“Green” polymeric electrospun fibers based on tree-gum hydrocolloids

CHAPTER

“Green” polymeric electrospun fibers based on tree-gum hydrocolloids: fabrication, characterization and applications

5

ˇ ´ k1 Vinod Vellora Thekkae Padil1, Chandra Senan2 and Miroslav Cernı 1

Department of Nanomaterials in Natural Sciences, Centre for Nanomaterials, Advanced Technologies and Innovation (CxI), Technical University of Liberec (TUL), Liberec, Czech Republic 2Centre for Water Soluble Polymers, Applied Science, Faculty of Arts, Science and Technology, Wrexham Glyndwr University, Wales, United Kingdom

5.1 INTRODUCTION In the past few decades, nanoparticles (NPs) and nanofibers (NFs) have demonstrated superior performance in numerous applications including energy, the environment, water purification, sensor devices, tissue engineering scaffolds, wound dressing, drug delivery and healthcare, etc. (Fryxell and Cao, 2007; Thavasi et al., 2008; Matlack, 2001; Pereao et al., 2016). Electrospinning is one of the most proficient and sophisticated methods used for the large-scale fabrication of NFs possessing a sizable surface area-to-volume ratio, high porosity, and stability (Jayaraman et al., 2004). Electrospinning process parameters such as system and process variable requirements have been meticulously reported in the literature (Greiner and Wendorff, 2007; Nie et al., 2008). In order to develop “green electrospinning” technology it is necessary to use nontoxic, inexpensive, and environmental friendly solvents and materials. Compared to the current electrospinning process, which utilizes hazardous, corrosive, and nonecological organic solvents, water-based solvents and polymers are being developed instead in order to produce electrospun NFs and membranes that make electrospinning processes more economical while simultaneously furnishing a greener technology for boosting environmental protection. Fibrous structures with nanoscale diameters offer a multitude of fascinating features such as excellent mechanical behavior and large surface area-to-volume ratios, making them attractive for many applications. Their extensive surface area also endows them with high functionalization capability. Among the many techniques available for generating NFs, electrospinning is rapidly emerging as a simple facile process in which the careful control of operating conditions and polymer Materials for Biomedical Engineering: Biopolymer Fibers. DOI: https://doi.org/10.1016/B978-0-12-816872-1.00005-4 © 2019 Elsevier Inc. All rights reserved.

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solution properties enables the production of highly porous structures of smooth NFs (Greiner and Wendorff, 2007; Ramakrishna et al., 2005). Compared to traditional phase-inversion techniques for membrane fabrication, electrospinning allows the formation of interconnected pores with uniform pore sizes and porosities exceeding 90%. Consequently, electrospun membranes are increasingly being applied to many water purification applications such as membrane distillation and pretreatment of feed water (prior to reverse osmosis or nanofiltration processes) by the removal of divalent metal ions, grease, and other contaminants (Matsumoto and Tanioka, 2011; Yoon et al., 2008). Although the use of electrospinning for membrane fabrication has previously been reviewed, the rapid surge in developments over recent years has necessitated the need for a review of the preparation and application of electrospun NFs membranes as the barrier layer for water treatment, with emphasis on the reinforcement and post-treatment of electrospun polymer membranes. Electrospinning is one of the most accomplished and advanced methods for the fabrication of submicron-sized fibers with large surface area-to-volume ratios (Jayaraman et al., 2004; Greiner and Wendorff, 2007). The effectiveness of the electrospinning process depends on many parameters, including solution properties (concentration, viscosity, surface tension, chain entanglement, molecular weight, degree of deacetylation, purity, solubility, charged group distribution, gelling behavior, and electrical conductivity); processing parameters (feed flow rate, tip-to-collector distance, collector composition, and geometry); and ambient parameters (temperature, humidity, and air flow) (Haider and Park, 2009; Toskas et al., 2011; Lubambo et al., 2013). In this chapter, we focus on the overall morphological, compositional and structural aspects of the industrially important tree gums, that is, gum Arabic (GA), gum Karaya (GK), gum Kondagogu (KG), gum Tragacanth (GT), and gum Ghatti (GG). The NPs of various types (e.g., metal/metal-oxide) obtained via the green synthesis route involving various gum matrices and their performance as antibacterial agents are summarized. In addition, the fabrication of “green electrospun” NFs based on tree gums and their subsequent employment in environmental and biomedical applications are also reviewed in this chapter. Fig. 5.1 is a schematic model showing nonfood applications of gum-based NPs, NFs, and functionalized materials to be exemplified in this chapter.

5.2 TREE GUMS—AN OVERVIEW Gums are hydrocolloids, which are hydrophilic in nature and are found in almost every biosphere on earth, ranging from plants and animals to numerous bacteria. They contain a large number of hydroxyl groups, usually arranged in a fairly regular manner along the backbone of the molecule. This allows for the chelation of mono- and divalent cations, thereby cross-linking the hydrocolloid chains together

5.2 Tree Gums—An Overview

FIGURE 5.1 Schematic representation of various applications (environmental and biomedical) of tree gum and their nanoparticles and nanofibers.

and forming complex macrostructures (Anderson and Weiping, 1992). Hydrocolloids are some of the most well well-known polysaccharides, having complex structures linked by glycosidic bonding. Most gums are heterogeneous polysaccharides with complicated structures and extremely high molecular masses (Anderson et al., 1982, Anderson and Bridgeman, 1985). The simplest interactions of hydrocolloids are (as the name suggests) with water and it is this interaction that is key to their use in foodstuffs. Gum hydrocolloids are effective water adsorbents and to a greater or lesser extent may be solubilized by water. Due to the high number of hydroxyl groups, water is held within the molecular structure (by hydrogen bonding) and also contained within the voids created by the complex molecular configurations (Hall, 2009; Phillips and Williams, 2001). The important tree exudate gums available on the market are as follows: GA, GK, GT, KG, and GG. Extensive research has been undertaken on various aspects of these tree gum polysaccharides, including their availability, molecular weight distributions, chemical structures, and food and nonfood applications (Hall, 2009; Phillips and Williams, 2001; Kennedy et al., 2012; Williams and Philips, 2009; Verbeken et al., 2003; Vinod et al., 2008a,b; Deshmukh et al., 2012). None of these gums are produced in developed countries and must be imported from developing countries. The chemical composition of these gums is complex and varies according to its source and age. It is thus not possible to provide detailed structural formulae of these biopolymers. Exudate gums are used in a multitude of applications, especially in the food industry but there are also numerous nonfood applications (Verbeken et al., 2003).

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5.2.1 GUM ARABIC GA or gum Acacia is a branched, neutral, or slightly acidic complex polysaccharide obtained as a mixed calcium, magnesium, and potassium salt. The backbone consists of 1-3-linked β-D-galactopyranosyl units. The side chains are composed of two to five 1-3-linked β-D-galactopyranosyl units, joined to the main chain by 1-6 linkages. Both the main and side chains contain units of α-L-arabinofuranosyl, α-L-rhamnopyranosyl, β-D glucuronopyranosyl, and 4-O-methyl-β-D-glucuronopyranosyl units, the latter two mostly as end-units. (Kennedy et al., 2012; Williams and Philips, 2009) The high-molecular-weight fraction of the gum has been ascribed to the large carbohydrate blocks it is composed of (which has a molecular mass of approximately 2.5 3 105 Da) that are attached individually to polypeptide chains. GA is obtained from the stems and branches of Acacia Senegal and Acacia Seyal and, being a branched polysaccharide, it exhibits unique structural, physical, and chemical properties (Verbeken et al., 2003; Mahendran et al., 2008). Hence, it is widely used in food and pharmaceutical applications (Kennedy et al., 2012; Williams and Philips, 2009; Verbeken et al., 2003; Mahendran et al., 2008).

5.2.2 GUM TRAGACANTH GT is one of the most widely used natural gums which has found applications in many areas because of its attractive features such as biodegradability, nontoxicity, natural availability, elevated resistance to microbial attacks, and long shelf-life. GT is a complex, highly branched, heterogeneous polysaccharide, occurring naturally as a slightly acidic calcium, magnesium, and potassium salt. It has a molecular mass of approximately 8.4 3 105 Da (Verbeken et al., 2003; Weiping, 2000; Singh and Sharma, 2014). The composition of the gum obtained from different Astragalus species shows considerable variation. This divergence is not surprising, since the genus Astragalus is the largest within the Leguminosae family, occurring worldwide in tropical regions and harboring around 2000 species, grouped into more than 100 subdivisions (Verbeken et al., 2003). GT consists of tragacanthic acid or bassorin (the first of two fractions), which is insoluble in water but has the capacity to swell and form a gel. The second fraction, tragacanthin is water-soluble. Both fractions contain small amounts of proteinaceous material and methoxyl groups, the latter being present in higher amounts in the water-soluble fraction (Verbeken et al., 2003; Weiping, 2000). The waterswellable tragacanthic acid fraction has a high molecular weight and a rod-like molecular conformation. The main chain is formed by 1,4-linked D-galactose residues with side chains of D-xylose units attached to the main chain by 1, 3 linkages. The water-soluble tragacanthin is a neutral, highly branched arabinogalactan with a spherical molecular shape. Its structure probably comprises a core of 1,6- and 1,3-linked D-galactose units with attached chains of 1,2-; 1,3-, and 1,5-linked L-arabinose (Verbeken et al., 2003; Singh and Sharma, 2014). GT is mainly used in the food and pharmaceutical fields.

5.2 Tree Gums—An Overview

5.2.3 GUM KARAYA GK is a complex, partially acetylated polysaccharide obtained as a calcium and magnesium salt. It has a branched structure and a high molecular mass of approximately 16 3 106 Da (Hall, 2009; Williams and Philips, 2009; Verbeken et al., 2003). The backbone of the gum consists of α-D-galacturonic acid and α-L-rhamnose residues. Side chains are attached by 1,2-linkages of β-D-galactose or by 1,3-linkages of β-D-glucuronic acid to the galacturonic acid of the main chain. Furthermore, half of the rhamnose residues of the main chain are 1,4-linked to β-D-galactose units (Verbeken et al., 2003; Weiping, 2000; Stephen and Churms, 1995). The chemical composition of gum samples obtained from various Sterculia species and from different places of origin was found to be quite similar (Weiping, 2000). Commercial GK contains approximately 13%
26% galactose and 15%
30% rhamnose, the latter being considerably higher than the rhamnose content of other commercial exudate gums (Stephen and Churms, 1995). However, the protein content of approximately 1% is lower than that of other exudate gums. GK also contains approximately 40% uronic acid residues and 8% of acetyl groups (Brito et al., 2005; Verbeken et al., 2003). Due to the presence of these acetyl groups, native GK is insoluble in water and merely swells up. Le Cerf et al. (1990), distinguished three fractions present in GK, based on their solubility in water. Only 10% of the native gum was solubilized in cold water, increasing to 30% in hot water. After deacetylation with dilute ammonia or NaOH, 90% of the native gum dissolved in water. The equivalent weight of the deacetylated-soluble fraction was higher than that of the cold-water-soluble fraction. This indicates that only lower-molecular-weight molecules are able to dissolve in cold water, while deacetylation leads to the solubilization of material of a higher molecular weight (Verbeken et al., 2003; Stephen and Churms, 1995; Le Cerf et al., 1990).

5.2.4 KONDAGOGU GUM KG belongs to the species Cochlospermum and family Bixaceae. Although GK (a.k.a. Indian tragacanth) and KG are classified in the same group, there are considerable differences in their physical and chemical properties (Janaki and Sashidhar, 1998). Extensive research has been carried out on KG (Cochlospermum gossypium), a gum extracted from the Kondagogu tree, which grows in India. This includes its morphological, physical, chemical, structural, rheological, pharmaceutical, and emulsifying properties as well as its toxicological evaluation as a food additive (Naidu et al., 2009a,b; Vinod et al., 2008a,b; Vinod and Sashidhar, 2009; Vinod et al., 2010a; Janaki and Sashidhar, 2000). Furthermore, this gum can also be used as a biosorbent for the removal of toxic metal contaminants from aqueous environments while also serving as an environmentally friendly material for stabilization (Vinod et al., 2009; Vinod et al., 2010b,c). Additionally, it can act as a reducing agent for the synthesis of

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metal/metal-oxide nanoparticles (Vinod et al., 2011a, Vinod and Sashidhar, 2011; ˇ ´k, 2013, Padil et al., 2013; Kora et al., 2010; Saravanan et al., Padil and Cernı 2012). Structural analysis of this biopolymer has shown that it contains sugars such as arabinose, rhamnose, glucose, galactose, mannose, glucuronic acid, and galacturonic acid. Based on spectroscopic characterization, the probable structural feature assigned to KG is (1-2) β-D-Gal p, (1-6) β-D-Gal p, (1-4) β-D-Glc p A, 4-0-Me-α-D-Glc p A, (1-2) α-L-Rha and (1-4) α-D-Gal p A (Vinod et al., 2008a,b).

5.2.5 GUM GHATTI GG, an Indian gum, is a nonstarch polysaccharide and its main species, Anogeissus latifolia (Combretaceae, Myrtales), is a large deciduous tree found in dry areas (Katayama et al., 2008; Ido et al., 2008). GG is used as an emulsifier and thickener in food industries (Castellani et al., 2010). Recently, Deshmukh et al. (2012) published a detailed review of the molecular structure, properties, and pharmaceutical applications of GG.

5.3 “GREEN” ELECTROSPINNING BASED ON TREE GUMS Fibers produced by electrospinning have been known for over 90 years, when the Czech-American physicist John Zeleny studied techniques known today as electrospinning and electro-spraying. When a conductive liquid in a capillary is exposed to an electric field of B10 kV, the liquid shape forms a cone, which emits a jet of liquid. Fibers are formed as a result of the solution drying during its flight to the opposite electrode (collector). Professor Oldrich Jirsak of TUL developed industrial production based on roller electrospinning in 2004 in the Czech Republic. Currently, submicron fibers and NFs can be formed from the following: solutions and melts; various chemicals and material mixtures; traditional or “green” materials. The aforementioned fibers can also be generated in a DC or AC field, and from a core-shell structure of two different materials. Akin to the broad spectrum of fiber type possibilities, the potential for their application is even wider. This includes the fields of biotechnology, mechanical engineering, optical, electronic, medicinal, and drug production together with the provision of environmental protection. The development of electrospun fibers and membranes based on natural renewable materials for energy and environmental applications is still underway. “Green” electrospinning technology relies on the development of nontoxic, inexpensive and environmentally friendly polymers and solvents (such as water or ionic solvents) for the fabrication of electrospun fibers and membranes. Electrospun natural biodegradable polymers have shown great applicability in many fields such as the development of filtration membranes, catalytic NFs,

5.3 “Green” Electrospinning Based on Tree Gums

tissue engineering, drug delivery, and sensors (Lee et al., 2009; Matsumoto and Tanioka, 2011). The application of electrospun NFs in the areas of biomedicine, drug delivery, tissue engineering, wound dressing, water purification, and energy has been reported (Ramakrishna et al., 2005, Greiner and Wendorff, 2007; Yoon et al., 2008; Jayaraman et al., 2004; Thavasi et al., 2008). Electrospun NFs derived from natural tree gum-based biopolymers are an innovative group of economic and environmentally friendly membranes with potential applications in the energy, environmental and biomedical fields. Natural biopolymers such as chitin, chitosan, and guar gum blended with synthetic biocompatible polymers (poly(vinyl alcohol) (PVA) or polyethylene oxide (PEO)) have been reported to be suitable for producing electrospun membranes (Toskas et al., 2011; Lubambo et al., 2013; Elsabee et al., 2012, Homayoni et al., 2009, Vashisth et al., 2014). Very recently, natural tree polymers such as GA, GT, GK, and KG have undergone electrospinning whereby the system and process parameters have been standardised to produce smooth and uniform NFs (Padil and Cernik, 2015b; Padil et al., 2015a,b,c,d; Padil et al., 2016; RanjbarMohammadi et al., 2013; Ranjbar-Mohammadi and Bahrami, 2015; RanjbarMohammadi et al., 2016a,b,c). Furthermore, many combinations of tree gums have been blended with PVA or PEO and the solubility of the polymer has been found to subsequently improve the spinnability, solubility, biocompatibility, biodegradability and mechanical properties of the electrospun membranes. In addition, both the gums as well as their chemical modification with dodecenyl succinic anhydride (DDSA) or Ag or Au or CuO NPs (to develop antibacterial functional membranes) have been reported (Padil et al., 2015b,c,d; Kora et al., 2010; Kora and Arunachalam, 2012; Kora et al., 2012; Ghayempour et al., 2016; Reddy et al., 2015; Chockalingam et al., 2010; Venkatesham et al., 2014; Wu and Chen, 2010).

5.3.1 ELECTROSPUN FIBERS AND MEMBRANES OF GUM ARABIC, GUM KARAYA, KONDAGOGU GUM, AND GUM TRAGACANTH As reported by Padil and Cernik (2015b), Padil et al. (2015a,b,c,d, and 2016), aqueous PVA (10
12 wt.%) was mixed with GA, GK, and KG solutions (varying from 2 to 5 wt.%) in different weight proportions of PVA or PEO with GA, GK, and KG (100/0, 50/50, 60/40, 70/30, 80/20, and 90/10), to determine the optimum spinnability and uniform size of NFs after electrospinning. The latter procedure was carried out on a nanospider electrospinning machine (Elmarco, NS IWS500U, Liberec, Czech Republic) with interchangeable electrode systems, working with both wateror nonwater-soluble polymers. The electrospinning conditions were as follows: spinning electrode width of 500 mm; effective NF layer width of 200
500 mm, spinning distance of 130
280 mm, substrate speed of 0.015
1.95 m/min, voltage of 0
55 kV, and process air flow of 20
150 m3/h. The ratios of the best combinations of the blend mixtures of gums were as follows: PVA was found to have a

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FIGURE 5.2 Scanning electron microscopy (SEM) photos of nanofibers (NFs) with different weight ratios of poly(vinyl alcohol) to gum Arabic (Left) (PVA/GA) weight ratios of (A) 50/50, (B) 60/40, (C) 70/30, (D) 80/20, (E) 90/10, and (F) 100/0 (pure PVA); (central) PVA/gum Karaya (GK) NFs fabricated at varying PVA:GK ratios in the blended solutions (A) 50:50, (B) 60:40, (C) 70:30, (D) 80:20, (E) 90:10, and (F) 100:0 (pure PVA); (Right) PVA/ Kondagogu gum (KG) NFs fabricated at varying PVA: KG ratios in the following blended solutions: (A) 50:50, (B) 60:40, (C) 70:30, (D) 80:20, (E) 90:10, and (F) 100:0 (pure PVA). Reprinted from Padil, V.V.T., et al., 2016. Int. J. Biol. Macromol. 91, 299
309, with permission from Elsevier.

30:70
10:90 ratio of gum/PVA in the final electrospinning mixture. The morphological characterizations of GA, GK, and KG with their electrospun fibers are presented in Fig. 5.2 (left, central, and right), respectively. GT and PVA were dissolved in deionized water using different mass ratios of GT/PVA, that is, 0/100, 30/70, 60/40, 50/50, 40/60, 70/30, 0/100, and NFs were then produced from these solutions using the electrospinning technique of Ranjbar-Mohammadi et al., 2013. The effect of different electrospinning parameters (such as the extrusion rate of polymer solutions, solution concentrations, electrode spacing distances and applied voltages) on the morphology of NFs was examined. Very recently, poly(ε-caprolactone) (PCL) or polylactic glycolic acid (PLGA) or polylactic acid (PLA)/GT NFs were fabricated via the electrospinning technique of Ranjbar-Mohammadi and Bahrami, 2015 and Ranjbar-Mohammadi et al., 2016a,c. In order to carry this out, a 7% GT solution was blended with a 20% PCL solution using a 2:1 PCL/GT mass ratio in acetic acid or, in addition, using PLA-GT in three different weight ratios, including 100:0, 75:25, 50:50 (wt. %) with 1,1,1,3,3,3-hexafluoro-2-propanol as the solvent at 40 C. The blended solution was electrospun applying the following parameters: 15 kV voltage, 15 cm nozzle to collector distance and 1 mL/h extrusion rate.

5.5 Cross-Linking and Stability of Electrospun Fibers

5.4 PLASMA TREATMENTS FOR FIBERS AND ITS CHARACTERISTICS Plasma-surface modification is an efficient and cost-effective surface treatment technique used in biomedical research such as sputtering and etching, implantation, deposition, polymerization, spraying, and laser plasma deposition (Chu et al., 2002; Guo et al., 2010). The unique advantage of plasma modification is that the surface properties and biocompatibility can be significantly altered, while the bulk qualities of the materials remain unchanged (Guo et al., 2010). Various gas plasma treatment methods (using oxygen, argon, and methane) have been developed to modify the surface properties of polymers, such as the balance of hydrophilicity/hydrophobicity and surface free energy (Daw et al., 1998). Typically, plasma treatment modifies the surface by grafting hydroxyl (
OH), carbonyl (
CO), and carboxylate (
COOH) groups (Svirachev and Tabaliov, 2005; Tan et al., 2010; Junkar et al., 2010). Through the processes of plasma modification, it is possible to influence the change of wettability and water contact angle—either to strongly hydrophilic or more hydrophobic—depending on the nature of the plasma used for the modification and the plasma treatment time (Junkar et al., 2010; Krupa et al., 2014; Bryjak and Gancarz, 2012). As stated in the literature, the treatment of membranes using various gas plasma treatment methods such as oxygen, argon, or nitrogen has been developed to modify the hydrophilic surface properties of polymers (Rangl et al., 2003; Jeong et al., 2009). However, methane or sulfur hexafluoride plasma treatment on various polymeric membranes has been used to enhance the hydrophobicity of the polymer surfaces, resulting in higher contact angles (Dong et al., 2013). The GA, GK, and KG fibers were treated with methane plasma to improve their hydrophobicities, stabilities, water contact angles and surface areas (Padil and Cernik, 2015b; Padil et al., 2015a,b,c; Padil et al., 2016). Preparation of the methane plasma treated membrane was undertaken in a 13.56 MHz radio frequency plasma reactor (BalTec Maschinenbau AG, Pfaffikon, Switzerland). The plasma chamber was thoroughly purged with a continuous flow of the gas used during the treatment to eliminate trace amounts of air and moisture. During the process, the gas flow was adjusted in order to keep a constant pressure of 20 Pa inside the chamber. The plasma conditions and process parameters were as follows: voltage of 300 V, power 20 W, time of 5 minutes, plasma gas purity of 99.997%, electrode area of 48 cm2, interelectrode distance of 50 mm and chamber volume of 1000 cm3.

5.5 CROSS-LINKING AND STABILITY OF ELECTROSPUN FIBERS Heat and plasma treatments were conducted on the fibers and membranes for their application in environmental remediation and antibacterial fields. The GA, GK,

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FIGURE 5.3 Scanning electron microscopy morphology of untreated and plasma-treated nanofibers of gum Arabic (GA), gum Karaya (GK), and Kondagogu gum (KG), respectively. Reprinted from Padil, V.V.T., et al., 2016. Int. J. Biol. Macromol. 91, 299
309, with permission from Elsevier.

and KG membranes were heated to 130 C
150 C and their stabilities were tested against acid, alkaline and aqueous solutions. All the heat-treated membranes were found to stable (up to 90%
95%) under all these tested conditions (Padil and Cernik, 2015b; Padil et al., 2015a,b,c; Padil et al., 2016). Subsequently, the water contact angle (θ), membrane thickness, porosity, apparent density, Brunauer
Emmett
Teller surface area, and degree of stability were found to have increased after methane plasma modification (Padil and Cernik, 2015b; Padil et al., 2015a,b,c; Padil et al., 2016). Fig. 5.3 presents the morphological changes that occurred due to the plasma treatments on the tree gums.

5.6 “GREEN” SYNTHESIS OF NANOPARTICLES Green chemistry is a set of principles or practices that encourages the design of products and processes that reduce or eliminate the use and generation of

5.6 “Green” Synthesis of Nanoparticles

hazardous substances (Anastas and Warner, 2000; Shamim and Sharma., 2013; Luque and Varma, 2012). Current green nanotechnology practices often involve the use of natural sources; nonhazardous solvents; biodegradable and biocompatible materials and energy-efficient processes in the preparation of NPs and NFs (Virkutyte and Varma, 2011; Varma, 2014, 2016; Iravani, 2011; Hebbalalu et al., 2013; Raveendran et al., 2003; Pereao et al., 2016). Tree gums (GA, GK, KG, GT, and GG) have been used as templates for the synthesis and stabilization of various metal (Ag, Au, Pt, Pd, Fe, Cu, Se, etc.) and metal-oxide (Fe3O4, CuO, ZnO, etc.) NPs (Wu and Chen, 2010; Kong et al., 2014; Padil et al., 2013, 2014; Padil and Cernı´k, 2015b; Padil et al., 2015a, 2015c; Mohan et al., 2007; Akele et al., 2015; Dong et al., 2014a,b; Djajadisastra et al., 2014; Shalaby et al., 2015; Kattumuri et al., 2007; Chockalingam et al., 2010; Venkatesham et al., 2014; pooja et al., 2015; Vinod et al., 2011a; Kora et al., 2010; Kora and Arunachalam, 2012; Kora and Rastogi, 2015; Mittal and Mishra, 2014; Saravanan et al., 2012; Ghayempour et al., 2016; Rastogi et al., 2014, 2017). All of the above-mentioned NPs (Table 5.1) were characterized using a variety of spectroscopic and microscopic analyses, such as UV-visible spectrophotometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and energy-dispersive spectroscopy. Vinod et al. (2011a) reported that the colloidal NPs with average sizes of Ag (5.5 6 2.5 nm), Au (9.7 6 2.3 nm), and Pt (2.4 6 0.7 nm) stabilized with KG were found to be stable even after 6 months at room temperature, and the reduction was attributed to the various functional groups (
OH,
COO,
C 5 O, and CH3CO
) present in the gum structure (Vinod et al., 2011a). The large number of hydroxyl, carboxylic, carbonyl, and acetyl groups on these gums facilitates the complexation of metal ions. Subsequently, these metal ions oxidize the hydroxyl groups to carbonyl groups, during which the metal ions are reduced to metallic NPs (Vinod et al., 2011a; Padil and Cernik, 2015b; Padil et al., 2015a; Kora et al., 2010; Kora and Arunachalam, 2012; Saravanan et al., 2012; Pooja et al., 2015). Furthermore, gums have three major parameters for the preparation of NPs and follow the cardinal principles of green chemistry as indicated by usage of environmentally benign solvent media (water and ionic, liquid-based green solvents) for the synthesis of NPs. Furthermore, the gums themselves act as reducing agents due to the presence of many functional groups (e.g.,
OH,
COO
,
CO, and CH3CO
) inherent in their structures. To underscore their green credentials even more, the gums are nontoxic, biodegradable materials that contribute to the stabilization of NPs. However, many studies have reported the continued use of toxic organic solvents together with the unceasing employment of toxic, highly reactive, and risky (both environmentally and biologically) reducing agents such as hydrazine, sodium borohydride, and dimethyl formide. The situation is exacerbated by the still persistent usage—for the synthesis of NPs—of capping agents (such as ethylenediaminetetraacetic acid, triethanolamine, and tetraethylammonium bromide), which are known to bioaccumulate in the environment and are

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Table 5.1 summarizes Some of the Literature Pertaining to Metal and MetalOxide Nanoparticles Synthesis Mediated by Various Tree Gum Polysaccharides

Tree Gums

Type of NPs; Composition and Method of Preparation

Gum Arabic (GA)

Ag-NPs; GA (0.5 wt.%); AgNO3 (0.5 wt.%); R.T. synthesis

GA

Ag-NPs; GA (0.5% (w/v)); AgNO3 (0.5%); microwaveassisted synthesis Ag-NPs; GA (1.0 wt.%); AgNO3 (0.1 wt.%); vigorous stirring for 3 h Ag; GA (0.01 wt.%; 2.0 mL); AgNO3 (0.1 wt.%; 0.2 mL) γ-Irradiation route Ag-NPs; 5% GA (5%); PVA (3%) and AgNO3 (1.0 mM); γ radiation-induced crosslinking Au-NPs; GA (1.2%, 8.2 mL); HAuCl (0.002 M; 1.5 mL); Heated at 55 C for 4 h. with continouos stirring Au-NPs; GA (12 mg, 6 mL); HAuCl4.2H2O (0.1 M, 1.0 mL) and 300 mg cumin seed; heated at 45 C for 10 min Au-NPs; Au(III) (0.3 mM);GA (10 mg/mL); Heated at 55 C for 4 h Au-NPs; GA (12 mg, 6 mL); NaAuCl4 (0.1 M, 0.1 mL); phosphor amino acid (0.1 M. 20 μL); continuous stirring Au-NPs; Fe3O4 (1 g); GA (5 mg, 1.0 mL); in situ formation of Au-NPs on the surface of GA-modified Fe3O4 NPs

GA

GA

GA

GA

GA

GA

GA

GA-Fe3O4

Characterizations of NPs

References

B5 nm in size; facecentered cubic structures with crystalline 16.0 6 2 nm; FCC

Mohan et al. (2007)

2
20 nm; spherical shape, single crystalline

Dong et al. (2014b)

3 nm; spherical shape; FCC crystalinity and

Rao et al. (2010)

10
40 nm

Juby et al. (2012)

6.52 6 0.66 nm, spherical in shape

Djajadisastra et al. (2014)

5.5 nm; spherical particles; crystalline

Shalaby et al. (2015)

21.1 6 4.6 nm with FCC structures, spherical shape 15
20 nm, spherical shape

Wu and Chen (2010)

2 nm, spherical

Wu and Chen (2010)

Akele et al. (2015)

Kattumuri et al. (2007)

(Continued)

5.6 “Green” Synthesis of Nanoparticles

Table 5.1 summarizes Some of the Literature Pertaining to Metal and MetalOxide Nanoparticles Synthesis Mediated by Various Tree Gum Polysaccharides Continued

Tree Gums GA

GA

GA

GA

Gum Karaya (GK)

GK

GK GK

GK

Type of NPs; Composition and Method of Preparation Se-NPs; GA (1 mg/mL); 0.6 M selenious acid; and magnetic stirring for 6 h; addition of 4.5 mL of 0.1 M aqueous ascorbic acid solution and then stirred for 0.5 h at R.T. Cu-NPs; GA (0.6 g, 30 mL); CuSO4 (0.3 g, 20 mL); hydrazine hydrate (2.1 mL); constant stirring for 1 h at R. T. Fe3O4-NPs

ZnO-NPs; GA (1 g); sodium acrylate; 10.63 mM; N-N0 methylene bis-acrylamide, 486.47 mM; potassium persulfate; (370.37 μM) and Zn(II), (1 g); in situ hydrothermal synthesis Ag-NPs; GK (1.0 wt.%, 10 mL); AgNO3 (5 3 1023 M, 100 μL); mixtures kept in an orbital shaker and heated for 65 C for 1 h Ag-NPs; autoclaving at a pressure of 15 psi and a temperature of 120 C, for 2 min Ag-NPs; oxidation-reduction reaction Au-NPs; GK (1 wt.%); AgNO3 (5 3 1023 M, 100 μL); mixture kept in an orbital shaker at 75 C for 1 h Au-NPs; GK (15 mg, 1.0 mL); HAuCl4 (10 mM, 100 μL); stirred magnetically for 1 h at 90 C

Characterizations of NPs

References

B34.9 nm, with spherical structures

Kong et al. (2014)

B3
9 nm with spherical particles; crystalline structure

Dong et al. (2014a,b)

B20 nm with nonspherical morphology 40
60 nm; polar strctures

Chockalingam et al. (2010)

12.5 6 2.5 nm, spherical particles, crystalline and stable for 6 months

Padil and Cernik (2015b)

4 6 2 nm, FCC with crystalline structure

Venkatesham et al. (2014)

7
10 nm, spherical

Padil et al. (2015d) Padil and Cernik (2015b)

7.8 6 1.8 nm, spherical, stabile for 6 months

20
25 nm, spherical

Bajpai et al. (2016)

Pooja et al. (2015)

(Continued)

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CHAPTER 5 “Green” polymeric electrospun fibers based on tree-gum

Table 5.1 summarizes Some of the Literature Pertaining to Metal and MetalOxide Nanoparticles Synthesis Mediated by Various Tree Gum Polysaccharides Continued

Tree Gums GK

GK

GK

Kondagogu Gum (KG)

KG

KG

KG

KG

KG

KG

Type of NPs; Composition and Method of Preparation Pt-NPs; GK (1 wt%); Pt (5 3 1023 M, 100 μL); autocaving at 103 kPa for 15 min CuO-NPs; GA (1.0 mg, 1.0 mL); CuCl2.2H2O (1 mM); colloid-thermal synthesis process Fe3O4-NPs; coprecipitation with Fe21 and Fe31 ions with NH4OH solution Ag NPs; KG (100 mg, 10 mL); AgNO3 (100 μL, 10 mM); agitation in an orbital shaker maintained at 45 C for 1 h. Ag NPs; KG (0.5%); AgNO3 (1 mM); autoclaving at 121 C at 15 psi for 1 h Ag NPs; Ag NPs; KG (0.5%); AgNO3 (1 mM); autoclaving at 121 C at 15 psi for 1 h Au NPs; KG (100 mg, 10 mL); HAuCl4 (100 μL, 10 mM); agitation in an orbital shaker maintained at 75 C for 1 h Au-NPs; KG (0.5% (w/v), 3 mL); HAuCl4 (1.0 mM, 1.0 mL); autoclaving at 15 psi, 120 C for 10 min Pd-NPs; KG (0.5%); PdCl2 (1.0 mM); autoclaving at 121 C and 15 psi for 30 min Pt-NPs; GK (100 mg, 10 mL); H2PtCl6 (100 μL, 10 mM); autoclaving at 15 psi for 15 min

Characterizations of NPs

References

5.0 6 1.2 nm, spherical

Padil and Cernik (2015b)

10.5 6 2.4 nm, spherical

Padil and Ï Cerník (2013)

18.5 6 3.5 nm, spherical

Padil and Cernik (2015b)

5.5 6 2.5 nm, spherical, FCC, stable for more than 6 months

Vinod et al. (2011a)

3 nm, spherical, highly stable

Rastogi et al. (2014)

3 nm, spherical, highly stable

Kora et al. (2010)

7.8 6 2.3 nm, spherical, stable for more than 6 months

Vinod et al. (2011a)

12 6 2 nm, nanocrystalline

Reddy et al. (2015)

6.5 6 2.3 nm and crystallized in FCC symmetry 2.4 6 0.7 nm, crystalline, stable for more than 6 months

Rastogi et al. (2017) Vinod et al. (2011a)

(Continued)

5.7 Applications of Gum Fibers: Environmental and Biomedical Fields

Table 5.1 summarizes Some of the Literature Pertaining to Metal and MetalOxide Nanoparticles Synthesis Mediated by Various Tree Gum Polysaccharides Continued

Tree Gums KG

Gum Tragacanth (GT) GT

Gum Ghatti (GG)

GG

Type of NPs; Composition and Method of Preparation Fe3 O4 NPs; KG (25 mg, 50 mL); Fe Cl2 and FeCl3 (Fe21/Fe31 5 2:1 ratio); coprecipitating Fe21 and Fe31 ions using ammonia solution under hydrothermal conditions Ag NPs; GT (0.1 wt.%); AgNO3 (1.0 mM); autoclaving at 15 psi for 30 min ZnO NPs; low-temperature ultrasonic irradiation

Ag NPs; autoclaving the 1 mM silver nitrate solutions containing 0.5% of KG at 121 C and 15 psi for 60 min Pd NPs; GG 0.5% (w/v); PdCl2 (1.0 mM); autoclaving at 121 C and 103 kPa for 30 min

Characterizations of NPs

References

8
15 nm; spherical size

Saravanan et al. (2012)

13.1 6 1.0 nm with spherical nanoparticles

Kora and Arunachalam (2012) Ghayempour et al. (2016)

55
80 nm, high crystalline nature and single phase of synthesized 5.7 6 0.2 nm, spherical nanoparticles

4.8 6 1.6 nm, spherical shape

Kora et al. (2012)

Kora and Rastogi (2015)

R.T, Room temperature.

long-lived pollutants, which may well have ecological and/or human health risks (Grassian, 2008; Varma, 2014; Varma, 2016; Shamim and Sharma, 2013; Raveendran et al., 2003; Sharma et al., 2015). The NPs synthesized and stabilized by natural gum fibers are rendered nontoxic toward cells, thereby qualifying them to be eminently suitable for performing various tasks, for example, the safe delivery of drugs, molecular imaging, and biomedical diagnostics. Both biocompatibility and antibacterial activity are the prerequisites for the use of metal NPs (such as Ag, Au, Cu, CuO, Fe3O4, etc.) as coating materials in biomedical devices and food packaging.

5.7 APPLICATIONS OF GUM FIBERS: ENVIRONMENTAL AND BIOMEDICAL FIELDS The simplicity of the fabrication scheme, the diversity of materials suitable for use with electrospinning—coupled with the unique and interesting features

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CHAPTER 5 “Green” polymeric electrospun fibers based on tree-gum

associated with electrospun NFs—all make these techniques and their resultant structures attractive for various applications such as filtration, pollutant degradation, drug delivery, sensor devices, tissue engineering scaffolds, wound dressing, etc. (Thavasi et al., 2008; Pereao et al., 2016; Ranjbar-Mohammadi et al., 2013; Ranjbar-Mohammadi and Bahrami, 2015; Ranjbar-Mohammadi et al., 2016a,b,c; Sahraei and Ghaem, 2017; Fosso-kankeu et al., 2016; Matsumoto and Tanioka, 2011; Lee et al., 2009). Nanotechnology for water remediation will play an increasingly crucial role in water security and consequently the food security of the world. Nanoscale filtration techniques, the adsorption of pollutants onto NPs, and the breakdown of contaminants by NP catalysts are the major applications of nanotechnology in the cleaning up of contaminated water (Pereao et al., 2016; Fryxell and Cao, 2007; Mishra and Clark, 2013). The twin advantages of electrospun NF membranes are that they can proffer both adsorption and filtration characteristics. Thus, NF membranes offer a viable and attractive means of conducting heavy metal removal. In this context, green electrospun fibers and membranes are emerging as truly innovative materials for a range of environmental bioremediation applications.

5.7.1 NATURAL GUM FIBERS, METAL/METAL-OXIDE NANOPARTICLES, AND THEIR ELECTROSPUN FIBERS FOR THE REMOVAL/ADSORPTION OF ENVIRONMENTAL CONTAMINANTS Biosorption is a process that utilizes inexpensive dead biomass to sequester toxic heavy metals, and it is particularly useful for the removal of contaminants from industrial effluents. Compared to conventional methods (such as precipitation, ion exchange, and electrochemical processes) for the removal of toxic metals from industrial effluents, the biosorption process offers the advantages of low operating costs and the minimization of the volume of chemical and/or biological sludge to be disposed. This process is highly effective in detoxifying very dilute effluents, thereby eliminating the problem of toxicity. It also reduces costs that would have been incurred in nutrient supply and culture maintenance for live microbial-based methods as these would now be unnecessary (Kratochvil and Volesky, 1998; Davis et al., 2003). The use of dead biomass is of particular economic interest because the biomaterials are utilized in the same manner that synthetic adsorbents or ion exchangers are employed (Klimmek et al., 2001). Various metal-binding mechanisms are thought to be involved in the biosorption process and these include ion-exchange, surface adsorption, chemisorption, complexation, and adsorption
complexation (Matheickal et al., 1999). There has been sustained interest in identifying newer biosorbents capable of reducing toxic metal concentrations to environmentally acceptable levels at an affordable cost, based on the philosophy of green chemistry. Heavy metals (Pb, Ni, Cu, Zn, Cr, Ar, Hg, As, and U) are a serious biological problem in aquatic systems. Adsorption and filtration are the commonly used methods for removal of these contaminants from the water. In a recent study,

5.7 Applications of Gum Fibers: Environmental and Biomedical Fields

gums and their functional materials were successfully used for the removal of various toxic heavy metals and radioactive and industrial effluents (Vinod et al., ˇ ´k, 2013; Padil 2009, 2010b,c; Vinod and Sashidhar, 2011; Padil and Cernı et al., 2014; Saravanan et al., 2012; Mittal and Mishra, 2014; Masoumi and Ghaemy, 2014; Sadeghi et al., 2014; Sahraei and Ghaem, 2017; Fosso-Kankeu et al., 2016; Banerjee and Chen, 2007; Sashidhar et al., 2015). FTIR analysis of the gums revealed the presence of various functional groups, that is, carboxyl (R-COO2), hydroxyl (OH2), ether (C-O-C), acetyl (CH3CO-), aliphatic (-CH), amine (-NH2), and carbonyl (C 5 O), which collectively represent the major binding groups responsible for metal biosorption. The experimental results illustrated that chemisorption, ion-exchange, functional group interactions, surface adsorption, physisorption, modified surface properties, and high surface areas were the possible mechanisms for the adsorption of toxic metals onto gum structures. Further adsorption studies were carried out to investigate the effect of metal biosorption on (1) pH, contact time, initial metal-ion concentration, and biosorbent dosage; (2) the application of Langmuir, Freundlich, Tempkin, and Dubinin— Radushkevich isotherm models to biosorption data; (3) kinetics (pseudofirst order and second order) of metal biosorption; (4) morphological changes of gum structures before and after metal biosorption which were evaluated by microscopy techniques (scanning electron microscopy-energy dispersive X-ray analysis (SEMEDXA)); (5) analysis of the functional groups involved in metal biosorption (based on FTIR and XPS analysis); and (6) XRD analysis that was used to investigate the nature of the physical form (amorphous and crystalline) before and after biosorption of metal ions by gums (Vinod et al., 2009, 2010b,c; Vinod and Sashidhar, ˇ ´k, 2013; Padil et al., 2014; Saravanan et al., 2012; Mittal and 2011; Padil and Cernı Mishra, 2014; Masoumi and Ghaemy, 2014; Sahraei and Ghaem, 2017; FossoKankeu et al., 2016; Banerjee and Chen, 2007; Sashidhar et al., 2015). There are potential environmental and health impacts of engineered nanomaterials due to the everincreasing presence of nanomaterials in commercial products. Currently, most sectors of nanotechnology are developing in an unregulated manner and in an environment suited for entrepreneurship. The lack of disposal guidelines for waste products will inevitably lead to potential contamination of water resources and ecosystems (Grassian, 2008). Nanomaterials and NPs are emerging and proliferating contaminants in water and show significant toxicity toward living systems. Studies are still ongoing in these three areas: (1) monitoring of the fate, transport, and transformation of nanoparticles; (2) nanocomposite bioavailability; and (3) exposure of humans and other living species to these potentially toxic materials (Colvin, 2003; Sharma et al., 2015). The electrospinning of polymers comprising various functionalities and the combination of different types of natural and synthetic polymeric materials (together with their potential applications for the removal of toxic heavy metals from water) are two topics that have been comprehensively reported on. (Pereao et al., 2016). Table 5.2 gives a summary of the literature concerned with natural gum fibers, functionalized metal/metal-oxide NPs, and their electrospun fibers for the

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CHAPTER 5 “Green” polymeric electrospun fibers based on tree-gum

Table 5.2 Electrospun Fibers and Matrixed Based on Gum Hydrocollids Used for the Removal/Adsorption of Environmental Contaminants Electrospun Fibers and Matrix Based on Tree Gum Hydrocollids

Type of Contaminants (Toxic Metals, Organic Dyes, Radioactive Materials, and NPs)

GA-Fe3O4

Cu21

GA/PVA electrospun fibers

Ag, Au, and Pt NPs

GT/grapheneoxide composite

Pd21, Cd21, and Ag1

GT/Ag-NPs

Methylene blue (MB) and Congo red (CR) Co21, Zn21, Cd21, and Cr31

GT/ polyamidoxime nanohydrogel

GT/poly(methyl methacrylate)/ Fe3O4-NPs

Cr61

GK

Hg21

GK/poly (acrylamidecoacrylic acid)/ Fe3O4-NPs GK/poly(acrylic acid) (PAA)/SiC NPs

Pb21, Ni21, and Cr61

Malachite green (MG) and rhodamine B (RhB)

Adsorption Capacity (mg/g), Kinetics, Adsorption Models Mechanisms

References

38.5 mg/g; Langmuir isotherm, pseudo-secondorder kineic model and complexation 119 6 0.45 (Ag); 196.4 6 0.69 (Au); 236.5 6 0.98 (Pt) and functional group interactions 142.50 (Pb21), 112.50 (Cd21); 132.12(Ag1), pseudo-first-order kinetic model, Langmuir model and chemical reaction and mass transfer 1.1 g/L; pseudofirst-order and catalytic reduction 100.0 (Co21), 76.92 (Zn21), 71.42 (Cr31), 66.67 (Cd21); Temkin isotherm, pseudo-second-order kinetic model and chelation 7.64 mg/g; Langmuir isotherm, pseudo-secondorder kinetic model and chemisorption 62.5 mg/g; Langmuir model, pseudo-secondorder kinetic model, microprecipitation, and ion-exchange process Charge neutralization, enmeshment, and hydroxylation
precipitation

Banerjee and Chen (2007)

757.57 (MG), 497.51 (RhB); Langmuir model; pseudo-second-order kinetic model and physical adsorption

Mittal et al. (2016)

Padil et al. (2015d)

Sahraei and Ghaem (2017)

Indana et al. (2016) Masoumi and Ghaemy (2014)

Sadeghi et al. (2014)

Vinod et al. (2011b)

FossoKankeu et al. (2016)

(Continued)

5.7 Applications of Gum Fibers: Environmental and Biomedical Fields

Table 5.2 Electrospun Fibers and Matrixed Based on Gum Hydrocollids Used for the Removal/Adsorption of Environmental Contaminants Continued Electrospun Fibers and Matrix Based on Tree Gum Hydrocollids

Type of Contaminants (Toxic Metals, Organic Dyes, Radioactive Materials, and NPs)

GK/poly(acrylic acid-acrylamide)/ SiO2 nanocomposite

Methylene blue

GK/Fe3O4-NPs

32

GK/PVA electrospun fibers (untreated)

Ag, Au, Pt, CuO, and Fe3O4 NPs

GK/PVA nanofibers (NFs) (plasma treated)

Ag, Au, Pt, CuO, and Fe3O4 NPs

Kondagogu Gum (KG)

Pb21, Cd21, Ni21, Cr31, Cr61, Fe21, Co21, Cu21, Zn21, As21 Se21, Hg21

KGnanocomposite

U (VI)

P

Adsorption Capacity (mg/g), Kinetics, Adsorption Models Mechanisms 1408.67 mg/g; pseudosecond-order kinetics; Langmuir monolayer isotherm model, and physical adsorption 15.68 GBq/g; complexation and surface precipitation Ag (25.5 6 0.4); Au (45.8 6 0.8); Pt (51.5 6 0.2); CuO (7.5 6 0.2); and Fe3O4 (5.2 6 0.2) Physisorption, functional group interactions, and complexation 116 (Ag), 261.1 (Au), 289.8 (Pt), 66.3 (CuO), and 49.9 (Fe3O4); Langmuir model and pseudo-second order kinetic Physisorption, functional group interactions, complexation, surface free energy, and high surface area Langmuir isotherm model; pseudo-second-order kinetics Physisorption, microprecipitation and ion exchange processes 487 mg/g; Langmuir isotherm model; pseudosecond-order kinetics precipitation, complexation and ion exchange

References Mittal et al. (2015)

Padil et al. (2014) Padil and Cernik (2015b)

Padil and Cernik (2015b)

Vinod et al. (2009, 2010b, c), Vinod and Sashidhar (2011) Sashidhar et al. (2015)

(Continued)

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CHAPTER 5 “Green” polymeric electrospun fibers based on tree-gum

Table 5.2 Electrospun Fibers and Matrixed Based on Gum Hydrocollids Used for the Removal/Adsorption of Environmental Contaminants Continued Electrospun Fibers and Matrix Based on Tree Gum Hydrocollids

Type of Contaminants (Toxic Metals, Organic Dyes, Radioactive Materials, and NPs)

KG-Fe3O4 nanocomposite

Cd21, Cu21, Pb21, Ni21, Zn21, and Hg 21

KG-Au nanocomposite

32

KG-PVA electrospun NFs (untreated)

Ag, Au, and Pt NPs

KG/PVA electrospun fibers (methane plasma treated)

Ag, Au, and Pt

GG
Pd-NPs

Coomassie brilliant blue G-250, methylene blue, methyl orange, and 4-nitrophenol

GG/poly(acrylic acidcoacrylamide)/ Fe3O4 NPs

Rhodamine B

P

Adsorption Capacity (mg/g), Kinetics, Adsorption Models Mechanisms 106.8 (Cd21), 56.6 (Pb21), 85.9 (Cu21), 49 (Ni21), 37 (Zn21), and 35 (Hg21) Langmuir isotherms model; pseudo-secondorder kinetics Functional groups interaction and physisorption The maximum biosorption (%) capacity of GK-AuNC for radioactive phosphates is 95.5 6 0.55% by using 1.0 g/L and electrostatic repulsion 143.4 (Ag); 173.5 (Au) and 270.4 (Pt); Langmuir isotherms model; pseudosecond order kinetic model and functioal group interaction 168.5 (Ag NP); 320.5 (Au NP); and 327.2 (Pt NP); Langmuir isotherms model; pseudo-secondorder kinetic models High surface properties, surface roughness and additional functional group formation after plasma treatment Coomassie brilliant blue G250 (150 μM), methylene blue (62.5 μM), methyl orange (30 μM), and 4nitrophenol (100 μM) and catalytic reduction 654.87 mg/g; Langmuir isotherm model; pseudosecond-order kinetic and electrostatic attraction

References Saravanan et al. (2012)

Vinod et al. (2011c)

Padil et al. (2015b)

Padil et al. (2015b)

Kora and Rastogi (2015)

Mittal and Mishra (2014)

5.7 Applications of Gum Fibers: Environmental and Biomedical Fields

adsorption/removal of environmental contaminants such as toxic heavy metals, radioactive materials, organic dyes, and NPs from aqueous and industrial effluents. Significant progress has recently been made concerning the use of both gumbased NPs and functionalized electrospun fibers for environmental applications. The GA functionalized Fe3O4 nanocomposites and GA/PVA NF membranes have been employed for the adsorption/removal of Cu21 and NPs (Ag, Au, and Pt) from water (Banerjee and Chen, 2007; Padil et al., 2015d). The GT-based Ag NPs, graphene-oxide composite, polyamidoxime nanohydrogel, and poly(methyl methacrylate)/Fe3O4 NPs have all been exploited for the adsorption/removal of metal ions (Pb21, Cd21, Ag1, Co21, Zn21, Cr31, and Cr61) as well as dyes (methylene blue and congo red) from aqueous solutions (Sahraei and Ghaem, 2017; Indana et al., 2016; Masoumi and Ghaemy, 2014; Sadeghi et al., 2014). GK fibers; GK functionalized NPs (GK/poly(acrylamide-coacrylic acid)/Fe3O4; GK/poly(acrylic acid)/SiC NPs; GK/poly(acrylic acid-acrylamide)/SiO2 NPs; GK/Fe3O4 NPs); and GK/PVA electrospun membranes (both untreated and methane plasma treated) have been demonstrated to be effective adsorbents for the removal of heavy metal ions (Hg21, Pb21, Cr31, Cr61, and Ni21) and NPs (Ag, Au, Pt, Fe3O4, and CuO) as well as for the eradication of organic dyes (malachite green and rhodamine B) and radioactive 32P effluent (Vinod et al., 2011b; Fosso-Kankeu et al., 2016; Mittal et al., 2015, 2016; Padil et al., 2014; Padil and Cernik, 2015b; Padil et al., 2015a,b). The trio of materials, namely KG matrices and KG-based nanocomposites and electrospun fibers, have been utilized for the remediation of heavy metals (Cd21, Cu21, Fe21, Pb21, Hg21, As21, Cr31, Cr61, Ni21, Zn21, Ni21, Se21, and U61); nuclear power station effluents; and radioactive waste generated from 32P-labeled nucleotide production and heavy metals from industrial effluents (Vinod et al., 2009, 2010b,c; Vinod and Sashidhar, 2011; Vinod et al., 2011c; Sashidhar et al., 2015). Additionally, GG-stabilized Pd NPs were studied by probing the reduction of dyes such as Coomassie Brilliant Blue G-250; methylene blue and methyl orange. A nitro compound, 4-nitrophenol, and GG cross-linked with poly (acrylic acid-coacrylamide) reinforced with ironoxide magnetic NPs, has also been utilized for the removal of rhodamine B (Kora and Rastogi, 2015; Mittal and Mishra, 2014). The electrospun membranes of GA, GK, GT, and KG were used effectively for the removal of metal and metal-oxide nanoparticles from water (Padil and Cernik, 2015b; Padil et al., 2015a; Sadeghi et al., 2014). The schematic in Fig. 5.4 illustrates the adsorption/filtration of NPs using plasma-treated electrospun membrane. The NFs were treated with methane plasma to improve their physico-chemical properties, which resulted in high adsorption capacities toward nanoparticles (Ag, Au, Pt, CuO, and Fe3O4) in comparison to an assessment with untreated membranes (Padil and Cernik, 2015b; Padil et al., 2015a; Padil et al., 2016). The adsorption capacities of the membrane for the removal of NPs from water diverge in the following order: Pt . Au . Ag . CuO . Fe3O4 (Padil and Cernik, 2015b;

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CHAPTER 5 “Green” polymeric electrospun fibers based on tree-gum

FIGURE 5.4 Schematic illustrating the adsorption/filtration of nanoparticles using plasma-treated electrospun membrane.

Padil et al., 2015a). There are various adsorption mechanisms pertaining to NP adsorption onto NFs. They include sorption; functional group interactions and complexation reactions between metal/metal-oxide NPs with different functional groups inherent in the NFs. Other adsorption mechanisms relate to modified surface properties (such as the balance of hydrophilicity/hydrophobicity), surface free energy considerations, and the high surface area of plasma-treated membranes (Padil and Cernik, 2015b; Padil et al., 2015a). Adsorption of the NPs on the surface of the plasma-treated NF membranes (PVA-GK) and their corresponding EDX (energy dispersive X-ray) spectra are presented in Fig. 5.5.

5.7.2 NATURAL GUM FUNCTIONALIZED NANOPARTICLES AND NANOFIBERS FOR ANTIBACTERIAL APPLICATIONS Many antimicrobial agents, such as metallic/metal-oxides (Ag, Au, Cu, ZnO, and CuO) and organic agents (quaternary ammonium salts and DDSA) functionalized with natural polymers, for example, chitosan, tree gums (GA, GK, KG, GT, and GG) and cellulose have been used in textiles and membranes for biomedical and

5.7 Applications of Gum Fibers: Environmental and Biomedical Fields

FIGURE 5.5 Scanning electron miscroscopy morphology of plasma-treated nanofibers and energy dispersive X-ray spectra of (A) gum Karaya (GK) interacted Au NP; (B) GK interacted Ag NP; (C) GK interacted Pt NP; (D) GK interacted Fe3O4 NP; and (E) GK interacted CuO NP. Reprinted from Padil, V.V.T., et al., 2015. J. Hazard. Mater. 287, 102
110, with permission from Elsevier.

antibacterial applications (Kora et al., 2010; Kora and Arunachalam, 2012; Kora et al., 2012; Kora and Sashidar, 2014; Kora and Rastogi, 2015; Mittal and Mishra, 2014; Venkatesham et al., 2014; Deshmukh et al., 2012; Kattumuri et al., 2007; Chockalingam et al., 2010; Venkatesham et al., 2014; Padil et al., 2013,

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CHAPTER 5 “Green” polymeric electrospun fibers based on tree-gum

2015b,c,d; Sahraei and Ghaem, 2017; Pooja et al., 2015; Reddy et al., 2015; Ranjbar-Mohammadi et al., 2013; Ranjbar-Mohammadi and Bahrami, 2015; Ranjbar-Mohammadi et al., 2016a,b,c). The usage of gums as mediators for the synthesis and stabilization of metallic/ metal-oxide NPs and their various applications in antibacterial fields is promising. These biogenic NPs have numerous potential advantages over their counterparts, the chemogenic NPs—not least because the latter are produced by utilizing various chemical reductants (e.g., sodium borohydride, citrate or hydrazine) and/or other organic materials with different capping and stabilizing agents (e.g., dodecyl sulfate, cetyltrimethylammonium chloride and poly vinyl pyrrolidone.) Since the chemogenic NPs are cytotoxic and thus not biocompatible, contamination from chemical precursors, toxic solvents, and the creation of hazardous byproducts are all likely to ensue. In stark contrast, biogenic NPs produced by using natural gums pose no such problems. Table 5.3 illustrates the antibacterial activity of metal/metal-oxide NPs synthesized using various gums. The bacterial strains were obtained from the American Type Culture Collection (ATCC) and served as model test strains for Gram-positive and Gram-negative bacteria. The Table 5.3 shows the particle sizes of various NPs used and their concentrations; the antibacterial susceptibilities—well diffusion method [zone of inhibition (ZOI)] and microbroth dilution method [the minimum inhibitory concentration (MIC); the minimum bactericidal concentration (MBC)] of bacterial strains toward NPs actions are also presented. Determination of the zone of inhibition using the well diffusion method is a qualitative measure to assess the antibacterial activity of synthesized NPs. Several of the experiments reported in Table 5.3 and the negative and positive controls (any antibiotic agent, e.g., streptomycin or erythromycin) have been used for testing antibacterial activity of gum-stabilized NPs. Based on the literature (Table 5.3), it can be seen that the synthesized NPs using gum fibers and membranes displayed significant antibacterial action on both Gram classes of bacteria. The promising antibacterial activity and surface functionalization shown enables these NPs to be biocompatible/cytotoxic in various biomedical and pharmaceutical applications. Antibacterial activities of the NPs (particularly for Ag-NPs) have been extensively studied. The use of Ag-NPs in the modification of materials for application in different fields—such as clothing, semiconductors, and the preparation of nanocomposite materials with improved performance—has been demonstrated (Prabhu and Poulose, 2012; Knetsch and Koole, 2011; EI-Rafie et al., 2012). A major problem confronting human health today is that many bacteria are resistant to antibacterial drugs (Hajipour et al., 2012). Biogenic Ag-NPs, which are produced by living organisms or gums, exercise a synergistic effect in conjunction with antibiotics such as erythromycin, chloramphenicol, ampicillin, and kanamycin against Gram-negative and Gram-positive bacteria (Devi and Joshi, 2012). Combination of biogenic Ag-NPs with antibiotics to produce efficient antibacterial activity has been shown (Kora and Sashidhar, 2014; Rastogi et al., 2015),

Table 5.3 Tree Gum Hydrocolloids Fibers and Its Electrospun Functional Membranes for Antibacterial Competences

NPs Composition

Type of Bacteria Tested

PVA-GA/Ag-NP

Gram-negative Escherichia coli

GA-Ag-NPs

Bacillus subtilis (Gram-positve) and Pseudomonas aeruginosa (Gramnegative) E. coli and Staphylococcus aureus

Protonated GADETA (diethylenetriamine) microgels GA/poly(sodium acrylate)/Ag-NPs hydrogel

E. coli

GA/poly (acrylate) hydrogel/ZnO NPs GT/ZnO nanorod

E. coli

GT/nano silver hydro citic acid and sodium hypophosphite hydrogel on cotton fabric

Gram-negative bacteria (E. coli) and Gram-positive bacteria (S. aureus)

E. coli (E. coli, ATCC 25922), S. aureus (S. aureus, ATCC 25923)

NP Size and Concentration 10
40 nm; GA (5%), PVA (3%), and Ag-NO3(1 mM) B35 nm; GA (0.2%) and AgNO3 (4.0 mM) 5
100 μm

20
30 nm; GA (1.0 g); sodium acrylate (10.63 mmol) and 0.117 mmol of AgNO3 40
60 nm; Zn (II) (2%), GA (1.0 g) 55
80 nm; Zn (NO3)2 6H2O (0.1 M), GT (1%) 77.55 nm; GT (0.8%) and AgNO3 (0.335%)

Antibacterial Susceptibility of Bacterial Strains Toward NPs (ZOIa/MICb/MBCc)

References




Juby et al. (2012)

19 mm (B. subtilis) and 11 mm (P. aeruginosa)

Thakur et al. (2013)

5 mg/mL (E. coli) and and 10 mg/ mL (S. aureus)

Farooq et al. (2017)




Bajpai. and Kumari (2015)

32 6 0.07 mm

Bajpai et al. (2016) Ghayempour et al. (2016)

3.3 6 0.1 mm (E. coli), 3.2 6 0.1 mm (S. aureus)

Reduction numbers of colonies against E. coli and S. aureus on various cotton fabrics were tested (98.01% and 99.69% for against E. coli and S. aureus, respectively)

Montazer et al. (2016)

(Continued)

Table 5.3 Tree Gum Hydrocolloids Fibers and Its Electrospun Functional Membranes for Antibacterial Competences Continued

NPs Composition

Type of Bacteria Tested

GT/Ag NPs

GT/PVA electrospun fibers

Gram-negative and Gram-positive bacterial strains with well diffusion method S. aureus (ATCC 25923) and E. coli (ATCC 25922), E. coli (ATCC 35218) and P. aeruginosa (ATCC 27853) S. aureus (ATCC 25923) and P. aeruginosa (ATCC 27853)

GK/Ag NPs

E. coli, Micrococcus luteus

GK/PVA/Ag NPs solution and membranes

Gram-negative E. coli (CCM 3954) and P. aeruginosa (CCM 3955) and Gram-positive S. aureus (CCM 3953)

GK/dodecenyl succinic anhydride (DDSA) composite

Gram-negative E. coli (CCM 3954) and P. aeruginosa (CCM 3955) and Gram-positive S. aureus (CCM 3953)

NP Size and Concentration

Antibacterial Susceptibility of Bacterial Strains Toward NPs (ZOIa/MICb/MBCc)

References

13.1 6 1.0 nm; GT (0.1%) and 1 mM AgNO3 and 5 μg of Ag-NPs

11.5 6 0.0 mm (S. aureus 25923) 9.5 6 0.4 mm (E. coli 25922); 5.5 6 0.0 mm (E. coli 35218); 10.5 6 0.0 mm (P. aeruginosa 27853)

Kora et al. (2012)

40% (GT) and 60% (PVA)

Showed good antimicrobial property against Gram-negative bacteria (P. aeruginosa) 12 mm for both E. coli and M. luteus

RanjbarMohammadi et al. (2013) Venkatesham et al. (2014)

E. coli (8.0 6 0.7 mm for solution and 7.9 6 0.7 for membrane) P. aeruginosa (8.0 6 0.8 mm for both solution and membrane); S. aureus (8.1 6 0.8 mm for solution and 8.0 6 0.8 mm for membrane) Gram-negative E. coli (14.2 6 0.8 mm); P. aeruginosa and Gram-positive S. aureus (15.0 6 0.8 mm), respectively for 10 wt.% concentration of DDSA/ DGK

Padil et al. (2015d)

2
4 nm; (g of AgNO3), (5 mg/mL) and GK (1.0 mg/mL) 7
10 nm; PVA (10 wt.%), GA (1 wt. %) and AgNO3 (1 mM)

DDSA-GK (10%)

Padil et al. (2015d)

GK/CuO-NPs

S. aureus (ATCC 25923) and E. coli (ATCC 25922)

4.8 6 1.6 nm; CuCl2 2H2O (1 mM) and GK (10 mg/mL)

S. aureus (25923) 14.5 6 0.8 nm; E. coli (25922), 16.2 6 0.8 mm

KG/Ag-NPs

The Gram-negative (E. coli (ATCC 25922), E. coli (ATCC 35218), P. aeruginosa (ATCC 27853) and Gram-positive S. aureus (ATCC 25923)

4.5 6 3.1 nm; 0.5% KG (0.5%) and AgNO3 (1 mM)

KG/Ag/NPs

S. aureus (ATCC 25923); S. aureus (ATCC 49834); E. coli (ATCC 25922) and P. aeruginosa (ATCC 27853) S. aureus and E. coli

5.8 6 2.4 nm; GKAgNPs(1 μg/mL)

The minimum inhibitory concentration (MIC) for S. aureus (10 μg/mL); P. aurgenous (5 μg/mL) and E. coli (2.0 μg/mL). The minimum bactericidal concentration (MBC) of silver nanoparticles against test bacterial strains for both S. aureus and P. aurgenous (12 μg/ mL) each and E. coli (2 μg/mL) E. coli (25922) 3.0 μg/mL; P. aeruginosa (27853) 5.0 μg/mL; S. aureus (25923) 5.0 μg/mL; S. aureus (49834) 5.0 μg/mL S. aureus (20 mm) and and E. coli (25 mm) S. aureus (ATCC 25923), 11 mm; E. coli (ATCC 25922), 8.0 mm; E. coli (ATCC 35218), 8.4 mm; and and P. aeruginosa (ATCC 27853), 8.7 mm E. coli (8.0 6 0.1 mm, 6.0 6 0.5 mm); P. aeruginosa (7.0 6 0.1, 4.5 6 0.6); S. aureus (9.0 6 0.1, 7.0 6 0.8) S. aureus, 25923 (12.25 mm); E. coli 25922 (9 mm); E. coli 35218 (8 mm); P. aeruginosa 27853 (11 mm)

KG/gelatin spon ciprofloxacin KG/Ag NPs

DDSA)/deacetylated KG fibers and membranes GG/Ag NPs

a

S. aureus (ATCC 25923); and E. coli (ATCC 25922), E. coli (ATCC 35218) and P. aeruginosa (ATCC 27853) Gram-negative E. coli (CCM 3954) and P. aeruginosa (CCM 3955) and Gram-positive S. aureus (CCM 3953) S. aureus (ATCC 25923); and E. coli (ATCC 25922); E. coli (ATCC 35218), and P. aeruginosa (ATCC 27853)

ZOI, zone of inhibition. MIC, the minimum inhibitory concentration. c MBC, the minimum bactericidal concentration. b

GK (1% w/v) and gelatin (3% w/v) KG (0.5%) and AgNO3 (1.0 mM)

(PVA, 10 wt%) and DDSA/DGK (10 wt %) 5.7 6 0.2 nm 0.1% GG and 1 mM AgNO3 5 μg of silver NPs

Padil and Ï Cerník (2013), Padil et al. (2013) Kora and Sashidhar (2014)

Rastogi et al. (2015)

Rathore et al. (2016) Kora et al. (2010)

Padil et al. (2015b)

Kora and Arunachalam (2012)

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with the aforementioned studies indicating that suitable NPs synthesized using gums can be selected to fight against specific bacteria. These biogenic Ag-NPs synthesized with various gums are highly stable and showed superior antibacterial action on both Gram classes of bacteria, in contrast to chemogenic Ag-NPs. The ZOI values observed with Ag-NPs—synthesized by gums such as GA, GK, KG, GG, and GT, at a concentration of 5 μg of Ag NP—were found to be higher in comparison with the corresponding values for Ag-NPs synthesized by chemical agents (Sadeghi et al., 2014; Thakkar et al., 2010). Furthermore, the Ag-NPs synthesized using KG, GT, and GG were reported to be more potent antibacterial agents in terms of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) (Kora et al., 2010; Kora and Arunachalam, 2012; Kora et al., 2012; Kora and Sashidhar, 2014; Kora and Rastogi, 2015). Recently the synthesis of Ag-NPs by using KG acted as both a reducing and stabilizing agent. The KG reduced/stabilized Ag-NPs were subsequently evaluated for their elevated antibacterial and antibiofilm potencies, in combination with various antibiotics (e.g., ciprofloxacin, streptomycin, and gentamicin) against Grampositive (Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. The data suggested that combination of antibiotics with KG-Ag-NPs resulted in enhanced antibacterial action. In addition, the KG-Ag-NPs were found to be biocompatible, up to a concentration of 2.5 μg/mL, as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay on the HeLa cell line. The findings suggest that GK-Ag-NPs could potentially be used in the form of “in vivo” antibacterial agents—in combination with antibiotics—to overcome the acute problem of antibiotic resistance (Kora and Sashidhar, 2014; Rastogi et al., 2015). The synthesized Ag-NPs had significant antibacterial action on both Gram classes of bacteria. Furthermore, KG stabilized Ag-NPs were employed to determine the mode of antibacterial action via a variety of susceptibility assays such as microbroth dilution, antibiofilm activity, growth kinetics, cytoplasmic content leakage, membrane permeabilization, etc. (Kora and Sashidhar, 2014). The generation of reactive oxygen species (ROS) and cell surface damage during bacterial nanoparticle interaction was also demonstrated using assays including dichlorodihydrofluorescein diacetate and N-acetylcysteine, prior to evaluating the results using SEM and energy dispersive X-ray spectral analysis (Kora and Sashidhar, 2014; Kora and Rastogi, 2015). Antibacterial properties of the DDSA/deacetylated GK (DGK) composite and electrospun membranes of DDSA/deacetyated KG (DKG), and GT/PVA composites have been reported (Padil et al., 2015b,d; Ranjbar-Mohammadi et al., 2013). The improved antimicrobial actions of DDSA/DGK and DDSA/DKG are related to two factors, that is, the balance of hydrophilicity/hydrophobicity and the increased surface roughness of DGK after derivatization with DDSA—the latter helping to increase contact between the surfaces of the material and the bacteria. Concerning nontoxicity, the derivatized natural gums (GK/DDSA, KG/DDSA, and GT/PVA) can be promoted as the leading antibacterial agents that could

5.7 Applications of Gum Fibers: Environmental and Biomedical Fields

FIGURE 5.6 Bacterial activity of plasma-treated nanofiber membrane (P-NFM) and untreated membranes (U-NFM) of DDSA/KG with zone of inhibition—(A) and (D) Gram-negative Pseudomonas aeruginosa; (B) and (E) Gram-positive Staphylococcus aureus; (C) and (F) Escherichia coli. Reprinted from Padil, V.V.T., et al., 2015. Surf. Coat. Technol. 271, 32
38, with permission from Elsevier.

realistically replace CuO-based polymeric materials (along with their toxic Ag ˇ ´k, and Cu constituents) in the crucial battle against microbes (Padil and Cernı 2015a,b; Ranjbar-Mohammadi et al., 2013). Fig. 5.6 shows the antibacterial efficiency test for plasma-treated NF membrane, untreated membranes of DDSA/ DKG, and DDSA/DGK with zone of inhibition against Gram-positive S. aureus, Gram-negative P. aeruginosa, and E. coli, respectively.

5.7.3 BIOSENSORS FOR ENVIRONMENTAL AND MEDICAL APPLICATION A highly sensitive and selective method has been reported for the colorimetric detection of Hg21 in aqueous systems by using label-free Ag-NPs synthesized using KG (Rastogi et al., 2015). The average size of the KG/Ag-NPs was found to be 5.07 6 2.8 nm; the NPs were stable between pH 4
11, and at salt concentrations ranging from 5
100 mM. The KG/Ag-NPs were used directly for the selective colorimetric reaction with Hg21 without any further modification. More importantly, detection of Hg21 in water was observed to be highly selective

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toward Hg21 as the absorption spectra were found to be unaffected by the presence of other ions such as Na, K, Mg, Ca, Cu, Ni, Co, As, Fe, Cd ions, etc. Furthermore, the proposed method was successfully applied to the determination of Hg21 in various groundwater samples. Palladium nanoparticles (Pd-NPs) synthesized by using KG were reported by Rastogi et al., 2017. In this preparation, GK served as both the reducing and stabilizing agent for the synthesis of Pd-NPs. Reaction parameters, such as the concentrations of gum and Pd chloride, as well as reaction pHs were standardized to bring about facile synthesis of GK-reduced/stabilized Pd-NPs. The NPs were characterized using UV-visible spectroscopy, TEM, and X-ray diffraction. Physical characterization revealed that the gum-synthesized Pd-NPs had dimensions of 6.5 6 2.3 nm and crystallized in face centered cubic (FCC) symmetry. The synthesized Pd-NPs were found to be highly stable in nature. Additionally, an intrinsic peroxidase-like activity of synthesized GK-Pd-NPs was utilized for the colorimetric detection of glucose in biological samples. The peroxidase catalytic activity of GK-Pd-NPs was observed to be dependent on pH, temperature, and concentration of GK-Pd-NPs

5.8 BIOMEDICAL APPLICATIONS OF GUM HYDROCOLLOIDSBASED FIBERS AND ELECTROSPUN MEMBRANES The biomedical importance of gum functionalized metal/metal-oxide NPs has been reported in many areas such as drug delivery, diagnosis, imaging, and biosensing. The high-solubility in water, biocompatibility, biodegradability, and the ease of furnishing chemical medications in aqueous media make gums and their electrospun membranes eminently attractive polymers in the synthesis of scaffolds for applications in tissue engineering. The pharmaceutical functionalization of various natural gums, mucilages, and their modified forms for the development of various drug-delivery systems has been extensively reviewed recently (Prajapati et al., 2013; Rana et al., 2011; Mano et al., 2007).

5.8.1 BIOMEDICAL APPLICATION OF GUM ARABIC HYDROCOLLOID Curcumin, also known as turmeric, is conjugated to GA to enhance the solubility and stability of the former. The potential application of this wonder drug depends on its transport to the cytoplasm of Hep G2 and MCF-7 cells, as reported by Sarika et al. (2015). The conjugate self- assembles into spherical nanomicelles (270 6 5 nm) spontaneously, when dispersed in aqueous media. Spherical morphology of the self-assembled conjugate is evidenced by field emission SEM and TEM. The self-assembly of the amphiphilic conjugate into micelles in aqueous media significantly enhances the solubility (900-fold compared to that of free curcumin) and stability of curcumin in physiological pH conditions. The anticancer

5.8 Biomedical Applications of Gum Hydrocolloids-Based Fibers

activity of the conjugate micelles is found to be higher in human hepatocellular carcinoma (Hep G2) cells than in human breast carcinoma (MCF-7) cells. The conjugate exhibits enhanced accumulation and toxicity in Hep G2 cells due to the targeting efficiency of the galactose groups present in GA. The synthesized GACur conjugate showed an impressive a 900-fold greater solubility than that of free curcumin. GA-Cur self-assembles into micelles in aqueous media due to the hydrophilic and hydrophobic interactions between GA and curcumin. MTT assays reveal the higher cytotoxicity of GA-Cur toward Hep G2 cells in comparison to MCF-7 cells, thereby confirming the targeting efficacy of galactose on GA. Cellular uptake studies show that the GA-Cur conjugate can successfully transport the drug to the cytoplasm of Hep G2 and MCF-7 cells. This new conjugate has the capability of overcoming the obstacles previously associated with curcumin and augurs well for its usage in a promising drug-delivery system. Singh et al. (2013) portrayed the synthesis of hydrogels using GA and carbopol. There have been attempts to explore the potential of these materials in designing new hydrogel wound dressings meant for slow release of gentamicin (an antibiotic drug) and to enhance the wound-healing capabilities. The hydrogel films were characterized by SEM, FTIR, XRD, and swelling studies. Biomedical properties of hydrogel films such as blood compatibility; antioxidant activity; mucoadhesion; antimicrobial activity; oxygen/water vapor permeability; microbial penetration; and mechanical properties (tensile strength, burst strength, resilience, relaxation and folding endurance) have been evaluated. Histological studies of wound healing were also carried out on Swiss albino mice of strain Balb C, and it was observed that in case of wounds covered with hydrogel dressings, faster wound healing, coupled with the formation of well-developed fibroblasts and blood capillaries occurred, as compared to open wounds. The biomedical properties indicated that hydrogel films are nonthrombogenic and nonhaemolytic, while being antioxidant and mucoadhesive in nature. In addition, these wound healing hydrogel films are also permeable to oxygen and moisture while being simultaneously impermeable to microorganisms. The hydrogel wound dressings were found to have absorbed a simulated wound fluid to the extent of 8.7 6 0.18 g. of fluid per gram of film. Release of the gentamicin drug from wound dressings took place, courtesy of a Fickian diffusion mechanism, in studies involving a simulated wound fluid. Both blood compatibility and antioxidant activity of the polymeric films contributed toward improved wound healing in the treated mice. The simulated wound fluid uptake and the release of antibiotics in the wound fluid indicate that these hydrogel wound dressings can absorb high volumes of fluid. They are thus suitable for moderate-to-high exuding wounds, given that they could release the antibiotic drugs in a controlled manner. GA hydrogels were synthesized by free-radical polymerization of acrylamide with GA, as reported by Aderibigbe et al. (2015). The effect of GA in the hydrogels on the release mechanism of nitrogen-containing bisphosphonate was studied at pHs 1.2 and 7.4. The hydrogels exhibited high swelling ratios at pH 7.4 and low swelling ratios at pH 1.2. Release mechanism studies were performed using

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UV-visible spectroscopy via complex formation with Fe (III) ions. The hydrogels were ascertained to be pH-sensitive and release profiles of bisphosphonate were observed to be influenced by the degree of cross-linking of the hydrogel network within GA. Furthermore, these hydrogels appear to be promising devices for controlled delivery of bisphosphonate to the gastrointestinal region. The presence of GA in the hydrogels prepared was found to improve its swelling ability. Moreover, GA hydrogels (which are potential drug-delivery systems) were found to exhibit higher swelling ratios than the blank hydrogel.

5.8.2 GUM KARAYA HYDROCOLLOID FOR BIOMEDICAL APPLICATIONS Modification of GK using N,N- methylenebisacrylamide as the cross-linker and ammonium persulfate (as initiator) to develop the hydrogels have been reported (Singh and Sharma, 2008). Polymeric networks were characterized by SEM, FTIR, and swelling studies. The release dynamics of model antiulcer drug (ranitidine hydrochloride) from the hydrogels has been monitored for the evaluation of the release mechanism and diffusion coefficients. The synthesis and characterization of thiolated GK by reacting GK with 80% thioglycolic acid (resulting in esterification and immobilization of thiol groups on the polymeric backbone) was reported by Bahulkara et al. (2015). Thiolated GK was characterized by FTIR, DSC, and XRD and was found to exhibit longer disintegration times as well as greater swelling and mucoadhesion, with an increase in the pH of the medium simulating the gastric and intestinal environment—in stark contrast to unesterified GK. Controlled drug release for more than 24 hours by Fickian diffusion following the Korsmeyer
Peppas model was observed with Metoprolol Succinate as a model drug (as compared to GK on its own). Drug release was observed to have exceeded 90% within 2 hours. Furthermore, synthesized thiolated GK displayed no cytotoxicity, as determined using the Hep G2 cell line. In 2015, Raizaday et al. reported a pH-sensitive microparticle (MP) of GK using distilled water as the solvent by means of spray drying. The pH-sensitive MPs of GK were effectively prepared using the aforementioned spraying technique, employing aqueous solvents and can thus be used for treating various conditions such as chronic hypertension, ulcerative colitis, and diverticulitis. An interpenetrating polymer network (IPN) composed of Zn-pectinate and GK for Gastroretentive Ziprasidone HCl delivery was reported by Bera et al. (2015). The development of IPN beads was accomplished by simultaneous ionotropic gelation and covalent cross-linking. Optimized IPN beads were found to demonstrate excellent mucoadhesion and buoyant properties, with a slower drug release profile. Studies suggested that development of pectinate-based GK hydrogel beads could show enormous potential in drug delivery and tissue engineering applications. Pooja et al. (2015) reported the synthesis of GK stabilized Au-NPs (GK/ Au-NPs) and the application of prepared nanoparticles in the delivery of the

5.8 Biomedical Applications of Gum Hydrocolloids-Based Fibers

anticancer drug, Gemcitabine hydrochloride (GEM). The preparation of GK/AuNPs was optimized for various parameters such as temperature, reaction time, gum concentration, gold concentration, and gold-to-gum solution ratio. GK was used as both reducing and capping agent for the synthesis of gold NPs. GK/AuNPs were characterized for particle shape, size, physical state, and thermal properties. The gum-stabilized NPs were found to be biocompatible during cytotoxic and hemolysis studies. As a drug-delivery carrier, GEM-Au-NP showed better anticancer activity, colony formation inhibition and ROS induction against human lung cancer cells, in comparison with plain GEM. This study supports the finding that GK/Au-NP, given its outstanding biocompatibility and stability, can be used as potential nanocarrier systems for delivery of anticancer drugs.

5.8.3 GUM TRAGACANTH AND ELECTROSPUN FIBERS A magnetic surface molecularly imprinted polymeric nanogel (MIPN) with coreshell morphology for quercetin (QC) as a template (using Fe3O4/SiO2 NPs as a magnetic core with N-vinyl imidazole (VI) as a functional monomer) was reported by Hemmati et al. in 2016. The MIPN displayed high binding affinity, specific binding selectivity and a fast adsorption kinetic rate for the template Q, compared to nonimprinted magnetic polymeric gel. The synthesized MIPN, possessing biocompatibility due to the presence of GT as well as other attributes— that is, easy preparation, fast mass transfer rate, satisfactory adsorption capacity, easy separation, and specific recognition capability toward the template QC— made this method and the MIPN material itself a promising polymeric device for application in the field of rapid drug separation and drug delivery. Electrospun fibers of poly (L-lactic acid)/GT [(PLLA/GT) both 3% (w/v) and in various ratios (100:0, 75:25 and 50:50)] have been fabricated by electrospinning (Ranjbar-Mohammadi et al., 2016a). FTIR analysis, water contact angle determination, in vitro biodegradation and tensile measurements were carried out to evaluate the chemical and mechanical properties of the different scaffolds. PLLA/GT (75:25 ratio) exhibited the most balanced properties compared to other scaffolds and was used for in vitro culture of nerve cells (PC-12) to assess the potential of using these scaffolds as a substrate for nerve regeneration. The authors showed that aligned PLLA/GT (75:25 ratios) NFs are promising substrates for application as bioengineered grafts in nerve tissue regeneration. GT and PVA were dissolved in deionized water in different weight ratios (i.e., 0/100, 30/70, 60/40, 50/50, 40/60, 70/30, and 0/100 mass ratios of GT/PVA) and NFs were subsequently produced using electrospinning techniques (RanjbarMohammadi et al., 2013). The effect of different electrospinning parameters (such as extrusion rate of polymer solutions, solution concentration, electrode spacing distance, and applied voltage) on the morphology of NFs was examined. Ratios of GT/PVA were varied and NFs with the best morphology were produced at 40/60 GT/PVA ratios. Hydrogen bonding between PVA and GT was confirmed by FTIR analysis. Human fibroblast cells were found to have adhered and

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proliferated well onto the GT/PVA NF scaffolds. MTT assays confirmed that GT/PVA NFs showed cell viability and biological compatibility. The biocompatibility and antibacterial properties of these NFs indicated that they are effective as wound dressing because they can protect the affected area from its surroundings, to avoid infection and dehydration. This in turn would speed up the healing process by providing an optimal microenvironment for healing, in addition to removing any excess wound exudates and permitting continuous tissue reconstruction. The wound healing potency of GT and PCL has produced nanofibrous patches for either skin tissue engineering or wound dressing applications (RanjbarMohammadi. and Bahrami, 2015). PCL/GT scaffolds containing different concentrations of PCL with various blend ratios of GT/PCL were produced created using 90% acetic acid as solvent. Of all the PCL/GT (3:1.5 ratios) combinations examined, the one with a PCL concentration of 20% (w/v) generated NFs with good morphology, as revealed by SEM analysis. The surface wettability, functional group distribution, porosity and tensile properties of NFs were evaluated. PCL/ GT NFs were used for the in vitro cell culture of human fibroblast cell lines AGO and NIH 3T3 fibroblast cells. MTT assays and SEM results showed that biocomposite PCL/GT mats enhanced fibroblast adhesion and proliferation to a greater extent than the PCL scaffolds. A drug-delivery device was fabricated via “blend and coaxial” electrospinning utilizing PLGA, GT, and tetracycline hydrochloride (TCH) as a hydrophilic model drug (in different combinations) and their performances as a drug carrier scaffold were evaluated (Ranjbar-Mohammadi et al., 2016a). SEM results indicated that fabricated PLGA, blended PLGA/GT and core-shell PLGA/GT NFs possessed smooth and beadless morphologies with the diameters ranging from 180 to 460 nm. Drug-release studies showed that both the fraction of GT within blended NFs and the core-shell structures can effectively control the TCH release rate from the nanofibrous membranes. By incorporation of TCH into core-shell NFs, drug release was sustained for 75 days with only 19% of burst release within the first 2 hours. This prolonged drug release, together with proven biocompatibility as well as the antibacterial and mechanical properties of the drug-loaded coreshell NFs, make them a promising candidate for use as drug-delivery systems in combating periodontal diseases. Electrospun curcumin (Cur)-loaded PCL/GT NFs for aiding wound healing in diabetic rats have been reported (Ranjbar-Mohammadi et al., 2016b). These scaffolds with antibacterial properties against both methicillin resistant Staphylococcus aureus (as gram-positive bacteria) and extended spectrum β lactamase (as gram-negative bacteria) were applied in two forms, that is, acellular and cell-seeded
for assessing their capabilities in healing full thickness wounds on the dorsum of rats. The pathological study revealed that the application of GT/PCL/Cur NFs caused markedly fast wound closure with well-formed granulation tissue—dominated by fibroblast proliferation, collagen deposition, complete early regeneration of the epithelial layer, and formation of sweat glands and hair follicles.

5.8 Biomedical Applications of Gum Hydrocolloids-Based Fibers

Ciprofloxacin loaded GT-based hydrogels for use in drug delivery to improve the pharmacotherapy of diverticulitis was reported by Singh and Sharma (2017). The polymers were characterized by SEM, FTIR, 13C NMR, XRD, TGA, DSC, gel strength, and swelling studies. The polymer network parameters, mucoadhesion, gel strength, drug-release mechanisms, and kinetic models were also evaluated. Drug release occurred via a nonFickian diffusion mechanism that was best fitted using the Korsmeyer
Peppas model. The pH of the swelling medium also exerted a strong effect on polymer network structure and its mechanical strength. These hydrogels with pH-responsive and mucoadhesive properties could be invaluable in spot specific drug delivery. GT and poly (acrylic acid)-based polymer hydrogels for drug-delivery systems relating to the antibiotic drug, amoxicillin, have been reported by Singh and Sharma (2014). The correlations between synthetic reaction parameters and structural criteria have been determined. A variety of models for studying release kinetics were applied to monitor the release profile of drugs from polymeric networks. The characterization of polymers was carried out by use of the following techniques: SEM, EDAX, FTIR, 13C NMR, XRD, TGA, and swelling studies.

5.8.4 GUM KONDAGOGU FOR BIOMEDICAL APPLICATIONS Naidu et al. (2009b) reported the preparation of polyelectrolyte complexes (PEC) of KG and chitosan by mixing polymeric solutions of different concentrations (0.02%
0.18% w/v). The complexes formed were loaded with diclofenac sodium and the release of the drug measured both in vitro and in vivo, along with the determination of particle size, zeta potential, complex formation, flow properties and loading efficiency. The maximum yield of PEC was observed at KG concentrations above 80% with the PEC showing a lower release of diclofenac sodium in 0.1 N HCl—as compared to the drug release in phosphate buffer (pH 6.8). The complex formation between KG and chitosan is via electrostatic interactions between the carboxyl group of KG and the amine group of chitosan. The stoichiometric ratio for effective complex formation was found to be in the range 4:1%
5:1% (w/w of KG/chitosan). The diclofenac-loaded polyelectrolyte complex of KG/chitosan was shown to change the drug release rate, in response to changes in pH. Drug release was higher at pH 6.8 (compared to pH 1.2) due to greater swelling of the complex at higher pH. The observations made in the investigation conclusively show that the KG/chitosan complex has great potential as a natural polymer-based delivery device in the controlled delivery of drugs such as diclofenac sodium. It has the added advantage of reducing the dosing frequency, thereby lowering gastric toxicity. Microwave-assisted grafting of KG onto poly(acrylamide) was carried out and subsequently employed in the in vitro release of diclofenac sodium from the matrix tablets of KG-poly(acrylamide) (Malik and Ahuja, 2011). The study revealed faster release of the drug from the graft copolymer matrix tablets, as compared to the ungrafted KG. Hence microwave-assisted graft copolymerization

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can be used as an efficient tool to modify the release properties of KG by grafting acrylamide onto the gum. Carboxymethylation of KG was carried out by Kumar and Ahuja (2012). The carboxymethylation of KG was found to reduce its viscosity and improve both its mucoadhesive properties and ionic gelling behavior. This study showed that carboxymethylation of KG provided the means of preparing mucoadhesive, sustained-release bead formulations of metformin (a drug used to treat people with type 2 diabetes) releasing the drug by zero-order kinetics. Fabrication of sponges by blending KG with gelatin (G) and impregnating with ciprofloxacin for the application of antibacterial and wound dressing has been reported (Rathore et al., 2016). The fabricated sponge was characterized in terms of swelling percentage and porosity together with SEM data. The results confirmed the porous nature of the sponge. The in vitro biocompatibility, cell adhesion, and proliferation tests were carried out using NIH 3T3 fibroblast and Human keratinocyte cell lines, and results indicated that the sponge is highly biocompatible.

5.9 CONCLUSIONS AND PROSPECTS To date, the development of economically viable NP synthesis and electrospinning processes using tree-based carbohydrate polymers to produce biogenic NPs and NFs in “green” pathways have been explored. The current advances in “green” synthesis and electrospinning technology provide important evidence and justification of the potential roles that these NPs and electrospun membranes can play in water purification, antibacterial environmental remediation, and biomedical applications (Padil et al., 2018). The use of tree-based polymers in various applications is relatively low (compared to synthetic polymers) due mainly to incompatibility of the chosen natural polymer for particular applications and in some cases due to poor chemical and mechanical properties. Nevertheless, further developments are imperative to discover new functionalized hybrid polymer systems, based on natural and synthetic polymers that are suitable for electrospinning with improved functionalities for various applications. In view of current studies and trends, there is no doubt that electrospun NFs based on natural hydrocolloids are expected to play a significantly vital role in many important applicational areas including water purification, renewable energy, biomedical research, the food industry, biotechnology and lastly but most importantly, to provide a major, long overdue boost for environmental protection.

ACKNOWLEDGMENTS The research reported in this paper was financially supported by the Ministry of Education, Youth and Sports, in the framework of the targeted support of the “National Programme for Sustainability I” LO 1201 and the OPR&DI project “Extension of CxI facilities”

References

(CZ.1.05/2.1.00/19.0386). The authors would also like to acknowledge the assistance provided by the Research Infrastructure NanoEnviCz, supported by the Ministry of Education, Youth and Sports of the Czech Republic in the framework of Project No. LM2015073. This work was also supported by the Ministry of Education, Youth and Sports of the Czech Republic and the European Union
European Structural and Investment Funds in the frames of Operational Program Research, Development and Education
Project Hybrid Materials for Hierarchical Structures (HyHi, Reg. No. CZ.02.1.01/0.0/0.0/16_019/ 0000843).

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