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Graphical abstract Abstract Polyelectrolyte multilayer (PEM) films display either a linear or an exponential increase of their thickness with increasing the number of polycation/polyanion deposition cycles. Each of these growth regimes is further associated with a specific mode of internal PEM charge compensation: either intrinsic in the case of linearly growing films, or extrinsic for exponentially growing films with incorporation of small ions from the neighbouring electrolyte solution. In this report, we investigate by electrochemistry the charge compensation mechanism operational for poly(diallyldimethyl ammonium chloride)-poly(acrylic acid sodium salt) (PDAMAC-PAA) n films recently found to be out-of-equilibrium immediately after the deposition process despite of their exponential growth mode. It is found here that these films are defined by a negative Donnan potential drop (ca. −160 mV), thus evidencing an extrinsic charge compensation process, and most importantly, by a remarkably slow kinetics for loading of hexacyanoferrate anions, a very unusual property for PEMs with exponential growth. Depending on the film thickness, the diffusion coefficient of the redox probe in the film is found to be of the order of 10−13 − 10−15 cm2 s−1, i.e. about 8 to 10 orders of magnitude less than that typically measured in aqueous solution. This results in a steady state filling of e.g. a 2.8 µm thick PEM film with the redox probe that is achieved after more than 40 h, a feature in line with the typical 4 to 5 days relaxation timescale of the film structure previously determined by atomic force microscopy and Raman micro-spectroscopy analyses. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Hypothesis The layer-by-layer deposition of films including polyoxometalates (POMs) results in a very interesting range of applications in various fields such as electrochemical devices and as photochromic coatings. However, the fundamental knowledge of the parameters responsible for tuning the properties of the film (i.e. relation between the structure and composition of the POM and the properties of the final film) is still lacking. Experiments The current work establishes the relationship between the film thickness, the quantity of POM incorporated in each layer and the electrochemical response of the (PAH-POM) x coatings, where PAH is poly(allylamine hydrochloride). Findings The results presented in this work show that the film thickness, composition and electrochemical activity scale proportionally with the number of W atoms in a series of heteropolytungstates ranging from 5 to 48 (P 2 W 5 , PW 12 , P 2 V 3 W 15 , P 2 W 18 , P 5 W 30 , P 8 W 48). The obtained results allow us to establish a method to predict the behavior as well as the properties of the film based on the nature of the POM used. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) are often used to functionalize surfaces with photochromic or electroactive compounds. Among the common deposition methods, besides the Langmuir-Blodgett deposition, the layer-by-layer (LBL) deposition method has become more and more popular due to its facility and versatility combined with the polyanionic character of POMs. The LBL deposition of POMs and oppositely charged nanoparticles is however poorly described in the literature. Using polydopamine nanoparticles (PDA) produced in the presence of poly(allylamine) and displaying a hydrodynamic diameter of 25 nm, we show that LBL films containing the large, cyclic P 8 W 48 polyanion and the PDA@PAH nanoparticles display reduction currents which are proportional to the number of deposition steps and hence to the film thickness. In addition the obtained films display not only the electrochemical properties of the POM but also that of PDA nanoparticles. Hence we demonstrate the feasibility to build up films based on particles only with the electrochemical behavior of each kind of particles being conserved. [ABSTRACT FROM AUTHOR]

The step-by-step assembly of tannic acid (TA) and of Fe 3+ cations allows to produce films of controlled thickness using exclusively small multivalent ions. In the present investigation, it is shown that even if electrostatic interactions are dominant over ligand to metal charge transfer interactions in stabilizing such films, those electrostatic interactions display a small sensitivity to concentration in NaCl used as a supporting electrolyte as well as to the concentration in sodium acetate in the absence of NaCl. This finding highlights the strong stability of the films obtained through the step-by-step deposition of TA and Fe 3+ cations. Complementarily, the films made from 6 deposition cycles of TA and Fe 3+ cations do not form Prussian Blue when put in contact with hexacyanoferrate anions. This shows that Fe 3+ is so tightly bound to the film that it is not able to form a coordination polymer with Fe(CN) 6 4− anions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Alkaline phosphatase was adsorbed on “polydopamine” films. [•] The enzymatic activity was evaluated as a function of storage time. [•] “Polydopamine” films display some phosphatase like activity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Proteins allow to control the size of dopamine-eumelanin particles. [•] The kinetics of dopamine-eumelanin formation is also accelerated in the presence of those proteins. [•] Fibroblasts keep their viability in the presence of HAS dopamine-eumelanin nanoparticles. [Copyright &y& Elsevier]

Highlights: [•] The zeta potential of (PAH-polyoxometalate) n films is measured as a function of the ionic strength. [•] The zeta potential is stable as a function of time when the ionic strength is higher than 50mM. [•] At smaller ionic strengths, the zeta potential decreases without desorption. [ABSTRACT FROM AUTHOR]

Highlights: [•] Step-by-step assembly of dopamine-eumelanin and metal cations (Cu2+, Fe3+, La3+) is possible. [•] The coatings made from trivalent cations growth faster than those made from Cu2+. [•] Fe3+ does not undergo a change in its redox state upon incorporation in the coatings. [ABSTRACT FROM AUTHOR]

Abstract: The formation of “polydopamine” thin films becomes a popular method to confer multifunctionality to solid–liquid interfaces through the available catechol groups of such films. The mechanism of film formation is, however, not well elucidated, and most investigators use the protocol developed by Messersmith et al. (H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Science 318 (2007) 426.) using a dopamine solution at a constant concentration of 2gL−1 in the presence of Tris(hydroxymethyl aminomethane) at pH 8.5. A particular finding of this initial study was that the film thickness reaches a constant value (almost substrate independent) of about 40nm. Herein, we investigate the change in the polydopamine film thickness, morphology, surface energy and electrochemical properties as a function of the concentration of the dopamine solution put in the presence of silicon substrates. As a surprising finding, we observe a constant increase in the maximal film thickness with an increase in the dopamine solution between 0.1 and 5gL−1. The surface morphology is also markedly affected by the concentration of the dopamine solution, whereas the different components of the surface energy stay unaffected by the dopamine solution concentration. In addition, electrochemical impedance spectroscopy shows that the higher the initial dopamine concentration, the more rapidly compact and impermeable films are formed. Finally, we propose a model for the deposition of polydopamine films taking all our findings into account. This model relies on a rate equation taking into account both attractive and repulsive interactions between small polydopamine aggregates on the surface and in solution. [Copyright &y& Elsevier]

Abstract: The deposition of polyelectrolyte multilayer films (PEMs) appears more and more as a versatile tool to functionalize a broad range of materials with coatings having controlled thicknesses and properties. To increase the control over the properties of such coatings, a good knowledge of their deposition mechanism is required. Since Cohen Stuart et al. (Langmuir 18 (2002) 5607–5612) showed that the adsorption of one polyelectrolyte could induce desorption of polyelectrolyte complexes instead of regular deposition, more and more findings highlight peculiarities in the deposition of such films. Herein we demonstrate that the association of sodium polyphosphate (PSP) as the polyanion and either poly(-L-lysine hydrobromide) (PLL) or poly(allylamine chloride) (PAH) as the polycations may lead to non-monotonous film deposition as a function of time. Complementary, films containing PSP and PLL can be obtained from a (PLL–HA) n template films after the exchange of HA (hyaluronic acid) from the sacrificial template by PSP from the solution. This exchange is accompanied by pronounced film erosion. However, when starting from a (PAH–HA) n template, the film erosion and exchange due to the contact with PSP is by far less pronounced, nevertheless the film morphology changes. These findings show that the nature of the polycation used to deposit the PEM film may have a profound influence of the film’s response to a competing polyanion. [Copyright &y& Elsevier]

Abstract: Dopamine–melanin films produced through the oxidation of dopamine in the presence of oxygen as an oxidant allow to reduce silver ions onto silver particles as already described in the paper by Lee et al. (H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Science 318 (2007) 426.). This reduction process has to occur through the oxidation of moieties present in the melanin film. This investigation shows that the free radicals present in the pseudomelanin film, quantified by means of electron spin resonance spectroscopy (ESR) for the first time, are not used in the transformation of Ag+ cations to deposit silver. The ESR signal is hardly affected by the deposition of silver particles. On the other hand, X-ray photoelectron spectroscopy shows a small increase in the density of quinone groups and a small decrease of catechol groups on the surface of the film during the deposition of silver. This suggests that the deposited pseudomelanin films contain a significant fraction of catechol groups able to trigger reduction processes of metallic cations. These silver nanoparticles remain adherent to the melanin films and allow for a quantitative killing of Escherichia coli over a broad range of bacterial dilutions. However, the presence of the bacteria induces a release of the nanoparticles. The pseudomelanin films cannot be reused again for a silver ion reduction step. Nevertheless, the easy preparation of the pseudomelanin–silver composite and its effective one shot bacterial killing activity renders the strategy presented in this paper attractive. Some fundamental questions about redox process allowed by the pseudomelanin films will also be asked. [Copyright &y& Elsevier]

Layer-by-layer-deposition of enzymes and polyphenols, like tannic acid may provide a reservoir of antioxidant and antibacterial molecules of controlled thickness and degradability with an additional activity due to the presence of the enzyme. The layer-by-layer deposition of films made from tannic acid and alkaline phosphatase is shown to yield an exponential growth with the number of deposited layer pairs. The films display the electrochemical behavior of tannic acid and the enzymatic activity of alkaline phosphatase. However, it is shown that only the enzyme close to the film-solution interface is active and follows the Michaelis-Menten mechanism. Similarly, only tannic acid close to the electrode-film interface can be oxidized. The enzymatic activity is almost completely lost when the multilayer film is treated with sodium periodate which oxidizes tannic acid even if the solubilized enzyme is not affected by the oxidant. This shows that the formation of covalent bonds between alkaline phosphatase and tannic acid is deleterious for its conformation and activity. [ABSTRACT FROM AUTHOR]

[Display omitted] The possibility to use hexamethylenediamine (HMDA) to impart film forming ability to natural polymers including eumelanins and plant polyphenols endowed with biological activity and functional properties has been recently explored with the aim to broaden the potential of polydopamine (PDA)-based films overcoming their inherent limitations. 5,6-dihydroxyindole-2-carboxylic acid, its methyl ester (MeDHICA) and eumelanins thereof were shown to exhibit potent reducing activity. MeDHICA and HMDA were reacted in aqueous buffer, pH 9.0 in the presence of different substrates to assess the film forming ability. The effect of different reaction parameters (pH, diamine chain length) on film formation was investigated. Voltammetric and AFM /SEM methods were applied for analysis of the film redox activity and morphology. HPLC, MALDI-MS and 1HNMR were used for chemical characterization. The film reducing activity was evaluated in comparison with PDA by chemical assays and using UV stressed human immortalized keratinocytes (HaCat) cells model. Regular and homogeneous yellowish films were obtained with moderately hydrophobic properties. Film deposition was optimal at pH 9, and specifically induced by HMDA. The film consisted of HMDA and monomeric MeDHICA accompanied by dimers/small oligomers, but no detectable MeDHICA/HMDA covalent conjugation products. Spontaneous assembly of self-organized networks held together mainly by electrostatic interactions of MeDHICA in the anion form and HMDA as the dication is proposed as film deposition mechanism. The film displayed potent reducing properties and exerted significant protective effects from oxidative stress on HaCaT. [ABSTRACT FROM AUTHOR]

Polydopamine (PDA) coatings appear as a universal functionalization methodology allowing to coat the surface of almost all kinds of known materials with a conformal, stable, robust and reactive material. Relatively few investigations were dedicated to the incorporation of other molecules in PDA coatings during their deposition from dopamine solutions under oxidative conditions. Herein we rely on the assumption that the basic building blocks of PDA could be porphyrin like tetramers (as well as higher order oligomers) of 5,6-dihydroxyindole and we investigate the influence of a cationic Cu(II) phtalocyanine, namely Alcian Blue (AB), on the deposition kinetics and on the properties of PDA films. We demonstrate that AB is indeed incorporated in the PDA films to yield a composite PDA–AB coating displaying the optical features of both PDA and AB. The amount of incorporated dye depends on its concentration in solution. The obtained PDA–AB films have a smaller thickness than their related PDA counterparts, a different morphology and a higher permeability to the anionic hexacyanoferrate redox probe. In addition, the incorporation of AB in the films is not homogeneous through their thickness as inferred by means of X-ray photoelectron spectroscopy. The reason for this interesting finding is discussed on the basis of the interactions between AB and PDA as well as on the basis of the structure of PDA films. [ABSTRACT FROM AUTHOR]

Anionic and cationic surfactants such as sodium dodecylsulfate (SDS) and hexadecyltrimethylammonium bromide (HTAB) are able to control the size of "polydopamine" particles produced from dopamine solutions and to simultaneously strongly inhibit the deposition of "polydopamine" on surfaces. Indeed, dynamic light scattering experiments allowed to show that the hydrodynamic radius of polydopamine progressively decreases from about 1 μm to a few nanometer upon an increase in the SDS and CTAB concentration. At the highest surfactant concentration used (50 mM) the size of the aggregates is only slightly larger than the size of the surfactant micelles. On the other hand, the non-ionic Triton X-100 surfactant has no significant influence on both phenomena. It is suggested that the observed effect originates from the anionic and cationic surfactants acting as a template in which the growth of "polydopamine" is confined. [ABSTRACT FROM AUTHOR]

The setting time and mechanical properties of cements are a major technical concern for a long time in civil engineering. More recently those practical problems became a major concern for biomedical applications -in bone surgery and in dentistry- in particular concerning the setting time which should be minimized. The possibility to add organic additives to interact with the different constituting ions in cements constitutes a way to modify the setting kinetics. We made the assumption that a hydrolysable polyphenol like tannic acid could modify the setting time and the physical properties of Mineral Trioxide Aggregate (MTA). Tannic acid is added in variable proportions to the water used to set MTA. The formation of the hybrid organic-mineral cements is investigated using a combination of structural, chemical and mechanical methods. X-ray tomography was also used to investigate the changes in porosity and pore size distribution upon incorporation of tannic acid in MTA based cements. The hydrophilicity of the cements was evaluated by measuring the permeation kinetics of small water droplets. We found that tannic acid allowed to reduce markedly the setting time of MTA based cements. The obtained cements have an increased hydrophilicity and display excellent resistance to compression. The number of pores but not the average pore size is also affected. The possible roles of tannic acid in modifying the cement properties are discussed. [ABSTRACT FROM AUTHOR]

“Polydopamine” (PDA) is the oxidation product of dopamine and can be obtained as thin films covering the surface of all kinds of known materials and simultaneously as insoluble and useless precipitates from dopamine solutions in the presence of appropriate oxidants. The valorization of such precipitates to obtain stable suspensions of functional nanomaterials is highly desirable owing to the chemical and optical properties of PDA. We show that a vast repertoire of polyelectrolytes polycations as well as polyanions, allow to control the size of PDA particles in the 10–100 nm size range. Simultaneously to the production of smaller nanoparticles, a progressive inhibition of PDA deposition on the surface of quartz plates (as well as on the surface of the reaction vessel) is found as the concentration of the polyelectrolytes is increased in the dopamine solution. The mechanism of size control-inhibition of film deposition is investigated in the particular case of poly(allylamine) but remains not understood in the case of polyanions. [ABSTRACT FROM AUTHOR]

Abstract: 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). [Copyright &y& Elsevier]

Abstract: We recently showed the possibility to build dopamine–melanin films of controlled thickness by successive immersions of a substrate in alkaline solutions of dopamine [F. Bernsmann, A. Ponche, C. Ringwald, J. Hemmerlé, J. Raya, B. Bechinger, J.-C. Voegel, P. Schaaf, V. Ball, J. Phys. Chem. C 113 (2009) 8234–8242]. In this work the structure and properties of such films are further explored. The ζ-potential of dopamine–melanin films is measured as a function of the total immersion time to build the film. It appears that the film bears a constant ζ-potential of (−39±3) mV after 12 immersion steps. These data are used to calculate the surface density of charged groups of the dopamine–melanin films at pH 8.5 that are mostly catechol or quinone imine chemical groups. Furthermore the ζ-potential is used to explain the adsorption of three model proteins (lysozyme, myoglobin, α-lactalbumin), which is monitored by quartz crystal microbalance. We come to the conclusion that protein adsorption on dopamine–melanin is not only determined by possible covalent binding between amino groups of the proteins and catechol groups of dopamine–melanin but that electrostatic interactions contribute to protein binding. Part of the adsorbed proteins can be desorbed by sodium dodecylsulfate solutions at the critical micellar concentration. The fraction of weakly bound proteins decreases with their isoelectric point. Additionally the number of available sites for covalent binding of amino groups on melanin grains is quantified. [Copyright &y& Elsevier]

Abstract: We apply herein the reactive layer-by-layer (LBL) spray deposition of a polycation (polyethyleneimine, PEI) and a water soluble initiator of titanium dioxide [Ti(IV) bis(ammoniumlactato)dihydroxide, TiBisLac] to produce thin hybrid films containing PEI and nearly monodisperse TiO2 anatase nanoparticles. The thickness of these coatings can be finely adjusted by either changing the number of deposition steps or the TiBisLac concentration. These films display intense absorption in the UV range and nearly full transparency above 365 nm and they also display photoinduced superhydrophilicity. These coatings can be produced either by reactive LBL spray deposition or reactive LBL dipping and may offer a wide range of applications from biology, as antibacterial coatings, to photoactive materials. [Copyright &y& Elsevier]