Anti-Thombogenic Surface by Polarization of Titania Nanotubes
Titanium, a metal forming a strong passive film (oxide layer) on its surface, is highly resistant to corrosion (rust) and is known as a very inactive material in human body. Therefore, most metal materials currently used in the body are titanium and its alloys. In particular, titanium implanted into bone, creates a state of "osseointegration" which bond to bone through very thin fibrous tissue layer only found by electron microscopes.
On the other hand, oxide layer of titanium becomes nanotubes by anodization under appropriate conditions. The titanium oxide (titania) nanotuibes stand upright from the surface, as shown in the right photo. Researches are underway to apply the titania nanotube layer as biomaterials , for example, as an anti-thrombogenic material (a material that prevents blood from clotting).
Titania is an oxide, so it is a ceramic and also an insulator. So, we hypothesized that polarized titania nanotubes prevent blood clotting by inhibition of attachment of platelets electrostatically.
The figure on the left shows a comparison of the antithrombogenicity of an untreated titanium, a titanium with titania nanotubes, and a titanium with polarized titania nanotubes, using commercially available bovine blood.
As seen in the photographs, simply forming titania nanotubes on the surface reduces the amount of blood clots formed by about one-tenth, but this is not sufficient.
However, after polarization, the antithrombogenicity on the positively polarized titania nanotubes decreased to about one-fortieth of that of original titanium surface (about one-third that of non-polarized titania nanotubes). Furthermore, no blood clots formed at all on the negatively polarized titania nanotubes.
Polarization always creates a positively and negatively polarized surfaces, simultaneously. However, by using the underlying titanium and platinum in contact with the outside of the nanotube as electrodes for polarization, only the anti-thrombogenic "negatively polarized surface" is formed on the surface of devices.
If higher antithrombogenicity of this negatively polarized titanua nanotubes than that of pyrolytic carbon is proven, this material could be used as a new blood-contact material for artificial heart valves and other applications.