose in the process of transition from solution to gel and opposite. This issue is extremely relevant, since the stability and predictability of thermophysical and rheological properties in such transformations, especially in the presence of components of the nutrient medium and immobilized microorganisms, come to the fore in terms of design and selection of modes of operation of the printing device promising 3-D bioprinters, as well as the system of preparation and storage of the presence of the hysteresis effect, both from the point of view of the kinetics of gel formation and from the point of view of the dependence of rheological properties on temperature, at different concentrations of modifying components, is shown. The obtained results allow to draw a conclusion about the possibility of using the scheme with preliminary preparation of the initial biogel for the implementation of bioprinting technology based on agarose, and to recommend the obtained values for modeling the operating modes of devices of this type.

Interactions of Organosilanes with Fibrinogen and Their Influence on Muscle Cell Proliferation in 3D Fibrin Hydrogels.

Silanization of biomacromolecules has emerged as a fruitful approach to prepare hybrid biohydrogels. However, very little is known about interactions between organosilanes and biopolymers in solution. Here we focused on fibrin, a protein of interest in the biomedical field, whose self-assembly process and resulting gel structure are highly sensitive to experimental conditions. Three main silanes were selected to decipher the relative influence of the silanol groups and organic functions. Whereas no protein denaturation was observed, silanes bearing hydrophobic groups had a surfactant-like behavior and could improve the dispersion of fibrinogen molecules, impacting gel formation kinetics and rheological properties. 3D cultures of myoblasts evidenced that organosilanes could promote or impede cell proliferation, suggesting interactions of silanols with fibrin. These results demonstrate that the two sides of the coin of organosilane reactivity are relevant at different stages of fibrin gel formation and must be considered for future development of hybrid biomaterials.

Agarose Gels with Bioresorbable Additives: the Kinetics of the Formation, Structure, Some Properties

For the purposes of prospective use in the creation of bioreactors by additive technology studied some properties of agarose gel of different concentrations with the addition of bioresorbable components. For investigation of the kinetics of gel formation the spectroscopic method was used. The decomposition of the spectrum of the radiation allows one to get more information about the state of the gel. The dependences of the spectral characteristic of the formation of a complex dispersed system on temperature were obtained. Evaporation of liquid from their surface, a process of gel relaxation, presents interest for practical usage. Liquid evaporation from gel mixture surface was studied. Dependencies of liquid evaporation from time were obtained for mixtures of agarose and starch. A non-linear dependency of evaporation speed was observed for all sets of mixtures. It was shown that presence of starch inhibits the process of liquid evaporation. The heat-conducting properties of agarose gel of different concentrations with the addition of bioresorbable components were investigated. It is shown that the study of the thermal properties of the gel should be carried out when it is heated.

Mechanism of Thermal Degradation-Induced Gel Formation in Polyamide 6/Ethylene Vinyl Alcohol Blend Nanocomposites Studied by Time-Resolved Rheology and Hyphenated Thermogravimetric Analyzer Fourier Transform Infrared Spectroscopy Mass Spectroscopy: Synergistic Role of Nanoparticles and Maleic-anhydride-Grafted Polypropylene.

In this study, polyamide 6 (PA) is blended with ethylene vinyl alcohol (EVOH) to yield packaging materials with a balance of mechanical and gas barrier properties. However, the formation of gel-like structures in both polymers because of thermal degradation at high temperatures leads to a processing challenge, particularly during thin-gauge film extrusion. To address this challenge, nanoclays are introduced either directly or via a masterbatch of maleic-anhydride-grafted polypropylene to the PA/EVOH blend and time-resolved rheometry is used to study the effect of different modes of nanoclay incorporation on the kinetics of thermo-oxidative degradation of PA/EVOH blend and its nanocomposites. Time-resolved rheometry measurements allow the acquisition of accurate frequency-dependent linear viscoelastic behavior and offer insights into the rate of degradation or gel formation kinetics and cross-link density. The thermal degradation was studied by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy and mass spectroscopy, allowing the prediction of the possible reactions that take place during the rheological property measurements. The results show that when nanoclays are incorporated directly, the oxidative reactions occur faster. In contrast, in the masterbatch method, oxidative degradation is hindered. The difference in the behaviors is shown to lie in the different nanoclay distributions in the blends; in the blends prepared by the masterbatch method, the nanoclays are dispersed at the interface. In conclusion, the masterbatch-containing blend nanocomposite would benefit processing and product development.

Gels of Amyloid Fibers.

Protein self-assembly and formation of amyloid fibers is an early event of numerous human diseases. Continuous aggregation of amyloid fibers in vitro produces biogels, which led us to suspect that amyloid plaques and neurofibrillary tangles in Alzheimer’s disease are of biogels in nature. We applied atomic force microscopy, size exclusion chromatography, and differential scanning calorimetry to elucidate the gel’s structure, kinetics of gel formation, and melting point. We found that (1) lysozyme gelation occurs when the protein concentration is above 5 mg/mL; (2) nonfibrous protein concentration decreases and plateaus after three days of gel synthesis reaction; (3) colloidal lysozyme aggregates are detectable by both atomic force microscopy (AFM) and fast protein liquid chromatography (FPLC); (4) the gels are a three-dimensional (3D) network crosslinked by fibers coiling around each other; (5) the gels have a high melting point at around around 110 °C, which is weakly dependent on protein concentration; (6) the gels are conductive under an electric field, and (7) they form faster in the presence than in the absence of salt in the reaction buffer. The potential role of the gels formed by amyloid fibers in amyloidosis, particularly in Alzheimer’s disease was thoroughly discussed, as gels with increased viscosity, are known to restrict bulk flow and then circulation of ions and molecules.

Carbohydrate-supramolecular gels: Adsorbents for chromium(VI) removal from wastewater

HypothesisTo overcome the contamination of water by heavy metals the adsorption of the pollutant on gel phases is an attractive solution since gels are inexpensive, potentially highly efficient and form a distinct phase while allowing diffusion of the contaminated water throughout the material. This work tests the chromium(VI) adsorbent capacity of new supramolecular gels for Chromium(VI) removal from wastewater. ExperimentsFirst hydrophobic imidazolium salts of carbohydrate anions were synthesised as new gelators. Subsequently, they were dissolved in a solvent by heating and, after cooling overnight, to give the formation of supramolecular gels. The properties of the resulting gels, such as thermal stability, mechanical strength, morphology, rheology, and kinetics of gel formation, were studied as a function of gelator structure, gelation solvent and pollutant removal efficiency. FindingsCarbohydrate-derived gels showed the best removal capacity, i.e. 97% in 24 h. Interestingly, in one case, the reduction of chromium(VI) to chromium(III) also occurred after the adsorption process, and this phenomenon has been analysed using 1H NMR spectroscopy, IR spectroscopy, and SEM. The most efficient gel can reach an adsorption capacity of 598 mg/g in contrast to a value of 153 mg/g for the most effectively best hydrogels reported to date. The new gel can be also recycled up to 4 times. These findings suggest that these new, supramolecular hydrogels have potential applications in environmental remediation.

The effect of bioresorbable additives and micro-bioobjects on gel formation, stabilization and thermophysical properties

The same properties of agarose gels containing neutral bioresorbable additives and living microorganisms which are important for use in additive technologies of bioreactors creation were considered. Data on the kinetics of gel formation from the solution during cooling were obtained by spectroscopic measurement by measuring the shift of the maximum spectrum of light passing through the gel, depending on the temperature. The dynamics of aging was investigated for gels of different concentrations of agarose, bioresorbable additives and living cells. The time dependences of the decrease in the optical transparency of such gels during the aging process, characterizing the changes in their structure, were obtained. Special attention was paid to the effect of liquid evaporation from gels in the process of gel formation and during long-term storage on relaxation processes leading to their spontaneous increase in density. Experiments were performed to determine the dynamics of the temperature fields simultaneously with heat flux measurements during the formation of studied gels with different concentrations. On the basis of the obtained experimental data and previously developed method, the thermophysical coefficients of agarose gels containing an admixture of starch and living yeast cells were calculated.

Complexation of κ-carrageenan with gelatin in the aqueous phase analysed by 1H NMR kinetics and relaxation

The 1H NMR spectroscopy is used to study the kinetics of gelation in the aqueous mixtures of κ-carrageenan with gelatin. The time dependence of NMR signals intensities shows that the kinetics of gel formation consists of classical ‘fast’ (rate constant k≈6h−1) and ‘slow’ (k≈1h−1) periods, corresponding to a coil→helix transition and subsequent aggregation of helices. Upon increase of the κ-carrageenan/gelatin (w/w) ratio Z the rate of the fast process slows down by a factor of 1.6–2.4. Further analysis was done by studying the dependence of spin-spin relaxation times of protons of gelatin on Z in the aqueous phase. A qualitative scheme describing hydrogel formation in the complex solution is given. It is hypothesized that at higher concentration of PECs the hydrogel structure network is stabilized by three types of nodes: triple helices of gelatin and intra-/inter-molecular double helices of κ-carrageenan.

Preparation of nanostructured titania thin films by sol–gel technology

This study is concerned with the preparation of hydrolytically active heteroligand complex [Ti(OC4H9)3.61(O2C5H7)0.39] from titanium butoxide and acetylacetone and with the gel formation kinetics in a solution of this complex upon hydrolysis and polycondensation. Single-layer and double-layer thin films of a solution of this precursor were coated on polished silicon substrates using the dip-coating method. The crystallization of nanostructured titania films during the heat treatment of these xerogel coatings was studied using various protocols; the anatase–rutile phase transition temperature was found to depend on the film thickness. The effects of the precursor solution viscosity on the film thickness and crystallite size were determined.

Preparation of nanostructured thin films of yttrium aluminum garnet (Y3Al5O12) by Sol—Gel technology

The synthesis of hydrolytically active heteroligand coordination compounds [M(C5H7O2)3‒x(C5H11Oi)x] (M = Fe3+ and Y3+) using iron and yttrium acetylacetonates has been studied. The gel formation kinetics in solutions of these compounds upon hydrolysis and polycondensation has also been studied. Thin films of a solution of these precursors have been applied to polished sapphire substrates by dip coating technology. The crystallization of nanostructured yttrium iron garnet (Y3Fe5O12) films during heat treatment of xerogel coatings under various conditions has been studied. How the phase composition, microstructure, and particle size depend on the synthesis parameters has been recognized.

Gelling characteristics and rheology of kappa/iota-hybrid carrageenans extracted from Mastocarpus stellatus dried at different temperatures

The effect of the seaweed drying temperatures (35, 45, 55 and 85 °C), prior to the biopolymer extraction, on the rheological properties of kappa/iota-hybrid carrageenan (KI) gels in NaCl extracted from Mastocarpus stellatus seaweed is reported, together with the thermal stability of obtained gels. The average molecular mass (ranged between 2.25 × 106 and 1.02 × 106 kg kmol−1) of extracted KI, determined by gel permeation chromatography, and estimated intrinsic viscosities (ranged between 0.935 and 0.258 m3 kg−1), conducted in a capillary viscometer, decreased with increase of the seaweed drying temperatures. The parameters (K and a) of the Mark-Houwink-Sakurada (MHS) equation for KI are also reported. Thermo-rheological oscillatory measurements were conducted in a stress-controlled rheometer in order to clarify the kinetics of gel formation and to characterize the structure of the matured gels. Rheological results indicated a weakening of the KI gelling properties at smaller average molecular masses (i.e. larger seaweed drying temperatures, above 45 °C). Even so, KI samples exhibited stable and weak gel properties (i.e. elastic modulus <200 Pa). KI gels reached stability after 20 min of maturation. Cooling and heating profiles showed a strong temperature dependency. Gel setting temperatures significantly depended on the biopolymer content, whereas gel melting temperatures (68.0 ± 0.3 °C) were unvaried. No complete thermal stability was observed for gels formed with tested biopolymers, the most thermal stable being those prepared with KI with larger molecular masses (i.e. lower seaweed drying temperatures, below 45 °C).

Effect of hydrophobic inclusions on polymer swelling kinetics studied by magnetic resonance imaging

The rate of drug release from polymer matrix-based sustained release formulations is often controlled by the thickness of a gel layer that forms upon contact with dissolution medium. The effect of formulation parameters on the kinetics of elementary rate processes that contribute to gel layer formation, such as water ingress, polymer swelling and erosion, is therefore of interest. In the present work, gel layer formation has been investigated by magnetic resonance imaging (MRI), which is a non-destructive method allowing direct visualization of effective water concentration inside the tablet and its surrounding. Using formulations with Levetiracetam as the active ingredient, HPMC as a hydrophilic matrix former and carnauba wax (CW) as a hydrophobic component in the matrix system, the effect of different ratios of these two ingredients on the kinetics of gel formation (MRI) and drug release (USP 4 like dissolution test) has been investigated and interpreted using a mathematical model.

The interplay of aggregation, fibrillization and gelation of an unexpected low molecular weight gelator: glycylalanylglycine in ethanol/water.

Hydrogels formed by polypeptides could be much-favored tools for drug delivery because their main ingredients are generally biodegradable. However, the gelation of peptides in aqueous solution generally requires a minimal length of the peptide as well as distinct sequences of hydrophilic and hydrophobic residues. The aggregation of short peptides like tripeptides, which are relatively cheap and offer a high degree of biodegradability, are generally thought to require a high hydrophobicity of their residues. We found that contrary to this expectation cationic glycylalanylglycine in 55 mol% ethanol/45 mol% water forms a gel below a melting temperature of ca. 36 °C. A pure hydrogel state can be obtained after allowing the ethanol component to evaporate. The gel phase consists of crystalline fibrils of several 100 μm, which form a sample-spanning network. Rheological data reveal a soft elastic solid gel. We investigated the kinetics of the various processes that lead to the final gel state of the ternary mixture by a unique combination of UV circular dichroism, infrared, vibrational circular dichroism (VCD) and rheological measurements. A mathematical analysis of our data show that gelation is preceded by the formation of peptide β-sheet like tapes or ribbons, which give rise to a significant enhancement of the amide I' VCD signal, and the subsequent formation of rather thick and long fibrils. The VCD signals indicate that the tapes exhibit a right-handed helicity at temperatures above 16 °C and a left-handed helicity below. The tapes'/ribbons' helicity change occurs at a temperature where the UVCD data reflect a relatively long nucleation process. The kinetics of gel formation probed by the storage and loss moduli are composed of a fast process that follows tape/ribbon/fibril formation and is clearly identifiable in a movie that shows the gelation process and a slow process that causes an additional gel stabilization. The rheological data indicate that left-handed fibrils observed at low temperatures form a more solid-like structure than their right-handed counterparts formed at higher temperatures. Taken together our data reveal GAG as an unexpected gelator, the formation of which is underlied by a set of distinguishable kinetic processes.

Influence of borate amount on the swelling and rheological properties of the Scleroglucan/borax system

ABSTRACTScleroglucan is a fungal polysaccharide that, when dispersed in water, assumes a very stable triple helix structure. It has numerous industrial applications in different fields, such as food industry, cosmetics, and pharmaceutics. In the presence of borate ions, this polymer forms weak gels that, after freeze‐drying and compaction, show an anisotropic swelling behavior, related to the borate/polymer ratio. By monitoring the evolution of the elastic and viscous moduli it was possible to follow the gel formation kinetics. The rheological properties of the network were studied as a function of crosslinking agent concentration and the corresponding flow curves and mechanical spectra were recorded. The kinetics of the crosslinking reaction was monitored by following the time evolution of the storage and loss moduli, after the addition of borate ions to the Scleroglucan system. Creep‐recovery experiments allowed acquiring recoverable strain values and those of the critical stress above which a very high compliance of the sample is reached. Obtained results are to be related to the specific type of bonds between the polysaccharide chains and the crosslinking agent. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42860.