Guy Louarn

Theoretical and experimental vibrational study of emeraldine in salt form. Part II

We present a complete study of the conductive form of the polyaniline emeraldine salt. The experimental spectra of emeraldine salt doped in the classical way and also by the action of camphorsulfonic acid–m-cresol are presented. Vibrational calculations on emeraldine salt are presented, considering the non-planar geometry of the polymer. A study of the influence of the torsion angle between cycles is proposed. Finally, a complete assignment of the Raman vibrational modes of emeraldine salt is discussed. Copyright

Spectroelectrochemical studies of poly(3,4-ethylenedioxythiophene) in aqueous medium

Abstract The in situ electrochemical doping process of the poly(3,4-ethylenedioxythiophene) (PEDT) has been studied in an aqueous micellar medium by means of optical spectroscopies. The cyclic voltammetry (CV) and optical absorption results were compared with previous ones obtained either in acetonitrile or in water without surfactant. No significant effect of the medium, water or acetonitrile, was found, but the presence or absence of surfactant in water give rise to different doping CVs, especially in the reductive part. Resonant Raman scattering experiments show a behavior of PEDT different from the one in acetonitrile. The doping mechanism we deduced from these results should imply a variation between an “intermediate” electronic conformation of the polymer in the reduced state to a predominant benzenic one during doping. The comparison with our previous results obtained in acetonitrile leads us to think that the reduced PEDT is in fact slightly oxidized by the aqueous medium.

Enhanced osseointegration of titanium implants with nanostructured surfaces: an experimental study in rabbits.

Titanium and its alloys are commonly used for dental implants because of their good mechanical properties and biocompatibility. The surface properties of titanium implants are key factors for rapid and stable bone tissue integration. Micro-rough surfaces are commonly prepared by grit-blasting and acid-etching. However, proteins and cells interact with implant surfaces in the nanometer range. The aim of this study was to compare the osseointegration of machined (MA), standard alumina grit-blasted and acid-etched (MICRO) and nanostructured (NANO) implants in rabbit femurs. The MICRO surface exhibited typical random cavities with an average roughness of 1.5 μm, while the NANO surface consisted of a regular array of titanium oxide nanotubes 37±11 nm in diameter and 160 nm thick. The MA and NANO surfaces had a similar average roughness of 0.5 μm. The three groups of implants were inserted into the femoral condyles of New Zealand White rabbits. After 4 weeks, the pull-out test gave higher values for the NANO than for the other groups. Histology corroborated a direct apposition of bone tissue on to the NANO surface. Both the bone-to-implant contact and bone growth values were higher for the NANO than for the other implant surfaces. Overall, this study shows that the nanostructured surface improved the osseointegration of titanium implants and may be an alternative to conventional grit-blasted and acid-etched surface treatments.

UV–VIS–NIR and Raman spectroelectrochemistry of regioregular poly(3-octylthiophene): comparison with its non-regioregular analogue

Spectroelectrochemical behaviour of regioregular poly(3-octylthiophene) has been investigated using UV–VIS–NIR and Raman spectroscopies. Static and dynamic UV–VIS–NIR spectroelectrochemical experiments combined with cyclic voltammetry show that oxidative doping of the regioregular polymer is a two-step process in which polarons (radical cations) are first created which then recombine to bipolarons (dications). This two-step oxidative doping mechanism is corroborated by FT Raman spectroelectrochemical studies which show significant changes in the positions and intensities of the Raman bands coinciding with the first and second oxidation peaks in cyclic voltammetry. These changes can be interpreted in terms of the doping induced formation of quinoid sequence of bands in the oxidized polymer. Vibrational calculations carried out for undoped and doped poly(3-octylthiophene) gave a very good agreement between the calculated Raman band frequencies and those recorded experimentally for the regioregular polymer.

Behaviour of mesenchymal stem cells, fibroblasts and osteoblasts on smooth surfaces.

Understanding of the interactions between cells and surfaces is essential in the field of tissue engineering and biomaterials. This study aimed to compare the adhesion, proliferation and differentiation of human mesenchymal stem cells (hMSCs), an osteoblast cell line (MC3T3-E1) and gingival fibroblasts (HGF-1) on tissue culture polystyrene (TCPS), glass and titanium (Ti). The average surface roughness was 5, 0.2 and 40×10(-3) μm for TCPS, glass and Ti, respectively. Immunocytochemistry and image analysis made it possible to quantify the number and morphology of adherent cells as well as the density of the focal points. Regardless of the substrate, both hMSCs and osteoblastic cells were mainly branch-shaped. HGF-1 exhibited a significantly higher number of focal points on Ti than on TCPS and glass. Alizarin red quantification indicated that both hMSCs and osteoblastic cells were more differentiated on TCPS than on Ti and glass. The surface properties of substrates, such as roughness, wettability and chemical composition, modulated the behaviour of the cells. Early events, such as cell adhesion, may influence the differentiation of hMSC and consequently tissue healing around implanted biomaterials.

Cell interaction with nanopatterned surface of implants.

Metals such as titanium and alloys are commonly used for manufacturing orthopedic and dental implants because their surface properties provide a biocompatible interface with peri-implant tissues. Strategies for modifying the nature of this interface frequently involve changes to the surface at the nanometer level, thereby affecting protein adsorption, cell-substrate interactions and tissue development. Recent methods to control these biological interactions at the nanometer scale on the surface of implants are reviewed. Future strategies to control peri-implant tissue healing are also discussed.

Structural properties of some conducting polymers and carbon nanotubes investigated by SERS spectroscopy

Abstract In this paper, we present Surface Enhanced Raman Scattering (SERS) experiments performed successfully on some conducting polymers and carbon nanotubes deposited in thin films on rough metallic surfaces. The enhancement mechanism in SERS has a twofold origin: electromagnetic and chemical. The electromagnetic enhancement is, however, the dominant mechanism and consists in the excitation of localized and delocalized surface plasmons (SP). The second enhancing mechanism for SERS, not yet convincingly supported by experimental data, is of chemical origin. This mechanism is due to the increase of the polarizability of the molecules on the metal surface under the action of the incident radiation, leading to the formation of new chemical bonds between the molecules and the metal surface. Unfortunately, the experimental data available to argue the presence of a chemical process are scarce and scattered. In this paper, we try to present some details regarding this aspect. In order to do so, we studied poly 3-hexylthiophene (3-PHT) and polyaniline (PAN) as a function of the type of the rough metallic support (Ag, Au or Cu), the oxidization state and thickness of the polymer layer. We studied also carbon single walled nanotubes. Our experiments reveal the existence of a chemical surface effect. The results obtained for 3-PHT show that SERS spectra depend on the oxidizing properties of the metal surface and on the nature of the solvent. This dependence is explained by the existence of some interfacial reactions that lead to the formation of interface compounds. The SERS measurements reported here reveal an increase of the intensities of the Raman lines, accompanied by a modification of the corresponding intensity ratios, when the degree of doping is increased. We observe for the first time by SERS spectroscopy that doping of 3-PHT with FeCl3 leads to the appearance of a state of disorder in the structure of the macromolecular chain, as a result of steric hindrance effects. The type of the rough metallic support can modify SERS spectra and such an effect is clearly shown for the polyaniline case. No such dependence on metallic support type is observed on the SERS spectra of carbon nanotubes.

Nanotechnology and Dental Implants

The long-term clinical success of dental implants is related to their early osseointegration. This paper reviews the different steps of the interactions between biological fluids, cells, tissues, and surfaces of implants. Immediately following implantation, implants are in contact with proteins and platelets from blood. The differentiation of mesenchymal stem cells will then condition the peri-implant tissue healing. Direct bone-to-implant contact is desired for a biomechanical anchoring of implants to bone rather than fibrous tissue encapsulation. Surfaces properties such as chemistry and roughness play a determinant role in these biological interactions. Physicochemical features in the nanometer range may ultimately control the adsorption of proteins as well as the adhesion and differentiation of cells. Nanotechnologies are increasingly used for surface modifications of dental implants. Another approach to enhance osseointegration is the application of thin calcium phosphate (CaP) coatings. Bioactive CaP nanocrystals deposited on titanium implants are resorbable and stimulate bone apposition and healing. Future nanometer-controlled surfaces may ultimately direct the nature of peri-implant tissues and improve their clinical success rate.

Comparison of the vibrational properties of polythiophene and polyalkylthiophenes

Abstract In this paper, we present a study of vibrational properties of conducting polymers containing thiophene rings : polythiophene and polyalkylthiophenes. The spectrocopic studies include Resonance Raman Scattering (RRS) and Fourier Transformed InfraRed absorption (FTIR), that we applied to the polymers mentionned above and to some thiophene oligomers. Results are interpreted by performing dynamical calculations based on a valence force field model. With the oligomer approach, the force constants are less numerous than the experimental frequencies and the results for our assignment much more reliable. The calculations provide a better understanding of Raman and infrared modes, leading to a clear comparison of the electronic and vibrational properties of neutral polythiophene, polymethylthiophene and polyoctylthiophene.

Spectroscopic properties of poly(3-alkylthiophenes) and their ‘head-to-head’, ‘tail-to-tail’ coupled analogues poly(4,4′-dialkyl-2,2′-bithiophenes)

Abstract Electrochemical doping of new soluble conducting polymers, namely, poly(4,4′-dialkyl-2,2′-bithiophenes), has been studied ‘in situ’ and ‘ex situ’ by various spectroscopic methods. These compounds represent the ‘head-to-head’ and ‘tail-to-tail’ analogues of poly(3-alkylthiophenes). The π→π ∗ transition in poly(4,4′-dialkyl-2,2′-bithiophenes) is blue shifted with respect to that characteristic of poly(3-alkylthiophenes) suggesting a higher torsion angle between the adjacent substituted thiophene rings. The doping-induced bipolaronic bands (Vis-NIR) are, however, located in essentially the same positions as the doping-induced ones in poly(3-alkylthiophenes). This observation may suggest that during doping, more twisted poly(4,4′-dialkyl-2,2′-bithiophenes) adopt a structure more similar to that of doped poly(3-alkylthiophenes). The changes in FT-IR spectra are also consistent with the bipolaron model since all the five expected doping-induced modes appear with the onset of the oxidation peak and grow in intensity with increasing potential.