SEARCH RESULT

Abstract Metals and their alloys used in the biomedical industry due to their high mechanical and good fatigue properties [1]. It is well known that titanium (Ti) and its alloys are the most popular metallic materials used as implant [2]. Ti alloys are classified into 3 main groups as microstructure. This are α type (e.g. pure Ti), α+β type (e.g. Ti6Al4V) and β type (e.g. Ti–29Nb–13Ta–4.6Zr, described as TNTZ) alloys [3-4]. The major properties for a metallic biomaterial are no doubt biocompatibility and corrosion resistance [5]. Farnoush et al. [6] found that bioglass which composed in HA/bioglass coatings behaves as aide for sintering process as well as responsible for transformation of HA to β-TCP which is thought to be more bioactive material due to ion exchange capability. Other findings of the study were that with addition of bioglass both bonding strength [7] and corrosion resistance were increased. Also with bioglass coating higher oxide film stability obtained in simulated body fluid. Another study was revealed that with bioglass addition and increased sintering temperatures up to 700°C is more protective than pristine Ti6Al4V substrates in terms of corrosion resistance [8]. In this study, bioglass (45S5) doped hydroxyapatite (Ca10(PO4)6(OH)2) coatings has been successfully synthesized by sol-gel technique on different Ti alloys. The corrosion resistances of the coatings have been measured under in-vitro conditions by a potentiostat/galvanostat. Potentiodynamic polarization scanning (PDS) tests were performed on the samples in the Ringer’s solution (simulated body fluid, SBF) [9]. The surface morphologies of the coated sample on the different Ti alloys are presented in Fig. 1 The PDS results of CP Ti, Ti6Al4V and TNTZ alloys in Ringer's solutions at 37°C were shown in Fig. 2a–c. In addition, some important parameters calculated from the curves have been collected in Table

International Symposium on Light Alloys and Composite Materials
UHAKS

Mehmet Topuz Burak Dikici Serap Koç Mitsuo Niinomi Masaaki Nakai

Elastic moduli of bones are generally much lower than those of metals. For example, Young’s modulus of bone is approximately 10–30 GPa, while Young’s moduli of most metals used for biomedical applications are much higher; a stainless steel (SUS316L) and a titanium alloy (Ti-6Al-4V ELI), both of which are used practically, exhibit Young’s moduli of approximately 200 and 110 GPa, respectively. Accordingly, the load transfer between a metallic implant and the surrounding bone is nonhomogeneous, resulting in a reduction of stress stimulation to the bone (stress shielding effect). Under such conditions, bone atrophy is likely to occur, leading to the loosening of the metallic implant and re- fracturing of the bone. In order to mitigate the stress shielding effect, metals with Young’s moduli equal to that of the bone are considered ideal for fabricating metallic implants. Therefore, many beta-type titanium alloys with low Young’s modulus have been developed in the last two decades. However, it was recently discovered that low Young’s modulus implants can sometimes be inconvenient for surgeons, depending on the implant type. For example, in spinal fixation devices, the amount of springback for the rod should be small enough to improve its handling ability during operations. The amount of springback of an implant is inversely associated with Young’s modulus: a low Young’s modulus leads to a large amount of springback. In other words, a high Young’s modulus is desired by surgeons, whereas a low Young’s modulus is desirable for patients. Thus, it is necessary to satisfy the contradictory requirements of surgeons and patients when developing spinal fixation devices. Under such the situations, we have proposed a novel concept, deformation- induced changeable Young’s modulus, in titanium alloys for biomedical applications as shown in Fig. 1 [1].

International Symposium on Light Alloys and Composite Materials
UHAKS

Masaaki Nakai

Ti–29Nb–13Ta–4.6Zr (TNTZ) composed of non-toxic and non-allergenic Nb, Ta, and Zr alloying elements, has been extensively investigated [1] as an alternative to the conventional metal based biomaterials. TNTZ must combine both excellent mechanical biocompatibility, corrosion resistance, good cell-implant interactions and healing. Microstructural features such as the grain diameter, secondary phases, residual stress, nature of the surface oxide film, and lattice defects can play a major role in determining the physical response of the material that influence the biocompatibility of TNTZ [1,2]. Severe plastic deformation (SPD) has been a proven technique for controlling the grain size in ultrafine-grained (UFG) (<1000 nm) and/or nanograined (NG) (<100 nm) scale [3]. Furthermore, the influence of ultrafine graining and nanograining on corrosion resistance differs among metallic materials [4,5]. Thorpe et al. [4] reported that there is no differences in corrosion resistance in Ni-based metallic materials and pure Cu. On the other hand, Rofagha et al.[5] reported lower corrosion resistance in nanocrystalline Ni-P compared to the conventional polycrystalline Ni. Clearly, there is a strong connection between corrosion resistance and the microstructural features of metallic materials. Moreover, UFG/NS materials exhibits higher cell attachments compared to their course grained (CG) counterparts [6]. It is well known that high pressure torsion (HPT) is an effective processing for producing NG TNTZ [7]. In this study, the microstructural evolution and its effect on electrochemical behaviour of solution treated TNTZ (TNTZST) and aging treated TNTZ (TNTZAT) subjected to HPT processing were evaluated by electrochemical impedance spectroscopy (EIS) measurements in simulated body fluid (SBF). While TNTZST exhibited a single β body centred cubic (BCC) grain structure having a diameter of 40 µm, the microstructure of TNTZAT consisted of randomly distributed needle-like α (HCP) precipitates in the equiaxed β grains having a diameter of 40 µm. The microstructure of TNTZAHPT consists of NG elongated β grains with a 50 nm having subgrains of non-uniform morphologies resulting from distortion by severe torsional deformation.

International Symposium on Light Alloys and Composite Materials
UHAKS

Hakan Yilmazer Burak Dikici Mitsuo Niinomi Masaaki Nakai

β-type titanium alloys have been developed all over the world, which widely used in several biomedical applications because of their good mechanical properties such as low Young’s modulus and corrosion resistance [1]. Niinomi et al. has also developed a β-type Ti-29Nb-13Ta-4.6Zr, referred to as TNTZ, which is composed of non-toxic and non-allergic elements such as Nb, Ta, and Zr, with low Young’s modulus [2]. It was also revealed that the cell viability on TNTZ is much superior than that on Ti-6Al-4V ELI [2,3]. Young’s modulus of TNTZ subjected has been found to be around 60 GPa at the microstructure having single β (BCC) phase for solution treatment and cold rolling [4-5]. It is much more closer to those (10-30 GPa) of bone than those (100 and 110 GPa) of commercial pure Ti and Ti-6Al-4V ELI.

International Symposium on Light Alloys and Composite Materials
UHAKS

Hakan Yilmazer Mazin Abed Mitsuo Niinomi Masaaki Nakai Huseyin Cimenoglu Murat Baydogan