2, Québec Metallurgy Center (CMQ), Trois Rivières, Quebec, Canada
Several types of non-degradable alloys are used for stent applications, for example AISI 316L stainless steel, Co-Cr alloys such as L605, and Nitinol. The used materials have to satisfy a series of requisites, such as for example excellent mechanical properties, suitable electrochemical resistance, and high cyto-/hemo-compatibility. The quest for an «ideal» material is still open, as for example AISI 316L and L605 are composed of elements (for example Ni) whose release in the bloodstream is known to be noxious. For this reason, a new Ti alloy containing only cytocompatible elements, Mo and Fe, was designed and produced to obtain a material with combined high mechanical resistance and high plastic deformation. The present work is a preliminary study of the surface features of this alloy and pure Ti after several treatments, to set the basis for a better understanding of the phenomena involved in enhanced biological properties.
Different kinds of surface treatments were performed on commercial pure Ti and cast Ti-9Mo-1.3Fe (TMF1.3) samples: mechanical polishing (MP), electropolishing (EP), a thermal treatment after electropolishing (TT) and oxygen plasma immersion ion implantation after electropolishing (PIII). The effect of these treatments on surface chemistry, morphology, physical properties and hemocompatibility were investigated by several techniques. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used, respectively, to analyze the surface chemical composition, morphology and roughness. Static water contact angle was also used to investigate the wettability. Hemocompatibility tests were performed on selected samples of the two materials, EP and PIII treated, to assess their resulting biological behavior.
Roughness, chemical composition, surface energy and biological property were all influenced by the treatment parameters. The PIII treatment was responsible for the highest roughness Ra, in both the alloys, respectively ~5 nm for pure Ti and ~ 3 nm for TMF1.3 (measured surface 1 mm2); while MP treatment resulted in smallest roughness Ra. The lowest contact angle, around 50°, was found for TMF1.3 in the PIII condition; while pure Ti in the MP condition showed the highest one (around 98°). In general, pure Ti showed higher contact angles for all the considered conditions. Mo traces were found in the EP condition of TMF1.3; the alloy oxidation covered the surface by a layer of Ti oxide. Hemocompatibility tests showed differences in terms of biological responses.