P. Schaaf

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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Publications (147)558.95 Total impact

  • T Garnier · A Dochter · N T T Chau · P Schaaf · L Jierry · F Boulmedais ·
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    ABSTRACT: Polyampholyte-based films can be efficiently self-assembled onto a surface in a one-pot manner. By using a gradient of protons, morphogens, generated at an electrode surface, a charge-shifting polyelectrolyte present in solution can be transformed into a polyampholyte, leading to the continuous buildup of a film based on polyelectrolyte complexation.
    Chemical Communications 08/2015; 51(74). DOI:10.1039/c5cc04477d · 6.83 Impact Factor

  • Wound Repair and Regeneration 11/2013; 21(6):A76-A76. · 2.75 Impact Factor
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    ABSTRACT: Prevention of pathogen colonization of medical implants is a major medical and financial issue since infection by microorganisms constitutes one of the most serious complications after surgery or critical care. Immobilization of antimicrobial molecules on biomaterials surfaces is an efficient approach to prevent biofilm formation. Herein, the first self-defensive coating against both bacteria and yeasts is reported, where the release of the antimicrobial peptide is triggered by enzymatic degradation of the film due to the pathogens themselves. Biocompatible and biodegradable polysaccharide multilayer films based on functionalized hyaluronic acid by cateslytin (CTL), an endogenous host-defensive antimicrobial peptide, and chitosan (HA-CTL-C/CHI) are deposited on a planar surface with the aim of designing both antibacterial and antifungal coating. After 24 h of incubation, HA-CTL-C/CHI films fully inhibit the development of Gram-positive Staphylococcus aureus bacteria and Candida albicans yeasts, which are common and virulent pathogens agents encountered in care-associated diseases. Hyaluronidase, secreted by the pathogens, leads to the film degradation and the antimicrobial action of the peptide. Furthermore, the limited fibroblasts adhesion, without cytotoxicity, on HA-CTL-C/CHI films highlights a medically relevant application to prevent infections on catheters or tracheal tubes where fibrous tissue encapsulation is undesirable.
    Advanced Functional Materials 04/2013; DOI:10.1002/adfm.201300416 · 11.81 Impact Factor
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    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.
    Langmuir 05/2012; 28(22):8470-8. DOI:10.1021/la300563s · 4.46 Impact Factor
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    ABSTRACT: In this paper, we report on the mechanical characterization of polyelectrolytes multilayer (PEM) films prepared from poly(glutamic acid)-poly(styrenesulfonate) (PGA-PSS) blends, deposited in alternated spray deposition with poly(allylamine hydrochloride) (PAR). The polyanion composition of the blended film was first investigated by Fourier transformed infrared spectroscopy in the attenuated total reflection mode. The monomer molar fraction of PGA, in the film increases almost linearly with x, i.e., the monomer molar fraction of PGA in the sprayed polyanion solution. The mechanical properties of the blended (PAH/PGA(x)-PSS(1-x))(n) film were measured using two methods: (i) the wrinkling metrology method and (ii) by colloidal probe atomic force microscopy. We demonstrate that Young's modulus of the PAH/PGA(x)-PSS(1-x) multilayer films can be systematically controlled by the chemical composition of these films, depending on x. Measurements indicate that increasing the monomer molar fraction of PGA in the blended film results in a decrease in film modulus up to 2 orders of magnitude as compared to the PAH/PSS system. At a monomer molar fraction of PGA in the film around x = 0.7, this system undergoes such a transition. We also show that for a given x the elastic properties of these films are significantly affected by the humidity conditions. For a (PAH/PGA(0.88)-PSS(0.12)) film, Young's modulus of the film varies from several hundred to few MPa by solely altering the relative humidity between 12.5% and 80%.
    Macromolecules 11/2011; 44(22):8954-8961. DOI:10.1021/ma201974g · 5.80 Impact Factor
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    ABSTRACT: Development of blood vessels remains a big challenge for vascular tissue engineering. We recently demonstrated that poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH/PSS) films are excellent substrates for vascular progenitor cell differentiation. However, no intact cell sheets could be harvested. Using a spraying procedure, we develop here a user-friendly technology for the development of small blood vessels based on alginate membranes. The key point of our approach is based on a multilayered PAH/PSS film built on micro-textured alginate gels, about 140 mu m thick and which can be peeled off. The alginate, calcium chloride and polyelectrolyte solutions are sprayed on a vertical glass substrate. Due to the drainage of the calcium chloride solution on the adsorbed alginate layer, an oriented micro-textured gel is obtained. The PAH/PSS film, built on top of the gel, induces a good proliferation without phenotype alteration of smooth muscle cells. Parallel micro-textures on the top of the gel allow the orientation of cells. After peeling off the substrate, the cellularized membrane is rolled around a mandrel. Confocal microscopy observations show the formation of concentric layers with a presence of cells. This work represents the initial stages of a new, original blood vessel reconstruction strategy via tissue engineering.
    Soft Matter 03/2011; 7(7-7):3621-3626. DOI:10.1039/C0SM00998A · 4.03 Impact Factor
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    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.
    Langmuir 03/2011; 27(8):4653-60. DOI:10.1021/la104809z · 4.46 Impact Factor

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    ABSTRACT: We report on a novel approach for the design of stimuli-responsive surfaces based on the immobilization of charged ABC triblock terpolymer micelles. The terpolymer consists of a hydrophobic polybutadiene (B) block, a weak anionic poly(methacrylic acid) (MAA) middle block, and a strong cationic end block of quaternized poly(2-(dimethylamino) ethyl methacrylate) (Dq) (BMAADq). In alkaline solutions, this polymer self-assembles into core-shell-corona micelles with a hydrophobic B core, a pH-sensitive MAA/Dq intramicellar interpolyelectrolyte complex (im-IPEC) shell, and a cationic corona of excess Dq. These micelles were directly adsorbed onto charged silica as a monolayer creating laterally structured surfaces. The adsorption kinetics was found to follow the theoretical model of random sequential adsorption (RSA). Exposure of the adsorbed micelles to external stimuli (at pH < pK(a,apparent) of PMAA) induces im-IPEC dissolution due to protonation of the MAA block resulting in a changed composition of the shell and both the length and charge density of the corona. Two types of conformational response to pH trigger and therefore, two types of dynamics coupled to short and long relaxation times are involved in the system. The response to pH cycling was shown to be reversible on the short-term scale while the long-term exposure to acidic media causes irreversible changes in the morphology of the micelles as a consequence of the micelles' core mobility and slow rearrangement. In particular, we find that exposure to low pH causes a shape transition to a "doughnut"-like morphology, exposing the core parts of the micelles. In contrast, adsorbed micelles with covalently crosslinked B cores show higher stability to irreversible morphology changes while maintaining the reversible response to pH cycling.
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    ABSTRACT: A biosensor is an analytical device which physically associates a biological receptor and a transducer [1]. The transducer transforms the interaction between the receptor and its target into an interpretable signal. No other step, such as the separation of free and complexed molecules or the addition of a further reagent, is required. Biosensors have been classified in terms of the transduction mode or the nature of the biological receptor [2-4]. The modes of transduction applicable to all molecular interactions, without labelling the molecules and whatever their nature, detect either a change in mass on a surface (surface plasmon resonance, acoustic biosensors), or a heat transfer (calorimetry) [6]. Among the devices using these transduction modes, the most widely used in biology at the present time are based on surface plasmon resonance (SPR). Since the commonest SPR biosensors are manufactured by Biacore AB, a company based in Uppsala, Sweden [5] (Biacore is a registered trademark), we begin by discussing the interpretation of SPR data obtained in this configuration.

  • P. Schaaf · J.-C. Voegel ·
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    ABSTRACT: The films known as polyelectrolyte multilayers are made by alternating deposition of polyanions (negatively charged polymers) and polycations (positively charged polymers). The development of these films, invented in the 1990s [1,3], has seen a considerable burst of interest, in particular due to their many applications. Indeed, these films are used to make electroluminescent diodes [4], anti-reflecting surfaces [5], water filtering substrates [6], and substrates for the separation of chiral molecules [7]. The alternating deposition of positive and 12 negative species can also be used to make films with a mechanical strength close to that of steel [8]. Applications to biosensors and especially biomaterials are currently under investigation [9]. This is the last example discussed in the present chapter. Polyelectrolytes are charged polymers, usually soluble in an aqueous solution. When a surface, supposed negatively charged, is set in contact with a solution of polycations (positively charged polyelectrolytes), the chains will immediately interact with the surface via electrostatic interaction and adsorb onto it. Like any other polymer, polyelectrolytes do not adsorb lengthwise against the surface, but form loops and tails. This adsorption is generally irreversible, and replacing the polycation solution by the solvent (water) alone will only lead to very slight desorption. This irreversibility of adsorption results from the formation of many anchoring points with the surfaces along the long polymer chains. Even if the interaction energy between a monomer, the basic building block of the polymer, and a surface is small, the fact that a number of contact points are set up makes the overall interaction between a polymer and a surface rather strong. Furthermore, in order for a chain to desorb, all the anchor points on the surface must be broken simultaneously, and such an event is highly improbable.
  • E. K. Mann · L. Heinrich · P. Schaaf · J. C. Voegel ·
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    ABSTRACT: The optical response of a dielectric interfacial film can be completely described, to second order in the film thickness, by three parameters called optical invariants. These allow the extraction of a maximum of information about the film while avoiding arbitrary models of that film. The information which can be obtained from experimental data on an isotropic film is, in order of decreasing precision: (i) the surface concentration of the adsorbed material, (ii) the average thickness of the layer through the first moment of the mass distribution in the layer, and (iii) a more complicated moment that gives an indication of the uniformity of the layer. This method of analysis is applied to scanning angle reflectometry data on two kinds of films at a water/silica interface: (i) Protein films, and in particular, antibody/antigen complexes forming at the interface. This provides a model of a film that is essentially homogenous in the direction parallel to the surface, but which may have concentration gradients perpendicular to the surface. (ii) Films of polystyrene latex particles. Here the information gained is the size and number of particles adsorbed at the interface, with an indication of the uniformity of the particle distribution.
    02/2008: pages 296-299;

  • B. Senger · J. Talbot · P. Schaaf · A. Schmitt · J.-C. Voegel ·
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    ABSTRACT: We study numerically the diffusion random sequential adsorption (DRSA) and random sequential adsorption (RSA) of hard disks on a one-dimensional lattice segment. The saturation coverages of the two processes, although similar, are clearly different within the errors of the simulation. The difference is explained by the nonuniform adsorption of disks within the available gaps when diffusion is permitted. We conclude that a recently proposed class of generalized parking problems cannot rigorously describe the DRSA process.
    EPL (Europhysics Letters) 07/2007; 21(2):135. DOI:10.1209/0295-5075/21/2/002 · 2.10 Impact Factor
  • G. J. M. Koper · P. Schaaf ·
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    ABSTRACT: Scanning-angle reflectometry around the Brewster angle has been used to measure the reflectivity of a flat silica surface sparsely seeded with latex particles. The reflectivity for such surfaces is composed of 1) the direct (Fresnel) reflection from the silica-water interface, 2) the (Mie) scattering of the adsorbed particles and 3) the interference between the two previously mentioned components. The analysis of the obtained curves of reflectivity vs. incidence angle yields three parameters: particle size, refractive index of the particle, and the adsorbed particle density.
    EPL (Europhysics Letters) 07/2007; 22(7):543. DOI:10.1209/0295-5075/22/7/011 · 2.10 Impact Factor
  • E. K. Mann · P. Wojtaszczyk · B. Senger · J.-C. Voegel · P. Schaaf ·
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    ABSTRACT: The irreversible deposition of small latex particles on a surface leads to configurations whose radial distribution functions g(r) are well predicted by the random sequential adsorption (RSA) model, whereas the variance σ2 of the density of adsorbed particles is inconsistent with this model. Since g(r) is related to σ2 by a general equation, this constitutes an (apparent) paradox. This article lifts this paradox by means of a simple generalized RSA model.
    EPL (Europhysics Letters) 07/2007; 30(5):261. DOI:10.1209/0295-5075/30/5/002 · 2.10 Impact Factor
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    ABSTRACT: This article first defines the conditions a material implanted in a living organism has to fulfil to be considered as a biomaterial. It presents then some examples in which natural or synthetic polymers can be used either to coat the surface of an implant, with the aim to simultaneously reduce non specific protein adsorption and to favour specific cell adhesion, or in the form of a gel in order to induce recolonisation of a tissue in an injured region of a living organism. It finally shows that more efficient polymers for a given purpose can be synthesised with the tools of combinatorial chemistry.

Publication Stats

7k Citations
558.95 Total Impact Points


  • 1989-2015
    • French National Centre for Scientific Research
      • Institut de Biologie Moléculaire des Plantes (IBMP)
      Lutetia Parisorum, Île-de-France, France
  • 1999-2013
    • University of Strasbourg
      • Institut Charles Sadron
      Strasburg, Alsace, France
  • 1993-2005
    • French Institute of Health and Medical Research
      • Unit of Biomaterials and Tissue Engineering
      Lutetia Parisorum, Île-de-France, France
  • 1997
    • Institut Universitaire de France
      Lutetia Parisorum, Île-de-France, France
  • 1995
    • Leiden University
      • Leiden Institute of Chemistry
      Leyden, South Holland, Netherlands
  • 1991-1994
    • Purdue University
      • School of Chemical Engineering
      ウェストラファイエット, Indiana, United States
  • 1992
    • IHU de Strasbourg
      Strasburg, Alsace, France
  • 1988-1990
    • University of California, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Ángeles, California, United States