Light-induced storage in layer-by-layer films of chitosan and an azo dye

The buildup of layer-by-layer (LBL) films from chitosan and the azodye Ponceau-S (PS) was investigated under various experimental conditions, and the resulting films were used in optical storage experiments. The kinetics for the writing process in optical storage was faster for LBL films prepared at low pHs, probably because the films had a larger free volume for isomerization of the chromophores. The nanostructured nature of the LBL films also affected the crystallinity of chitosan, which was considerably decreased in this type of film as chitosan became protonated because of the electrostatic interactions between adjacent layers.     

LBL structured chitosan-layered silicate intercalated composites based fibrous mats for protein delivery

Organic rectorite (OREC) was used to prepare intercalated composites with chitosan. The negatively charged cellulose acetate (CA) fibrous mats were modified with multilayers of the positively charged chitosan or chitosan-OREC intercalated composites and the negatively charged bovine serum albumin (BSA) via electrostatic layer-by-layer (LBL) self-assembly technique. The morphology and protein delivery properties of the resultant samples were investigated by regulating the number of deposition bilayers, the outermost layer and the composition of coating bilayers. The thickness of LBL films coated CA mats increased as the number of bilayers was increased and OREC was added. X-ray photoelectron spectroscopy indicated that chitosan and OREC were deposited on CA fibers. Small angle X-ray diffraction patterns showed that OREC was intercalated by chitosan. The in vitro BSA encapsulation and release experiments demonstrated that OREC could affect the degree of protein loading capacity and release efficiency of the LBL films coating.     

LBL fabricated biopolymer-layered silicate based nanofibrous mats and their cell compatibility studies

N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC) was synthesized from chitosan (CS). Organic rectorite (OREC) added into cellulose acetate (CA) was used to fabricate electrospun nanofibrous mats with improved thermal properties, as a result of depositing multilayers of the positively charged HTCC-OREC composites and the negatively charged sodium alginate (ALG) via layer-by-layer (LBL) technique. The morphology was affected by the number of deposition bilayers and the component of the outmost layer. Observed from the field emission scanning electron microscopy (FE-SEM) images, the LBL structured nanofibrous mats had much larger fiber sizes than CA-OREC nanofibrous mats. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results further confirmed that HTCC-OREC was assembled on nanofibrous mats. Additionally, cell experiments and MTT results demonstrated that OREC had little effect on the cytotoxicity of LBL template, but obviously affected both the cytotoxicity and the cell compatibility of LBL structured mats when OREC was in the deposition films.     

Chitosan/halloysite nanotubes bionanocomposites: Structure, mechanical properties and biocompatibility

Incorporation of nanosized reinforcements into chitosan usually results in improved properties and changed microstructures. Naturally occurred halloysite nanotubes (HNTs) are incorporated into chitosan for forming bionanocomposite films via solution casting. The electrostatic attraction and hydrogen bonding interactions between HNTs and chitosan are confirmed. HNTs are uniformly dispersed in chitosan matrix. The tensile strength and Young's modulus of chitosan are enhanced by HNTs. The storage modulus and glass transition temperature of chitosan/HNTs films also increase significantly. Blending with HNTs induces changes in surface nanotopography and increase of roughness of chitosan films. In vitro fibroblasts response demonstrates that both chitosan and chitosan/HNTs nanocomposite films are cytocompatibility even when the loading of HNTs is 10%. In summary, these results provide insights into understanding of the structural relationships of chitosan/HNTs bionanocomposite films in potential applications, such as scaffold materials in tissue engineering.     

Physical, mechanical, and antibacterial properties of chitosan/PEO blend films

Films formed by blending of two polymers usually have modified physical and mechanical properties compared to films made of the individual components. Our preliminary studies indicated that incorporation of chitosan in polyethylene oxide (PEO) films may provide additional functionality to the PEO films and may decrease their tendency to spherulitic crystallization. The objective of this study was to determine the correlation between chitosan/PEO weight ratio and the physical, mechanical, and antibacterial properties of corresponding films. Films with chitosan/PEO weight ratios from 100/0 to 50/50 in 10% increments were characterized by measuring thickness, puncture strength (PS), tensile strength (TS), elongation at break (%E), water vapor permeability (WVP), and water solubility (WS). Additionally, the films were examined by polarized microscopy, wide-angle X-ray diffraction (WAXD), and Fourier transform infrared (FTIR) spectroscopy, and their antibacterial properties were tested against Escherichia coli. The chitosan fraction contributes to antimicrobial effect of the films, decreases tendency to spherulitic crystallization of PEO, and enhances puncture and tensile strength of the films, while addition of the PEO results in thinner films with lower water vapor permeability. Films with 90/10 blend ratio of chitosan/PEO showed the most satisfactory PS, TS, %E, and antibacterial properties of all tested ratios.     

位相分辨偏振灵敏光学相干层析术:组织双折射特性的成像与定量分析

我们研制了一种基于光纤的位相分辨偏振灵敏光学相干层析成像系统。该系统中的偏振状态控制设量在参考臂而非光源臂上,因而使得光抵达样品的传输效率大大提高。鉴于光源的部分偏振性,入射于样品上的光含有任意偏振状态的分量,通过对参考光偏振状态的调制,就可相干地提取对应于入射光四种正交偏振状态并经样品后向散射的光信号。基于斯托克斯矢量夹角在无损光纤系统传输的变换不变性,我们能利用测量臂中光信号的斯托克斯参数来确定双折射样品深度分辨的位相延迟信息。利用所研制的偏振灵敏光学相干层析成像系统,不仅确认了韧带和软骨的双折射性质,而且定量分析了不同条件下韧带的双折射变化．研究结果表明：韧带松弛可使其双折射特性明显减弱,而韧带经拉伸后,其双折射特性的变化却不明显。     

Development and characterization of edible chitosan/olive oil emulsion films

The properties of plasticized chitosan-olive oil emulsion films prepared with increasing oil concentrations were investigated. Emulsifying nature of chitosan was enough to stabilize olive oil droplets in the film forming emulsions; hence homogeneous, thin and translucent films were obtained in all cases. The homogeneity of the lipid globules distribution in the films was confirmed by contact angle measurements and optical microscopy. All the tensile properties (Young Modulus, strength and maximum elongation) increased with olive oil concentration and were explained considering the interactions developed between lipid and carbohydrate phases in addition to the lubricant characteristics of the oil. Moisture sorption, water vapor permeation through the films and effective diffusion coefficients decreased as oil concentration increases, as a result of the non-polar nature of the lipid. Total soluble matter measurements were used to confirm the development of strong associations between chitosan and olive oil.     

Flow birefringence of xanthan and other polysaccharide solutions

A xanthan sample with molecular weight M = 2.2 x 10(6) was investigated in three solvents: bidistilled water, 0.2 M aqueous NaCl and cadoxen by flow birefringence and viscometry methods in dilute solutions. It was shown that the optical shear rate coefficients of xanthan in aqueous and cadoxen media differ by two orders of magnitude. An estimation of xanthan optical anisotropy in different conformational states has been made and compared with values for other polysaccharides: dextran, pullulan, cellulose and chitosan. The process of denaturation and the flow birefringence of renaturated xanthan in aqueous solutions (after heat treatment at 121 degrees C) have also been studied.     

Tuning the Hydrophilic/Hydrophobic Balance to Control the Structure of Chitosan Films and Their Protein Release Behavior

The control over the crystallinity of chitosan and chitosan/ovalbumin films can be achieved via an appropriate balance of the hydrophilic/hydrophobic interactions during the film formation process, which then controls the release kinetics of ovalbumin. Chitosan films were prepared by solvent casting. The presence of the anhydrous allomorph can be viewed as a probe of the hydrophobic conditions at the neutralization step. The semicrystalline structure, the swelling behavior of the films, the protein/chitosan interactions, and the release behavior of the films were impacted by the DA and the film processing parameters. At low DAs, the chitosan films neutralized in the solid state corresponded to the most hydrophobic environment, inducing the crystallization of the anhydrous allomorph with and without protein. The most hydrophilic conditions, leading to the hydrated allomorph, corresponded to non-neutralized films for the highest DAs. For the non-neutralized chitosan acetate (amorphous) films, the swelling increased when the DA decreased, whereas for the neutralized chitosan films, the swelling decreased. The in vitro release of ovalbumin (model protein) from chitosan films was controlled by their swelling behavior. For fast swelling films (DA?=?45%), a burst effect was observed. On the contrary, a lag time was evidenced for DA?=?2.5% with a limited release of the protein. Furthermore, by blending chitosans (DA?=?2.5% and 45%), the release behavior was improved by reducing the burst effect and the lag time. The secondary structure of ovalbumin was partially maintained in the solid state, and the ovalbumin was released under its native form.     

Birefringence of actin.

The total strain birefringence of F-actin isolated from chicken gizzards was measured as a function of elongation in thin transparent films. Each film held at a certain elongation in a jig was allowed to swell in a penetrating but nondissolving liquid. Seven liquids with different refractive indices were employed. The thickness of the film in each swelling liquid was obtained once equilibrium was established. At each elongation, from 0 to 16%, a Wiener curve was obtained. The minima of the Wiener curves yielded the intrinsic birefringence of F-actin as a function of elongation. The intrinsic birefringence increases with elongation up to 16%, above which the thin films break. The form birefringence at a set refractive index also increases with elongation. The implication of the strain birefringence of F-actin is discussed as it affects the optical properties, mainly light scattering, of tissues such as the fiber cells of lens of the eye.     

Retinal nerve fiber layer birefringence evaluated with polarization sensitive spectral domain OCT and scanning laser polarimetry: A comparison

A polarization‐sensitive spectral domain optical coherence tomography (PS‐SD‐OCT) system is used to measure phase retardation and birefringence of the human retinal nerve fiber layer (RNFL) in vivo. The instrument records three parameters simultaneously: intensity, phase retardation and optic‐axis orientation. 3D data sets are recorded in the optic nerve‐head area of a healthy and a glaucomatous eye, and the results are presented in various ways: En‐face phase‐retardation maps of the RNFL are generated from the recorded 3D data and results are compared with scanning laser polarimetry (SLP). The depth information provided by OCT is used to segment the RNFL in the intensity image and measure the RNFL thickness. From the retardation and thickness data, 2D birefringence maps of the RNFL are derived. Circumpapillary plots of RNFL retardation and thickness obtained by PS‐SD‐OCT are quantitatively compared with those obtained by SLP. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of N-vanillyl chitosan and 4-hydroxybenzyl chitosan and their physico-mechanical, optical, barrier, and antimicrobial properties

Chitosan derivatives such as N-vanillyl chitosan and 4-hydroxybenzyl chitosan were prepared by reacting chitosan with 4-hydroxy-3-methoxybenzaldehyde (vanillin) and 4-hydroxybenzaldehyde. Amino groups on chitosan reacts with these aldehydes to form a Schiff base intermediate, which is later on converted into N-alkyl chitosans by reduction with sodium cyanoborohydride. The chemical reaction was monitored by ¹H NMR spectroscopy and the absence of aldehydic proton at 9.83 ppm in NMR spectra was observed for both the modified chitosan derivatives confirming the reaction. Modified chitosan films were later prepared by solution casting method and their physico-mechanical, barrier, optical and thermal properties were studied. The results clearly indicated significant change in tensile strength, water vapour transmission rate, and haze properties of modified chitosans. Modified chitosan films were also studied for their antimicrobial activity against Aspergillus flavus. The results showed a marked reduction of aflatoxins produced by the fungus in the presence of the N-vanillyl chitosan and 4-hydroxybenzyl chitosan film discs to 98.9% and non-detectable levels, respectively.     

Microstructural imaging and characterization of the mechanical, chemical, thermal, and swelling properties of starch-chitosan blend films

Chitosan has wide range of applications as a biomaterial, but barriers still exist to its broader use due to its physical and chemical limitations. The present study evaluated the properties of the polymeric blend films obtained from chitosan and potato starch by the casting/solvent evaporation method. The swelling properties of the different films studied as a function of pH showed that the sorption ability of the blend films increased with the increasing content of starch. Fourier transform infrared (FTIR) analyses confirmed that interactions were present between the hydroxyl groups of starch and the amino groups of chitosan in the blend films while the x-ray diffraction (XRD) studies revealed the films to exhibit an amorphous character. Thermogravimetric analyses showed that in the blend films, the thermal stability increased with the increasing starch content and the stability of starch and chitosan powders reduced when they were converted to film. The differential scanning calorimetry (DSC) studies revealed an endotherm corresponding to water evaporation around 100 degrees C in all the films and an exotherm, corresponding to the decomposition in the chitosan and blend films. Scanning electron microscopy (SEM) observations indicated that the blend films were less homogenous and atomic force microscopy (AFM) studies revealed the chitosan films to be smooth and homogenous, while the starch films revealed characteristic granular pattern. The blend films exhibited an intermediate character with a slight microphase separation. The starch-chitosan blend films exhibited a higher flexibility and incorporation of potato starch into chitosan films improved the percentage elongation.     

Environmentally friendly films based on chitosan and tetrahydrocurcuminoid derivatives exhibiting antibacterial and antioxidative properties

Environmentally friendly films exhibiting both antibacterial and antioxidative properties were elaborated from chitosan and tetrahydrocurcuminoids (THCs). Two tetrahydrocurcuminoids, THC1 (5-hydroxy-1,7-bis(4-hydroxy-3-methoxyphenyl)hept-4-en-3-one) and THC2 (5-hydroxy-1,7-bis(4-hydroxy-3,5-dimethoxyphenyl)hept-4-en-3-one), were incorporated into a chitosan film. THC1 could be prepared from natural curcumin extracted from turmeric roots (Curcuma longa L.). The resulting tetrahydrocurcuminoid–chitosan films exhibited a high free-radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) in methanol, which was due to a progressive release of the THCs into the solvent. The release kinetics was governed both by molecular interactions between chitosan and THCs and probably by electrostatic forces between the ammonium units in chitosan and the aromatic rings in THCs. These interactions were clearly evidenced by the presence of new absorption bands in the visible regions of the electronic absorption spectra of the THCs. The molecular nature of these interactions was shown using glucosamine, the main monomer of chitosan. When associated with THCs, chitosan retained its bioactivity against Listeria innocua; THCs alone were not bioactive enough against listerial strains.     

Interplay between structure and dynamics in chitosan films investigated with solid-state NMR, dynamic mechanical analysis, and X-ray diffraction

Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl(-)) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl(-) counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content.     

Chitosan-cholesterol and chitosan-stearic acid interactions at the air-water interface

We report in this work the isotherms of cholesterol and stearic acid at the air-water interface modified by different chitosans (chitosan chloride, hydrophobic modified chitosan, and medium and high molecular weight chitosans) in the aqueous subphase. The Langmuir-Blodgett films of the complexes cholesterol-chitosan and stearic acid-chitosan are analyzed by atomic force microscopy (AFM), and a molecular simulation was performed to visualize the chitosan-lipid interactions. Strong modifications are obtained in the isotherms as a result of the chitosan interactions with cholesterol and stearic acid at the air-water interface. These modifications were dependent on the type and concentration of chitosan. Severe modifications of all phases were noticed with larger molecular areas, and the observed changes in the compressional modulus were dependent on the type of chitosan used. The complexes of chitosan-stearic acid were more flexible than the ones of chitosan-cholesterol. The AFM images demonstrated that chitosan was disaggregated by the cholesterol and stearic acid interactions producing more homogeneous surfaces in some cases. The hydrophobic chitosan showed more affinity with stearic acid, while both medium and high molecular weight chitosans produced homogeneous surfaces with cholesterol. The simulated chitosan chains interacting with cholesterol and stearic acid demonstrated the possibility of specific sites of electrostatic bonds between these molecules. Adsorption of cholesterol on the different powdered chitosans, performed by HPLC, showed that the medium and high molecular weight chitosans could retain higher proportions of cholesterol compared with the other analyzed samples.     

Interaction of gentamicin with phosphatidylserine/phosphatidylcholine mixtures in adsorption monolayers and thin liquid films: morphology and thermodynamic properties

Gentamicin possesses strong adverse actions like oto and nephrotoxicity. The latter is a result of strong gentamicin–acid phospholipid interactions, resulting in cell fusion, fission, etc., ions as calcium interact with gentamicin and effectively deter its toxicity. In this work, the interactions of gentamicin and Ca²⁺ with phosphatidylserine/phosphatidylcholine (PS/PC) mixtures of different ratio are experimentally characterized. Special attention is paid to bridge thermodynamic and morphological properties of adsorption monolayers and thin liquid films (TLFs) composed of these lipid mixtures. Our results show that gentamicin decreases the stability of common black TLFs formed of pure PS coupled with suppression of lipid surface adsorption to the monolayers at the air–water interface; also, gentamicin reveals effects of lowering of lipid spreading on the interface and significant loss of material during monolayer cycling, increase of condensed phase, and organization of dense net-like domain monolayer texture. Gentamicin addition results in opposite effects for films formed of DPPC/PS (95:5) mixture. It increases the stability of Newton black TLFs formed by DPPC/PS correlated with faster and stronger surface adsorption and better surface spreading; also, gentamicin lowers the amount of condensed phase and organization of domains of smaller size. We also showed that Ca²⁺ itself decreases the stability of common black TLFs formed of PS accompanied with weaker surface adsorption, formation of higher amounts of condensed phase and organization of domains. In our experiments, Ca²⁺ softens, even deters, the effects of gentamicin on both PS and DPPC/PS films.     

Mediation of a phase transition in hyaluronate films by the counterions Li, Cs, Mg and Ca as observed by infrared spectroscopy, optical microscopy and optical birefringence

Infrared (IR) spectroscopy and optical microscopy have been performed as a function of relative humidity (rh) on wet-spun oriented films of hyaluronate (HA) prepared with various counterions. Complete swelling measurements have been obtained through optical microscopy for films of Cs-, Mg-, and CaHA. IR spectroscopy of Cs-, Mg-, Ca-, and LiHA films was performed for skeletal vibrations (800-1000 cm(-1)) and for vibrational modes (1150-1300 cm(-1)) attributed to C-C and C-O stretching modes and C-C-H and C-O-H bending modes. These techniques reveal evidence of a counterion-dependent phase transition occuring at high relative humidities. Optical birefringence measurements on the polycrystalline samples showed order before and disorder after the transition from lower to higher humidity.     

Superior reinforcement effect of TEMPO-oxidized cellulose nanofibrils in polystyrene matrix: optical, thermal, and mechanical studies

Polystyrene (PS) composites reinforced with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) with various weight ratios were fabricated by casting and vacuum-drying mixtures of PS/N,N-dimethylformamide (DMF) solution and TOCN/DMF dispersion. TOCNs of 3 to 4 nm width were dispersed homogeneously at the individual nanofibril level in the PS matrix, such that the TOCN/PS nanocomposite films exhibited high optical transparencies and their tensile strengths, elastic moduli, and thermal dimensional stabilities increased with increasing TOCN content. Dynamic mechanical analysis showed that the storage modulus of the TOCN/PS films increased significantly with TOCN content above the glass-transition temperature of PS by the formation of an interfibrillar network structure of TOCNs in the PS matrix, based on percolation theory. The outstanding and effective polymer reinforcement by TOCNs results from their high aspect ratio, high crystallinity, and nanodispersibility in the PS matrix.     

Surface structure of chitosan and hybrid chitosan-amylose films-restoration of the antibacterial properties of chitosan in the amylose film

The surface structure of films prepared by casting aqueous solutions of mixtures of water soluble chitosan (WSC) and amylose as well as a fully deacetylated chitosan was studied. Zeta potential measurements indicated that the surface of WSC and fully deacetylated chitosan films is positively charged but very weakly, whereas, a film of amylose blended with WSC exhibited an obvious positive charge. X-ray photoelectron spectra of these films suggest that less amino groups are exposed on the surface of WSC and fully deacetylated chitosan films, whereas, more amino groups are exposed on the surface of a WSC film blended with amylose. A sheet structure in which free amino groups are less exposed on the surface of the film of WSC or fully deacetylated chitosan is proposed. This accounts for the loss of antibacterial activity of chitosan on the WSC film surface. When blended with amylose, the morphology of the film may be disrupted, resulting in strong antibacterial properties.