Application of porous ceramics for the attachment of load bearing internal orthopedic applications

The present review surveys studies on physical-chemical properties and biological response of living tissues to NiTi (Nitinol) carried out recently, aiming at an understanding of the place of this material among the implant alloys in use. Advantages of shape memory and superelasticity are analyzed in respect to functionality of implants in the body. Various approaches to surface treatment, sterilization procedures, and resulting surface conditions are analyzed. A review of corrosion studies conducted both on wrought and as-cast alloys using potentiodynamic and potentiostatic techniques in various corrosive media and in actual body fluids is also given. The parameters of localized and galvanic corrosion are presented. The corrosion behavior is analyzed with respect to alloy composition, phase state, surface treatment, and strain and compared to that of conventional implant alloys. Biocompatibility of porous Nitinol, Ni release and its effect on living cells are analyzed based on understanding of the surface conditions and corrosion behavior. Additionally, the paper offers a brief overview of the comparative toxicity of metals, components of commonly used medical alloys, indicating that the biocompatibility profile of Nitinol is conducive to present in vivo applications.

Surface, corrosion and biocompatibility aspects of Nitinol as an implant material.

This chapter covers information on the composition, microstructure and physico-chemical properties of thin oxide films on titanium and titanium alloys. The focus is on thin layers in the sense of ‘natural’ oxide films grown at ambient or higher temperatures with emphasis on titanium oxide, with some selected additional information on oxides related to metals commonly used as alloying elements in titanium alloys for biomedical applications. This chapter does not, however, include thicker oxide films such as those produced by electrochemical or plasma techniques, which are covered in Chap. 8.

Properties and Biological Significance of Natural Oxide Films on Titanium and Its Alloys

Corrosion resistance tests on NiTi shape memory alloy.

Nickel-titanium (NiTi) alloy derives its biocompatibility and good corrosion resistance from a homogeneous oxide layer mainly composed of TiO(2), with a very low concentration of nickel. In this article, we described the corrosion behavior of NiTi alloys after mechanical polishing, electropolishing, and sterilization processes using cyclic polarization and atomic absorption. As a preparative surface treatment, electropolishing decreased the amount of nickel on the surface and remarkably improved the corrosion behavior of the alloy by increasing the mean breakdown potential value and the reproducibility of the results (0.99 +/- 0.05 V/SCE vs. 0.53 +/- 0. 42). Ethylene oxide and Sterrad(R) sterilization techniques did not modify the corrosion resistance of electropolished NiTi, whereas a steam autoclave and, to a lesser extent, peracetic acid sterilization produced scattered breakdown potential. In comparing the corrosion resistance of common biomaterials, NiTi ranked between 316L stainless steel and Ti6A14V even after sterilization. Electropolished NiTi and 316L stainless-steel alloys released similar amounts of nickel after a few days of immersion in Hank's solution. Measurements by atomic absorption have shown that the amount of released nickel from passive dissolution was below the expected toxic level in the human body. Auger electron spectroscopy analyses indicated surface contamination by Ca and P on NiTi during immersion, but no significant modification in oxide thickness was observed.

R. Winston Revie

Papers

Comparison of the in vivo and in vitro corrosion of 18-8 stainless steel and titanium.

Corrosion behaviour of surgical implant materials: I. effects of sterilization

Corrosion behaviour of surgical implant materials: II. Effects of surface preparation