Modification of ulvans via periodate-chlorite oxidation: Chemical characterization and anticoagulant activity

Ulvans are not equal - Linkage and substitution patterns in ulvan polysaccharides differ with Ulva morphology

Ulva are hardy green seaweeds that contain the sulfated polysaccharide ulvan and grow in two distinct morphologies: foliose and tubular. The authors hypothesise that ulvan from tubular species are more structurally complex than ulvans from foliose species. Herein, using standardised methods, the glycosyl linkage positions and sulfate ester substitutions of constituent monosaccharides of ulvan isolated from foliose (U. lacinulata and U. stenophylloides) and tubular (U. prolifera and U. ralfsii) species of Ulva were investigated. Comparison of native ulvans with 80 and 100 °C desulfated counterparts indicated that 4-linked rhamnose is predominantly 3-O-sulfated in all four ulvans. Ulvans from the foliose species predominantly contained →3,4)-Rhap-(1→, →4)-GlcAp-(1→ and →4)-IdoAp-(1→, collectively accounting for 67 to 81 mol% of the total linkages. In contrast, these same linkages in ulvans from the tubular species only collectively accounted for 29 to 36 mol%. Instead, ulvan from tubular species contained a combination of →2,3,4)-Rhap-(1→, terminal Rhap-(1→, →4)-GlcAp-(1→, →4)-Xylp-(1→, and/or →4)-Galp-(1→ in high proportions; some of the latter three residues were also likely O-2 sulfated. The results presented here suggest that ulvan from foliose species are predominantly unbranched polysaccharides composed of repeat disaccharides while ulvans from tubular species contain a greater diversity of branch and sulfate substitution locations.

Semisynthesis of new sulfated heterorhamnan derivatives obtained from green seaweed Gayralia brasiliensis and evaluation of their anticoagulant activity

Marine green algae produce sulfated polysaccharides with diverse structures and a wide range of biological activities. This study aimed to enhance the biotechnological potential of sulfated heterorhamnan (Gb1) from Gayralia brasiliensis by chemically modifying it for improved or new biological functions. Using controlled Smith Degradation (GBS) and O-alkylation with 3-chloropropylamine, we synthesized partially water-soluble amine derivatives. GBS modification increase sulfate groups (29.3 to 37.5 %) and α-l-rhamnose units (69.9 to 81.2 mol%), reducing xylose and glucose, compared to Gb1. The backbone featured predominantly 3- and 2-linked α-l-rhamnosyl and 2,3- linked α-l-rhamnosyl units as branching points. Infrared and NMR analyses confirmed the substitution of hydroxyl groups with aminoalkyl groups. The modified compounds, GBS-AHCs and GBS-AHK, exhibited altered anticoagulant properties. GBS-AHCs showed reduced effectiveness in the APTT assay, while GBS-AHK maintained a similar anticoagulant activity level to Gb1 and GBS. Increased nitrogen content and N-alkylation in GBS-AHCs compared to GBS-AHK may explain their structural differences. The chemical modification proposed did not enhance its anticoagulant activity, possibly due to the introduction of amino groups and a positive charge to the polymer. This characteristic presents new opportunities for investigating the potential of these polysaccharides in various biological applications, such as antimicrobial and antitumoral activities.

Structurally Modified Polysaccharides: Physicochemical Properties, Biological Activities, Structure-Activity Relationship, and Applications

Polysaccharides are an important class of biomolecules derived from several sources. However, the inherent structure of polysaccharides prevents them from exhibiting favorable physicochemical properties, which restricts their development in agriculture, industry, food, and biomedicine. This paper systematically summarizes the changes in the primary and advanced structures of modified polysaccharides, and focuses on the effects of various modification methods on the hydrophobicity, rheological properties, emulsifying properties, antioxidant activity, hypoglycemic, and hypolipidemic activities of polysaccharides. Then there is a list the applications of modified polysaccharides in treating heavy metal pollutants, purifying water resources, improving beverage stability and bread quality, and precisely delivering the drug. When summarized and reviewed, the information above can shed further light on the relationship between polysaccharide structure and function. Determining the structure-activity relationship provides a scientific basis for the direction of molecular modifications of polysaccharides.

Development and characterization of films from Campomanesia xanthocarpa and commercial citrus pectins with different degrees of methyl-esterification

In this study, pectins from commercial citrus and isolated from gabiroba (Campomanesia xanthocarpa) fruits, were obtained with different degrees of methyl-esterification (DM) and applied in the films. The DM ranged from 0 % to 62.5 % and the gradual de-esterification process was confirmed by mono-dimensional analysis (1H NMR). In order to investigate the influence of DM values in pectin film properties, PCP (DM: 62.5 %); PCP-5 (DM: 37.4 %); PCP-15 (DM: 19.1 %), and a fully de-esterified sample PCP-35 (DM: 0 %) were selected. The functional properties of the films clearly showed that the DM and cross-linking process are necessary to obtain a material with water resistance. Furthermore, pectin isolated from the fruits of gabiroba was purified (GW-Na, DM: 51.9 %) and partially de-esterified (GW-Na-5, DM: 37.1 %). These pectins were used, for the first time, in development of films and the physical and mechanical properties were compared with films made with PCP and PCP-5 samples. GW-Na and GW-Na-5 films presented suitable properties, with reduced solubility reduced (57.1 and 26.2 %), high degree of swelling (2.14 and 2.26), low flexibility (18.05 and 6.11 MPa), respectively. High strength and rigidity (99.36 and 1040.9 MPa), for both films (GW-Na and GW-Na-5) were demonstrated, similar to that obtained by analyzed citrus pectin.

Structure-activity relationships of bioactive polysaccharides extracted from macroalgae towards biomedical application: A review

Macroalgae are valuable and structurally diverse sources of bioactive compounds among marine resources. The cell walls of macroalgae are rich in polysaccharides which exhibit a wide range of biological activities, such as anticoagulant, antioxidant, antiviral, anti-inflammatory, immunomodulatory, and antitumor activities. Macroalgae polysaccharides (MPs) have been recognized as one of the most promising candidates in the biomedical field. However, the structure-activity relationships of bioactive polysaccharides extracted from macroalgae are complex and influenced by various factors. A clear understanding of these relationships is indeed critical in developing effective biomedical applications with MPs. In line with these challenges and knowledge gaps, this paper summarized the structural characteristics of marine MPs from different sources and relevant functional and bioactive properties and particularly highlighted those essential effects of the structure-bioactivity relationships presented in biomedical applications. This review not only focused on elucidating a particular action mechanism of MPs, but also intended to identify a novel or potential application of these valued compounds in the biomedical field in terms of their structural characteristics. In the last, the challenges and prospects of MPs in structure-bioactivity elucidation were further discussed and predicted, where they were emphasized on exploring modern biotechnology approaches potentially applied to expand their promising biomedical applications.

Rehashing Our Insight of Seaweeds as a Potential Source of Foods, Nutraceuticals, and Pharmaceuticals

In a few Southeast Asian nations, seaweeds have been a staple of the cuisine since prehistoric times. Seaweeds are currently becoming more and more popular around the world due to their superior nutritional value and medicinal properties. This is because of rising seaweed production on a global scale and substantial research on their composition and bioactivities over the past 20 years. By reviewing several articles in the literature, this review aimed to provide comprehensive information about the primary and secondary metabolites and various classes of bioactive compounds, such as polysaccharides, polyphenols, proteins, and essential fatty acids, along with their bioactivities, in a single article. This review also highlights the potential of seaweeds in the development of nutraceuticals, with a particular focus on their ability to enhance human health and overall well-being. In addition, we discuss the challenges and potential opportunities associated with the advancement of pharmaceuticals and nutraceuticals derived from seaweeds, as well as their incorporation into different industrial sectors. Furthermore, we find that many bioactive constituents found in seaweeds have demonstrated potential in terms of different therapeutic attributes, including antioxidative, anti-inflammatory, anticancer, and other properties. In conclusion, seaweed-based bioactive compounds have a huge potential to play an important role in the food, nutraceutical, and pharmaceutical sectors. However, future research should pay more attention to developing efficient techniques for the extraction and purification of compounds as well as their toxicity analysis, clinical efficacy, mode of action, and interactions with regular diets.

Insights into the Edible and Biodegradable Ulvan-Based Films and Coatings for Food Packaging

Recently, edible films or coatings that are made from algal polysaccharides have become promising candidates for replacing plastic-based packaging materials for food storage due to their non-toxic, biodegradable, biocompatible, and bioactive characteristics. Ulvan, a significant biopolymer with unique functional properties derived from marine green algae, has been extensively used in various sectors. However, there are fewer commercial applications of this sugar in the food packaging industry compared to many other algae-derived polysaccharides, such as alginates, carrageenan, and agar. This article aims to review the unparalleled chemical composition/structure and physiochemical properties of ulvan and the latest developments in ulvan-based edible films and coatings, thus highlighting their potential applications in the food packaging industry.

Structural Characterization and Anti-Nonalcoholic Fatty Liver Effect of High-Sulfated Ulva pertusa Polysaccharide

The high-sulfated derivative of Ulva pertusa polysaccharide (HU), with unclear structure, has better anti-hyperlipidmia activity than U pertusa polysaccharide ulvan (U). In this study, we explore the main structure of HU and its therapeutic effect against nonalcoholic fatty liver disease (NAFLD). The main structure of HU was elucidated using FT-IR and NMR (13C, 1H, COSY, HSQC, HMBC). The anti-NAFLD activity of HU was explored using the high-fat diet mouse model to detect indicators of blood lipid and liver function and observe the pathologic changes in epididymal fat and the liver. Results showed that HU had these main structural fragments: →4)-β-D-Glcp(1→4)-α-L-Rhap2,3S(1→; →4)-α-L-Rhap3S(1→4)-β-D-Xylp2,3S(1→; →4)-α-L-Rhap3S(1→4)-β-D-Xylp(1→; →4)-α-L-IdopA3S(1→4)-α-L-Rhap3S(1→; →4)-β-D-GlcpA(1→3)-α-L-Rhap(1→; →4)-α-L-IdopA3S(1→4)-β-D-Glcp3Me(1→; →4)-β-D-Xylp2,3S(1→4)-α-L-IdopA3S(1→; and →4)-β-D-Xylp(1→4)-α-L-IdopA3S(1→. Treatment results indicated that HU markedly decreased levels of TC, LDL-C, TG, and AST. Furthermore, lipid droplets in the liver were reduced, and the abnormal enlargement of epididymal fat cells was suppressed. Thus, HU appears to have a protective effect on the development of NAFLD.

Green approaches for extraction, chemical modification and processing of marine polysaccharides for biomedical applications

Over the past few decades, natural-origin polysaccharides have received increasing attention across different fields of application, including biomedicine and biotechnology, because of their specific physicochemical and biological properties that have afforded the fabrication of a plethora of multifunctional devices for healthcare applications. More recently, marine raw materials from fisheries and aquaculture have emerged as a highly sustainable approach to convert marine biomass into added-value polysaccharides for human benefit. Nowadays, significant efforts have been made to combine such circular bio-based approach with cost-effective and environmentally-friendly technologies that enable the isolation of marine-origin polysaccharides up to the final construction of a biomedical device, thus developing an entirely sustainable pipeline. In this regard, the present review intends to provide an up-to-date outlook on the current green extraction methodologies of marine-origin polysaccharides and their molecular engineering toolbox for designing a multitude of biomaterial platforms for healthcare. Furthermore, we discuss how to foster circular bio-based approaches to pursue the further development of added-value biomedical devices, while preserving the marine ecosystem.

Structural characterization of ulvans extracted from blade (Ulva ohnoi) and filamentous (Ulva tepida and Ulva prolifera) species of cultivated Ulva

Ulvans from Ulva ohnoi, Ulva tepida and Ulva prolifera were extracted under mild acidic conditions, isolated and their composition and structure determined. The ulvans contained mostly rhamnose (31.6-46.7 mol%) and glucuronic acid (26.6-37.5 mol%), with smaller amounts of xylose (3.4-10.4 mol%) and iduronic acid (3.1-7.6 mol%). In addition, the ulvan samples also contained galactose (4.4-26.0 mol%). Glycosyl linkage analysis showed that ulvan from U. ohnoi contained mostly →4)-GlcpA-(1→ and →3,4)-Rhap-(1→. Preparation of partially methylated alditol acetate standards of idose showed that U. ohnoi contained →4)-IdopA-(1→. In addition to these residues, glycosyl linkage analysis of U. tepida and U. prolifera showed the presence of →2,3,4)-Rhap-(1→, →4)-Xylp-(1→, →2,4)-GlcpA-(1→ and →3,4)-GlcpA-(1→. These two species also contained galactose linkages. These data, together with nuclear magnetic resonance (NMR) spectroscopy indicated that U. ohnoi comprised mostly of type A_3S ulvanobiuronic acid repeats [→4)-β-D-GlcpA-(1→4)-α-L-Rhap3S-(1→], together with smaller amounts of type B_3S ulvanobiuronic acid repeats [→4)-α-L-IdopA-(1→4)-α-L-Rhap3S-(1→] and ulvanobiose (U_3S [→4)-β-D-Xylp-(1→4)-α-L-Rhap3S-(1→]). NMR spectra of U. tepida and U. prolifera showed resonances not detected in U. ohnoi, highlighting the complexity of the ulvans from these species. Regardless of the structural diversity of the ulvan samples there was very little antioxidant or inhibitory activity detected on enzymatic processes investigated.

Nutraceutical potentials of algal ulvan for healthy aging

Several theories for aging are constantly put forth to explain the underlying mechanisms. Oxidative stress, DNA dysfunction, inflammation, and mitochondrial dysfunction, along with the release of cytochrome c are some of these theories. Diseases such as type 2 diabetes mellitus, intestinal dysfunction, cardiovascular diseases, hepatic injury, and even cancer develop with age and eventually cause death. Ulva polysaccharides, owing to their special structures and various functions, have emerged as desirable materials for keeping healthy. These polysaccharide structures are found to be closely related to the extraction methods, seaweed strains, and culture conditions. Ulvan is a promising bioactive substance, a potential functional food, which can regulate immune cells to augment inflammation, control the activity of aging-related genes, promote tumor senescence, enhance mitochondrial function, maintain liver balance, and protect the gut microbiome from inflammatory attacks. Given the desirable physiochemical and gelling properties of ulvan, it would serve to improve the quality and shelf-life of food.

Semi-synthesis of hybrid ulvan-kappa-carrabiose polysaccharides and evaluation of their cytotoxic and anticoagulant effects

In this study we described the synthesis of a hybrid polysaccharide harboring moieties of ulvan and kappa-carrabiose. Alkylamines (1,3-diaminopropane and 1,6-diaminohexane) were selectively inserted into β-D-GlcAp and α-L-IdoAp units in the ulvan structure via an amide bond formation producing ulvan-amide derivatives F-DAP (N% = 1.77; M_w = 208 kg mol^-1) and F-DAH (N% = 1.77; M_w = 202 kg mol^-1), which were reacted with kappa-carrabiose via reductive amination to produce hybrid ulvan-kappa-carrabiose polysaccharides F-DAP-Kb (N% = 1.56; M_w = 206 kg mol^-1) and F-DAH-Kb (N% = 1.16; M_w = 200 kg mol^-1). All the ulvan derivatives were characterized by ¹H and ¹³C NMR spectroscopy and did not show cytotoxicity against human dermal fibroblasts (HDFa) at the concentrations of 25, 100, and 500 μg mL^-1, neither anticoagulant properties at the range of 10-150 μg mL^-1. Therefore, the ulvan-amide derivatives and the hybrid ulvan-kappa-carrabiose polysaccharides showed good biocompatibility in vitro, presenting as worthy candidates for tailoring scaffolds for biomedical applications.

Seaweed polysaccharides: Emerging extraction technologies, chemical modifications and bioactive properties

Nowadays, consumers are increasingly aware of the relationship between diet and health, showing a greater preference of products from natural origin. In the last decade, seaweeds have outlined as one of the natural sources with more potential to obtain bioactive carbohydrates. Numerous seaweed polysaccharides have aroused the interest of the scientific community, due to their biological activities and their high potential on biomedical, functional food and technological applications. To obtain polysaccharides from seaweeds, it is necessary to find methodologies that improve both yield and quality and that they are profitable. Nowadays, environmentally friendly extraction technologies are a viable alternative to conventional methods for obtaining these products, providing several advantages like reduced number of solvents, energy and time. On the other hand, chemical modification of their structure is a useful approach to improve their solubility and biological properties, and thus enhance the extent of their potential applications since some uses of polysaccharides are still limited. The present review aimed to compile current information about the most relevant seaweed polysaccharides, available extraction and modification methods, as well as a summary of their biological activities, to evaluate knowledge gaps and future trends for the industrial applications of these compounds.Key teaching pointsStructure and biological functions of main seaweed polysaccharides.Emerging extraction methods for sulfate polysaccharides.Chemical modification of seaweeds polysaccharides.Potential industrial applications of seaweed polysaccharides.Biological activities, knowledge gaps and future trends of seaweed polysaccharides.

Chemical structure of native and modified sulfated heterorhamnans from the green seaweed Gayralia brasiliensis and their cytotoxic effect on U87MG human glioma cells

A water-soluble sulfated heterorhamnan (Gb1) was isolated from the green seaweed Gayralia brasiliensis and purified by ultrafiltration, yielding a homogeneous polysaccharide (Gb1r). Both fractions contained rhamnose, xylose, galacturonic and glucuronic acids, galactose, and glucose. Chemical and spectroscopic methods allowed the determination of Gb1 and Gb1r chemical structure. Their backbones were constituted by 3-, 2-, and 2,3-linked rhamnosyl units (1:0.49:0.13 and 1:0.58:0.17, respectively), which are unsulfated (13.5 and 14.6%), disulfated (16.6 and 17.8%) or monosulfated at C-2 (8 and 8.6%) and C-4 (24.5 and 23.4%). Gb1 was oversulfated giving rise to Gb1-OS, which presented ~2.5-fold higher content of disulfated rhamnosyl units than Gb1, as determined by methylation analyses and NMR spectroscopy. Gb1 and Gb1-OS potently reduced the viability of U87MG human glioblastoma cells. Gb1 caused cell cycle arrest in the G₁ phase, increased annexin V-stained cells, and no DNA fragmentation, while Gb1-OS increased the percentage of cells in the S and G₂ phases and the levels of fragmented DNA and cells double-stained with annexin V/propidium iodide, suggesting an apoptosis mechanism. The results suggest that the different effects of Gb1 and Gb1-OS were related to differences in the sulfate content and position of these groups along the polysaccharide chains.

Are all ulvans equal? A comparative assessment of the chemical and gelling properties of ulvan from blade and filamentous Ulva

Green seaweeds of the genus Ulva are rich in the bioactive sulfated polysaccharide ulvan. Herein we characterise ulvan from Ulva species collected from the Bay of Plenty, Aotearoa New Zealand. Using standardised procedures, we quantified, characterised, and compared ulvans from blade (U. australis, U. rigida, U. sp. B, and Ulva sp.) and filamentous (U. flexuosa, U. compressa, U. prolifera, and U. ralfsii) Ulva species. There were distinct differences in composition and structure of ulvans between morphologies. Ulvan isolated from blade species had higher yields (14.0-19.3 %) and iduronic acid content (IdoA = 7-18 mol%), and lower molecular weight (Mw = 190-254 kDa) and storage moduli (G' = 0.1-6.6 Pa) than filamentous species (yield = 7.2-14.6 %; IdoA = 4-7 mol%; Mw = 260-406 kDa; G' = 22.7-74.2 Pa). These results highlight the variability of the physicochemical properties of ulvan from different Ulva sources, and identifies a morphology-based division within the genus Ulva.

Ulva intestinalis Extract Acts as Biostimulant and Modulates Metabolites and Hormone Balance in Basil (Ocimum basilicum L.) and Parsley (Petroselinum crispum L.)

Natural elicitors from macroalgae may affect plant secondary metabolites. Ulvan is a sulfated heteropolysaccharide extracted from green seaweed, acting as both a plant biotic protecting agent, and a plant elicitor, leading to the synthesis of signal molecules. In this work, the aqueous extract of Ulva intestinalis L., mainly composed of ulvan, was used as foliar-spraying treatment and its eliciting effect was investigated in basil (Ocimum basilicum L.) and parsley (Petroselinum crispum L.). Antioxidant metabolites (polyphenols and carotenoids), volatile compounds (both in headspace emissions and hydrodistilled essential oils), and hormones (jasmonic acid, salicylic acid, salicylic acid 2-O-β-D-glucoside, abscisic acid, and azelaic acid) were quantified. The foliar-spraying treatment with U. intestinalis extract increased salicylic acid and its β-glucoside in parsley; in basil, it induced the accumulation of jasmonic and abscisic acids, indicating the presence of a priming effect. In basil, the elicitation caused a change of the essential oil (EO) chemotype from methyl eugenol/eugenol to epi-α-cadinol and increased sesquiterpenes. In parsley EO it caused a significant accumulation of 1,3,8-p-menthatriene, responsible of the typical “parsley-like” smell. In both species, the phenylpropanoids decreased in headspace and EO compositions, while the salicylic acid concentration increased; this could indicate a primarily defensive response to U. intestinalis extract. Due to the evidenced significant biological activity, U. intestinalis extract used as an elicitor may represent a suitable tool to obtain higher amounts of metabolites for optimizing plant flavor metabolites.

Hydrogel-Forming Algae Polysaccharides: From Seaweed to Biomedical Applications

With the increasing growth of the algae industry and the development of algae biorefinery, there is a growing need for high-value applications of algae-extracted biopolymers. The utilization of such biopolymers in the biomedical field can be considered as one of the most attractive applications but is challenging to implement. Historically, polysaccharides extracted from seaweed have been used for a long time in biomedical research, for example, agarose gels for electrophoresis and bacterial culture. To overcome the current challenges in polysaccharides and help further the development of high-added-value applications, an overview of the entire polysaccharide journey from seaweed to biomedical applications is needed. This encompasses algae culture, extraction, chemistry, characterization, processing, and an understanding of the interactions of soft matter with living organisms. In this review, we present algae polysaccharides that intrinsically form hydrogels: alginate, carrageenan, ulvan, starch, agarose, porphyran, and (nano)cellulose and classify these by their gelation mechanisms. The focus of this review further lays on the culture and extraction strategies to obtain pure polysaccharides, their structure-properties relationships, the current advances in chemical backbone modifications, and how these modifications can be used to tune the polysaccharide properties. The available techniques to characterize each organization scale of a polysaccharide hydrogel are presented, and the impact on their interactions with biological systems is discussed. Finally, a perspective of the anticipated development of the whole field and how the further utilization of hydrogel-forming polysaccharides extracted from algae can revolutionize the current algae industry are suggested.

Effect of extraction procedures on the chemical structure, antitumor and anticoagulant properties of ulvan from Ulva lactuca of Tunisia coast

The effect of extraction procedures on chemical composition, structural, antitumor and anticoagulant properties of the sulphated polysaccharide 'ulvan' from the green seaweed Ulva lactuca were investigated. The structural features of ulvans were carried out by FTIR and by one- and two- dimensional ¹H and ¹³C NMR spectroscopic. The ulvans were mainly composed of rhamnose, xylose, and uronic acid. Chemical and spectroscopic analyses demonstrated that ulvans were constituted of (1→4)-β-glucuronic acid, (1→3,4)-α-L-rhamnose-3-sulphate and (1→4)-α-xylose. The extraction procedures effect were observed in chemical structure, Mw and biological activities. Cytotoxic activity of enzymatic-chemical extract on cervical cancer cells (HeLa) (IC₅₀ = 1000 μg/mL) was higher than on normal peripheral blood lymphocytes cells (PBL). Acid extracts promoted to reduce HeLa cells and to grow PBL cells. At high concentrations, acid extracts showed the highest APTT and TT clotting time. Antitumoral and anticoagulant activities of ulvans from Ulva lactuca promote their use as effective therapeutic agent.

Ulvan dialdehyde-gelatin hydrogels for removal of heavy metals and methylene blue from aqueous solution

Hydrogels based on the polysaccharide ulvan from the green macroalgae Ulva fenestrata were synthesized and evaluated as an adsorbent for heavy metals ions and methylene blue. Ulvan was extracted from Ulva fenestrata using diluted hydrochloric acid and recovered by precipitation with EtOH. The extracted ulvan was converted into ulvan dialdehyde via periodate-oxidation and subsequently combined with gelatin yielding hydrogels. The hydrogels showed good water-uptake capacity with a maximum swelling degree of 2400 % in water and 900 % in PBS buffer. Adsorption tests of methylene blue showed a maximum adsorption capacity of 465 mg/g. The adsorption data of methylene blue followed the pseudo-second order kinetics and agreed with the Langmuir adsorption isotherm. The maximum adsorption capacity of heavy metal ions was 14 mg/g for Cu²⁺, 7 mg/g for Co²⁺and 6 mg/g for Ni²⁺and Zn²⁺ indicating that the hydrogels have a stronger affinity for Cu²⁺ than for Co²⁺, Ni²⁺, and Zn²⁺.

Ulvan, a bioactive marine sulphated polysaccharide as a key constituent of hybrid biomaterials: A review

Ulvan, a sulphated polysaccharide located in the cell walls of green algae that possesses unique structural properties albeit its repeating unit shares chemical affinity with glycosoaminoglycans, such as hyaluronan and chondroitin sulphate, has been increasingly studied over the years for applications in the pharmaceutical field. The increasing knowledge on ulvan's chemical properties and biological activities has triggered its utilization in hybrid materials, given its potential efficacy in biomedical applications. In the present review, the use of ulvan in the design of different biomaterials, including membranes, particles, hydrogels, 3D porous structures and nanofibers, is presented. The applications of these structures may vary from drug delivery to wound dressing or bone tissue engineering. In this context, general information regarding the structure and chemical variability, extraction processes, physicochemical properties, and biological activities of ulvan is reported.