Role of salt ions and molecular weights on the formation of Mesona chinensis polysaccharide-chitosan polyelectrolyte complex hydrogel

Effect of curdlan on the gel properties and interactions of whey protein isolate gels

This study investigated the influence of curdlan on the gel properties of whey protein isolate (WPI). Results demonstrated that curdlan significantly improved the water-holding capacity, gel strength and rheological properties of the WPI gels. Moreover, it promoted the unfolding of the molecular structures of WPI, which was manifested by the transition from α-helix to β-sheet, an increase in free sulfhydryl content and a decrease in surface hydrophobicity. Furthermore, 4 % curdlan promoted the formation of WPI with uniform and compact elastic gel network structures, primarily attributed to disulphide bonds, hydrogen bonds and hydrophobic interactions. However, when the addition of curdlan exceeds 4 %, excessive entanglement of curdlan chains and steric hindrance effects hinder the unfolding and folding of protein structures, weaken their interaction, result in a loose network structure and affect the gel properties. In conclusion, this study demonstrates that curdlan can effectively improve the gelling properties of WPI, suggesting its potential application in low-calorie gel-based dairy products.

Preparation technologies, structural features, and biological activities of polysaccharides from Mesona chinensis Benth.: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Mesona chinensis Benth. (or Platostoma palustre (Blume) A. J. Paton) is an important medicinal and edible plant also known as the Hsian-tsao in China and Southeast Asian countries. It is cold in nature and sweet in taste, with the effects of clearing heat, relieving heatstroke and diuretic, and traditionally used to treat heatstroke, erysipelas, hypertension, joint pain and other diseases in folk medicine. It is also a popular supplement with the function of detoxifying and heat-clearing use in Asia. It is used to be processed into the popular tea, Bean jelly, and so on. Published studies have demonstrated that polysaccharides from M. chinensis (MCPs) are one of the principal bioactive ingredients with a variety of health-promoting effects in the prevention and treatment of diseases, including antioxidant, immunomodulation, anti-inflammatory, hepatoprotective, anti-tumor, hypoglycemic, regulation of gut microbiota, and other pharmacological properties.

AIM OF THE REVIEW

This review aims to compile the extraction and purification methods, structural characteristics, pharmacological activities including the mechanism of action of MCPs, and to further understand the applications of M. chinensis in order to lay the foundation for the development of MCPs.

MATERIALS AND METHODS

By inputting the search term "Mesona chinensis polysaccharides", relevant research information was obtained from databases such as PubMed, Google Scholar, Web of Science, and China National Knowledge Infrastructure (CNKI).

RESULTS

More than 40 polysaccharides have been extracted from M. chinensis, different extraction and purification methods have been described, as well as the structural features and pharmacological activities of MCPs have been systematically reviewed. Polysaccharides, as important components of M. chinensis, were mainly extracted by methods such as hot water dipping method, hot alkali extraction method, enzyme-assisted extraction method and ultrasonic-assisted extraction method, subsequently obtained by decolorization, deproteinization, removal of other small molecules and separation on various chromatographic columns. The chemical composition and structure of MCPs show diversity and have a variety of pharmacological activities, including antioxidant, immunomodulation, anti-inflammatory, hepatoprotective, anti-tumor, hypoglycemic, regulation of gut microbiota, and so on.

CONCLUSIONS

This article systematically reviews the research progress of MCPs in terms of extraction and purification, structural characteristics, rheological gel properties, pharmacological properties, and safety assessment. The potentials and roles of M. chinensis in the field of medicine, functional food, and materials are further highlighted to provide references and bases for the high-value processing and utilization of MCPs.

Functionality and Health-Promoting Properties of Polysaccharide and Plant-Derived Substances from Mesona chinensis

Mesona chinensis, in Thai called Chao Kuay and in Chinese Hsian-tsao, belongs to the Lamiaceae family. This herbal plant grows widely in Southern China, Taiwan (China), Malaysia, the Philippines, Indonesia, Vietnam, and Thailand. The Mesona plant is used to make functional products such as drinks and soft textured sweet treats, and also traditional medicine, to treat heat stroke, high blood pressure, heart attack, high blood sugar, hepatic diseases, colon diseases, inflammatory conditions, and to alleviate myalgia. The proximate composition of M. chinensis is a mixture of protein, fat, fiber, ash, and minerals. The main biological compounds in M. chinensis extracts are polysaccharides, terpenoids, flavonoids, and polyphenols, with wide-ranging pharmacological properties including antioxidant, antidiabetic, antilipidemic, carcinoma-inhibitory, renal-protective, antihypertensive, DNA damage-protective, and anti-inflammatory effects. This review investigated the proximate composition, polysaccharide type, and pharmacological properties of M. chinensis extracts. Phytochemical properties enhance the actions of the gut microbiota and improve health benefits. This review assessed the functional and medicinal activities of M. chinensis extracts. Future studies should further elucidate the in vitro/in vivo mechanisms of this plant extract and its impact on gut health.

Antioxidant stability and in vitro digestion of β-carotene-loaded oil-in-water emulsions stabilized by whey protein isolate-Mesona chinensis polysaccharide conjugates

The aim of this study was to investigate the delivery of functional factor β-carotene by emulsion stabilized with whey protein isolate-Mesona chinensis polysaccharide (WPI-MCP) conjugate. Results showed that the WPI-MCP complex had better antioxidant properties than WPI. Correspondingly, the emulsions stabilized by this complex also had better oxidative stability compared with protein emulsions alone. The particle size of WPI-MCP emulsion was smaller and had a better stability when MCP was added at 0.2 % (w/v). The sizes of WPI-MCP and WPI emulsions were 3594.33 and 7765.67 nm at pH 4, indicating improved emulsion stability around isoelectric point of WPI. At different NaCl concentrations, the absolute values of zeta-potential of WPI-MCP emulsions were larger than that of WPI emulsions except 0.1 % (mol/L) NaCl. The sizes of WPI and WPI-MCP emulsions were 2384.32 and 790.12 nm, respectively. During in vitro digestion, WPI-MCP stabilized emulsions slowed down the release of free fatty acids and achieved about 80 % bioaccessibility of β-carotene, indicating that WPI-MCP-stabilized emulsions encapsulating β-carotene can effectively control the release of bioactive substances. These studies have potential significance and value for the construction of food-grade emulsion delivery system.

Effect of Na+ and Ca2+ on the texture, structure and microstructure of composite protein gel of mung bean protein and wheat gluten

To investigate the change of ionic strength on the gel characteristics during the processing of mung bean protein-based foods, the effects of NaCl and CaCl2 at different concentrations (0-0.005 g/mL) on the properties of mung bean protein (MBP) and wheat gluten (WG) composite protein gel were studied. The results showed that low concentration (0.001-0.002 g/mL) could significantly improve the water holding capacity (WHC), storage modulus (G') and texture properties of composite protein gel (MBP/WG), while the surface hydrophobicity (H0) and solubility were significantly decreased (P < 0.05). With the increase of ion concentration, the secondary structures of MBP/WG shifted from α-helix to β-sheet, and the fluorescence spectra also showed fluorescence quenching phenomenon. By analyzing the intermolecular forces of MBP/WG, it was found that with the addition of salt ions, the hydrogen bonds was weakened and the electrostatic interactions, hydrophobic interactions and disulfide bonds were enhanced, which in turn the aggregation behavior of MBP/WG composite protein gel was affected and larger aggregates between the proteins were formed. It could be also demonstrated that the gel network was denser due to the addition of these large aggregates, thus the gel properties of MBP/WG was improved. However, too many salt ions could disrupt the stable network structure of protein gel. This study can provide theoretical support to expand the development of new mung bean protein products.

Plant-Derived Biomaterials and Their Potential in Cardiac Tissue Repair

Cardiovascular disease remains the leading cause of mortality worldwide. The inability of cardiac tissue to regenerate after an infarction results in scar tissue formation, leading to cardiac dysfunction. Therefore, cardiac repair has always been a popular research topic. Recent advances in tissue engineering and regenerative medicine offer promising solutions combining stem cells and biomaterials to construct tissue substitutes that could have functions similar to healthy cardiac tissue. Among these biomaterials, plant-derived biomaterials show great promise in supporting cell growth due to their inherent biocompatibility, biodegradability, and mechanical stability. More importantly, plant-derived materials have reduced immunogenic properties compared to popular animal-derived materials (e.g., collagen and gelatin). In addition, they also offer improved wettability compared to synthetic materials. To date, limited literature is available to systemically summarize the progression of plant-derived biomaterials in cardiac tissue repair. Herein, this paper highlights the most common plant-derived biomaterials from both land and marine plants. The beneficial properties of these materials for tissue repair are further discussed. More importantly, the applications of plant-derived biomaterials in cardiac tissue engineering, including tissue-engineered scaffolds, bioink in 3D biofabrication, delivery vehicles, and bioactive molecules, are also summarized using the latest preclinical and clinical examples.

Effect of Chitosan on Rheological, Mechanical, and Adhesive Properties of Pectin-Calcium Gel

In the present study, chitosan was included in the pectin ionotropic gel to improve its mechanical and bioadhesive properties. Pectin-chitosan gels P-Ch0, P-Ch1, P-Ch2, and P-Ch3 of chitosan weight fractions of 0.00, 0.25, 0.50, and 0.75 were prepared and characterized by dynamic rheological tests, penetration tests, and serosal adhesion ex vivo assays. The storage modulus (G') and loss modulus (G″) values, gel hardness, and elasticity of P-Ch1 were significantly higher than those of P-Ch0 gel. However, a further increase in the content of chitosan in the gel significantly reduced these parameters. The inclusion of chitosan into the pectin gel led to a decrease in weight and an increase in hardness during incubation in Hanks' solution at pH 5.0, 7.4, and 8.0. The adhesion of P-Ch1 and P-Ch2 to rat intestinal serosa ex vivo was 1.3 and 1.7 times stronger, whereas that of P-Ch3 was similar to that of a P-Ch0 gel. Pre-incubation in Hanks' solution at pH 5.0 and 7.4 reduced the adhesivity of gels; however, the adhesivity of P-Ch1 and P-Ch2 exceeded that of P-Ch0 and P-Ch3. Thus, serosal adhesion combined with higher mechanical stability in a wide pH range appeared to be advantages of the inclusion of chitosan into pectin gel.

Role of metal chlorides in the gelation and properties of fucoidan/κ-carrageenan hydrogels

Metal ions play a crucial role in forming hydrogels, and their effects on fucoidan (FUC): κ-carrageenan (KC) mixed gels were investigated. The results indicated that the FUC: KC mixed gels (FC) were promoted by K⁺ and Ca²⁺ but destroyed by Fe³⁺. The gel strength of FC was enhanced by K⁺ and Ca²⁺, with G' and G″ being highest at 50 mmol/L KCl and 25 mmol/L CaCl₂, respectively. Water mobility was weakened after the addition of KCl and CaCl₂ in accordance with the decrease in T₂₃ relaxation time (free water, 100-1000 ms). After addition of KCl and CaCl₂, the FC groups presented a typical three-dimensional network structure in contrast to the lamellar, disordered, and broken structure of FUC. Moreover, the FT-IR spectrum certified the enhancement of hydrogen bonds and the occurrence of electrostatic interactions during gel formation by the red-shift of the OH stretching vibration of the Ca²⁺ group and the blue-shift of the COS vibrations. The XRD results confirmed that the binding of Ca²⁺ to FC was tighter than that of K⁺ at the same charge content. These results provide a theoretical basis for understanding the interaction mechanism of FC with metal ions.

Effects of Abelmoschus manihot gum content, heating temperature and salt ions on the texture and rheology properties of konjac gum/Abelmoschus manihot gum composite gel

To improve the gelling property of konjac gum (KGM) and enhance the application value of Abelmoschus manihot (L.) medic gum (AMG), a novel type of gel was prepared using KGM and AMG in this study. The effects of AMG content, heating temperature and salt ions on the characteristics of KGM/AMG composite gels were studied by Fourier transform infrared spectroscopy (FTIR), zeta potential, texture analysis and dynamic rheological behavior analysis. The results indicated that the AMG content, heating temperature and salt ions could affect the gel strength of KGM/AMG composite gels. Hardness, springiness, resilience, G', G* and η* of KGM/AMG composite gels increased when AMG content increased from 0 to 2.0 %, but they decreased when AMG increased from 2.0 % to 3.5 %. High-temperature treatment significantly enhanced the texture and rheological properties of KGM/AMG composite gels. The addition of salt ions reduced the zeta potential absolute value and weakened the texture and rheological properties of KGM/AMG composite gels. Furthermore, the KGM/AMG composite gels could be classified as non-covalent gels. The non-covalent linkages included hydrogen bonding and electrostatic interactions. These findings would help understand the properties and formation mechanism of KGM/AMG composite gels and help improve the application value of KGM and AMG.

Textural characterization of calcium salts-induced mung bean starch-flaxseed protein composite gels as dysphagia food

Effects of calcium gluconate (CG), calcium lactate (CL) and calcium dihydrogen phosphate (CDP) on the structural and functional properties of mung bean starch (MBS)-flaxseed protein (FP) composite gels were investigated to explore the feasibility of developing dysphagia food. The water-immobilizing, rheological and structural properties of MBS-FP composite gels adding different calcium salts (10, 30, and 50 mmol/L) were analyzed by low-field nuclear magnetic resonance measurement, rheological and textural analyses, fourier transform infrared spectroscopy, scanning electron microscopy and confocal laser scanning microscopy. Results showed that calcium salts imparted various soft gel properties to the composite gels by influencing the interactions between MBS and FP. Calcium salts could affect the conformation of amylose chains, accelerate the aggregation of FP molecules, and increase the cross-linking between starch and protein aggregates, resulting in the formation of large aggregates and a weak gel network. Consequently, calcium salts-induced composite gels showed lower viscoelastic moduli and gel strength than the control gel. In particular, different calcium salts had various impacts on the gel properties due to their diverse ability forming hydrogen bonds. Compared with CL and CDP, the gels containing CG presented the higher viscoelastic moduli and hardness, and possessed an irregular cellular network with the increased pore number and the decreased wall thickness. The gel containing 50 mmol/L CL had the highest water-holding capacity, in all the gels tested, by retaining more immobilized and mobile water in the compact gel network with larger cavities. The gels adding CDP presented lower hardness and gumminess due to the obvious lamellar structure within the network. International dysphagia diet standardization initiative (IDDSI) tests indicated that the gels adding CG and CL could be categorized into level 6 (soft and bite-sized) dysphagia diet, while the samples adding CDP could be classified into level 5 (minced and moist). These findings provide insights for the development of the novel soft gel-type dysphagia food.

Stretchable and fatigue resistant hydrogels constructed by natural galactomannan for flexible sensing application

Exploration of sustainable and functional materials from biomolecules has received much interest, while the limited mechanical property and possible bacterial contamination were proved to be their major shortages. Here, we proposed novel double network (DN) hydrogels based on galactomannan (GM) polysaccharide as backbone. Folic acid (FA) and polyacrylamide (PAM) were introduced to form hydrogen bond linkages and covalent bond networks respectively. The three-dimensional hydrogel networks showed greatly improved mechanical strength. Impressive compressive fatigue resistance was present for 100 cycles' compression forming only 0.7 % shape deformation. The phenomenon was mainly attributed to promoted stress-bearing and energy dissipation from the DN cross-linking. The GM hydrogels also exhibited good electronic conductivity and excellent anti-bacterial capabilities with inhibition against more than 80 % of E. coli., attributing to the tunable attachments of FA. Thus, we provided multi-functional hydrogels of high potential serving as anti-fatigue/bacterial and conductive strain sensors on the fields of wearable devices.

Eco-Friendly Extraction, Structure, and Gel Properties of ι-Carrageenan Extracted Using Ca(OH)2

An eco-friendly method for ι-carrageenan extraction from seaweed Eucheuma denticulatum through boiling and using a low concentration of Ca(OH)2 is reported. Compared to the traditional method of ι-carrageenan extraction using NaOH, the reported method using Ca(OH)2 had the advantages of using 93.3% less alkali and 86.8% less water, having a 25.0% shorter total extraction time, a 17.6% higher yield, and a 43.3% higher gel strength of the product. In addition, we evaluated the gel properties and structures of ι-carrageenan products extracted by Ca(OH)2 (Ca-IC) and NaOH (Na-IC). The Fourier transform infrared spectroscopy results showed that the structures of Ca-IC and Na-IC did not change remarkably. The results of the thermogravimetric analysis and differential scanning calorimetry showed that Ca-IC had the same thermal stability as Na-IC. The results of the textural analysis showed that Ca-IC had a higher hardness and better chewiness compared to Na-IC. Rheological results indicated that Ca-IC and Na-IC exhibited shear-thinning and non-Newtonian fluid properties, whereas the viscosity of Ca-IC was less than that of Na-IC. In conclusion, this new method of ι-carrageenan extraction using Ca-IC is markedly better and yields higher quality carrageenan than the conventional method of using Na-IC.

A self-healing and self-adhesive chitosan based ion-conducting hydrogel sensor by ultrafast polymerization

Recently, owing to the wide applications in electronic skin and human activity monitoring, flexible hydrogel strain sensors have attracted great attention. And the better preparation with more efficient is always common aspiration. In this work, acrylamide (AM) was in situ polymerized in chitosan (CS) matrix to prepare hydrogels (PAM@CS). Inspired by the adhesion of natural mussels, plant polyphenol tannic acid (TA) was introduced into the system, Fe³⁺ was also introduced as redox agent to perform an ultrafast polymerization, and the composite hydrogel PAM@CS/TA-Fe can be prepared at 60 °C within 1 min. The hydrogels are ion conductive and show good sensing performance in detecting major and subtle body motions. Benefiting from the multiple dynamic noncovalent bonds, the PAM@CS/TA-Fe hydrogels also show excellent adhesion performance and good self-healing property, which would expand their application range in wearable and flexible electronic equipment.

Preparation and Characterizations of PSS/PDADMACPolyelectrolyte Complex Hydrogel

Polyelectrolyte complex (PEC) hydrogel, formed via physically electrostatic crosslinks between polyanion and polycation, is an interesting hydrogel in terms of its nontoxicity and solvent-free technique. In this work, poly (sodium 4-styrenesulfonate) (PSS)/poly (diallyl dimethyl ammonium chloride) (PDADMAC) complex hydrogels were prepared. Firstly, the PSS/PDADMAC complex aggregates using various PSS/PDADMAC mole fractions that were prepared in the presence of NaCl solution. Then, the aggregates were resolubilized under stirring at 70 °C for 2 h to obtain a homogeneous PEC solution. Finally, the PEC solution was dialyzed using a dialysis membrane with 3500 molecular cut-off for 1 day. The dialysis bath was changed every interval period of 2 h to control the rate of reversible electrostatic interaction, resulting in the homogenous PEC hydrogel with porous morphology as revealed by SEM and BET investigations. The dimensional stability and viscoelasticity of the PEC hydrogel was studied by DMA experiment, which showed the viscoelastic behavior at a compressive force ranging from 0 to 0.1 N. Finally, PSS/PDADMAC hydrogels showed a high water absorbency property and excellent affinity to textile anionic dyes.

Fabrication of Zein/Mesona chinensis Polysaccharide Nanoparticles: Physical Characteristics and Delivery of Quercetin

Polysaccharides are considered to be highly stable, nontoxic, hydrophilic, biodegradable, and biocompatible, coupled with the diverse chemical functions they contain, making them promising biomaterials for the development of nutrient delivery systems. In this study, we prepared zein-Mesona chinensis polysaccharide (MCP) nanoparticles by antisolvent precipitation. Zien and MCP self-assembly formed smooth spherical nanoparticles (Z-M NPs) under hydrophobic, hydrogen bonding, and electrostatic interactions. Results showed that MCP concentration (0% to 0.2%), pH (3 to 7), and addition sequence have a great effect on the particle size (165 to 463 nm), potential (-18.46 to -38.6 mV), and rheological properties of Z-M NPs. Moreover, Z-M NPs had good redispersibility and favorable encapsulation efficiency (92.8%) for quercetin. Compared with free quercetin, quercetin-loaded Z-M NPs significantly downregulated the expression of NO, TNF-α, IL-1β, and IL-6 in RAW264.7 induced by lipopolysaccharide, which resulted in higher in vitro anti-inflammatory activity. Therefore, Z-M NPs have the potential to be applied to encapsulate hydrophobic natural phytochemicals as food-based functional biomaterials.

Novel Water-in-Oil Emulsions for Co-Loading Sialic Acid and Chitosan: Formulation, Characterization, and Stability Evaluation

This study was designed to co-load sialic acid (SA) and chitosan in a water-in-oil (W/O) emulsion and investigated its characterization and stability. Emulsions were prepared using two different oils (olive oil and maize oil) and polyglycerol polyricinoleate (PGPR) alone or in combination with lecithin (LE) as emulsifiers. The results revealed that the aqueous phase of 5% (w/v) SA and 2% (w/v) chitosan could form a stable complex and make the aqueous phase into a transparent colloidal state. Increasing the concentration of PGPR and LE presented different effects on emulsion formation between olive oil-base and maize oil-base. Two stable W/O emulsions that were olive oil-based with 1.5% (w/v) PGPR+ 0.5% (w/v) LE and maize oil-based with 2% (w/v) PGPR+ 0% (w/v) LE were obtained. Initial droplet size distribution curves of the two stable emulsions displayed unimodal distribution, and the rheological curves displayed the characteristics of shear thinning and low static shear viscosity. Moreover, the storage stability showed that there was no significant change in droplet size distribution and Sauter mean diameter of the emulsions at room temperature (25 °C) for 30 days. These results indicated that the W/O emulsions could effectively co-load and protect sialic acid and chitosan and thus could be a novel method for increasing the stability of these water-soluble bioactive compounds.

Cytocompatible drug delivery hydrogels based on carboxymethylagarose/chitosan pH-responsive polyelectrolyte complexes

Several drugs are chemically unstable in the gastric environment and have low bioavailability restricted by intestinal absorption, which motivates the development of alternative routes for drug release, such as transdermal drug carriers for drug delivery to specific areas of the skin. Herein, novel polyelectrolyte complexes (PEC) consisting of carboxymethylagarose (CMA) and chitosan (CS) were prepared. pH-responsive CMA/CS hydrogels were obtained by mixing CMA and CS at various weight ratios. Swelling ratio was modulated by varying the CMA and CS weight ratio, and the highest swelling values were achieved for 2:1 wt% hydrogels at 25 °C and pH 6.0. PEC films were characterized by ATR-FTIR spectroscopy, TGA, DSC, and SEM. Results indicated that CMA and CS were successfully crosslinked by ionic complexation. As a model drug, diclofenac sodium (DS) was loaded in CMA/CS PECs. Association efficiency and loading capacity were ca. 69% and 79%, respectively, exhibiting 67% cumulative release after 72 h at 37 °C and pH 6.0 through Fickian diffusion mechanism. Viability assay of immortalized human keratinocyte (HaCat) cells showed ca. 100% survival in the presence of hydrogels and DS. Therefore, this work suggests that CMA/CS PECs can be applied as pH-responsive carriers for dermal drug delivery.

Resilient and Self-Healing Hyaluronic Acid/Chitosan Hydrogel With Ion Conductivity, Low Water Loss, and Freeze-Tolerance for Flexible and Wearable Strain Sensor

Conductive hydrogel is a vital candidate for the fabrication of flexible and wearable electric sensors due to its good designability and biocompatibility. These well-designed conductive hydrogel–based flexible strain sensors show great potential in human motion monitoring, artificial skin, brain computer interface (BCI), and so on. However, easy drying and freezing of conductive hydrogels with high water content greatly limited their further application. Herein, we proposed a natural polymer-based conductive hydrogel with excellent mechanical property, low water loss, and freeze-tolerance. The main hydrogel network was formed by the Schiff base reaction between the hydrazide-grafted hyaluronic acid and the oxidized chitosan, and the added KCl worked as the conductive filler. The reversible crosslinking in the prepared hydrogel resulted in its resilience and self-healing feature. At the same time, the synthetic effect of KCl and glycerol endowed our hydrogel with outstanding anti-freezing property, while glycerol also endowed this hydrogel with anti-drying property. When this hydrogel was assembled as a flexible strain sensor, it showed good sensitivity (GF = 2.64), durability, and stability even under cold condition (−37°C).

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.

Fucoidan hydrogels induced by κ-carrageenan: Rheological, thermal and structural characterization

Fucoidan (FUC) is a non-gelling polysaccharide but could interact with κ-carrageenan (KC) to form a stable gel blend. However, their interaction mechanism is unclear. Herein, FUC and KC blended gels are prepared by mixing FUC (10 and 20 mg/mL) and KC (6, 7 and 8 mg/mL) solutions, and characterized through LF-NMR, rheology, DSC, Cryo-SEM, and FTIR. The FTIR analysis confirms the formation of hydrogen bonds between FUC and KC chains. The KC addition to FUC significantly improves the water retention and frost resistance. The viscoelastic measurements reveal higher gelling nature of the FUC-KC binary mixtures, and the DSC results confirm the higher thermal stability. The Cryo-SEM images clearly reveal the gel network structure. The outcome of this study deemed to further the FUC use in food and non-food applications.

Rheological properties and interactions of fish gelatin-κ-carrageenan polyelectrolyte hydrogels: The effects of salt

This study mainly explored the effects of low-concentration salts (0.1, 0.5 mM NaCl and Na₂ SO₄ ) on the gel, rheological and structural properties of fish gelatin (FG)-κ-carrageenan (κC) polyelectrolyte hydrogels. The results showed that κC could increase the gel strength, hardness, and chewiness of the FG-κC polyelectrolyte hydrogels, while the addition of salts had a negative effect. The rheological behaviors showed that the addition of salts reduced the apparent viscosity, gel, and melting points of the FG-κC polyelectrolyte hydrogels. Compared with NaCl, Na₂ SO₄ -treated FG-κC had lower gel strength, hardness, viscosity, gelation, and melting points, while the addition of salts increased the fluorescence intensity by unfolding FG molecules. The secondary structure analysis results showed that the addition of NaCl and Na₂ SO₄ decreased α-helix and β-sheet contents of FG-κC by destroying the hydrogen bond of FG-κC.

Role of chitosan-based hydrogels in pollutants adsorption and freshwater harvesting: A critical review

The shortage of freshwater resources is an urgent problem worldwide, especially for some areas that lack rainfall conditions. The development of reliable wastewater treatment and freshwater harvesting equipment has become an urgent demand. Hydrogel is a porous 3D network structure with good pollutant adsorption capacity, water holding capacity, water adsorption capacity, and reversible swelling ability, which has been widely used in water treatment. Chitosan (CH), as the abundant bioactive material in nature, is commonly used to prepare hydrogels with low-cost, favorable stability, good antimicrobial activity, high mechanical properties, biodegradability, and environmental friendliness. Therefore, this review presents a comprehensive review of the various applications of CH-based hydrogels in water treatment including various pollutant adsorption, oil-water separation, seawater desalination, and atmospheric condensation. The relevant mechanisms, application potential, and challenge are also illustrated. This review aims to provide a viable idea to address the shortage of freshwater resources.