Quantitative Nanomechanical Properties of Multilayer Films Made of Polysaccharides through Spray Assisted Layer-by-Layer Assembly.

Nanomechanical properties of alginate/chitosan (Alg/Chi) multilayer films, obtained through spray assisted layer-by-layer assembly, were studied by means of PeakForce quantitative nanomechanical mapping atomic force microscopy (PF-QNM AFM). Prepared at two different alginate concentrations (1.0 and 2.5 mg/mL) and a fixed chitosan concentration (1.0 mg/mL), Alg/Chi films have an exponential growth in thickness with a transition to a linear growth toward a plateau by increasing the number of deposited bilayers. Height, elastic modulus, deformation, and adhesion maps were simultaneously recorded depending on the number of deposited bilayers. The elastic modulus of Alg/Chi films was found to be related to the mechanism of growth in contrast to the adhesion and deformation. A comparison of the nanomechanical properties obtained for non-cross-linked and thermally cross-linked Alg/Chi films revealed an increase of the elastic modulus after cross-linking regardless alginate concentration. The incorporation of iron oxide nanoparticles (NPs), during the spray preparation of the films, gave rise to nanocomposite Alg/Chi films with increased elastic moduli with the number of incorporated NPs layers. Deformation maps of the films strongly suggested the presence of empty spaces associated with the method of preparation. Finally, adhesion measurements point out to a significant role of NPs on the increase of the adhesion values found for nanocomposite films.journal article2017 01 092016 12 15importe

Compact Saloplastic Poly(Acrylic Acid)/Poly(Allylamine) Complexes: Kinetic Control Over Composition, Microstructure, and Mechanical Properties

Durable compact polyelectrolyte complexes (CoPECs) with controlled porosity and mechanical properties are prepared by ultracentrifugation. Because thestarting materials, poly(allylamine hydrochloride) (PAH) and poly(acrylic acidsodium salt) (PAA), are weak acids/bases, both composition and morphology are controlled by solution pH. In addition, the nonequilibrium nature of polyelectrolyte complexation can be exploited to provide a range of compositions and porosities under the infl uence of polyelectrolyte addition order and speed, and concentration. Confocal microscopy shows these “saloplastic” materials to be highly porous, where pore formation is attributed to a combination of deswelling of the polyelectrolyte matrix and expansion of small inhomogenities by osmotic pressure. The porosity (15–70%) and the pore size ( < 5 μ m to > 70 μ m) of these materials can be tuned by adjusting the PAA to PAH ratio, the salt concentration, and the pH. The modulus of these CoPECs depends on the ratio of the two polyelectrolytes, with stoichiometric complexes being the stiffest due to optimized charge pairing, which correlates with maximized crosslinking density. Mechanical properties, pore sizes, and pore density of these materials make them well suited to three dimensional supports for tissue engineering applications

Polyelectrolyte multilayer films as substrates for photoreceptor cells.

Reconstruction of extracellular matrix substrates for delivery of functional photoreceptors is crucial in pathologies such as retinal degeneration and age-related macular degeneration. In this study, we assembled polyelectrolyte films using the layer-by-layer deposition method. The buildup of three different films composed of poly(L-lysine)/chondroitin sulfate (PLL/CSA), poly(L-lysine)/poly(styrenesulfonate) (PLL/PSS), or poly(L-lysine)/hyaluronic acid (PLL/HA) was followed by means of quartz crystal microbalance measurements, optical waveguide light mode spectroscopy, confocal microscopy, and atomic force microscopy. The exponential growth regime and the diffusion of PLL chains from the bulk through the PLL/CSA, PLL/PSS, and PLL/HA films was examined. Evaluation of photoreceptor cell viability was optimal on one layer of PLL (PLL(1)), followed by 10 bilayers of PLL/HA [(PLL/HA)(10)] and 10 bilayers of PLL/CSA [(PLL/CSA)(10)]. The number of bilayers and the type of terminating layer also had a significant influence on the number of photoreceptor cells attached. Functionalized polyelectrolyte multilayer films were obtained by adsorbing basic fibroblastic factor (bFGF) or the insoluble fraction of interphotoreceptor matrix (IPM) on or within polyelectrolyte multilayers. bFGF and IPM adsorption on top of the (PLL/CSA)(10)/PLL polyelectrolyte films increased the number of photoreceptor cells attached and maintained the differentiation of rod and cone cells.journal articleresearch support, non-u.s. gov't2006 Janimporte

Turbidity diagrams of polyanion/polycation complexes in solution as a potential tool to predict the occurrence of polyelectrolyte multilayer deposition.

Surface functionalization with polyelectrolyte multilayer films (PEM films) has become very popular owing to its simplicity and versatility. However, even if some research is already available, this field of surface chemistry lacks a systematic knowledge of how the polyelectrolyte structure and solution conditions influence the growth of PEM films. In this investigation, we focus on the possible relationship between turbidity of polycation and polyanion mixtures in solution, and the buildup of PEM films made from the same polyelectrolytes in the same physicochemical conditions, namely pH, temperature and ionic strength. It comes out that for six different polycation/polyanion combinations there is a clear correlation between the turbidity evolution of polycation/polyanion complexes with the salt concentration and the evolution of the film deposition with the same parameter. In this investigation, the complexes in solution were prepared in conditions where the ratio between the number of cationic to anionic groups was close to unity. Even if there is a correlation between turbidity in solution and PEM film deposition, we found some exceptions in the low salt concentration regime. This work is an extension of the preliminary works of Cohen Stuart (D. Kovačević et al. Langmuir 18 (2002) 5607-5612) and Sukishvili et al. (S.A. Sukhishvili, E. Kharlampieva and V. Izumrudov, Macromolecules 39 (2006) 8873-8881).journal articleresearch support, non-u.s. gov't2010 Jun 012010 02 21importe

Tunable synthesis of Prussian Blue in exponentially growing polyelectrolyte multilayer films.

Polyelectrolyte multilayer (PEM) films have become very popular for surface functionalization and the design of functional architectures such as hollow polyelectrolyte capsules. It is known that properties such as permeability to small ionic solutes are strongly dependent on the buildup regime of the PEM films. This permeability can be modified by tuning the ionization degree of the polycations or polyanions, provided the film is made from weak polyelectrolytes. In most previous investigations, this was achieved by playing on the solution pH either during the film buildup or by a postbuildup pH modification. Herein we investigate the functionalization of poly(allylamine hydrochloride)/poly(glutamic acid) (PAH/PGA) multilayers by ferrocyanide and Prussian Blue (PB). We demonstrate that dynamic exchange processes between the film and polyelectrolyte solutions containing one of the component polyelectrolyte allow one to modify its Donnan potential and, as a consequence, the amount of ferrocyanide anions able to be retained in the PAH/PGA film. This ability of the film to be a tunable reservoir of ferrocyanide anions is then used to produce a composite film containing PB particles obtained by a single precipitation reaction with a solution containing Fe(3+) cations in contact with the film. The presence of PB in the PEM films then provides magnetic as well as electrochemical properties to the whole architecture.journal article2009 Dec 15importe

On the benefits of rubbing salt in the cut: self-healing of saloplastic PAA/PAH compact polyelectrolyte complexes.

The inherent room temperature mending and self-healing properties of saloplastic PAA/PAH CoPECs are studied. After ultracentrifugation of PAA/PAH polyelectrolyte complexes, tough, elastic materials are obtained that undergo self-healing facilitated by salt. At intermediate salt concentrations the CoPECs remain elastic enough to recover their original shape while the chains are mobile enough to repair the cut, thus leading to actual self-healing behavior.journal articleresearch support, non-u.s. gov'tresearch support, u.s. gov't, non-p.h.s.2014 Apr 232014 01 29importe

Polysaccharide films built by simultaneous or alternate spray: a rapid way to engineer biomaterial surfaces.

We investigated polysaccharide films obtained by simultaneous and alternate spraying of a chitosan (CHI) solution as polycation and hyaluronic acid (HA), alginate (ALG), and chondroitin sulfate (CS) solutions as polyanions. For simultaneous spraying, the film thickness increases linearly with the cumulative spraying time and passes through a maximum for polyanion/CHI molar charge ratios lying between 0.6 and 1.2. The size of polyanion/CHI complexes formed in solution was compared with the simultaneously sprayed film growth rate as a function of the polyanion/CHI molar charge ratio. A good correlation was found. This suggests the importance of polyanion/polycation complexation in the simultaneous spraying process. Depending on the system, the film topography is either liquid-like or granular. Film biocompatibility was evaluated using human gingival fibroblasts. A small or no difference is observed in cell viability and adhesion between the two deposition processes. The CHI/HA system appears to be the best for cell adhesion inducing the clustering of CD44, a cell surface HA receptor, at the membrane of cells. Simultaneous or alternate spraying of CHI/HA appears thus to be a convenient and fast procedure for biomaterial surface modifications.journal articleresearch support, non-u.s. gov't2012 Jun 052012 05 23importe

Bioaffinity sensor based on nanoarchitectonic films: control of the specific adsorption of proteins through the dual role of an ethylene oxide spacer.

The identification and quantification of biomarkers or proteins is a real challenge in allowing the early detection of diseases. The functionalization of the biosensor surface has to be properly designed to prevent nonspecific interactions and to detect the biomolecule of interest specifically. A multilayered nanoarchitecture, based on polyelectrolyte multilayers (PEM) and the sequential immobilization of streptavidin and a biotinylated antibody, was elaborated as a promising platform for the label-free sensing of targeted proteins. We choose ovalbumin as an example. Thanks to the versatility of PEM films, the platform was built on two types of sensor surface and was evaluated using both optical- and viscoelastic-based techniques, namely, optical waveguide lightmode spectroscopy and the quartz crystal microbalance, respectively. A library of biotinylated poly(acrylic acids) (PAAs) was synthesized by grafting biotin moieties at different grafting ratios (GR). The biotin moieties were linked to the PAA chains through ethylene oxide (EO) spacers of different lengths. The adsorption of the PAA-EOn-biotin (GR) layer on a PEM precursor film allows tuning the surface density in biotin and thus the streptavidin adsorption mainly through the grafting ratio. The nonspecific adsorption of serum was reduced and even suppressed depending on the length of the EO arms. We showed that to obtain an antifouling polyelectrolyte the grafting of EO9 or EO19 chains at 25% in GR is sufficient. Thus, the spacer has a dual role: ensuring the antifouling property and allowing the accessibility of biotin moieties. Finally, an optimized platform based on the PAA-EO9-biotin (25%)/streptavidin/biotinylated-antibody architecture was built and demonstrated promising performance as interface architecture for bioaffinity sensing of a targeted protein, in our case, ovalbumin.journal articleresearch support, non-u.s. gov't2013 Jun 182013 02 11importe

Effect of the supporting electrolyte anion on the thickness of PSS/PAH multilayer films and on their permeability to an electroactive probe.

Quartz crystal microbalance and cyclic voltammetry are used to investigate the influence of the supporting salt of polyelectrolyte solutions on the buildup and the structure of PSS/PAH polyelectrolyte multilayers (PSS: poly(4-styrene sulfonate); PAH: poly(allylamine hydrochloride)). This film constitutes a model polyelectrolyte multilayer system. The supporting electrolytes were sodium salts where the nature of the anion was changed by following the Hofmeister series from cosmotropic to chaotropic anions (F-, Cl-, NO3-, ClO4-). For all the investigated anions, the film thickness increases linearly with the number of deposition steps.Wefind that chaotropic anions lead to larger thickness increments per bilayer during the film buildup than cosmotropic ones, confirming results found on PSS/PDADMA multilayers (PDADMA:poly(diallyldimethylammonium)). Films constituted by more than nine PSS/PAH bilayers are still permeable to hexacyanoferrate(II) ions, Fe(CN)(6)4-, whatever the nature of the supporting salt anion. On the other hand, these films are impermeable to ruthenium(II) hexamine ions, Ru(NH3)(6)2+, after the third PAH layer in the presence of NaF, NaCl, or NaNO3. These results are explained by the presence of an excess of positive charges in the film, which leads to a positive Donnan potential. We find that this potential is more positive when more chaotropic anions are used during the film buildup. We also find that a film constructed in the presence of chaotropic anions swells and becomes more permeable to Fe(CN)(6)4- ions when the film is brought into contact with a solution containing more cosmotropic anions. All our experimental findings can be explained by a strong interaction between chaotropic anions with the NH3+groups of PAH that is equivalent, as far as the multilayer buildup and electrochemical response is concerned, to a deprotonation of PAH as it is observed when the film is constructed at a higher pH. We thus arrive to a coherent explanation of the effect of the nature of the anions of the supporting electrolyte on the polyelectrolyte multilayer. We also find that great care must be taken when investigating polyelectrolyte multilayer films by electrochemical probing because electrochemical reactions involving the probes can appreciably modify the multilayer structure.journal articleresearch support, non-u.s. gov't2009 Feb 17importe