Preparation and characterization of salicylic acid grafted chitosan electrospun fibers

Chitosan (chi) and its modified forms as electrospun nanofibers have potential applications in advanced water treatment and biomedicine. Polyethylene oxide (PEO) is an additive commonly used to facilitate the formation of chitosan electrospun fibers because PEO (Mw ≥ 400 kDa) affords chain entanglement that stabilize the electrospinning jet, leading to enhanced formation of chi-based electrospun fibers. Herein, we report on the preparation of chitosan grafted with salicylic acid and its utility to afford improved electrospun fibers with low molecular weight (LMw) PEO (Mw » 100 kDa). A comparison of the interactions between original and grafted chitosan with PEO reveals that stable supramolecular assemblies are established between grafted chitosan and PEO, which provides support that such supramolecular interactions favor formation of chitosan electrospun fibers. Moreover, a porous chitosan electrospun nanofiber was prepared through physical treatment that reveals notably higher (ca. 4-fold) dye uptake than the pristine (unmodified) chitosan electrospun nanofibers.

De Novo Ion-Exchange Membranes Based on Nanofibers

The unique functions of nanofibers (NFs) are based on their nanoscale cross-section, high specific surface area, and high molecular orientation, and/or their confined polymer chains inside the fibers. The introduction of ion-exchange (IEX) groups on the surface and/or inside the NFs provides de novo ion-exchangers. In particular, the combination of large surface areas and ionizable groups in the IEX-NFs improves their performance through indices such as extremely rapid ion-exchange kinetics and high ion-exchange capacities. In reality, the membranes based on ion-exchange NFs exhibit superior properties such as high catalytic efficiency, high ion-exchange and adsorption capacities, and high ionic conductivities. The present review highlights the fundamental aspects of IEX-NFs (i.e., their unique size-dependent properties), scalable production methods, and the recent advancements in their applications in catalysis, separation/adsorption processes, and fuel cells, as well as the future perspectives and endeavors of NF-based IEMs.

An Overview of the Design of Chitosan-Based Fiber Composite Materials

Chitosan composite fibrous materials continue to generate significant interest for wastewater treatment, food packaging, and biomedical applications. This relates to the relatively high surface area and porosity of such fibrous chitosan materials that synergize with their unique physicochemical properties. Various methods are involved in the preparation of chitosan composite fibrous materials, which include the modification of the biopolymer that serve to alter the solubility of chitosan, along with post-treatment of the composite materials to improve the water stability or to achieve tailored functional properties. Two promising methods to produce such composite fibrous materials involve freeze-drying and electrospinning. Future developments of such composite fibrous materials demands an understanding of the various modes of preparation and methods of structural characterization of such materials. This review contributes to an understanding of the structure–property relationships of composite fibrous materials that contain chitosan, along with an overview of recent advancements concerning their preparation.

Antibacterial and Osteoconductive Effects of Chitosan/Polyethylene Oxide (PEO)/Bioactive Glass Nanofibers for Orthopedic Applications

This study investigated the efficiency of chitosan/polyethylene oxide (PEO)-based nanofibers with incorporated bioactive glass particles as a coating for titanium alloy, in order to improve the bacteriostatic behavior and, concurrently, promote the production of mineralized tissue. Nanofibers with and without bioglass powder were fabricated by electrospinning technique and characterized using several microscopic and spectroscopic techniques in order to study their morphological and physiochemical properties. Subsequently, the substrates were tested in vitro against Staphylococcus epidermidis and SaOS-2 human osteosarcoma cell line. After in vitro testing, viability and CFU counting assays combined with fluorescence microscopy showed a clear decrease in bacterial growth on all substrates with increasing time. However, this trend was stronger for substrates coated with nanofibers. Formation of mineralized matrix upon exposure to osteoblasts was confirmed by means of SEM/EDX and the content/distribution of osteocalcin and osteopontin estimated by fluorescence microscopy. Incorporation of bioglass promoted biomineralization and stimulated osteoblasts to produce a higher amount of bone extracellular matrix. The present results suggest that a chitosan/PEO/bioactive glass nanofiber composite applied as coating on titanium alloys could concurrently improve antibacterial and osteoconductive properties and could be a potential candidate for dental and orthopedic applications.

Fabrication and evaluation of cationic exchange nanofibers for controlled drug delivery systems

The number of ion exchange fibers in development has increased over the last several years. However, few studies have reported the use ion-exchange fibers in drug delivery system. In this study polystyrene nanofiber ion exchangers (PSNIE) were fabricated by electrospinning techniques, crosslinking and sulfonation. The degree of crosslinking and the ion exchange capacity (IEC) were determined. The morphology and diameter of the nanofiber mats were analyzed using scanning electron microscopy (SEM). Five cationic model drugs (dextromethorphan, chlorpheniramine, diphenhydramine, propranolol and salbutamol) were loaded into PSNIE. The loading capacity, release and release kinetics of the exchangers were investigated. PSNIE were successfully prepared by electrospinning and were allowed to crosslink for 10 min, resulting in a maximum IEC of 2.86±0.1 meq/g dry PSNIE. The diameter of the fibers after sulfonation was 464±35 nm. Dextromethorphan provided the highest loading in PSNIE while diphenhydramine gave the highest percentage release in both simulated gastric and intestinal fluid (SGF and SIF). The release kinetics of all drugs in SGF and SIF provided the best fit with the particle diffusion model. Our results showed that the development of a PSNIE-based drug delivery system was successful, and PSNIE were able to control drug release.

Biomedical exploitation of chitin and chitosan via mechano-chemical disassembly, electrospinning, dissolution in imidazolium ionic liquids, and supercritical drying

Recently developed technology permits to optimize simultaneously surface area, porosity, density, rigidity and surface morphology of chitin-derived materials of biomedical interest. Safe and ecofriendly disassembly of chitin has superseded the dangerous acid hydrolysis and provides higher yields and scaling-up possibilities: the chitosan nanofibrils are finding applications in reinforced bone scaffolds and composite dressings for dermal wounds. Electrospun chitosan nanofibers, in the form of biocompatible thin mats and non-wovens, are being actively studied: composites of gelatin + chitosan + polyurethane have been proposed for cardiac valves and for nerve conduits; fibers are also manufactured from electrospun particles that self-assemble during subsequent freeze-drying. Ionic liquids (salts of alkylated imidazolium) are suitable as non-aqueous solvents that permit desirable reactions to occur for drug delivery purposes. Gel drying with supercritical CO₂ leads to structures most similar to the extracellular matrix, even when the chitosan is crosslinked, or in combination with metal oxides of interest in orthopedics.

Functionality in Electrospun Nanofibrous Membranes Based on Fiber's Size, Surface Area, and Molecular Orientation

Electrospinning is a versatile method for forming continuous thin fibers based on an electrohydrodynamic process. This method has the following advantages: (i) the ability to produce thin fibers with diameters in the micrometer and nanometer ranges; (ii) one-step forming of the two- or three-dimensional nanofiber network assemblies (nanofibrous membranes); and (iii) applicability for a broad spectrum of molecules, such as synthetic and biological polymers and polymerless sol-gel systems. Electrospun nanofibrous membranes have received significant attention in terms of their practical applications. The major advantages of nanofibers or nanofibrous membranes are the functionalities based on their nanoscaled-size, highly specific surface area, and highly molecular orientation. These functionalities of the nanofibrous membranes can be controlled by their fiber diameter, surface chemistry and topology, and internal structure of the nanofibers. This report focuses on our studies and describes fundamental aspects and applications of electrospun nanofibrous membranes.

Engineering nanoassemblies of polysaccharides

Polysaccharides offer a wealth of biochemical and biomechanical functionality that can be used to develop new biomaterials. In mammalian tissues, polysaccharides often exhibit a hierarchy of structure, which includes assembly at the nanometer length scale. Furthermore, their biochemical function is determined by their nanoscale organization. These biological nanostructures provide the inspiration for developing techniques to tune the assembly of polysaccharides at the nanoscale. These new polysaccharide nanostructures are being used for the stabilization and delivery of drugs, proteins, and genes, the engineering of cells and tissues, and as new platforms on which to study biochemistry. In biological systems polysaccharide nanostructures are assembled via bottom-up processes. Many biologically derived polysaccharides behave as polyelectrolytes, and their polyelectrolyte nature can be used to tune their bottom-up assembly. New techniques designed to tune the structure and composition of polysaccharides at the nanoscale are enabling researchers to study in detail the emergent biological properties that arise from the nanoassembly of these important biological macromolecules.

Characterization of chitosan nanofiber fabric by electrospray deposition: Electrokinetic and adsorption behavior

Cationic biopolymer nanofiber fabrics were prepared from a chitosan/poly(ethylene oxide) blend solution by electrospray deposition. Their electrokinetic properties and DNA adsorption behavior were analyzed as a function of pH. The zeta potential was determined from streaming potential/streaming current measurements. The adsorption of DNA onto the fabrics was investigated by spectrophotoscopy. The adsorption behavior of DNA correlated well with the electrokinetic properties of the fabrics. This revealed that the electrokinetic approach was a useful option for characterization of novel nanofiber assemblies made by the electrostatic spray process. In addition, these results provided fundamental information about chitosan nanofiber fabrics for both biomedical and analytical applications.

Effect of ion-exchange nanofiber fabrics on water splitting in bipolar membrane

In the present study, the effect of ion-exchange fiber fabric made by electrospray deposition (ESD) on water splitting in a composite bipolar membrane (CBM) was investigated. Cation- and anion-exchange fiber (CEF and AEF) fabrics, which were composed of very thin fibers, were prepared by ESD and postdeposition chemical modification and then used as the intermediate layer of a CBM. The current-voltage characteristics under reverse bias conditions showed that the AEF fabrics enhanced water splitting. The water dissociation is accelerated by the AEF fabric, which contains both tertiary pyridyl groups and quaternary pyridinium groups and has a high specific surface area. On the other hand, the CEF fabric, which contains sulfonic acid groups and has an insufficient specific surface area, reduced water splitting. These results indicate that fiber fabric with catalytic activity and a high surface area obtained by ESD can improve the performance of a CBM.

Preparation of ion-exchange fiber fabrics by electrospray deposition

Ion-exchange fiber (IEF) fabrics were prepared by electrospray deposition (ESD) and post-deposition chemical modification of their surfaces. Nonwoven fibrous fabrics were obtained from the solutions of synthetic polymers-polystyrene (PS) and poly(4-vinylpyridine) (P4VP)-of various concentrations. The diameter of the fiber in the fabrics ranged from 600 nm to 1.70 microm. Cation- and anion-exchange fiber (CEF and AEF) fabrics were obtained from the sulfonation of PS fabrics and the quaternization of P4VP fabrics, respectively. These fabrics were thoroughly characterized by a series of techniques, such as scanning electron microscopy (SEM), permporometry, nitrogen adsorption measurements, and potentiometric titrations. The SEM images showed that the fabrics had a porous structure after their chemical modification. The mean pore size, porosity, and specific surface area of the flow-through pores were 1.67-3.53 microm, about 80%, and 13 m(2)/g, respectively. The ion-exchange capacity was in the range from 0.78 to 1.34 mmol/g. The AEF fabric, on the other hand, showed a high specific surface area, i.e., the Brunauer-Emmett-Teller (BET) surface area of 600 m(2)/g, due to the formation of much smaller pores on the surface of the fiber structure in the fabric. The secondary chemical modification of the nano-microfiber fabrics by ESD provides novel functional materials with a large adsorption capacity and a high catalytic activity.