Crosslinked Chitosan Films Research Articles

Nano and micro mechanical properties of uncross-linked and cross-linked chitosan films

The aim of this study is to determine the nano and micro mechanical properties for uncross-linked and cross-linked chitosan films. Specifically, we looked at nanoindentation hardness, microhardness, and elastic modulus. It is important to study the nano and microscale mechanical properties of chitosan since chitosan has been widely used for biomedical applications. Using the solvent-cast method, the chitosan films were prepared at room temperature on the cleaned glass plates. The chitosan solution was prepared by dissolving chitosan in acetic acid 1% (v/v). Tripolyphosphate (TPP) was used to create the cross-links between amine groups in chitosan and phosphate groups in TPP. In this study, atomic force microscopy was used to measure the nanoindentation hardness and surface topography of the uncross-linked and cross-linked chitosan films. Elastic modulus was then calculated from the nanoindentation results. The effective elastic modulus was determined by microhardness with some modifications to previous theories. The microhardness of the chitosan films were measured using Vicker’s hardness meter under three different loads. Our results show that the microhardness and elastic modulus for cross-linked chitosan films are higher than the uncross-linked films. However, the cross-linked chitosan films show increased brittleness when compared to uncross-linked films. By increasing the load magnitude, the microhardness increases for both uncross-linked and cross-linked chitosan films.

Efficient decolorization of azo dye solution by visible light-induced photocatalytic process using SnO2/ZnO heterojunction immobilized in chitosan matrix

SnO2/ZnO quantum dot (3–5nm diameters) heterojunction immobilized on crosslinked chitosan films (SnO2/ZnO/chitosan films) were prepared successfully and characterized by high-resolution transmission electron microscope (HRTEM), scanning electron microscope (SEM) and X-ray diffraction (XRD). In the presence of SnO2/ZnO/chitosan films and under visible light irradiation, decolorization of azo dye methyl orange (MO) in aqueous solution was studied. The effects of key operational parameters such as aeration, photocatalyst dosage, MO initial concentration and electrolytes were discussed. SnO2/ZnO/chitosan films exhibited a good adsorption–photocatalytic activity for decolorization of MO and could be reused expediently by simple filtration from treated solution. The decolorization process of MO solution was accelerated with increased photocatalyst dosage and decreased initial MO concentration. The presence of coexisting anions had impeditive effects on photocatalytic decolorization of MO dye. Kinetics analysis indicated that the dye photocatalytic decolorization rates could be approximated by pseudo-first-order model. With weak aeration MO solution was decolorized successfully excess 99% by SnO2/ZnO/chitosan films after 210min of visible light irradiation. As an inorganic/organic composite material, SnO2/ZnO/chitosan films exhibited enhanced properties due to the combination of SnO2/ZnO quantum dot heterojunction and organic matrix at nanometer scale. Cycling experiments indicated that SnO2/ZnO/chitosan films were efficient and stable visible light photocatalyst.

The Effect of Polymer Molecular Weight on Citrate Crosslinked Chitosan Films for Site-Specific Delivery of a Non-Polar Drug

Purpose: To develop citrate crosslinked chitosan films using chitosan of different molecular weights (MW) in order to achieve site-specific delivery of a model non-polar drug, indomethacin.Methods: Films prepared with different molecular weights of chitosan and incorporating indomethacin as a non-polar model drug were obtained by a casting/solvent evaporation method. The chitosan films were crosslinked by dipping in varying concentrations of sodium citrate solution and for different crosslinking times. The films were assessed by, amongst others, scanning electron microscopy (SEM), dissolution studies and differential scanning calorimetry (DSC) for surface morphology, drug release and ingredient compatibility, respectively.Results: Crosslinking time and concentration of crosslinking agent significantly (p < 0.05) influenced the in vitro release of indomethacin as well as swelling of the films. Also, the higher the molecular weight (MW) of chitosan the lower the drug release rate (p < 0.05). Furthermore, film swelling index rose as chitosan MW decreased (p < 0.05). The practical absence of the sharp endothermic peak characteristic of indomethacin in the films suggests that crosslinking may have transformed the drug from the crystalline to the amorphous state.Conclusion: The citrate-crosslinked chitosan films can be modulated to vary swelling and drug release at pH 3.5 and 6.2; this feature makes them useful tools for designing site-specific delivery systems.Keywords: Chitosan film, Sodium citrate, Site-specific delivery, Crosslinking, IndomethacinTropical Journal of Pharmaceutical Research December 2010; 9 (6): 525-531

Copper, mercury and chromium adsorption on natural and crosslinked chitosan films: An XPS investigation of mechanism

Although biopolymers are focusing the attention of researchers as potential adsorbents for heavy metal removal, little information is given about the properties of the resulting complexes. This information would also bring a better understanding of the mechanisms involved in metal binding to the polymer. XPS (X-ray photo-electron spectroscopy) is a powerful technique to investigate how metal ions bind onto these matrices. In this study, copper, chromium and mercury ions were adsorbed on natural and crosslinked (glutaraldehyde and epichlorohydrin) chitosan matrices, which present diverse functional groups and may induce different adsorption mechanisms. X-ray photoelectron spectroscopy (XPS) revealed that these metals bind to glutaraldehyde-crosslinked chitosan, differently from the other two kinds of matrices. Hence, amino group availability and the formation of new structures such as imino bonds are key factors. Copper(II) stabilization was found to be poor in glutaraldehyde-crosslinked chitosan. Conversely, Hg(II) ions present higher adsorption capacity in this kind of matrix. Chromium(VI) was reduced in all three matrices. In this case, chromium(VI) is probably not well stabilized by the functional groups of these polymers and may also undergo the action of their reducing groups.

Electro-Induced Covalent Cross-Linking of Chitosan and Formation of Chitosan Hydrogel Films: Its Application as an Enzyme Immobilization Matrix for Use in a Phenol Sensor

We report a novel electrochemical method for making covalently cross-linked chitosan films on the surface of a screen printed carbon electrode. In the presence of a freely diffusing ruthenium complex, Ru(bpy)(2)Cl(2), soluble chitosan becomes irreversibly cross-linked in response to a reducing potential and subsequently deposits on the electrode surface to form a hydrogel film which shows robustness in harsh acidic conditions. The cross-linked chitosan film presents excellent ability to facilitate the diffusion and electron transfer process of the negatively charged redox couple [Fe(CN)(6)](3-)/[Fe(CN)(6)](4-) at the electrode surface, while its impact on the positively charged redox couple [Ru(NH(3))(6)](2+)/[Ru(NH(3))(6)](3+) is minimal. By covalently immobilizing the enzyme tyrosinase in a preformed cross-linked chitosan film via a similar mechanism, a sensitive phenol sensor is constructed with a broad dynamic range. The potential advantages of this method are also discussed.

Composite Membranes Based on a Selective Chitosan−Poly(ethylene glycol) Hybrid Layer: Synthesis, Characterization, and Performance in Oil−Water Purification

A series of poly(ethylene glycol) diglycidyl ether−cross-linked chitosan (chi−PEG hybrid) films were prepared to elucidate their potential as fouling-resistant ultrafiltration (UF) membrane coating layers. Water permeability increased as the poly(ethylene glycol) diglycidyl ether to chitosan ratio in the prepolymerization mixture increased due to increased porosity in the polymer matrix resulting from phase separation during polymerization. Composite membranes for oil−water emulsion filtration were prepared by coating an optimized member of the chi−PEG hybrid family onto a commercial polysulfone ultrafiltration membrane. Scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (FTIR), and pure water permeance measurements indicated that, depending on the concentration of chitosan in the coating solution, the coating layer thickness could be controlled, so water permeance could be optimized. These composite membranes exhibited water flux values more than 5 ti...

Formulation of chitosan-based ciprofloxacin and diclofenac film for periodontitis therapy

Purpose: This study was designed to develop and evaluate chitosan films containing ciprofloxacin and diclofenac sodium for the topical treatment of periodontitis. Methods: Chitosan films containing ciprofloxacin alone and in combination with diclofenac sodium were prepared by solvent casting method. Some of the drug-loaded films were crosslinked with 2% gluteraldehyde for 2 and 4 h, respectively. The films were then evaluated for their physicochemical properties including weight variation, thickness, tensile strength, in vitro release, stability and antibacterial activity. Results: Mean weight and thickness data showed that the different films were uniform. Tensile strength was maximum for drug-free films and minimum for films containing the highest amount of drug(s). In vitro drug release data indicate that the films showed an initial burst release followed by sustained release of the drug(s). Films stored at refrigerated conditions exhibited slower degradation rate. The drug-loaded films that were crosslinked for 4 h had inhibitory effect on Staph mutans for up to 24 days. Conclusion: The study suggests that crosslinked chitosan film containing ciprofloxacin and diclofenac is a potential drug delivery device for the topical treatment of periodontitis. Good physicochemical properties were shown by the films. Keywords: kChitosan, Ciprofloxacin, Crosslinking, Diclofenac, Films, Topical delivery, PeriodontitisTropical Journal of Pharmaceutical Research Vol. 8 (1) 2009: pp. 33-41

Localized Surface Plasmon Resonance of Gold Nanoparticle-Modified Chitosan Films for Heavy-Metal Ions Sensing

Gold nanoparticles (Au NPs) were entrapped within, and in between, a cross-linked thin chitosan film, casted onto a glass substrate. The glass/chitosan/Au NPs interface was formed by casting Au NPs-chitosan solutions onto flat glass supports, followed by exposure to Au NPs in solution and repeating the casting procedure for the desired number of layers. The optical properties of the resulting interfaces and their ability to sense various heavy metal ions, such as Fe3+ and Cu2+, were investigated utilizing the phenomenon of localized surface plasmon resonance (LSPR) visualized by UV/V is absorption spectroscopy. The interfaces investigated showed different optical behavior to the presence of the different metal ions. An increase of the LSRP absorption maximum at lamdamax = 517 nm was observed upon Fe3+ binding with a detection limit of 0.5 microM and a linear range up to approximately 2 microM. Due to a lower binding capability of Cu2+, the detection limit is 0.5 mM with a linear range up to approximately 5 mM.

An Investigation into the Digestion of Chitosan (Noncrosslinked and Crosslinked) by Human Colonic Bacteria

Chitosan salts are being investigated as materials for bacterially triggered colonic drug delivery, via the oral route, based on the assumption that they will be degraded by the enzymes produced by the human colonic bacteria. The actual susceptibility of chitosan to these enzymes is, however, unclear. The digestion of chitosan films (noncrosslinked, and crosslinked with glutaraldehyde or tripolyphosphate) by human colonic bacteria (using human faecal material) was therefore investigated, and in addition, their digestion by pancreatic enzymes (of porcine origin) was assessed. Noncrosslinked chitosan films were digested by both pancreatic and colonic enzymes within 4 h, while glutaraldehyde crosslinked chitosan films were resistant to both enzyme systems. In contrast, tripolyphosphate crosslinked chitosan films resisted pancreatic digestion, but were susceptible to faecal digestion over the same 4 h time period. As expected, lowering crosslinker concentration and increasing incubation time (to 18 h) allowed greater digestion. The difference between the crosslinkers is attributed to the mechanism of crosslinking, and the associated degree of film swelling in an aqueous environment. Swelling studies in acidic conditions suggest that only glutaraldehyde or higher concentrations of tripolyphosphate would be able to prevent film dissolution in gastric conditions.

Thionine immobilized in crosslinked chitosan films

Abstract Redox and acid–base properties of thionine immobilized in crosslinked chitosan films are analyzed. The experimental conditions for the preparation of the films are described. Results obtained with cyclic voltammetry, spectroelectrochemistry and spectrophotometry indicate that the immobilized dye retains the redox and acid–base activity of free thionine. An acid dissociation constant ( K a ) for the immobilized dye of K a = 2.7 × 10 −11 was obtained. Due to the stable and reversible pH dependent optical signal of the studied film, this membrane can be used as a building component of an optical pH sensor.

Preparation and characterization of poly(ethylene glycol) crosslinked chitosan films

AbstractPoly(ethylene glycol) (PEG) crosslinked chitosan films with various PEG to chitosan ratio and PEG molecular weight were successfully prepared via the epoxy‐amine reaction between chitosan and PEG‐epoxy. The thermal and mechanical properties and swelling behavior were studied for the PEG crosslinked chitosan films. The mechanical strength of chitosan films were greatly enforced by the introduction of PEG‐epoxy, achieving an elongation of about 80%. It was found that the crosslinked chitosan films form hydrogel in water, achieving a swelling ratio higher than 20 times of original weight. The swelling behavior of chitosan films relied greatly on the molecular weight of the crosslinker PEG‐epoxy and the weight percent of PEG‐epoxy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Physicochemical, Antimicrobial, and Cytotoxic Characteristics of a Chitosan Film Cross-Linked by a Naturally Occurring Cross-Linking Agent, Aglycone Geniposidic Acid

The purpose of this study was to evaluate the characteristics of a chitosan film cross-linked by a naturally occurring compound, aglycone geniposidic acid (aGSA). This newly developed aGSA-cross-linked chitosan film may be used as an edible film. The chitosan film without cross-linking (fresh) and the glutaraldehyde-cross-linked chitosan film were used as controls. The characteristics of test chitosan films evaluated were their degree of cross-linking, swelling ratio, mechanical properties, water vapor permeability, antimicrobial capability, cytotoxicity, and enzymatic degradability. It was found that cross-linking of chitosan films by aGSA (at a concentration up to 0.8 mM) significantly increased its ultimate tensile strength but reduced its strain at fracture and swelling ratio. There was no significant difference in the antimicrobial capability between the cross-linked chitosan films and their fresh counterpart. However, the aGSA-cross-linked chitosan film had a lower cytotoxicity, a slower degradation rate, and a relatively lower water vapor permeability as compared to the glutaraldehyde-cross-linked film. These results suggested that the aGSA-cross-linked chitosan film may be a promising material as an edible film.

In vitro biomineralization of glutaraldehyde crosslinked chitosan films

The biomimetic approach was applied to study the in vitro biomineralization of series of the chitosan films crosslinked by glutaraldehyde. The deposited calcium phosphate coatings were studied using scanning electron microscopy and energy dispersive X-ray analysis. Initially, the treatment in simulated body fluid (SBF) results in the formation of single layer of calcium phosphate particles over the film surface. As immersion time in SBF increases, further nucleation and growth produce a simulated calcium phosphate coating. The Cal P molar ratio of the calcium phosphate increases with the immersion time, showing a rapid formation of calcium-deficient phosphate material from the phase of octac 1 alcium phosphate. The different glutaraldehyde crosslinking degree influences the morphology and magnitude of the calcium phosphate coatings on the surface of the chitosan films.

Physical, mechanical and degradation properties, and Schwann cell affinity of cross-linked chitosan films

Three kinds of cross-linked chitosan films were prepared with hexamethylene diisocyanate (HDI), epichlorohydrin (ECH) and glutaraldehyde (GA) as cross-linking agents, respectively. The physical and mechanical properties, biodegradability and Schwann cell affinity of the cross-linked films were investigated. A significant decrease in the degradation rate in lysozyme solution and a large change in the mechanical properties were observed compared with non-cross-linked chitosan films. The protein adsorption on chitosan films was determined by means of enzyme-linked immunosorbent assay (ELISA). In comparison with the non-cross-linked films, the chitosan films cross-linked with HDI showed a significant increase (up to 40–50%) in both fibronectin and laminin adsorption, while the protein adsorption on the other two kinds of cross-linked films was similar to that on non-cross-linked films. In addition, cell culture revealed that the HDI cross-linked chitosan films enhanced the spread and proliferation of Schwann cells while the other cross-linked films delayed the cell proliferation. These results suggest that HDI cross-linking of chitosan films provides a combination of physical properties, biodegradability and Schwann cell affinity suitable for peripheral nerve regeneration.

Color changes in chitosan and poly(allyl amine) films upon metal binding

The intense coloration of butterflies, snakes, hummingbirds and arthropods is due to reflective interference by stacked thin film layers of alternating high and low index of refraction materials. By controlling film thickness, it is also possible to create a single layer film of similar materials with well-defined color. Cross-linked chitosan and poly(allyl amine) hydrochloride thin films were assembled by dropping a dilute solution onto a spinning silicon substrate. Film quality and reproducibility were investigated, as well as the effects of cross-linking. Control of thickness could be used to determine film color. When dipped into a variety of metal ion solutions, the cross-linked films changed in thickness and color.

The influence of multivalent phosphate structure on the properties of ionically cross-linked chitosan films for controlled drug release

The aim of this paper was to investigate the electrostatic interactions between multivalent phosphates (phosphate (Phos), pyrophosphate (Pyro) and tripolyphosphate (TPP)) and chitosan, as well as the influence of electrostatic interactions on the properties of chitosan films ionically cross-linked by the above mentioned phosphates. The charge number of Phos was too low to interact with chitosan, while Pyro and TPP with more negative charges showed a significant ability to ionically cross-link chitosan. Solution pH played an important role on the charge numbers carried by Pyro, TPP and chitosan, especially for Pyro/chitosan. For instance, at pH less than 2.0 the interaction between Pyro and chitosan disappeared, while for TPP/chitosan even in solutions at pH less than 0.5 it still existed. Media pH and ionic strength also had a significant influence on the properties of cross-linked chitosan film with multivalent phosphates. Usually these films swelled and drug was released quickly in acidic conditions (such as in simulated gastric fluid) while under neutral conditions (such as in simulated intestinal fluid) they remained in a shrinkage state and drug was released slowly. Compared to TPP/chitosan films, Pyro/chitosan films exhibited much better pH-sensitive swelling and controlled release properties due to their relatively weak electrostatic interaction. The same reasoning was used to explain the significant acceleration of Pyro/chitosan film swelling and model drug release observed on adding sodium chloride. These films may be promising for site-specific drug delivery in the stomach.

Cross-linked Chitosan and Poly(allyl amine) Thin Films

ABSTRACTThe alternation of chitin layers with various compounds allows nature to create novel materials with selective refractive properties. Various organisms employ layered materials for survival; for example, in butterflies such materials cause the apparent disappearance and reappearance during flight to evade predators. The selective light refraction is achieved through control of the thickness and index of refraction of the multiple layers. With the ultimate goal of reproducing these layers, thin single films of chitosan, the soluble form of chitin, and poly(allyl amine) have been prepared and their optical properties analyzed. Ellipsometry, reflectance IR, reflectance spectroscopy, SEM and software modeling were used to characterize these films. Possible applications for optical layered materials range from medical diagnostics to environmental monitoring.

Novel pH-sensitive citrate cross-linked chitosan film for drug controlled release

Turbidimetric titration revealed that there were electrostatic attractive interactions between citrate and chitosan in the pH region of 4.3–7.6, depending on their degree of ionization. Citrate cross-linked chitosan film was prepared simply by dipping chitosan film into sodium citrate solution. The swelling ratio of citrate/chitosan film was sensitive to pH, ionic strength etc. Under acidic conditions, citrate/chitosan film swelled and even dissociated in the pH less than 3.5, and the model drugs (brilliant blue and riboflavin) incorporated in the film were released quickly (usually within 2 h released completely in simulated gastric fluid at 37°C) while under neutral conditions the swelling ratio of citrate/chitosan film was less significant and the release rate of brilliant blue and riboflavin was low (less than 40% released in simulated intestinal fluid in 24 h). Sodium chloride weakened the electrostatic interaction between citrate and chitosan, and therefore facilitated the film swelling and accelerated drug release. The parameters of film preparation such as citrate concentration, solution pH etc. influencing the film swelling and drug release profiles were examined. The lower concentration and the higher pH of citrate solution resulted in a larger swelling ratio and quicker riboflavin release. To improve the drug controlled release properties of citrate/chitosan film, heparin, pectin and alginate were further coated on the film surface. Among them only the coating of alginate prolonged riboflavin release noticeably (for 80% of drug released the time was extended from 1.5 to 3.5 h with 0.5% w/v alginate used). The results indicated that the citrate/chitosan film was useful in drug delivery such as for the site-specific drug controlled release in stomach.

Synthesis and solvent-sensitive fluorescence properties of a novel surface-functionalized chitosan film: potential materials for reversible information storage

Pyrenesulfonylchloride (PSC) was prepared and convalently bound to glutaraldehyde (Glu) crosslinked chitosan (CS) films by a post modification method. The monomer emission of pyrene (Py) immobilized on the CS films was weak both at dry and wet state if super-pure water was used to wet the films. However, upon addition of salts or replacing the super-pure water with tap water the monomer emission increased dramatically whereas the change in the excimer emission was hardly observed. Furthermore, the increasing process could last as long as 7 h. In contrast, the emission returned to the original intensity at once when the films were washed with super-pure water three to four times. The process could be repeated for at least five times.

Functional packaging properties of chitosan films

The barrier properties of chitosan and cross-linked chitosan films with respect to water vapour at three water activities, oxygen transmission rates and grease resistance values have been determined. Other properties evaluated include tensile strength, tear resistance and burst strength. In general, the cross-linked chitosan films possessed greater permeabilities and lesser values for mechanical properties. The water vapour permeabilities were found to be influenced by water activity, obeying non-Fickian behaviour characteristic of hydrophilic polymers.