Molecular origin of the two-step mechanism of gellan aggregation

Gellan Gum Biosynthesis in Microorganisms: Current Status and Future Directions

Gellan gum is a widely used gel polysaccharide that is gaining market preference because of its unique gel characteristics. Although the biological synthesis of gellan gum dates back to the 1970s, research into its synthetic metabolic pathways has lagged behind that of other polysaccharides because of a lack of clarity. In recent years, driven by growing market demand and advancements in our understanding of metabolic pathways, as well as the rapid development of genetic engineering tools, the biological synthesis of gellan gum has progressed significantly. This article summarizes the developmental history of Sphingomonas paucimobilis ATCC 31461 and the structure of gellan gum, with a particular focus on the metabolic pathway involved in the production of gellan gum by these strains. This review discusses the metabolic engineering and research progress of key genes at different stages of the synthesis pathway. Additionally, this article introduces strategies for obtaining high-titer strains using traditional breeding methods and metabolic engineering approaches. Finally, it addresses the methods for producing low-molecular-weight-gellan gum. We discuss ongoing disputes in the field and highlight promising directions for future research. This review aims to address the bottlenecks in gellan gum production by promoting a greener and more sustainable manufacturing process.

Gellan-based hydrogels and microgels: A rheological perspective

Gellan gum-based systems have gained significant attention due to their versatility for multiple applications. In particular, they have shown a great potentiality in the field of cultural heritage, as efficient paper artwork cleaning agents in restoration processes. This efficacy is enhanced when gellan gum is assembled to form stable microgels, by controlling the gelation process under shear. Moreover, the use of methacrylated gellan gum provides additional functionality to the systems, that are also able to remove hydrophobic residues during the cleaning process. However, in order to optimize the manufacturing process, it is fundamental to obtain a thorough understanding of the rheological behaviour of the employed gellan gels in the optimal working conditions for paper cleaning. The present work aims to thoroughly characterize the rheological properties of low-acyl gellan gum, also during hydrogel and microgel formation, assessing the role of temperature (25-80 °C), gellan concentration (0.5-5 % for hydrogels and 0.1-0.5 % for microgels), methacrylation, presence of different cations (Na+, Ca2+) and salt concentration (0.25-5.0 mM for hydrogels and 100 mM for microgels), on the behaviour of viscosity and viscoelastic moduli. We find the notable result that gellan hydrogels and microgels exhibit a double yielding behaviour in the conditions where they are mostly efficient for art restoration. Furthermore, we identify the optimal rheological conditions of these gels for efficient artwork restoration, opening the possibility to extend their applications to different substrates and in other fields.

Unveiling the self-assembly process of gellan-chitosan complexes through a combination of atomistic simulations and experiments

Polyelectrolyte complexes (PECs), formed via the self-assembly of oppositely charged polysaccharides, are highly valued for their biocompatibility, biodegradability, and hydrophilicity, offering significant potential for biotechnological applications. However, the complex nature and lack of insight at a molecular level into polyelectrolytes conformation and aggregation often hinders the possibility of achieving an optimal control of PEC systems, limiting their practical applications. To address this problem, an in-depth investigation of PECs microscopic structural organization is required. In this work, for the first time, a hybrid approach that combines experimental techniques with atomistic molecular dynamics simulations is used to elucidate, at a molecular level, the mechanisms underlying the aggregation and structural organization of complexes formed by gellan and chitosan, i.e. PECs commonly used in food technology. This combined analysis reveals a two-step complexation process: gellan initially self-assembles into a double-helix structure, subsequently surrounded and stabilized by chitosan via electrostatic interactions. Furthermore, these results show that complexation preserves the individual conformation and intrinsic functionality of both polyelectrolytes, thereby ensuring the efficacy of the PECs in biotechnological applications.

An Antifreezing Scaffold-Based Cryopreservation Platform of Stem Cells for Convenient Application in Wound Repair

Efficient cryopreservation of stem cells is crucial to fabricating off-the-shelf cell products for tissue engineering and regeneration medicine. However, it remains challenging due to utilization of toxic cryoprotectants for reducing ice-related cryodamages to stem cells during freeze-thaw cycle, stringent post-thaw washing process, and further integration of stem cells with scaffolds to form tissue engineering constructs for downstream applications. Herein, a novel cryopreservation platform of stem cells based on an antifreezing polyvinylpyrrolidone/gellan gum/gelatin (PGG) scaffold together is reported with an L-proline assisted cell pre-dehydration strategy. Results show that this platform is capable of inhibiting extra-/intracellular ice, thus can achieve high cryoprotection efficacy to stem cells (≈95%) without using any toxic cryoprotectants and eliminate traditional washing process. Meanwhile, the post-thawed stem cells can maintain their proliferation, differentiation, and paracrine functionalities. More importantly, due to the biocompatibility and three dimensional structure of the PGG scaffold, the post-thawed stem cell-laden PGG scaffold can be directly used as tissue engineering constructs for wound repair by mitigating inflammation and promoting collagen deposition at regenerating tissue sites. This present work demonstrates the feasibility of antifreezing scaffold-based cryopreservation platform of stem cells, which may advance the off-the-shelf stem cell-laden tissue engineering constructs for clinical translation.

Synergistic potential of gellan gum methacrylate and keratin hydrogel for visceral hemostasis and skin tissue regeneration

In recent years, the development of biodegradable hydrogels as an alternative over the traditional wound dressing has become increasingly significant. These specific hydrogels are able to offer suitable microenvironments to further aid the process of tissue or organ regeneration. However, application of biodegradable hydrogels in clinical medicine remains uncommon due to most biodegradable hydrogels struggle with achieving satisfactory adhesiveness property, high mechanical support and cell compatibility simultaneously. In order to overcome these constraints and enhance the applicability of biodegradable hydrogels, methods have been employed in this study. By reacting gellan gum with methacrylic anhydride and incorporating a biodegradable protein, keratin, we endowed the hydrogels with high pliability via photo-polymerization chain extension, thereby obtaining a biodegradable hydrogel with exceptional properties. Through a series of in vitro tests, GGMA/keratin hydrogels exhibited great cell compatibility via providing an appropriate environment for cell proliferation. Furthermore, this hydrogel not only exhibits extraordinary adhesive ability on visceral tissues but also extends to scenarios involving skin or organ damage, offering valuable assistance in wound healing. Our design provides a suitable platform for cell proliferation and tissue regeneration, which shows prospects for future medical research and clinical applications.

Ammonia/pH super-sensitive colorimetric labels based on gellan gum, sodium carboxymethyl cellulose, and dyes for monitoring freshness of lamb meat

This study aimed to develop an ammonia and pH super-sensitive label by incorporating methyl red and bromothymol blue (MR-BTB, MB) into gellan gum/sodium carboxymethyl cellulose (GG/CMC-Na, GC). Furthermore, E-nose as an auxiliary tool combined with the labels to monitor meat freshness. Results showed that MB had more color change than pure MR or BTB, and the detection limit of ammonia about the MR-BTB (1:2) group was only 2.82 ppm. The addition of MB significantly increased tensile strength, moisture content, and water solubility, but decreased elongation at break and transmittance of the GC label (p < 0.05). The result of FTIR and SEM indicated the formation of hydrogen bonds and well compatibility between MB and GC. Furthermore, the color of the GC-10.0MB label was constantly obviously changing during meat storage, indicating that the GC-10.0MB label had great potential for monitoring the freshness of the lamb meat. A high correlation was found between ΔE of GC-10.0MB label and TVB-N (R2 = 0.9092) and pH (R2 = 0.9114) of meat. Interestingly, the high correlation between ΔE of GC-10.0 MB label and the response value of S2 (R2 = 0.7531), S6 (R2 = 0.9921), and S7 sensor (R2 = 0.8325) of E-nose was also found.

Transient, Image-Guided Gel-Dissection for Percutaneous Thermal Ablation

Image-guided tumor ablative therapies are mainstay cancer treatment options but often require intra-procedural protective tissue displacement to reduce the risk of collateral damage to neighboring organs. Standard of care strategies, such as hydrodissection (fluidic injection), are limited by rapid diffusion of fluid and poor retention time, risking injury to adjacent organs, increasing cancer recurrence rates from incomplete tumor ablations, and limiting patient qualification. Herein, a "gel-dissection" technique is developed, leveraging injectable hydrogels for longer-lasting, shapeable, and transient tissue separation to empower clinicans with improved ablation operation windows and greater control. A rheological model is designed to understand and tune gel-dissection parameters. In swine models, gel-dissection achieves 24 times longer-lasting tissue separation dynamics compared to saline, with 40% less injected volume. Gel-dissection achieves anti-dependent dissection between free-floating organs in the peritoneal cavity and clinically significant thermal protection, with the potential to expand minimally invasive therapeutic techniques, especially across locoregional therapies including radiation, cryoablation, endoscopy, and surgery.

Ultrasound-Stimulated PVA Microbubbles as a Green and Handy Tool for the Cleaning of Cellulose-Based Materials

One of the main issues in the cultural heritage field of restoration chemistry is the identification of greener and more effective methods for the wet cleaning of paper artefacts, which serve as witnesses to human history and custodians of cultural values. In this context, we propose a biocompatible method to perform wet cleaning on paper based on the use of 1 MHz ultrasound in combination with water-dispersed polyvinyl alcohol microbubbles (PVAMBs), followed by dabbing with PVA-based hydrogel. This method can be applied to both old and new papers. FTIR spectroscopy, X-ray diffraction, HPLC analysis, pH measurements and tensile tests were performed on paper samples, to assess the efficacy of the cleaning system. According to the results, ultrasound-activated PVAMB application allows for an efficient interaction with rough and porous cellulose paper profiles, promoting the removal of cellulose degradation byproducts, while the following hydrogel dabbing treatment guarantees the removal of cleaning materials residues. Moreover, the results also pointed out that after the treatment no thermal or mechanical damages had affected the paper. In conclusion, the readability of these kinds of artifacts can be improved without causing an alteration of their structural properties, while mitigating the risk of ink diffusion.

Diversity of Bioinspired Hydrogels: From Structure to Applications

Hydrogels are three-dimensional networks with a variety of structures and functions that have a remarkable ability to absorb huge amounts of water or biological fluids. They can incorporate active compounds and release them in a controlled manner. Hydrogels can also be designed to be sensitive to external stimuli: temperature, pH, ionic strength, electrical or magnetic stimuli, specific molecules, etc. Alternative methods for the development of various hydrogels have been outlined in the literature over time. Some hydrogels are toxic and therefore are avoided when obtaining biomaterials, pharmaceuticals, or therapeutic products. Nature is a permanent source of inspiration for new structures and new functionalities of more and more competitive materials. Natural compounds present a series of physico-chemical and biological characteristics suitable for biomaterials, such as biocompatibility, antimicrobial properties, biodegradability, and nontoxicity. Thus, they can generate microenvironments comparable to the intracellular or extracellular matrices in the human body. This paper discusses the main advantages of the presence of biomolecules (polysaccharides, proteins, and polypeptides) in hydrogels. Structural aspects induced by natural compounds and their specific properties are emphasized. The most suitable applications will be highlighted, including drug delivery, self-healing materials for regenerative medicine, cell culture, wound dressings, 3D bioprinting, foods, etc.