powder productıon and nano materıals - 6th International Powder ...

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6. ULUSLARARASI TOZ METALURJİSİ KONFERANSI ve SERGİSİ
th INTERNATIONAL POWDER METALLURGY CONFERENCE & EXHIBITION
THE PROCESSING OF Ni-RICH TiNi FOAMS WITH Mg SPACE HOLDER
TECNIqUE AND IN-VIVO EvALUATION AS GRAFT MATERIAL
G.İpek NAKAŞ*, B.Bertan ARPAK**, Şakir BOR***
*Middle East Technical University, Department of Metallurgical and Materials Engineering, 06800, Ankara, Türkiye,
inakas@metu.edu.tr
** Başkent University Faculty of Dentistry, Department of Oral and Maxillofacial Surgery, 06680, Ankara, Türkiye,
bertanarpak@gmail.com
***Middle East Technical University, Department of Metallurgical and Materials Engineering, 06800, Ankara,
Türkiye, bor@metu.edu.tr
ABSTRACT
Porous TiNi alloys are very promising materials for the biomedical applications due to their superelastic properties
and shape memory behavior in combination with the elastic module that are similar to that of bone. Surface roughness,
which is a critical parameter to employ the material as a graft, can be achieved by the powder metallurgical
processes. However, the close control of the pore size, geometry and orientation is still difficult to maintain. In this
study, magnesium space holder technique is employed for manufacturing TiNi foams that consist of interconnected
pores with homogeneous shape, size and distribution in addition to the surface quality necessary for bone growth.
Porous TiNi alloys, which were processed from prealloyed nickel-rich (50.8 at.%Ni) TiNi powder via sintering at
1100 ºC for 1 hours under protective gas atmosphere, were placed into the created defects on the femur of rats
for a period of 90 days to evaluate the bone healing process. Afterwards, processing technique was improved via
increasing sintering temperature and time to 1200 ºC and 2 hours, respectively. The processed TiNi foams that have
uniformly distributed and interconnected spherical pores within a size range of 250-600 µm, were in fully austenitic
state and the formation of secondary intermetallics as well as the oxidation, which is a major problem in dealing
with titanium alloys, was prevented according to the X-ray Diffraction (XRD) and scanning electron microscope
(SEM) analysis. Bone ingrowth was achieved in TiNi foams that have pore ratio in the range of 59-73 vol.%, and
no infection was observed for these osseointegrated grafts according to the histopathological evaluation. Although
no failure or bone resorption was observed for the grafted TiNi foams, the newly processed porous TiNi alloys were
subjected to compression tests in order to evaluate the mechanical compatibility for biomedical applications. It was
found that the mechanical properties could be adjusted by the alteration of the pore ratio and “stress shielding”
problem could be eliminated.
keywords: TiNi, porous, graft, compression, biocompatibility, bone growth
1. INTRODUCTION
Titanium and its alloys have been extensively studied and applied in the field of biomedical applications [1-3].
Among Ti alloys, TiNi has outstanding properties such as shape memory and superelasticity in addition to its elastic
modulus that is similar to that of cortical bone [2, 4]. Processing the TiNi alloys in porous form further enhances the
applicability of this alloy since the control of the mechanical response become possible via the adjustment of the
pore characteristics. On the other hand, there has been a debate about the biocompatibility, especially in terms of
possible toxic effects of Ni [5-8]. However, there are several inquiries indicating that Ni release will not occur since
the implant will not be subjected to such a corrosive environment that is strong enough to reduce the passive TiO2
layer formed on TiNi [6-8].
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