Nowadays, much research have been focused on marine algae as a source of potential biopolymer for large-scale production of nanofibers as they are ubiquitous and abundant in nature and easy to harvest. Moreover, marine algal biopolymers such as sodium alginate, agar, fucoidan, and carrageenans fall under GRAS category recognized by FDA (Tavassoli-Kafrani, Shekarchizadeh, & Masoudpour-Behabadi, 2016). Some researchers have successfully synthesized nanofibers from different kinds of marine algal biopolymers by electrospun methods such as alginate (Saquing et al., 2013; Hu, Gong, & Zhou, 2015; Wongkanya et al., 2017), ulvan (Kikionis, Ioannou, Toskas, & Roussis, 2015), agar and agarose (Sadrearhami, Morshed, & Varshosaz, 2015; Cho, Singu, Na, & Yoon, 2016), fucoidan (Jang, Hong, Jung Ro & Yoon, 2015; Zhang et al., 2017) and carrageenan (Basilia, Robles, Ledda, & Dagbay, 2008; Tort & Acartürk, 2016; Goonoo et al., 2017). In aqueous solution whole biopolymers alone cannot be fabricated by electrospinning due to their poor mechanical properties and processing. Therefore, some synthetic polymers have to be added with biopolymers as blending agents to form strong intermolecular hydrogen bond which helps easy spinning of nanofibers (Safi et al., 2007; Saquing et al., 2013; Zhao et al., 2016). Many synthetic, semisynthetic and natural polymers have been applied for production of electrospun nanofibers. Synthetic polymers and copolymers such as poly (lactic acid) (PLA), poly (lactic-co-glycolic acid) (PLGA), poly(?-caprolactone) (PCL), poly(vinyl pyrrolidone) (PVP) and poly(ethyleneoxide) (PEO) have been used to produce Nanofibers (Brandelli & Taylor, 2015; Akhgari, Shakib, & Sanati, 2017; Wen et al., 2017). Various marine algal biopolymers blended with synthetic polymers for nanofibers synthesis is shown in Table 2.
Sodium alginate. Alginates or sodium alginate (SA) or algins are biopolymer composed of two different linear copolymers such as uronic acids, ?-D-mannuronic acid (M) and ?-L-guluronic acid (G) linked in position 1?4. The salt forms (alginates), with several cations (Na+, K+, Mg2+ and Ca2+), are the significant components of brown seaweed cell walls and also of the intracellular matrix (Fathi et al., 2014; Pérez, Falqué, & Domínguez, 2016; Abdul Khalil et al., 2017). It is hydrophilic in nature with the molecular weight of alginate ranging between 500 and 1000 kDa (Pérez et al., 2016). Due to its biocompatibility, biodegradability, nontoxicity and low cost, sodium alginate has been well recognized for nanofibers synthesis in food application. Alginate is distinct from chitosan due to its high solubility in water (Zhao et al., 2016) which is an additional advantage to be used in electrospinning to produce nanofibers mats. In general, sodium alginate is composed of three different types of regions such as G, M and MG distributed in different extent in the polymeric chain which determine the physical properties of alginate. The gelling property of alginate is mainly decided by G region which are composed of L-glucuronic acids and M regions entirely composed of D-mannuronic acid. MG regions consist of both M and G which determine the dissolving property of alginate in many solvents (Tavassoli-Kafrani et al., 2016). Sodium alginate makes strong bond with multivalent cations particularly calcium ions by producing hard gel which is the exclusive property of alginate (Tavassoli-Kafrani et al., 2016; Abdul Khalil et al., 2017). Therefore, SA is highly suitable for making nanofibers mat because most of the cross-linking of biopolymers depends on calcium ions which strengthens the nanofibers.
Sodium alginate is the most studied biopolymer for electrospinning among other biopolymers from marine algae. Saquing et al. (2013) produced alginate nanofibers blend with synthetic polymer Polyethylene Oxide (PEO) by electrospinning method. Hajiali et al. (2015) fabricated sodium alginate nanofibers containing lavender oil by the electrospinning method and demonstrated potential growth inhibition using bioactive nanofibers against S.aureus. Citric acid cross-linked sodium alginate/PVA electrospun nanofibers were prepared by a team of Stone, Gosavi, Athauda, & Ozer (2013). They used a homogeneous blend of sodium alginate-polyvinyl alcohol (1:1 weight ratio) containing cross-linking agent citric acid (5 wt%) for electrospinning and found that cross-linked nanofibers were more heat stable and water-insoluble even after two days of immersion in water than the non-cross linked electrospun nanofibers which dissolved immediately. Recently Rafiq, Hussain, Abid, Nazir, & Masood. (2018) successfully immobilized some essential oils (EOs) such as cinnamon, clove, and lavender on electrospun nanofibers synthesized from alginate and polyvinyl alcohol (PVA) blend and evaluated antimicrobial activity against S. aureus. The results showed that all EOs displayed good antimicrobial activity and the FTIR study confirmed the successful incorporation of essential oils in nanofibers.
Carrageenan. Carrageenan is a sulfated water-soluble polysaccharide present in red algae, which consists of a linear sequence of other residues forming (AB)n sequence, where A and B are units of galactose residues. They are linked by alternating ?-(1?3) (unit A) and ?-(1?4) (unit B) glycosidic bonds. Carrageenans are polyanions due to the presence of sulfated groups (Cardoso, Costa, & Mano, 2016). Carrageenans are classified into three groups based on degree of sulfation: as kappa (?) which contain 4-sulfated galactose and a 4-linked 3,6-anhydrogalactose, iota (?) is like kappa but with addition of sulfate ester group on C-2 of the 3,6-anhydrogalactose residue and lambda (?) containing 2-sulfated, 3-linked galactose unit, and a 2,6-disulfated 4-linked galactose unit (Tavassoli-Kafrani et al., 2016). Generally, carrageenan is extracted from marine algal species including Kappaphycus alvarezii, Eucheuma denticulatum, Hypnea musciformis, Lamoroux and Solieria filiformis (Tavassoli-Kafrani et al., 2016; Cardoso et al., 2016)
Carrageenan is widely used as a functional ingredient in many food industries for various purposes (Tavassoli-Kafrani et al., 2016; Abdul Khalil et al., 2017). These three different carrageenan exhibit distinct gelation properties to each other. i.e., ? -carrageenan produce rigid and brittle gels, ?-carrageenan produces softer, elastic and cohesive gels and ? -carrageenan doesn’t form gels. This is due to the presence of different sulphate groups and anhydro bridges in carrageenan (Abdul Khalil et al., 2017). Some authors pointed out that carrageenans have biological properties such as anticoagulant, antitumor, immunomodulatory, anti-hyperlipidemic and antioxidant activities. They also have protective action against bacteria, fungi and some viruses (Silva et al., 2010; Zhou et al., 2004; Panlasigui, Baello, Dimatangal, ; Dumelod, 2003; De Souza et al., 2007).
Basilia et al. (2008) produced polycaprolactone/carrageenan nanofibers by the electrospinning method and studied in vitro and in vivo for tissue engineering applications. Carter (2016) successfully encapsulated two essential oils such as carvacrol and eugenol in nanofibers synthesized from iota-carrageenan and tested against food pathogens L.monocytogenes and L.innocua. His results elucidated that carrageenan nanofiber encapsulated essential oils effectively inhibited the growth of tested food pathogens and potential release characteristic features. Another team led by Goonoo (2017), have reported the possibilities of producing nanofibers from mixed components of biodegradable polyhydroxybutyrate (PHB) or polyhydroxybutyrate valerate (PHBV) with the anionic sulfated polysaccharide ?-carrageenan (?-CG) by electrospinning method. Carrageenans make strong bonds with polycations compounds (Eg. chitosan), thus, applying organic solvents and toxic cross-linkers can be avoided during nanofibers synthesis (Cardoso et al., 2016). It is an added advantage to using carrageenans for nanofibers synthesis by electrospinning technique.
Ulvan. Ulvan is a complex, water-soluble sulfated anionic polysaccharide obtained from cell wall matrix of the members of green algae, Ulvales (Chlorophyta) (Toskas et al., 2011). The name ulvan is derived from the original terms ulvin and ulvacin which usually are extracted by the process of hydrolysis at around 80-90°C using divalent cation chelator such as ammonium oxalate (Lahaye ; Robic, 2007). Generally, ulvan are extracted from following species such as Ulva pertusa, Ulva lactuca, Ulva clathrata, Ulva compressa, Ulva conglobata, and Enteromorpha prolifera (Majee, Avlani, Ghosh, ; Biswas, 2018). Ulvan is typically composed of ?- and ?-(1?4)-linked sugar residues, namely ?-1,4- and ?-1,2,4-linked L-rhamnose 3-sulphate, with branching at O-2 of rhamnose, ?-1,4- and terminally linked D-glucuronic acid and ?-1,4-linked D-xylose, partially sulphated on O-2. The primary structural units found in ulvan include ?-D-glucuronosyluronic acid- (1,4)-L-rhamnose 3-sulphate dimer (?-D-GlcpA-(1?4)-LRhap 3-sulphate) and ?-L-IdopA-(1?4)-?-L-Rhap 3-sulphate, also known as ulvanobiuronic acid A and B, respectively. The main difference between these aldobiuronic acids is the presence of glucuronic acid in A, which is replaced by iduronic acid in B (Lahaye, 1998; Quemener, Lahaye, ; Bobin-Dubigeon, 1997; Alves, Sousa, ; Reis, 2013).
One extraordinary feature of ulvan is the occurrence of uncommon sugars within its fibers, i.e., sulphated rhamnose and iduronic acid. Rhamnose is an unusual sugar, typically found in bacteria, plants and accumulates uncommonly in animals. Branching of O-2 of 1, the associated ?-L-rhamnose residue, was found only on an exopolysaccharide produced by the bacterium Arthrobacter sp. The presence of iduronic acid in the ulvan chain is a significant feature since it is not recognized in algal polysaccharides (Quemener et al. 1997; Alves et al., 2013). The possibility of producing nanofibers from ulvan using electrospinning technique was first reported by Toskas et al. (2011). They obtained various sizes of nanofibers with different ratios of ulvan and copolymer PVA. For the rate of ulvan/PVA (50:50), they obtained nanofiber of size approximately 105±4 nm, for 70:30 as 84±4nm and for 85:15 ratio as 60±5nm. Many reports indicated that higher concentration biopolymer than the synthetic copolymer in the mixer lead to the formation of beads in nanofibers. In contrary, in their findings, a higher concentration of ulvan showed smaller size of nanofibers without any bead formation as evidenced from SEM and TEM analyses. Another research report published by Kikionis et al. (2015) demonstrated that ulvan could be converted into electrospun nanofiber by blending with two biodegradable synthetic polymers such as polyethylene oxide (PEO) and polycaprolactone (PCL). They investigated the synthesized nanofibers by SEM, FTIR which revealed the strong interaction and good compatibility between ulvan and the two copolymers. Moreover, the stability of ulvan nanofibers was examined and found that it does not lose its balance even after 18 months of storage which concluded that ulvan could represent new promising biomaterials for producing strong nanofibers for various biological applications.
Agar and agarose. Agar and agarose are widely used as a gelling agent in the food industry and microbiological purposes, extracted from red seaweeds (Khalil et al., 2017). In general, agar is composed of two polysaccharides such as agarose and agaropectin with similar structural and functional properties as carrageenans. Agarose is the significant component of agar than agaropectin, and it consists of high molecular weight polysaccharides composed of repeating units of (1?3)-?-D-galactopyranosyl-(1?4)-3,6-anhydro-?-L-galactopyranose. The structure of agaropectin, with a lower molecular weight than agarose, is mainly made up of alternating (1?3)- ? -D-galactopyranose and (1?4)-3,6-anhydro- ? -L-galacto-pyranose residues (Pérez et al., 2016). Agar and agarose are associated with several biomedical applications especially as hydrogels for the release of bioactive agents, taking advantage of its ability to gel, biocompatibility and biodegradability in nature (Cardoso et al., 2016). Only sparse details are available on nanofiber synthesis from agar and agarose as limited research have been carried out on electrospinning of this marine algal polysaccharides.
Sadrearhami et al. (2015) attempted to produce nanofibers from agar with polyacrylonitrile as copolymer to immobilize methotrexate for cancer therapy and succeeded by electrospinning method. To evaluate the effects of polymer ratio and drug concentration on release rate, solutions with different polyacrylonitrile/agar ratios were prepared and subsequently electrospun with varying proportions of methotrexate-polymer. The results demonstrated that increasing the drug and agar concentration led to rising in diameter due to increase in the solution blend viscosity which was confirmed by SEM analysis. Moreover, drug release rates increased with increasing agar ratio due to the increased hydrophilicity of the drug delivery systems. They concluded that novel agar nanofibers proved to be a potential candidate for controlled release of drugs or any other bioactive compounds for various biological applications. UV-irradiated agarose/polyacrylamide cross-linked double-network electrospun nanofibers were produced in the range of 187 nm (Cho et al., 2016). Moreover, they analyzed the thermal stability of double-network nanofibers using thermogravimetric analysis (TGA) and showed the excellent thermal property at 290–500 °C. From the results, they recommended that agarose/polyacrylamide nanofibers could be used as possible material in biomedical and bioengineering applications.
Fucoidan. Fucoidan is a water-soluble sulfate-rich polysaccharide mainly composed of fucose (Puvaneswary et al., 2016). The molecular weight of fucoidan have been recorded in the range of 100 to 1600 kDa, and the differences are due to differing composition and chemical structure including the degree of branching, substituents, sulphation and type of linkages (Rioux, Turgeon, ; Beaulieu, 2007; Pérez et al., 2016). Mostly fucoidans are extracted from seaweeds like Laminaria spp., Analipus japonicus, Cladosiphon okamuranus, Chorda filum, Ascophyllum nodosum and Fucus sp. The molecular structure of fucoidans comprises of backbone structure of (1?3)-linked ?-L-fucopyranosyl ? (1?3) and ? (1?4)-linked L-fucopyranosyls (Tutor ; Meyer, 2013; Pérez et al., 2016). Names like fucans, fucosans, fucose is used for this group of polysaccharide extracted from other marine species, but fucoidan is the term held for the algal source by IUPAC naming system (Pérez et al., 2016).
Lee et al. (2012) fabricated nanofiber using fucoidan and polycaprolactone (PCL) by electrospinning technique at various concentrations of fucoidan as 1, 2, 3, and 10 %w/v. The result showed that electrospun nanocomposites of fucoidan/PCL exhibited improved hydrophilicity, tensile strength than the PCL fiber mats. In another study, fucoidan nanofiber was successfully produced with Chitosan and Poly(vinyl alcohol) for vascular tissue engineering (Zhang et al., 2017). After electrospinning, they obtained well defined interconnected nanofibers composed of F/CS/PVA which was evidenced by SEM and FTIR analysis. Moreover through XRD pattern it was confirmed that electrospinning process of F/CS/PVA mixer had lowered the crystallinity of the polymers and have more excellent water uptake ability, sufficient porosity and enhanced drug release. Besides, fucoidan per se has various biological functions like anticoagulant, antiviral, immunomodulatory activity (Lee et al., 2012) and potential antibacterial activity against food pathogens (De Jesus Raposo et al., 2015; Chua et al., 2015). Hence, fucoidan is also one of the promising candidates for making nanofibers to incorporate natural antimicrobial agents to preserve foods.


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