Jürgen Breme

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.

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.

Osteoblast responses to different oxide coatings produced by the sol–gel process on titanium substrates☆

In order to improve the osseointegration of endosseous implants made from titanium, the structure and composition of the surface were modified. Mirror-polished commercially pure (cp) titanium substrates were coated by the sol-gel process with different oxides: TiO(2), SiO(2), Nb(2)O(5) and SiO(2)-TiO(2). The coatings were physically and biologically characterized. Infrared spectroscopy confirmed the absence of organic residues. Ellipsometry determined the thickness of layers to be approximately 100nm. High resolution scanning electron microscopy (SEM) and atomice force microscopy revealed a nanoporous structure in the TiO(2) and Nb(2)O(5) layers, whereas the SiO(2) and SiO(2)-TiO(2) layers appeared almost smooth. The R(a) values, as determined by white-light interferometry, ranged from 20 to 50nm. The surface energy determined by the sessile-drop contact angle method revealed the highest polar component for SiO(2) (30.7mJm(-2)) and the lowest for cp-Ti and 316L stainless steel (6.7mJm(-2)). Cytocompatibility of the oxide layers was investigated with MC3T3-E1 osteoblasts in vitro (proliferation, vitality, morphology and cytochemical/immunolabelling of actin and vinculin). Higher cell proliferation rates were found in SiO(2)-TiO(2) and TiO(2), and lower in Nb(2)O(5) and SiO(2); whereas the vitality rates increased for cp-Ti and Nb(2)O(5). Cytochemical assays showed that all substrates induced a normal cytoskeleton and well-developed focal adhesion contacts. SEM revealed good cell attachment for all coating layers. In conclusion, the sol-gel-derived oxide layers were thin, pure and nanostructured; consequent different osteoblast responses to those coatings are explained by the mutual action and coadjustment of different interrelated surface parameters.

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.

Influence of titanium–vanadium alloys on cell morphology: electron microscopy and ESCA studies

Titanium and its alloys provide optimum metallurgical properties for implants. The formation of an oxide layer favours compatibility with the adjacent hard and soft tissues. Research focuses on further optimizing the passive layer, particularly with respect to minimizing metal ion migration into the tissues. The present study concentrates on two alloys (Ti6A14V and Til.5A125V) coated with oxide layers generated by different techniques: thermal oxidation, anodic oxidation and sol-gel treatment. Only thermal oxidation fails to reduce surface and subsurface concentrations of vanadium, whereas other treatments avoid the element in the outermost surface areas of the alloys. Additionally, the thermally oxidized specimens show impairment of cells. Obviously, anodic oxidation and sol-gel treatment in terms of implantology are superior to thermal oxidation.

Cytocompatibility and bio-corrosion of implant alloys in different cell culture systems

Any implant introduced into the human organism may undergo degradation depending on the physicio-chemical qualities of the concerned materials. Although the in vivo degradation and corrosion of implants and prostheses have largely been demonstrated in patients, very few experiments have been conducted to assess the corrosion behaviour of implant alloys under biological conditions, which tend to simulate the complex environment leading to corrosion. The present work was conducted on 5 different alloys representative for multiple biomedical use: Ti6Al4V, NiTi (49/51), NiCr (59/26), 316L, PdAg (62/28), and 2 pure metals: hp-Ni and cp-Ti. The electrolytes for the electrochemical assays were artificial saliva pH 6.8 and RPMI cell culture medium as biological milieu with and without cells. The rest potential and the global polarisation were established. The CEM line, human lymphoid cells, (ATCC-TIB95) was used for the electrochemical assays. The cell reaction was assessed by in vitro proliferation test on L132 human epithelial cells (ATCC-CCL5). Actin labelling was performed to assess their adhesion behaviour. Ion analyses by ICP-AES were carried out in the culture medium after the electrochemical assays and proliferation tests. The electrochemical assays reveal a different corrosion behaviour of all alloys in the three electrolytes: RPMI with/without cells generally increase corrosion and diminish the break-down potential. These differences are significant for 316L, NiCr and hp-Ni, less notable for PdAg and nearly absent for the Ti-base alloys. A similar classification can be obtained by the cell proliferation tests. Actin labelling revealed important and well aligned intracellular filaments on the control and the Ti6Al4V, and a little less on cp-Ti, PdAg, and 316L. These fibres were more reduced on NiTi and NiCr and absent on hp-Ni. Chemical analyses by ICP demonstrated an increased ion release from ORIGINAL ARBEITEN J.-C. Hornez: Cytocompatibility and bio-corrosion of implant alloys in different cell culture systems

Interzellulärkontakt von Endothelzellen in vitro als Indikator für die Kompatibilität von Biomaterialien

Endothelial cells cover the inner surface of blood vessels and form the interface between the blood and the surrounding tissues. Endothelial cells are involved in regulating barrier function, which is maintained by the interendothelial cell contacts. These interendothelial cell contacts are functional units, which are influenced by the interaction of different molecules. Since endothelial cells are an important ARBEITEN ORIGINAL Kirsten Peters: Interzellulärkontakt von Endothelzellen 7-13_bio1_05_peters 04.04.2005 14:53 Uhr Seite 11