Accepted Manuscript Title: Comprehensive review on electrospinning of starch polymer for biomedical applications Authors: T. Hemamalini, V.R. Giri Dev PII: DOI: Reference:

S0141-8130(17)31749-X http://dx.doi.org/doi:10.1016/j.ijbiomac.2017.08.079 BIOMAC 8071

To appear in:

International Journal of Biological Macromolecules

Received date: Revised date: Accepted date:

16-5-2017 10-8-2017 11-8-2017

Please cite this article as: T.Hemamalini, V.R.Giri Dev, Comprehensive review on electrospinning of starch polymer for biomedical applications, International Journal of Biological Macromoleculeshttp://dx.doi.org/10.1016/j.ijbiomac.2017.08.079 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Comprehensive review on electrospinning of starch polymer for biomedical applications T. Hemamalini and V.R. Giri Dev Department of Textile Technology, Anna University, Chennai – 600025.

Abstract Starch is an emerging polymer in biomedical research area due to its ease of availability, lowcost and biological values. Starch polymer has been used as powder and film in applications such as tissue engineering and hemostatic application. Starch in fibrous form is very difficult to produce due to the branched amylopectin structure. With the advent of electrospinning fibrous form of starch is attempted by various researchers. The present paper reports comprehensive review of attempts made on electrospinning of starch and its potential applications in biomedical and tissue engineering. Keywords: Biomedical, Biopolymers, Electrospinning, Starch.

1.

Introduction Nowadays, polymers are widely used in various applications such as automotive,

aerospace, medical, construction, consumer goods and packing due to its low density, high strength to weight ratio, relatively low cost, biodegradability, ease of manufacturing etc. Generally, polymers are classified into two broad categories such as natural and synthetic polymers. Among these two types, natural polymers and their derivatives are widely used in biomedical applications due to its biodegradability, biocompatibility, nontoxicity, non inflammatory and ease of availability [1]. As natural polymers are generally biodegradable, they can be broken down into biologically acceptable molecules either by enzyme, hydrolytic or combination of degradation technique that can be metabolized and removed from the body via normal metabolic pathways [2]. It is classified into three types based on their origin as plants, animals and microbes as shown in Fig.1. Plant based polymers includes polysaccharides such as cellulose, starch, alginate, pectin, carrageen gums whereas animal based polymers are further classified into two types such as proteins (gelatin, albumin) and polysaccharides (chitin, chitosan)[3]. Polyester (polyhydroxyalkanaotes) and hyaluronate polysaccharide are the

examples of microbes based natural polymer. Natural polymer is further classified into four categories based on the structure such as polysaccharides (cellulose, alginate, dextran, chitosan and pullulan), polypeptides and proteins (gelatin, albumin, lectin and legumin), polynucleotide (DNA, RNA), and polyester (polyhydroxyalkanaotes, polylactic acid and polymalic acid). Among all the natural polymers, polysaccharides finds its application in various fields, extending from food to medicinal areas due to its unique properties and availability as shown in Fig. 2 [4]. Polysaccharides as the name imply is a combination of homopolymers or copolymers of monosaccharide [5]. It is a long-chain polymer composed of glucose units linked together by glycosidic bonds either in linear or branched configuration. The polysaccharides are mostly used in biomedical application due to its functionality and biological activity. It can be attributed to their different chemical structure, chemical composition, molecular weight and ionic nature [6 – 7]. In the present review, some of the natural polysaccharides and their properties are outlined with an emphasis on starch polymer. Chitin is an abundant natural polymer obtained from crustacean exoskeletons (crabs, shrimps) or generated via a fungal fermentation process. It is composed of (1, 4) linked N-acetyl β-D-glucosamine groups. Chitosan is the deacetylated form of chitin, with deacetylation up to 50 %. It is a biosynthetic polysaccharide composed of (1, 4) linked β-D-glucosamine groups. Due to its polyelectrolyte nature, it is widely used in medical application to various forms such as gels, powders, films and fibers. Chitosan offers excellent cell binding capacity, promotes wound healing, also has antibacterial and antifungal activities [4, 6, 8]. Alginate is naturally-occurring renewable polysaccharide composed of two monomer such as mannuronic and guluronic acid. It is obtained from the seaweed as a long chain of alginic acid and its salts. Though the natural alginate is biocompatible, it is not degradable in physiological condition hence it is dissolved in divalent ions such as calcium and is widely used in wound dressing, scaffolds and hemostat [4, 6, 8-9]. Cellulose is the first abundant polysaccharide available in nature and is made of (1, 4) linked β-D-glucose units [8]. One of the serious limitations of cellulose is that the processability is difficult due to minimal solubility in organic solvent and inability to melt due to strong

hydrogen bonds. Next to cellulose, starch plays a significant role in biomedical application due to its low-cost and ease of availability .The starch in fibrous form is still a challenge among global research fraternity, and this paper reports the work carried out on preparation of starch in fibrous form.

2.

Starch Among all the polysaccharides, starch is the second abundant compound available in the

green plants next to cellulose. It is semicrystalline in nature, and the structure of the starch is composed of glucose units linked by glycosidic bonds [10]. Starch is deposited and stored in the stem of plants, tuberous tissues, seeds and also in algae. It consists of two types of molecules namely amylose and amylopectin. Amylose is lightly branched polymer comprising of α (1, 4) glucopyranose with degree of polymerization of 6000 and molecular mass ranging from 105 to 107 g/mol. Amylopectin is highly branched polymer consisting of α (1, 4) glucopyranose linked by α (1, 6) bonds and degree of polymerization about 2 million. The molecular mass of amylopectin ranges from 107 to 109 g/mol [11]. Amylose is amorphous in nature while amylopectin is crystalline. The chain length between branched groups varies from 20 to 25 glucose units. About 70 % of starch is amorphous and rest in crystalline. Depending on the source of starch it contains 20 to 25 % amylose and 75 to 80 % amylopectin by weight [12]. Based on the botanical origin and genetic background, composition of amylose and amylopectin varies. In addition to amylose and amylopectin, composition of the starch includes lipids, proteins, ashes and phosphates. Lipids such as phospholipids tend to form a helical complex with amylose, resulting in reduced water binding capacity, swelling and stability of starch molecule. Protein in the starch plays a critical role in formation of clear and transparent solution. Phosphate in the starch in the form of monophosphate causes improved stability of solution and also leads to slow retrogradation rate.

2.1

Gelatinization and retrogradation The structure of a starch molecule consists of amylose and amylopectin. The disruption of

granular structure of starch causes the granule to swell, hydrate and solubilise and is called as gelatinization process. It is also defined as the process of breaking down the intermolecular

bonds of starch molecule in the presence of solvent and heat, allowing the hydrogen bonding sites to engage with the solvent. On heating the starch with water or any other solvent, individual starch granules absorb the liquid and results in swelling. This causes liquid to thicken and results in increase in viscosity of the solution [13]. The gelatinization temperature is defined as temperature at which maximum swelling of starch granules takes place. Waxy starch is fully composed of amylopectin molecule, and higher energy is required for gelatinization due to its high crystallinty. Retrogradation is the process of reassociation and recrystallisation of the polysaccharide chains after the gelatinization of starch. Retrogradation rate of amylose is higher than amylopectin due to linear and long chain, which tends to align and crystallize faster [14].

3.

Electrospinning of starch The starch for biomedical applications is available in various forms as shown in Fig 3.

However, the challenges lie in achieving starch polymer in fibrous form. Achieving starch in fibrous form is difficult due to its low strength, water resistibility, thermal instability and poor processability. With the advent of electrospinning, getting polymers in fibrous form is easy. Electrospun webs are widely used due to its higher surface area to volume ratio, high porosity, small pore size, superior mechanical properties and higher flexibility. The process is a versatile which can be used to produce fibers with varying diameter from micrometers to nanometers [15] and is advantageous over other nanofibres production technique such as template synthesis, phase separation, drawing, self assembly. The details of electrospinning are discussed in detail elsewhere [16-18].

3.1

Electrospinning of pure starch fibers Kong and Zeigler developed pure starch microfibers web by modifying the conventional

electrospinning technique with coagulation bath (electro wet spinning), in order to replace the synthetic petroleum products. The idea behind this work was to electrospin pure starch fibers without inclusion of other biopolymers. The spinning dope solution was prepared by heating Gelose 80 (amylose content – 80%) in 95 % Dimethyl Sulfoxide (DMSO) until the gelatinization of starch took place. Ethanol was chosen as solvent for the coagulation bath since it is miscible with DMSO but not with starch. The reason to modify the electrospinning technique with

coagulation bath was to obtain solid fibers as evaporation of DMSO was difficult due to its non volatility. Highly amorphous electrospun web was achieved when pure ethanol was used in coagulation bath. Increasing the water proportion in ethanol coagulation bath led to increase in crystallinity of starch web to 43%. The average diameter of electrospun starch fibers was 2.60µm.The developed electrospun web was heat treated to improve crystallinity and stability of the mat against water was improved by crosslinking with glutaraldehyde. The paper only highlights the production of starch and its use in field of medical applications is yet to be explored [19]. Cardenas et al. produced microfibers from potato starch using the electro wet spinning technique mentioned above. It was reported that the treatment of starch in DMSO does not alter chemical nature of native starch [20]. Kong and Zeigler have summarized the spinnability of starch by using different spinning techniques [21]. The same group of researchers further investigated the electrospinnability of starch along with inclusion of bioactive agents such as palmitic acid (PA), ascorbyl palmitate (AP) and cetyl trimethyl ammonium bromide (CTAB) [22]. The agents were included into mat by dope mixing and bath mixing. The dope mixing involves the addition of heat stable agent such as PA during the solution preparation. The heat labile agent such as AP was added to cool gelatinized solution. Since PA and AP showed poor solubility in ethanol, CTAB was dissolved in coagulation bath containing ethanol on which gelatinized starch was electrospun. It was also reported that 100% ethanol resulted in the fast collapse of starch and 75% w/w of ethanol gave fibers of uniform morphology. They also studied the effect of entanglement concentration in electrospinning of starch fibers which is critical in electrospinning. Generally, the polymer concentration must be at least 2-2.5 times more than the entanglement concentration for electrospinning of fibers. To validate it, starches with different amylose content were chosen to study the role of molecular entanglements for the fiber formation. Gelose 80(80% amylose), Hylon VII (70% amylose), Hylon V (50% amylose), Mung Bean (35% amylose), Melojel (25% amylose) and Amioca starches (1% amylose) were used to study ability of fiber formation by electrospinning technique. At concentration beyond 10% (w/v), shear thinning took place resulting in the fiber formation. It was also reported that amylose plays an essential role in fiber formation and starch with high amylose content resulted in uniform fiber formation due to extended coils of amylose.

At low amylose content fibers, were not formed because of low entanglement concentration and moreover amylopectin acts as hard ellipsoid due to its branched structure [23]. Quantitative relationship between fiber diameter and spinning parameters were analyzed by Kong and Zeigler by varying four parameters such as starch concentration, voltage, feed rate and spinning distance. The parameters were varied, and regression equations were developed. It is reported that spinning parameters has significant influence on the diameters of the fibers produced. Surface tension and viscosity also have an influence on the fiber morphology [24]. Wang et al. developed electrospun starch nanofibres containing Hylon VII (70% amylose) using DMSO as solvent. The starch polymer was heated at 70 ̊ C in DMSO and electrospun. The developed web was crosslinked using vapor phase glutaraldehyde. The developed web had excellent water stability than native starch since the number of hydroxyl groups was reduced by crosslinking mechanism. The tensile property of the nanofibres web was found 10 times higher than native starch. The cytotoxic studies reveal that the developed web is nontoxic. At the same time, the crosslinked web showed higher contact angle of 81 ̊, indicating the developed web is hydrophobic [25]. Divers et al. studied the effect of formic acid and formic acid/water mixture in destruction and hydrolysis of starch. It was reported that increase in reaction time in formic acid resulted in decrease in molecular weight due to random scission of chains during the hydrolysis reaction. It was reported that dilution of formic acid resulted in increase in gelatinization time as water cannot hydrolyze the starch polymer chain [26]. Starch undergoes esterification reaction in the presence of formic acid, by generating formate group at C6 position of glucose units present in the starch. Starch can even undergo gelatinization at room temperature with salt solutions such as sodium chloride, calcium chloride, potassium cyanide etc. It was also reported that starch can be dissolved in ionic liquids such as N-Methyl Morpholine and proved that it undergoes gelatinization at room temperature [27]. Anica et al. studied the electrospinnability of starch in formic acid. Hylon VII (17 % w/v) starch which contains 70% of amylose was dissolved in different dilutions of formic acid with water. It was reported that increasing water content increases the gelatinization time. In presence of formic acid, starch undergoes dissolution by leaching of amylose from amylopectin structure

resulted in swelling of molecule. It was claimed that uniform bead free fibers were formed when 100 % and 90 % w/v formic acid was used as solvent. The mechanical stability was higher for starch electrospun web with pure formic acid. The o-formylation in starch provides scope for blending of starch with other biopolymers [28]. Anica et al. developed starch formate compound fibers as encapsulating material for drug release application which is to be used in biotherapeutics field. Coaxial spinning is a recent advancement in electrospinning technique which consists of inner and outer orifice, allowing to electrospin two different materials into composite nanofibres. This technique is also called as core and sheath technique as the core and sheath nanofibres were made from two distinct polymers [29]. This technique is used in drug delivery applications since the drug can be loaded into core fiber, which can be encapsulated by sheath fibers. This technique was used to form starch formate as sheath fibers and glycerol at the core which acts as cryo-protectant. Glycerol has miscibility with starch/formic acid solution but the structure of electrospun web showed a distinct interface between the liquid core and solid sheath though glycerol tends to disrupt the hydrogen bonds between the polymer chains. It was reported that core sheath interface facilitate the proper encapsulation of Newtonian fluid like glycerol. Encapsulation efficiency of lactobacillus paracasei bacteria was also studied in the developed electrospun web. It was reported that survival rate of the bacteria increased in encapsulated state rather in free form [30]. Centrifugal spinning is another technique to produce nanofibres, developed based on cotton candy machine. Unlike electrospinning, centrifugal spinning does not use electrostatic force instead uses the centrifugal force to form nanofibres. Due to high speed action of centrifugal force, polymer solution ejects from the nozzle and forms nanofibres [31]. The advantage of this technique is that porous and well aligned structures can be formed with utmost ease. Li et al. attempted to produce microfibers by centrifugal spinning technique from various starch such as amylose rich starch, amylopectin rich starch, potato starch and waxy starch. The solution was prepared by dissolving different starch in sodium hydroxide solution, followed by centrifugal spinning by application of hot air, to facilitate the evaporation of solvent. It was reported that amylose , amylopectin rich and potato starch formed micro fibers with average diameter of 1.4µm whereas waxy starch were not capable of forming fibers due to amylopectin. The presence of amylopectin resulted in bead formation [32].

3.2

Electrospinning of modified starch Due to lack of electrospinnability of starch, starch can be modified and electrospun into

nanofibres. Starch can be modified into starch acetate by grafting it in presence of acetic acid or acetic anhydride either with or without catalyst such as perchloric acid or sulfuric acid. Starch acetate is reported to have superior mechanical properties than starch. The electrospun mat had porous architecture making it suitable for drug release application. Xu and Yang et al. prepared an electrospun web from starch acetate by dissolving it in formic acid and studied the electrospinnability. Starch acetate was prepared by dissolving starch in acetic anhydride in mini reactor followed by addition of aqueous sodium hydroxide solution. The reaction was terminated by addition of cold water. Then the resulted starch acetate was dissolved in formic acid and then electrospun. The drug was loaded on the starch acetate with degree of substitution of 1.1 and 2.3 and the drug release efficiency was studied. It was reported that drug release was slow in starch acetate with degree of substitution 2.3 due to hydrophobicity and high affinity between drug and starch acetate fibers [33]. Silva et al. suggested that starch can be electrospun by modification of starch into hydroxypropyl starch since native starch lack the desired physical properties and is also difficult to electrospin. It was blended with polyethylene oxide (PEO) in different ratios by dissolving in boiling water. It was reported that uniform nanofibres were obtained with hydroxypropyl starch with concentration of 80 % wt. Since selected polymers are less water resistant, it was coated with polymethyl methaacrylate. The degradation of the developed web created porous structure at the same time integrity of the mat was maintained. Fibroblast was loaded on the developed web to study the cytotoxic effect, it was claimed that hydroxypropyl starch/PEO nanofibres was non cytotoxic and promoted cell growth and adhesion. The developed web with porous architecture in fibers makes it suitable for tissue engineering applications [34]. Oktay et al. attempted to produce nanofibres by inducing thermal modification between soluble starch and poly (ethylene-alt-maleic anhydride) (PE-Alt-Ma) composite nanofibres. 2.5% Starch and 10 % PE-Alt-Ma solution were prepared in water and DMSO respectively. Different blend ratios of both solutions were heated to obtain esterified starch and then resulted solution was electrospun. The fibers in the web were highly porous and insoluble in water due to thermally induced esterfication reaction. Electrospun mat from the web have higher thermal

stability than pure starch. The reaction scheme between starch and PE-Alt-Ma is shown in Fig 4. Due to its porous architecture and insolubility in water, applications ranging from tissue engineering to filtration application were suggested by the authors [35]. Oblea et al. attempted to produce nanofilaments by electrospinning technique with modified corn starch. Native corn starch was modified using sodium succinate, which resulted in the formation of succinated starch since electrospinning of native starch was impossible. The modified starch resulted in the decrease in viscosity of the solution from 644 cP to 26 cP. The electrospinning solution was prepared by dissolving succinated starch, glycerol and tween 20 detergent in water. It was reported that addition of glycerol and tween 20 increased the dielectric constant of the solution resulting in uniform fibers. The produced electrospun web was hydrophobic in nature compared to native starch [36].

3.3.

Electrospinning with other biopolymers Blending with synthetic polymers was carried out to enhance the properties of starch

molecules. Mostly synthetic polymers such as polycaprolactone, polyvinyl alcohol, poly lactic acid and poly lactide-co-glycolide were used for blending followed by electrospinning. The polymers were blended with starch to provide structural integrity and hydrophilicity to the mat.

3.3.1 Electrospinning of starch with Polycaprolactone Gomes et al. developed scaffold material containing starch and polycaprolactone by melt spinning technique. PCL and starch were blended in weight ratio (70:30) and heated to a high temperature of 150 ̊ C. The resulted solution was extruded through extruder into the cold water bath. Then, solid fibers were collected with an average diameter of 180 µm with porous architecture. The scaffold material was prepared by fiber bonding technique, which involves cutting and sintering the melt spun fibers into required specification. Further, the scaffold material was annealed at - 15 ̊ C and sterilized using ethylene oxide. The degradation activities of Starch PCL melt spun (SPCL) were studied using phosphate buffer solution, lipase, α- amylase and their combination, 100% weight loss was observed in phosphate buffer solution and lipase combination, but slower degradation was seen in α- amylase and lipase combination. The work ensured that the degradation of the fibrous mat was influenced by an enzyme present in the body.

The mechanical properties of the web were studied and the results suggest they are suitable for cell growth and adhesion [37]. Another technique to produce starch based fibers from SPCL scaffolding material is modified wet spinning process. Unlike melt spinning, this method does not degrade the material and avoids processing of material at high temperature, which in turn avoids the monomer formation during extrusion process. The solution was prepared by dissolving melt spun SPCL in chloroform and extruded it through the extruder into coagulation bath. Considering the advantages of this spinning technique, Tuzlakoglu et al. reported that wet spun fibrous mesh structure produced by this method can be used for tissue engineering applications. In order to improve the osteoblast cell growth on SPCL fibrous mesh, it was plasma treated in argon atmosphere which resulted in surface modification suitable for cell growth. The growth of osteoblasts was studied on both untreated and treated wet spun fibrous mesh. It was clearly seen that cell viability in plasma treated web was higher due to functionalization of the surface [38]. Rapid prototyping is another technique to produce starch based scaffold material for tissue engineering applications. This is an emerging polymer processing technique due to its flexibility, versatility and reproducibility in creating scaffolds. The advantage to this technique is that it uses computer aided design to produce customized shapes and structures. Martins et al. attempted to produce hierarchical starch based fibrous scaffold by combined rapid prototyping and electrospinning of SPCL and PCL respectively. The micro portion of the scaffold material was made by prototyping technique which involves heating SPCL in a heated cartridge at 140 ̊ C. The hierarchical structure was made by electrospinning of PCL solution on the micro SPCL scaffolding web. The presence of micro and nanofibres mimics the extra cellular matrix present in human body and also provides good mechanical stability for cell growth. The osteoblast cells seeded on the composite web resulted in homogenous growth of cells and there was no significant difference on the growth of cells depending on the architecture of the scaffold material. The integration of micro and nanofibres has led to reduced porosity at the same time gas, nutrient and waste transport through the structure was not hindered which is essential for an ideal scaffold material [39]. Tuzlakoglu et al. produced nano and micro fiber combined scaffold material for bone tissue engineering. The solution for preparing scaffold was prepared by dissolving SPCL in

chloroform and dimethyl formamide in the ratio of 7:3 for the electrospinning process. The solution was electrospun on both sides of melt spun SPCL scaffolding material simulating extracellular matrix. The cell growth on the developed web was studied using osteoblast cells, stretched cell growth was seen due to presence of nanofibres. The growth of cells on the developed web was better [40]. Jukola et al. attempted to produce nanofibers from SPCL melt spun scaffolds material. SPCL was dissolved either in acetic acid or chloroform at various concentration and fiber spinnability was studied. The SEM morphology showed that starch particle was interconnected by PCL nanofibres. When acetic acid was used as solvent, more beads were formed in the fibers with an average diameter of 130 nm and particle size of 10 mm whereas in chloroform solvent system, diameter of the particle size was about 180 nm and average diameter of fibers was about 180 nm [41]. Komur et al. produced starch PCL composite nanofibres by co-axial spinning with starch in sheath and PCL in core. The spinning solution was prepared by dissolving starch in DMSO followed by gelatinization and PCL was dissolved in dimethyl formamide which was then loaded in two different syringe and electrospun. It was seen that an increase in starch concentration resulted in increase in viscosity and conductivity of the solution. The analysis of surface morphology of the developed composite fibers showed that starch polymer formed beads whereas PCL formed uniform nanofibres. The fiber diameter was found to increase with increase in starch concentration [42]. The developed PCL starch nanofibres were biocompatible and biodegradable.

3.3.2. Electrospinning of starch with Polylactic acid Electrospinning was carried out between two immiscible liquids by conjugate solvent technique an idea reported by Jackapon et al. Polylactic acid (PLA) was dissolved in dichloromethane (DCM) and cassava starch was dissolved in dimethylsulfoxide (DMSO). These two solutions did not mix completely even on vigorous mixing anfd resulted in phase separation.

Hence, solvent (methanol) with intermediate polarity index was used to bridge these polymers. It was reported that the volume of starch solution should be 2.25 greater than times volume of PLA solution. This was carried out to avoid the precipitation of starch due to the excess amount of methanol. The developed web contains uniform and bead free fibers [43]. It was also attempted to produce starch- PLA composite nanofibers by the same group of researchers with assistance of acetonitrile to blend the two immiscible solutions. Separate solutions were prepared by dissolving PLA and starch in DCM and DMSO respectively. These solutions were blended by adding acetonitrile to make solid content up to 18.27 %. Then, the solutions were electrospun. Fibers with an average diameter in the range of 2000 nm were formed. It was found that contact angle of the web increased with an increase in collection time and surface roughness of electrospun mat [44].

3.3.3. Electrospinning of starch with poly lactide -co-glycolide Poly lactide co- glycolide (PLGA) is a semicrystalline polymer produced from two monomers such as L-lactide and glycolide in the ratio of 80:20. The disadvantage of PLGA is that it is highly hydrophobic and less bioactive. This is overcome by blending with other natural biopolymers. Zhang et al. focused on producing modified biopolymer scaffold for tissue engineering applications by coaxial electrospinning technique. The solution preparation involves dissolving PLGA in tetrahydrofuran and dimethyl formamide in the ratio of 3:1 and the starch is gelatinized at 140 ̊ C in DMSO. PLGA and starch solution was independently fed through two needles with starch as sheath and PLGA as core respectively. The study revealed that the degradation rate of starch/PLGA was faster than PLGA nanofibres in phosphate buffer solution due to hydrophilic nature of starch. The contact angle of starch/PLGA and PLGA was 96 ̊ and 130 ̊ was achieved and it is claimed that the mat is hydrophilic in nature [45].

3.3.4. Electrospinning of starch with Polyvinyl alcohol Sukyte et al. attempted to produce PVA/Starch nanofibres by electrospinning technique by overcoming the disadvantages of PVA such as low degradation and moisture barrier properties. The solution was prepared by dissolving 7 wt % polyvinyl alcohol with different concentration of potato starch such as 0, 1, 3, 5 wt % based on weight of final solution. Further,

ethanol was added to the solution to improve the conductivity and to study its effect on nanofiber formation. Electrospinning was carried out with pure PVA solution in which addition of ethanol had no significant influence on the diameter of PVA fibers. The maximum concentration of starch used to form nanofibres along with PVA is limited to 3%. On increasing the starch concentration to 5 % weight, the viscosity of the solution increased and it was not suitable for electrospinning. On addition of ethanol to the solution, significant increase in the diameter of nanofibres was observed. Addition of ethanol also decreases the voltage required for electrospinning due to high conductivity. However, on further increase in the ethanol content, increased number of spots on electrospun fibrous material was observed [46]. Nanofibres were produced from the blend of polyvinyl alcohol and oxidized starch by electrospinning technique for the first time by Wang et al. In this literature, corn starch was modified using an oxidizing agent. The electrospinnability of the blend solution by varying the concentration of oxidized starch at the constant concentration of PVA was studied. It was clearly seen that polyelectrolyte nature of oxidized starch influences the fiber formability since it carries cationic charge on its surface. When the charge density of the solution was high, higher electric field was required to form uniform fibers by overcoming the charge at the surface of the jet. Solution concentration played a critical role in deciding the fiber morphology. Uniform fibers were found to form at 19 % wt of final solution with average diameter of 410 nm. It was reported that upon increasing the oxidized starch concentration in the final solution, conductivity of the electrospinning solution increased which resulted in formation of thin fibers. On addition of starch to PVA solution, there was a shift from the melting temperature of PVA from 220 ̊ C to 154 ̊ C [47]. Electrospinning of cationic starch along with PVA has been studied by using two types of electrodes such as tines electrodes and rotational cylinder electrode by Sukyte et al. Cationic starch and PVA solution was prepared in water, further the solution was diluted with ethanol and the effect of ethanol on fiber formation was studied. The surface tension of the solution was not varied on addition of cationic starch to the solution. It is stated that electrode with tines showed dense fiber collection than the rotating cylinder collector. Addition of ethanol to the solution drastically reduced the voltage required to form nanofibres from 65kV to 30kV due to its higher

dielectric constant. It was confirmed from the SEM images that increasing the ethanol content resulted in an increase in diameter of fibers [48]. Bubble electrospinning is a recent development in electrospinning technique to produce nanofibres. The advantage of bubble electrospinning is that it encourages multiple jet initiations unlike conventional electrospinning and suitable method for spinning aqeous solutions [49]. Liu and He attempted to produce PVA and soluble starch blended nanofibres using this technique. Different proportions of soluble starch and PVA were prepared in water and used for bubble electrospinning. It was claimed that uniform fibers were obtained with increase in PVA concentration [50]. Tang et al. fabricated starch based composite nanofiber along with ampicillin and with polymers such as PVA and PEO. It is reported that it is very difficult to produce pristine starch fibers using starch with high amylopectin content. On blending, uniform and bead free fibers are obtained [51]. Prashanthini and Kalyani attempted to produce hybrid nanofibres from polyvinyl alcohol, rice husk and starch for bone tissue engineering [52]. The polymers were dissolved in distilled water and electrospun. It resulted in bead free uniform fibers with porous fiber architecture. The developed composite nanofibres was loaded with osteoblastic cells and studied for cell viability. It was found that there was no negative impact on cell growth and the presence of rice husk which was rich in silica plays an essential role in bone growth along with starch and polyvinyl alcohol. The usage of electrospun starch is not only limited with biomedical application but is also getting extended to other applications. Blending of starch along with other polymers such as Gaur gum to encapsulate active food ingredients [53], PVA and graphene to improve conductivity [54], polyacrylonitrile for sensors application [55], polyvinyl alcohol for filtration [56] and polyvinyl alcohol, polylactic acid and cellulose nanocrystals for barrier properties [57] is being pursued actively by the researcher fraternity.

4.

Conclusions

Starch polymer is one of the promising polysaccharide finding wide range of biomedical applications. Starch polymer is at present commercially available in the form of powder, hydrogel, film and sponges. Starch in the form of fibres is of great interest for the researchers working in this domain. The purpose of the review is to provide comprehensive report on the production of starch in fibrous form. It is pertinent to note from the research that production of pristine starch fibres is possible only from highly amylose rich starch source. The modification of starch has not been quite successful for production of fibrous starch. Blending of starch with other biopolymers have been successful to certain extent but achieving uniform bead free fibres in the web is yet to be realized. The identification of suitable solvent combination for blending starch with other polymer needs to be worked upon to achieve uniform bead free fibres with good handleability. The review provides an overall gist of the work carried out on production of fibrous starch and the major lacuna lies in finding suitable solvent combination for blending. The application of fibrous starch in various biomedical applications will further open up plethora of challenges which needs to addressed by the research community.

Acknowledgements We have not received any financial support from any funding sources for this work.

Reference [1]

H. A. Pawar, S. R. Kamat, P. R. Choudhary, An overview of natural polysaccharides as biological macromolecules: their chemical modifications and pharmaceutical application, Biol. Med. 7 (2015) 1-9.

[2]

L. S. Nair, C. T. Laurencin, Biodegradable polymers as biomaterials, Prog. Polym. Sci. 32 (2007) 762–798.

[3]

Ololade Olatunji, Classification of Polymers, in: Ololade Olatunji (Eds.), Natural Polymers: Industrial techniques and application, Springer International Publishing, Switzerland, 2016 pp. 1- 17.

[4]

M. E. Gomes, R. L. Reis, Biodegradable polymers and composites in biomedical applications: from catgut to tissue engineering part 1 available systems and their properties, Int. Mater. Review 49(2004) 261-273.

[5]

V. R. Sinha, R. Kumria, Polysaccharides in colon specific drug delivery, Int. J. Pharm. 224 (2001) 19-38.

[6]

Y. Le, S. C. Anand, A. R .Horrocks, Recent development in fibres and materials for wound management, Indian J. Fibre Text. Res. 22(1997) 337-347.

[7]

R. C. Thomson, M. C. Wake, M. Yaszemki, A. G. Mikos, Biodegradable polymer scaffolds for regenerate organs, Adv. Polym. Sci. 122 (1995), 245 – 274.

[8]

K. Y. Lee, L. Jeong, Y. O. Kang, S. J. Lee, W. H. Park, Electrospinning of polysaccharides for regenerative medicine, Adv. Drug Deliv. Rev. 61(2009) 1020-1032.

[9]

Y. Qin, Alginate fibres: an overview of production processes and application in wound management, Polym. Int. 57(2008) 171-180.

[10]

F. R. Torres, S. Commeaux, O. P. Troncoso, Starch based biomaterials for wound dressing applications, Starch 65 (2013) 543-551.

[11]

D. R. Lu, C. M. Xiao, S. J. Xu, Starch based biodegradable polymer materials, Exp. Polym. Lett. 3(2009) 366-375.

[12]

Chung-wai Chiu, Daniel Solarek, Modification of starches in: James BeMiller, Roy Whistler (Eds.) Starch: Chemistry and Technology, Academic Press, USA, 629 – 655.

[13]

J. Jane, Starch properties, modification and applications, J. Macromol. Sci. A 32 (1995) 751 – 757.

[14]

Marie-Astrid Ottenhof , Imad A. Farhat, Starch Retrogradation, Biotechnol. Genet. Eng. Rev. 21 (2004) 215- 228.

[15]

Z. M. Huang, Y. Z. Zhang, M. Kotaki, S. Ramakrishna, A review on polymer nanofibers by electrospinning and their applications in nanocomposite, Compos. Sci. Technol. 63(2003) 2223- 2253.

[16]

D. Liang, B. S. Hsiao, B. Chu, Functional electrospun nanofibrous scaffolds for biomedical application, Adv. Drug Deliv. Rev. 59 (2007) 1392–1412.

[17]

S. Agarwal, J.H. Wendorff, A. Greiner, Use of electrospinning technique for biomedical applications, Polymer 49 (2008) 5603–5621.

[18]

T. J. Sill, H. A. Von Recum, Electrospinning: Applications in drug delivery and tissue engineering, Biomaterials 29 (2008) 1989- 2006.

[19]

L. Kong, G. R. Zeigler, Fabrication of pure starch fibers by electrospinning, Food Hydrocolloid 36(2013) 20-25.

[20]

W. Cardenas, E. Y. Gomes Pachon, E. Munoz, R.Vera Graziano, Preparation of potato starch microfibers obtained by electro wet spinning, Mater. Sci. Eng. 138 (2016).

[21]

L. Kong, G. R. Zeigler, Formation of starch-guest inclusion complexes in electrospun starch fibers, Food Hydrocolloid 38 (2014) 211-219.

[22]

L. Kong, G. R. Zeigler, Patents on fiber spinning from starches, Recent Patent on Food, Nutrition & Agriculture 4(2012) 210 – 219.

[23]

L. Kong, G. R. Zeigler, Role of molecular entanglements in starch fiber formation by electrospinning, Biomacromolecules 13(2012) 2247-2253.

[24]

L. Kong, G. R. Zeigler, Quantitative relationship between electrospinning parameters and starch fiber diameter, Carbohydr. Polym. 92(2013) 1416-1422.

[25]

W. Wang, X. Jin, Y. Zhu, C. Zhu, J.Yang, H. Wang, Effect of vapor phase glutaraldehyde crosslinking on electrospun starch fibers, Carbohydr. Polym. 140 (2016) 356-361.

[26]

T. Divers, I. Pillin, J. F. Feller, G. Levesque, Y. Grohens, Starch modification, destruction and hydrolysis during o-formylation, Starch 56 (2004) 389- 398.

[27]

Nagamani Koganti, John R. Mitchell, Roger N. Ibbett and Tim J. Foster, Solvent Effects in Starch Dissolution and Gelantinization, Biomacromolecules 12 (2011) 2888-2893.

[28]

Anica Lancuski, Gleb Vasilyev, Jean Luc Putaux, Eyal Zussman, Rheological properties and electrospinnability of high amylose starch n formic acid, Biomacromolecules 16 (2015) 2529-2536.

[29]

Phillip McClellan, William J. Landis, Recent applications of coaxial and emulsion electrospinning methods in the field of tissue engineering, BioRes. Open Access 5(2016) 212-227.

[30]

Anica Lancuski, Aiman Abu Ammar, Ron Avrahami, Rita Vilensky, Gleb Vasilyev, Design of starch-formate compound fibers as encapsulation platform for biotherapeutics, Carbohydr. Polym. 158 (2017) 68–76.

[31]

L. Amalorpava Mary, T. Senthilram, S. Suganya, L. Nagarajan, J. Venugopal, S. Ramakrishna, V. R. Giri Dev, Centrifugal spun ultrafine fibrous web as a potential drug delivery vehicle, Exp. Polym. Lett. 3 (2013) 238-248.

[32]

Xianglong Li, Huanhuan Chen, Bin Yang, Centrifugally spun starch-based fibers from amylopectin rich starches, Carbohydr. Polym. 137 (2016) 459-465.

[33]

Weijie Xu, Wen Yang, Yiqi Yang, Electrospun starch acetate nanaofibers: development, properties and potential application in drug delivery, Biotechnol Prog. 25 (2009) 1788 – 1795.

[34]

I. Silva, M. Gurruchaga, I. Goni, M. Feranandez Gutierrez, B. Vazquez, J. San Roman, Scaffolds based on hydroxypropyl starch: Processing, morphology, characterization, and biological behavior, J. Appl. Polym. Sci. 127 (2013) 1475 – 1484.

[35]

B. Oktay, E. Basturk, N. Kayaman Apohan, M. Vezir Kahraman, Highly Porous starch/ Poly (ethylene-alt-maleic anhyride) composite nanofiber mesh, Polym. Compos. 34 (2013) 1321- 1324.

[36]

J. G. L. Oblea, E. M. Sanchez, M. G. Martinaze, Corn starch nanofilaments obtained by electrospinning, Rev. Mex. Ing. Quim. 14 (2015) 497 – 502.

[37]

M. E. Gomes , H. S. Azevado , A. R. Moreira,V. Ella , M. Kellomaki, R. L. Reis, Starch-polycaprolactone and starch- polylactic acid fibre mesh scaffolds for one tissue engineering applications: structure, mechanical properties and degradation behaviour, J. Tissue Eng. Regen. Med. 2 (2008) 243-252.

[38]

K. Tuzlakoglu , I. Pashkuleva , M. T. Rodrigues ,M. E. Gomes, G.H. Van Lethe , R. Muller, R. L. Reis, A new route to produce starch based fiber mesh scaffolds by wet spinning and subsequent surface modification as a way to improve cell attachment and proliferation, J. Biomed. Mater. Res. Part A 10 (2009) 369-377.

[39]

A. Martins, S. Chung, A. J. Pedro, R. A. Sousa, A. P. Marques, R. L. Reis, N. M. Neves, Hierarchical starch based fibrous scaffold for bone tissue engineering applications, J. Tissue Eng. Regen. Med. 3 (2009) 37 – 42.

[40]

K. Tuzlakoglu, N. Bolgen , J. Salgado , M. E. Gomes, E. Piskin, R. L. Reis, Nano and micro fiber combined scaffolds: a new architecture for bone tissue engineering, J. Mater. Sci. 16 (2005) 1099-1104.

[41]

H. Jukola , L. Nikkola, M. E. Gomes, R. L. Reis, N. Ashammakhi, Electrospun starch polycaprolactone nanofiber based constructs for tissue engineering , Eur. Cells Mater. 67 (2008) 971-974.

[42]

B. Komur , F. Bayrak , N. Ekren , M. S. Eroglu, F. N. Oktar, Z. A. Sinirlioglu, S. Yucel, O. Guler, O.Gunduz, Starch/PCL composite nanofibers by co-axial

electrospinning technique for biomedical applications, Biomed. Eng. 16 (2017) 113. [43]

Jackapon Sunthornvarabhas, Pathama Chatakononda, Kuakoon Piyachomkwan, Klanarong Sriroth, Electrospun Polylactic Acid and Cassava Starch Fiber by Conjugated Solvent Technique, Mater. Lett. 65 (2011) 985- 987.

[44]

Jackapon Sunthornvarabhas, Pathama Chatakononda, Kuakoon Piyachomkwan, Klanarong Sriroth, Electrospun starch composite nanofibers: fabrication and characterization, Starch Update 2011: The 6th International Conference on Starch Technology (2011)281 – 286.

[45]

H. B. Zhang, M. Zhu, R. Q. You, Modified biopolymer scaffolds by co-axial electrospinning, Advanced Materials Research 160-162 (2011) 1062-1066.

[46]

Sukyte J. Adomaviciute and R. Milasius , Investigation of the possibility of forming nanofibres with potato starch, Fibres Text. East. Eur. 18(2010) 24-27.

[47]

H. Wang, H. Wang, S. Jiang, S. Jiang , L. Zhai, Q. Jiang, Polyvinyl alcohol/ oxidised starch via electrospinning technique: fabrication and characterisation , Iran. Polym. J. 20 (2011) 551-558.

[48]

J. Sukyte, E. Adomaviciute, R. Milasius, J. Bendoraitiene, P. P. Danilovas, Formation of poly (vinyl alcohol)/cationic starch blend nanofibres via the electrospinning technique: the influence of different factors, Fibres Text. East. Eur. 20 (2012) 16-20.

[49]

Yong Liu, Ji-Huan He, Jian Yong Yu, Bubble-Electrospinning: A Novel Method for Making Nanofibres, J. Phys.: Confer. Ser. 96 (2008) 1-4.

[50]

Zhi Liu, Ji Huan He, Polyvinyl alcohol/starch composite nanofibres by bubble electrospinning, Int. J. Therm. Sci. 18 (2014) 1473-1475.

[51]

S. Tang, Z. Zhao, G. Chen, Y. Su, L. Lu, B. Li, D. Liang, R. Jin, Fabrication of ampicillin/starch/polymer composite nanofibers with controlled drug release properties by electrospinning, J. Sol-Gel Sci. Technol. 77 (2016) 594–603.

[52]

L. K. Prashanthini, D. Kalyani , Preparation of scaffold using rice husk and starch for bone regeneration, Inter. J. Res. Appl. Sci. Eng. Technol. 3 (2015) 598- 603.

[53]

W. Yang , A. M. M. Sousa, X. Li , P. M. Tomasula , L. Liu, Electrospinning of Guar Gum/Corn Starch Blends, SOJ Mater. Sci. Eng. 4(1) 1-7.

[54]

Jobin Jose, Mamdouh A. Al-Harthi, Mariam Al-Ali AlMa Adeed, Jolly Bhadra Dakua, Sadhan K. De, Effect of graphene loading on thermomechanical properties of poly(vinyl alcohol)/starch blend, J. Appl. Polym. Sci. (2015) 1-5.

[55]

A. N. R. da Silva, M. L. P. da Silva, R. N. R. Diasb, L. Sayuri and E. R. Fachini, PAN/starch composite nanofibers as a selective membrane for sensors and microTAS, J. Phys. Confer. Ser. 421 (2012) 16- 19.

[56]

S. Woranuch, A. Pangon, K. Puagsuntia, N. Subjalearndee , V. Intasanta, Rice flour-based nanostructures via a water-based system: transformation from powder to electrospun nanofibers under hydrogen-bonding induced viscosity, crystallinity and improved mechanical property, RSC Adv. 7 (2017) 19960–19966.

[57]

Carol Lopez de Dicastillo, Karina Roa , Luan Garrido , Alejandro Pereira, Maria Jose Galotto, Novel polyvinyl alcohol/starch electrospun fibers as a strategy to disperse cellulose nanocrystals into poly(lactic acid), Polymers 9 (2017) 1 -16.

Fig.1. Classification of polysaccharides

Fig.2. Properties and applications of polysaccharides

Fig. 3. Forms of starch for biomedical applications

Fig.4. Esterification reaction between starch and PE-Alt-Ma