Preparation, characterization, and application of high-whiteness agar bleached with hydrogen peroxide

Fabrication and Characterization of Agar- and Seaweed-Derived Biomembrane Films for Biomedical and Other Applications

This study focused on seaweed-based biomembrane development. The physical, mechanical, thermal, and biological properties of the fabricated films with different combinations of materials, such as agar, chitosan, poly(vinyl) alcohol (PVA), and quercetin, were characterized. The surface morphology of the films was analyzed using SEM. The maximum tensile strength (53.11 N/mm2), elongation at break (3.42%), and Young's modulus (15.52) of the biomembrane were recorded for the agar + chitosan combination. FT-Raman analysis confirmed the functional groups shift between the biopolymer and plasticizer used in this study. TG-DSC analysis of the biomembranes revealed a Tg in the range of 92.80°C-115°C. The maximum antioxidant activity was reported for quercetin (58.62%), and the maximum antimicrobial activity was observed for the chitosan and quercetin compounds against E. coli. A minimum hemolysis of 0.95% was achieved for the combination of agar + quercetin (AQ), agar + PEG (APE), Gracilaria corticata extract + PVA + quercetin (GCPQ) and agar + chitosan (AC) biomembranes. The minimum cytotoxicity of the biomembrane was 62.51% and 63.87% for Gracilaria corticata extract + PVA + quercetin (GCPQ), and agar + PVA, respectively. The proposed biomembrane films were found to be suitable for biomedical and packaging applications.

Development of quaternized agar-based materials for the coronavirus inactivation

The COVID-19 pandemic has revealed weaknesses in healthcare systems and underscored the need for advanced antimicrobial materials. This study investigates the quaternization of agar, a seaweed-derived polysaccharide, and the development of electrospun membranes for air filtration in facemasks and biomedical applications. Using the betacoronavirus MHV-3 as a model, quaternized agar and membranes achieved a 90-99.99 % reduction in viral load, without associated cytotoxicity. The quaternization process reduced the viscosity of the solution from 1.19 ± 0.005 to 0.64 ± 0.005 Pa.s and consequently the electrospun fiber diameter ranged from 360 to 185 nm. Membranes synthesized based on polyvinyl alcohol and thermally cross-linked with citric acid exhibited lower water permeability. Avoiding organic solvents in the electrospinning technique ensured eco-friendly production. This approach offers a promising way to develop biocompatible and functional materials for healthcare and environmental applications.

Super absorbent glutaric anhydride-modified agar: Structure, properties, and application in biomaterial delivery

Agar was modified with glutaric anhydride (GA) in this study to expand its application in food and medicine. Glutaric anhydride-modified agar (GAR) can maintain high gel strength (1247.4 g/cm²) and improved transparency (82.7 %). The esterified agar formed by GA further formed a cross-linking molecule structure by increasing the reaction temperature. Notably, excellent freeze-thaw stability (24.1 %) and swelling property (3116.6 %) of GAR indicated that the carboxyl-terminal of modified agar improves its affinity with water. Therefore, satisfactory water permeability and expansive stone enable agar films to achieve high water absorption. Furthermore, GAR films exhibit a specific absorption capacity of tetracycline hydrochloride in weak acid solution, thereby suggesting its potential application as a sustainable drug delivery carrier. Finally, the structure of the modified agar was analyzed to explain the mechanism of binding water. Cryo-scanning electron microscopy (SEM) depicted the porous structure of the agar gel responsible for swelling, drug loading, and release. Low-field NMR results showed that GA improves agar gel's binding and free water content. According to our research results, these GAR hydrogel membranes with excellent properties have the potential to be used as effective drug delivery materials.

Chemical modifications in the structure of marine polysaccharide as serviceable food processing and preservation assistant: A review

Marine polysaccharides are a kind of natural polysaccharides which isolated and extracted from marine organisms. Now some marine polysaccharides, such as chitosan, sodium alginate and agar, have been proven to exhibit antibacterial, antioxidant functions and biocompatibility, which are often used to preserve food or improve the physicochemical properties of food. However, they still have the defects of unsatisfactory preservation effect and biological activity, which can be remedied by its modification. Chemical modification is the most effective of all modification methods. The advances in common chemical modification methods of chitosan, sodium alginate, agar and other marine polysaccharides and research progress of modified products in food processing and preservation were summarized, and the influence of additional reaction conditions on the existence of chemical modification sites of polysaccharides was discussed. The modification of functional groups in natural marine polysaccharides leads to the change of molecular structure, which can improve the physical, chemical and biological properties of marine polysaccharides. Chemically modified products have been used in various fields of food applications, such as food preservatives, food additives, food packaging, and food processing aids. In general, chemical modification has excellent potential for food processing and preservation, which can improve the function of marine polysaccharides.

An agar-polyvinyl alcohol hydrogel loaded with tannic acid with efficient hemostatic and antibacterial capacity for wound dressing

Rapid hemostasis, antibacterial effect and promotion of wound healing are the most important functions that wound dressings need to have. In this work, we designed and prepared a hydrogel with antibacterial effect, hemostatic ability and wound healing promotion using agar, polyvinyl alcohol (PVA) and tannic acid (TA). We performed a series of tests to characterize the structure and properties of AGAR@PVA-TA hydrogels. The results showed that the AGAR@PVA-TA hydrogels had good mechanical properties and excellent antibacterial ability as well as good hemocompatibility. The cytotoxicity results showed that the AGAR@PVA-TA hydrogels had good cytocompatibility. And the TA loaded hydrogels also presented some good performances in animal studies. In the liver hemostasis model, the AGAR@PVA-TA hydrogel showed good hemostatic ability. Also, the AGAR@PVA-TA hydrogel was able to promote wound healing in an S. aureus-infected rat wound model. More importantly, our research results demonstrated that compared to other polyphenols (such as proanthocyanidins), TA could better improve the mechanical properties, antibacterial ability and rapid hemostasis of hydrogels, which illustrated the uniqueness of TA. Therefore, the TA loaded hydrogel (AGAR@PVA-TA hydrogel) has the potential to be applied as a wound dressing.

Comparison of the Physicochemical Properties of Carboxymethyl Agar Synthesized by Microwave-Assisted and Conventional Methods

The microwave-assisted carboxymethylation of agar to improve its physicochemical properties was investigated. Microwave power, reaction time, and temperature, ethanol concentration, and amounts of chloroacetic acid and sodium hydroxide were assessed for their effects on synthetic yield and degree of substitution (DS). All factors were positively correlated with DS within a certain range. Using optimized conditions, samples with different DS were prepared, and the physicochemical properties of unmodified and carboxymethyl agars prepared by microwave and conventional methods were compared. Carboxymethylation significantly changed the physicochemical properties of the agar, improving gel transparency and reducing dissolution temperature, gel strength, gel hardness, molecular weight, and molecular size; DS was the key factor. Specifically, higher DS values resulted in greater changes. The microwave-assisted method significantly shortened the reaction time and preserved molecular weight, gel strength, and texture hardness of the agar. Therefore, as an environmentally friendly method, microwave-assisted synthesis shows great promise for producing carboxymethyl agar.

Preparation and Characterization of κ-Carrageenan Modified with Maleic Anhydride and Its Application in Films

In this work, the physicochemical properties of maleic anhydride (MAH)-modified κ-carrageenan (κCar) (MC) were characterized and compared with those of native κ-carrageenan (NC). The Fourier transform infrared spectrum of MC exhibited that κCar was successfully modified. Thermogravimetric analysis indicated that the thermal stability of MC was decreased. When the degree of substitution was 0.032, MC exhibited a low gel strength (759 g/cm²), gelling temperature (33.3 °C), and dehydration rate (60.3%). Given the excellent film-forming ability of κCar, MC films were then prepared and were found to have better mechanical and barrier properties (UV and water) than NC films. With regard to optical properties, MC films could completely absorb UV light in the range of 200–236 nm. The water contact angle of MC films was higher than that of NC films. Moreover, the elongation at break increased from 26.9% to 163%. These physicochemical property changes imply that MC can be employed in polysaccharide-based films.

Convenient Agarose Preparation with Hydrogen Peroxide and Desulfation Process Analysis

Agarose is a natural seaweed polysaccharide and widely used in the medicine, food, and biological fields because of its high gel strength, non-toxicity, and electrical neutrality. The sulfate group is one of the main charged groups that affect the performance of agarose. In the present study, a simple, eco-friendly, and efficient method was explored for agarose preparation. After desulfation with hydrogen peroxide (H₂O₂), the sulfate content of agar reached 0.21%. Together with gel strength, electroendosmosis, gelling and melting temperature, the indicators of desulfated agar met the standards of commercially available agarose. Notably, the desulfated agar can be used as an agarose gel electrophoresis medium to separate DNA molecules, and the separation effect is as good as that of commercially available agarose. Further, the H₂O₂ desulfation process was analyzed. The addition of a hydroxyl radical (HO•) scavenger remarkably decreased the H₂O₂ desulfation rate, indicating that HO• has a certain role in agar desulfation. Sulfate content detection indicated that sulfur was removed from agar molecules in the form of sulfate ions (SO₄²⁻) and metal sulfate. The band absence at 850 cm⁻¹ indicated that the sulfate groups at C-4 of D-galactose in sulfated galactan were eliminated.

Synthesizing environmentally friendly non-silicone oxygen bleaching stabilizer for linen yarn using oligomeric acrylic acid

Using potassium peroxodisulfate as an initiator and acrylic acid as a monomer, an acrylic acid oligomer was synthesized and then compounded with magnesium salt to form a non-silicone oxygen bleaching stabilizer. By investigating the effects of reaction temperature, reaction time, initiator concentration, monomer concentration, and magnesium salt dosage on product performance, the effect of stabilizers on linen yarn bleaching was analyzed. The synthetic conditions of oxygen bleaching stabilizer were determined by orthogonal test method, namely, acrylic acid monomer concentration 25%, initiator dosage 5%, oligomeric acrylic acid and magnesium salt compound ratio 5:1, reaction temperature 65 °C, reaction time 4 h. At this time, the chelated iron value of the product was as high as 239.314 mg/g, and the chelated calcium value also reached 145.000 mg/g. The dosage of the synthesized stabilizer were determined to be 4 g/L through indicators such as the decomposition rate of hydrogen peroxide and whiteness. The results showed that the environmentally friendly non-silicone oxygen bleaching stabilizer not only had a good ability to inhibit the decomposition of hydrogen peroxide, but also provided bleached linen yarn with a superior degree of whiteness and less metal ion residue, which can effectively solve the "silicon scale" problem and improve the quality of the pre-treatmented products.