Bioceramics 23

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Authors: Seiji Yamaguchi, Hiroaki Takadama, Tomiharu Matsushita, Akinobu Fukuda, Takashi Nakamura, Tadashi Kokubo
Abstract: Ti-15Zr-4Nb-4Ta alloy is an attractive metal for orthopaedic implants, since it is free from cytotoxic elements and shows high mechanical strength. It was recently shown by an animal experiment [1] that this alloy tightly bonds to living bone, when it was subjected to 5 M NaOH solution and 100 mM CaCl2 solution treatments, heat treatment at 600 or 700 °C, and final water treatment at 80 °C. The bonding strength was increased markedly when the heat treatment temperature was increased from 600 to 700 °C. This increase of the bonding strength was attributed to the increase in apatite-forming ability of the treated alloy in a simulated body fluid (SBF) [2] with ion concentrations nearly equal to human blood plasma, although its reason was not revealed yet.
Authors: Seung Hoon Um, Sang Hoon Rhee
Abstract: Effect of oxide layer formed on commercially pure titanium by heat-treatment on adhesion of serum proteins and differentiation activity of osteoblasts. Commercially pure titanium disks were polished and then heat-treated at 700°C for 30 minutes. Titanium oxide layer (rutile phase) was observed to form on the titanium disk surface after heat-treatment. The contact angle of a water droplet on the heat-treated titanium disk was about 14o while that of non-heat treated one was about 68o. The amount of adsorbed total serum protein on heat-treated titanium disk was four times higher than that on non-heat treated one. ALP activity of primary cultured mouse calvarial osteoblasts on heat-treated titanium disk was also higher than that on non-heat treated one with statistical significance of p < 0.05. It implies that the serum proteins preferentially adsorbed on titanium oxide layer formed on commercially pure titanium and it is likely to enhance the differentiation activity of primary cultured mouse cultured osteoblasts.
Authors: Emin Erkan Aşik, Gül Ipek Nakaş, Şakir Bor
Abstract: Porous titanium alloys have been extensively studied in biomedical applications due to their elastic moduli similar to that of bone compared to other implant materials. Accordingly, TiNi and Ti-6Al-4V foams have been widely characterized in terms of their various mechanical properties; however, their fatigue properties have not been well studied, even though, it has a vital importance in structural applications such as medical implants. In this study, porous titanium alloys were processed via sintering at 1200 °C for 2 hours employing Mg space holder technique. TiNi and Ti-6Al-4V alloys with a porosity of 49 and 51 vol.%, respectively, were mechanically characterized by monotonic and cyclic compression tests. The compressive strength was determined to be 148 MPa for TiNi foams whereas 172 MPa for Ti-6Al-4V foams with homogenously distributed pores having diameters in the range of 250-600 µm. Endurance limit values were determined relative to the yield strength of each porous alloy in order to enable the comparison of fatigue behavior. The fatigue tests applied with a frequency of 5 Hz and a constant stress ratio (σminmax) of 0.1 have revealed that porous TiNi alloys have an endurance limit of approximately 0.6 σy whereas porous Ti-6Al-4V alloys have an endurance limit of approximately 0.75 σy. The differences and similarities in the microstructure and their effect on mechanical behavior of the two alloys were also studied by employing scanning electron microscope (SEM).
Authors: Satoshi Hayakawa, Keita Uetsuki, Akinori Kochi, Yuki Shirosaki, Akiyoshi Osaka
Abstract: A recently developed “GRAPE® technology” provides titanium or titanium alloy implants with spontaneous apatite-forming ability in vitro, which requires properly designed gaps and optimum heat treatment in air. In this study, pure titanium pieces were thermally oxidized in air and pre-irradiated by UV-light under different environmental conditions such as in air or in ultra-pure water before aligning pairs of specimens in the GRAPE® set-up, i.e., two pieces of titanium substrates were aligned parallel to each other with optimum gap width (spatial design). Then, they were soaked in Kokubo’s simulated body fluid (SBF, pH7.4, 36.5°C) for 1-2 days to clarify how the UV-light pre-irradiation affects the in vitro apatite nucleation on the substrates under the specific spatial design. UV-light pre-irradiation in water led to the deposition of a large number of apatite particles within 1 day, and showed apatite X-ray diffraction, although UV-light pre-irradiation in air and non-pretreated specimens gave the deposition of a few apatite particles and did not show any apatite X-ray diffraction. These results indicated that the rate of primary heterogeneous nucleation of apatite increased by UV-light pre-irradiation in ultra-pure water. TF-XRD patterns of the surface of the substrates thermally oxidized in air at 500°C showed the peak at 2θ = 27º assignable to the 110 diffraction of rutile phase of titanium dioxide (ICDD-JCPDS data #21-1276). Previous studies reported that the primary heterogeneous nucleation must be induced by Ti-OH groups on titanium oxide layer. Probably, the UV-light pre-irradiation in ultra-pure water can increase the number of Ti-OH groups on the surface, resulting in accelerated primary heterogeneous nucleation of apatite.

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