Cation interactions in gellan: An x-ray study of the potassium salt

Design of in-situ implant for the brain-targeted drug delivery using cross-linked gellan gum polymer through response surface methodology

The analysis aimed to prepare an in-situ implant (ISFI) formulation holding dimethyl fumarate as (a model drug) using cross-linked gellan gum by homogenization method. Cross-linking of gellan gum was done with L-cysteine to improve its gelation properties. Fourier transform infrared spectroscopy (FTIR) and (DSC) Differential scanning calorimetry were used to test the compatibility of the drug-polymer. The diverse formulations were prepared and tested using Design Expert® ver 8.0.1 software to optimize the experiment technique and employ the response surface. The tissue compatibility of the test verified the existence of non-irritants in the established formulation. All preparations contained the drug content from approximately 97.98 to 99.88%. Viscosities are ideal for injection in the optimized formulation (1,55 percent w/w in water). The optimized formula was monitored, and up to 156hours, it was found to be 95.7%. The result was that ISFI can effectively monitor and control the delivery of several powerful drug products.

Frontier in gellan gum-based microcapsules obtained by emulsification: Core-shell structure, interaction mechanism, intervention strategies

As a translucent functional gel with biodegradability, non-toxicity and acid resistance, gellan gum has been widely used in probiotic packaging, drug delivery, wound dressing, metal ion adsorption and other fields in recent years. Because of its remarkable gelation characteristics, gellan gum is suitable as the shell material of microcapsules to encapsulate functional substances, by which the functional components can improve stability and achieve delayed release. In recent years, many academically or commercially reliable products have rapidly emerged, but there is still a lack of relevant reports on in-depth research and systematic summaries regarding the process of microcapsule formation and its corresponding mechanisms. To address this challenge, this review focuses on the formation process and applications of gellan gum-based microcapsules, and details the commonly used preparation methods in microcapsule production. Additionally, it explores the impact of factors such as ion types, ion strength, temperature, pH, and others present in the solution on the performance of the microcapsules. On this basis, it summarizes and analyzes the prospects of gellan gum-based microcapsule products. The comprehensive insights from this review are expected to provide inspiration and design ideas for researchers.

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.

Ascorbic acid-loaded gellan-g-poly(ethylene glycol) methacrylate matrix as a wound-healing material

Ascorbic acid (AA) is one of the important biomolecules involved in all phases of wound healing. The aim of this study was to develop a new hydrogel system that offers topical delivery of ascorbic acid to wounds during wound care management. In this work, we grafted poly (ethylene glycol) methacrylate onto a renewable biopolymer gellan, and the graft copolymer (GPMA) formed was crosslinked covalently and ionically, and used as a matrix for delivering AA to the wounds. By the processes of grafting and crosslinking, the mechanical properties of the gellan increased several fold compared to mechanically weak native gellan. In vitro cytotoxicity evaluation showed that GPMA was non-cytotoxic to fibroblast cells. GPMA hydrogel matrix allowed the sustained release of AA. When AA was incorporated in GPMA, a significant improvement in wound closure was observed in scratch wound assay performed with keratinocytes. Since AA acts as a cofactor in collagen synthesis, the controlled delivery of AA to the wound microenvironment favors the up-regulation of colα1 gene expression. This study revealed that ascorbic acid, at a concentration of 150 μM, has a favorable impact on wound healing when tested in vitro. Overall results indicate that the GPMA matrix could be a promising material for wound healing applications.

Molecular origin of the two-step mechanism of gellan aggregation

Among hydrocolloids, gellan is one of the most studied polysaccharides due to its ability to form mechanically stable gels. Despite its long-standing use, the gellan aggregation mechanism is still not understood because of the lack of atomistic information. Here, we fill this gap by developing a new gellan force field. Our simulations offer the first microscopic overview of gellan aggregation, detecting the coil to single-helix transition at dilute conditions and the formation of higher-order aggregates at high concentration through a two-step process: first, the formation of double helices and then their assembly into superstructures. For both steps, we also assess the role of monovalent and divalent cations, complementing simulations with rheology and atomic force microscopy experiments and highlighting the leading role of divalent cations. These results pave the way for future use of gellan-based systems in a variety of applications, from food science to art restoration.

Rheological properties and decomposition rates of Gellan gum/hyaluronic acid/β-tricalcium phosphate mixtures

The effects of β-tricalcium phosphate (TCP) on the mixture of low acyl gellan gum (LA-GAGR) and hyaluronic acid (HA) were investigated for the rheological properties and decomposition rates. All the tested mixture samples exhibited shear-thinning and typical viscoelastic behaviors. The sample made with 1.0% TCP and 0.30% LA-GAGR had the highest viscosity and loss and storage moduli and displayed gel-like behavior with the highest swelling capacity. The same mixture also exhibited the lowest average cumulative decomposition rate. High concentrations of LA-GAGR and TCP increased the degree of cross-linking of the polysaccharides, and as a result, the mixture was more elastic and less fluidic and decomposed slower. The samples prepared by gradual mixing of LA-GAGR and TCP decomposed slower than the sample prepared by sudden mixing, which indicates the well-dispersed TCP enhanced cross-linking of the polymers. This study demonstrates the possible applicability of natural polysaccharide-based shear-thinning gels for biomedical applications.

In vivo and in vitro Evaluation of in situ Gel Formulation of Pemirolast Potassium in Allergic Conjunctivitis

Background

To establish a novel delivery system of pemirolast potassium-loaded gellan gum in situ gel in allergic conjunctivitis therapy.

Methods

The prepared in situ gels were studied in the following aspects: in vitro gelation, in vitro release, stability, viscosity measurement, in vivo tear kinetics and pharmacodynamics.

Results

In this study, the results showed that the viscosity of the in situ gels significantly increased when the preparation was in contact with simulated tear fluid and it also exhibited good stability in a period of three months. In vitro release showed that the release of pemirolast potassium from in situ gels had a good sustained release ability. No ocular damage or abnormal clinical signs to the cornea, iris, or conjunctivae were visible. Consistent with the in vitro studies, pemirolast potassium in situ gels were highly efficient in suppressing the inflammatory symptoms and improving the ocular bioavailability.

Conclusion

Pemirolast potassium ocular in situ gels are safe and promising therapeutic alternatives to the existing medications for allergic conjunctivitis therapy.

Multiscale porosity in a 3D printed gellan-gelatin composite for bone tissue engineering

The aim of this work was to develop a complex-shaped gelatin-gellan composite scaffold with multiscale porosity using a combination of cryogenic 3D printing and lyophilization for bone tissue engineering. Cryogenic 3D printing was used to fabricate a low-concentration composite of complex-shaped macroporous gelatin-gellan structures with a pore size of 919 ± 89 µm. This was followed by lyophilization to introduce micropores of size 20-250 µm and nanometre-level surface functionalities, thus achieving a hierarchical porous structure. These multiscale porous scaffolds (GMu) were compared with two other types of scaffolds having only microporosity (GMi) and macroporosity (GMa) with regard to their physical andin vitrobiological properties. GMu scaffolds were found to be better than GMi and GMa in terms of swelling percentage, degradation rate, uniform pore distribution, cellular infiltration, attachment, proliferation, protein generation and mineralization. In conclusion, we have developed a controlled hierarchical bone-like structure, biomimicking natural bone, together with a reproducible process of manufacture by coupling soft hydrogel 3D printing with lyophilization. This enables the development of complex-shaped patient-specific 3D printed hydrogel scaffolds with enhanced performancein vitroand great potential in the fields of tissue engineering, bioprinting and regenerative medicine.

Synthesis of the Microbial Polysaccharide Gellan from Dairy and Plant-Based Processing Coproducts

This review examines the production of the microbial polysaccharide gellan, synthesized by Sphingomonas elodea, on dairy and plant-based processing coproducts. Gellan is a water-soluble gum that structurally exists as a tetrasaccharide comprised of 20% glucuronic acid, 60% glucose and 20% rhamnose, for which various food, non-food and biomedical applications have been reported. A number of carbon and nitrogen sources have been tested to determine whether they can support bacterial gellan production, with several studies attempting to optimize gellan production by varying the culture conditions. The genetics of the biosynthesis of gellan has been explored in a number of investigations and specific genes have been identified that encode the enzymes responsible for the synthesis of this polysaccharide. Genetic mutants exhibiting overproduction of gellan have also been identified and characterized. Several dairy and plant-based processing coproducts have been screened to learn whether they can support the production of gellan in an attempt to lower the cost of synthesizing the microbial polysaccharide. Of the processing coproducts explored, soluble starch as a carbon source supported the highest gellan production by S. elodea grown at 30 °C. The corn processing coproducts corn steep liquor or condensed distillers solubles appear to be effective nitrogen sources for gellan production. It was concluded that further research on producing gellan using a combination of processing coproducts could be an effective solution in lowering its overall production costs.

Rigid, Fibrillar Quaternary Structures Induced by Divalent Ions in a Carboxylated Linear Polysaccharide

Polysaccharides are ubiquitous in nature; they serve fundamental roles in vivo and are used for a multitude of food, pharmaceutical, cosmetic biomaterials, and biomedical applications. Here, the structure-property function for low acetylated Gellan gum hydrogels induced by divalent ions was established by means of optical, rheological, and microscopic techniques. The hydrogels interacted with visible light as revealed by birefringence and multiple scattering, as a consequence of quaternary, supramolecular fibrillar structures. The molecular assembly and structure were elucidated by statistical analysis and polymer physics concepts applied to high-resolution AFM height images and further supported by FTIR. This revealed intramolecular coil-to-single helix transitions, followed by lateral aggregation of single helices into rigid, fibrillar quaternary structures, ultimately responsible for gelation of the system. Calcium and magnesium chloride were shown to lead to fibrils up to heights of 6.0 nm and persistence lengths of several micrometers. The change in molecular structure affected the macroscopic gel stiffness, with the plateau shear modulus reaching ∼10⁵ Pa. These results shed light on the two-step gelation mechanism of linear polysaccharides, their conformational molecular changes at the single polymer level and ultimately the macroscale properties of the ensued gels.

Tunable antibiotic delivery from gellan hydrogels

Hydrogels are used extensively in wound management. Many wounds are highly susceptible to infection and hydrogels can provide localized antibacterial delivery to treat and prevent this infection. There are several key considerations in designing antibacterial hydrogels for wound therapy, including preserving activity of encapsulated antibacterial agents, controlling drug release timescales and concentrations, and having the ability to conform to various wound configurations. In this work, we have used gellan, a U.S. Food and Drug Administration approved food additive, to develop antibiotic loaded hydrogels focusing on these criteria. These hydrogels were formed to exhibit a range of mechanical properties, which were investigated using oscillatory rheology. We denoted hydrogels formed using 1% w/v gellan and 1 mM CaCl₂"ointment" hydrogels and those formed using 4% w/v gellan and 7 mM CaCl₂"sheet" hydrogels. Vancomycin, a broad-spectrum antibiotic against Gram-positive bacteria, was encapsulated in these hydrogels both directly and/or in graphitized carbon black nanoparticles (CNPs). We found that vancomycin released from both sheet and ointment hydrogels at therapeutically effective concentrations over 9 days with CNPs and 6 days without CNPs. Applying the Ritger-Peppas and Peppas-Sahlin semi-empirical drug release models to sheet hydrogels, we determined that Fickian diffusion dominates release while case II relaxation also has a small contribution. The sheet hydrogels exhibited a larger overall release of the drug (83.6 ± 1.6% compared to 67.0 ± 2.6% for ointments), which was attributed to the larger swelling resulting from osmotic pressure differences between the hydrogel formulations and the release buffer. We also suggest that final drug release amounts are influenced by intermolecular interactions between vancomycin and gellan, which were observed via quartz crystal microbalance with dissipation monitoring. Lastly, we examined the potential for future in vivo translation. We demonstrated in vitro growth inhibition of Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus in the presence of these hydrogels, demonstrating that vancomycin activity is preserved upon encapsulation. We also showed that these hydrogels are non-toxic to important wound healing cells including fibroblasts and mesenchymal stem cells.

Effects of Different Acyl Gellan Gums on the Rheological Properties and Colloidal Stability of Blueberry Cloudy Juice

In this study, gellan gums with different acyl contents were prepared, and their effects on blueberry cloudy juices were compared. The rheological properties, stability coefficients, sedimentations, color parameters and particle size distributions of blueberry cloudy juices with 0.035% (w/w) of gellan gum were measured. As the acyl content increased, the viscosity increased, and the sedimentation and stability coefficient values decreased. Gellan gums with higher acyl contents provided better beverage stabilizing capabilities through stricter enforcement of the molecular associations. Overall, this study provides valuable information for enhancing the gelation and stabilization of blueberry cloudy juices, confirms the superiority of high acyl gellan gums for inhibiting the color fading of anthocyanins, and further guides the development of novel product concepts.

PRACTICAL APPLICATION

Cloudy juices made from blueberries have many benefits. However, the particles in cloudy juices will flocculate during storage, resulting in an undesirable precipitate. In our work, gellan gums with different acyl contents were prepared and applied to blueberry juice to prevent aggregation. The results provide valuable information for enhancing the stabilization of blueberry juices, confirm the superiority of high acyl gellan for inhibiting color fading, and further guide the development of novel product concepts.

Role of process variables on the formation and in vitro digestion of gellan gels

Gellan gels were produced using different approaches forming structures with varied potential applications. Gels were characterized from appearance, mechanical properties, water holding capacity (WHC) and microstructure. In addition, in vitro digestibility of these gels was evaluated to understand the effect of gastrointestinal environment on their structure stability. All gels presented high WHC (>80% w/w) but gels were stronger with salt or acid addition, which was associated to the reduction of double helices repulsion of the negatively charged carboxyl groups of gellan. Moreover, low gelation rate induced a more controlled gellan helices aggregation, strengthening even more gels structure. Gellan gels presented resistance to digestion conditions but hardness of these gels during digestion mainly depended on the gelation rate. Based on these findings it would be possible to tune gel properties for a specific application as texture modifier or even as a faecal bulk formation assistant and an "ileal break" inducer.

Ophthalmic gels: Past, present and future

Aqueous gels formulated using hydrophilic polymers (hydrogels) along with those based on stimuli responsive polymers (in situ gelling or gel forming systems) continue to attract increasing interest for various eye health-related applications. They allow the incorporation of a variety of ophthalmic pharmaceuticals to achieve therapeutic levels of drugs and bioactives at target ocular sites. The integration of sophisticated drug delivery technologies such as nanotechnology-based ones with intelligent and environment responsive systems can extend current treatment duration to provide more clinically relevant time courses (weeks and months instead of hours and days) which will inevitably reduce dose frequency, increase patient compliance and improve clinical outcomes. Novel applications and design of contact lenses and intracanalicular delivery devices along with the move towards integrating gels into various drug delivery devices like intraocular pumps, injections and implants has the potential to reduce comorbidities caused by glaucoma, corneal keratopathy, cataract, diabetic retinopathies and age-related macular degeneration. This review describes ophthalmic gelling systems with emphasis on mechanism of gel formation and application in ophthalmology. It provides a critical appraisal of the techniques and methods used in the characterization of ophthalmic preformed gels and in situ gelling systems along with a thorough insight into the safety and biocompatibility of these systems. Newly developed ophthalmic gels, hydrogels, preformed gels and in situ gelling systems including the latest in the area of stimuli responsive gels, molecularly imprinted gels, nanogels, 3D printed hydrogels; 3D printed devices comprising ophthalmic gels are covered. Finally, new applications of gels in the production of artificial corneas, corneal wound healing and hydrogel contact lenses are described.

Case Studies of Physical and Chemical Gels Based on Microbial Polysaccharides

Microbial anionic polysaccharides, although structurally closely related, exhibit strikingly different gelling properties in aqueous media (physical gels formation). Experimental observations are traced to differences, minor differences in some instances, in primary structures. Chemical gels have been prepared using deacylated gellan by means of an interchain partial esterification procedure, and a sample subjected to preliminary characterization in terms of swelling properties. NMR water proton relaxation data show that such amples display a remarkable water retention capability.

A novel in situ gel formulation of ranitidine for oral sustained delivery

The main purpose of this study was to develop a novel, in situ gel system for sustained delivery of ranitidine hydrochloride. Ranitidine in situ gels at 0.2%, 0.5%, and 1.0% gellan gum concentration (w/v) were prepared, respectively, and characterized in terms of preparation, viscosity and in vitro release. The viscosity of the gellan gum formulations in solution increased with increasing concentrations of gellan gum. In vitro study showed that the release of ranitidine from these gels was characterized by an initial phase of high release (burst effect) and translated to the second phase of moderate release. Single photon emission computing tomography technique was used to evaluate the stomach residence time of gel containing ^99mTc tracer. The animal experiment suggested in situ gel had feasibility of forming gels in stomach and sustained the ranitidine release from the gels over the period of at least 8 h. In conclusion, the in situ gel system is a promising approach for the oral delivery of ranitidine for the therapeutic effects improvement.

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+) .

Development of a synovial fluid analogue with bio-relevant rheology for wear testing of orthopaedic implants

The rheological properties of synovial fluid (SF) are crucial to the performance of joint prostheses. During the development of joint prostheses, wear tests are performed, which simulate joint movements in diluted solutions (usually between 25 and 33% v/v) of bovine serum which has very different rheological properties compared with native SF, where rheology is maintained by hyaluronan. Consequently, there is a need to develop a more suitable artificial SF. In this study, we used rheological techniques to understand SF flow properties which provided an insight into the mechanical behaviour required of a practical SF analogue. Steady-shear viscosity measurements were performed to reveal changes as a function of shear rate. To analyse the viscoelastic properties small deformation oscillatory measurements of storage modulus (G') loss modulus (G″) and complex viscosity (η(⁎)) were made. The rheological properties of the SF where compared with those of the polysaccharides sodium alginate, gellan gum and mixtures of both polymers. Initial results revealed classic shear thinning behaviour for the SF with a small Newtonian plateau at low shear rates with a gradual reduction in viscosity with increasing shear rate. Viscoelasticity measurements also showed that at low frequencies of oscillation there was a viscous response with G″ greater than G' and at higher frequencies there was an elastic response. Rheological properties were found to be similar to that of a 50:50 mix of 2% w/v high molecular weight alginate and 0.75% w/v gellan gum. Importantly, the lubricating behaviour of the serum differed significantly from the biopolymer blend over a full range of sliding velocities. The biopolymer blend was shown to lubricate the opposing surfaces more effectively. This difference was attributed to the more rapid alignment of the polysaccharide during shear when compared with the bovine albumin (the most abundant protein in serum), which typically exhibits a globular structure and has a tendency for self-association. These results suggest that polysaccharide solutions with bio-relevant rheology maybe be suitable as lubricants for in vitro orthopaedic prosthetic wear tests.

PolySac3DB: an annotated data base of 3 dimensional structures of polysaccharides

Background

Polysaccharides are ubiquitously present in the living world. Their structural versatility makes them important and interesting components in numerous biological and technological processes ranging from structural stabilization to a variety of immunologically important molecular recognition events. The knowledge of polysaccharide three-dimensional (3D) structure is important in studying carbohydrate-mediated host-pathogen interactions, interactions with other bio-macromolecules, drug design and vaccine development as well as material science applications or production of bio-ethanol.

Description

PolySac3DB is an annotated database that contains the 3D structural information of 157 polysaccharide entries that have been collected from an extensive screening of scientific literature. They have been systematically organized using standard names in the field of carbohydrate research into 18 categories representing polysaccharide families. Structure-related information includes the saccharides making up the repeat unit(s) and their glycosidic linkages, the expanded 3D representation of the repeat unit, unit cell dimensions and space group, helix type, diffraction diagram(s) (when applicable), experimental and/or simulation methods used for structure description, link to the abstract of the publication, reference and the atomic coordinate files for visualization and download. The database is accompanied by a user-friendly graphical user interface (GUI). It features interactive displays of polysaccharide structures and customized search options for beginners and experts, respectively. The site also serves as an information portal for polysaccharide structure determination techniques. The web-interface also references external links where other carbohydrate-related resources are available.

Conclusion

PolySac3DB is established to maintain information on the detailed 3D structures of polysaccharides. All the data and features are available via the web-interface utilizing the search engine and can be accessed at http://polysac3db.cermav.cnrs.fr.

Hydroxyapatite/gelatin/gellan sponges as nanocomposite scaffolds for bone reconstruction

The aim of this work was the morphological, physicochemical, mechanical and biological characterization of a new composite system, based on gelatin, gellan and hydroxyapatite, and mimicking the composition of natural bone. Porous scaffolds were prepared by freeze-drying technique, under three different conditions of freezing. The morphological analysis showed a homogeneous porosity, with well interconnected pores, for the sample which underwent a more rapid freezing. The elastic modulus of the same sample was close to that of the natural bone. The presence of interactions among the components was demonstrated through the physicochemical investigation. In addition, the infrared chemical imaging analysis pointed out the similarity among the composite scaffold and the natural bone, in terms of chemical composition, homogeneity, molecular interactions and structural conformation. Preliminary biological characterization showed a good adhesion and proliferation of human mesenchymal stem cells.