7 research outputs found
New 2-in-1 Polyelectrolyte Step-by-Step Film Buildup without Solution Alternation: From PEDOT-PSS to Polyelectrolyte Complexes
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 <i>2-in-1 method</i>, allows obtaining
regular and controlled film buildup with a single liquid containing
polyelectrolyte complexes and opens a new route for surface functionalization
with polyelectrolytes
Boric Acid as an Efficient Agent for the Control of Polydopamine Self-Assembly and Surface Properties
The deposition of polydopamine (PDA)
films on surfaces, a versatile
deposition method with respect to the nature of the used substrate,
is unfortunately accompanied by deposition of insoluble precipitates
in solution after a prolonged oxidation time of dopamine solutions.
Therefore, there is evident interest to find methods able to stop
the deposition of PDA on surfaces and to simultaneously control the
self-assembly of PDA in solution to get stable colloidal aggregates.
In addition to proposed methods relying on the use of polymers like
poly(vinyl alcohol) and proteins like human serum albumin, we show
herein that boric acid is an efficient adjuvant that is simultaneously
able to stop the self-assembly of PDA in solution as well as on surfaces
and to change the adhesive properties of the resulting PDA coatings
Layer-by-Layer Enzymatic Platform for Stretched-Induced Reactive Release
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
Efficient Gas and Water Vapor Barrier Properties of Thin Poly(lactic acid) Packaging Films: Functionalization with Moisture Resistant Nafion and Clay Multilayers
Poly(lactic acid) (PLA) represents
one of the most promising and
attractive biobased polymer for the industrial development of environmentally
sustainable packaging. However, oxygen and water barrier properties
of PLA based films cannot compete with those of commercially available
composite multilayers. To fill this gap, we used the layer-by-layer
deposition technique on commercially used PLA thin films (30 μm
thick) in order to increase their barrier properties to oxygen and
water vapor. Nanometric films were grown by alternating branched poly(ethylene
imine) (BPEI), hydrophobic fluorinated polymer (Nafion), and montmorillonite
clay (MMT) layers with the aim of obtaining low gas permeability in
both dry and moist conditions as well as low water vapor permeability.
Two different kinds of architectures were designed and successfully
prepared, based on a 4 layer repeating unit (BPEI/MMT/BPEI/Nafion),
represented here as quadlayer (QL), and on a 6 layer repeating-unit
((BPEI/Nafion)<sub>2</sub>/BPEI/MMT), hexalayer (HL). Reduction in
oxygen and water permeabilities is observed for films based on both
types of repeat units. The reduction of the permeabilities increases
with the number of quad and hexalayers achieving reductions in terms
of oxygen permeability in both dry and humid conditions up to 98%
and 97% respectively for 10 HL and QL. Furthermore, a reduction of
78% of water vapor transmission rate through the functionalized film
was obtained for these films. As far as oxygen permeability is concerned,
HL films are more efficient than QL films for smaller numbers of deposition
units. These properties are shown to result from the complementarity
between the presence of BPEI/Nafion and MMT layers
Nanosized Films Based on Multicharged Small Molecules and Oppositely Charged Polyelectrolytes Obtained by Simultaneous Spray Coating of Interacting Species
Simultaneous spraying of polyelectrolytes
and small multicharged
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 α-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 and 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<sup>–</sup> + COOH) with respect
to amines (NH<sub>2</sub> + NH<sub>3</sub><sup>+</sup>). Yet, the
ratio (COO<sup>–</sup>/NH<sub>3</sub><sup>+</sup>) 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
Collagen-Based Fibrillar Multilayer Films Cross-Linked by a Natural Agent
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
Biomimetic Cryptic Site Surfaces for Reversible Chemo- and Cyto-Mechanoresponsive Substrates
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 for specific and fully reversible adhesion of proteins or cells promoted by mechanical action. Silicone sheets are first plasma treated and then functionalized by grafting sequentially under stretching poly(ethylene glycol) (PEG) chains and biotin or arginine-glycine-aspartic acid (RGD) peptides. At unstretched position, these ligands are not accessible for their receptors. Under a mechanical deformation, the surface becomes specifically interactive to streptavidin, biotin antibodies, or adherent for cells, the interactions both for proteins and cells being fully reversible by stretching/unstretching, revealing a reversible exposure process of the ligands. By varying the degree of stretching, the amount of interacting proteins can be varied continuously