Chitin and chitosan: Transformations due to the electrospinning process

Electrospinning of Chitosan for Antibacterial Applications—Current Trends

Chitosan is a natural biopolymer that can be suitable for a wide range of applications due to its biocompatibility, rigid structure, and biodegradability. Moreover, it has been proven to have an antibacterial effect against several bacteria strains by incorporating the advantages of the electrospinning technique, with which tailored nanofibrous scaffolds can be produced. A literature search is conducted in this review regarding the antibacterial effectiveness of chitosan-based nanofibers in the filtration, biomedicine, and food protection industries. The results are promising in terms of research into sustainable materials. This review focuses on the electrospinning of chitosan for antibacterial applications and shows current trends in this field. In addition, various aspects such as the parameters affecting the antibacterial properties of chitosan are presented, and the application areas of electrospun chitosan nanofibers in the fields of air and water filtration, food storage, wound treatment, and tissue engineering are discussed in more detail.

Preparation and platelet adhesion of chitosan/PVA nanofibrous membrane

In this study, chitosan (CTS) dissolved in acetic acid was electrospun together with aqueous poly(vinyl alcohol) solution (PVA) to prepare membranes (CTS/PVA) with nanofibers. The morphology of the membranes varied with the electrospinning conditions. High polymer concentration, high distance or high voltage was facilitative in obtaining a membrane with nanofibers. A CTS/PVA membrane with evenly distributed nanofibers (50 nm dia.) was obtained under the following conditions: 4·5 g CTS in 55 ml 27% acetic acid, 0·4 g PVA in 5 ml water (H2O), 0·1 g sodium chloride (NaCl), electrospinning voltage of 40 kV and distance of 25 cm from the injector to the collector. The water contact angle of CTS/PVA membranes increased after cross-linking with glutaraldehyde steam. Platelet adhesion measurement expressed that CTS/PVA with only nanofibers had no platelet adhesion, indicating good blood compatibility. Cross-linked CTS/PVA mats were stable while in contact with phosphate-buffered saline solution.

Dissolution, gelation, functionalization, and material preparation of chitin using ionic liquids

In this article, a review of the research endeavors concerning ionic liquids, that have been used as media for dissolution, gelation, functionalization, and material preparation of chitin, is presented. Although chitin has been identified to show difficulty in solubility and processability, leading to mostly an unutilized organic resource, some ionic liquids have been found to dissolve chitin in certain concentrations. For example, the author found that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), dissolved chitin in concentrations up to 4.8 wt% and formed ion gels at higher contents of chitin. Cellulose/chitin binary ion gel and film were also obtained from the individually prepared polysaccharide solutions with ionic liquids. The binary ion gel was applied as a novel electrolyte for an electric double layer capacitor. Acetylation of chitin using acetic anhydride in AMIMBr gave chitin acetates with high degrees of substitution. The modification technique in the AMIMBr solvent was applied to the synthesis of a chitin macroinitiator for atom transfer radical polymerization (ATRP). Grafting of styrene by ATRP from the resulting macroinitiator was conducted to give chitin–graft–polystyrene. Self-assembled chitin nanofibers were fabricated in a methanol dispersion obtained by regeneration from the chitin ion gel with AMIMBr using methanol, which formed a film by subjecting the dispersion to filtration. Co-regeneration from the chitin ion gel coexisting poly(vinyl alcohol) (PVA) gave a self-assembled chitin nanofiber/PVA composite film. The self-assembled chitin nanofibers have also been used as a reinforcing agent for cellulose derivatives to produce composite films.

Antimicrobial Nanomaterials Derived from Natural Products-A Review

Modern medicine has relied heavily on the availability of effective antibiotics to manage infections and enable invasive surgery. With the emergence of antibiotic-resistant bacteria, novel approaches are necessary to prevent the formation of biofilms on sensitive surfaces such as medical implants. Advances in nanotechnology have resulted in novel materials and the ability to create novel surface topographies. This review article provides an overview of advances in the fabrication of antimicrobial nanomaterials that are derived from biological polymers or that rely on the incorporation of natural compounds with antimicrobial activity in nanofibers made from synthetic materials. The availability of these novel materials will contribute to ensuring that the current level of medical care can be maintained as more bacteria are expected to develop resistance against existing antibiotics.

Fabrication of nanostructured and microstructured chitin materials through gelation with suitable dispersion media

Regeneration from chitin gels with suitable dispersion media results in the efficient fabrication of nano- and microstructured materials.

Post-Processing of Chitosan Based Nanofibers Prepared by Electrospinning

Recently, electrospinning of nanofibers based on chitosan has been widely studied and numerous chitosan based nanofibers have been prepared, for the enormous possibilities of applications in various areas such as filtration, enzyme immobilization, tissue engineering, wound dressing, drug delivery, and catalysis. Because most of the chitosan based nanofibers are soluble in aqueous solutions and the other properties such as mechanical properties are not suitable for the further applications. It is necessary to improve the properties of chitosan based nanofibers. Various post-processing has been done to the chitosan based nanofibers and many post-processing products have emerged. This article discusses the post-processing of the chitosan based nanofibers involving methods, mechanisms, changes of nanofiber properties, and applications of the post-processing products in details. The post-processing is divided into alkali treatment, crosslinking, and functionalizing.

Electrospun chitosan microspheres for complete encapsulation of anionic proteins: controlling particle size and encapsulation efficiency

Electrospinning was employed to fabricate chitosan microspheres by a single-step encapsulation of proteins without organic solvents. Chitosan in acetic acid was electrospun toward a grounded sodium carbonate solution at various electric potential and feeding rates. Electrospun microspheres became insoluble and solidified in the sodium carbonate solution by neutralization of chitosan acetate. When the freeze-dried microspheres were examined by scanning electron microscopy, the small particle size was obtained at higher voltages. This is explained by the chitosan droplet size at the electrospinning needle was clearly controllable by the electric potential. The recovery yield of chitosan microspheres was dependent on the concentration of chitosan solution due to the viscosity is the major factor affecting formation of chitosan droplet during curling of the electrospinning jets. For protein encapsulation, fluorescently labeled bovine serum albumin (BSA) was codissolved with chitosan in the solution and electrospun. At higher concentration of sodium carbonate solution and longer solidification time in the solution, the encapsulation efficiency of the protein was confirmed to be significantly high. The high encapsulation efficiency was achievable by instant solidification of microspheres and electrostatic interactions between chitosan and BSA. Release profiles of BSA from the microspheres showed that the protein release was faster in acidic solution due to dissolution of chitosan. Reversed-phase chromatography of the released fractions confirmed that exposure of BSA to acidic solution during the electrospinning did not result in structural changes of the encapsulated protein.

Effects of processing parameters on particle size of ultrasound prepared chitosan nanoparticles: an Artificial Neural Networks Study

The pharmacokinetic properties of chitosan nanoparticles have been shown to mainly depend on its particle size. The aim of this study was to concurrently evaluate and model the effective parameters, namely, chitosan concentration, buffer pH, amplitude and time of sonication, on the particle size of chitosan nanoparticles. Chitosan solutions were prepared and sonicated with different values for the above mentioned parameters. The data were then modeled using artificial neural networks (ANNs). The results illustrated that all four input parameters affect the size of prepared chitosan nanoparticles. While a reverse effect was observed between the size and the buffer pH as well as time and amplitude of sonication, the concentration was found to directly influence the particle size. The optimum condition to obtain the minimum size of nanoparticles in the range of 50-200 nm was found to be high values of pH and sonication time (i.e. approximately 4.9 and 500 s, respectively) and amplitude values of more than ~55.

New crosslinkers for electrospun chitosan fibre mats. I. Chemical analysis

Chitosan (CS), the deacetylated form of chitin, the second most abundant, natural polysaccharide, is attractive for applications in the biomedical field because of its biocompatibility and resorption rates, which are higher than chitin. Crosslinking improves chemical and mechanical stability of CS. Here, we report the successful utilization of a new set of crosslinkers for electrospun CS. Genipin, hexamethylene-1,6-diaminocarboxysulphonate (HDACS) and epichlorohydrin (ECH) have not been previously explored for crosslinking of electrospun CS. In this first part of a two-part publication, we report the morphology, determined by field emission scanning electron microscopy (FESEM), and chemical interactions, determined by Fourier transform infrared microscopy, respectively. FESEM revealed that CS could successfully be electrospun from trifluoroacetic acid with genipin, HDACS and ECH added to the solution. Diameters were 267 ± 199 nm, 644 ± 359 nm and 896 ± 435 nm for CS-genipin, CS-HDACS and CS-ECH, respectively. Short- (15 min) and long-term (72 h) dissolution tests (T(600)) were performed in acidic, neutral and basic pHs (3, 7 and 12). Post-spinning activation by heat and base to enhance crosslinking of CS-HDACS and CS-ECH decreased the fibre diameters and improved the stability. In the second part of this publication, we report the mechanical properties of the fibres.

Co-electrospun nanofibrous membranes of collagen and zein for wound healing

To develop biocompatible nanofibrous membranes for wound healing, we investigated the coelectrospinning of two proteins (collagen and zein) in aqueous acetic acid solution. It was found that the combination of zein could improve the electrospinnability of collagen. For the resultant electrospun membrane, its fiber diameter, surface wettability, mechanical, and in vitro degradable properties as well as cell adhesive ability could be modulated by the change of collagen/zein blending ratio. Moreover, berberine drug could be incorporated in situ into the electrospun nanofibrous membrane for its controlled release and antibacterial activity. The addition of berberine showed little effects on the fiber morphology and cell viability. In addition, the wound healing performance of the as-obtained nanofibrous membranes was examined in vivo by using female Sprague-Dawley rats and histological observation.

Natural-synthetic hybrid polymers developed via electrospinning: the effect of PET in chitosan/starch system

Chitosan is an amino polysaccharide found in nature, which is biodegradable, nontoxic and biocompatible. It has versatile features and can be used in a variety of applications including films, packaging, and also in medical surgery. Recently a possibility to diversify chitosan properties has emerged by combining it with synthetic materials to produce novel natural-synthetic hybrid polymers. We have studied structural and thermophysical properties of chitosan + starch + poly(ethylene terephthalate) (Ch + S + PET) fibers developed via electrospinning. Properties of these hybrids polymers are compared with extant chitosan containing hybrids synthesized by electrospinning. Molecular interactions and orientation in the fibers are analyzed by infrared and Raman spectroscopies respectively, morphology by scanning electron microscopy and thermophysical properties by thermogravimetric analysis and differential scanning calorimetry. Addition of PET to Ch + S systems results in improved thermal stability at elevated temperatures.

Sorption efficiency of chitosan nanofibers toward metal ions at low concentrations

Chitosan fibers showing narrow diameter distribution with a mean of 42 nm were produced by electrospinning and utilized for the sorption of Fe(III), Cu(II), Ag(I), and Cd(II) ions from aqueous solutions. The ion concentrations in the supernatant solutions were determined using inductively coupled plasma-mass spectrometry (ICP-MS). The filtration efficiency of the fibers toward these ions was studied by both batch and microcolumn methods. High efficiency in sorption of the metal ions was obtained in the both methods. The effects of sorbent amount (0.10-0.50 mg), shaking time (15-120 min), initial metal ion concentration (10.0-1000.0 μg·L(-1)), and temperature (25 and 50 °C) on the extent of sorption were examined. The sorbent amount did not significantly alter the efficiency of sorption; however, shaking time, temperature, and metal ion concentration were found to have a strong influence on sorption. By virtue of its mechanical integrity, the applicability of the chitosan mat in solid phase extraction under continuous flow looks promising.

Application of spectroscopic methods for structural analysis of chitin and chitosan

Chitin, the second most important natural polymer in the world, and its N-deacetylated derivative chitosan, have been identified as versatile biopolymers for a broad range of applications in medicine, agriculture and the food industry. Two of the main reasons for this are firstly the unique chemical, physicochemical and biological properties of chitin and chitosan, and secondly the unlimited supply of raw materials for their production. These polymers exhibit widely differing physicochemical properties depending on the chitin source and the conditions of chitosan production. The presence of reactive functional groups as well as the polysaccharide nature of these biopolymers enables them to undergo diverse chemical modifications. A complete chemical and physicochemical characterization of chitin, chitosan and their derivatives is not possible without using spectroscopic techniques. This review focuses on the application of spectroscopic methods for the structural analysis of these compounds.