Laurence Ponsonnet

Relationship between surface properties (roughness, wettability) of titanium and titanium alloys and cell behaviour

Cell attachment and spreading to titanium-based alloy surfaces is a major parameter in implant technology. In this paper, substratum surface hydrophobicity, surface free energy, interfacial free energy and surface roughness were investigated to ascertain which of these parameters is predominant in human fibroblast spreading. Two methods for contact angle measurement were compared: the sessile drop method and the captive bubble two-probe method. The relationship between surface roughness and the sessile drop contact angles of various engineered titanium surfaces such as commercial pure titanium (cp-Ti), titanium–aluminium–vanadium alloy (Ti–6Al–4V), and titanium–nickel (NiTi), was shown. Surface free energy (SFE) calculations were performed from contact angles obtained on smooth samples based on the same alloys in order to eliminate the roughness effect. SFE of the surfaces have been calculated using the Owens–Wendt (OW) and Van Oss (VO) approaches with the sessile drop method. The OW calculations are used to obtain the dispersive (γd) and polar (γp) component of SFE, and the VO approach allows to reach the apolar (γLW) and the polar acid–base component (γab) of the surface. From captive bubble contact angle experiments (air or octane bubble under water), the interfacial free energy of the different surfaces in water was obtained. A relationship between cell spreading and the polar component of SFE was found. Interfacial free energy values were low for all the investigated surfaces indicating good biocompatibility for such alloys.

Effect of surface topography and chemistry on adhesion, orientation and growth of fibroblasts on nickel-titanium substrates

Abstract Nickel–titanium alloy (NiTi) is a metallic biomaterial known for its mechanical and shape memory properties. These properties suggest that it could be used for medical purposes such as surgical implants. To evaluate the effects of the chemical composition and microtexture of the metal surface on the cellular behaviour, the adhesion, orientation and proliferation of human gingival fibroblasts were studied with substrates having different surface roughnesses. To separate the effects of material roughness and composition on the fibroblast response, we have chosen to compare substrates of different surface roughnesses but of the same chemical composition (NiTi). Moreover, substrates of different surface compositions (Ti6Al4V, cp-Ti, 316L stainless steel) but of similar smooth surface topography were also tested. The texture, chemical state and composition of the surfaces were determined using a surface-tracing instrument for roughness characterisation and X-ray photoelectron spectroscopy (XPS) for chemical analysis. The effect of γ-sterilisation on the chemical composition was studied. Human gingival fibroblasts attached, spread and proliferated on all titanium-based surfaces. On samples exhibiting the highest roughness, the cells were oriented in a parallel order along the grooves caused by mechanical polishing, whereas on smooth surfaces, they appeared to grow with no specific orientation. We observed low cell proliferation on the NiTi surfaces of the highest roughness.

EELS analysis of hydrogenated diamond-like carbon films

Abstract Electron energy-loss spectroscopy (EELS) has been used to analyze the structure of hydrogenated diamond-like carbon (DLC) films deposited by plasma-assisted CVD (PACVD) under a variety of conditions. Spectra obtained from highly oriented pyrolytic graphite and amorphous carbon were used as references. The ratio sp 3 (tetragonal) to sp 2 (trigonal) carbon sites in the DLC films was quantified for different hydrogen contents from the near-edge structure (ELNES) of the carbon K-edge and compared with a constrained network structure model. The results were in agreement with this model and showed an increase of the ratio sp 3 to sp 2 with increasing hydrogen content in the material. The irradiation damage caused by the electron beam increased the sp 2 fraction even when using a N 2 -cooled specimen holder. In order to better identify the chemical bonding from the carbon K near-edge structure, the first two peaks of the edge were deconvoluted to obtain the peaks of individual transitions, after subtracting the simulation of the carbon K-edge continuum to extract the core-excitation peaks. The relative contributions of 1s/ π * (CC), 1s/ σ * (C–H) and 1s/ σ * (C–C) were thus obtained. The position in energy of each peak is discussed.

Injection modifications by ITO functionalization with a self-assembled monolayer in OLEDs

Abstract Operating conditions of OLEDs are very sensitive to the surface properties of indium tin oxide (ITO). Wettability measurements have been performed to characterize ITO surface properties and their modification upon deposition of a self-assembled monolayer. Contact angle measurements demonstrate that ITO surface is basic. Upon grafting with phosphonic acid, the surface becomes acid. The I ( V ) characteristics of light-emitting diodes (LEDs) based on a soluble PPV derivative: poly(2-octoxy-5-methoxy-1,4-phenylenevinylene) (POMX) by such functionalized ITO show a reduction of the onset voltage and a rectification ratio enhancement. The electrical characteristics follow a space–charge limited conduction (SCLC) behavior. Such modified ITO electrodes lead to main improvements of the diode properties through operating voltage reduction and stability increase.

Adhesion-related glycocalyx study: quantitative approach with imaging-spectrum in the energy filtering transmission electron microscope (EFTEM)

Large polysaccharide molecules composing the glycocalyx have been shown to prevent cell adhesion. However, this process was not observed microscopically. Terbium labeling, combined with a new quantitative imaging method based on electron energy loss spectroscopy, allowed specific glycocalyx staining with excellent contrast. Image analysis enabled us to compare glycocalyx structure in free membrane areas and contacts between monocytic cells and bound erythrocytes. Apparent glycocalyx thickness, in contact areas, was half of the sum of glycocalyx thicknesses in free areas without label density increase. Ultrastructural immunogold localization of CD43 molecules, a major component of glycocalyx, was also demonstrated to be excluded from contact areas during adhesion. Thus, both approaches strongly suggest that some glycocalyx elements must exit from contact to allow binding of adhesion molecules.

Chemical bond mapping of carbon by image-spectrum EELS in the second derivative mode

Abstract Electron Energy-Loss Near Edge Structure (ELNES) mapping has been performed by using an energy-filtering TEM and the recently developed image-spectrum acquisition technique. The performance of the method in terms of spatial and energy resolution was evaluated by using a Zeiss 902 EFTEM and a specific software for this application. The experimental model was calcite material (CaCO3) deposited on a pure carbon film. This specimen contains two chemical bondings for carbon atoms, namely the CC and the CO bondings. Selected-area EELS spectra of the carbon K-edges showing the characteristic 1 s π ∗ transitions could be extracted from 8 nm diameter zones from series of energy-filtered images. The predicted change in the EELS spectrum of sp2 hybridised carbon K-edge due to a chemical shift is clearly visible. The mapping of the 1 s π ∗ (CC) molecular transition (peaking at 285 eV) was clearly distinguished from the 1 s σ ∗ (CO) one at 299 eV. For mapping the 1 s π ∗ (CO) at 291 eV as well as the 1 s s ∗ (CC) molecular transitions, a second derivative method was found to remove the background more correctly with the advantage to reduce the number of images (and therefore the dose). In the state of our knowledge, this represents the first molecular orbital mapping by EFTEM with a 256 × 256 image size where two chemical bondings of an element can be separated.

Contact angle measurement on xerogel sensitive layer for optical fibre sensor

This paper deals with approach for the detection of chemical vapours based on refractive-index changes of a silica xerogel layer deposited as an optical cladding on the fibre core. The fibre is multimode fibre excited with an inclined collimated beam. The refractive-index changes are evaluated by means of changes of the output power at the end put of the fibre. The optical properties of the sensitive cladding (refractive index and absorption coefficient) can be obtained with modelisation program. The sensitivities of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS)-based xerogel layers to toluene and water are presented in the paper. The hydrophobicity of the two-xerogel layers and their surface-free energy has been determined with contact angle measurements. A correlation between optical detection results and contact angle measurements can be done.

High resolution chemical mapping in the energy-filtering TEM: application to interface layers in ceramics

Image-spectrum EELS (electron energy-loss spectroscopy) consists of acquiring sequences of energy-filtered images of a specimen with an energy-selecting TEM (or an imaging filter in general). A special software was developed for this application and allows the immediate display of an energy-filtered image or an EELS spectrum to be obtained, interactively. The method is able to produce semi-quantitative chemical mapping of elements at a sub-nanometric spatial resolution. This image-spectrum EELS method (called IMEELS) has been implemented on a Zeiss CEM 902 TEM microscope. The applications of this method for materials and biological specimens has already been described elsewhere. This work presents the capabilities of the IMEELS method to produce fast chemical mapping and EELS spectra in thin films interfaces of ceramic materials, with a high spatial resolution and in a short experimental time (typically a few minutes).