Pyridylamino‐β‐cyclodextrin as a Molecular Chaperone for Lipopolysaccharide Embedded in a Multilayered Polyelectrolyte Architecture

Layer‐by‐layer self‐assembled polyelectrolyte films containing a charged cyclodextrin and lipopolysaccharide (LPS) are developed for the first time as a potential model for local endotoxin antagonist delivery. We have examined the biological activity of a lipopolysaccharide from E. coli incorporated into multilayered architectures made of poly‐(L ‐lysine) and poly‐(L ‐glutamic acid). Used in such build‐ups, a polycationic cyclodextrin, heptakis(6‐deoxy‐6‐pyridylamino)‐β‐cyclodextrin showed molecular chaperone properties by enabling restoration of the LPS biological activity whenever lost upon interaction with poly‐(L ‐lysine).     

Primary Cell Adhesion on RGD‐Functionalized and Covalently Crosslinked Thin Polyelectrolyte Multilayer Films

Polyelectrolyte multilayers (PEMs) are now widely used for biomedical applications. In this work, we investigated the primary osteoblast adhesion properties of PEMs of poly(L ‐lysine) (PLL), poly(L ‐glutamic acid) (PGA), poly(alginic acid) (Palg), and poly(galacturonic acid) (Pgal). In order to compensate for the poor adhesion of the as‐synthesized films, two kinds of film modifications were achieved: a purely physical modification by film crosslinking, and a chemical modification by grafting a arginine–glycine–aspartic acid (RGD) peptide to PGA. Crosslinking was performed using a water‐soluble carbodiimide in combination with N‐hydroxysulfosuccinimide (sulfo‐NHS) to induce amide formation. This reaction was followed by Fourier‐transform IR spectroscopy. For film functionalization, a 15‐amino‐acid peptide was grafted to PGA and deposited as the top layer of the film. PLL/PGA, PLL/Palg, and PLL/Pgal films were crosslinked or functionalized. The films were tested for both short‐term adhesion properties and long‐term proliferation of primary osteoblasts. Whereas the effect of film crosslinking on short‐term adhesion was moderate, it was much more important for the RGD‐functionalized films. On the other hand, the long‐term proliferation was the same or even higher for the crosslinked films as compared with the functionalized films. This effect was particularly enhanced for the PLL/Palg and PLL/Pgal films. Finally, we functionalized PLL/PGA that had been crosslinked prior to PGA‐RGD deposition. These architectures exhibited even higher short‐term adhesion and proliferation. These results clearly show the important role of the physical properties of the films, besides their chemical properties, for the modulation of primary cell‐adhesion behavior.     

Biofunctional Polyelectrolyte Multilayers and Microcapsules: Control of Non‐Specific and Bio‐Specific Protein Adsorption

Layers of the polyelectrolytes poly(allylamine hydrochloride) (PAH, polycationic) and poly(styrene sulfonate) (PSS, polyanionic) are consecutively adsorbed on flat silicon oxide surfaces, forming stable, ultrathin multilayer films. Subsequently, a final monolayer of the polycationic copolymer poly(L ‐lysine)‐graft‐poly(ethylene glycol) (PLL‐g‐PEG) is adsorbed onto the PSS‐terminated multilayer in order to impart protein resistance to the surface. The growth of each of the polyelectrolyte layers and the protein resistance of the resulting [PAH/PPS]_n(PLL‐g‐PEG) multilayer (n = 1–4) are followed quantitatively ex situ using X‐ray photoelectron spectroscopy and in situ using real‐time optical‐waveguide lightmode spectroscopy. In a second approach, the same type of [PAH/PSS]_n(PLL‐g‐PEG) multilayer coatings are successfully formed on the surface of colloidal particles in order to produce surface‐functionalized, hollow microcapsules after dissolution of the core materials (melamine formaldehyde (MF) and poly(lactic acid) (PLA; colloid diameters: 1.2–20 μm). Microelectrophoresis and confocal laser scanning microscopy are used to study multilayer formation on the colloids and protein resistance of the final capsule. The quality of the PLL‐g‐PEG layer on the microcapsules depends on both the type of core material and the dissolution protocols used. The greatest protein resistance is achieved using PLA cores and coating the polyelectrolyte microcapsules with PLL‐g‐PEG after dissolution of the cores. Protein adsorption from full serum on [PAH/PPS]_n(PLL‐g‐PEG) multilayers (on both flat substrates and microcapsules) decreases by three orders of magnitude in comparison to the standard [PAH/PPS]_n layer. Finally, biofunctional capsules of the type [PAH/PPS]_n(PLL‐g‐PEG/PEG‐biotin) (top copolymer layer with a fraction of the PEG chains end‐functionalized with biotin) are produced which allow for specific recognition and immobilization of controlled amounts of streptavidin at the surface of the capsules. Biofunctional multilayer films and capsules are believed to have a potential for future applications as novel platforms for biotechnological applications such as biosensors and carriers for targeted drug delivery.     

Targeting of Cancer Cells Using Quantum Dot–Polypeptide Hybrid Assemblies That Function as Molecular Imaging Agents and Carrier Systems

A highly tunable quantum dot (QD)–polypeptide hybrid assembly system with potential uses for both molecular imaging and delivery of biomolecular cargo to cancer cells is reported. The tunability of the assembly system, its application for imaging cancer cells, and its ability to carry a biomolecule are demonstrated. The assemblies are formed through the self‐assembly of carboxyl‐functionalized QDs and poly(diethylene glycol‐L ‐lysine)‐poly(L ‐lysine) (PEGLL‐PLL) diblock copolypeptide molecules, and they are modified with peptide ligands containing a cyclic arginine‐glycine‐aspartate [c(RGD)] motif that has affinity for αvβ3 and αvβ5 integrins overexpressed on the tumor vasculature. To illustrate the tunability of the QD‐polypeptide assembly system, it is shown that binding to U87MG glioblastoma cells can be modulated and optimized by changing either the conditions under which the assemblies are formed or the relative lengths of the PEGLL and PLL blocks in the PEGLL‐PLL molecules. The optimized c(RGD)‐modified assemblies bind integrin receptors on U87MG cells and are endocytosed, as demonstrated by flow cytometry and live‐cell imaging. Binding specificity is confirmed by competition with an excess of free c(RGD) peptide. Finally, it is shown that the QD–polypeptide assemblies can be loaded with fluorescently labeled ovalbumin, as a proof‐of‐concept for their potential use in biomolecule delivery.     

Build‐up of Polypeptide Multilayer Coatings with Anti‐Inflammatory Properties Based on the Embedding of Piroxicam–Cyclodextrin Complexes

We describe the build‐up of biomaterial coatings based on polypeptide multilayers possessing anti‐inflammatory properties. Poly(L ‐lysine) (PLL) and poly(L ‐glutamic acid) (PGA) are used as polypeptides, and piroxicam (Px) is used as the anti‐inflammatory agent. In order to embed high enough amounts of Px, the drug is incorporated in the films in the form of complexes with a charged 6^A‐carboxymethylthio‐β‐cyclodextrin (cCD). It is shown that this cyclodextrin can solubilize higher amounts of Px than the cyclodextrins used commercially. The anti‐inflammatory properties are evaluated by determining the inhibition of TNFα production by human monocytic THP‐1 cells stimulated with lipopolysaccharide (LPS) bacterial endotoxin. Using Fourier‐transform (FT) Raman spectroscopy, we show that Px is mainly in the neutral form in cCD–Px complexes in solution, and that it remains biologically active under this form, whereas up to now only the zwitterionic form was reported to possess anti‐inflammatory properties. When incorporated in PLL/PGA multilayers, Px in the cCD–Px complexes changes from the neutral to the zwitterionic form. It is shown that these films present anti‐inflammatory properties, which can be delayed, and whose duration can be tuned by changing the film architecture.     

Charge‐Reversal Drug Conjugate for Targeted Cancer Cell Nuclear Drug Delivery

DNA‐toxin anticancer drugs target nuclear DNA or its associated enzymes to elicit their pharmaceutical effects, but cancer cells have not only membrane‐associated but also many intracellular drug‐resistance mechanisms that limit their nuclear localization. Thus, delivering such drugs directly to the nucleus would bypass the drug‐resistance barriers. The cationic polymer poly(L ‐lysine) (PLL) is capable of nuclear localization and may be used as a drug carrier for nuclear drug delivery, but its cationic charges make it toxic and cause problems in in‐vivo applications. Herein, PLL is used to demonstrate a pH‐triggered charge‐reversal carrier to solve this problem. PLL's primary amines are amidized as acid‐labile β‐carboxylic amides (PLL/amide). The negatively charged PLL/amide has a very low toxicity and low interaction with cells and, therefore, may be used in vivo. But once in cancer cells' acidic lysosomes, the acid‐labile amides hydrolyze into primary amines. The regenerated PLL escapes from the lysosomes and traverses into the nucleus. A cancer‐cell targeted nuclear‐localization polymer–drug conjugate has, thereby, been developed by introducing folic‐acid targeting groups and an anticancer drug camptothecin (CPT) to PLL/amide (FA‐PLL/amide‐CPT). The conjugate efficiently enters folate‐receptor overexpressing cancer cells and traverses to their nuclei. The CPT conjugated to the carrier by intracellular cleavable disulfide bonds shows much improved cytotoxicity.     

Controlled Electrodissolution of Polyelectrolyte Multilayers: A Platform Technology Towards the Surface‐Initiated Delivery of Drugs

A novel method for the electrochemical dissolution of polyelectrolyte multilayers from the surface of an electrode for applications in controlled drug delivery is reported. Biodegradable and biocompatible multilayer films based on poly(L ‐lysine) and heparin have been selected as a model system, and have been built on an indium tin oxide semiconductor substrate. The build‐up and dissolution processes of the multilayers is followed by electrochemical optical waveguide light mode spectroscopy. The formation and stability of the polyelectrolyte multilayers have been found to depend on the applied potential and the ionic strength of the buffer. The application of potentials above a threshold of 1.8 V induces dissolution, which follows single‐exponential kinetics, of the polyelectrolyte multilayer film. The rate of this process can be varied by an on–off profile of the potential, leading to the controlled release of heparin into the bulk. Atomic force microscopy investigations show that the electrodissolution of the polyelectrolyte multilayers is a local phenomenon that leads to the formation of nanoporous films.     

Ultrathin Single Bilayer Separation Membranes Based on Hyperbranched Sulfonated Poly(aryleneoxindole)

The layer‐by‐layer method is an attractive technique for the fabrication of ultrathin nanostructured polyelectrolyte multilayer membranes (PEMM). A simple two‐step procedure is described here for the preparation of an ultrathin, nanostructured membrane comprising a 5–7 nm thick selective layer, consisting only of one single bilayer of poly(diallyldimethylammoniumchloride) and hyperbranched sulfonated poly(aryleneoxindole). These single bilayered membranes exhibit an outstanding solvent‐resistant nanofiltration performance, which is superior to that of commercial membranes as well as to previously reported multilayer membranes having 10–20 bilayers. A comparative study between hyperbranched polyelectrolyte (HPE) and linear polyelectrolyte supports the role of the specific 3D structure of the hyperbranched polyelectrolyte in these excellent separation properties. The work thus encompasses the use of HPEs as an ideal choice for PEMMs, which opens up a new route to significantly decrease the overall membrane preparation time while realizing excellent filtration properties.     

VEGF‐Functionalized Polyelectrolyte Multilayers as Proangiogenic Prosthetic Coatings

Stimulation of transprosthetic vascularization represents an interesting strategy in implantology to allow rapid tissue integration and finally to avoid prosthetic rejection. To achieve this goal, we modified the surface of porous titanium implants with polyelectrolyte multilayer (PEM) films functionalized with vascular endothelial growth factor (VEGF). Among the two PEM systems investigated, poly(L‐lysine)/poly(L‐glutamic acid) (PLL/PGA) and poly(allylamine hydrochloride)/poly(sodium 4‐styrenesulfonate) (PAH/PSS), the (PAH/PSS)₄ architecture was selected to functionalize porous titanium, both for its high efficiency to adsorb VEGF and for its biocompatibility toward endothelial cells. In an original way, we unambiguously demonstrated that VEGF adsorbed on (PAH/PSS)₄ maintains its bioactivity in vitro and stimulates endothelial cells proliferation. This effect was correlated with specific activation of intracellular signaling pathways induced by successive phosphorylation of the endothelial VEGF receptor VEGFR2 and mitogen‐activated protein kinases (MAPK) ERK1/2. By clearly demonstrating the proangiogenic activity of the VEGF‐PEM coating in vitro, the present study constitutes a first step toward in vivo application.     

Designing a New Generation of Proton‐Exchange Membranes Using Layer‐by‐Layer Deposition of Polyelectrolytes

All fuel cells utilizing the membrane‐electrode assembly have their ion‐conductive membrane sandwiched between bipolar plates. Unfortunately, applying conventional techniques to isolated polyelectrolyte membranes is challenging and difficult. A more practical alternative is to use the layer‐by‐layer assembly technique to fabricate a membrane‐electrode assembly that is technologically relatively simple, economic, and robust. The process presented here paves the way to fabricate ion‐conductive membranes tailored for optimum performance in terms of controlled thickness, structural morphology, and catalyst loading. Composite membranes are constructed through the layered assembly of ionically conductive multilayer thin films atop a porous polycarbonate membrane. Under ambient conditions, a fuel cell using a poly(ethylene oxide)/poly(acrylic acid) (PEO/PAA) composite membrane delivers a maximum power density of 16.5 mW cm^–2 at a relative humidity of 55 %, which is close to that of some commercial fuel cells operating under the same conditions. Further optimization of these systems may lead to new, ultrathin, flexible fuel cells for portable power and micropower applications.     

Self‐Defensive Biomaterial Coating Against Bacteria and Yeasts: Polysaccharide Multilayer Film with Embedded Antimicrobial Peptide

Prevention of pathogen colonization of medical implants is a major medical and financial issue since infection by microorganisms constitutes one of the most serious complications after surgery or critical care. Immobilization of antimicrobial molecules on biomaterials surfaces is an efficient approach to prevent biofilm formation. Herein, the first self‐defensive coating against both bacteria and yeasts is reported, where the release of the antimicrobial peptide is triggered by enzymatic degradation of the film due to the pathogens themselves. Biocompatible and biodegradable polysaccharide multilayer films based on functionalized hyaluronic acid by cateslytin (CTL), an endogenous host‐defensive antimicrobial peptide, and chitosan (HA‐CTL‐C/CHI) are deposited on a planar surface with the aim of designing both antibacterial and antifungal coating. After 24 h of incubation, HA‐CTL‐C/CHI films fully inhibit the development of Gram‐positive Staphylococcus aureus bacteria and Candida albicans yeasts, which are common and virulent pathogens agents encountered in care‐associated diseases. Hyaluronidase, secreted by the pathogens, leads to the film degradation and the antimicrobial action of the peptide. Furthermore, the limited fibroblasts adhesion, without cytotoxicity, on HA‐CTL‐C/CHI films highlights a medically relevant application to prevent infections on catheters or tracheal tubes where fibrous tissue encapsulation is undesirable.     

Enhanced Electrochromism with Rapid Growth Layer‐by‐Layer Assembly of Polyelectrolyte Complexes

In this work, a facile method to deposit fast growing electrochromic multilayer films with enhanced electrochemical properties using layer‐by‐layer (LbL) self‐assembly of complex polyelectrolyte is demonstrated. Two linear polymers, poly(acrylic acid) (PAA) and polyethylenimine (PEI), are used to formulate stable complexes under specific pH to prepare polyaniline (PANI)/PAA‐PEI multilayer films via LbL deposition. By introducing polymeric complexes as building blocks, [PANI/PAA‐PEI]_n films grow much faster compared with [PANI/PAA]_n films, which are deposited under the same condition. Unlike the compact [PANI/PAA]_n films, [PANI/PAA‐PEI]_n films exhibit porous structure that is beneficial to the electrochemical process and leads to improved electrochromic properties. An enhanced optical modulation of 30% is achieved with [PANI/PAA‐PEI]₃₀ films at 630 nm compared with the lower optical modulation of 11% measured from [PANI/PAA]₃₀ films. The switching time of [PANI/PAA‐PEI]₃₀ films is only half of that of [PANI/PAA]₃₀ films, which indicates a faster redox process. Utilizing polyelectrolyte complexes as building blocks is a promising approach to prepare fast growing LbL films for high performance electrochemical device applications.     

Sol‐Gel/Polyelectrolyte Active Corrosion Protection System

This work presents a new type of feed‐back active coating with inhibitor‐containing reservoirs for corrosion protection of metallic substrates. The reservoirs are composed of stratified layers of oppositely charged polyelectrolytes deposited on AA2024 aluminum alloy coated with hybrid sol‐gel film. The layer‐by‐layer assembled polyelectrolyte film with the entrapped corrosion inhibitor is constructed by sequential spray‐coating deposition of water solutions of poly(ethyleneimine), poly(sodium styrenesulfonate) and 8‐hydroxyquiniline on the top of the sol‐gel coating. The active corrosion protection of AA2024 alloy coated with SiO₂/ZrO₂ sol‐gel film and modified by polyelectrolytes is demonstrated by electrochemical impedance spectroscopy and scanning vibrating electrode technique. The results obtained here show that polyelectrolyte films deposited atop of the hybrid sol‐gel coating on AA2024 alloy remarkably improve the long‐term protection performance providing additional “intelligent” anticorrosion effect that results from delivery of inhibiting species “on demand”. This becomes possible since the configuration of the polyelectrolyte molecules depends on the presence of H⁺ ions making the polyelectrolyte film sensitive to the pH of the surrounding solution. The source of local pH changes is the corrosion process starting in the micro‐ and nano‐defects leading to increased permeability of the polyelectrolyte reservoir and, consequently, to controllable release of entrapped inhibitor.     

Pseudobilayer Vesicle Formation via Layer‐by‐Layer Assembly of Hydrophobically Modified Polymers on Sacrificial Substrates

A bilayer of a hydrophobically modified polyelectrolyte, octadecyl poly(acrylamide) (PAAm), sandwiched between the layers of a hydrophilic polyelectrolyte, poly(ethyleneimine) (PEI), is prepared by the sequential electrostatic–hydrophobic–electrostatic‐interaction‐driven self‐assembly on planar and colloid substrates. This process results in a PEI/[PAAm]₂/PEI‐multilayer‐coated substrate. The removal of a PAA/PEI/[PAAm]₂/PEI‐multilayer‐coated decomposable colloidal template produces hollow capsules. Irregular hydrophobic domains of the [PAAm]₂ bilayer in the PEI/[PAAm]₂/PEI‐multilayer capsule are infiltrated with a lipid to obtain a uniform, distinct hydrophobic layer, imparting the capsule with a pseudobilayer vesicle structure.     

Self‐Healing Actuating Adhesive Based on Polyelectrolyte Multilayers

Creating actuators capable of mechanical motion in response to external stimuli is a key for design and preparation of smart materials. The lifetime of such materials is limited by their eventual wear. Here, self‐healable and adhesive actuating materials are demonstrated by taking advantage of the solvent responsive of weak polyelectrolyte multilayers consisting of branched poly(ethylenimine)/poly(acrylic acid) (BPEI/PAA). BPEI/PAA multilayers are dehydrated and contract upon contact with organic solvent and become sticky when wetted with water. By constructing an asymmetric heterostructure consisting of a responsive BPEI/PAA multilayer block and a nonresponsive component through either layer‐by‐layer assembly or the paste‐to‐curl process, smart films that actuate upon exposure to alcohol are realized. The curl degree, defined as degrees from horizontal that the actuated material reaches, can be as high as ≈228.9°. With evaporation of the ethanol, the curled film returns to its initial state, and water triggers fast self‐healing extends the actuator's lifetime. Meanwhile, the adhesive nature of the wet material allows it to be attached to various substrates for possible combination with hydrophobic functional surfaces and/or applications in biological environments. This self‐healable adhesive for controlled fast actuation represents a considerable advance in polyelectrolyte multilayers for design and fabrication of robust smart advanced materials.     

Multifunctional Graphene–PEDOT Microelectrodes for On‐Chip Manipulation of Human Mesenchymal Stem Cells

All‐solution‐processed multifunctional organic bioelectronics composed of reduced graphene oxide (rGO) and dexamethasone 21‐phosphate disodium salt (DEX)‐loaded poly(3,4‐ethylenedioxythiophene) (PEDOT) microelectrode arrays on indium tin oxide glass are reported. They can be used to manipulate the differentiation of human mesenchymal stem cells (hMSCs). In the devices, the rGO material functions as an adhesive coating to promote the adhesion and alignment of hMSC cells and to accelerate their osteogenic differentiation. The poly(L ‐lysine‐graft‐ethylene glycol) (PLL‐g‐PEG)‐coated PEDOT electrodes serve as electroactive drug‐releasing electrodes. In addition, the corresponding three‐zone parallel devices operate as efficient drug‐releasing components through spatial‐temporal control of the release of the drug DEX from the PEDOT matrix. Such devices can be used for long‐term cell culturing and controlled differentiation of hMSCs through electrical stimulation.     

General Photo‐Patterning of Polyelectrolyte Thin Films via Efficient Ionic Bis(Fluorinated Phenyl Azide) Photo‐Crosslinkers and their Post‐Deposition Modification

We have extended the well known bisfluorinated(phenyl azide) (bisFPA) methodology to develop an ionic bisFPA process suitable for photo‐crosslinking a wide variety of polyelectrolyte thin films. The crosslinking efficiencies (0.1–1.0 crosslink per photo‐reaction) are sufficiently high for the gel fraction to exceed 80 % for crosslinker concentrations of only a few weight %. This method is based on the photo‐induced formation of singlet nitrenes from FPAs and their insertion into unactivated C–H or other bonds, which thus general and not dependent on the presence of specific chemical functional groups. By derivatizing with ionic charge groups, we obtained ionic bisFPAs that can be properly dispersed into polyelectrolyte thin films. The sorbed moisture always present in these films however severely limits the photo‐crosslinking efficiency, apparently through nitrene protonation and intersystem crossing. This can be avoided by dehydration of the films, in some cases, to 130 °C for 10 min in nitrogen before photo‐exposure. We found that efficient photo‐crosslinking can then be achieved for polyelectrolytes even when they have nucleophilic groups. These include poly(styrenesulfonic acid) and their salts, poly(acrylic acid) and their salts, poly(dimethyldiallylammonium salts), as well as the electrically‐conducting poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonic acid) complex (PEDT:PSSH). We further demonstrate using this ionic bisFPA methodology both photo‐patterning and post‐deposition chemical modifications of polyelectrolyte thin films. This opens broad new possibilities in membrane, sensor and actuator technologies, as well as for organic semiconductor plastic electronics (such as field‐effect transistors) and polyelectrolyte‐based devices.     

Surface‐Engineered Nanocontainers for Entrapment of Corrosion Inhibitors

The release properties and reloading ability of polyelectrolyte‐modified halloysite nanotubes, polyelectrolyte‐modified SiO₂ nanoparticles, and polyelectrolyte capsules are studied. Three containers are distinguished by keeping the low‐molecular‐weight corrosion inhibitor benzotriazole in a hollow lumen inside or within the polyelectrolyte matrix and allowing release in either one direction or into all space dimensions. Polyelectrolyte shells, which modify the outer surface of the nanocontainers, are fabricated by using layer‐by‐layer assembly of poly(diallyldimethylammonium chloride)/poly(styrene sulfonate), poly(allylamine hydrochloride)/poly(styrene sulfonate), and poly(allylamine hydrochloride)/poly(methacrylic acid) polyelectrolyte bilayers. All nanocontainers reveal an increase of the benzotriazole release in aqueous solution at alkaline or acidic pH. The highest reloading efficiency (up to 80 %) is observed for halloysite‐based nanocontainers; however, after five reloading cycles the efficiency decreases to 20 %. The application of appropriate nanocontainers depends on the demands required from feedback‐active anticorrosion coatings. For coatings where the immediate release of the inhibitor is necessary, SiO₂‐based or halloysite‐based nanocontainers with a shell consisting of weak polyelectrolytes are preferable. When continuous, gradual release is required, halloysite‐based nanocontainers with a shell consisting of one weak and one or two strong polyelectrolytes are preferable.     

Preparation and Organization of Nanoscale Polyelectrolyte‐Coated Gold Nanoparticles

The layer‐by‐layer (LbL) desposition of oppositely charged polyelectrolytes from adsorption solutions of different ionic strength onto ～7 nm diameter carboxylic acid‐derivatized gold nanoparticles has been studied. The polyelectrolyte‐modified nanoparticles were characterized by UV‐vis spectrophotometry, microelectrophoresis, analytical ultracentrifugation, and transmission electron microscopy. UV‐vis data showed that the peak plasmon absorption wavelength of the gold nanoparticles red‐shifted after each adsorption step, and microelectrophoresis experiments revealed a reversal in the surface charge of the nanoparticles following deposition of each layer. These data are consistent with the formation of polyelectrolyte layers on the nanoparticles. Analytical ultracentrifugation showed an increase in mean nanoparticle diameter on adsorption of the polyelectrolytes, confirming the formation of gold‐core/polyelectrolyte‐shell nanoparticles. Transmission electron microscopy studies showed no signs of aggregation of the polyelectrolyte‐coated nanoparticles. The adsorption of the polyelectrolyte‐coated gold nanoparticles onto oppositely charged planar supports has also been examined. UV‐vis spectrophotometry and atomic force microscopy showed increased amounts of nanoparticles were adsorbed with increasing ionic strength of the nanoparticle dispersions. This allows control of the nanoparticle surface loading by varying the salt content in the nanoparticle dispersions used for adsorption. The LbL strategy used in this work is expected to be applicable to other nanoparticles (e.g., semiconductors, phosphors), thus providing a facile means for their controlled surface modification through polyelectrolyte nanolayering. Such nanoparticles are envisaged to have applications in the biomedical and bioanalytical fields, and to be useful building blocks for the creation of advanced nanoparticle‐based films.     

Incorporation of a Hydrophobic Antibacterial Peptide into Amphiphilic Polyelectrolyte Multilayers: A Bioinspired Approach to Prepare Biocidal Thin Coatings

A non‐water‐soluble natural antibacterial peptide, gramicidin A, has been successfully incorporated into polyelectrolyte assemblies to elaborate biocidal thin films. For this, we used a double strategy, the first step of which consists of complexing the peptide by a non‐denaturing anionic amphiphilic polysaccharide, namely a hydrophobically modified carboxymethylpullulan. We demonstrate that the use of this amphiphilic anionic derivative allows to efficiently solubilize the peptide in aqueous solution, without denaturation. The amount of peptide solubilized by the amphiphilic polysaccharide was optimized by systematically varying the hydrophobicity and the molar mass of the CMP derivative. In a second step, the negatively charged complex was layer‐by‐layer assembled with cationic poly(L‐lysine) to form biofunctionalized thin films. The amount of peptide incorporated in the multilayers was controlled by changing the number of deposited complex layers, and was quantified by UV spectroscopy. The antibacterial activity of the resulting biofunctionalized films was evidenced against a gram‐positive bacterium, E. faecalis. We demonstrated that the biocidal activity resulted from a double mechanism: contact between bacteria and the film surface, and release of the peptide into the solution surrounding the film. We also showed that the peptide was not completely removed from the film after rinsing, which insured preservation of the biocidal activity of the film surface.