Deposition Of Polyelectrolyte Multilayers Research Articles

Enhancing biological properties with straightforward deposition of durable heparin/chitosan surface coatings on wettable poly(ε-caprolactone)/Tween-20 electrospun fibers

Poly(ε-caprolactone) (PCL) is a hydrophobic aliphatic polyester commonly used as a biomaterial due to its cytocompatibility and biodegradability. However, PCL-based materials are hydrophobic and susceptible to bacterial adhesion and proliferation. To address these disadvantages, this study proposes a direct and practical method for functionalizing the surface and enhancing the biological properties of electrospun PCL fibers using Tween-20 surfactant, followed by the deposition of polyelectrolyte multilayers (PEMs). Tween-20, a neutral and cytocompatible surfactant, was directly incorporated into the fibers without prior surface modifications. The surfactant significantly increased the wettability of the PCL fibers, resulting in water contact angles of 0 degrees, facilitating subsequent functionalization with heparin and chitosan PEMs (with 10, 20, and 30 layers). The materials were characterized through scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), water contact angle and mechanical measurements, Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The PEMs remain stable on the fiber surfaces for up to 14 days in a buffer at 37°C. The samples supported high cell viability with no observed cytotoxicity toward human adipose-derived stem cells and no hemolytic activity toward human red blood cells. Antibacterial assays (live/dead and proliferation tests) demonstrated that the coated PCL fibers inhibited the proliferation of Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa). The PEM coatings significantly enhanced the antimicrobial activity, resulting in a high number of damaged and dead bacterial cells attached to the coated fibers. Therefore, the heparin/chitosan PEMs on Tween-20-modified PCL fibers can prevent bacterial infections while supporting viable mammalian cells.

Automated, High-Throughput Screening of Hybrid Elastin-like Polypeptide/Polysaccharide Multilayer Film Deposition.

The self-assembled layer-by-layer technique has attracted a great deal of attention as a method for engineering bio-functional surfaces under mild chemical conditions. The production of multilayer films, starting from newly designed building blocks, may be laborious, considering the inherent limitations for anticipating how minimal changes in the macromolecular composition may impact both film deposition and performance. This paper presents an automated, high-throughput approach to depositing polyelectrolyte multilayers (PEMs) in multiwell plates, enabling the screening of nearly 100 film formulations in the same process. This high-throughput layer-by-layer (HT-LbL) method runs in an affordable, fully commercial platform using Python-coded routines that can be easily adapted for the materials science lab settings. The HT-LbL system was validated by investigating the deposition of polysaccharide-based films in multiwell plates, probing the absorbance signal of ionically stained polyelectrolyte multilayers (PEMs) prepared in one single batch. The HT-LbL method was also used to investigate the deposition of PEMs with a small library of genetically engineered elastin-like polypeptides (ELPs) with different levels of ionizable and hydrophobic amino acid residues. The deposition of ELP/chitosan films was assessed based on the signal of fluorescently labeled species (chitosan or ELP-mCherry), demonstrating that both electrostatic and hydrophobic residues are essential for film buildup. The growth and surface properties of ELP-mCherry/chitosan films also seemed susceptible to the assembly pH, forming a higher film growth and a rougher and more hydrophobic surface for both polyelectrolytes deposited under a low ionization degree. Overall, this study illustrates the challenge of predicting the growth and properties of multilayer films and how the HT-LbL can accelerate the development of multilayer films that demand high levels of testing and optimization.

A Quartz Crystal Microbalance (QCM) Study on the Formation of Aqueous κ-Carrageenan-Chitosan Composite Bilayers with NaCl and Graphene Oxide

Biomaterials and thin biofilms play a fundamental role in the medical, food and pharmaceutical industries. The Quartz crystal microbalance (QCM) measurement technique is one of the attractive techniques which have been used for monitoring the thin-film formation process. In the current work described here, κ-carrageenan and chitosan solutions were used for the layer-by-layer (LBL) deposition of polyelectrolyte multilayers (PEMs) on the gold surface of a 5 MHz AT-cut (thickness-shear mode) quartz crystal in a flow module. A sensitive QCM system was designed to detect 0.1 Hz differences in the resonance frequency (Δf) and 10−7 changes in the energy dissipation (ΔD) values, which are the measures of the deposited mass and the film rigidity, respectively. Negatively charged carrageenan and positively charged chitosan biomolecules in the solutions were used to build up sequential and very thin bilayers on the modified gold surface. The effects of NaCl and graphene oxide (GO) addition on the mass of the deposited films were also investigated. Intermolecular interactions between the biopolymer chains, Na+ cations and GO sheets were explained by interactions between molecules, such as electrostatic forces and hydrogen bondings.

Layer-by-Layer Assembly Monitored by PEDOT-Polyamine-Based Organic Electrochemical Transistors

In this work, we present the fabrication of PEDOT–PAH-based organic electrochemical transistors (OECTs), that are employed to monitor the deposition of polyelectrolyte multilayers on their surface. We first explore different synthesis conditions in order to optimize the electrical characteristics of the devices, such as threshold voltage and voltage of maximum transconductance. Next, the transistors showing the desired features are chosen to investigate the process of the layer-by-layer (LbL) assembly through (i) the analysis of the transfer characteristics curves and (ii) the changes in the registered drain–source current. It is demonstrated that the OECTs are able to monitor the assembly of the different polyelectrolyte layers in real time in both modes of operation, yielding information about conductivity and surface potential changes in the channel. Next, the transient characteristics of the devices are studied upon the assembly of the different layers, providing information about the changes in the ionic transport through the whole film during the ON and OFF switching. Finally, the kinetic response of the OECTs toward the monitoring of charged macromolecules is fitted to a two-step adsorption model and compared against graphene field-effect transistors and surface plasmon resonance. The monitoring of the LbL assembly by the changes in the PEDOT–PAH OECT response illustrates the use of these transistors for sensing interactions with charged species in solution and supports the development of sensing platforms by integration of specific recognition elements on the conducting polymer channel.

Polyelectrolyte-Coated Mesoporous Bioactive Glasses via Layer-by-Layer Deposition for Sustained Co-Delivery of Therapeutic Ions and Drugs.

In the field of bone regeneration, considerable attention has been addressed towards the use of mesoporous bioactive glasses (MBGs), as multifunctional therapeutic platforms for advanced medical devices. In fact, their extremely high exposed surface area and pore volume allow to load and the release of several drugs, while their framework can be enriched with specific therapeutic ions allowing to boost the tissue regeneration. However, due to the open and easily accessible mesopore structure of MBG, the release of the incorporated therapeutic molecules shows an initial burst effect leading to unsuitable release kinetics. Hence, a still open challenge in the design of drug delivery systems based on MBGs is the control of their release behavior. In this work, Layer-by-layer (LbL) deposition of polyelectrolyte multi-layers was exploited as a powerful and versatile technique for coating the surface of Cu-substituted MBG nanoparticles with innovative multifunctional drug delivery systems for co-releasing of therapeutic copper ions (exerting pro-angiogenic and anti-bacterial effects) and an anti-inflammatory drug (ibuprofen). Two different routes were investigated: in the first strategy, chitosan and alginate were assembled by forming the multi-layered surface, and, successively, ibuprofen was loaded by incipient wetness impregnation, while in the second approach, alginate was replaced by ibuprofen, introduced as polyelectrolyte layer. Zeta-potential, TGA and FT-IR spectroscopy were measured after the addition of each polyelectrolyte layer, confirming the occurrence of the stepwise deposition. In addition, the in vitro bioactivity and the ability to modulate the release of the cargo were evaluated. The polyelectrolyte coated-MBGs were proved to retain the peculiar ability to induce hydroxyapatite formation after 7 days of soaking in Simulated Body Fluid. Both copper ions and ibuprofen were co-released over time, showing a sustained release profile up to 14 days and 24 h, respectively, with a significantly lower burst release compared to the bare MBG particles.

Immobilization of osteopontin on poly(ε-caprolactone) scaffolds by polyelectrolyte multilayer deposition to improve the osteogenic differentiation of MC3T3-E1 cells

Immobilization of osteopontin on poly(ε-caprolactone) scaffolds by polyelectrolyte multilayer deposition to improve the osteogenic differentiation of MC3T3-E1 cells

Robust transparent conducting electrode based on silver nanowire coating on polyelectrolytes multilayers

Transparent conductive electrodes were fabricated by the deposition of silver nanowires (AgNW) on various substrates modified by the deposition of polyelectrolyte multilayers (PEM) as primer. The PEM primer films were coated on the glass substrate by the sequential deposition of 7 or 8 layers of poly(diallyl dimethyl ammonium chloride) (PDADMAC) and poly(styrene sulfonate) to improve the adhesion of AgNW and produce flexible transparent conducting electrode. AgNW, with a diameter of 20–30 nm and 10–30 µm in length, were synthesized using a modified solvothermal method using glycerol and poly(vinyl pyrrolidone) as reducing and capping agent. The physicochemical properties of the AgNW coated PEM were characterized using UV–Vis spectroscopy, atomic force microscope and field emission scanning electron microscope. The electrical conductivity of the layer was measured by 4 points probe and a standard scotch tape peeling test was used to investigate the stability of the coated AgNW on the PEM. The PEM 7 layers (with PDADMAC as outer layer) gave the best results to immobilize AgNW with the lowest sheet resistance (14 Ω/square) while maintaining excellent transparency (85% transmission at 550 nm) even after up to 6 peeling test cycles. Finally, to demonstrate the benefit of this method, poly(ethylene terephthalate) sheet was coated with PEM primer and AgNW to produce flexible transparent conducting electrode.

Anomalous Influence of Salt Concentration on Deposition of Poly(l-Lysine)/Cellulose Sulfate Multilayers Evidenced by In Situ ATR-FTIR.

The deposition of polyelectrolyte (PEL) multilayers (PEMs) of poly(l-lysine)/cellulose sulfate (PLL/CS) onto germanium (Ge) substrates depending on salt concentration (cS) and deposition step z at constant PEL concentration cPEL = 0.01 M and pH = 7.0 was studied. In situ ATR-FTIR spectroscopy was used for the quantitative determination of alternate PLL/CS deposition profiles (adsorbed amount versus z) and total deposited PEM amount. By varying cS from 0 M to 1.0 M, a maximum of deposited amount was obtained at 0.1 M, so that both no salinity (0 M) and high salinity (1.0 M) revealed deposited amounts that were far lower than for mean salinity (0.1 M). Furthermore, in situ ATR-FTIR allowed to determine the detailed modulation of the PEL composition during the consecutive PEM deposition, which was interpreted as being due to both diffusion of given PEL from the PEM interior towards the outermost region and release of the PEM upon contact with the bulk oppositely charged PEL solution. Finally, ex situ ATR-FTIR measurements on the PEL solutions after deposition of PEM-20 revealed the distinct release of PEL from the PEM solely for cS = 1.0 M, due to the highest mobility of PEL under high salt conditions. These studies help to prepare functional PEM coatings with defined thicknesses and morphologies for the passivation and activation of material surfaces in the biomedical and food field.

Effect of the Buffer on the Buildup and Stability of Tannic Acid/Collagen Multilayer Films Applied as Antibacterial Coatings.

The deposition of polyelectrolyte multilayers, obtained by the layer-by-layer (LbL) method, is a well-established technology to design biocompatible and antibacterial coatings aimed at preventing implant-associated infections. Several types of LbL films have been reported to exhibit antiadhesive and/or antibacterial (contact-killing or release-killing) properties governed not only by the incorporated compounds but also by their buildup conditions or their postbuildup treatments. Tannic acid (TA), a natural polyphenol, is known to inhibit the growth of several bacterial strains. In this work, we developed TA/collagen (TA/COL) LbL films built in acetate or citrate buffers at pH 4. Surprisingly, the used buffer impacts not only the physicochemical but also the antibacterial properties of the films. When incubated in physiological conditions, both types of TA/COL films released almost the same amount of TA depending on the last layer and showed an antibacterial effect against Staphylococcus aureus only for citrate-built films. Because of their granular topography, TA/COL citrate films exhibited an efficient release-killing effect with no cytotoxicity toward human gingival fibroblasts. Emphasis is put on a comprehensive evaluation of the physicochemical parameters driving the buildup and the antibacterial property of citrate films. Specifically, complexation strengths between TA and COL are different in the presence of the two buffers affecting the LbL deposition. This work constitutes an important step toward the use of polyphenols as an antibacterial agent when incorporated in LbL films.

PDMS membranes modified by polyelectrolyte multilayer deposition to improve OSN separation of diluted solutes in toluene

New functionalized poly(dimethylsiloxane) (PDMS) membranes were prepared by the surface modification of the commercially available PERVAP4060 membrane (Sulzer™) through cold plasma activation followed by the layer-by-layer assembly method. Four different pairs of polyelectrolytes, i.e., poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA), PAH/poly(sodium 4-styrene sulfonate) (PSS), poly(diallyldimethylammonium chloride) (PDDA)/PAA, and PDDA/PSS, were used to coat the PDMS layer by the controlled deposition of successive nanolayers (20–50 nm).PERVAP4060 was systematically modified by the deposition of 10 bilayers of polyelectrolyte pairs. These membranes were characterized by contact angle measurements, scanning electron microscopy (SEM), ellipsometry, and atomic force microscopy (AFM). The nanofiltration membrane performance for the rejection of four diluted solutes—two soluble catalysts 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (R-BINAP) and tetraoctylammonium bromide (ToABr) and two linear aliphatic molecules n-Tetratetracontane (C44H90 or C44) and n-Hexadecane (C16H34 or C16)—was studied in the toluene feed solution at up to 40 bar pressure. It was shown that the organic solvent nanofiltration (OSN) mass transfer properties differ clearly depended on the layer-by-layer chemical structure and the characteristics of the solutes. Thus, the intrinsic permeance of toluene in the PEL multilayers were calculated by applying resistance-in-series model. Despite the highly diluted concentrations of the solutes, i.e., <1 wt% for R-BINAP and ToABr, and the high solvent permeate flux, the ToABr, R-BINAP, and C44 solutes were markedly rejected by all the membranes. ToABr had the highest rejection coefficient, up to 97%. As a trend, higher the polarity of the bilayer assembly, lower was the mass transfer of the solvent compared to that of the pristine membrane. The results indicated that a solution–diffusion mechanism is likely to apply. The best rejection of R-BINAP (up to 88%) was obtained when the membrane was coated with 10 bilayers of PAH/PSS. Thus, these prepared polyelectrolyte (PEL)-modified membranes have potential applications in homogeneous catalysis industry, for example in olefin metathesis for expanding the lifetime of soluble catalysts by separating them at mild OSN condition while ensuring the permeation of products.

The Anomalous Influence of Polyelectrolyte Concentration on the Deposition and Nanostructure of Poly(ethyleneimine)/Poly(acrylic acid) Multilayers.

The deposition and nanostructure of polyelectrolyte (PEL) multilayers (PEMs) of branched poly(ethyleneimine)/poly(acrylic acid) (PEI/PAA) onto silicon substrates was studied in terms of the dependence of pH and the PEL concentration (cPEL) in the individual adsorption steps z. Both a commercial automatic dipping device and a homebuilt automatic stream coating device (flow cell) were used. Gravimetry, SFM, transmission (TRANS) and in situ attenuated total reflection (ATR) FTIR spectroscopy were used for the quantitative determination of the adsorbed amount, thickness, chemical composition and morphology of deposited PEMs, respectively. Firstly, the combination of pH = 10 for PEI and pH = 4 for PAA, where both PEL were predominantly in the neutral state, resulted in an extraordinarily high PEM deposition, while pH combinations, where one PEL component was charged, resulted in a significantly lower PEM deposition. This was attributed to both PEL conformation effects and acid/base interactions between basic PEI and acidic PAA. Secondly, for that pH combination an exponential relationship between PEM thickness and adsorption step z was found. Thirdly, based on the results of three independent methods, the course of the deposited amount of a PEM-10 (z = 10) versus cPEL in the range 0.001 to 0.015 M at pH = 10/4 was non-monotonous showing a pronounced maximum at cPEL = 0.005 M. Analogously, for cPEL = 0.005 M a maximum of roughness and structure size was found. Fourthly, related to that finding, in situ ATR-FTIR measurements gave evidence for the release of outermost located PEI upon PAA immersion (even step) and of outermost PAA upon PEI immersion (odd step) under formation of PEL complexes in solution. These studies help us to prepare PEL-based films with a defined thickness and morphology for interaction with biofluids in the biomedical and food fields.

Optimizing the mechanical properties of papers reinforced with refining and layer-by-layer treated recycled fibers using response surface methodology

Layer-by-layer (LbL) treated recycled fibers were investigated in mixtures with refined pulp relative to the mechanical properties of paper. The LbL treatments were conducted to assemble consecutive cationic and anionic starch layers on the fibers of old corrugated container (OCC) pulp. Fibers zeta potential was measured to examine the success of LbL treatment. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to reveal the differences between treated and untreated fibers surface and network. Subsequently, the LbL-treated fibers were added to the refined OCC pulps. Optimization of paper (60 ± 3 g m-2 basis weight) strength properties including: tensile index, Scott bond (internal bonding), and ring crush test (RCT) was carried out by response surface methodology (RSM). The meaningful change of zeta potential substantiated cationic/anionic starch layers construction. The AFM results showed that the surface of fibers were covered with starch, which was consistent with deposition of polyelectrolyte multi-layers (PEMs). The surfaces of the LbL-treated fibers were rough in comparison with untreated fibers. The optimization of mechanical parameters using RSM indicated that refining time significantly affected the paper’s mechanical properties. The property values of 44.5 N.m/g tensile index, 149 J/m2 Scott bond, 32 mN RCT, and 245% strain at break were achieved at optimal conditions of 16 min refining time and the addition ratio of 17.6% LbL treated pulp respectively.

Advanced fibroblast proliferation inhibition for biocompatible coating by electrostatic layer-by-layer assemblies of heparin and chitosan derivatives

Heparin and different chitosan derivatives were applied to produce stable electrostatic layer-by-layer assemblies and further used as coating technique to inhibit natural inflammatory response to implants. Heparin was assembled with chitosan and N-methylated chitosan derivatives, namely N,N-dimethyl chitosan (DMC) and N,N,N-trimethyl chitosan (TMC), by dipping method. DMC and TMC (chitosan derivatives) were synthesized and characterized before LbL assembly. Ellipsometry, quartz crystal microbalance (QCM-D), and contact angle were used to demonstrate the deposition of polyelectrolyte multilayers onto silicon wafers using polyelectrolyte solutions with different ionic strength. The biological properties of these films were evaluated by cell culture assays using NIH/3T3 fibroblast cells. LbL assemblies of Heparin and chitosan derivatives showed to be biocompatible, and at the same time they strongly hinder the proliferation speed of fibroblasts up to 40-fold factors. Therefore, the multilayers prepared from heparin and chitosan derivatives have good features to be used as an alternative coating treatment for biomedical implants with reduced body rejection properties.

Polyelectrolyte multilayer-calcium phosphate composite coatings for metal implants.

The preparation of organic-inorganic composite coatings with the purpose to increase the bioactivity of bioinert metal implants was investigated. As substrates, glass plates and rough titanium surfaces (Ti-SLA) were employed. The method comprises the deposition of polyelectrolyte multilayers (PEMLs) followed by immersion of the coated substrate into a calcifying solution of low supersaturation (MCS). Single or mixed PEMLs were constructed from poly-L-lysine (PLL) alternating with poly-L-glutamate, (PGA), poly-L-aspartate (PAA), and/or chondroitin sulfate (CS). ATR-FTIR spectra reveal that (PLL/PGA)10 multilayers and mixed multilayers with a (PLL/PGA)5 base contain intermolecular β-sheet structures, which are absent in pure (PLL/PAA)10 and (PLL/CS)10 assemblies. All PEML coatings had a grainy topography with aggregate sizes and size distributions increasing in the order: (PLL/PGA)n < (PLL/PAA)n < (PLL/CS)n. In mixed multilayers with a (PLL/PGA)n base and a (PLL/PAA)n or (PLL/CS)n top, the aggregate sizes were greatly reduced. The PEMLs promoted calcium phosphate nucleation and early crystal growth, the intensity of the effect depending on the composition of the terminal layer(s) of the polymer. In contrast, crystal morphology and structure depended on the supersaturation, pH, and ionic strength of the MCS, rather than on the composition of the organic matrix. Crystals grown on both uncoated and coated substrates were mostly platelets of calcium deficient carbonate apatite, with the Ca/P ratio depending on the precipitation conditions.

Galactosylated electrospun membranes for hepatocyte sandwich culture

In this work, we developed a galactocylated electrospun polyurethane membrane for sandwich culture of hepatocyte sandwich culture. The electrospun fibrous membranes were bio-functionalized with galactose molecules by a UV-crosslinked layer-by-layer polyelectrolyte multilayer deposition technique. The galactosylated electrospun membranes were employed as a top support membrane for the sandwich culture of HepG2/C3A cells on a collagen substrate. Our results demonstrate that HepG2/C3A cells covered by the galactosylated PU membranes form multi-cellular aggregates and lead to improved albumin secretion ability compared to the control membranes (unmodified PU or poly(ethylene imine)-modified PU). Our study reveals the potential of galactosylated electrospun membranes in the application of liver tissue engineering and the regeneration of liver-tissue substitutes.

Polyelectrolyte Multilayers Deposition on Nitinol Modified by In Situ Generated Diazonium in Gentle Conditions

This work is an investigation of the electrografting of in situ generated 4-sulfonic acid phenyldiazonium salt (PD-SO3H) on Nitinol followed by layer-by-layer (LBL) deposition of polyelectrolyte (chitosan and alginate) multilayers (PEM). Nitinol is interesting for many biomedical applications. A great deal of attention has thus been paid to its surface modification in order to impart and/or improve its surface properties. This can be achieved using PEM deposition which requires an adhesion promoter i.e. PD-SO3H in this work. Results show the successful electrografting of PD-SO3H and the preservation of the TiO2 surface layer (which provides its biocompatibility to Nitinol) allowed by the gentle conditions used for the in situ generation. Nitinol corrosion resistance has been shown to be preserved. Based on XPS analysis, PD-SO3H has been shown to be grafted in its deprotonated form and hypothesis of C-O-M and C-N=N-O-M covalent bonds formation between the grafted layer and the Nitinol surface could be made. It can therefore act effectively as adhesion promoter for PEM deposition as confirmed by the deposition, accumulation and alternation of the deposited chitosan and alginate layers. PEM further improve Nitinol corrosion resistance and its resulting hydrophilicity has been shown to be controlled by the last deposited layer.

Catalytic Polyelectrolyte Multilayers at the Bipolar Membrane Interface

Bipolar membranes are laminated anion and cation exchange membranes that split water at their interface very efficiently upon application of an electric field. This paper investigates the layer-by-layer (LbL) deposition of polyelectrolyte multilayers, as a tool to introduce molecularly thin catalyst groups at this interface of bipolar membranes. The bipolar membranes were prepared by first modifying an anion exchange membrane by consecutive dipping LbL assembly, then casting a thin highly charged intermediate layer followed by casting a cation exchange layer. The results reveal that polyelectrolytes of higher charge density coated on the anion exchange layer yield better performance. Several parameters of the LbL interface deposition were varied. Out of the investigated LbL assembly parameters, ionic strength and number of layers have shown the largest influence on catalytic activity as well as ionic selectivity. The membrane with two bilayers of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and poly(ethyleneimine) (PEI), where the PEI was prepared in 0.5 M NaCl, gave rise to the best performance. Surprisingly, detailed data analysis at low electrical potential suggests that the interface layers of a bipolar membrane play a major role in its permselectivity. Previously, only the bulk thickness of the anion and cation exchange membrane was assumed to influence the bipolar membrane selectivity.

Chitosan and Alginate Layer-by-Layer Assembly on Phynox (Co-Cr Alloy) Surface Modified by Alkylcarboxylicammoniumphosphonate Derivatives

Phynox is an austenitic cobalt-chromium alloy that presents a great variety of properties (such as good fatigue strength, resistance to corrosion and high passivity in contact with human tissues) that makes Phynox interesting where high mechanical performances are required for applications (such as springs in watch motors, aeronautical equipments, …) and for biomedical applications. This work aims to study the deposition of polyelectrolyte multilayer (i.e. chitosan and alginate) on modified Phynox substrates and more specifically to compare different pathways for the deposition of the first chitosan layer. After the synthesis and the grafting of 11-methylundecanoateammoniumphosphonate (or NPCOOMe), the first chitosan layer has been deposited either by ionic interactions or by a covalent grafting via an amidation reaction (under conventional and induction heating) with the monolayer present on the modified Phynox substrate. The amidation reaction under induction heating leads to the grafting of a higher amount of chitosan. Finally, the feasibility of successive polyelectrolyte multilayer deposition has been demonstrated.

Simultaneous improvement of the monovalent anion selectivity and antifouling properties of an anion exchange membrane in an electrodialysis process, using polyelectrolyte multilayer deposition

Selectivity for monovalent anions is very important property of anion exchange membranes (AEMs) for making drinking water along with high antifouling property. Generally, standard AEMs show higher selectivity for multivalent anions than monovalent anions. We simultaneously improved the monovalent anion selectivity and antifouling potential of standard AEMs in electrodialysis using layer-by-layer (LbL). Poly(sodium 4-styrene sulfonate) (PSS) was used as a polyanion, with poly(allylamine hydrochloride) as a polycation. The monovalent anion selectivity was evaluated using the transport number ratio between sulfate and chloride ions. The antifouling potential of the AEMs was evaluated using the time elapsed before the onset of fouling using sodium dodecilbenzene sulfonate as a foulant. The monovalent anion selectivity of the PSS-top-layer membrane improved with the number of layers. This was attributed to the increase in the total excess negative charge within the LbL layers. The antifouling potential was also improved by the LbL deposition, although the optimum condition was different from that for the monovalent anion selectivity. This was attributed to the increased hydrophilicity and the negatively charged membrane surface. Modified AEMs with an odd number of LbL layers (PSS top layer) above 15 had sufficient monovalent anion selectivity for practical use, and showed high antifouling potential.

Layer-by-Layer Surface Modification of Fruits with Edible Nano-Coatings

A new method for the surface modification of the surface of fruits based on the Layer-by-Layer (LbL) deposition of polyelectrolyte multilayers (PEM) is presented. Mangoes fruits were coated by sequential dipping in solutions of either Poly(diallyldimethylammonium chloride), (PDADMAC) or Poly(styrene sulfonate sodium salt) (PSS). After the deposition of only few polyelectrolyte layers, the skin of the fruits was changed from hydrophobic to hydrophilic as shown by contact angles measurements decreasing from 90 to 10. Fourier transform infrared spectroscopy (FTIR) was used to confirm the deposition of the PEM coating on the fruit which was then used as a matrix to load curcumin as model compound. Ultraviolet Visible (UV-Vis) spectroscopy was used to evaluate the amount of a curcumin loaded on the fruit surface as a function of the thickness of the film by indirect leaching in ethanol. This coating method provides a new approach to dope active compound on the fruit surface such as anti-oxidant, fragrance, color and other nutriment which could increase the market value of fruits.