Changes In Gel Structure Research Articles

Solubilization of Phenols in Anionic Polyelectrolyte Gels with Adsorbed Cationic Surfactant

Solubilization isotherms for various phenols in cetylpyridinium chloride (CPC)-polyelectrolyte gel aggregates have been determined in order to compare solubilization within these aggregates with that in free micelles and to examine the effects of gel chemistry and structure on solubilization. The isotherms describing solubilization are quite similar to those found for free surfactant in solution. Solutes that are more hydrophobic give rise to larger solubilization constants with trends similar to what is seen for hydrophobic effects in adsorption from aqueous solutions onto hydrophobic solids. The solubilization constants decrease as the fraction of solute in the aggregates increases, indicating that the solutes partition into the palisade region of the aggregates. Solubilization is found to be quite insensitive to changes in gel structure (cross-linker varying from 1% to 3%) and chemistry (poly(acrylic acid) versus poly(methacrylic acid) and neutralization from 50% to 100%). However, the switch from poly(acrylic acid) to poly(methacrylic acid) did give rise to a slight decrease in magnitude of the slope of the isotherm. The most significant factors appear to be the initial concentration of surfactant in solution and the ratio of surfactant solution to gel amount. A decrease in surfactant concentration (especially combined with an increase in solution volume) gives rise to a decrease in solubilization constants.

A novel pH- and ionic-strength-sensitive carboxy methyl dextran hydrogel

A fast and simple method for the preparation of pH-sensitive hydrogel membranes for drug delivery and tissue engineering applications has been developed using carbodiimide chemistry. The hydrogels were formed by the intermolecular cross-linking of carboxymethyl dextran (CM-dextran) using 1-ethyl-(3-3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). Infrared spectra of the hydrogels suggest the formation of ester bonds between the hydroxyl and carboxyl groups in the CM-dextran. The porosity of the hydrogels produced, as shown by protein diffusion, increases in response to changes in the pH and the ionic strength of the external medium. The results show pH-dependent swelling behaviour arising from the acidic pedant groups in the polymer network. The diffusion of the protein lysozyme through the hydrogel membranes increased with increases in both pH (5.0–9.0) and ionic strength. The effect of changes of pH and ionic strength on the hydrogel's permeability was shown to be reversible. Scanning electron microscopy of these hydrogels showed that pH-dependent changes in permeability are mirrored by morphological changes in gel structure.

Encapsulating chondrocytes in degrading PEG hydrogels with high modulus: engineering gel structural changes to facilitate cartilaginous tissue production.

A major challenge when designing cell scaffolds for chondrocyte delivery in vivo is creating scaffolds with sufficient mechanical properties to restore initial function while simultaneously controlling temporal changes in the gel structure to facilitate tissue formation. To address this design challenge, degradable photocrosslinked hydrogels based on poly(ethylene glycol) were investigated. To alter the gel's initial mechanical properties, hydrogels were fabricated by varying the initial macromer concentration from 10% to 15% to 20%. A twofold increase in macromer concentration resulted in an eightfold increase in the initial compressive modulus from 60 to 500 kPa. Gel degradation was tailored by incorporating fast-degrading crosslinks that enable maximal extracellular matrix (ECM) diffusion with time and a minimal number of nondegrading (or slowly degrading) crosslinks to maintain scaffold integrity and prevent complete gel erosion during tissue formation. Chondrocytes encapsulated in these gels produced cartilaginous tissue rich in glycosaminoglycans and collagen as seen biochemically and histologically. Interestingly, mass loss appeared to more closely match tissue secretion in gels fabricated from a 15% macromer concentration. However, the spatial ECM distribution was grossly similar in all three gels. By tailoring gel degradation and controlling network evolution during degradation, gels with optimal properties can be fabricated to support initially physiologic compressive loads while simultaneously supporting the formation of a neotissue.

Rheological and microstructural changes in gels made from high and low quality sardine mince with added egg white during frozen storage

This paper examines the influence of freezing temperature (–40°C or –18°C) and frozen storage temperature (–18°C or –12°C) on gels made from two different sardine minces (M1, high functional quality; M2, low functional quality), with the addition of egg white as a gel enhancing ingredient. To characterize the washed mince, proximate analyses and protein functionality were determined. Freezing at either –40°C or –18°C caused no drastic changes in gel structure. Throughout the course of frozen storage of all samples, a decrease in the water holding capacity (WHC) was detected, along with an increase in the amount of protein soluble in 8 M urea. At 90 days the gels frozen at –40°C exhibited numerous ice micro-crystals; however, they did not affect the external appearance of the gel and had hardly any effect on gel strength, shear strength, hardness, cohesiveness or elasticity. On the other hand, at 90 days the gels frozen at –18°C and stored at either temperature exhibited large, macroscopically visible ice crystals. In these samples, gel strength and shear strength increased while hardness decreased. No definite changes attributable to mince quality were detected during frozen storage.

The Effect of Additives on the Perovskite-like Phase Formation from Bi-Ti Complex Alkoxide Solutions

Bi-Ti複アルコキシド溶液の部分加水分解の際に添加する触媒種と量が, Bi4Ti3O12 薄膜の結晶相の出現にどのような影響を与えるか調査した。その結果, 0.01mol の水のみを添加した条件でペロブスカイト-類縁相の出現率が高いことが明らかになった。本研究で合成した Bi-Ti 複アルコキシド溶液のように酢酸基を含むアルコキシド溶液の場合は,添加剤の効果が顕著であり,添加する触媒種により複アルコキシドの構造と加水分解および重縮合反応,さらには析出したフィルムのゲル構造が大きく変化したと考えることができる。またこれらの結果から,得られるセラミックス薄膜の結晶相がコントロールできる可能性が示された。

The effects of ageing on the rheological, dielectric and mucoadhesive properties of poly(acrylic acid) gel systems.

The purpose of this study was to investigate the effects of storage on the physical properties of a series of poly(acrylic acid) (PAA) hydrogels, using two dynamic techniques, oscillatory rheology and dielectric spectroscopy. Furthermore, the effects of ageing on the mucoadhesive properties were evaluated and related to the changes in structure. Three carbomers (Carbopols 934P, 974P and EX-214) and polycarbophil (Noveon AA-1) have been formulated as hydrogels with a range of neutralising agents (NaOH, triethanolamine and tromethamine). The effects of storage for six months on the gel structure were measured using oscillatory rheology and low frequency dielectric analysis. Mucoadhesive performance was studied by means of a detachment force test. A substantial decrease in the rheological storage moduli was noted for all samples, while the tan delta values remained unchanged for the majority of systems. Dielectric studies revealed that gels neutralised with triethanolamine showed a greater degree of binding of neutralising ions to the gel network than did the other two agents. It was also found by the dielectric analysis that, on storage, the distribution of ions within the gel systems changed. This may be due to the neutralising ions being liberated from the gel network into the bulk aqueous phase, thereby contributing to the decrease in rheological storage modulus. Mucoadhesion studies indicated that, despite the substantial changes in gel structure, there was no alteration in the bioadhesive force of detachment for the majority of systems during a six month period. A redistribution of cations between the polymer cluster and the bulk of medium is proposed as a possible additional mechanism of ageing of PAA hydrogels. The results obtained support the hypothesis outlined previously that the mucoadhesive strength is related to the tan delta value rather than the viscosity of the gel.

Small angle neutron scattering studies of structural characteristics of agarose gels

The 30 m small angle neutron scattering facility at the National Institutes of Standards and Technology has been used to examine neutron scattering from agarose gels formed in D 2O. Differential scattering cross sections have been acquired over a continuous range of Q between 0.005 and 0.3 Å −1. Subtle changes in gel structure are observed when pre-gelation agarose concentration is varied. Similarly, except when the gelling solution is rapidly cooled to a low temperature, the rate at which the gels are formed does not seem to have much effect. Clearer evidence of structural rearrangement is observed when the solvent quality is changed by the addition of dimethyl sulfoxide, or when the temperature of the gel is elevated above 70°C. These data are consistent with a description of a randomly structured polymer network containing discrete self-similar, hydrogen-bonded, junctions normally of minimal thickness ≈ 35–40 Å.

Study of polymer networks using paramagnetic probes: Vanadyl in chemically cross-linked polyacrylamide gels

Electron spin resonance (e.s.r.) spectra of the vanadyl probe VO(H 2O) 2+ 5 in chemically cross-linked polyacrylamide (PAA) gels with pore diameters of 7–58 Å were used to analyse the changes in gel structure as a function of temperature and solvent composition. The PAA networks were swollen by water and acetone/water mixtures containing 0.1–0.6 volume fraction of acetone. Spectroscopic evidence has been obtained that indicates the absence of bulk water in all the networks studied. Depending upon experimental conditions, bimodal distributions of pore sizes have been detected for all networks. The appearance of this distribution is triggered by lowering the gel temperature in networks swollen by water; alternatively, the bimodal distribution appears for a homogeneous gel at a constant temperature, by adding acetone to the swelling fluid. Unlike the ionic gels, the transition from a homogeneous PAA gel to a gel having a bimodal distribution of pore sizes is gradual as a function of temperature in water swollen gels, and of the acetone content in gels swollen by the solvent mixtures. The microviscosity in the pores appears to depend on the free volume in the pores; this is evident from the Fujita-Dolittle plots in PAA swollen by water, at three different temperatures.

Immunochemistry of counterimmunoelectrophoresis and the effect of electroendosmotic flow on reactivity

During investigation concerning the application of counter immunoelectrophoresis (CEP) for the detection of hepatitis antigen (HBAg) in serum, it was decided that an understanding of both the immunochemical and physicochemical events that occurred during this form of electrophoresis was warranted. These studies were initiated, therefore, to determine those properties which were critical for ensuring reproducibility and optimal immunological reactivity. Quantitative analysis with 125I-labelled BSA in CEP shows: (1) increased sensitivity; (2) a narrower range of optimal proportions; and (3) marked asymmetry with a tendency for inhibition with higher antigen concentration, when compared to precipitation obtained with gel diffusion. Optimal reactivity, or the broadest zone of precipitation, was dependent upon serum dilution and more specifically, on electroendosmotic flow and the distribution of gamma globulin. Changes in gel structure brought about by aging or adding fixed charges were shown to increase electroendosmotic flow and to decrease serological reactivity. Optimal reactivity was obtained with minimum electroendosmosis (EE) where antigen migrated through a gradient of gamma globulin formed in the reaction zone close to the edge of the antibody well. These studies show that although increased sensitivity can be obtained in CEP, the increased sensitivity can only be assured by careful control of the electrical and physical properties of the system of which EE appeared to be the most critical factor.

The reaction of gelatin/gum arabic coacervate gels with glutaraldehyde

The consumption of glut by various gelatin/gum arabic (GGA) coacervate gels has been examined over a range of conditions. Both acid- and alkali-precursor gelatins were used to form the coacervates. Glut consumptions by several gelatin gels were also determined. All gels examined consumed 0.3 to 1.6 mmole glut/g gelatin. Acid and alkali GGA gels had similar glut uptakes at 4°C. Glut consumption by acid-precursor GGA gels increased significantly with increasing gelation temperature (4–28°C) due to temperature-dependent changes in gel structure. The use of commercial versus redistilled glut had no detectable effect upon glut uptakes. Reaction of a gel with glut caused a high degree of insolubilization as a result of intermolecular crosslink formation. Most treated gels were at least 85 wt% insoluble at 55°C in phosphate buffer after 4–28 days extraction. That fraction of a gel solubilized by the extraction process contained both gelatin and gum arabic. Thus, despite the fact that gum arabic has little tendency to react with glut, it is effectively entrapped in the crosslinked GGA gel structure. Gels with lowest glut uptakes were the most soluble ones. They also were the only ones with solubilities that increased upon treatment with NaHSO 3 before the gel fraction extraction process. Insolubilization of GGA gels by glut causes their swelling behavior and composition to become essentially independent of pH. Composition and swelling behavior of uncrosslinked gels vary markedly with pH due to the reversible nature of the intermolecular bridges responsible for gelation.

RELATIONSHIPS BETWEEN BINDING QUALITY OF MEAT AND MYOFIBRILLAR PROTEINS V. Effect of ‘Setting’ and Pyrophosphate on Rheological Properties of Heated Minced‐Meat Gel

Abstract‘Setting’ was observed in minced hen meat stored with 3.5% wt/wt added NaCl. When gels were made from the ‘set’ sol the breaking energy was greatly increased and the relaxation modulus was characterized by a wide ‘quasi‐equilibrium’ region. The effect of added pyrophosphate on the rheological properties of the gel prepared at pH 6.0 from ground ‘set’ sol was very similar to that previously observed for ATP in gels prepared at pH 6.0 from ‘unset’ sols. When pyrophosphate or ATP were added at pH 7.0 to the ‘unset’ minced meat sol, the strain at the breaking point and the ratio of the equilibrium to the instantaneous modulus of the heated gel were increased. A comparison with previous results from a model system suggests that pyrophosphate brings about a change in gel structure by dissociating ‘myosin B’ into myosin A and F‐actin.

On the coagulation of muscle plasma. II.―The solubility of myosin

It is a matter of some importance in the physiology of muscle whether myosin, the water-insoluble globulin of muscle, is in the dispersed (sol) or solid (gel) state, and whether it is capable under physiological conditions, such as during contraction or in rigor mortis of changing from one state to the other. The fact of the coagulation of muscle plasma, discovered by Kühne, would suggest that the proteins are present in the soI form, but it was shown in a previous paper (smith, 1930) that it is necessary to add neutral salt to the muscle before a coagulable plasma can be expressed. A more precise study has now been made of the conditions which affect the dispersion of myosin, and the results suggest that in living muscle not more than 10% of the myosin is dispersed. In the preparation of muscle plasma freezing and/or the addition of salt are required to liquefy the remaining 90% so that the plasma may be expressed. The subsequent clotting of this expressate is of no physiological significance. It is probably due to admixture of the salt plasma with water formed from the melting muscle snow. The important fact to which these experiments draw attention is the probable necessity of finding an explanation of rigor mortis in terms of changes in gel structure rather that in terms of the precipitation of a dispersed colloid.