<I>In Vivo</I> Result of Porous TiNi Shape Memory Alloy: Bone Response and Growth

Abstract

Porous titanium-nickel shape memory alloys (TiNi SMA) can be fabricated using special engineering technique. This material is a whole porous material with interconnected pores. This porous TiNi SMA retains the unique properties of solid TiNi SMA. Its porosity and pore size can be controlled. Its application to orthopaedic field is very expected especially in bone substitute and bone implant and so on. The purpose of this study was to evaluate bone tissue response and histocompatibility of porous TiNi SMA in vivo. Thirty block implants (5 mm × 5 mm × 7 mm) of porous TiNi SMA were prepared. Analysis of pore structure of the implant was performed using Hg-porosimetry and scanning electron microscope. Fifteen New Zealand white rabbits were used. Sterile porous TiNi SMA implant was implanted in the defects of proximal tibia metaphysis. Limbs of five rabbits were harvested respectively at 2, 4 and 6 weeks post implantation. Each specimen was embedded in PMMA. Embedded specimen was sectioned into 300 µm thickness with isomet-diamond saw. Quantitative histomorphometric analysis was performed within the each implant. The pore sizes of porous TiNi SMA were 323 ± 89 µm. Porosity was 55.3 ± 6.7%. No apparent adverse reactions such as inflammation and foreign body reaction were noted on or around all implanted porous TiNi SMA blocks. Bone ingrowth was found in the pore space of all implanted blocks. The percent bone ingrowth into the pore space of porous TiNi SMA increased over time. At six week post-implantation, bone ingrowth into pore in TiNi SMA block was very excellent (at 6 week, 78.3 ± 9.7%). This percent bone ingrowth was much higher than that of other porous materials. This in vivo response of porous TiNi SMA observed in this study opens to the possibility that porous TiNi SMA could be used as an ideal bone substitute.

High strength, low stiffness, porous NiTi with superelastic properties

“…Currently, surface porosity is produced on monolithic implants to improve anchorage of bone [1,4,5], but with minimal reduction of implant stiffness. By contrast, a fully porous prosthetic material can decrease stiffness and the stress-shielding effect while also, if appropriate pore size and connectivity are achieved, allowing bone ingrowth, thus improving the strength of the implant/bone interconnection [6,7].…”

“…Near-stoichiometric nickel-titanium alloys (abbreviated as NiTi in the following) are particularly promising for such applications, as they exhibit proven biocompatibility [6,11] and the lowest stiffness of any bio-compatible metals (55-80 GPa, depending on temperature, for austenitic NiTi [12]). It should thus be possible to match the stiffness of human bone with porous NiTi at porosity levels that are much lower than those needed for the other bio-compatible metals [7].…”

Powder Metallurgical Near‐Net‐Shape Fabrication of Porous NiTi Shape Memory Alloys for Use as Long‐Term Implants by the Combination of the Metal Injection Molding Process with the Space‐Holder Technique

“…[5,8,9] The pseudoelasticity in Ni-rich NiTi allows the material to recover up to 8% strain by a reversible stress-induced transformation. [10] Since human bone also recovers strains up to 2%, [2] NiTi matches its mechanical properties very well.…”

Fabrication and characteristics of bioactive sodium titanate/titania graded film on NiTi shape memory alloy

“…Owing to its unique shape memory effect and superelastic properties, NiTi SMA has been frequently used in medicine, such as orthopedic implants, stents, etc. [22][23][24][25][26][27][28][29][30][31] However, it contains a large amount of Ni (about 50 at %), which can lead to the allergic and toxic responses. 32,33 Therefore, the bioactivity induced by chemical treatment can make NiTi implants be used in medicine more safely and widely.…”