The Possibility of Obtaining Films by Single Sedimentation of Polyelectrolyte Complexes

Surface coatings obtained by a step-by-step (SBS) deposition process of polymers carrying mutually complementary moieties (like polycations and polyanions) allow for a versatile multifunctionalization of a vast kind of materials. However the SBS deposition process can be extremely time-consuming when it is performed by alternatively dipping the substrates in the solutions carrying the interacting species. There is hence an important need to obtain coatings of similar composition as those obtained in the SBS manner but in a “one pot” manner. Here we show that the sedimentation of stoichiometric polyelectrolyte complexes can lead to a homogeneous coating. This is possible if the polylectrolyte complexes display a high internal mobility. The film growth rate is then in direct relation with the sedimentation rate of its constituting complexes. On the other hand when the interactions between the oppositely charged polyelectrolytes are too strong, the obtained coating is neither continuous nor homogeneous

Enhanced Adhesion over Aluminum Solid Substrates by Controlled Atmospheric Plasma Deposition of Amine-Rich Primers

Controlled chemical modification of aluminum surface is carried by atmospheric plasma polymerization of allylamine. The amine-rich coatings are characterized and tested for their behavior as adhesion promoter. The adhesion strength of aluminum-epoxy assemblies is shown to increase according to primary amino group content and coating thickness, which in turn can be regulated by plasma power parameters, allowing tailoring the coating chemical properties. The increase in adherence can be correlated to the total and primary amino group contents in the film, indicating covalent bonding of epoxy groups to the primer as the basis of the mechanical improvement

Giant Liposome Microreactors for Controlled Production of Calcium Phosphate Crystals

Calcium phosphates are among the most important biominerals in living organisms, where they play both a mechanical and a calcium storage role. Their growth in vivo is under strong biological control, and this process occurs in closed spaces. Our aim in this paper is to describe a microreactor system able to control the mineralization process within closed spaces. To this aim we produce giant liposomes containing calcium ions as active ions in the mineralization process, spermine as an activator of crystal growth, and alkaline phosphatase as a catalyst to convert phosphate esters into phosphates. These phosphate esters are provided in the form of p-nitrophenyl phosphate outside of the liposomes. It is demonstrated that these amphiphilic molecules are able to diffuse through the lipidic container and to be subsequently hydrolyzed under enzymatic catalysis into active phosphate species which interact with the already available calcium and spermine to produce calcium phosphates only in the interior of the liposomes. This opens the route to control the calcium phosphate particle size in biomimetic systems

Layer-by-Layer Self-Assembled Polyelectrolyte Multilayers with Embedded Liposomes: Immobilized Submicronic Reactors for Mineralization

The development of chemical reactions in nanospaces is of paramount importance for the development of active nanodevices, particularly in nanofluidics. It has been shown in a previous paper that phospholipid vesicles can be incorporated without spontaneous bilayer rupture into poly-l-glutamic acid/poly(allylamine) (PGA/PAH) multilayered polyelectrolyte films. The aim of the present study was to use such a system as an “embedded submicronic reactor” able to trigger precipitation of calcium phosphates within closed spaces through an enzymatic reaction, the enzyme also being encapsulated in the vesicle interior. To this aim, large unilamellar vesicles (LUVs) were produced containing calcium ions as active ions in the mineralization process, spermine as an activator of crystal growth, and alkaline phosphatase as a catalyst to convert phosphate esters into phosphates. After stabilization by adding a layer of poly-(d-lysine), these vesicles were embedded in a (PGA-PAH)n film. A paranitrophenyl phosphate containing solution was then put in contact with this film. It is shown by means of infrared spectroscopy in the attenuated total reflection mode that, consecutively to this contact, calcium phosphates are growing inside the embedded vesicles. By using scanning near-field fluorescence microscopy, it is demonstrated that the alkaline phosphatase enzymes are most probably located inside the vesicles after their embedding. In addition, atomic force microscopy was used to show, after chemical removal of the organic top layer of the film, that the inorganic platelets produced after the precipitation reaction are localized in volumes of similar size and shape as that of the vesicles into which the phosphate ester hydrolysis and subsequent precipitation reaction did occur

Dopamine−Melanin Film Deposition Depends on the Used Oxidant and Buffer Solution

The deposition of “polydopamine” films, from an aqueous solution containing dopamine or other catecholamines, constitutes a new and versatile way to functionalize solid−liquid interfaces. Indeed such films can be deposited on almost all kinds of materials. Their deposition kinetics does not depend markedly on the surface chemistry of the substrate, and the films can reach thickness of a few tens of nanometers in a single reaction step. Up to now, even if a lot is known about the oxidation mechanism of dopamine in solution, only little information is available to describe the deposition mechanism on surfaces either by oxidation in solution or by electrodeposition. The deposition kinetics of melanin was only investigated from dopamine solutions using oxygen or ammonium persulfate as an oxidant and from a tris(hydroxymethyl) aminomethane (Tris) containing buffer solutions at pH 8.5. Many other oxidants could be used, and the buffer agent containing a primary amine group may influence the deposition process. Herein we show that the deposition kinetics of melanin from dopamine containing buffers at pH 8.5 can be markedly modified using Cu2+ instead of O2 as an oxidant: the deposition kinetics remains linear up to thicknesses of more than 70 nm, whereas the film growth stops at 45 ± 5 nm in the presence of 02. In addition, the films prepared from Cu2+ containing solutions display an absorption spectrum with defined peaks at 320 and 370 nm, which are absent in the spectra of films prepared in oxygenated solutions. The replacement of Tris buffer by phosphate buffer also has a marked effect on the melanin deposition kinetics

Design of Flexible Free Standing Plasma Polymer-Based Films As Hosts for Enzyme Immobilization

This article deals with the elaboration and characterization of an original and easy way to produce templates able to host dyes and enzymes. The template films are made of plasma methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) copolymers and allow for the design of a free-standing matrix able to host active enzymes. Plasma copolymers based on 80/20% molar ratio MAA and EGDMA were prepared to obtain stable chemical plasma films containing carboxyl groups. The amount of such functional groups was quantified by chemical derivatization, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopies. The analysis reveals the possibility to produce stable coatings with accessible functional groups to control the affinity of the film for dyes such as toluidine blue and enzymes such as alkaline phosphatase. We showed that this kind of plasma film is able to entrap enzymes whose catalytic activity is still preserved. Enzymatic activity was studied by measuring the production of paranitrophenol from the hydrolysis of paranitrophenyl phosphate (PNP). This distribution of the enzyme across the film thickness was investigated by means of laser confocal scanning microscopy and time of flight secondary ion mass spectrometry. Some desorption of enzyme was observed during and after the first enzymatic assay, but stable activity was obtained thereafter. The mechanism by which the negatively charged enzyme is entrapped in the plasma polymer matrix, also carrying negatively charged groups, is briefly discussed

wAIHA baseline characteristics in the whole cohort and comparison between patients with or without VTE.

wAIHA baseline characteristics in the whole cohort and comparison between patients with or without VTE.</p

Flowchart of patients.

Flowchart of patients.</p

Comparison of Synthetic Dopamine–Eumelanin Formed in the Presence of Oxygen and Cu²⁺ Cations as Oxidants

Eumelanin is not only a ubiquitous pigment among living organisms with photoprotective and antioxidant functions, but is also the subject of intense interest in materials science due to its photoconductivity and as a possible universal coating platform, known as “polydopamine films”. The structure of eumelanin remains largely elusive, relying either on a polymeric model or on a heterogeneous aggregate structure. The structure of eumelanin as well as that of the closely related “polydopamine films” can be modified by playing on the nature of the oxidant used to oxidize dopamine or related compounds. In this investigation, we show that dopamine–eumelanins produced from dopamine in the presence of either air (O₂ being the oxidant) or Cu²⁺ cations display drastically different optical and colloidal properties in relation with a different supramolecular assembly of the oligomers of 5,6 dihydroxyindole, the final oxidation product of dopamine. The possible origin of these differences is discussed on the basis of Cu²⁺ incorporation in Cu dopamine–eumelanin

Characteristics of patients with VTE.

Characteristics of patients with VTE.</p