Evaluation of the haemocompatibility of titanium based biomaterials.

The increased use of metallic biomaterials in contact with blood e.g. for the application as coronary stents leads to the development of new biomaterials. The main requirements for stents are high flexibility, high cold deformability and sufficient mechanical strength (static and dynamic), which can be obtained by strain hardening, radio-opacity and haemocompatibility. In order to investigate the properties of the metallic biomaterials in contact with blood, a comparison of the haemocompatibility of newly developed materials with established materials has been performed. To evaluate haemocompatibility without the influence of the geometry of the material, spherical powders produced by rotating electrode process (REP) were used in a dynamic test system with full human blood under two different stress conditions. The high shear stress simulates the arterial and the low shear stress simulates the venous situation. The use of a dimensionless score point (SP) system where the parameters of the haemocompatibility are determined with and without a material exposition allows an objective comparison of the materials used.

Cell orientation and cytoskeleton organisation on ground titanium surfaces.

A stable connection between the biomaterial surface and the surrounding tissue is one of the most important prerequisites for the long-term success of implants. Therefore, a strong adhesion of the cells on the biomaterial surface is required. Beside the surface composition the surface topography influences the properties of the adherent cells. The quality of the connection between the cell and the biomaterial is-among other factors-determined by the dimensions of the surface topography. Osteoblasts and fibroblast-like cells in contact with a ground biomaterial surface spread in the direction of the surface structures. These aligned cells provide a more favourable adhesion behaviour than a spherically shaped cell. To determine the influence of the surface structure on the cell alignment and cytoskeleton organisation or arrangement, substrate discs of cp-titanium were ground, producing different roughness of the substrates. The oriented cells had a higher density of focal contacts when they were in contact with the edges of the grooves and showed a better organisation of the cytoskeleton and stronger actin fibres. These changes of the aligned cells depend on the peak to valley height of the surface structures.

Interactions between cells and titanium surfaces.

The interaction between cells and implant materials is determined by the surface structure and/or surface composition of the material. In the past years, titanium and titanium alloys have proved their superiority over other implant materials in many clinical applications. This predominant behaviour is caused by a dense passive oxide layer which forms within milliseconds in oxidizing media. Titanium dioxide layers of 100 nm thickness were produced on the surface of cp-titanium grade 2, and on an experimental alloy of high vanadium content (Ti1.5Al25V) as a harmful control. The layers were produced by thermal and anodic oxidation and by coating by means of the sol-gel process. The resulting oxide layers were characterized with respect of their structure and chemical composition. In cell tests (proliferation, MTT, morphology, actin staining), the reaction of the cells was examined. It was shown that the sol-gel-produced titanium oxide layer is able to shield the cells from toxic alloying elements, with the result that the cell reaction is influenced only by the thin titanium oxide surface layer and not by the composition of the bulk material.

Preparation of TiO(2) layers on cp-Ti and Ti6Al4V by thermal and anodic oxidation and by sol-gel coating techniques and their characterization.

The excellent biocompatibility of titanium and its alloys used, for example, for medical devices, is associated with the properties of their surface oxide. For a better understanding of the tissue reaction in contact with the oxide layer, knowledge of the chemical and physical properties of this layer is of increasing interest. In this study, titania films were produced on cp-Ti and Ti6Al4V substrates by thermal oxidation, anodic oxidation, and by the sol-gel process. The thickness and structure of the films produced under different conditions were determined by ellipsometry, infrared spectroscopy, and X-ray diffraction measurements. The corrosion properties of these layers were investigated by current density-potential curves under physiological conditions. The oxide layers produced on cp-Ti and Ti6Al4V by thermal oxidation consist of TiO(2) in the rutile structure. For the anodized samples the structure of TiO(2) is a mixture of amorphous phase and anatase. The structure of the coatings produced by the sol-gel process for a constant annealing time depends on the annealing temperature, and with increasing temperature successively amorphous, anatase, and rutile structure is observed. Compared to the uncoated, polished substrate with a natural oxide layer, the corrosion resistance of cp-Ti and Ti6Al4V is increased for the samples with an oxide layer thickness of about 100 nm, independent of the oxidation procedure.

[Malignant fibrous histiocytoma of bone 20 years after femoral fracture treated by plate-screw fixation: analysis of corrosion products and their role in malignancy]. / Histiocytofibrome malin de l'os 20 ans après ostéosynthèse par lame-plaque d'une fracture du fémur : analyse des produits de corrosion et de leur rôle dans la malignité

We report a case of malignant fibrous histiocytoma of the bone that developed 20 years after a femoral fracture treated by plate-screw fixation. Similar cases reported over the past fifteen years in the literature suggest the possible mechanisms of sarcomatous degeneration. The possible carcinogenic effect of corrosion products is emphasized. Dispersion energy spectrometry of intracellular particles on the periphery and at the center of the tumor demonstrated the presence of chromium, iron and nickel at different concentrations. The association with other elements clearly demonstrates that the corrosion products were metabolized. The presence of metallic components in tumoral cells suggests a possible relationship between metallic implants and malignancy. These observations emphasize the importance of creating a national, or even international, registry of malignant tumors that develop in contact with metallic implants in order to search for a possible cause and effect relationship.

Development and functionality of isoelastic dental implants of titanium alloys.

Two types of isoelastic endosseous dental implants were produced and their functionality was tested. One type consisted of a porous sintered TiTa30 alloy, the other had a special surface structure consisting of titanium wire loops. Their mechanical properties were optimized by the production parameter (sintering and diffusion bonding, respectively). The functionality was tested after insertion into an artificial jaw which had properties corresponding to the natural mandibular. The elastic properties of both implants were similar to the properties of the bone. In addition the implants have a safe anchorage bone ingrowth. In animal experiments using the implant with surface loops it was observed that the bone entered the loops and even extremely small surface cavities in the wire loops.