Electrospinning of Chitin and Chitosan Nanofibres
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Trends Biomater. Artif. Organs, VolElectrospinning 22(3), pp 179-201 of(2009) Chitin and Chitosan Nanofibres http://www.sbaoi.org175 Electrospinning of Chitin and Chitosan Nanofibres C. K. S. Pillai and Chandra P. Sharma* Division of Biosurface Technology, Biomedical Technology Wing, Sree Chitra Thirunal Institute for Medical Sciences & Technology, Poojappura, Thiruvananthapuram 695 012 INDIA * Corresponding author [email protected] Received 5 February 2009; Accepted 25 February 2009; published online 17 March 2009 The electrospinning technique is a versatile method to spin polymers into continuous fibers with diameters ranging from a few micrometers to a few nanometers. Electrospinning creates seemingly endless ultra fine fibers that collect in a random pattern. These nanofibers can form non-woven textile mats, oriented fibrous bundles and even three-dimensional structured scaffolds, all with large surface areas and high porosity. It is, thus, the most extensively used fabrication method that offers vast opportunities for control of the morphology of the electrospun fibers. Due to their intrinsic features, polymeric nanofibers are attractive for biomedical and biotechnological applications such as tissue engineering, nanocomposites for dental application, controlled drug delivery, medical implants, wound dressings, biosensors and filtration. The applications of chitin and chitosan (CS) nanofibers in these areas are reviewed in this paper. Because of the inherent biodegradability, biofunctionality and biocompatibility of the biopolymer, electrospun chitin and CS fibers have special advantages whereby properties such as cytocompatibility, tissue responses etc. could be controlled in critical applications. © Society for Biomaterials and Artificial Organs (India), 20090205-21. Introduction Electrospinning of nanofibers based on natural polymers have recently emerged as having Chitin and CS are polysaccharides having enormous possibilities for better utilization of excellent biocompatibility and admirable bio-based materials [17]. This paper focuses biodegradability with versatile biological its attention to discuss this highly promising activities such as antimicrobial activity, low area on electrospinning of nanofibers from immunogenicity and low toxicity [1-5]. Coupled chitin and CS. Chitin and CS fibers are unique with the possibility of preparing a variety of as they carry an acetamido/amino functionality chemically or enzymatically modified products that impart many biological properties. CS fiber and processes, these biopolymers having the is unlike other fibers is unique: it carries a rare amino functionality and two hydroxyl groups positive ionic charge, it has remarkable affinity for chemical modifications are potential to proteins, it can be functionalized and it is materials in a variety of applications in renewable [9,18-22]. biomedical, biotechnological and pharmaceutical areas [6-8]. Despite its huge Although chitin fibers could be made into textile annual production and easy availability, chitin materials [23, 24], its application as sutures is still remains an under utilized resource primarily remarkable because it can accelerate wound because of its intractable molecular structure. healing. [3,6,8,15,23,25-28, 28a]. CS-poly(L- Chitin and CS fibers have attracted much glutamic acid) and CS-polyacrylic acid fiber are attention due to their highly promising finding potential industrial applications due to applications in textile materials, sutures and as their enhanced tensile strength and scaffold materials for tissue engineering [9-16]. environmental biodegradability [29]. One study 180 C.K.S. Pillai and C.P. Sharma reports that chitin fibres have comparable properties to those of collagen and lactide fibres [30]. Rathke and Hudson [11] pointed out that chitin’s microfibrillar structure indicated its potential as fiber- and film-former, but as chitin was found to be insoluble in common organic solvents, the N-deacetylated derivative of chitin, CS, was developed. The polymeric linear chain structure of chitin is expected to give rise to fibre formation and film forming ability similar to those of cellulose [11]. Thus, the presence of the micro fibrils of chitin with diameters from 2.5 to 2.8 nm which are usually embedded in a protein matrix indicates that chitin can be spun into fibres [31, 32]. The polyamide-type structure should be broken up to enable solubilisation of chitin into a solvent [33]. This requires either melting or dissolution in appropriate solvents. Melt spinning is ruled out as chitin decomposes prior to melting. There have been many attempts at dissolution of chitin and spinning of chitin and CS into fibre form. Variuos methods have been developed to produce chitin and CS fibres whose properties and applications are covered in a number of reviews [9-12]. The electrospinning technique is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers [34-36, 36a]. Considering the potential applications of chitin and CS fibres, it appears that a consolidation of the data relating to the electrospinning technology and its applications in chitin and CS polymers seems to be worthwhile. The electrospinning process The electrospinning method of producing non- woven nanofibrous mats [37] is attractive due mainly to its cost effectiveness, reproducibility Figure 1: Electro spinning apparaturs: (a) The schematic setup for manufac-turing and simplicity. It is a process by which polymer nonwovens by electrospinning 1 - high voltage nanofibers can be produced using an source, 2 - polymer container, 3 - tip of metal electrostatically driven jet of polymer solution tube, 4 - droplet of polymer solution in the (or polymer melt). The method produces fibers conical shape known as Taylor cone, 5 - 103 times larger specific surface to volume rectilinear part of jet, 6 - electrically-driven ratios, increased flexibility in surface bending instability of the jet (insta-bility region), functionalities, improved mechanical 7 - collector a-lower electrode (grounded); b) performances, and smaller pores than fibers photograph of the main parts of the apparatus, produced using traditional methods. One front view; c) photograph of the electrically- reason for the upsurge in nanofibers fabrication driven bending instability of the jet. research in the 1990s, was due to new found (Reproduced from reference [40] with permission from Text. Fibres Eastern Eur. interest in producing polymeric nanofibers Poland) Electrospinning of Chitin and Chitosan Nanofibres 181 under laboratory conditions. These nanofibers to support electrospinning. Nevertheless, form non-woven textile mats, oriented fibrous several research groups have succeeded in the bundles and even three-dimensional structured preparation of CS based composite fibers by scaffolds, all with large surface areas and high blending it with other polymers such as porosity [38]. Applying a strong electric potential polyethylene oxide (PEO) [43-47,47a], or on a polymer solution or melt produces polyvinyl alcohol (PVA) [48-53]. Fabrication and nanoscale fibers. Polymer solutions of characterization of poly (vinyl alcohol)/ CS blend sufficient viscosity are metered through a nanofibers produced by electrospinning method capillary and placed under high electric potential [54] in acetic, acrylic, or other acids [55]. In this in the range of 10–30 kV. The large potential case, the excellent fiber forming properties of causes a droplet of solution to accelerate the co-spinning agent are utilized. CS has also towards a grounded or oppositely charged been successfully blended with other natural collector. The solvent gets evaporated quickly biopolymers such as collagen that are more from the polymer ‘jet’, reducing the jet diameter easily electrospun [56,57] and increasing the charge density on the surface. The dry polymer fibers are deposited Application of electrospinning [58] to CS fibres on the collector on the grounded target. The and was first applied by Ohkawa et al.[59]. They necessary components of an electrospinning prepared homogenous non-woven fabrics of apparatus include a high power voltage supply, nano-scaled fibers successfully with the -4 a capillary tube with a needle or pipette, and a samples of Mw 158 and 180× 10 having the collector that is usually composed of a average fiber diameters of 83, and 60 nm conducting material [35, 39]. Electrospinning is respectively [60]. influenced by a variety of process parameters such as the operating voltage, the tip-to-target Westbroek and group have shown that distance, the temperature, the pressure, and parameters such as type of solvent, pH, the flow rate [39a, 39b]. Of these parameters, concentration of CS viscosity, charge density, the applied voltage is the most important one applied voltage, solution flow rate, distance from since it determines the degree of electrostatic nozzle tip to collector surface and time play a interaction forces that induce the expulsion of a role in the characteristics of the obtained polymer jet [39]. The schematic setup for nanofibrous structures [61]. They provide a electrospinning is given in Fig. 1 [40]. description of the setup for electrospinning and the method of production of fibres in detail. At Electrospinning creates seemingly endless longer production time, nano fibres spun from ultra fine fibers that collect in a random pattern. a 3% CS in 90% acetic acid solution split