Nanomedicine, Volume IIA: Biocompatibility
© 2003 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume IIA: Biocompatibility, Landes Bioscience, Georgetown, TX, 2003
188.8.131.52 Corrosion Degradation Effects
Haubold et al  have pointed out that in the “practical” galvanic series , carbon falls with the noble metals. The sequence from least to most “noble” (cathodic) is silver, titanium, graphite, gold, and platinum. When coupled in vivo with less noble or “base” (anodic) metals, carbon can accelerate corrosion by galvanic action, especially when the ratio of the surface area of carbon to that of the metal is large. Mixed potential corrosion theory and potentiostatic polarization data from Thompson et al  suggest that LTI carbon in contact with stainless steel in isotonic saline can accelerate the in vitro corrosion rate through the pitting mechanism, a conclusion shared by Rostoker et al . Stainless steel screws in contact with a large LTI carbon percutaneous device in simulated body fluids in vitro produced a small corrosion current (1.5 µamp at 120 millivolts) flowing from carbon to steel, although subsequent tests failed to confirm any actual corrosion effects in vivo . Graphite and other carbon-containing composite materials are electrochemically compatible with various titanium, Cr/Co, and nickel alloys in 3.5% saline solution .
Even diamond may not be entirely immune from these effects, though the results will seldom be clinically relevant. At high temperature or pressure, carbon from diamond in direct contact with carbide-forming metals such as W, Ta, Ti, and Zr can migrate and form a metal carbide phase . Metal oxides of Cu, Fe, Co, and Ni in contact with diamond are reduced to the metal (a redox reaction with the carbon escaping as oxide) upon heating in vacuo  (Section 184.108.40.206.6).
Last updated on 30 April 2004