Abstract
Metastable Ti-Nb-based shape memory and superelastic alloys are known to be strong candidates for bone implant applications. The issues of the materials’ biochemical and biomechanical compatibility and its characterization are reviewed. Thermomechanical treatment is conventionally applied to these alloys in order to obtain supreme functional properties; the processing scheme comprises cold rolling and post-deformation air annealing. The structure and electrochemical characteristics of annealing-induced oxide films were studied by scanning electron microscopy, open circuit potential measurement and voltammetry. It is shown that the samples after the annealing treatment exhibit higher steady-state potential value and lower anodic dissolution current density in simulated biological solution, compared with the samples with mechanically removed oxide films. At the same time, the samples with thermal oxide films exhibited lower rate of passive layer recovery than those subjected to mechanical renewal of the oxidized surface. This fact underlies the recommendation to remove the annealing-induced oxide film from the implants operating under friction conditions.
Highlights
One of the major research areas in biomedical materials science is the development of bone replacement materials [1,2,3,4]
The samples were further subjected to thermomechanical treatment leading to the formation of nanosubgrain substructure with improved functional properties [8]: cold rolling with a true strain of 0.3, mechanical polishing down to Ra = 0.05 μm of roughness, and 1-hour post-deformation annealing in air at 600 °C with subsequent water quenching
The influence of thermomechanical treatment on the electrochemical characteristics of nanostructured superelastic Ti-21.8Nb-6.0Zr alloy designed for medical implants is studied
Summary
One of the major research areas in biomedical materials science is the development of bone replacement materials [1,2,3,4]. Despite of the great progress in this field during the past decades, there is still no perfect material that would fulfil all the strict requirements for such medical devices. An implantable material must be biocompatible; from the “bio-mimicking” standpoint, the structure and properties of a bonereplacing substance should be as close to those of bone as possible [3,4]. The biocompatibility requirements comprise the aspects of biomechanical and biochemical compatibility. Biochemical compatibility implies the absence of prolonged adverse reactions between host tissues and implanted material. From this standpoint, pure metals can be classified as toxic (Co, Cu, Ni, V), capsule (Fe, Al, Mo, etc.) and vital (Ti, Nb, Ta, Zr, Pt) [5]. The products of corrosion, wear and other mediumassisted degradation processes must be safe for the biological environment
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