Biomedical Engineering Reference
In-Depth Information
11
Magnetoelectropolished Titanium Biomaterial
Tadeusz Hryniewicz
1
, Ryszard Rokicki
2
and Krzysztof Rokosz
1
1
Politechnika Koszalińska, Division of Surface Electrochemistry
2
Electrobright, Macungie PA
1
Poland
2
USA
1. Introduction
The high standard and bio-electrochemical stability of any metallic biomaterial components
are the main conditions for their safe implantation into human body. The most critically
indispensable properties for metallic biomaterials are their corrosion resistance, inertness,
low toxicity, and durability. The work aims at analyzing the titanium biomaterial
characterization after electrolytic polishing in a magnetic field, named as the
magnetoelectropolishing (MEP), in comparison with the material finish after a conventional
electropolishing (EP).
Titanium and titanium alloys gradually became the main biomedical materials used
presently in orthopaedic applications. The leaching of metallic ions such as nickel during the
corrosion process from other biomaterials such as: 316L stainless steel, L-605 cobalt-
chromium alloy, or Nitinol, has caused considerable concerns due to the allergies,
inflammations, etc. It appears to be non existent when CP titanium is employed. Titanium is
also insensitive to oxygen concentration and by this titanium ions release by this mechanism
is not applicable in this case. Also it is well known that when titanium is exposed to body
fluids, its surface undergoes spontaneous modification by Ca
2+
and PO
4
3-
ions and prolong
exposure leads to formation of hydroxyapatite layer, which is indispensable to bone-implant
osseointegration.
High quality metal alloys of titanium are commonly used for orthopaedic prostheses as
bone plates, nails, screws, etc. Fortunately, the oxides and hydroxides of titanium have
extremely low solubilities so a passive oxide film readily and spontaneously forms over
the titanium's surface. In spite of its very high corrosion resistance the spontaneously
formed oxide film consists of some inclusion and discontinuity spots, which can cause the
problems in integration at the bone-implant interface. To overcome these problems, several
surface treatments are employed: chemical etching, plasma treatment, ion implantation,
electrochemical or wet chemical hydroxyapatite precipitation following either hydrothermal
treatment or sintering, anodizing, electropolishing, etc. The electropolishing process seems
to be the best way to eliminate these problems. By dissolving the existing imperfect oxide,
electropolishing process creates the base for formation the more perfect homogeneous oxide
over the base titanium metal. As it was shown in many works, including also previous ours,
it is the presence of this oxide film that is responsible for titanium's excellent corrosion
resistance, which enables it to be used in surgical applications.
