Biocompatibility Studies of the Nitinol Thin Films
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Biocompatibility Studies of the Nitinol Thin Films C.Z. Dinu1, R. Tanasa2, V.C. Dinca1, A. Barbalat1, C. Grigoriu1, E.O. Bucur2, A. Dauscher3, V. Ferrari DeStefano4, M. Dinescu1 1 National Institute for Laser, Plasma and Radiation Physics, PO Box MG–16, RO 76900, Bucharest, Romania, 2 Pasteur Institute S.A, Calea Giulesti 333, Bucharest, 77 826, Romania 3 Laboratories of Materials Physic (LPM), INPL, Ecole des Mines de Nancy, Parc de Saurupt, F-54042 Nancy, France 4 University of Rome “La Sapienza”, Dept. of Electronics, 00186 Rome, Italy ABSTRACT Pulsed Laser Deposition method (PLD) was used to grow nitinol (NiTi) thin films with goal of investigating their biocompatibility. High purity Ni and Ti targets were alternatively ablated in vacuum with a laser beam (λ=355 nm, 10 Hz) and the material was collected on room temperature Ti substrates. X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and atomic force microscopy analyses have been performed to investigate the chemical composition, crystalline structure and surface morphology of the NiTi films. The nitinol layers biocompatibility has been tested using as a metric the extent to which the cells adhere during the culture period on the surface of NiTi layers deposited on Ti substrates. Vero and fibroblast cell lines dispersed into MEM (Eagle) solution containing 8% fetal bovine serum, at 370 C, were used for tests. Preliminary studies indicate that the interaction at the interface is specifically controlled by the surface morphology, (especially by surface roughness), and by the chemical state of the surface. Cell behavior after contact with NiTi/Ti structure for different intervals (18, 22 and 25 days for the Vero cells, and after 10 and 25 days for fibroblasts) supports the conclusion that NiTi is a very good candidate as a biocompatible material. 1. INTRODUCTION Nickel-titanium (Ni-Ti, nitinol), a thermo elastic alloy with a composition of approximately 50 atomic % nickel, exhibits special properties like shape memory effect, superelasticity, radiopacity, plateau stresses and transformation temperatures that makes it an attractive candidate for an increasing number of medical applications such as orthopedic implants, needles, guide wires, orthodontic wires, bone substitution material and endoscopic instruments to implant (stents and filters). However, there are still a small amount of biocompatibility data available so far. A number of studies have been performed in vitro in order to prove the nitinol biocompatibility, some of them covering the behavior during and after sterilization [1]. The results of the studies performed in vivo, regarding the cytotoxicity of the Ni-Ti in long term behavior are ambiguous: part of the reports notice good biocompatibility for this alloy [2-4], but there are also reports about the negative potential impact on biological systems [5, 6]. It is well known that the toxic effects of different metals can be well quantified in vitro, although cell culture studies cannot directly mimic the cellular
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