Protein adsorption kinetics in charged agarose gels: Effect of agarose content and modeling

The adsorption kinetics of myoglobin in charged gels of varying agarose content have been measured macroscopically, through batch uptake experiments, and microscopically, using light microscopy with gels supported in microfluidics chips. The apparent effective pore diffusivities, determined by fitting either set of rate data to the shrinking core model, were greater than the free solution diffusivity and concentration‐dependent. Moreover, the microscopically derived concentration profiles were qualitatively different from the predicted ones. Therefore, a new model taking into account an assumed favorable partitioning of the protein in the pore liquid is proposed to describe the adsorption kinetics. The new model yields effective pore diffusivities that are in approximate agreement with the values determined chromatographically under nonbinding conditions and with hindered diffusion theory. In addition, it predicts concentration profiles in the gel that are consistent with those observed microscopically. The overall increase in mass transfer is attributed to the favorable partitioning of the protein in the pores at low ionic strength, which results in a greater diffusional driving force. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Macroporous temperature‐sensitive gels with fast response: Comparison of preparation methods

Application of thermo‐responsive gels as soft actuators for microfluidic devices with repeating “open–close” cycles requires high rates of water transport driven by changes in temperature. These rates are conventionally evaluated by comparison of water retention curves in T‐jump tests with fixed initial and final temperatures. A shortcoming of this method is that it does not allow changes in diffusivity with temperature to be assessed quantitatively. To characterize cooperative diffusivity of water molecules, we propose a novel approach based on modeling the responses of temperature‐sensitive gels in equilibrium swelling tests and T‐jump experiments. Analysis of observations on poly(N‐isopropylacrylamide) gels synthesized in aqueous solutions of pore‐forming agents reveals that formation of a macroporous structure in a gel is a necessary, but not sufficient condition for acceleration of water transport. The effect of cosolvents used under preparation (phenol, ethanol, methanol, diethyl ether, dioxane, sucrose, and dodecyl dimethyl benzyl ammonium bromide) on water diffusivity is studied in detail. It is shown that the most pronounced enhancement of diffusivities under deswelling and reswelling is reached when the gels are synthesized in aqueous solutions of the surfactant at subzero temperatures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46353.     

The use of environmental scanning electron microscopy for imaging the microstructure of gels for profile control and water shutoff treatments

The use of gel systems as profile control and water shutoff agents has become a wide practice in recent years for oil recovery applications. But few systematic studies have been carried out on the microstructure of gels. In this study, environmental scanning electron microscopy (ESEM) was employed to investigate the microstructure of gels in their natural state. It was directly observed that a three‐dimensional network structure formed in chromium or zirconium crosslinked polymer gels is the same as organic/ inorganic crosslinked gels. However, there is a dense flat structure in phenol resin crosslinked polymer gels or phenolic resin gels. The differences between the microstructures can be attributed to the different crosslinking sites and crosslinking density, and this affect the gel's stability at reservoir temperatures. In addition, this paper also introduced the crosslinking mechanism and macro‐morphology of the bulk gels. It can contribute to a better understanding of the gel's microstructure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39946.     

香豆素小分子有机凝胶剂的合成及其凝胶化能力的测3

本文合成了四种带有不同烷基链的香豆素衍生物(1a、1b、2a、2b).通过观察成凝胶情况发现,带有三个烷基链的香豆素衍生物2能使有机溶剂凝胶化,而烷基链的长短对成其成凝胶的影响也是非常大的.与其它化合物相比,4d具有很好的凝胶化能力.能够通过加热冷却、超声处理等方法使多种溶剂凝胶化.由于香豆素化合物具有很强的荧光且具有...     

Water‐soluble polymers and gels from the polycondensation between cyclodextrins and poly(carboxylic acid)s: A study of the preparation parameters

Native cyclodextrins (CDx) and some of their derivatives were reacted with poly(carboxylic acid)s (PCAs) [citric acid (CTR), 1,2,3,4‐butanetetracarboxylic acid (BTCA), and poly(acrylic acid) (PAA)]. These reactions were carried out in the dry state at a temperature greater than 140°C in air or in vacuo. They resulted in water‐soluble and insoluble polymers formed by polyesterification between CDx and PCA. In this study, the parameters of the reaction were studied, and their influence on the water solubility or swellability of the obtained polymers was investigated. High reaction temperatures, high PCA/CDx molar ratios, and long reaction times preferably yielded insoluble gels, whereas softer conditions resulted in very soluble polymers. The gels could swell up to 10 times their initial volume in water, and the water‐soluble fraction had a solubility of 1 g/mL. A reaction mechanism was proposed that required the use of PCA carrying at least three neighboring carboxylic groups (CTR, BTCA, and PAA), and it was confirmed experimentally by the unsuccessful use of some dicarboxylic acids. A preliminary characterization by Fourier transform infrared spectroscopy and size exclusion chromatography was also conducted. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 433–442, 2005     

Influence of thermal treatments on the structure and stability of gelatin gels

The influence of thermal history on the structure of gelatin gels has been investigated by measuring the specific optical rotation [α]_λ at λ = 436 nm. The helix content χ in the gels was derived by reference to the native collagen. Two types of thermal treatments have been applied: (a) cooling and heating at constant rates, and (b) quenching and annealing for long periods. Our results support the idea that the gels are non-equilibrium systems and exhibit thermal hysteresis. The kinetics of helix formation were analysed by the Avrami theory and compared to other techniques. The stability of the structures formed suggests the existence of several mechanisms of hydrogen bonding of the helices: disordered aggregation or partial collagen renaturation.     

Understanding the role of d-Allulose and soy protein addition in pectin gels

d -Allulose (a monosaccharide and C3 epimer of fructose), one of the common rare sugars is getting attention due to its low caloric values. In this study, d -Allulose was used as a replacement of sucrose at different ratios (d -Allulose/Sucrose: 35/0, 20/15, 10/25, 0/35) to formulate pectin-based soft confectionery gels. Soy protein isolate was also added to increase the protein content. Physical properties, such as hardness, moisture content, pH, and color, were measured for the gels. Higher hardness values were obtained for the soy protein containing gels due to pectin–soy protein interaction (p < 0.05). Also, higher moisture content was observed in soy protein containing gels (p < 0.05). In addition, nuclear magnetic resonance T₂ relaxation times were measured at low field (~0.5 T) to determine how the water distribution in the samples changed and to observe how d -Allulose affected the polymer–water interactions. The study also showed that the presence of d -Allulose increased the crystallization tendency (% crystallinity of 7.9) of the pectin gels. X-ray diffraction results showed the d -allulose peaks at 33.76 and 48.68^oθ. Morphologies of the gels were also examined by scanning electron microscope. Sugar type and soy protein isolate addition were found to have significant impact on the gel formulations.     

Study of the rheological properties and solution microstructure of progressively cross-linked aqueous gels

A stepwise cross-linking polyacrylamide hydrogel was prepared using the laboratory homemade stepwise crosslinker PVC-PP-Cr and partially hydrolyzed polyacrylamide. The microstructure was investigated by using the scanning electron microscope and dynamic light scattering. The results show that the system has a controllable cross-linking time of 4 ~ 6 h, good heat resistance, and maximum gel strength of >300,000 mPa.S. In terms of viscoelastic behavior, a stepwise cross-linking process between crosslinker and hydrolyzed polyacrylamide (HPAM) is presented, and the viscoelasticity is increased step by step. During the stepwise cross-linking process, the dendritic structure, network structure and lamellar structure to a stable spatial network structure is obtained. Here, the cross-linked structure between polymer molecular chains is formed after addition of the crosslinker, which increases the steric hindrance of macromolecular chains and further enhances the stability of the system. With the gradual release of chromium ions from the PVC-PP-Cr stepwise crosslinker, the gel system is formed continuously. When intermolecular friction stopped increasing, intermolecular entanglement and interaction are enhanced, and elasticity is also increased.     

Stabilization of pluronic gels in the presence of different polysaccharides

Several different polysaccharides have been added to pluronic F127 (poloxamer 407) gels to test their ability to stabilize the gels against dissolution in aqueous media over time. The studied polysaccharides include κ‐carrageenan, chitosan, hyaluronic acid, pectin, alginate, hydroxyethylcellulose, and ethyl(hydroxyethyl)cellulose. Although all the considered polysaccharides slowed down the dissolution time of the pluronic gels, unmodified polysaccharides only had a modest stabilization effect. However, hydrophobic modification of polysaccharides with a sufficiently long hydrocarbon chain (C₁₆) was found to partly prevent the gels from dissolving for more than 6 months. Shorter hydrocarbon chains did not have the same effect, even at high degrees of hydrophobicity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40465.     

Thermogelation of methylcellulose from solution in N,N‐dimethylformamide and characterization of the transparent gels

A transparent gel was prepared through the cooling of a methylcellulose (MC) solution in N,N‐dimethylformamide (DMF) at 80°C to a lower temperature. The temperature at which gelation occurred was dependent on the concentration of the solution. The gel temperature increased with an increase in the concentration of MC. The gelation of MC in DMF was studied by means of optical microscopy (OM), differential scanning calorimetry, and dynamic mechanical analysis (DMA). The OM studies revealed the presence of loosely bound beads of MC with DMF at a lower concentration. These beads became interconnected to rods, and subsequently, a continuous, thick gel was formed as the concentration increased. From DMA studies, it was observed that the loss modulus of the gel crossed over the storage modulus at two different frequencies. This indicated the presence of two types of network structures generated from the weak and strong associations of MC with the organic solvent DMF. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Modeling the rheology of gelatin gels for finite deformations. Part 2. Viscoelastic solid model

The viscoelastic solid model proposed in this work can predict the rheological responses of gelatin gels for finite deformations. This rheological model considers a degree of physical cross-links at a given maturation time, which is partially attained from those links totally available when a pure elastic network is achieved. Thus, both an elastic network formed by permanent links on the average and a viscoelastic network composed of the remaining adaptive links are described at each maturation time. This model for gelatin gels considers appropriately the interplay between the networks involving: (a) viscoelastic relaxation as a consequence of an imposed mechanical history, (b) average degree of physical cross-links in the partially generated permanent network acting in the short-term mechanical response. In this context of analysis the standard viscoelastic solid is obtained asymptotically for small deformations. Also the effect of shear rate on the shear test is studied and the braking phenomenon is analysed in relation to the formation of microstructure by considering viscoelastic parameters.     

Modeling the rheology of gelatin gels for finite deformations. Part 1. Elastic rheological model

The rheological behavior of gelatin gels is studied through a constitutive equation derived in the literature from the classical hyperelasticity theory by using a nonlinear strain energy density. Gelatin gels are assumed to be an elastic solid here, which at a given maturation time has a degree of physical cross-links composing a permanent elastic network. It is also studied in particular: (a) the validation of the elastic rheological model proposed here in relation to the prediction of two data sets pertaining to different experimental tests (shear and simple compression) by using fixed values of rheological parameters, (b) the increase of the stress-strain nonlinearity with increasing maturation time, at a given protein concentration, (c) the evolution of the stress-strain nonlinearity with increasing gelatin concentration. It is found that gelatin gels exhibit a strong nonlinear strain energy density, which is expressed through two shear modules related to nucleation and growing of junction zones.     

Fast transient fluorescence (FTRF) technique to study swelling of densely and loosely formed gels

A Strobe Master System (SMS) is introduced for studying the swelling of cylindrical densely (DG) and loosely (LG) formed gels. Gels were prepared by free radical copolymerization of methyl (methacrylate) (MMA) and ethylene glycol dimethacrylate (EGDM). Pyrene (P) was introduced as a fluorescence probe during polymerization, and the lifetimes of P were measured using (SMS) during in situ swelling processes. Chloroform was used as a swelling agent. A model is derived for low quenching efficiencies to measure mean lifetimes 〈τ〉 of P, and it was observed that 〈τ〉 values decreased as the swelling proceeded. The Li‐Tanaka equation was employed to determined the time constants, τ_c, and cooperative diffusion coefficients, D_c, which were found to be around 400 min and 10⁻⁵ cm²s⁻¹, respectively. No differences were detected in τ_c and D_c values of DG and LG gels. Quenching rate constants, κ, and the mutual diffusion coefficient, D_m, were measured and found to be around 10⁵ M⁻¹s⁻¹ and 10⁻¹⁰ cm²s⁻¹ for DG and LG gel samples. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1494–1502, 2000     

Evaluation of pH‐sensitive hydrogels to control the permeability anisotropy of oil reservoirs

In stratified or fractured oil reservoirs, the oil recovery efficiency tends to be low as the injected fluid flows mainly through the matrix's most permeable regions, leaving behind part of the displaceable oil in the matrix's unswept zones. Given this issue, this study aims to evaluate the potential of applying seven commercial samples, based on poly(acrylic acid), to control the anisotropic permeability profile of reservoirs. To perform this study, first, continuous and oscillatory shear tests were conducted to characterize the hydrogel's rheological and viscoelastic behavior in various subsurface conditions (salinity, temperature, and/or pH value). Second, polymer dispersion elution tests were performed in a porous medium to evaluate the matrix's permeability reduction after treatment with hydrogels. The seven commercial samples were classified as pseudoplastic fluids at pH values ranging from 1 to 10. Under typical reservoir conditions, PAAr 70 (which has intermediate molar mass and intermediate number of crosslinks) was the only sample to behave as a strong gel (G′/G″ > 10). Elution tests confirmed that the PAAr 70 hydrogel gelified inside the consolidated sandstone plugs and reduced the matrix's permeability four‐fold. Therefore, samples based on poly(acrylic acid) with high crosslink density proved to be the most promising for controlling the anisotropic permeability profile of heterogeneous oil reservoirs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40665.     

A SAXS study of the structure of gels formed by mixtures of polyoxyalkylene triblock copolymers

Small‐angle X‐ray scattering was used to characterise aqueous micellar gels of triblock copolymers E₁₃₇S₁₈E₁₃₇, E₈₂S₉E₈₂, E₇₆S₅E₇₆, E₆₂P₃₉E₆₂, and of two mixtures: E₁₃₇S₁₈E₁₃₇ and E₆₂P₃₉E₆₂ (Mix 1) and E₈₂S₉E₈₂ and E₆₂P₃₉E₆₂ (Mix 2), each 50/50 wt%. E = oxyethylene, CH₂CH₂O; S = oxyphenylethylene, OCH₂CH(C₆H₅); and P = oxypropylene, OCH₂CH(CH₃). Within the concentration and temperature ranges investigated (30–40 wt% copolymer, 20–80 °C), spherical micelles of copolymers E₁₃₇S₁₈E₁₃₇, E₈₂S₉E₈₂ and E₆₂P₃₉E₆₂ packed into body‐centred cubic (BCC) structures. Gels of E₇₆S₅E₇₆ were stable only at high concentrations and low temperatures, and a 70 wt% copolymer solution at T = 30 °C formed a hexagonal gel consistent with cylindrical micelles. It is likely that the mixed copolymers would form two distributions of micelles, and more complex structures were expected. However, gels of Mix 2 had well‐ordered BCC structures, while the less ordered gels of Mix 1 were also best characterised as BCC. Copyright © 2006 Society of Chemical Industry     

Partial removal of protein associated with arabinoxylans: Impact on the viscoelasticity,crosslinking content,and microstructure of the gels formed

Arabinoxylans (AX) treated with protease and dialyzed (AXP) or only dialyzed (AXD) formed gels showing an increase in the elastic modulus G′ (1291 and 1419 Pa, respectively) and the ferulic acid dimers (3.34 and 3.10 μg/mg polysaccharide, respectively) and trimers (0.51 and 0.53 μg/mg polysaccharide, respectively) in comparison to AX gels (767 Pa, 0.56 and 0.12 μg/mg polysaccharide, respectively). Nevertheless, the G′ values and crosslinking contents were not different among the AXP and AXD gels, suggesting that the amount of protein removed (54%) does not affect these parameters. Confocal laser scanning microscopy analysis showed that AXP treatment promotes the homogeneity of the gels. In addition, scanning electron microscopy observations indicated that AXD and particularly AXP gels had a more compact microstructure. Thus, the partial removal of protein associated with AX does not impact the viscoelasticity and crosslinking content of the gels formed but could improve their microstructural characteristics. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47300.     

Rheological destructuring of aqueous gels composed of cellulose ethers following storage in the presence of redox agents

Despite their widespread use, there is a paucity of information concerning the effect of storage on the rheological properties of pharmaceutical gels that contain organic and inorganic additives. Therefore, this study examined the effect of storage (1 month at either 4 or 37°C) on the rheological and mechanical properties of gels composed of either hydroxypropylmethylcellulose (3–5% w/w, HPMC) or hydroxyethylcellulose (3–5% w/w, HEC) and containing or devoid of dispersed organic (tetracycline hydrochloride 2% w/w) or inorganic (iron oxide 0.1% w/w) agents. The mechanical properties were measured using texture profile analysis whereas the rheological properties were analyzed using continuous shear rheometry and modeled using the Power Law model. All formulations exhibited pseudoplastic flow with minimal thixotropy. Increasing polymer concentration (3–5% w/w) significantly increased the consistency, hardness, compressibility, and adhesiveness of the formulations due to increased polymer chain entanglement. Following storage (1 month at 4 and 37°C) the consistency and mechanical properties of additive free HPMC gels (but not HEC gels) increased, due to the time‐dependent development of polymer chain entanglements. Incorporation of tetracycline hydrochloride significantly decreased and increased the rheological and mechanical properties of HPMC and HEC gels, respectively. Conversely, the incorporation of iron oxide did not affect these properties. Following storage, the rheological and mechanical properties of HPMC and HEC formulations were markedly compromised. This effect was greater following storage at 37 than at 4°C and, additionally, greater in the presence of tetracycline hydrochloride than iron oxide. It is suggested that the loss of rheological/mechanical structure was due to chain depolymerization, facilitated by the redox properties of tetracycline hydrochloride and iron oxide. These observations have direct implications for the design and formulation of gels containing an active pharmaceutical ingredient. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 852–859, 2005     

Preparation of chemically crosslinked gels with maleate‐denatured poly(vinyl alcohol) and its application to drug release

Maleate‐denatured poly(vinyl alcohol) (M‐PVA) was crosslinked with heating. The mechanism of crosslinking was studied with several procedures: titration, Fourier transform infrared, and solubility. The carboxyl groups of M‐PVA consisted of carboxylates and a few free carboxyl groups. The crosslink was the ester linkage between hydroxyl and carboxyl groups. Several kinds of M‐PVA tablets were prepared under different conditions: pressures of 200–600 kgf/cm² and grain sizes of 75 (pass) to 250 μm (on). The swelling behavior of these chemically crosslinked tablets was studied in a buffer solution of pH 7.4, mainly at 37°C. Moreover, the effect of temperature from 5 to 50°C and the effect of repeated swell–dry cycles on the behavior of the tablets in a buffer solution [106 μm (on), 200 kgf/cm²] were studied. The release of p‐acetamidophenol from those tablets in the pH 7.4 buffer solution was studied. The different release patterns were due to the differences in the swelling behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1178–1184, 2002; DOI 10.1002/app.10411     

Mathematical analysis of sensors based on affinity interactions between competitive receptor-protein pairs

Affinity sensors with detection principle of competitive displacement of a responsive protein from an immobilised receptor by an analyte were subject to mathematical analysis. The model considered two competing binding reactions between the analyte and the responsive protein for the immobilised receptor in the solid phase. A cubic algebraic equation generated from the analysis was solved to get theoretical calibration curves for the sensor relating the signal generated, which is the bulk concentration of the responsive protein detected in solution, to the analyte concentration. The simulated results indicated several important system variables to consider when optimising the sensor's performance. They are the concentration of the responsive protein initially loaded, the density of the immobilised receptor, and the relative binding strength of both the analyte and the responsive protein toward the receptor. To test this model, experiments were carried out with a hypothetical sensor system, using bovine chymosin as the responsive protein, pepstatin–agarose as the immobilised receptor, and pepsin as the analyte. The model in general can describe the behavior of this type of affinity sensor reasonably well. From kinetic study of chymosin displacement in the model system, the effect of binding strength between responsive protein and receptor on the response of the sensor was also discussed.     

应用计算机设计计算低浓度气体吸收填料塔

本文就应用电子计算机计算低浓度气体填料吸收塔填料高度，提出了相应的计算方法和计算机程序。