A Review of Chitosan and Chitosan Nanofiber: Preparation, Characterization, and Its Potential Applications

Chitosan is produced by deacetylating the abundant natural chitin polymer. It has been employed in a variety of applications due to its unique solubility as well as its chemical and biological properties. In addition to being biodegradable and biocompatible, it also possesses a lot of reactive amino side groups that allow for chemical modification and the creation of a wide range of useful derivatives. The physical and chemical characteristics of chitosan, as well as how it is used in the food, environmental, and medical industries, have all been covered in a number of academic publications. Chitosan offers a wide range of possibilities in environmentally friendly textile processes because of its superior absorption and biological characteristics. Chitosan has the ability to give textile fibers and fabrics antibacterial, antiviral, anti-odor, and other biological functions. One of the most well-known and frequently used methods to create nanofibers is electrospinning. This technique is adaptable and effective for creating continuous nanofibers. In the field of biomaterials, new materials include nanofibers made of chitosan. Numerous medications, including antibiotics, chemotherapeutic agents, proteins, and analgesics for inflammatory pain, have been successfully loaded onto electro-spun nanofibers, according to recent investigations. Chitosan nanofibers have several exceptional qualities that make them ideal for use in important pharmaceutical applications, such as tissue engineering, drug delivery systems, wound dressing, and enzyme immobilization. The preparation of chitosan nanofibers, followed by a discussion of the biocompatibility and degradation of chitosan nanofibers, followed by a description of how to load the drug into the nanofibers, are the first issues highlighted by this review of chitosan nanofibers in drug delivery applications. The main uses of chitosan nanofibers in drug delivery systems will be discussed last.

The application of conventional or magnetic materials to support immobilization of amylolytic enzymes for batch and continuous operation of starch hydrolysis processes

In the production of ethanol, starches are converted into reducing sugars by liquefaction and saccharification processes, which mainly use soluble amylases. These processes are considered wasteful operations as operations to recover the enzymes are not practical economically so immobilizations of amylases to perform both processes appear to be a promising way to obtain more stable and reusable enzymes, to lower costs of enzymatic conversions, and to reduce enzymes degradation/contamination. Although many reviews on enzyme immobilizations are found, they only discuss immobilizations of α-amylase immobilizations on nanoparticles, but other amylases and support types are not well informed or poorly stated. As the knowledge of the developed supports for most amylase immobilizations being used in starch hydrolysis is important, a review describing about their preparations, characteristics, and applications is herewith presented. Based on the results, two major groups were discovered in the last 20 years, which include conventional and magnetic-based supports. Furthermore, several strategies for preparation and immobilization processes, which are more advanced than the previous generation, were also revealed. Although most of the starch hydrolysis processes were conducted in batches, opportunities to develop continuous reactors are offered. However, the continuous operations are difficult to be employed by magnetic-based amylases.

Tailor-made novel electrospun polystyrene/poly(d,l-lactide-co-glycolide) for oxidoreductases immobilization: Improvement of catalytic properties under extreme reaction conditions

Immobilized enzymes find applications in many areas such as pharmacy, medicine, food production and environmental protection. However, protecting these biocatalysts against harsh reaction conditions and retaining their enzymatic activity even after several biocatalytic cycles are major challenges. Properly selected supports and type of surface modifier therefore seem to be crucial for achieving high retention of catalytic activity of immobilized biomolecules. Here we propose production of novel composite electrospun fibers from polystyrene/poly(d,l-lactide-co-glycolide) (PS/PDLG) and its application as a support for immobilization of oxidoreductases such as alcohol dehydrogenase (ADH) and laccase (LAC). Two strategies of covalent binding, (i) (3-aminopropyl)triethoxysilane (APTES) with glutaraldehyde (GA) and (ii) polydopamine (PDA), were applied to attach oxidoreductases to PS/PDLG. The average fiber diameter was shown to increase from 1.252 µm to even 3.367 µm after enzyme immobilization. Effective production of PS/PDLG fibers and biomolecule attachment were confirmed by Fourier transform infrared spectroscopy analysis. The highest substrate conversion efficiency was observed at pH 6.5 and 5 for ADH and LAC, respectively, and at 25 °C for enzymes attached using the APTES + GA approach. Improvement of enzyme stabilization at high temperatures was confirmed in that relative activities of enzymes immobilized onto PS/PDLG fibers were over 20% higher than those of the free biomolecules, and enzyme leaching from the support using acetate and MES buffers was below 10 mg/g.

The effect of surface modification of poly-lactide-co-glycolide/carbon nanotube nanofibrous scaffolds by laminin protein on nerve tissue engineering

The presence of biological cues to promote the attachment, proliferation, and differentiation of neuronal cells is important in the process of nerve regeneration. In this study, laminin as a neurite promoting protein, has been used to modify poly-lactide-co-glycolide/carbon nanotube (PLGA/CNT) electrospun nanofibrous scaffolds by means of either mussel-inspired poly(dopamine) (PD) coating or via direct physical adsorption as a simple route for the functionalization of biomaterials. The laminin-modified scaffolds were characterized by a combination of field emission scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, and contact angle measurements. Subsequently, various properties of scaffolds such as degradation time, amount of attached laminin and the rate of CNT release were investigated. The synergistic effect of topographical and biological cues for PC12 cell attachment, proliferation, and differentiation were then studied by SEM and confocal microscopy. The results of degradation study showed that laminin-modified scaffolds were biodegradable with good structural integrity that persisted about 4 weeks. The amount of laminin attached to the PLGA/CNT and PLGA/CNT-PD scaffolds was 3.12 ± 0.6 and 3.04 ± 071 μg per mg of the scaffold, respectively. Although laminin-modified scaffolds could improve cell proliferation identically, neurite extensions on the PLGA/CNT scaffold modified via PD coating (PLGA/CNT-PD-lam scaffold) were significantly longer than those observed on PLGA/CNT scaffold modified via physical adsorption (PLGA/CNT-lam scaffold) and unmodified scaffolds. Together, these results indicated that surface modification via PD coating could be a promising strategy to fabricate biomimetic scaffolds capable of sustaining longer neuronal growth for nerve tissue engineering.

Fluorescent fibrous mats assembled with self-propagating probes for visual sensing of hydrogen peroxide and choline

Challenges remain in the facile, rapid and sensitive detection of substances at ultralow levels. In the current study, visual sensors of hydrogen peroxide (H2O2) and choline are developed via the integration of an ultrafine fibrous substrate and self-propagating and aggregation-induced emission (AIE) probes. Self-immolative probes (SIPs) composed of phenylboronic acid triggers and choline units are grafted on electrospun polyethylene terephthalate (PET) fibers, followed by electrostatic adsorption of tetraphenylethene derivatives (TPE-SO3) to obtain fluorescent PET-Ch/TPE fibers. Choline oxidase (ChOX) is immobilized on polystyrene-co-maleic anhydride (PSMA) fibers to obtain PSMA-ChOX, followed by assembly into PET-Ch/TPE@PSMA-ChOX composite mats. The presence of H2O2 initiates the cleavage of phenylboronic acid triggers in SIPs to release choline and choline/TPE complexes from PET-Ch/TPE fibers. The released choline is oxidized by PSMA-ChOX fibers to generate H2O2 that then activates a cascade of self-propagating reactions until the release of all choline/TPE complexes, leading to the alleviation of AIE effect and gradual fluorescence fading of fibrous mats. Thus, the hydrogen peroxide and choline concentrations can be read out from the fluorescence fading time of fibrous mats with a detection limit of 0.5 μM H2O2 within 30 min, providing potential self-test devices for a real-time, naked-eye and sensitive detection of bioactive substances.

Immobilization of Enzymes on a Phospholipid Bionically Modified Polysulfone Gradient-Pore Membrane for the Enhanced Performance of Enzymatic Membrane Bioreactors

Enzymatic membrane bioreactors (EMBRs), with synergistic catalysis-separation performance, have increasingly been used for practical applications. Generally, the membrane properties, particularly the pore structures and interface interactions, have a significant impact on the catalytic efficiency of the EMBR. Therefore, a biomimetic interface based on a phospholipid assembled onto a polysulfone hollow-fiber membrane with perfect radial gradient pores (RGM-PSF) has been prepared in this work to construct a highly efficient and stable EMBR. On account of the special pore structure of the RGM-PSF with the apertures decreasing gradually from the inner side to the outer side, the enzyme molecules could be evenly distributed on the three-dimensional skeleton of the membrane. In addition, the supported phospholipid layer in the membrane, prepared by physical adsorption, was used for the immobilization of the enzymes, which provides sufficient linkage to prevent the enzymes from leaching but also accommodates as many enzyme molecules as possible to retain high bioactivity. The properties of the EMBR were studied by using lipase from Candida rugosa for the hydrolysis of glycerol triacetate as a model. Energy-dispersive X-ray and circular dichroism spectroscopy were employed to observe the effect of lecithin on the membrane and structure changes in the enzyme, respectively. The operational conditions were investigated to optimize the performance of the EMBR by testing substrate concentrations from 0.05 to 0.25 M, membrane fluxes from 25.5 to 350.0 L·m-2·h-1, and temperatures from 15 to 55 °C. As a result, the obtained EMBR showed a desirable performance with 42% improved enzymatic activity and 78% improved catalytic efficiency relative to the unmodified membrane.

Encoding materials for programming a temporal sequence of actions

Materials are usually synthesized to allow a function that is either independent of time or that can be triggered in a specific environment.

Cofactor-embedded nanoporous activated carbon matrices for the immobilization of intracellular enzymes and degradation of endocrine disruptor

The mixed intracellular enzyme (MICE) from Citrobacter freundii, capable of degrading o-phenylene diamine (OPD), was extracted and characterized. Cofactors such as zinc and copper ions enhanced the MICE activity. The functionalized nanoporous-activated carbon (FNAC) matrix, zinc-impregnated FNAC matrix (Zn²⁺ -FNAC), copper-impregnated FNAC matrix (Cu²⁺ -FNAC), and zinc- and copper-impregnated FNAC matrix (Zn²⁺ -Cu²⁺ -FNAC) were prepared and characterized to immobilize MICE. The parameters such as time (0-240 Min), pH (1-10), temperature (20-50 ºC), amount of MICE (1-5 mg), particle size of carbon (100-600 μm), and mass of carbon (0.5-2.5 g) were optimized for immobilization of MICE on different FNAC matrices. The carrier matrices in the free and MICE immobilized form were characterized using SEM, FT-IR, XPS, XRD, thermogravimetric analysis (TGA), and DSC analyses. The kinetic and adsorption models for the immobilization of MICE on FNAC matrices were studied. The parameters such as time, pH, temperature, concentration of OPD, and agitation speed were optimized for the degradation of OPD using FNAC-MICE and MICE-immobilized metal-impregnated FNAC matrices. The maximum amount of pyruvic acid formed was found to be 133 μg/mg of OPD using Zn²⁺ -Cu²⁺ -FNAC-MICE matrix. The kinetic models were studied for the formation of pyruvic acid on OPD degradation and confirmed using FT-IR spectroscopy.

Nanobiocatalysis: Nanostructured materials – a minireview

The field of nanobiocatalysis has experienced a rapid growth due to recent advances in nanotechnology. However, biocatalytic processes are often limited by the lack of stability of the enzymes and their short lifetime. Therefore, immobilization is key to the successful implementation of industrial processes based on enzymes. Immobilization of enzymes on functionalized nanostructured materials could give higher stability to nanobiocatalysts while maintaining free enzyme activity and easy recyclability under various conditions. This review will discuss recent developments in nanobiocatalysis to improve the stability of the enzyme using various nanostructured materials such as mesoporous materials, nanofibers, nanoparticles, nanotubes, and individual nanoparticles enzymes. Also, this review summarizes the recent evolution of nanostructured biocatalysts with an emphasis on those formed with polymers. Based on the synthetic procedures used, established methods fall into two important categories: “grafting onto” and “grafting from”. The fundamentals of each method in enhancing enzyme stability and the use of these new nanobiocatalysts as tools for different applications in different areas are discussed.

Time-regulated drug delivery system based on coaxially incorporated platelet α-granules for biomedical use

Aim: Platelet derivatives serve as an efficient source of natural growth factors. In the current study, α-granules were incorporated into coaxial nanofibers. Materials & methods: A nanofiber scaffold containing α-granules was prepared by coaxial electrospinning. The biological potential of the nanofiber scaffold was evaluated in chondrocyte and mesenchymal stem cell cultivation studies. Additionally, the concentration of TGF-β1 was determined. Results: Microscopy studies showed that intact α-granules were incorporated into the coaxial nanofibers. The cultivation tests showed that the novel scaffold stimulated viability and extracellular matrix production of chondrocytes and mesenchymal stem cells. In addition, the concentration of growth factors necessary for the induction of cell proliferation significantly decreased. Conclusion: The system preserved α-granule bioactivity and stimulated cell viability and chondrogenic differentiation of mesenchymal stem cells. Core/shell nanofibers incorporating α-granules are a promising system for tissue engineering, particularly cartilage engineering.

Original submitted 21 March 2012; Revised submitted 8 August 2012; Published online 2 December 2012

Preparation of coaxial-electrospun poly[bis(p-methylphenoxy)]phosphazene nanofiber membrane for enzyme immobilization

A core/sheath nanofiber membrane with poly[bis(p-methylphenoxy)]phosphazene (PMPPh) as the sheath and easily spinnable polyacrylonitrile (PAN) as the core was prepared via a coaxial electrospinning process. Field-emission scanning electron microscopy and transmission electron microscopy were used to characterize the morphology of the nanofiber membrane. It was found that the concentration of the PAN spinning solution and the ratio of the core/sheath solution flow rates played a decisive role in the coaxial electrospinning process. In addition, the stabilized core/sheath PMPPh nanofiber membrane was investigated as a support for enzyme immobilization because of its excellent biocompatibility, high surface/volume ratio, and large porosity. Lipase from Candida rugosa was immobilized on the nanofiber membrane by adsorption. The properties of the immobilized lipase on the polyphosphazene nanofiber membrane were studied and compared with those of a PAN nanofiber membrane. The results showed that the adsorption capacity (20.4 ± 2.7 mg/g) and activity retention (63.7%) of the immobilized lipase on the polyphosphazene nanofiber membrane were higher than those on the PAN membrane.

Application of novel electrospun nanofibrous membranes with different modifications for immobilising glutamine synthetase

BACKGROUND

Theanine synthesis is of interest because of the physiological and pharmacological benefits of theanine. Glutamine synthetase (GS, EC 6.3.1.2) from Pseudomonas taetrolens can be used for theanine biosynthesis. In this study, GS was immobilised in polyvinyl alcohol electrospun nanofibres, and the properties of immobilised GS with different solidifying modifications were studied.

RESULTS

Electrospinning is a good method for enzyme immobilisation. When carbon nanotubes were used as an adsorbent, the activity retention of immobilised GS was 92.3%. With glutaraldehyde as a crosslinker, the enzyme activity retention was only 50.7%; however, by adding collagen or peptide to the electrospinning solution with glutaraldehyde, the activity retention could be improved to 85.9 or 59.6% respectively. Scanning electron micrographs showed that the modifiers induced morphological changes in the nanofibres. The optimum pH and temperature of immobilised GS also changed. In addition, the reusability and storage stability of immobilised GS with glutaraldehyde were much better than those of immobilised GS with carbon nanotubes.

CONCLUSION

A novel method has been established in this study for the immobilisation of GS in electrospun nanofibrous membranes. Carbon nanotubes and glutaraldehyde enhanced the immobilisation, while collagen or peptide inclusion could recover the activity loss caused by glutaraldehyde. The obtained immobilised enzyme achieved high reusability and storage stability.

Size-dependent mechanical properties of PVA nanofibers reduced via air plasma treatment

Organic nanowires/fibers have great potential in applications such as organic electronics and soft electronic techniques. Therefore investigation of their mechanical performance is of importance. The Young's modulus of poly(vinyl alcohol) (PVA) nanofibers was analyzed by scanning probe microscopy (SPM) methods. Air plasma treatment was used to reduce the nanofibers to different sizes. Size-dependent mechanical properties of PVA nanofibers were studied and revealed that the Young's modulus increased dramatically when the scales became very small (<80 nm).

Electrospun Polyacrylonitrile Nanofibrous Membranes Tailored for Acetylcholinesterase Immobilization

Nanofibrous polyacrylonitrile membranes (PANNFM) were obtained by electrospinning and then prepared for immobilizing acetylcholinesterase (AChE). Initially, the chemical modification of PANNFM with ethylenediamine produced reactive groups to overcome their inertness and hydrophobicity. The natural polymer, chitosan, was then tethered on the nanofibrous membranes to improve their biocompatibility. Scanning electron microscopy (SEM) and cross-section SEM were used to determine morphological and porosity changes of the membranes. The immobilized AChE had greater relative activity as well as thermal and storage stability compared to the free enzyme. The bound AChE showed excellent reusability. Chitosan-modified PANNFM was shown to be a suitable strategy for facile immobilization of AChE to produce a promising system that effectively supports biocatalysts.

The immobilization of proteins on biodegradable fibers via biotin-streptavidin bridges

This paper aims at developing novel bioactive fibrous mats for protein immobilization and for protein separation/purification. For this purpose, an amphiphilic triblock copolymer, biotinylated poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-lysine) was co-electrospun together with poly(L-lactide-co-glycolide) into ultrafine fibers approximately 2 microm in diameter, and a layer of blocking agent was coated on the fiber surfaces to block off possible non-specific binding of proteins. The biotin species retained their ability to specifically recognize and bind streptavidin, and the immobilized streptavidin could further combine with biotinylated antibodies, antigens and other biological moieties. Horseradish peroxidase-labeled streptavidin and fluorescein isothiocyanate-labeled goat globulin were used to detect the immobilizations of streptavidin and rabbit anti-goat IgG(H+L) via enzyme-linked immunoassay and confocal laser scanning microscope, respectively. The immobilized antigen was eluted from the fiber substrate with a glycine/HCl solution and the eluted antigen retained its bioactivity. Therefore, these biotin-carrying composite fibers have a variety of uses, including selective immobilization of functional proteins, antigen/antibody separation and purification, and vaccine preparation.

Covalent immobilization of lipase from Candida rugosa onto poly(acrylonitrile-co-2-hydroxyethyl methacrylate) electrospun fibrous membranes for potential bioreactor application

A simple way of fabricating enzymatic membrane reactor with high enzyme loading and activity retention from the conjugation between nanofibrous membrane and lipase was devised. Poly(acrylonitrile-co-2-hydroxyethyl methacrylate) (PANCHEMA) was electrospun into fibrous membrane and used as support for enzyme immobilization. The hydroxyl groups on the fibrous membrane surface were activated with epichlorohydrin, cyanuric chloride or p-benzoquinone, respectively. Lipase from Candida rugosa was covalently immobilized on these fibrous membranes. The resulted bioactive fibrous membranes were examined in catalytic efficiency and activity for hydrolysis. The observed enzyme loading on the fibrous membrane with fiber diameter of 80-150 nm was up to 1.6% (wt/wt), which was as thrice as that on the fibrous membrane with fiber diameter of 800-1,000 nm. Activity retention for the immobilized lipase varied between 32.5% and 40.6% with the activation methods of hydroxyl groups. Stabilities of the immobilized lipase were obviously improved. In addition, continuous hydrolysis was carried out with an enzyme-immobilized fibrous membrane bioreactor and a steady hydrolysis conversion (3.6%) was obtained at a 0.23 mL/min flow rate under optimum condition.

Preparation and Surface Modification of Poly(acrylonitrile-co-acrylic acid) Electrospun Nanofibrous Membranes

Poly(acrylonitrile-co-acrylic acid) (PANCAA) was synthesized and fabricated into nanofibrous membranes by an electrospinning technique. Scanning electron microscopy revealed that membranes composed of uniformly thin and smooth nanofibres were obtained under optimized processing parameters. Surface modification with chitosan on these nanofibrous membranes was accomplished by a coupling reaction between the carboxylic groups of PANCAA and the primary amino groups of chitosan. Fluorescent labelling, weight measurement, FT-IR/ATR spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to confirm the modification process and determine the immobilization degree of chitosan. Platelet adhesion experiments were further carried out to evaluate the hemocompatibility of the studied nanofibrous membranes. Preliminary results indicated that the immobilization of chitosan on the PANCAA nanofibrous membranes was favourable for platelet adhesion.