Final Storage Modulus Research Articles

Sprayable ciprofloxacin-loaded poloxamer hydrogels for wound infection treatment.

Topical antimicrobial treatments for severe burns and chronic wounds provide effective treatment against infections, but cause pain and discomfort with application. This study aimed to develop an antimicrobial topical formulation comprising thermoreversible poloxamers (Pluronic F127 and F68) and a broad-spectrum antimicrobial agent (ciprofloxacin hydrochloride, CH), that could be sprayed to eliminate application pain while maintaining antimicrobial activity. Formulations were characterized to determine their sprayability under cold conditions, gelation temperature, final storage modulus at skin temperature, drug release profile, ex vivo permeation through impaired porcine skin, and inhibition against common bacterial pathogens that colonize wounds. All cold formulations were sprayable from simple hand-held, pump-action sprayers due to their low viscosity. Upon heating, 17 and 20% Pluronic F127 formulations produced hydrogels eight to ten degrees below skin temperature, independent of ciprofloxacin loading. Increasing concentrations of Pluronic F127 increased the final storage modulus and viscosity of the gels, while inclusion of Pluronic F68 reduced these properties, showing that hydrogel rheological properties at skin temperature can be tuned via choice of formulation. Drug release was directly correlated to the rheological properties, with stiffer gels resulting in a decrease in drug release rate. Overall, gels released about 65-90% of their load within 12 hours. Ex vivo skin permeation demonstrated that drug was well retained in impaired porcine skin, which is desired to continuously treat bacteria localized to the wound. A well-diffusion assay indicated that the hydrogels had greater bacterial inhibition against Pseudomonas aeruginosa, Escherichia coli, and two strains of Staphylococcus aureus when compared to commercial controls. Overall, the results show the potential of CH-loaded poloxamer formulations as suitable sprayable topical dressings to deliver antimicrobials directly to wounds.

Sigmoidal temporal increase in shear viscosity of titania–toluene–ethanol colloidal suspensions

The shear viscosity of toluene-based TiO2 nanoparticle/poly(vinyl acetate) suspensions initially increased gradually, then increased steeply, and finally levelled off under shearing in the presence of ethanol as a polar additive. This non-linear response followed a sigmoidal function with a characteristic rate constant for a given composition. The rate constant reached a maximum at a critical ethanol concentration, resulting in maxima of the final viscosity and storage modulus that have not been previously reported for non-aqueous macroscopically miscible systems. This viscosity anomaly was attributed to the preferential adsorption of the polar solvent and the resulting alcohol-clustering-induced particle networking in the non-polar medium. The temporal variations in viscosity were reproduced using a proposed kinetic model that newly considered inter-particle bonding assisted by ethanol adsorption. These results elucidate the transient rheological responses of suspensions containing polar/non-polar solvents for coating applications.

Microstructural evolution during acid induced gelation of cow, goat, and sheep milk probed by time-resolved (ultra)-small angle neutron scattering

Milks from small ruminant animals, such as goat and sheep, have gained increasing interest from the industry for the manufacture of various dairy products such as yoghurts. Heat treatment of milk is typically applied to improve the yoghurt texture. Here, time-resolved ultra-small angle neutron scattering (USANS) and small-angle neutron scattering (SANS) were employed to probe in situ the microstructural evolution of cow, goat, and sheep milks in D2O during acidification as affected by the heat treatment. Milk gelation can be envisaged as the progressive aggregation of the building blocks (casein micelles) in a fractal manner, which leads to the formation of micron scaled (∼3–10 μm) protein agglomerates. The heat treatment considerably enhanced the gelation of all milks, which is reflected by a faster increase in the fractal dimensions and aggregate sizes. For all three types of milks, similar final plateau fractal dimensions were observed for unheated (∼2.2–2.4) and heated milks (∼2.4–2.5), suggesting similar mass fractal microstructures in the size range probed by USANS. The final storage modulus after 10 h (G′final) follow the order of heated sheep milk ≈ sheep milk ≈ heated cow milk > cow milk > heated goat milk > goat milk. The colloidal calcium phosphate (CCP) dissolution kinetics tracked by SANS followed a similar trend as the evolution of the sample acidity (pD-value) and are not significantly affected by the types of milk or the heat treatment. This study shows a great potential of using time resolved USANS and SANS to investigate the microstructural evolution of protein aggregation and gelation.

Role of Free Catecholamine in Thiol-Ene Crosslinking for Hyaluronic Acid Hydrogels with High Loading Efficiency of Anticancer Drugs.

Hyaluronic acid (HA) is a widely used polysaccharide in biomedical field because of its excellent biocompatibility. Its chemical structure can be modified with various functional groups. Recently, dopamine has been tethered onto the polymeric backbone to ensure long-term stability and tissue adhesiveness of HA hydrogel. However, the radical scavenging effect of dopamine on typical photo-induced crosslinking for hydrogels has not been specifically studied. Photo-crosslinkable norbornene-modified HA (NorHA) was synthesized and crosslinked by dithiothreitol containing dopamine at different concentrations. During in situ ultraviolet light-triggered crosslinking, storage moduli were monitored using an oscillatory rheometer. Additionally, the amount of thiol utilized for HA crosslinking was investigated under the presence and absence of dopamine. Finally, doxorubicin was encapsulated in the hydrogels, and the drug loading efficiency and release kinetics were measured. Adding dopamine into the NorHA pre-gel solution delayed the gelation time, yet the final storage modulus of the hydrogel remained constant. That is, dopamine might partially consume the energy required for thiol-ene reaction to generate semiquinone radicals. Furthermore, the residual thiols which were not involved in the crosslinking decreased when the hydrogel was formed at a high concentration of dopamine, indicating the formation of Michael adducts of semiquinone and thiols. Interestingly, the presence of dopamine in the hydrogel increased the loading efficiency of the hydrophobic drugs due to π-π stacking and hydrogen bonding between dopamine and drugs. The presence of free catecholamines in a photo-crosslinkable polymer can delay the gelation time but improve the drug loading efficiency.

Functional and structural properties of soy 11S globulin: Influence of reverse micelle extraction.

The effect of the reverse micelle extraction method (RMEM) on the physicochemical properties of soy 11S globulin was studied and compared with that of the traditional alkali solution-acid precipitation method (ASAPM). The results showed that the β-sheet structure content of soy 11S globulin obtained by RMEM was lower, while the β-turn structure content was higher compared with that obtained by ASAPM. Furthermore, the protein unfolding degree and surface hydrophobicity were lower than those observed using ASAPM. Therefore, RMEM better maintained the natural molecular structure of soy 11S globulin. The thermodynamic and rheological properties of soy 11S globulin obtained by these two methods were further compared, showing that the highest denaturation temperature and transition heat of soy 11S globulin extracted using ASAPM were different from those obtained using RMEM. Furthermore, soy 11S globulin extracted by RMEM showed stronger heat resistance and a higher denaturation temperature than that extracted by ASAPM. The final storage modulus and frequency sweep results showed that the gel formed by soy 11S globulin obtained using RMEM had high storage modulus and loss modulus. PRACTICAL APPLICATION: In this study, the effects of two different extraction methods on structural and functional properties of soy 11S globulin, such as thermodynamics and rheology, were investigated. We can know the 11S globulin extracted using the reverse micelle environment was more heat-resistant and heat-induced gel quality of 11S globulin was improved by the reverse micelle environment. These results will provide theoretical basis that would help determine the potential applications of soy 11S globulin in the food system.

Synergistic Effect of Heating pH and Transglutaminase on the Gelation Kinetics and Texture of Yak Skim Milk Gels

Textural defects (including syneresis and poor consistency) often occur in yogurt gels produced from yak milk. In this research, the synergistic effects of transglutaminase (TGase) and heating pH on the textural properties of acidified yak skim milk gels, as well as the related mechanism of action, were investigated. The pH values of yak skim milk were adjusted to 6.3, 6.7, and 7.1, respectively. The samples were heated at 80°C for 30 min and then cooled to 42°C. After treatment with different contents of TGase (0, 3, and 10 U TGase per gram proteins), the samples were acidified with glucono-delta-lactone. For a given TGase content, the final storage modulus (G′) of gels was positively related to the heating pH, whereas the opposite trend was observed for the gelation time. This effect was obvious between pH 6.3 and 6.7. At a definite heating pH value, the final G′ of the gels was highest at 3 U TGase per gram proteins. The highest water holding capacity and firmness value were observed in gels prepared using pH 7.1 and 3 U TGase per gram proteins. In the samples treated with 3 U TGase per gram proteins (preheating pH 7.1), more rigid network structures were seen in the gel than 0 or 10 U TGase per gram proteins. Therefore, adjusting the heating pH values and TGase contents is an effective way of improving the textural properties of yak milk gels.

Influence of an O/W emulsion on the gelatinization, retrogradation and digestibility of rice starch with varying amylose contents

The present study aimed to explore the effects of oil-in-water emulsion on the gelatinization, retrogradation, and digestibility of indica rice starch (IRS), japonica rice starch (JRS), and glutinous rice starch (GRS). With the emulsion, the three types of starch granules exhibited limited swelling and increased gelatinization enthalpy during heating, and changed the peak viscosity and final storage modulus of starch gelatinization. After being refrigerated at 4 °C, the emulsion changed the firmness of starch gel, reduced the water migration, and increased the water-holding capacity of the three starch gels. X-ray diffraction and scanning electron microscopy revealed that the emulsion could delay the retrogradation of the three types of starches, and the inhibitory effect was related to the content of amylose. The results of in vitro digestion showed that the emulsion significantly increased the slowly digestible starch and resistant starch contents in the three types of starch. These findings indicated that the emulsion could inhibit the gelatinization and retrogradation properties, as well as delay the digestion of different types of starch, providing a theoretical basis for expanding the application of the emulsion in starch foods.

Influence of fat substitution by inulin on fermentation process and physical properties of set yoghurt evaluated by an optical sensor

Inulin is a natural product with beneficial effects for human health commonly used as a source of dietary fiber, bulking agent and fat substitute in products like cheese and yoghurt. There are some confusing or contradictory results in the literature about the water holding capacity of inulin and its effect on syneresis, coagulation kinetics, rheology and texture of yoghurt, so in this study those effects were evaluated. Yoghurt fermentation tests were conducted with three fat concentrations (0.4, 1.6 and 3.6%) and three inulin levels (0, 1.6 and 3.2%). The coagulation process was monitored for the first time using simultaneously an inline light backscatter sensor, inline potentiometry and a rheometer. The increase in milk fat concentration from 0 to 3.6% delayed the start of coagulation and increased time to pH=4.8 in 11min. 3.2% of inulin addition increased yoghurt acidification rate, reduced 12min the time to pH=4.8, and increased final storage modulus and gel firmness. It was also determined that 3.2% of inulin addition increased 32% the spontaneous syneresis and had no effect on the water holding capacity of set yoghurt.

Effect of seasonal variations on the acid gelation of milk

We investigated the effect of seasonal variations on the acid gelation properties of bovine milk in a seasonal-calving New Zealand herd for 2 full milking seasons. We tested the formation of acid gels in 2 milk systems: unstandardized skim milk and standardized whole milk (4.6% protein, 4.0% fat). For unstandardized skim milk, late-season milk acid gels had a longer gelation time and a lower gelation pH than early- and mid-season milk acid gels, but we found no consistent seasonal variation in the final storage modulus. For standardized milk, late-season milk had the most inferior acid gelation properties during the year, including the lowest final storage modulus, the lowest gelation pH, and the longest gelation time. Standardization alleviated but did not eliminate the prolonged gelation time of late-season milk. These results indicated that the physicochemical properties of seasonal milk contributed greatly to its acid gelation, independent of differences in protein content. Standardization was not adequate to stabilize the acid gelation properties of late-season milk. Desirable acid gelation properties correlated with lower glycosylated κ-casein content, lower β-lactoglobulin:α-lactalbumin ratio, lower extent of whey protein-casein micelle association, and lower total calcium and ionic calcium content. We discuss the possible effects of the correlating variables on the acid gelation properties of seasonal milk. Natural variations in the glycosylation degree of κ-casein might play an important role in acid gel structural development by altering the electrostatic and hydrophobic interactions among the milk proteins.

Effect of reverse micelle on physicochemical properties of soybean 7S globulins

In this paper, the structural, thermodynamic, and rheological properties of soybean 7S globulins extracted by bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT)/isooctane reverse micelle method and alkali extraction-acid precipitation method were studied. Amino acid composition results showed that the 7S globulin produced by reverse micelle had more hydrophobic and sulfur-containing amino acids. Fourier transform infrared spectroscopy results demonstrated that the 7S globulin extracted by reverse micelle had more β-sheets but less turn structure, and formed a more compact conformation. However, lower surface hydrophobicity was observed in the 7S globulin extracted by reverse micelle, indicating that the reverse micelle environment could protect the native folded structure of protein. Thermal stability tests showed that the 7S globulin extracted by reverse micelle had poorer thermostability with lower denaturation temperature, which was in accordance with the results of initial gelling temperature. Final storage modulus (G’) and frequency sweep results revealed that the 7S globulin obtained by reverse micelle produced a harder textured gel.

Crosslinking Kinetics of Methylcellulose Aqueous Solution and Its Potential as a Scaffold for Tissue Engineering.

Thermosensitive, physically crosslinked injectable hydrogels are in the area of interests of various scientific fields. One of the representatives of this materials group is an aqueous solution of methylcellulose. At ambient conditions, methylcellulose (MC) is a sol while on heating up to 37 °C, MC undergoes physical crosslinking and transforms into a gel. Injectability at room temperature, and crosslinkability during subsequent heating to physiological temperature raises hopes, especially for tissue engineering applications. This research work aimed at studying crosslinking kinetics, thermal, viscoelastic, and biological properties of MC aqueous solution in a broad range of MC concentrations. It was evidenced by Differential Scanning Calorimetry (DSC) that crosslinking of MC is a reversible two-stage process, manifested by the appearance of two endothermic effects, related to the destruction of water cages around methoxy groups, followed by crosslinking via the formation of hydrophobic interactions between methoxy groups in the polymeric chains. The DSC results also allowed the determination of MC crosslinking kinetics. Complementary measurements of MC crosslinking kinetics performed by dynamic mechanical analysis (DMA) provided information on the final storage modulus, which was important from the perspective of tissue engineering applications. Cytotoxicity tests were performed using mouse fibroblasts and showed that MC at low concentration did not cause cytotoxicity. All these efforts allowed to assess MC hydrogel relevance for tissue engineering applications.

The beneficial effects of rutin on myofibrillar protein gel properties and related changes in protein conformation

Effects of different levels of rutin (0, 10, 50, 100 and 200 μmol/g protein) on the conformational changes and gel properties of myofibrillar protein (MP) were investigated. Rutin at 200 μmol/g caused the greatest carbonyl content. The incorporation of rutin caused the losses of thiol, free amine and α-helix contents, reduction in tryptophan intrinsic fluorescence intensity, and enhanced exposure of hydrophobic groups and protein cross-linking. When compared with control, the MP gels with 10, 50 and 100 μmol/g rutin had higher gel strength but slight lower water-holding capacity; the gels appeared to have compact microstructure with few visible pores. However, 200 μmol/g rutin was detrimental to gel properties. All the gels with rutin presented higher final storage modulus and converted to elasticity-dominant gel types. The results indicate that a slightly high concentration of rutin could improve MP gel properties which are related to the protein conformational changes induced by rutin.

Improving the textural properties of camel milk acid gel by treatment with trisodium citrate and transglutaminase

This study aimed to solve the problems of the weak acid-induced gelation ability of camel milk by the synergistic effect of trisodium citrate and microbial transglutaminase (mTGase). As the trisodium citrate concentration increased from 0 to 30 mmol/L, the final storage modulus of mTGase-treated camel milk acid gels increased from 11.9 ± 0.3 to 72.5 ± 2.4 Pa, the firmness increased from 0.7 ± 0.2 to 1.8 ± 0.1 N, and water holding capacity increased from 41.0 ± 1.8% to 99.6 ± 0.8%. A denser gel network structure with the smallest pore size was observed with 30 mmol/L trisodium citrate, which was selected as the optimum concentration. The number average diameter of the casein particles decreased significantly from 183.5 ± 5.9 to 37.4 ± 3.0 nm and the degree of crosslinking of the acid gel increased significantly from 19.3 ± 1.2% to 38.9 ± 2.4% in the presence of trisodium citrate. This study indicated that smaller casein particles with a higher level of covalent crosslinking can form a camel milk gel with better textural properties, which has enormous potential for manufacture of acid-induced camel milk gel products.

Combined Use of Trisodium Citrate and Transglutaminase to Enhance the Stiffness and Water-Holding Capacity of Acidified Yak Milk Gels

In this research, the synergistic effect of trisodium citrate (TSC) and microbial transglutaminase (TGase) treatment on the textural properties of acidified yak skim milk gels was investigated. TSC was added to yak skim milk to concentrations of 0, 20, and 40 mmol/L, followed by adjusting the pH to 6.7. The samples were incubated with TGase for the cross-linking reaction, after which the samples were acidified with 1.4% (w/v) gluconodelta-lactone (GDL) at 42°C for 4 h to form gels. The stiffness and water holding capacity (WHC) of gels exhibited higher values at 20 or 40 mmol/L than without TSC. The final storage modulus (G′) of yak milk gels was positively related to the concentration of TSC prior to TGase treatment. Cryoscanning electron microscopy observations showed that the gel networks were more rigid with higher TSC concentrations. Overall, TSC dissociated particles in yak milk into smaller ones. The newly formed particles in yak skim milk could form acid-induced gels with greater stiffness and higher WHC in the presence of TGase.

The role of calcium in wheat starch-Mesona chinensis polysaccharide gels: Rheological properties, in vitro digestibility and enzyme inhibitory activities

The interaction between Mesona chinensis polysaccharide (MCP) and wheat starch was dependent on the presence of calcium that is naturally present in the extract of Mesona chinensis (MC). Partial removal of the calcium from MCP resulted in a 55% decrease in the final storage modulus (G’) and 20% increase in digestibility of a 100 mg/g wheat starch gel containing 50 mg/g MCP. The weakening of the gel was associated with a reduction in MCP-MCP interactions, as a result of an increase in electrostatic repulsive forces upon partial calcium removal. This resulted in the formation of a less extended network comprising of amylose and fractions of uninteracting MCP. A combination of lower gel strength and formation of less amylose-MCP complexes was thought to be responsible for the increase in the digestibility of the gel. “Calcium-reduced MCP” was found to inhibit the activities of α-amylase and α-glucosidase uncompetitively. Partial reduction of calcium was likely to alter the conformation of MCP, resulting in a polysaccharide conformation that is favourable for α-amylase binding but less so for α-glucosidase binding.

The Use of Trisodium Citrate to Improve the Textural Properties of Acid-Induced, Transglutaminase-Treated Micellar Casein Gels.

In this study, the effect of trisodium citrate on the textural properties and microstructure of acid-induced, transglutaminase-treated micellar casein gels was investigated. Various concentrations of trisodium citrate (0 mmol/L, 10 mmol/L, 20 mmol/L, and 30 mmol/L) were added to micellar casein dispersions. After being treated with microbial transglutaminase (mTGase), all dispersions were acidified with 1.3% (w/v) gluconodelta-lactone (GDL) to pH 4.4–4.6. As the concentration of trisodium citrate increased from 0 mmol/L to 30 mmol/L, the firmness and water-holding capacity increased significantly. The final storage modulus (G′) of casein gels was positively related to the concentration of trisodium citrate prior to mTGase treatment of micellar casein dispersions. Cryo-scanning electron microscopy images indicated that more interconnected networks and smaller pores were present in the gels with higher concentrations of trisodium citrate. Overall, when micellar casein dispersions are treated with trisodium citrate prior to mTGase crosslinking, the resulted acid-induced gels are firmer and the syneresis is reduced.

Reversibly photo-crosslinkable aliphatic polycarbonates functionalized with coumarin

Cinnamoyl and coumarin groups can be used to introduce photo-responsive behaviour to polymer systems, but they have never been directly compared within the same polymer system. Thus, this study examined cinnamoyl and coumarin functionalized aliphatic polycarbonate copolymers to determine their relative suitability for use as biomaterials. Coumarin functionalized polycarbonates photo-crosslinked significantly faster and resulted in networks with high crosslink density when irradiated with UVA radiation. Real-time tracking using rheometry showed that increasing the degree of coumarin functionalization on the aliphatic polycarbonate copolymers resulted in quicker gelation and higher final storage modulus. In addition, decreasing the UV intensity and increasing the sample thickness also increased the final storage modulus. Although no appreciable reversibility was detected for solvent-free or solvent-swelled crosslinked polymer networks, rapid reversibility upon exposure to 254 nm light was observed in dilute solutions. The kinetics of photo-dimerization were third order while the photo-cleavage reaction kinetics were second order with respect to the concentration of the photoactive group. Overall, the photo-reversible crosslinking of coumarin functionalized aliphatic polycarbonates was demonstrated. These polymers have potential for use in photo-crosslinking or photo-reversible biomaterials applications.

Synthesis of stimuli–responsive chitosan–based hydrogels by Diels–Alder cross–linking `click´ reaction as potential carriers for drug administration

Stimuli–responsive chitosan–based hydrogels for biomedical applications using the Diels–Alder reaction were prepared. Furan modified chitosan (Cs–Fu) was cross–linked with polyetheramine derived bismaleimide at different equivalent ratios in order to determine the effect in the swelling and release properties on the final CsFu:BMI hydrogels. The Diels Alder cross–linking reaction was monitored by UV–vis spectroscopy and rheological measurements. Both the sol–gel transition value and the final storage modulus for the different formulations were similar and close to 40 min and 400 Pa, respectively. On the contrary, the swelling degree was found to be strongly dependent on the amount of bismaleimide, mainly in acidic medium, where the increased cross–linking reduced the swelling value in 25%, but maintaining the sustained drug release in the simulated gastrointestinal environment. Our study suggested that these DA–cross–linked chitosan hydrogels could be potential carriers for targeted drug administration.

Effects of l‐lysine/l‐arginine on the emulsion stability, textural, rheological and microstructural characteristics of chicken sausages

SummaryThe effects of l‐lysine (Lys), l‐arginine (Arg) and soya protein isolated (SPI) on the physicochemical properties of chicken sausages were investigated. The results showed that the addition of Lys/Arg significantly decreased total expressible fluid and expressible fat, but significantly increased hardness, springiness, cohesiveness and chewiness of chicken sausage. Moreover, Lys and Arg were more effective than SPI. Rheology indicated that Lys/Arg increased final storage modulus and final loss modulus. Also, scanning electron microscope and confocal laser scanning microscopy disclosed that Lys or Arg was conducive to the formation of regular and uniform oil droplet surrounded integrate membrane. Overall, Lys/Arg exhibited a potential in the preparation of emulsion‐type meat products.

Interactions in casein micelle - Pea protein system (Part II): Mixture acid gelation with glucono-δ-lactone

In our preceding study (Part I), the thermal denaturation and aggregation of enriched pea protein fractions, namely vicilin/convicilin 7S (Vic) and legumin 11S (Leg), were investigated in the absence or in presence of casein micelles (CM) at pH ≈ 7.1. The present report (Part II) focuses on the glucono-δ-lactone (GDL) acid-induced gelation of either co-heated proteins in admixture (namely route 1) or thermally-aggregated pea proteins mixed with unheated CM (route 2), while applying a pea protein (either non fractionated PP or Vic or Leg) - to - CM weight ratio of 1: 1 and total protein concentration of 3.6 wt%. The pea protein thermal aggregates obtained by route 1 were of lower size and less soluble than those yielded in isolation. For route 1, gelation of the heated CM – Vic mixture was triggered at a higher pH value and led to higher final storage modulus G′ than corresponding protein samples in isolation. In contrast, the presence of large and sedimentable aggregates in the case of the CM – PP and CM – Leg mixtures impaired gelation. Concerning route 2, either the PP or Vic aggregates mixed with unheated CM resulted in rapid gelation and higher final G’ values than those measured for their single-protein sample counterparts. Viscoelastic properties of the mixed gel depended on the pea protein fraction used, thermal aggregation route, extent of physical interactions between pea proteins during acidification and further involvement of CM. Hence, route 2 would be more reliable than route 1 to produce a “mixed” dairy-like gelled product containing pea proteins with improved texture properties.