Preparation and characterization of stimuli-resistible hydrogels nano-coated with polyelectrolyte multilayer films

Alginate (ALG) hydrogels were nano-coated with polyelectrolyte multilayer (PEM) films composed of poly(diallyldimethyl ammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS). Non- and nano-coated ALG hydrogels were immersed into salt solutions (pH 6, ionic strength: 0.01 M), and the swelling behavior of these ALG hydrogels was observed by optical microscopy. The increases in the diameter of the 10-step coated ALG hydrogels were one fourth or less than that of the non-coated hydrogels. These results indicate that the characteristics of nano-coated ALG hydrogels remain unchanged independent of how the external environment is changed (e.g., pH, ionic strength). Consequently, tolerant ionic hydrogels may be prepared by the nano-coating of hydrogel surfaces with PEM films and may be useful for technological and biomedical applications.     

Antibacterial protection of suture material by chlorhexidine-functionalized polyelectrolyte multilayer films

The formation of bacterial biofilms on the surface of implanted materials is a critical factor that may lead to chronic microbial infection and tissue necrosis. In the present study we analysed the stability of polyelectrolyte multilayer (ML) films on suture materials and the antibacterial effect obtained with chlorhexidine (CHX)-functionalized films built on different types of suture materials such as silk, polyester and copolymer of glycolide and l-lactide. The comparison of Escherichia coli culture on glass coverslips and glass coverslips with ML and CHX showed at 24 h an inhibition of the bacterial relative luminescence (40.68%, P < 0.5) and at 48 h (99.46%, P < 0.001). In another way, simple soaking of suture material overnight in CHX digluconate 20% without polyelectrolyte films did not at all protect sutures from bacterial colonization but CHX-functionalized polyelectrolyte films, made from poly-l-glutamic acid and poly-l-lysine, inhibited Escherichia coli proliferation. Youssef Haikel and Constant Vodouhê contributed in an equal way to the management of the project.     

Surface characteristics of water-repellent polyelectrolyte multilayer films containing various silica contents

Water-repellent films were dip-coated onto glass substrate by mimicking a unique surface feature of the lotus leaf by a layer-by-layer deposition of polyelectrolyte, followed by SiO₂ particle to modify surface roughness, and finally a semifluorinated silane to lower the surface energy. Two types of the SiO₂, a fine-sized Aerosil^® 200 and a coarse-sized Aeroperl^® 300/30, were employed at various contents to modify the films' surface roughness. SEM and AFM analysis revealed that the Aerosil^® 200 had more uniform deposition onto the etched polyelectrolyte layer due to its very fined size while the Aeroperl^® 300/30 had less uniform deposition due to its coarser size. In both cases, higher SiO₂ content in the films led to more surface roughness and more hydrophobicity, although the effect was not dramatic in the case of Aerosil^® 200. The films containing the Aerosil^® 200 had very high contact angles of 167-175°and very low surface energy of 0.03-0.51 mJ m^− 2, while the films containing the Aeroperl^® 300/30 had lower contact angles of 132-154°and higher surface energy of 3.07-11.29 mJ m^− 2.     

Molecular depth profiling of multilayer polymer films using time-of-flight secondary ion mass spectrometry

The low penetration depth and high sputter rates obtained using polyatomic primary ions have facilitated their use for the molecular depth profiling of some spin-cast polymer films by secondary ion mass spectrometry (SIMS). In this study, dual-beam time-of-flight (TOF) SIMS (sputter ion, 5 keV SF(5)(+); analysis ion, 10 keV Ar(+)) was used to depth profile spin-cast multilayers of poly(methyl methacrylate) (PMMA), poly(2-hydroxyethyl methacrylate) (PHEMA), and trifluoroacetic anhydride-derivatized poly(2-hydroxyethyl methacrylate) (TFAA-PHEMA) on silicon substrates. Characteristic positive and negative secondary ions were monitored as a function of depth using SF(5)(+) primary ion doses necessary to sputter through the polymer layer and uncover the silicon substrate (>5 x10(14) ions/cm(2)). The sputter rates of the polymers in the multilayers were typically less than for corresponding single-layer films, and the order of the polymers in the multilayer affected the sputter rates of the polymers. Multilayer samples with PHEMA as the outermost layer resulted in lowered sputter rates for the underlying polymer layer due to increased ion-induced damage accumulation rates in PHEMA. Additionally, the presence of a PMMA or PHEMA overlayer significantly decreased the sputter rate of TFAA-PHEMA underlayers due to ion-induced damage accumulation in the overlayer. Typical interface widths between adjacent polymer layers were 10-15 nm for bilayer films and increased with depth to approximately 35 nm for the trilayer films. The increase in interface width and observations using optical microscopy showed the formation of sputter-induced surface roughness during the depth profiles of the trilayer polymer films. This study shows that polyatomic primary ions can be used for the molecular depth profiling of some multilayer polymer films and presents new opportunities for the analysis of thin organic films using TOF-SIMS.     

Chitosan and alginate polyelectrolyte complex membranes and their properties for wound dressing application

This study investigated the characteristics and drug release properties of membranes of chitosan and alginate prepared via a casting/solvent evaporation technique. Membranes of chitosan and alginate with silver sulfadiazine as model drug incorporated in different concentrations and different membrane compositions were obtained. The polyblend solution viscosity reached to the highest at the composition polyblends of (1:1). This chitosan/alginate membranes showed pH- and ionic strength-dependent water uptake properties and had the WVTR rang from 442 to 618 g/m²/day. The maximum value of the dry membrane of breaking strength was 52.16 MPa and the maximum value of the wet membrane breaking elongation was 46.28%. The results of controlled release studies showed that the silver sulfadiazine release rate was the fastest when the alginate content was 50%. On the basis of the requisite physical properties, the chitosan–alginate PEC membrane can be considered for potential wound dressing or controlled release application.     

Preparation of ultrathin self-standing polyelectrolyte multilayer membranes at physiological conditions using pH-responsive film segments as sacrificial layers

A new system to obtain ultrathin self-standing polyelectrolyte multilayer membranes at physiological conditions is introduced. On the surface of a substrate, a hybrid film structure composed of two compartments, (1) a pH-responsive film segment formed via hydrogen bonds and (2) a polyelectrolyte multilayer film on top of 1, was assembled. The pH-responsive polymer multilayer segments disintegrate at a neutral pH and release self-standing polyelectrolyte multilayer films. The obtained self-supporting polyelectrolyte multilayer membranes had thicknesses of 55 to several hundred nanometers and areas of a few square centimeters, approximately. The preparation method introduced here avoids harsh release conditions and thus broadens the choice of materials that can be incorporated into the self-standing film.     

氧化海藻酸钠交联壳聚糖载药复合体系的制备及其药物缓释初步研究

为获得一种新型的药物释放复合体系,本实验首先通过乳化交联法制备壳聚糖(CS)包载四环素(TC)微球,然后利用氧化海藻酸钠交联聚磷酸钙/壳聚糖(CPP/CS)复合材料,用冷冻干燥法制备了载药微球复合体系.并用傅立叶红外光谱仪(IR)、扫描电镜(SEM)及药物的体外释放等方法对该载药微球复合体系进行分析和表征.结果显示,经...     

Preparation and characterization of polyoxometalate-Ag nanoparticles composite multilayer films

The multifunctional thin films (BW₁₂/Ag NPs)_n (BW₁₂ = BW₁₂O₄₀, NPs = nanoparticles) were prepared by layer-by-layer self-assembly method. The (BW₁₂/PEI-Ag⁺)_n (PEI = polyethylenimine) composite films were achieved through alternately depositing anionic BW₁₂ and cationic PEI-Ag⁺ complex. The deposition process of (BW₁₂/PEI-Ag⁺)₁₀ multilayer is linear layer-by-layer self-assembly. Under UV irradiation, Ag ions in (BW₁₂/PEI-Ag⁺)_n multilayer films were reduced photochemically into Ag NPs and (BW₁₂/Ag NPs)₁₀ films were obtained. Through UV-vis measurements, the presence of surface plasma absorption peak at 445 nm demonstrated the formation of silver NPs. The electrochemical and antibacterial activities of (BW₁₂/Ag NPs)_n films were investigated. The electrochemical results indicate that the glassy carbon electrode modified with (BW₁₂/Ag NP)_n film exhibits the electroreduction toward O₂. Moreover, the (BW₁₂/Ag NP)₁₀ multilayer films exhibit long-lasting antibacterial properties toward Escherichia coli (E. coli).     

Optical and electrochemical properties of multilayer polyelectrolyte thin films incorporating spherical, gold colloid nanomaterials

Polyelectrolyte multilayer (PEM) films incorporating various types of spherical, gold nanomaterials (NMs) were investigated to assess the existence of electrochemical and/or optical signal enhancement effects directly attributable to embedded NMs and the relationship of these effects to film structure and composition. Specifically, electrostatically assembled films of cationic poly-l-lysine (PLL) and anionic poly(4-styrene sulfonate) (PSS) incorporating one of four types of spherical, gold colloid NMs were constructed on 3-(aminopropyl)trimethoxysilane (3-APTMS)-modified glass substrates for optical studies or 11-mercaptoundecanoic (MUA)-modified gold electrodes for electrochemical studies. The NMs inserted into the PEM films include citrate-stabilized gold nanoparticles, thioctic acid-stabilized gold nanoparticles (TAS-NPs), MUA-modified monolayer protected gold clusters, and hollow gold nanoshells (Au-NSs). Optical sensitivity of the NM-embedded films, in terms of absorbance, surface plasmon band shifts, and the dependence of these optical responses on film thickness, varied depending on the type of NM within the film (e.g., TAS-NPs versus Au-NSs) but exhibited no corresponding electrochemical effects in the diffusional voltammetry of a ferricyanide redox probe. While not correlated to optical responses, the increased Faradaic current achieved during voltammetry at NM-embedded PEM films suggested that electrochemical effects of NMs were less dependent on the type of NMs and were, instead, more related to their location within the film and the electrostatic interactions built into the interfacial chemistry of the films. These results should prove useful for developing strategies constructing thin films with NMs that are specifically designed for optical or electrochemical sensing, taking full advantage of the signal enhancements provided by individual types of NMs.     

Modelling of multilayer films using spectroscopic ellipsometry

A systematic investigation of the ellipsometric parameters of MBE-grown heterostructures of ln_xGa_1–x As on GaAs substrate has been completed. The index of refraction n, and extinction coefficient, k, values of the above heterostructure in the wavelength range 500–800 nm, are presented, a region of interest in many applications. A model has been proposed for the multilayered structures, through which the thickness of the oxide layer can be determined and the observed optical characteristics of these heterostructures explained. The validity of the model was established by the excellent agreement between the measured and calculated values of the ellipsometric parameters and .     

Preparation and characterization of poly(amide-imide) multilayer films

Multilayer films of poly(amide-imide)s were prepared as follows: (1) monolayers of long alkyl amine salts of poly(amide-amic acid) were prepared at the air- water interface; (2) these monolayers were deposited on an appropriate plate by the Langmuir-Blodgett method; (3) the multilayers of poly(amide-amic acid) salts on the solid support were treated with acetic anhydride to afford poly(amide-imide) multilayer films. The monolayer thickness of the poly(amide-imide) multilayer films were 0.43–0.55 nm.     

Selective permeation of hydrogen peroxide through polyelectrolyte multilayer films and its use for amperometric biosensors.

A platinum electrode was coated with polyelectrolyte multilayer (PEM) films to prepare an amperometric hydrogen peroxide sensor which can be used in the presence of possible interferences such as ascorbic acid, uric acid, and acetaminophen. The PEM films were prepared on the surface of a Pt disk electrode by an alternate deposition of polycation and polyanion from the aqueous solutions through electrostatic force of attraction. The Pt electrodes coated with a poly(allylamine)/poly(vinyl sulfate) or poly(allylamine)/poly(styrenesulfonate) film were used successfully for detecting H2O2 selectively in the presence of the possible interfering agents. It was suggested that H2O2 can diffuse into the PEM film smoothly while the ascorbic acid, uric acid, and acetaminophen cannot penetrate the film by a size exclusion mechanism. On the other hand, the electrodes coated with PEM films containing poly(ethyleneimine) or poly(diallyldimethylammonium chloride) were not useful for the selective determination of H2O2. The results were rationalized based on the different permeability of the films due to the different molecular density or packing in the PEM films. The PEM film-coated electrode was useful for constructing glucose biosensors by coupling with glucose oxidase.     

Layer-by-layer self-assembly of multilayer films of polyelectrolyte/Ag nanoparticles for enzymeless hydrogen peroxide detection

In the paper, we report on the layer-by-layer self-assembly of multilayer films of polyelectrolyte/Ag nanoparticles (AgNPs). The films were constructed by the alternate adsorption of the oppositely charged poly [(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co-(1-vinylpyrrolidone)] (PQ11) and negatively charged citrate-stabilized AgNPs on solid substrates. The multilayer film growth process on quartz slides was monitored by UV-vis absorption spectroscopy. The resulting films exhibit good catalytic activity toward the reduction of hydrogen peroxide (H₂O₂). The enzymeless H₂O₂ sensor based on such films exhibits a fast amperometric response time of less than 5 s. The linear detection range is estimated to be from 100 μM to 110 mM (R² = 0.996), and the detection limit is estimated to be 78 μM at a signal-to-noise ratio of 3.     

Self-assembly of Keggin-type tungstoborate-based multilayer films and their electrochemical behavior

Using electrostatic layer-by-layer self-assembly, ultrathin films consisting of layer-pairs of oppositely charged poly(ethylenimine) and tungstoborate were grown onto quartz substrate or glassy carbon electrode. The multilayers were characterized by UV–vis absorption spectroscopy, cyclic voltammetry, and atomic force microscopy. Cyclic voltammetry indicates that the electrochemical properties of the polyoxometalate clusters are maintained in the multilayer films. Moreover, electron transfer to Fe(CN)₆^{3− / 4−} electrochemically active probe molecules was also investigated by cyclic voltammetry.     

Design of antihistaminic transdermal films based on alginate–chitosan polyelectrolyte complexes: characterization and permeation studies

The purpose of this study was to develop suitable matrix-type transdermal drug delivery systems of Ketotifen fumarate (KF) as antiasthmatic drugs. Chitosan–alginate polyelectrolyte complex (PEC) films were used as drug release regulators for KF. Antihistaminic films with variable PEC compositions were prepared using different ratios of chitosan (CTS) to sodium alginate (ALG). Propylene glycol (PG) was used as plasticizer; Tween 80 (T₈₀) and Span 20 (S₂₀) were used as permeability enhancers. Nine formulations were obtained by film casting method and characterized in terms of weight uniformity, thickness, folding endurance, moisture lost, and moisture absorption. In addition, drug release and permeation through rat abdominal skin mounted in Franz cell were investigated. All formulations were found to be suitable in terms of physicochemical characteristics, and there was no significant interaction between the used drug and polymers. It was noticed that when T₂₀ is used as permeation enhancer, a satisfactory drug release pattern was found where 99.88% of drug was released and an amount of 2.121?mg/cm² of KF was permeated after 24?h. For the optimal formulation, a permeability coefficient of 14.00?±?0.001?cm h^?1 and a latency time of 0.35?±?0.02?h were found. The in-vitro analysis showed controlled release profile which was fitted by Korsmeyer–Peppas model (R²?=?0.998). The obtained results suggested that new controlled release transdermal formulations of asthmatic drugs could be suitably designed as an alternative to the common forms.     

Brominated tyrosine and polyelectrolyte multilayer analysis by laser desorption vacuum ultraviolet postionization and secondary ion mass spectrometry

The small molecular analyte 3,5-dibromotyrosine (Br(2)Y) and chitosan-alginate polyelectrolyte multilayers (PEM) with and without adsorbed Br(2)Y were analyzed by laser desorption postionization-mass spectrometry (LDPI-MS). LDPI-MS using a 7.87 eV laser and tunable 8-12.5 eV synchrotron vacuum ultraviolet (VUV) radiation found that desorption of clusters from Br(2)Y films allowed detection by ≤8 eV single photon ionization. Thermal desorption and electronic structure calculations determined the ionization energy of Br(2)Y to be ~8.3 ± 0.1 eV and further indicated that the lower ionization energies of clusters permitted their detection at ≤8 eV photon energies. However, single photon ionization could only detect Br(2)Y adsorbed within PEMs when using either higher photon energies or matrix addition to the sample. All samples were also analyzed by 25 keV Bi(3)(+) secondary ion mass spectrometry (SIMS), with the negative ion spectra showing strong parent ion signal which complemented that observed by LDPI-MS. However, the negative ion SIMS appeared strongly dependent on the high electron affinity of this specific analyte and the analyte's condensed phase environment.     

Synthesis of bismuth-based high-Tc superconducting fibres by using sodium alginate as a polyelectrolyte

The thermal pyrolysis processes and solid-state reactions in the synthesis of bismuth-based high-Tc superconducting fibre obtained by using sodium alginates are studied. This alginate is a polyelectrolyte and has not only an excellent ion-exchange property but also a gelation to synthesize long fibrous precursors. We first determined the optimum conditions to promote ion-exchange of this polyelectrolyte which yields high contents of metal ions in the precursor. The thermal pyrolysis of a precursor was studied by DTA and IR absorption. On the basis of the DTA and XRD, the solid-state reactions associated with the formation of the 2 2 1 2 phase were revealed. Our method can be applied easily to synthesize Ag-sheathed fibre having an improved tensile strength. This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation and characterization of oxidized alginate covalently cross-linked galactosylated chitosan scaffold for liver tissue engineering

Liver tissue engineering (LTE) requires a perfect extracellular matrix (ECM) for hepatocytes culture to maintain high level of liver-specific functions. Here, we reported a LTE scaffold derived from oxidized alginate covalently cross-linked galactosylated chitosan via Schiff base reaction, without employing any extraneous chemical cross-linking agent. The structure of galactosylated chitosan (GC) and oxidized alginate was confirmed by Fourier transformed infrared (FTIR) spectra, proton nuclear magnetic resonance (¹H-NMR) spectroscopy, X-ray diffraction (XRD) or thermogravimetric (TG) analysis. The structure and properties of a series of the scaffolds were characterized by FTIR, XRD, scanning electron microscopy (SEM), porosity, equilibrium swelling, mechanical properties, thermal stability and in vitro degradation. FTIR spectra confirmed the characteristic peak of Schiff base groups in the scaffolds and XRD indicated the scaffolds could be amorphous. SEM analysis showed that the scaffolds displayed highly porous surfaces with average pore size of 50-150 μm and interconnected pore structure in the internal structure with average pore size of 100-250 μm. Porosity measurement suggested the scaffolds had a porosity of about 70%. The compressive modulus of the scaffolds (hydrated) was in the range of 4.2-6.3 kPa. Further studies showed that, with the increase of the oxidized alginate content, the equilibrium swelling and in vitro degradation rate of the scaffolds decreased and the thermal stability slightly increased, which might mainly attribute to the difference of the degree of cross-linking and the nature properties of the raw materials. Additionally, the biocompatibility of the scaffolds was evaluated in vitro. The results showed that the hepatocytes cultured on the scaffolds had a typical spheroidal morphology, formed multi-cellular aggregates and presented perfect integration with the scaffolds, which suggested that the scaffolds may be potential candidates for LTE strategies.     

Layer-by-layer self-assembly of dye-polyoxometalate multilayer composite films and their fluorescent properties

The layer-by-layer (LbL) self-assembly technique was successfully applied to the fabrication of dye-polyoxometalate multilayer composite films consisting of two dye molecules Rhodamine B (RB) and Rhodamine 6G (R6G) and a Keggin-type polyoxometalate [α-SiW₁₂O₄₀]⁴⁻ (α-SiW₁₂). The composite films were characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), and fluorescence spectroscopy. UV-vis spectra show that the characteristic absorbance values of the multilayer films increase almost linearly with the number of dye/α-SiW₁₂ bilayers, suggesting that the deposition process is regular and highly reproducible from layer to layer. SEM micrographs indicate that the film surface is a little rough with some individual granular domains. In addition, the fluorescent properties of these composite films were also investigated by fluorescence spectroscopy.     

Cell apoptosis control using BMP4 and noggin embedded in a polyelectrolyte multilayer film

Programmed cell death (apoptosis) is a genetically regulated process of cell elimination essential during development. During development, programmed cell death is involved in the specific shaping of organs, in the elimination of cells having achieved their program, and in regulating the number of cells to differentiate. Tooth development includes these three aspects and was used here as a model to study the control of apoptosis. Bone morphogenetic proteins (BMPs) are currently considered as playing a major role in signaling apoptosis. This apoptosis could be stopped by treatments with a BMP antagonist ("Noggin"). We selected a model system made by a layer-by-layer approach using poly-L-glutamic acid (PlGA) and poly-L-lysine (PlL) films into which BMP4 and/or Noggin have been embedded. Our results indicate that in situ control of apoptosis during tooth differentiation mediated by both BMP4 and Noggin embedded in a polyelectrolyte multilayer film is possible. We show here for the first time that in the presence of BMP4 and Noggin embedded in a multilayered film, we can induce or inhibit cell death in tooth differentiation, and conserve their biological effects.