Red Algae-Derived Carrageenan Coatings for Marine Antifouling Applications

Synergistic Effect of Multilayered Alginate/Poly(SBMA) Coatings on Marine Antifouling Property

Alginate (Alg) coatings have attracted attention as protective layers on solid surfaces for marine antifouling applications due to their strong water binding capability and environmentally friendly characteristics. However, the effectiveness of Alg coatings in preventing marine fouling diminishes upon interaction with divalent cations present in seawater. To address this issue, post-modification of the Alg coating is conducted. The carboxyl groups of Alg, which are susceptible sites for interaction with divalent cations, are conjugated with polymerization initiators through metal-mediated coordination bond formation. Subsequently, poly(sulfobetaine methacrylate) (poly(SBMA)) brushes are grown from the initiator-immobilized Alg coatings, resulting in the formation of multilayered Alg/poly(SBMA) coatings. In marine diatom adhesion assays using Amphora Coffeaeformis, multilayered Alg/poly(SBMA) coatings exhibited superior antifouling performance compared to single-layered Alg or poly(SBMA) coating controls.

Techniques, applications and prospects of polysaccharide and protein based biopolymer coatings: A review

The growing relevance of sustainable materials has recently led to the exploration of naturally derived biopolymeric hydrogels as coating materials due to their biodegradability, biocompatibility, ease of fabrication and modification. Although many review articles exist on biopolymeric coatings, they mainly focus on a specific polysaccharide, protein biopolymer, or a particular application- biomedical engineering or food preservation. The current review first summarizes the commonly used polysaccharide and protein-based biopolymers like chitosan, alginate, carrageenan, pectin, cellulose, starch, pullulan, agarose and silk fibroin, gelatin, respectively, with a systematic description of the techniques widely used for physical coating on substrates. Then, broad applications of these biopolymeric coatings on various substrates in biomedical engineering- 3D scaffolds, biomedical implants, and nanoparticles are described in detail. It also entails the application of biopolymeric coatings for food preservation in the form of food packaging and edible coatings. A brief discussion on the newly discovered interest in exploring biopolymers for anticorrosive coating applications is also included. Finally, concluding remarks on the role of biopolymer microstructures in forming homogeneous coatings, prospective alternatives to the currently used biopolymers as coating material and the advent of computer-aided technologies to expedite experimental findings are presented.

Metal-Assisted Injection Spinning of Ultra Strong Fibers from Megamolecular LC Polysaccharides

The molecular orientation of liquid crystalline (LC) hydrogels has the potential to induce a range of functionalities that can deliver great mechanical strength. Sacran is a supergiant LC polysaccharide isolated from the cyanobacterium Aphanothece sacrum with a high amount of anionic functional groups such as sulfates and carboxylates. In this article, ultra-strong sacran hydrogels and their dried fibers were produced by cross-linking under injection flow with trivalent metal ions such as Al3+, Cr3+, Fe3+, In3+, and rare-earth metal ions such Er3+ and Sr3+. Crossed-polarizing microscopy and X-ray diffraction imaging revealed a uniaxial molecular orientation in the LC gel fiber, resulting in outstanding mechanical characteristics.

Role of Algal-derived Bioactive Compounds in Human Health

Algae is emerging as a bioresource with high biological potential. Various algal strains have been used in traditional medicines and human diets worldwide. They are a rich source of bioactive compounds like ascorbic acid, riboflavin, pantothenate, biotin, folic acid, nicotinic acid, phycocyanins, gamma-linolenic acid (GLA), adrenic acid (ARA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), etc. Beta-carotene, astaxanthin, and phycobiliproteins are different classes of pigments that are found in algae. They possess antioxidant, anti-inflammatory and anticancer properties. The sulfur-coated polysaccharides in algae have been used as an anticancer, antibacterial, and antiviral agent. Scientists have exploited algal-derived bioactive compounds for developing lead molecules against several diseases. Due to the surge in research on bioactive molecules from algae, industries have started showing interest in patenting for the large-scale production of bioactive compounds having applications in sectors like pharmaceuticals, food, and beverage. In the food industry, algae are used as a thickening, gelling, and stabilizing agent. Due to their gelling and thickening characteristics, the most valuable algae products are macroalgal polysaccharides such as agar, alginates, and carrageenan. The high protein, lipid, and nutrient content in microalgae makes it a superfood for aquaculture. The present review aims at describing various non-energy-based applications of algae in pharmaceuticals, food and beverage, cosmetics, and nutraceuticals. This review attempts to analyze information on algal-derived drugs that have shown better potential and reached clinical trials.

Coordination-driven robust antibacterial coatings using catechol-conjugated carboxymethyl chitosan

To prevent bacterial contamination on solid surfaces, a simple yet efficient antibacterial coating was developed in a substrate-independent manner by using the catechol-conjugated carboxymethyl chitosan (CMC-DOPA). The CMC-DOPA was firstly synthesized via an aza-Michael reaction with methyl acrylate and the subsequent acyl substitution with dopamine. The coating strategy consists of spin-coating-assisted deposition of CMC-DOPA on polydopamine-coated substrates and coordination-driven crosslinks between catechol groups and Fe3+ ions in sequence, producing the multilayered CMC-DOPA films. The film thickness was controllable depending on the concentration of CMC-DOPA. Compared to bare controls, the CMC-DOPA-coated substrates reduced the bacterial adhesion by up to 99.8 % and 96.2 % for E. coli and S. aureus, respectively. It is demonstrated that the CMC-DOPA coating can be a robust antibacterial coating across various pH environments, inhibiting bacterial adhesion by 78.7 %, 95.1 %, and 93.2 %, respectively, compared to the control, even after 7 days of acidic, physiological, and alkaline pH treatment. The current coating approach could be applied to various substrates including silicon dioxide, titanium dioxide, and polyurethane. Given its simple and versatile coating capability, we think that the coordination-driven CMC-DOPA coating could be useful for various medical devices and implants.

Exploring carbohydrate extraction from biomass using deep eutectic solvents: Factors and mechanisms

Deep eutectic solvents (DESs) are increasingly being recognized as sustainable and promising solvents because of their unique properties: low melting point, low cost, and biocompatibility. Some DESs possess high viscosity, remarkable stability, and minimal toxicity, enhancing their appeal for diverse applications. Notably, they hold promise in biomass pretreatment, a crucial step in biomass conversion, although their potential in algal biomass carbohydrates extraction remains largely unexplored. Understanding the correlation between DESs' properties and their behavior in carbohydrate extraction, alongside cellulose degradation mechanisms, remains a gap. This review provides an overview of the use of DESs in extracting carbohydrates from lignocellulosic and algal biomass, explores the factors that influence the behavior of DESs in carbohydrate extraction, and sheds light on the mechanism of cellulose degradation by DESs. Additionally, the review discusses potential future developments and applications of DESs, particularly extracting carbohydrates from algal biomass.

Surface Coating with Naphthalene Trisulfonate/Hafnium(IV) Complexes: Versatility and Post-Functionalization

Naphthalene trisulfonate is found to have versatile surface coating capability when combined with hafnium(IV) ions, thereby forming complexes. Solid substrates such as titanium/titanium dioxide, glass, and nylon immersed in a solution of naphthalene trisulfonate and Hf^IV produces naphthalene trisulfonate/Hf^IV complex coating. The coating is not produced when the Hf^IV ions are absent or when naphthalene monosulfonate replaces naphthalene trisulfonate; this indicates the significance of Hf^IV ions and multiple sulfonates in this coating system. The versatile surface coating property of naphthalene trisulfonate/Hf^IV complexes is attributed to the coexistence of hydrophobic aromatic and hydrophilic side groups in naphthalene trisulfonate. Additionally, Hf^IV ion-mediated cross-linking reactions between naphthalene trisulfonate molecules induce molecular assembly, facilitating versatile surface coating. Post-functionalization of the coating is accomplished through additional Hf^IV-mediated coordinate bond formation; alginate and λ-carrageenan are successfully grafted onto the coating for nonbiofouling applications.

Effect of N-Methylation on Dopamine Surface Chemistry

Dopamine (DA) surface chemistry has received significant attention because of its applicability in a wide range of research fields and the ability to graft functional molecules onto numerous solid surfaces. Various DA derivatives have been newly synthesized to identify key factors affecting the coating efficiency and to advance the coating system development. The oxidation of catechol into quinone followed by internal cyclization via the nucleophilic attack of primary amine is crucial for DA-based surface coating. Thus, it is expected that the amine group's nucleophilicity control directly affects the coating efficiency. However, it has not been systematically investigated, and most studies have been conducted with the focus on the transformation of amines into amides, despite such approaches decreasing the coating efficiency; the nitrogen in amides is less nucleophilic than that in free amines. In this study, we investigated the effect of N-alkylation on dopamine surface chemistry. N,N-Dimethyldopamine (DMDA) was newly synthesized, and the coating efficiency was systematically compared with DA and N-methyldopamine (MDA). DA N-monomethylation improved the coating rate by increasing the nitrogen nucleophilicity, whereas N,N-dimethylation dramatically decreased the DA surface coating property. In addition, MDA remained capable of universal surface coating and secondary reactions using the surface catechols. This study provides opportunities for developing coating materials with advanced functions and an improved coating rate.

Crawling and adhesion behavior of Halamphora sp. based on different parts of Folium Sennae-like film: Evaluation of analytical methods for anti-diatom experimental results

Anti-diatom testing is a basic method to evaluate the anti-fouling performance of coatings. Many existing results of anti-diatom performances are evaluated based on their attachment number or coverage area, ignoring the influence of the crawling and adhesion behavior of diatoms on the analysis results. Here, a Folium Sennae-like film with multiple structural units was prepared by considering the influence of diatom attachment behaviors on the analysis results. The anti-diatom performances of different parts (divided and called four parts: edge, surface, cross striation, and vertical pattern) on the Folium Sennae-like film were evaluated using the counting and area methods. Obviously, the anti-diatom performance of the Folium Sennae-like film was superior to that of epoxy resin without structure. Under equal areas, the average numbers of diatoms on the cross striation and the vertical pattern were similar to the surface. It was found that the attachment behavior of Halamphora sp. is affected by microstructure units, rather than the combined structure of which the scale is much larger than that of diatoms. Meanwhile, the average attachment area for the unit number of diatoms was calculated. The diatom attachment area without microstructure, surface, cross striation, or vertical pattern was 81.751, 106.950, 73.904, and 84.376 μm², respectively. Moreover, the static and dynamic motion behaviors of Halamphora sp. were studied, and the theory for Halamphora sp. attachment was modeled in three dimensions. The variable morphology of Halamphora sp. lead to inaccurate results for diatom analyses based on the counting and area methods, which is summarized here. This study discusses the evaluation method of coatings by anti-diatom performance, further promoting the research of diatoms in the field of antifouling.

Food-grade carrageenans and their implications in health and disease

Food additives, often used to guarantee the texture, shelf-life, taste, and appearance of processed foods, have gained widespread attention due to their increased link to the growing incidence of chronic diseases. As one of the most common additives, carrageenans have been used in human diets for hundreds of years. While classified as generally recognized as safe (GRAS) for human consumption, numerous studies since the 1980s have suggested that carrageenans, particularly those with random coil conformations, may have adverse effects on gastrointestinal health, including aggravating intestinal inflammation. While these studies have provided some evidence of adverse effects, the topic is still controversial. Some have suggested that the negative consequence of the consumption of carrageenans may be structure dependent. Furthermore, pre-existing conditions may predispose individuals to varied outcomes of carrageenan intake. In this review, structure-function relationships of various carrageenans in the context of food safety are discussed. We reviewed the molecular mechanisms by which carrageenans exert their biological effects. We summarized the findings associated with carrageenan intake in animal models and clinical trials. Moreover, we examined the interactions between carrageenans and the gut microbiome in the pathogenesis of gastrointestinal disorders. This review argues for personalized guidance on carrageenan intake based on individuals' health status. Future research efforts that aim to close the knowledge gap on the effect of low-dose and chronic carrageenan intake as well as interactions among food additives should be conducive to the improved safety profile of carrageenans in processed food products.

The mussel-inspired micro-nano structure for antifouling:A flowering tree

Mussels are typical marine fouling organisms that attach to surfaces though secretions, which is generally the focus of research on mussel-related fouling. This study reveals "a flowering tree" structure on mussel shells with antifouling performance. Based on the antifouling mechanism of surface microstructure, we prepared mussel-like shells (P) using the biomimetic replication method. Mussel adhesion experiments were conducted to examine the anti-mussel performances of the mussel shells and P. The anti-diatom performances of the mussel-like shells were also evaluated using three types of diatoms. The mussels responded differently to different locations on the shells, and the flowering tree microstructure exhibited excellent antifouling performance. In addition, VP (P immersed in vinyl silicon oil) and HP (P immersed in hydroxyl silicone oil) were prepared. The anti-diatom performance of VP was better than those of P and HP, indicating that hydrophobicity has a greater influence on anti-diatom performance than electronegativity. The newly discovered antifouling micro-nano structure was parameterized, revealing that a branch of the flowering tree has an inclination of 13.3° to the surface with a height of 210.1 nm. The results of this study provide insights for further investigations of bionic micro-nano structures in the field of antifouling.

Universal Surface Coating with a Non-Phenolic Molecule, Sulfonated Pyrene

Nature-inspired small molecules such as catecholamines and polyphenols have gained a great deal of attention because of the exceptional surface-coating property that is applicable to many diverse substrates. Many researchers have conducted studies to expand molecular pools with surface-coating properties, but previous reports have still been limited to phenolic molecules as surface-coating agents. In this study, we describe for the first time the material-independent coating properties of nonphenolic molecules, namely, sulfonated pyrenes with Zr^IV ions. Owing to the binding capability with several oxygen-containing ligands, Zr^IV can be used for the molecular assembly of sulfonated pyrenes. We also report on the mixing of multiple sulfonated pyrenes and Zr^IV results in cross-linked complexes that can coat diverse solid substrates. The resulting coating can serve as a platform for grafting functional polysaccharides.

A critical review on production of biopolymers from algae biomass and their applications

Algae is abundantly present in our ecosystems and can be easily extracted and used for production of biopolymers. Algae does not produce any anthropogenic, harmful effects, has a good growth rate, and cultivable in wastewater. This literature elucidates the potential of algae biomass by comparing various seaweed and microalgae strains. The routes for biopolymer production were portrayed and their novel methods of isolation such as microwave assisted, ultrasound assisted, and subcritical water assisted extraction are discussed in detail. These novel methods are observed to be highly efficient compared to conventional solvent extraction, with the microwave assisted and ultrasound assisted processes yielding 33% and 5% more biopolymer respectively than the conventional method. Biopolymers are used in variety of applications such as environmental remediation, adsorbent and antioxidant. Biopolymer is shown to be highly effective in the removal of potentially toxic elements and is seen to extract more than 40 mg PTE/g biopolymer.