Rheometric study of the gelation of chitosan in aqueous solution without cross-linking agent

A new process of formation of chitosan physical hydrogels in aqueous solution, without any organic solvent or cross-linking additive, was studied. The three conditions required for the physical gelation were an initial polymer concentration over C*, a critical value of the balance between hydrophilic and hydrophobic interactions, and a physicochemical perturbation responsible for a bidimensional percolating mechanism. The time necessary to reach the gel point was determined by rheometry, and gelations were compared according to different initial conditions. Thus, we investigated the influence of the polymer concentration and the degree of acetylation (DA) of chitosan on gelation. The number of junctions per unit volume at the gel point varied with the initial polymer concentration, i.e., the initial number of chain entanglements per unit volume or the number of gel precursors. The time to reach the gel point decreased with both higher DAs and concentrations. For a chitosan of DA = 36.7%, a second critical initial concentration close to 1.8% (w/w) was observed. Above this concentration, the decrease of the time to reach the gel point was higher and fewer additional junctions had to be formed to induce gelation. To optimize these physical hydrogels, to be used for cartilage regeneration, their final rheological properties were studied as a function of their degree of acetylation and their polymer concentration. Our results allowed us to define the most appropriate gel for the targeted application corresponding to a final concentration of chitosan in the gel of near 1.5% (w/w) and a DA close to 40%.     

New aspects of the formation of physical hydrogels of chitosan in a hydroalcoholic medium

New aspects concerning the mechanism of formation of chitosan physical hydrogels without any cross-linking agent were studied. The gelation took place during the evaporation of a hydroalcoholic solution of chitosan. We first demonstrated that it was possible to form a physical hydrogel from a hydrochloride form of chitosan. Chromatographic methods showed that during the gel formation, when the initial concentration is over C, the critical concentration of chain entanglement, the water and acid used for the solubilization of the polymer were both eliminated. This particular situation contributed to decrease the dielectric constant of the medium and the apparent charge density of chitosan chains, thus inducing the formation of a three-dimensional network through hydrophobic interactions and hydrogen bonding. In the gelation process, this step was kinetically determining. The speed of evaporation of water and acid were determined and different initial conditions were compared. Thus, we investigated the influence of: the initial polymer concentration, the nature of the counterion and the alcohol, the temperature and the geometry of the reactor. Our results allowed us to confirm the existence of a second critical initial concentration C, from which the evaporation of water became more difficult. We suggested that C corresponded to a reorganization of the solution involving the presence of gel precursors. Then, a mechanism of formation of physical hydrogels of chitosan in a hydroalcoholic medium could be proposed. For the first time, we demonstrated that it was possible to generate physical hydrogels in the presence of various diols, which size of the carbonated chain appeared as a limiting factor for the gelation process. These physical hydrogels of chitosan are currently used in our laboratory for tissue engineering in the treatment of third degree burns with the possibility to adapt their mechanical properties from the choice of both the acid or the alcohol used.     

Study of the near-neutral pH-sensitivity of chitosan/gelatin hydrogels by turbidimetry and microcantilever deflection

The fundamental properties and pH-sensitivity of chitosan/gelating hydrogels were investigated using spectroscopic and microelectro mechanical (MEMS) measurement approaches. Turbidimetric titration revealed that there were electrostatic attractive interactions between tripolyphosphate (TPP), chitosan, and gelatin in the acidic pH range, depending on their degree of ionization. The pH-sensitive swelling behavior of the hydrogels was investigated by monitoring the deflection of hydrogel-coated microcantilevers, which exhibited a sensitive and repeatable response to solution pH. The deflection of the microcantilever increased as the pH decreased, and the response speed of the system exhibited a nearly linear relationship with pH. The effects of the pH and concentration of TPP solution, as well as the ratio of chitosan to gelatin in gel precursor solutions, on the pH sensitivity of the hydrogels were also investigated. It was found that the swelling of the hydrogel is mainly a result of chain relaxation of chitosan-TPP complexes caused by protonation of free amino groups in chitosan, which depends on the crosslinking density set during the formation of the network. An increase in initial crosslink density induced a decrease in swelling and pH sensitivity. It can be concluded from this study that pH-sensitive chitosan gel properties can be tuned by preparatory conditions and inclusion of gelatin. Furthermore, microcantilevers can be used as a platform for gaining increased understanding of environmentally sensitive polymers.     

The influence of polymer molecular weight in lamellar gels based on PEG-lipids.

We report x-ray scattering, rheological, and freeze-fracture and polarizing microscopy studies of a liquid crystalline hydrogel called Lalpha,g. The hydrogel, found in DMPC, pentanol, water, and PEG-DMPE mixtures, differs from traditional hydrogels, which require high MW polymer, are disordered, and gel only at polymer concentrations exceeding an "overlap" concentration. In contrast, the Lalpha,g uses very low-molecular-weight polymer-lipids (1212, 2689, and 5817 g/mole), shows lamellar order, and requires a lower PEG-DMPE concentration to gel as water concentration increases. Significantly, the Lalpha,g contains fluid membranes, unlike Lbeta' gels, which gel via chain ordering. A recent model of gelation in Lalpha phases predicts that polymer-lipids both promote and stabilize defects; these defects, resisting shear in all directions, then produce elasticity. We compare our observations to this model, with particular attention to the dependence of gelation on the PEG MW used. We also use x-ray lineshape analysis of scattering from samples spanning the fluid-gel transition to obtain the elasticity coefficients kappa and B; this analysis demonstrates that although B in particular depends strongly on PEG-DMPE concentration, gelation is uncorrelated to changes in membrane elasticity.     

Studies on effect of pH on cross-linking of chitosan with sodium tripolyphosphate: A technical note

The ionotropic gelation method for formation of crosslinked chitosan particles can be easily modified from ionic cross-linking to deprotonation by adjusting the pH of TPP. Chitosan was cross-linked ionically with TPP at lower pH and by deprotonation mechanism at higher pH. The swelling behavior of cross-linked chitosan appeared to depend on the pH of TPP. The ionically cross-linked chitosan showed higher swelling ability. Thus the nature of crosslinked chitosan can be tailor made to obtain the desired properties in terms of cross-linking density, crystallinity, and hydrophilicity.     

Sulfasalazine release from alginate-N,O-carboxymethyl chitosan gel beads coated by chitosan

In the present study, spherical beads were prepared from a water-soluble chitosan (N,O-carboxymethyl chitosan, NOCC) and alginate with ionic gelation method. Then, swollen calcium–alginate–NOCC beads were coated with chitosan. To prepare drug loaded beads, sulfasalazine (SA) was added to the initial aqueous polymer solution. The effect of coating, as well as drying procedure, on the swelling behavior of unloaded beads and SA release of drug loaded ones were evaluated in simulated gastrointestinal tract fluid. The rate of swelling and drug release were decreased for air-dried and coated beads in comparison with freeze-dried and uncoated ones, respectively. No burst release of drug was observed from whole tested beads. Chitosan coated beads released approximately 40% of encapsulated drug in simulated gastric and small intestine tract fluid. Based on these results, the chitosan coated alginate–NOCC hydrogel may be used as potential polymeric carrier for colon-specific delivery of sulfasalazine.     

Characterization of the chemical degradation of hyaluronic acid during chemical gelation in the presence of different cross-linker agents

Dynamic light scattering (DLS) and rheological experiments have been performed on semidilute aqueous hyaluronic acid (HA) solutions during the chemical cross-linking process with a water-soluble carbodiimide (WSC) to produce a hydrogel. The formation and destruction of the gel are characterized. The results suggest that the gel is cross-linked via ester linkages and at later stage in the process, the omnipresent hydrolysis of interpolymer ester linkages and glycosidic bonds prevails, leading to disruption of the gel. The process of forming and breaking the gel is affected by the cross-linker concentration and pH. The cross-linking of HA with WSC in the presence of L-lysine methyl ester produced a gel with a longer time of gelation and the degradation of the gel was prolonged because of the more stable amide bond formation as the cross-link. By using the Ugi multicomponent condensation reaction, interpolymer cross-linking occurs via the formation of amide linkages and a stable gel evolves, which is only slightly degraded over an extended time window. DLS measurements on HA solutions with WSC show the emergence of a long-time power-law tail in the correlation functions at conditions both before and beyond the viscosity maximum. At a late stage in the gel-breakage regime, the power-law profile of the decay disappears and the long-time tail of the correlation function can be portrayed by a stretched exponential. The findings indicate that the power-law feature is associated with the confinement of chain dynamics and anomalous diffusion in the system. At later times, the connectivity is lost due to fragmentation of the network, and the long-time stretched exponential decay in the correlation function reflects the relaxation of clusters of various sizes.     

An Investigation and Characterization on Alginate Hydogel Dressing Loaded with Metronidazole Prepared by Combined Inotropic Gelation and Freeze-Thawing Cycles for Controlled Release

The purpose of this study was to investigate the effect of combined Ca²⁺ cross-linking and freeze-thawing cycle method on metronidazole (model drug) drug release and prepare a wound film dressing with improved swelling property. The hydrogel films were prepared with sodium alginate (SA) using the freeze-thawing method alone or in combination with ionotropic gelation with CaCl₂. The gel properties such as morphology, swelling, film thickness, and content uniformity and in vitro dissolution profiles using Franz diffusion cell were investigated. The cross-linking process was confirmed by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. In vitro protein adsorption test, in vivo wound-healing test, and histopathology were also performed. The hydrogel (F2) composed of 6% sodium alginate and 1% metronidazole prepared by combined Ca²⁺ cross-linking and freeze-thawing cycles showed good swelling. This will help to provide moist environment at the wound site. With the in vivo wound-healing and histological studies, F2 was found to improve the wound-healing effect compared with the hydrogel without the drug, and the conventional product.KEY WORDS: alginate, Ca²⁺ cross-linking, freeze-thawing, swelling, wound dressing     

Rheological characterization of in situ crosslinkable hydrogels formulated from oxidized dextran and N-carboxyethyl chitosan

The gelation kinetics of an in situ gelable hydrogel formulated from oxidized dextran (Odex) and N-carboxyethyl chitosan (CEC) was investigated rheologically. Both Schiff base mediated chemical and physical crosslinking account for its rapid gelation (30-600 s) between 5 and 37 degrees C. The correlation between gelation kinetics and hydrogel properties with Odex/CEC concentration, their feed ratio, and temperature were elucidated. The gelation time determined from crossing over of storage moduli (G') and loss moduli (G' ') was in good agreement with that deduced from frequency sweeping tests according to the Winter-Chambon power law. The power law exponents for a 2% (w/v) Odex/CEC solution (ratio 5:5) at the gel point was 0.61, which is in excellent agreement with the value predicted from percolation theory (2/3). Temperature dependence of gelation time for the same hydrogel formulation is well-described by an Arrhenius plot with its apparent activation energy calculated at 51.9 kJ/mol.     

Proliferation and Differentiation Potential of Human Adipose-Derived Stem Cells Grown on Chitosan Hydrogel

Applied tissue engineering in regenerative medicine warrants our enhanced understanding of the biomaterials and its function. The aim of this study was to evaluate the proliferation and differentiation potential of human adipose-derived stem cells (hADSCs) grown on chitosan hydrogel. The stability of this hydrogel is pH-dependent and its swelling property is pivotal in providing a favorable matrix for cell growth. The study utilized an economical method of cross linking the chitosan with 0.5% glutaraldehyde. Following the isolation of hADSCs from omentum tissue, these cells were cultured and characterized on chitosan hydrogel. Subsequent assays that were performed included JC-1 staining for the mitochondrial integrity as a surrogate marker for viability, cell proliferation and growth kinetics by MTT assay, lineage specific differentiation under two-dimensional culture conditions. Confocal imaging, scanning electron microscopy (SEM), and flow cytometry were used to evaluate these assays. The study revealed that chitosan hydrogel promotes cell proliferation coupled with > 90% cell viability. Cytotoxicity assays demonstrated safety profile. Furthermore, glutaraldehyde cross linked chitosan showed < 5% cytotoxicity, thus serving as a scaffold and facilitating the expansion and differentiation of hADSCs across endoderm, ectoderm and mesoderm lineages. Additional functionalities can be added to this hydrogel, particularly those that regulate stem cell fate.     

Synthesis and characterization of pH-sensitive hydrogel composed of carboxymethyl chitosan for colon targeted delivery of ornidazole

In the present study, carboxymethyl chitosan was prepared from chitosan, crosslinked with glutaraldehyde and evaluated in vitro as a potential carrier for colon targeted drug delivery of ornidazole. Ornidazole was incorporated at the time of crosslinking of carboxymethyl chitosan. The chitosan was evaluated for its degree of deacetylation (DD) and average molecular weight; which were found to be 84.6% and 3.5×10(4) Da, respectively. The degree of substitution on prepared carboxymethyl chitosan was found to be 0.68. All hydrogel formulations showed more than 85% and 74% yield and drug loading, respectively. The swelling behaviour of prepared hydrogels checked in different pH values, 1.2, 6.8 and 7.4, indicated pH responsive swelling characteristic with very less swelling at pH 1.2 and quick swelling at pH 6.8 followed by linear swelling at pH 7.4 with slight increase. In vitro release profile was carried out at the same conditions as in swelling and drug release was found to be dependant on swelling of hydrogels and showed biphasic release pattern with non-fickian diffusion kinetics at higher pH. The carboxymethylation of chitosan, entrapment of drug and its interaction in prepared hydrogels were checked by FTIR, (1)H NMR, DSC and p-XRD studies, which confirmed formation of carboxymethyl chitosan from chitosan and absence of any significant chemical change in ornidazole after being entrapped in crosslinked hydrogel formulations. The surface morphology of formulation S6 checked before and after dissolution, revealed open channel like pores formation after dissolution.     

Evaluation of mucoadhesive properties of chitosan microspheres prepared by different methods

The mucoadhesive properties of chitosan microspheres prepared by different method were evaluated by studying the interaction between mucin and microspheres in aqueous solution. The interaction was determined by the measurement of mucin adsorbed on the microspheres. A strong interaction between chitosan microspheres and mucin was detected. The intensity of the interaction was dependent upon the method of preparation of chitosan microspheres and the amount of mucin added. The extent of mucus adsorption was proportional to the absolute values of the positive zeta potential of chitosan microspheres. The zeta potential in turn was found to be dependent upon the method of preparation of microspheres. The adsorption of type III mucin (1% sialic acid content) was interpreted using Freundlich or Langmuir adsorption isotherms. The values ofr ² were greater for Langmuir isotherm as compared with Freundlich isotherm. The adsorption of a suspension of chitosan microspheres in the rat small intestine indicated that chitosan microspheres prepared by tripolyphosphate cross-linking and emulsification ionotropic gelation can be used as an excellent mucoadhesive delivery system. The microspheres prepared by glutaraldehyde and thermal cross-linking showed good stability in HC1 as compared with microspheres prepared by tripolyphosphate and emulsification ionotropic gelation.     

In situ forming chitosan hydrogels prepared via ionic/covalent co-cross-linking

In situ forming chitosan hydrogels have been prepared via coupled ionic and covalent cross-linking. Thus, different amounts of genipin (0.05, 0.10, 0.15, and 0.20% (w/w)), used as a chemical cross-linker, were added to a solution of chitosan that was previously neutralized with a glycerol-phosphate complex (ionic cross-linker). In this way, it was possible to overcome the pH barrier of the chitosan solution, to preserve its thermosensitive character, and to enhance the extent of cross-linking in the matrix simultaneously. To investigate the contributions of the ionic cross-linking and the chemical cross-linking, separately, we prepared the hydrogels without the addition of either genipin or the glycerol-phosphate complex. The addition of genipin to the neutralized solution disturbs the ionic cross-linking process and the chemical cross-linking becomes the dominant process. Moreover, the genipin concentration was used to modulate the network structure and performance. The more promising formulations were fully characterized, in a hydrated state, with respect to any equilibrium swelling, the development of internal structure, the occurrence of in vitro degradability and cytotoxicity, and the creation of in vivo injectability. Each of the hydrogel systems exhibited a notably high equilibrium water content, arising from the fact that their internal structure (examined by conventional SEM, and environmental SEM) was highly porous with interconnecting pores. The porosity and the pore size distribution were quantified by mercury intrusion porosimetry. Although all gels became degraded in the presence of lysozyme, their degradation rate greatly depended on the genipin load. Through in vitro viability tests, the hydrogel-based formulations were shown to be nontoxic. The in vivo injection of a co-cross-linking formulation revealed that the gel was rapidly formed and localized at the injection site, remaining in position for at least 1 week.     

Characterization of photo-cross-linked oligo[poly(ethylene glycol) fumarate] hydrogels for cartilage tissue engineering

Photo-cross-linkable oligo[poly(ethylene glycol) fumarate] (OPF) hydrogels have been developed for use in tissue engineering applications. We demonstrated that compressive modulus of these hydrogels increased with increasing polymer concentration, and hydrogels with different mechanical properties were formed by altering the ratio of cross-linker/polymer in precursor solution. Conversely, swelling of hydrogels decreased with increasing polymer concentration and cross-linker/polymer ratio. These hydrogels are degradable and degradation rates vary with the change in cross-linking level. Chondrocyte attachment was quantified as a method for evaluating adhesion of cells to the hydrogels. These data revealed that cross-linking density affects cell behavior on the hydrogel surfaces. Cell attachment was greater on the samples with increased cross-linking density. Chondrocytes on these samples exhibited spread morphology with distinct actin stress fibers, whereas they maintained their rounded morphology on the samples with lower cross-linking density. Moreover, chondrocytes were photoencapsulated within various hydrogel networks. Our results revealed that cells encapsulated within 2-mm thick OPF hydrogel disks remained viable throughout the 3-week culture period, with no difference in viability across the thickness of hydrogels. Photoencapsulated chondrocytes expressed the mRNA of type II collagen and produced cartilaginous matrix within the hydrogel constructs after three weeks. These findings suggest that photo-cross-linkable OPF hydrogels may be useful for cartilage tissue engineering and cell delivery applications.     

Some studies of crosslinking chitosan-glutaraldehyde interaction in a homogeneous system.

Chitosan dissolved in acetic acid reacted with glutaraldehyde solution, ranging in concentration from 0.10 to 25.0 x 10(-2) mol dm3. The modified polymers were characterized by means of carbon, hydrogen and nitrogen elemental analysis, scanning electron microscopy, X-ray diffractometry, 13C nuclear magnetic resonance (NMR), infrared and Raman spectroscopies. The uptake of metallic cations in aqueous medium was checked through copper. The obtained data from 13C NMR, infrared and Raman spectroscopies evidenced the formation of an ethylenic double bond in the chitosan glutaraldehyde interaction. These data suggest that free pendant amine groups of chitosan polymer interact with the aldehydic group of the glutaraldehyde to form stable imine bonds, due to the resonance established with adjacent double ethylenic bonds. The crosslinking is formed by the nonuniform length of chains and by terminal unities. The crosslinking formation can involve two chitosan unities belonging, or not, to the same polymeric chain. The sequence of reactions was established for a chitosan:glutaraldehyde molar proportion of 1:20. The degree of crystallinity and particle size decreased as the amount of glutaraldehyde was increased in the polymer. Physical and chemical properties are not just affected for the chitosan glutaraldehyde reaction, but are also affected strongly by the dissolution of the natural chitosan.     

Solute adsorption and enzyme immobilization on chitosan beads prepared from shrimp shell wastes

The equilibrium and kinetics of adsorption of reactive dye RR222 and Cu²⁺, and the activity of immobilization of acid phosphatase, on highly swollen chitosan beads were examined at 30°C. The chitosan was prepared from shrimp shell wastes and was cross-linked with different dosages of glutaraldehyde or glyoxal (100–80,000 mg/l). It was shown that the amounts of solute adsorption and the immobilization capacity of acid phosphatase on cross-linked chitosan beads were substantially affected by their degree of cross-linking. The cross-linking rate of chitosan with glutaraldehyde could be described by a pseudo-second-order equation and the cross-linking equilibrium by the Freundlich equation. This provided an experimental method to control the degree of cross-linking of chitosan beads. Finally, the activity and lifetime of the immobilized enzyme were measured to evaluate the application potential.     

Molecular dynamic simulations of the water absorbency of hydrogels

A polymer gel can imbibe solvent molecules through surface tension effect. When the solvent happens to be water, the gel can swell to a large extent and forms an aggregate called hydrogel. The large deformation caused by such swelling makes it difficult to study the behaviors of hydrogels. Currently, few molecular dynamic simulation works have been reported on the water absorbing mechanism of hydrogels. In this paper, we first use molecular dynamic simulation to study the water absorbing mechanism of hydrogels and propose a hydrogel-water interface model to study the water absorbency of the hydrogel surface. Also, the saturated water content and volume expansion rate of the hydrogel are investigated by building a hydrogel model with different cross-linking degree and by comparing the water absorption curves under different temperatures. The sample hydrogel model used consists of Polyethylene glycol diglycidyl ether (PEGDGE) as epoxy and the Jeffamine, poly-oxy-alkylene-amines, as curing agent. The conclusions obtained are useful for further investigation on PEGDGE/Jeffamine hydrogel. Moreover, the simulation methods, including hydrogel-water interface modeling, we first propose are also suitable to study the water absorbing mechanism of other hydrogels.     

Evaluation of Ionotropic Cross-Linked Chitosan/Gelatin B Microspheres of Tramadol Hydrochloride

Microspheres of tramadol hydrochloride (TM) for oral delivery were prepared by complex coacervation method without the use of chemical cross-linking agents such as glutaraldehyde to avoid the toxic reactions and other undesirable effects of the chemical cross-linking agents. Alternatively, ionotropic gelation was employed by using sodium-tripolyphosphate as cross-linking agent. Chitosan and gelatin B were used as polymer and copolymer, respectively. All the prepared microspheres were subjected to various physicochemical studies, such as drug–polymer compatibility by thin layer chromatography (TLC) and Fourier transform infrared (FTIR) spectroscopy, surface morphology by scanning electron microscopy, frequency distribution, drug entrapment efficiency, in vitro drug release characteristics and release kinetics. The physical state of drug in the microspheres was determined by differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). TLC and FTIR studies indicated no drug–polymer incompatibility. All the microspheres showed initial burst release followed by a fickian diffusion mechanism. DSC and XRD analysis indicated that the TM trapped in the microspheres existed in an amorphous or disordered-crystalline status in the polymer matrix. From the preliminary trials, it was observed that it may be possible to formulate TM microspheres by using biodegradable natural polymers such as chitosan and gelatin B to overcome the drawbacks of TM and to increase the patient compliance.     

Physicochemical and structural characterization of a polyionic matrix of interest in biotechnology, in the pharmaceutical and biomedical fields

This paper reports on the swelling degree and the rheological and structural characteristics of a hydrogel composed by chitosan and xanthan. The latter is a polyionic hydrogel obtained by complexation between the both polysaccharides. The swelling degree has been found to be influenced by the time of coacervation, the pH of the solution of chitosan used to form the hydrogel and the pH of the swelling solution. The molecular weight and the degree of acetylation of the chitosan also influence the swelling degree of this matrix. The connectivity between chitosan and xanthan affects the swelling degree of this matrix. A rheological study has been carried out in order to understand the formation of the coacervate and of the subsequent hydrogel. The evolution of the storage modulus with time during the coacervation has allowed to optimize the time of coacervation required for a subsequently hydrogel, with desirable swelling degree. The kinetics has shown that (a) the coacervate is formed in two distinct steps and (b) the storage modulus of the hydrogel reaches a stable plateau. The values of the storage modulus have been correlated with the swelling degree. The microscopic characterization has shown the presence of a porous network with a fibrillar structure. To complete the characterization studies fine powder of this hydrogel has been used to determine the surface, perimeter, Feret diameter and sphericity factor distribution of dry and hydrated (swollen) particles.     

A gel network constituted by rigid schizophyllan chains and nonpermanent cross-links

This work reports a gel network formed by rigid schizophyllan (SPG) chains with Borax as a cross-linking agent. The formed cross-links are non-permanent and somewhat dynamic in nature because the cross-linking reaction is governed by a complexation equilibrium. Gelation processes are traced by dynamic viscoelastic measurements to examine the effects of Borax content, SPG concentration, temperature, salt concentration, salt type, and strain. The first-order kinetic model containing three parameters, t(0) (induction time), 1/tau(c) (gelation rate), and (saturated storage modulus), is successfully applied to describe the gelation of the SPG-Borax system. Gelation occurs faster at higher Borax content, higher SPG concentration, higher salt concentration, or lower temperature. Moreover the gelation is cation-type-specific. Storage modulus is a linear function of both Borax content and SPG concentration. The linear relationship between storage modulus and Borax content can be explained by a modified ideal rubber elasticity theory with a front factor alpha to take into account the presence of ineffective cross-links and the effect of SPG chain rigidity. On the other hand, the linear dependence of storage modulus on SPG concentration could be explained on the basis of chain-chain contacting behavior of extended SPG chains. Apparent activation energy and cross-linking enthalpy are calculated to be -74.5 and -32.4 kJ/mol for the present system. Strain sweep measurements manifest that the elasticity behavior of this gel starts to deviate from Gaussian-chain network at a small strain of 10%.