Nicole Jaffrezic

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.

A laponite clay-poly(pyrrole–pyridinium) matrix for the fabrication of conductimetric microbiosensors

Abstract The functionalization of an interdigitated microelectrode array by a composite matrix containing urease molecules and its application to the conductimetric detection of urea is described. Urease was entrapped in laponite clay gel and cross-linked by glutaraldehyde. The latter coating was adsorbed onto an electrochemically generated poly(pyrrole–pyridinium) film. The comparison of different organic and inorganic host matrices in terms of storage and operational stabilities clearly demonstrated the advantages of the composite matrix. Finally, in order to illustrate the potentialities of the composite matrix for the fabrication of conductimetric microbiosensors, the immobilization of glucose oxidase on microelectrode arrays and the conductimetric detection of glucose were successfully performed.

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.