Structural and Functional (Superficial) Biocompatibility of new Amorphous / Quasicrystalline Ti-based Composites

H. Lefaix*, P. Vermaut*, S. Zanna, A. Galtayries, F. Prima* and R. Portier*
LPCS, UMR-CNRS 7045, ENSCP, 11 rue P. et M. Curie, 75231 Paris, France
* Groupe de Métallurgie Structurale, LPCS, UMR-CNRS 7045

Titanium and its alloys are frequently used as implants due to their high mechanical strength, low elastic modulus (structural biocompatibility) and biocompatibility (functional or superficial biocompatibility). However, as these materials have a poor wear resistance, tribo-chemical reactions during use produce debris accumulation, resulting in adverse cellular response. It is then possible to generate different micro (nano) structures for the bulk and for the superficial parts of the specimen, by different thermal treatments (composite).
After a quick survey on the structural biocompatibility, this work deals with biocompatibility of new amorphous quasicrystalline Ti-based composites displaying high functional properties. We focussed on the Ti45Zr38Ni17 system which is able to form amorphous phase as well as quasicrystals (QC) by rapid-quenching techniques. Their high wear resistance and hardness make them potential candidates for improving tribological properties of metallic implants. Up to far, no studies have dealt with the biocompatibility of such non periodical structures.
In order to control and to understand the formation of amorphous and quasicrystalline structures, we characterize first the microstructures of planar-flow cast Ti45Zr38Ni17 ribbons, using different quenching rates. Microstructural analyses highlight the possibility by adapting elaboration parameters, to control the as-quenched structure from nanostructured amorphous to β + QC states.
Since improved knowledge of the chemical composition of biomaterial surfaces and a better understanding of interactions between biomolecules and substrates will allow a more rational design of biomaterials, surface characterisation of alloys is an essential aspect of this approach. First of all, native oxide layer was characterized using X-ray photoelectron spectroscopy. At the surface of these nanostructured ribbons, the oxide layer is composed by TiO2 and ZrO2. Ni is mainly present at the oxide/alloy interface. Fibronectin adsorption on a Ti-based quasicrystals-forming alloy were also studied by XPS and compared to those obtained on pure titanium substrates (cpTi). The results indicate that fibronectin is adsorbed on Ti45Zr38Ni17 in the similar way than on cpTi. Concerning general biocompatibility of these ternary alloys, the osteoblastic cells, cultured on Ti45Zr38Ni17, have the same behavior whatever the microstructure. The cellular development from adhesion to differentiation evidences the middle-term biocompatibility of Ti45Zr38Ni17.

Keywords: titanium, rapid-quenching, quasicrystal, amorphous, biomaterial, oxidation, cells cultures