-
[show abstract]
[hide abstract]
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.
Materials Science and Engineering: C.
-
[show abstract]
[hide abstract]
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.
Synthetic Metals.
-
[show abstract]
[hide abstract]
ABSTRACT: Wettability studies have been performed to probe the surface properties of ITO substrates, aimed to be used as hole injecting electrode in OLEDs. The elimination of organic contaminants upon the cleaning treatment (ultrasonic bath in organic solvents) leads to an increase of the free energy of the ITO surface becoming hydrophilic. The surface energy components calculated from the Van Oss model show the appearance of a basic component upon the cleaning treatment. A thermal treatment at 100 °C for 3 h leads to a decrease of the surface free energy due to surface dehydration. These properties are attributed to the hydroxides formed at the ITO surface inducing improved adhesion at the ITO/polymer interface. The ITO surfaces have been functionalised with a chloroethylphosphonic acid mono-layer to increase their stability. The appearance of an acid–base component leads to a dipolar character of the ITO surface. The formation of a compact layer of a spin coated poly(phenylenevinylene) derivative induces the shielding of the ITO basic character. The weakening of the near infrared absorption associated to ITO free carriers confirms the formation of a dipole layer at the interface with the molecular layer in contact with ITO. Improved injection properties, shown by the current/voltage characteristics, result from the interface modifications.
Thin Solid Films 516(7):1341-1344. · 1.89 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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.
Materials Science and Engineering: C.
