In vivo 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 au ideal bone substitute.