K. Yeung, R. Y. Chan, J. K. Lam, W. W. Lu, D. Chan, K. D. Luk, K. M. Cheung, The University of Hong Kong, Hong Kong, Hong Kong; S. L. Wu, J. C. Chung, P. K. Chu, City University of Hong Kong, Hong Kong, China; X. Liu, City University of Hong Kong, Hong Kong, Hong Kong; X. Liu, Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai, China; C. L. Chu, Southeast University, Nanjing, China
NiTi possesses super-elasticity and shape memory that most other current biomedical metals do not have. It is therefore potentially useful in orthopaedic. However, nickel ion release remains a major concern particularly for orthopaedic implants on which fretting is always expected at the implant junction. We have invented a novel surface treatment using plasma immersion ion implantation (PIII) technology to alter the material surface chemistry in order to suppress nickel release. This paper describes the surface wear and hardness properties, corrosion resistance; cytocompatibility together with in-vivo behavior of PIII treated and untreated samples. NiTi discs with 50.8% Ni were treated by nitrogen PIII at 40kV and 200Hz. After PIII, a thin layer of titanium nitride (TiN) is formed on the surfaces. Compared to the untreated samples, the corrosion properties, surface hardness and elastic modulus of the plasma treated samples are enhanced. The Ni concentration leached into the simulated body fluids from nitrogen treated sample is undetectable, whereas that from the untreated sample is 30ppm. Although there is a significant difference in cell proliferation on nitrogen treated and untreated surfaces in short term, the result of long term co-culture suggests no significant difference is found in terms of cell alkaline phosphate activity. However, the
in vivo bone formation is found to be better on the nitrogen treated surface at every time points. All these improvements can be attributed to the formation of TiN on the surfaces. Therefore, the PIII treated NiTi is proved to be suitable for orthopedics without inducing harmful effects.
Summary: NiTi possesses super-elasticity and shape memory effect that most other current biomedical metals do not have. It is therefore potentially useful in orthopaedic. However, nickel ion release remains a major concern particularly for orthopaedic implants on which fretting is always expected at the implant junction. We have invented a novel surface treatment using plasma immersion ion implantation technology to alter the material surface chemistry in order to suppress nickel release. This paper describes the surface wear and hardness properties, corrosion resistance, cytocompatibility together with in-vivo behavior of PIII treated and untreated samples.
