Mechanical characterization of network formation during heat-induced gelation of whey protein dispersions

The formation of gel network structures during isothermal heating of whey protein aqueous dispersions was probed by mechanical spectroscopy. It was anticipated that the pathway of the sol-to-gel transition of whey protein dispersions is quite different from that of ordinary cross-linking polymers (e.g., percolation-type transition), since aqueous solutions of native whey proteins have been shown to be highly structured even before gelation, in our previous study. At 20 degrees C, aqueous dispersions of beta-lactoglobulin, the major whey protein, and those of whey protein isolate (WPI), a mixture of whey proteins, exhibited solid-like mechanical spectra, i.e., the predominant storage modulus G' over the loss modulus G", in a certain range of the frequency omega (1-100 rad/s), regardless of the presence or absence of added NaCl. The existence of the added salt was, however, a critical factor for determining transitions in mechanical spectra during gelation at 70 degrees C. beta-Lactoglobulin dispersions in 0.1 mol/dm(3) NaCl maintained the solid-like nature during the entire gelation process and, after passing through the gelation point, satisfied parallel power laws (G' approximately G" approximately omega(n)) that have been proposed for a critical gel (i.e., the gel at the gelation point) that possesses a self-similar or fractal network structure. In contrast, beta-lactoglobulin dispersions without added salt exhibited a transition from solid-like [G'(omega) > G"(omega)] to liquid-like [G'(omega) < G"(omega)] mechanical spectra before gelation, but no parallel power law behavior was recognized at the gelation point. During extended heating time (aging), beta-lactoglobulin gels with 0.1 mol/dm(3) NaCl showed deviations from the parallel power laws, while spectra of gels without added NaCl approached the parallel power laws, suggesting that post-gelation reactions also significantly affect gel network structures. A percolation-type sol-to-gel transition was found only for WPI dispersions without added salt.     

Effect of concentration and temperature on the rheological behavior of collagen solution

Dynamic viscoelastic properties of collagen solutions with concentrations of 0.5-1.5% (w/w) were characterized by means of oscillatory rheometry at temperatures ranging from 20 to 32.5 degrees C. All collagen solutions showed a shear-thinning flow behavior. The complex viscosity exhibited an exponential increase and the loss tangent decreased with the increase of collagen concentration (C(COL)) when the C(COL)> or =0.75%. Both storage modulus (G') and loss modulus (G') increased with the increase of frequency and concentration, but decreased with the increase of temperature and behaved without regularity at 32.5 degrees C. The relaxation times decreased with the increase of temperature for 1.0% collagen solution. According to a three-zone model, dynamic modulus of collagen solutions showed terminal-zone and plateau-zone behavior when C(COL) was no more than 1.25% or the stated temperature was no more than 30 degrees C. The concentrated solution (1.5%) behaved being entirely in plateau zone. An application of the time-temperature superposition (TTS) allowed the construction of master curve and an Arrhenius-type TTS principle was used to yield the activation energy of 161.4 kJ mol(-1).     

Unique gelation behavior of cellulose in NaOH/urea aqueous solution

A transparent cellulose solution was prepared by mixing 7 wt % NaOH with 12 wt % urea aqueous solution which was precooled to below -10 degrees C and which was able to rapidly dissolve cellulose at ambient temperature. The rheological properties and behavior of the gel-formed cellulose solution were investigated by using dynamic viscoelastic measurement. The effects of temperature, time, cellulose molecular weight, and concentrations on both the shear storage modulus (G') and the loss modulus (G") were analyzed. The cellulose solution having a viscosity-average molecular weight (M(eta)) of 11.4 x 10(4) had its sol-gel transition temperature decreased from 60.3 to 30.5 degrees C with an increase of its concentration from 3 to 5 wt %. The gelation temperature of a 4 wt % cellulose solution dropped from 59.4 to 30.5 degrees C as the M(eta) value was increased from 4.5 x 10(4) to 11.4 x 10(4). Interestingly, at either higher temperature (above 30 degrees C), or lower temperature (below -3 degrees C), or for longer gelation time, gels could form in the cellulose solutions. However, the cellulose solution remains a liquid state for a long time at the temperature range from 0 to 5 degrees C. For the first time, we revealed an irreversible gelation in the cellulose solution system. The gel having been formed did not dissolve even when cooled to the temperature of -10 degrees C, at which it was dissolved previously. Therefore, this indicates that either heating or cooling treatment could not break such stable gels. A high apparent activation energy (E(a)) of the cellulose solution below 0 degrees C was obtained and was used to explain the gel formation under the cooling process.     

Gelation behaviour of konjac glucomannan with different molecular weights

The deacetylation and gelation of konjac glucomannan (KGM) following alkali addition was investigated by Fourier transform infrared, while the rheological properties of KGM with different molecular weights were studied by dynamic viscoelastic measurements in shear mode and penetration force tests. It was found that gelation occurred after significant deacetylation had taken place. Rheometrical studies revealed that KGM with different molecular weights exhibited different gelation characteristics in small amplitude oscillatory shear flow. For the samples of fractionated KGM with lower molecular weights, a decrease in both the storage shear modulus (G') and loss shear modulus (G") was observed during gelation at temperatures above 75 degrees C. It is suggested that the decrease results from the wall slip between sample and measuring geometry owing to a rapid gelation process with syneresis and/or disentanglement of molecular chains adsorbed on the surface of parallel plates from those located in the bulk. Penetration force tests were employed to confirm the occurrence of slippage and thereby no decreases in rigidity of samples were observed during gelation. For the native KGM samples decreases in G' and G" during gelation were not observed, and it is suggested that this is due to the effect of the higher molecular weight and increased solution viscosity of these samples on the gelation kinetics.     

Viscoelastic evaluation of topical creams containing microcrystalline cellulose/sodium carboxymethyl cellulose as stabilizer

The purpose of this study was to examine the viscoelastic properties of topical creams containing various concentrations of microcrystalline cellulose and sodium carboxymethyl cellulose (Avicel(R) CL-611) as a stabilizer. Avicel CL-611 was used at 4 different levels (1%, 2%, 4%, and 6% dispersion) to prepare topical creams, and hydrocortisone acetate was used as a model drug. The viscoelastic properties such as loss modulus (G"), storage modulus (G'), and loss tangent (tan delta) of these creams were measured using a TA Instruments AR 1000 Rheometer and compared to a commercially available formulation. Continuous flow test to determine the yield stress and thixotropic behavior, and dynamic mechanical tests for determining the linear viscosity time sweep data, were performed. Drug release from the various formulations was studied using an Enhancer TM Cell assembly. Formulations containing 1% and 2% Avicel CL-611 had relative viscosity, yield stress, and thixotropic values that were similar to those of the commercial formulation. The elastic modulus (G') of the 1% and 2% formulation was relatively high and did not cross the loss modulus (G"), indicating that the gels were strong. In the commercial formulation, G' increased after preshearing and broke down after 600 seconds. The strain sweep tests showed that for all formulations containing Avicel CL-611, the G' was above G" with a good distance between them. The gel strength and the predominance of G' can be ranked 6% > 4% > 2%. The strain profiles for the 1% and 2% formulations were similar to those of the commercial formulation. The delta values for the 1% and 2% formulations were similar, and the formulations containing 4% Avicel CL-611 had lower delta values, indicating greater elasticity. Drug release from the commercial preparation was fastest compared to the formulations prepared using Avicel CL-611, a correlation with the viscoelastic properties. It was found that viscoelastic data, especially the strain sweep profiles of products containing Avicel CL-611 1% and 2%, correlated with the commercial formulation. Rheological tests that measure the viscosity, yield stress, thixotropic behavior, other oscillatory parameters such as G' and G" are necessary tools in predicting performance of semisolids.     

Scleroglucan gelation by in situ neutralization of the alkaline solution

Scleroglucan gels were prepared by neutralization of aqueous alkaline solution of scleroglucan by in situ release of acid. Transition of scleroglucan chains in a disordered state to the triple-helical state result in cross-linking of the polysaccharide. The pH and the storage and loss moduli, G' and G' ', were determined as a function of time after initiating the pH reduction. Experiments were performed in the temperature range from 20 to 90 degrees C and in the polymer concentration range from C(p) = 10-200 mg/mL. The concentration dependence of the apparent plateau value of the storage modulus showed a lower critical concentration, C(p,0), in the range 12-15 mg/mL needed for gelation and a second power dependence of G' on concentration in the range 50-200 mg/mL. In situ pH reduction was achieved using formamide (methanoic acid) or ethyl acetate (ethyl ethanoate) which hydrolyze in alkaline solution, yielding carboxylic acids. The more rapid hydrolyses of ethyl acetate compared to formamide yielded a faster decrease of pH in solution and a more rapid increase of the storage modulus. The present gelation process of scleroglucan based on the in situ reduction of pH has advantages in applications where external control of the conditions is difficult to achieve.     

Characterization of Different Substituted Carboxymethyl Starch Microgels and Their Interactions with Lysozyme

A carboxymethyl starch (CMS) microgel system was prepared for the control of uptaking and releasing proteins (lysozyme). The physicochemical properties of microgels in various degrees of substitution (DS) were determined by thermal gravimetric analysis (TGA), swelling degree, and rheological analysis. The microgel particle size mostly ranged from 25 µm to 45 µm. The result obtained from the TGA studies indicated that carboxymethylation decreased the thermal stability of starch, but crosslinking increased the thermal stability of CMS. The CMS microgels showed typical pH sensitivity, and the swelling degree of microgel increased with the increasing of DS and pH, because of the large amounts of carboxyl group ionization. The samples (2.25%) could behave as viscoelastic solids since the storage modulus was larger than the loss modulus over the entire frequency range. The protein uptake increased with increasing pH and DS at low salt concentration. The optimal pH shifted to lower pH with increasing ionic strength. The saturated protein uptake decreased with increasing ionic strength at each pH. The protein was easily released from the microgel with high pH and high salt concentration.     

Dynamic viscoelastic properties of cellulose carbamate dissolved in NaOH aqueous solution

Dynamic viscoelastic properties of cellulose carbamate (CC) dissolved in NaOH aqueous solution were systematically studied for the first time. CC was microwave-assisted synthesized from the mixture of cellulose and urea and then dissolved in 7 wt % NaOH aqueous solution precooled to -7 °C. The obtained CC solution is transparent and has good liquidity. To clarify the rheological behavior of the solution, the CC solutions were investigated by dynamic viscoelastic measurements. The shear storage modulus (G') and loss modulus (G') as a function of the angular frequency (ω), concentration (c), nitrogen content (N %), viscosity-average molecular weight (M(η)), temperature (T), and time (t) were analyzed and discussed in detail. The sol-gel transition temperature of CC (M(η) = 7.78 × 10(4)) solution decreased from 36.5 to 31.3 °C with an increase of the concentration from 3.0 to 4.3 wt % and decreased from 35.7 to 27.5 °C with an increase of the nitrogen content from 1.718 to 5.878%. The gelation temperature of a 3.8 wt % CC solution dropped from 38.2 to 34.4 °C with the M(η) of CC increased from 6.35 × 10(4) to 9.56 × 10(4). The gelation time of the CC solution was relatively short at 30 °C, but the solution was stable for a long time at about 15 °C. Moreover, the gels already formed at elevated temperature were irreversible; that is, after cooling to a lower temperature including the dissolution temperature (-7 °C), they could not be dissolved to become liquid.     

Alpha and beta mechanical dispersions in high sugar/acyl gellan mixtures

The real (G') and imaginary (G") components of the complex modulus have been measured between 0.1 and 100 rad/s in the temperature range of 70--55 degrees C for a mixture of 1% high acyl gellan with 79% glucose syrup, and 79% glucose syrup. The method of reduced variables gave superposed curves of G' and G" as a function of timescale of measurement, which matched the thermal profiles of shear modulus obtained by scanning at the constant rate of 1 degrees C/min. Data of the gellan/co-solute mixture could be analysed in terms of two distinct mechanisms. For the alpha dispersion, G' and G" superposed with the horizontal reduction factor a(T) whose temperature dependence followed an equation of the Williams-Landel-Ferry form. Mechanical spectra of the beta dispersion also superposed with the factor a(T) whose temperature dependence, however, corresponded to a constant energy of activation. Relaxation spectra have been calculated for both dispersions. Those for the alpha mechanism were attributed to the chain backbone motions and the friction coefficient per tetrasaccharide repeat unit in backbone motion was calculated from the extended Rouse theory. When the contribution of the solvent alone was studied, no spectra for the beta dispersion were observed supporting the hypothesis of the dispersion being attributed to the side-chain motions of the acyl groups. The spectra of the beta mechanism were relatively broader than for the alpha dispersion. The relative location of the beta dispersion on the time scale or temperature range was found to be between the alpha dispersion (glass transition region) and the glassy state.     

Structural changes during heat-induced gelation of globular protein dispersions

Macroscopic and molecular structural changes during heat-induced gelation of beta-lactoglobulin, bovine serum albumin, ovalbumin, and alpha-lactalbumin aqueous dispersions were probed by the mechanical and CD spectroscopy, respectively. Aqueous solutions of the native globular proteins, except for alpha-lactalbumin, exhibited solid-like mechanical spectra-namely, the predominant storage modulus G' over the loss modulus G" in the entire frequency range examined (0.1-100 rad/s), suggesting that these protein solutions were highly structured even before gelation, possibly due to strong repulsions among protein molecules. Such solid-like structures were susceptible to nonlinearly large shear but recovered almost immediately at rest. During gelation by isothermal heating, major changes in the secondary structure of the globular proteins completed within a few minutes, while values of the modulus continued to develop for hours with maintaining values of tandelta (= G"/G') less than unity. As a result, a conventional criterion for mechanically defining the gelation point, such as a crossover between G' and G", was inapplicable to these globular protein systems. beta-Lactoglobulin gels that had passed the gelation point satisfied power laws (G' approximately G" approximately omega(n)) believed to be valid only at the gelation point, suggesting that fractal gel networks, similar to those of critical gels (i.e., gels at the gelation point), were formed.     

Rheological and structural properties of aqueous alginate during gelation via the Ugi multicomponent condensation reaction

Turbidity, structure, and rheological features during gelation via the Ugi multicomponent condensation reaction of semidilute solutions of alginate have been investigated at different polymer and cross-linker concentrations and reaction temperatures. The gelation time of the system decreased with increasing polymer and cross-linker concentrations, and a temperature rise resulted in a faster gelation. At the gel point, a power law frequency dependence of the dynamic storage modulus (G' proportional, variant omega(n)(')) and loss modulus (G' ' proportional, variant omega(n)(' ')) was observed for all gelling systems with n' = n' ' = n. By varying the cross-linker density at a fixed polymer concentration (2.2 wt %), the power law exponent is consistent with that predicted (0.7) from the percolation model. The value of n decreases with increasing polymer concentration, whereas higher temperatures give rise to higher values of n. The elastic properties of the gels continue to grow over a long time in the postgel region, and at later stages in the gelation process, a solidlike response is observed. The turbidity of the gelling system increases as the gel evolves, and this effect is more pronounced at higher cross-linker concentration. The small-angle neutron scattering results reveal large-scale inhomogeneities of the gels, and this effect is enhanced as the cross-linker density increases. The structural, turbidity, and rheological features were found to change over an extended time after the formation of the incipient gel. It was demonstrated that temperature, polymer, and cross-linker concentrations could be utilized to tune the physical properties of the Ugi gels such as structure, transparency, and viscoelasticity.     

Disentangling alpha from beta mechanical relaxations in the rubber-to-glass transition of high-sugar-chitosan mixtures

The occurrence of molecular motions in addition to those of the glass-transition region (alpha mechanism) were investigated in chitosan and a branched derivative substituted with alkyl chains having eight carbon atoms. Once hydrophobic interactions of the alkyl groups in aqueous solution were demonstrated, polymers were mixed with glucose syrup at high levels of solids. The real (G') and imaginary (G") components of the complex dynamic modulus in high-solid mixtures were measured between 0.1 and 100 rad s(-1) in the temperature range from -55 to 50 degrees C. The method of reduced variables gave superposed curves of G' and G", which unveiled an anomaly in the dispersion of the alkylated derivative both in terms of higher modulus values and dominant elastic component of the polymeric network, as compared with the glass-transition region of chitosan. It was proposed that the new mechanical feature was due to beta mechanism, and master curves of viscoelastic functions and relaxation processes were constructed to rationalize it.     

Doxorubicin uptake and release from microgel thin films

We report investigations on the thermally regulated uptake and release of the chemotherapeutic drug doxorubicin from microgel thin films. A spin coating, layer-by-layer (scLbL) assembly approach was used to prepare thin films composed of thermoresponsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-AAc) microgels by alternatively exposing a 3-aminopropyltrimethoxysilane (APTMS) functionalized glass substrate to polyanionic pNIPAm-AAc microgels and polycationic poly(allylamine hydrochloride) (PAH). Using this method, 10, 20, and 30 microgel layer films were constructed with uniform layer buildup, as confirmed by quartz crystal microgravimetry (QCM). The films were subsequently loaded with doxorubicin by cycling the temperature of the film in an aqueous doxorubicin solution between 25 and 50 degrees C. Release characteristics were then examined using UV-vis spectroscopy, which revealed temperature-dependent release properties.     

Rheology and dynamic light scattering of silk fibroin solution extracted from the middle division of Bombyx mori silkworm

Dynamic light scattering (DLS) and rheological measurements were performed on aqueous silk fibroin solutions extracted from the middle division of Bombyx mori silkworm over a wide range of polymer concentration C from 0.08 to 27.5 wt %. DLS results obtained in the dilute region of C less than 1 wt % are consistent with a model that an elementary unit is a large protein complex consisting of silk fibroin and P25 with a 6:1 molar ratio. Rheological measurements in the dilute C region reveal that those units (or clusters) with the hydrodynamic radius of about 100 nm form a network extending over the whole sample volume with small pseudoplateau modulus mainly by ionic bonding between COO(-) ions of the fibroin molecules and divalent metallic ions such as Ca(2+) or Mg(2+) ions present in the sample and also that, after a yield stress is reached, steady plastic flow is induced with viscosity much lower than the zero-shear viscosity estimated from creep and creep recovery measurements by 4-6 orders of magnitude. Angular frequency omega dependencies of the storage and the loss shear moduli, G'(omega) and G' '(omega), measured in the linear viscoelastic region, indicate that all solutions possess the pseudoplateau modulus in the low omega region and samples become highly viscoleastic for C greater, similar 4.2 wt %. Above C = 11.2 wt % another plateau appears at the high omega end accompanied by a distinct maximum of G' ' in the intermediate omega region. The relaxation motion with tau = 0.5 s corresponding to the maximum of G' ' is one of characteristic properties of the fibroin solutions in the high C region. Thermorheological behaviors of the solution with C = 27.5 wt % show that the network structure formed in the MM part of the silk gland is susceptible to temperature and a more stable homogeneous network is realized by raising the temperature up to T = 65 degrees C.     

Self-association of mucin

Aggregation phenomena in aqueous solutions of purified human tracheobronchial mucin have been studied by rheological methods, steady-state fluorescence, quasielastic light scattering, and spin probe techniques. At temperatures below 30 degrees C and concentrations above 15 mg/mL and in the absence of chaotropic agents, mucin solutions are viscoelastic gels. A gel-sol transition is observed at temperatures above 30 degrees C that is manifested by the diminishing storage modulus and a loss tangent above unity throughout the studied frequency range of the oscillatory shear. No decline in the mucin molecular weight is observed by size-exclusion chromatography above 30 degrees C in the absence of redox agents or proteolytic enzymes. Aggregation of hydrophobic protein segments of the mucin chains at 37 degrees C is indicated by QELS experiments. The decreasing polarity of the microenvironment of pyrene solubilized into mucin solutions at temperatures above 30 degrees C, concomitant with the gel-sol transition, shows the hydrophobicity of the formed aggregates. ESR spectra of the fatty acid spin probe, 16-doxylstearic acid indicate that the aggregate-aqueous interface becomes more developed at elevated temperatures.     

Rheological characterization of bioadhesive binary polymeric systems designed as platforms for drug delivery implants

This study describes the formulation and characterization of binary interactive polymeric systems, designed as platforms for improved drug delivery to mucosal sites. Binary interactive systems were manufactured containing hydroxyethylcellulose (HEC; 1-5% w/w) and polycarbophil (PC; 1-5% w/w) at pH 7, and their rheological (flow and dynamic), mechanical, and mucoadhesive properties were characterized, both before and after dilution with phosphate buffered saline (designed to mimic dilution by biological fluids). Physical interactions between HEC and PC were confirmed by the observed rheological synergy. Within the binary interactive systems increasing polymer concentration increased the storage modulus (G'), loss modulus (G' '), dynamic viscosity (eta'), hardness, compressibility, consistency, and mucoadhesion yet decreased the loss tangent. This was attributed to enhanced entanglements and interactions between adjacent polymer chains. Dilution with PBS altered the above properties; however, the binary interactive systems, particularly those containing higher concentrations of HEC, still exhibited predominantly elastic properties (high G', low tan delta). In light of this, it is suggested that the rheological and mucoadhesive properties of binary interactive systems composed of HEC (5% w/w) and PC (1-3% w/w) offered particular promise as platforms for topical mucosal drug delivery systems.     

Changes in denaturation and rheological properties of collagen-hyaluronic acid scaffolds as a result of temperature dependencies

This report describes the effect of temperature on the mechanical viscoelastic properties such as: storage modulus (E′), loss modulus (E″), and loss tangent (tan δ) of the collagen sponges modified with hyaluronic acid (HA). In order to detect collagen–HA copolymer denaturation and to assess its thermal stability, the differential scanning calorimetry (DSC) supplemented by thermogravimetric (TG) measurements was used. The denaturation temperature (T_d) of unmodified collagen samples increased from 69 to 86 °C for cross-linked samples, respectively. These temperature dependencies show remarkable changes in E′ and E″ at selected temperature up to 226 °C for all samples due to the release of loosely and strongly bound water. The influence of HA on the viscoelastic behavior of collagen is manifested by a shift of the tan δ peak associated with the process of decomposition towards higher temperatures resulting in a higher thermo-stability of the modified scaffolds.     

Characteristics of Precipitation-formed Polyethylene Glycol Microgels Are Controlled by Molecular Weight of Reactants

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Precipitation reactions offer several advantages over traditional microsphere fabrication techniques. Contrary to emulsion, suspension, and dispersion techniques, microgels formed by precipitation are of uniform shape and size, i.e. low polydispersity index, without the use of organic solvents or stabilizers. The mild conditions of the precipitation reaction, customizable properties of the microgels, and low viscosity for injections make them applicable for in vivo purposes. Unlike other fabrication techniques, microgel characteristics can be modified by changing the starting polymer molecular weight. Increasing the starting PEG molecular weight increased microgel diameter and swelling ratio. Further modifications are suggested such as encapsulating molecules during microgel crosslinking. Simple adaptations to the PEG microgel building blocks are explored for future applications of microgels as drug delivery vehicles and tissue engineering scaffolds.     

Proteolytic degradation of cold-water fish gelatin solutions and gels

The stability of cold-water fish gelatin (FG), both in solution and in the gel phase, has been studied as function of both temperature and exposure towards novel proteases of marine origin. A 1% (w/v) FG solution was readily degraded by such proteases above 20 degrees C, which was expected since FG at this temperature is a random coil molecule lacking the protective triple helical structure found in collagen. The dynamic storage modulus for a 10% (w/v) FG gel increased monotonically at 4 degrees C. Ramping the temperature to 6, 8 or 10 degrees C led to a drastic reduction in G', but an apparent partial recovery of the network (increasing G') was observed with time at all temperatures. In the presence of proteases, a lower storage modulus was observed. At constant 4 degrees C, an apparent maximum value was reached after curing for 2h followed by a decrease in G' indicating protease activity. Ramping of temperature in the presence of proteases led to an even more drastic reduction in G' and no recovery of structure was observed with time. In this case, the overall rheological behaviour is a complex function of both thermal influence as well as proteolytic activity. In an endeavour to quantify the effect of the presence of proteolytic enzymes on the gelatin network, rheological investigation were undertaken where the dynamic storage moduli were recorded on different 10% (w/v) FG samples that had been acid hydrolysed to yield different average molecular weights. A significant reduction in storage modulus for average molecular weights below 50 kDa was found. This critical molecular weight most probably reflects the on-set of a regime where shorter chain lengths prevent percolation due to an increase in the loose end and sol fraction as well as a reduction in the average length of the pyrrolidine-rich regions reducing the number of possible junction zones.     

Synergistic gel formation of xyloglucan/gellan mixtures as sudied by rheology, DSC, and circular dichroism

The gelation behavior of mixtures of tamarind seed xyloglucan (TSX) and sodium form gellan (Na-G) was investigated. The storage and loss shear moduli, G' and G', of the mixtures showed that a thermoreversible gel was obtained although each polysaccharide alone did not form a gel at experimental conditions. The viscoelastic behavior of the mixtures showed a gel formation of TSX and Na-G induced by synergistic interaction. This synergistic interaction was also revealed by differential scanning calorimetry (DSC) and circular dichroism. Although TSX alone did not show any peak in DSC curves, mixtures with only a small amount of Na-G, which by itself did not show any peak, showed a single peak. With increasing Na-G content, another peak began to appear at the same temperature at which a peak of Na-G alone appeared. Thermally induced changes in circular dichroism of the mixtures were different from those expected from the individual behavior of TSX and Na-G.