Effect of monovalent and divalent cations on the rheological properties of gellan gels

An innovative rheology analysis method applies to the formulation optimization of Panax notoginseng total saponins ocular gel

Emphasizing the viscoelasticity of ophthalmic gels is crucial for understanding the residence time, structure, and stability of hydrogels. This study primarily aimed to propose an innovative rheology analysis method for ophthalmic gels, considering complex eye movements. This method was applied to select ophthalmic gels with favorable rheological characteristics. Additionally, the physical characteristics and in vitro release of the selected Panax notoginseng total saponins (PNS) gel were demonstrated. The selected PNS gel significantly increased the activities of SOD and decreased intracellular levels of MDA, TNF-α, and IL-1β in H2O2-treated ARPE-19 cells. Finally, the optimal formulation was selected as a suitable platform for ophthalmic delivery and was shown to significantly rescue ARPE-19 cells from oxidative cellular damage.

Interactions between pea protein and gellan gum for the development of plant-based structures

Plant-based analogs have been developed to mimic foods from animal sources by using ingredients from vegetable sources. Among the strategies to produce plant-based structures is the gelation of mixtures between plant proteins and polysaccharides. In this study, our aim was to investigate gels of pea proteins and gellan gum with high protein concentration and the addition of salt (potassium and sodium chloride). In the first step, a qualitative mapping was performed to select pea protein and gellan gum concentrations to produce self-sustainable gels. After that, the effect of salt addition was investigated for the formulations containing 10-15 % (wt) pea protein and 0.5-1 % (wt) gellan gum. The results showed that the gels containing potassium ions were more rigid and less deformable, with lesser water loss by syneresis. The morphological analysis showed a spatial exclusion of pea protein from the gel network mainly structured by the gellan gum. While potassium ions led to a more compact network, calcium ions promoted higher pores in the structure. Depending on the composition, the mechanical properties of gels were similar to some products from animal sources. So, the information obtained from these gels can be applied to the structuring of formulations in the development of plant-based analogs.

Analysis of the gel properties, microstructural characteristics, and intermolecular forces of soybean protein isolate gel induced by transglutaminase

Soybean protein isolate (SPI) is a high-quality plant protein that is primarily used to process various soybean products coagulated by transglutaminase (TGase). In this study, the degree of hydrolysis (DH), sulfhydryl content (SH), surface hydrophobicity (H0 ), secondary structural constitution, and microstructure of TGase-treated soybean protein (SPI, 7S, and 11S) were determined, as well as the effects of NaCl, urea, and SDS on the properties and intermolecular forces of SPI gel were analyzed. The results show that the H0 and SH content of SPI, 7S, and 11S decreased significantly with TGase treatment time (p < .05), while the DH gradually increased and reached its highest value (3.72%, 7.41%, and 1.27%, respectively) at 30 min. As the concentration of these two secondary structures exhibited an inverse relationship, the degradation of β-turns resulted in the increase in β-sheets. The microstructures of SPI and 11S gels were similar, being denser and more ordered than 7S gel. The low concentration of NaCl solution (0.2 mol/L) enhanced gel properties and intermolecular forces, promoting the formation of SPI gel, whereas a high concentration (0.4-0.8 mol/L) had a significant inhibitory effect. Urea and SDS solutions substantially inhibited the formation of SPI gel, leading to significant decreases in the water holding capacity and hardness as well as a considerable increase in the coagulation time (p < .05). The results revealed that hydrogen bonds and hydrophobic interactions were the main intermolecular forces responsible for the gel formation. This study provides adequate technical support and a theoretical basis for soybean protein gel products.

The gelling behavior of gellan in the presence of different sodium salts

It is well known that metal ions have great effects on gelling behaviors of gellan aqueous systems, however, the effects of their co-ions - anions have rarely been studied. Herein, we investigated the effects of four kinds of sodium salts with different anions (NaCl, CH₃COONa, Na₂C₂O₄ and Na₃C₆H₅O₇) on gelling behaviors of gellan aqueous systems in terms of gelling temperature and gel hardness. It was found that, when [Na⁺] was low (20 mM), the salt with Cl^- or CH₃COO^- favored the gelling of gellan aqueous systems, while the salt with C₂O₄^2- or C₆H₅O₇^3- took adverse effects probably because C₂O₄^2- or C₆H₅O₇^3- could react with divalent cations (Ca²⁺ and Mg²⁺) in gellan to form precipitates or chelates and break their interactions with gellan (salt bridges). When [Na⁺] was high (50 or 80 mM), all the four kinds of salts facilitated gelling due to the shielding effects of high concentrations of Na⁺ on the negative charges along the gellan chains, and followed the order of: Cl^- > CH₃COO^- > C₂O₄^2- > C₆H₅O₇^3-. This study demonstrates the effects of anion kind of salts on gelling behaviors of gellan aqueous systems and provides references for the application of gellan.

Fabrication and Characterization of Polysaccharide Metallohydrogel Obtained from Succinoglycan and Trivalent Chromium

In the present study, a polysaccharide metallohydrogel was successfully fabricated using succinoglycan and trivalent chromium and was verified via Fourier transform infrared spectroscopy, differential scanning calorimetry analysis, thermogravimetric analysis (TGA), field emission scanning electron microscopy, and rheological measurements. Thermal behavior analysis via TGA indicated that the final mass loss of pure succinoglycan was 87.8% although it was reduced to 65.8% by forming a hydrogel with trivalent chromium cations. Moreover, succinoglycan-based metallohydrogels exhibited improved mechanical properties based on the added concentration of Cr³⁺ and displayed a 10 times higher compressive stress and enhanced storage modulus (G′) of 230% at the same strain. In addition, the pore size of the obtained SCx could be adjusted by changing the concentration of Cr³⁺. Gelation can also be adjusted based on the initial pH of the metallohydrogel formulation. This was attributed to crosslinking between chromium trivalent ions and hydroxyl/carboxyl groups of succinoglycan, each of which exhibits a specific pH-dependent behavior in aqueous solutions. It could be used as a soft sensor to detect Cr³⁺ in certain biological systems, or as a soft matrix for bioseparation that allows control of pore size and mechanical strength by tuning the Cr³⁺ concentration.

Structural, gelation properties and microstructure of rice glutelin/sugar beet pectin composite gels: Effects of ionic strengths

In this study, the rice glutelin (RG)/sugar beet pectin (SBP) composite gels were prepared by laccase induced cross-linking and subsequent heat treatment, and the effects of different calcium ion concentrations (0-400 mM) on the gelation, structural properties and microstructure of the RG/SBP composite gels were investigated. The results showed that the addition of 200 mM calcium ion could improve the rheological, textural properties and water holding capacity of the RG/SBP composite gels. The addition of SBP and calcium ions enhanced the hydrophobic interaction between RG molecules, thereby increased the gel properties of RG. The changes in Raman spectroscopy reflected the positive effect of the addition of SBP and calcium ions on the formation of a denser and more homogeneous protein gel, as evidenced by the results of scanning electron microscopy. Overall, SBP and calcium ions could be applied to the plant protein gel systems as gel-strengthening agents.

Determination of available breaking stress of agar and gellan gum plate culture methods and the duration of bacterial culture under strong acidic conditions

AIMS

Several acidophilic bacteria have not been cultured, primarily owing to the lack of suitable culture methods under strong acidic conditions. This study aimed to quantitatively evaluate the strengths of the agar plates (AP) and gellan gum plates (GP), and optimal culture periods under strong acidic conditions.

METHODS AND RESULTS

To define the lower limit of plate strength for bacterial isolation culture, the diameter of Escherichia coli K12 colonies and the breaking stress of plates at different concentrations of gelling agents, medium composition and pH conditions were determined. The lower limit of available strength of AP and GP was 19·6 and 14·8 kPa, respectively. Medium composition slightly affected AP breaking stress, although GP with a high cationic concentration medium could not be prepared.

CONCLUSIONS

Assessment of the strength limits of AP and GP revealed that AP is not suitable for prolonged bacterial culture (≥72 h). Furthermore, GP was completely ineffective for bacterial culture under highly acidic conditions (≤pH 1·0).

SIGNIFICANCE AND IMPACT OF THE STUDY

Our quantitative evaluation method based on breaking stress is a potentially valuable tool to understand the state and the suitable limit of plate culture methods in more detail under various conditions.

Electrospun nanofibers - A promising solid in-situ gelling alternative for ocular drug delivery

A serious problem of the treatment of eye diseases is the very short residence time of the drug. The majority of the drug is cleared within few seconds due to the poor capability of the eye to accommodate additional liquids. We developed a new ocular drug delivery system, which is applied in dry form and forms immediately a gel after administration. The system is based on gellan gum/pullulan electrospun nanofibers. The rheological behavior of the spinning solution was investigated followed by further characterization of the in situ formed gel. Three-dimensional X-ray imaging with nanometric resolution (nano-CT) and electron scanning microscopy were used for a detailed characterization of the diameter and alignment of the fibers. A high porosity (87.5 ± 0.5%) and pore interconnectivity (99%) was found. To ensure a good fit to the eye anatomy, the prepared fibers were shaped into curved geometries. Additionally, a new innovative moistening chamber for the in vitro determination of the ocular residence time in porcine eyes was developed which mimics the tear turnover. A clear prolongation of the fluorescein residence time compared to conventional eye drops was achieved with the application of the curved nanofiber in situ gelling mat. In summary, the developed in situ gelling system with adapted geometry is a promising alternative system for ocular drug delivery.

A gellan-based fluid gel carrier to enhance topical spray delivery

Autologous cell transplantation was introduced to clinical practice nearly four decades ago to enhance burn wound re-epithelialisation. Autologous cultured or uncultured cells are often delivered to the surface in saline-like suspensions. This delivery method is limited because droplets of the sprayed suspension form upon deposition and run across the wound bed, leading to uneven coverage and cell loss. One way to circumvent this problem would be to use a gel-based material to enhance surface retention. Fibrin systems have been explored as co-delivery system with keratinocytes or as adjunct to 'seal' the cells following spray delivery, but the high costs and need for autologous blood has impeded its widespread use. Aside from fibrin gel, which can exhibit variable properties, it has not been possible to develop a gel-based carrier that solidifies on the skin surface. This is because it is challenging to develop a material that is sprayable but gels on contact with the skin surface. The manuscript reports the use of an engineered carrier device to deliver cells via spraying, to enhance retention upon a wound. The device involves shear-structuring of a gelling biopolymer, gellan, during the gelation process; forming a yield-stress fluid with shear-sensitive behaviours, known as a fluid gel. In this study, a formulation of gellan gum fluid gels are reported, formed with from 0.75 or 0.9% (w/v) polymer and varying the salt concentrations. The rheological properties and the propensity of the material to wet a surface were determined for polymer modified and non-polymer modified cell suspensions. The gellan fluid gels had a significantly higher viscosity and contact angle when compared to the non-polymer carrier. Viability of cells was not impeded by encapsulation in the gellan fluid gel or spraying. The shear thinning property of the material enabled it to be applied using an airbrush and spray angle, distance and air pressure were optimised for coverage and viability. STATEMENT OF SIGNIFICANCE: Spray delivery of skin cells has successfully translated to clinical practice. However, it has not yet been widely accepted due to limited retention and disputable cell viability in the wound. Here, we report a method for delivering cells onto wound surfaces using a gellan-based shear-thinning gel system. The viscoelastic properties allow the material to liquefy upon spraying and restructure rapidly on the surface. Our results demonstrate reduced run-off from the surface compared to currently used low-viscosity cell carriers. Moreover, encapsulated cells remain viable throughout the process. Although this paper studies the encapsulation of one cell type, a similar approach could potentially be adopted for other cell types. Our data supports further studies to confirm these results in in vivo models.

Addition of Salt Ions before Spraying Improves Heat- and Cold-Induced Gel Properties of Soy Protein Isolate (SPI)

Spray drying is used in the food industry to convert liquids into dry powders. The effect of the addition of salt ions before spray drying to improve the heat- and cold-induced gel properties of soy protein isolate (SPI) was investigated. Certain concentrations of Na+ (0.005–0.01 M), Mg2+ (0.005 M), and Ca2+ (0.005 M) significantly increased the hardness, springiness, cohesiveness, chewiness, gumminess, resilience, and water holding capacity of the heat- and cold-induced gels. This effect arises predominantly due to the functional groups buried in the protein matrix that are partially exposed to improve the interactions between the protein molecules. The main interactions that promoted gel formation and maintained the three-dimensional structure of the heat- and cold-induced gels were hydrophobic and disulfide interactions. Analysis using scanning electron microscopy showed that the heat- and cold-induced gels were uniform, had smooth surfaces, and had smaller pores with added Na+ (0.01 M), Mg2+ (0.005 M), and Ca2+ (0.005 M). The results indicate that we might broaden the applications of SPI by simulating the industrial gel manufacturing process for products such as fish balls and chiba tofu. Overall, adding salt ions before spray drying could offer great potential for the development of SPI with enhanced functionality suitable for comminuted meat products.

Large amplitude oscillatory shear behavior and gelation procedure of high and low acyl gellan gum in aqueous solution

The rheological properties of gellan fluid gels were investigated using large amplitude oscillatory shear (LAOS) technique in both linear and non-linear viscoelastic regimes, with consideration of high acyl (HA)/low acyl (LA) gellan ratio and Ca²⁺ concentration. The Lissajous curves and Chebyshev coefficients were used to analyze the LAOS data and successfully provided visual and quantitative representation of microstructural differences between HA and LA gellan gum, respectively. Temperature sweep measurements were performed to monitor the gelation procedure of gellan gum solution. The results show that HA gellan gum forms softer but more stable gels than LA gellan gum, especially at high temperature. And a synergistic interaction between HA and LA gellan gum may exist in the presence of abundant Ca²⁺ ions. The abovementioned study can allow a better understanding of structural characteristic of gellan gum and provide a practical approach to rheological assessment that facilitates the processing and diversified application of mixed gellan gum.

Engineered Gellan Polysaccharides in the Design of Controlled Drug Delivery Systems

Natural polysaccharides are getting increasing attention in the development of pharmaceutical dosage forms due to their encouraging reports on nontoxicity and biodegradability. Natural gums can also be engineered to have better materials for drug delivery system design. Gellan gum originates from microbial fermentation and has been declared as safe by US FDA for human consumption. It possesses gelling ability in presence of multivalent earth metal cations and thus enabled the design of mutiparticulate drug delivery systems in completely aqueous environment avoiding the use of organic solvents. Due to faster drug release profiles of divalent cation-induced gellan gum particles, nowadays chemically modified forms of gellan polysaccharide are currently being investigated for the controlled release of drugs. This chapter discusses the factors contributing to the varying gelling characteristics of gellan gum and the recent developments in its chemical modification towards the fabrication of novel controlled drug delivery devices.

Effect of various gelling cations on the physical properties of "wet" alginate films

In this study, the physical properties of "wet" alginate films gelled with various divalent cations (Ba(2+) , Ca(2+) , Mg(2+) , Sr(2+) , and Zn(2+) ) were explored. Additionally, the effect of adding NaCl to the alginate film-forming solution prior to gelling was evaluated. Aside from Mg(2+) , all of the divalent cations were able to produce workable "wet" alginate films. Films gelled with BaCl2 (without added NaCl) had the highest (P < 0.05) tensile strength and Young's modulus while films gelled with CaCl2 (alone) had the highest puncture strength. The Zn-alginate and Sr-alginate films had the highest elongation at break values. Adding NaCl to the alginate film-forming solution increased the viscosity of the solution. Films with added NaCl were less transparent and had lower tensile strength, elongation, and puncture strength than films formed without NaCl in the film-forming solution. ATR-FTIR results showed a slight shift in the asymmetric COO(-) vibrational peak of the alginate when the "wet" alginate films were gelled with Zn(2+) .

Oscillatory rheological study of the gelation mechanism of whey protein concentrate solutions: effects of physicochemical variables on gel formation

The thermal gelation of a commercially available whey protein concentrate was studied by oscillatory rheometry using a Bohlin rheometer. Gelation time increased with decreasing protein concentration with a critical protein concentration (at infinite gelation time) of 6·6%. The effect of temperature in the range 65–90 °C on gelation time was described by an Arrhenius equation with an activation energy of 154 kJ/mol. Gelation time was a minimum at pH 4–6, the isoelectric region of the whey proteins. Small additions of NaCl or CaCl2 dramatically decreased gelation time. Higher protein concentrations always produced higher storage modulus (G′) values after any heating time. Loss modulus (G″) v. time curves exhibited maxima at relatively short times for protein concentrations of 30 and 35%. G′ values for 10% protein concentration increased with temperature for heating times up to 59·5 min. G′ values at 59·5 min for 25% protein concentration were higher at 78 °C than at either 85 or 90 °C. The results are discussed in terms of current theories for biopolymer gelation.

The reinfocement of gellan gel network by the immersion into salt solution

The effect of immersion into salt solutions on rheological properties of gellan gels was investigated. The storage Young's modulus of gellan gels increased with time during the immersion into salt solutions. The increase of the storage Young's modulus can not be explained solely by change in the concentration of gellan. The ellipticity at 202 nm decreased by the immersion, suggesting the formation and aggregation of gellan helices. It was considered that during immersion cations penetrated into gellan gels to induce the formation and aggregation of gellan helices in gels, resulting in reinforcement of the gel network.

Scleroglucan: a versatile polysaccharide for modified drug delivery

Scleroglucan is a natural polysaccharide, produced by fungi of the genus Sclerotium, that has been extensively studied for various commercial applications (secondary oil recovery, ceramic glazes, food, paints, etc.) and also shows several interesting pharmacological properties. This review focuses its attention on the use of scleroglucan, and some derivatives, in the field of pharmaceutics and in particular for the formulation of modified-release dosage forms. The reported investigations refer mainly to the following topics: natural scleroglucan suitable for the preparation of sustained release tablets and ocular formulations; oxidized and crosslinked scleroglucan used as a matrix for dosage forms sensitive to environmental conditions; co-crosslinked scleroglucan/gellan whose delivery rate can be affected by calcium ions. Furthermore, a novel hydrogel obtained with this polysaccharide and borate ions is described, and the particular structure of this hydrogel network has been interpreted in terms of conformational analysis and molecular dynamics. Profound attention is devoted to the mechanisms involved in drug release from the tested dosage forms that depend, according to the specific preparation, on swelling and/or diffusion. Experimental data are also discussed on the basis of a mathematical approach that allows a better understanding of the behavior of the tested polymeric materials.

Gellan film as an implant for insulin delivery

Gellan gum is an anionic polysaccharide produced by the aerobic fermentation of Pseudomonas elodea in batch culture. Gellan undergoes calcium-induced cross-linking to form a three-dimensional network, and this property makes it particularly attractive for the incorporation of biological moieties such as proteins. In this study, a procedure for the preparation of gellan films was developed and optimized, and the characteristics of these films were investigated. In addition, the effects of the concentration of each ingredient in gellan films and in vitro release behavior of fluorescein isothiocyanate dextran from these films was examined. This film device was implanted for insulin delivery in diabetic rats. The blood glucose levels of the diabetic rats implanted with insulin-loaded films were about half of those implanted with blank films, and this therapeutic effect of insulin could last for one week. Both in vitro and in vivo studies indicated that the gellan film could be an ideal candidate in the development of protein delivery systems.