[Show abstract][Hide abstract] ABSTRACT: PEDOT-PSS 2-In-1 step-by-step film buildup Thermal annealing Nanometric thickness control Electronic conductivity Inelastic cut-offs of scaling a b s t r a c t The fine influence of several key parameters onto the recently reported 2-in-1 step-by-step construction of PEDOT-PSS nanofilms by spin-coating is investigated by laser ellipsometry, UV–vis–NIR spectrometry, tapping-mode AFM and 4-point probe conductimetry following Van der Pauw geometry. First, the thick-ness of the film increases when deposited under good ventilation. Then, the linearity of film thickness with respect to the PEDOT-PSS deposition step number is maintained by thermal treatment at 423 K dur-ing 30 min, showing that the 2-in-1 deposition method is compatible with the thermal annealing steps used in electronic devices containing PEDOT-PSS. Moreover, the concentration of the PEDOT-PSS suspen-sion used for the deposition exerts major influence on the film buildup rate, with a minimum one needed for the method to process at reasonable pace. Finally, analogously to what is known for films obtained by a sole deposition step, the conductivity of 2-in-1 PEDOT-PSS nanofilms is shown to behave differently at ambient to high temperature (373 K) than at the lower temperatures where the conductivity studies are usually made. All these results will be precious for the construction of devices containing a PEDOT-PSS film with a thickness needing to be controlled reproducibly at the nanoscale.
[Show abstract][Hide abstract] ABSTRACT: The fine influence of several key parameters onto the recently reported 2-in-1 step-by-step construction of PEDOT-PSS nanofilms by spin-coating is investigated by laser ellipsometry, UV–vis–NIR spectrometry, tapping-mode AFM and 4-point probe conductimetry following Van der Pauw geometry. First, the thickness of the film increases when deposited under good ventilation. Then, the linearity of film thickness with respect to the PEDOT-PSS deposition step number is maintained by thermal treatment at 423 K during 30 min, showing that the 2-in-1 deposition method is compatible with the thermal annealing steps used in electronic devices containing PEDOT-PSS. Moreover, the concentration of the PEDOT-PSS suspension used for the deposition exerts major influence on the film buildup rate, with a minimum one needed for the method to process at reasonable pace. Finally, analogously to what is known for films obtained by a sole deposition step, the conductivity of 2-in-1 PEDOT-PSS nanofilms is shown to behave differently at ambient to high temperature (373 K) than at the lower temperatures where the conductivity studies are usually made. All these results will be precious for the construction of devices containing a PEDOT-PSS film with a thickness needing to be controlled reproducibly at the nanoscale.
[Show abstract][Hide abstract] ABSTRACT: Simultaneous spraying of polyelectrolytes and small multi-charged molecules of opposite charges onto a vertical substrate leads to continuous buildups of organic films. Here, we investigate the rules governing the buildup of two such systems: poly(allylamine hydrochloride)/sodium citrate (PAH/citrate) and PAH/sulfated alpha-cyclodextrin (PAH/CD-S). Special attention is paid to the film growth rate as a function of the spraying rate ratio of the two constituents. This parameter was varied by increasing the spraying rate of one of the constituents while maintaining constant that of the other. For PAH/CD-S systems, whatever the constituent (PAH or CD-S) whose spraying rate was kept fixed, the film growth rate first increases, passes through a maximum before decreasing when the spraying rate of the other constituent is increased. For PAH/citrate, the film growth rate reaches a plateau value when the spraying rate of citrate is increased while that of PAH is maintained constant whereas when the spraying rate of citrate is maintained constant and that of PAH is increased, a behavior similar to that of PAH/CD-S is observed. The composition of PAH/CD-S sprayed films determined by X-ray photoelectron spectroscopy is independent of the spraying rate ratio of the two constituents and corresponds to one allylamine for one sulfate group. For PAH/citrate, by increasing the PAH/citrate spraying rate ratio, the carboxylic/nitrogen ratio in the film increases and tends to 1. There is thus always a deficit of carboxylic groups (COO- + COOH) with respect to amines (NH2 + NH3+). Yet, the ratio (COO-/NH3+) is always close to 1 ensuring exact charge compensation. The film morphology determined by atomic force microscopy is granular for PAH/CD-S and is smooth and liquid-like for PAH/citrate. A model based on strong (respectively weak) interactions between PAH and CD-S (respectively citrate) is proposed to explain these features.
[Show abstract][Hide abstract] ABSTRACT: Proper staining of grids is critical for transmission electron microscopy (TEM). Staining must be done as quickly as possible using minimal reagents and with consideration for the environment. We developed a new device for efficient staining of multiple TEM grids. We studied reagent evaporation, rinsing volume, flow rate and re-use of uranyl acetate, and provide here a procedure for efficient staining using the new device. Our device permits TEM grids to be stained with less reagent than alternative staining apparatuses; staining requires a total volume of 260 μl for five grids. Reagent evaporation is less than 6% even if used at 37° C. Moreover, our staining apparatus reduces chemical waste and shortens experiment time by staining several grids simultaneously. Our staining device is a compromise between time-consuming single grid processing and expensive commercial devices that consume large amounts of reagents.
[Show abstract][Hide abstract] ABSTRACT: In this article, we focus on hypomaturation autosomal-recessive-type amelogenesis imperfecta (type IIA2) and describe 2 new causal Matrix metalloproteinase 20 (MMP20) mutations validated in two unrelated families: a missense mutation p.T130I at the expected homozygous state, and a compound heterozygous mutation having the same mutation combined with a nucleotide deletion, leading to a premature stop codon (p.N120fz*2). We characterized the enamel structure of the latter case using scanning electron microscopy analysis and microanalysis (Energy-dispersive X-ray Spectroscopy, EDX) and confirmed the hypomaturation-type amelogenesis imperfecta as identified in the clinical diagnosis. The mineralized content was slightly decreased, with magnesium substituting for calcium in the crystal structure. The anomalies affected enamel with minimal inter-rod enamel present and apatite crystals perpendicular to the enamel prisms, suggesting a possible new role for MMP20 in enamel formation.
Journal of dental research 04/2013; · 3.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We propose a simple method to elaborate a filler-free stretchable PDMS surface strong enough to resist to successive elongation/retraction cycles even at high degree of stretching. It consists in creating free radicals on a filler-containing PDMS surface by argon plasma exposure and reacting them with a filler-free PDMS resin during the crosslinking step. Changes of physical and chemical properties upon plasma modification are monitored by FTIR and XPS spectroscopies, contact angle measurements and atomic force microscopy. Electron spin resonance (ESR) is used to identify the nature of radicals involved in interfacial bonding. Although a brittle silica-like layer is created on the filler-containing PDMS surface after plasma treatment, an increase in the PDMS/PDMS interfacial strength is observed and a high interfacial resistance has been found under elongation/retraction (stretching/relaxation) cycles.
[Show abstract][Hide abstract] ABSTRACT: Chemo-mechanotransduction, the way by which mechanical forces are transformed into chemical signals, plays a fundamental role in many biological processes. The first step of mechanotransduction often relies on exposure, under stretching, of cryptic sites buried in adhesion proteins. Likewise, here we report the first example of synthetic surfaces allowing specific interactions with proteins or cells promoted by mechanical action in a fully reversible manner. Silicone sheets are first plasma treated and then functionalized by grafting sequentially under stretching poly(ethyleneglycol) (PEG) chains and biotin or arginine-glycine-aspartic acid (RGD) peptides. At rest position these ligands are not accessible for their receptors. Under stretching the surface becomes specifically interactive to streptavidin, biotin-antibodies or adherent for cells, the interactions being fully reversible by stretching/unstretching both for proteins and cells, revealing a reversible exposure process of the ligands. By changing the degree of stretching, the amount of interacting proteins can be varied continuously.
[Show abstract][Hide abstract] ABSTRACT: Surface functionalization plays an important role in the design of biomedical implants, especially when layer forming cells, such as endothelial or epithelial cells, are needed. In this study, we define a novel nanoscale surface coating composed of collagen/alginate polyelectrolyte multilayers and cross-linked for stability with genipin. This buildup follows an exponential growth regime versus the number of deposition cycles with a distinct nanofibrillar structure that is not damaged by the cross-linking step. Stability and cell compatibility of the cross-linked coatings were studied with human umbilical vein endothelial cells. The surface coating can be covered by a monolayer of vascular endothelial cells within 5 days. Genipin cross-linking renders the surface more suitable for cell attachment and proliferation compared to glutaraldehyde (more conventional cross-linker) cross-linked surfaces, where cell clumps in dispersed areas were observed. In summary, it is possible with the defined system to build fibrillar structures with a nanoscale control of film thickness, which would be useful for in vivo applications such as inner lining of lumens for vascular and tracheal implants.
[Show abstract][Hide abstract] ABSTRACT: Although never emphasized and increasingly used in organic electronics, PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)) layer-by-layer (lbl) film construction violates the alternation of polyanion and polycation rule stated as a prerequisit for a step-by-step film buildup. To demonstrate that this alternation is not always necessary, we studied the step-by-step construction of films using a single solution containing polycation/polyanion complexes. We investigated four different systems: PEDOT-PSS, bPEI-PSS (branched poly(ethylene imine)-poly(sodium 4-styrene sulfonate)), PDADMA-PSS (poly(diallyl dimethyl ammonium)-PSS), and PAH-PSS (poly(allylamine hydrochloride)-PSS). The film buildup obtained by spin-coating or dipping-and-drying process was monitored by ellipsometry, UV-vis-NIR spectrophotometry, and quartz-crystal microbalance. The surface morphology of the films was characterized by atomic force microscopy in tapping mode. After an initial transient regime, the different films have a linear buildup with the number of deposition steps. It appears that, when the particles composed of polyanion-polycation complex and complex aggregates in solution are more or less liquid (case of PEDOT-PSS and bPEI-PSS), our method leads to smooth films (roughness on the order of 1-2 nm). On the other hand, when these complexes are more or less solid particles (case of PDADMA-PSS and PAH-PSS), the resulting films are much rougher (typically 10 nm). Polycation/polyanion molar ratios in monomer unit of the liquid, rinsing, and drying steps are key parameters governing the film buildup process with an optimal polycation/polyanion molar ratio leading to the fastest film growth. This new and general lbl method, designated as 2-in-1 method, allows obtaining regular and controlled film buildup with a single liquid containing polyelectrolyte complexes and opens a new route for surface functionalization with polyelectrolytes.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: An original “all-in-one” platform combining polymers, enzymes, and enzymatic substrates in a unique film is designed. A polymeric barrier stratum prevents any contact between enzymes adsorbed on top of the film and substrates loaded in an underlying reservoir. Upon stretching of the film, a continuous diffusion of substrates through the barrier is triggered, followed by a catalytic reaction. This leads to the formation of products that are released from the film. This new platform acts as a stretch-induced reactive release system and emerges as an innovative concept in mechano-responsive materials.
[Show abstract][Hide abstract] ABSTRACT: Cell adhesion processes take place through mechanotransduction mechanisms where stretching of proteins results in biological responses. In this work, we present the first cyto-mechanoresponsive surface that mimics such behavior by becoming cell-adhesive through exhibition of arginine-glycine-aspartic acid (RGD) adhesion peptides under stretching. This mechanoresponsive surface is based on polyelectrolyte multilayer films built on a silicone sheet and where RGD-grafted polyelectrolytes are embedded under antifouling phosphorylcholine-grafted polyelectrolytes. The stretching of this film induces an increase in fibroblast cell viability and adhesion.
Journal of the American Chemical Society 12/2011; 134(1):83-6. · 10.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The construction of films with complex architectures through one-pot reactions taking place exclusively on a surface remains a challenge. Recently, to address this problem, we introduced a concept based on morphogen-driven film buildup. We used Cu(i) as morphogen and the Huisgens click-reaction between azide and al
[Show abstract][Hide abstract] ABSTRACT: Films prepared according to a layer-by-layer (LBL) manner find increasing importance in many applications such as coatings with dedicated optical or electronic properties, particularly when including nanomaterials. An alternative way to prepare such hybrid layer-by-layer coatings is to perform sol-gel chemistry in a layer-by-layer manner. In this article, we highlight the importance of the NaCl concentration as a parameter to control the growth as well as the properties of LBL films made from poly(ethylene imine) as the organic counterpart and titanium IV (bisammoniumlactato)dihydroxyde ([Ti(lac)(2)(OH)(2)](2-)) as the precursor of TiO(2). An increase in the sodium chloride concentration leads to the faster growth of the film and to a decrease in the number of hexacyanoferrate anions remaining in the film after a buffer rinse. This may be due to a progressive increase in the fraction of negatively charged TiO(2) as suggested by transmission electron microscopy. In the presence of 0.5 M NaCl, the fraction of TiO(2) is close to 60% in mass. As a surprising finding, the films produced from 0.15 M NaCl are not homogeneously filled with TiO(2) even if the film is produced in an LBL fashion. The increased concentration of TiO(2) at the film-solution interface could constitute a barrier for the incorporation of the negatively charged redox probe.
[Show abstract][Hide abstract] ABSTRACT: Simultaneous spraying of two solutions of interacting species onto a substrate held vertically leads to the formation of nanometer-sized coatings. Here we investigate the simultaneous spraying of poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) solutions leading to the formation of a film composed of PSS/PAH complexes. The thickness of this film increases linearly with the cumulative spraying time. For a given spraying rate of PAH (respectively PSS), the growth rate of the film depends strongly upon the PSS/PAH ratio and passes through a maximum for a PSS/PAH ratio lying between 0.55 and 0.8. For a PSS/PAH ratio that is maintained constant, the growth speed of the film increases linearly with the spraying rate of polyelectrolyte of both solutions. Using X-ray photoelectron spectroscopy, we find that the film composition is almost independent of the PSS/PAH (spayed) ratio, with composition very close to 1:1 in PSS:PAH film. The 1:1 PSS:PAH composition is explained by the fact that the simultaneous spraying experiments are carried out with salt-free solutions; thus, electroneutrality in the film requires exact matching of the charges carried by the polyanions and the polycations. Zeta potential measurements reveal that, depending on whether the PSS/PAH spraying rate ratio lies below or above the optimal spraying rate ratio, the film acquires a positive or a negative excess charge. We also find that the overall film morphology, investigated by AFM, is independent of the spraying rate ratio and appears to be composed of nanometer-sized grains which are typically in the 100 nm range.
[Show abstract][Hide abstract] ABSTRACT: Multilayer films are used to design complex surfaces with permeability towards specific molecules adjusted. As an example of application, enzymatic activity of these architectures was tuned when mechanical stretching was applied to the architecture. Tailored design of mechanically Mechanically sensitive surfaces responding to mechanical forces constitute an attractive emerging field of research. This requires the engineering of complex surfaces with finely controlled properties, especially regarding the permeability behaviour towards specific molecules. Here we designed such surfaces using polyelectrolyte multilayer nanostructures. Polylysine/hyaluronic acid multilayer films were used as a micro-container of enzymes and denser multilayers deposited on top of the reservoir were tailored to control their permeability. We find that permeability towards fluorescein diphosphate (FDP) not only depends on the number of bilayers constituting the barrier but more surprisingly on the deposition time of the polyelectrolytes during the barrier buildup, a long contact time (10 min) leading to porous barriers. This effect is explained by diffusion and exchange processes taking place in the reservoir during the buildup process. For films composed of a non-permeable barrier towards enzymatic substrate FDP, we tested the enzymatic activity when mechanical stretching was applied to the architecture. Under stretch and in the presence of FDP on top of the film, the catalytic activity was switched on. These biologically inspired surfaces constitute a first step to the development of novel platforms able to trigger and to modulate chemical reactions under a mechanical stimulus.
Journal of Materials Chemistry 01/2011; 21(23):8324-8331. · 5.97 Impact Factor