[Bone histocompatibility of surface modified nitinol memory alloy by coating titanium-niobium alloy]

Surface modification of nitinol (NiTi) shape memory alloy is an available method to prevent nickel ion release and coating with titanium-niobium (TiNb) alloy will not affect the superelasticity and shape memory of NiTi. To evaluate the bone histocompatibility of NiTi shape memory alloy implants coated by TiNb in vivo.

NiTi memory alloy columns which were 4 mm in diameter and 12 mm in length were coated with Ti (Ti-coating group) and TiNb alloy (TiNb-coating group) respectively by magnetron sputtering technique. And NiTi group were not coated on the surface. Fifteen mongrel dogs were divided into 3 groups randomly with 5 dogs in each group. NiTi, Ti-coating and TiNb-coating columns were implanted into the lateral femoral cortex of each group, respectively. There were 10 columns embedded in each dog's femur whose distance was 1.0 cm to 1.5 cm from each other. The materials were obtained 12 months after operation. After X-ray photography, only those columns which were perpendicular to the cortex of the femur shaft were selected for subsequent analysis. Push-out tests were performed to attain the maximum shear strength (the number of specimens of TiNi group, Ti-coating group, and TiNb-coating group were 12, 10, and 14, respectively). Undecalcified sections were used for histological observation and the calculation of osseointegration rate (the number of specimens of TiNi group, Ti-coating group, and TiNb-coating group were 8, 5, and 10, respectively).

The maximum shear strength of Ti-coating group (95.10 +/- 10.03) MPa, and TiNb-coating group (91.20 +/- 15.42) MPa were significantly higher than that of NiTi group (71.60 +/- 14.24) MPa (P < 0.01). Gimesa staining showed that no obvious macrophage and inflammation cell was observed in 3 groups. The osseointegration rates of NiTi group, Ti-coating group, and TiNb-coating group were (21.30% +/- 0.23%), (32.50% +/- 0.31%), and (38.60% +/- 0.58%), respectively; there were significant differences among 3 groups (P < 0.01).

The implants of 3 groups all have good bone histocompatibility. But the osseointegration rate and the shear strength in the Ti-coating group and the TiNb-coating group were better than those in the NiTi group, the TiNb-coating group is the best among them.