Question

Describe corrosion as it pertains to metallic implants. Explain the effect of passivation on corrosion and how it functions.

Answer 1

When it comes to metallic implants their surfaces are often oxides that react with other metals and or the environment of the human body.This reactivitycauses the metallic implant’s material structure to break down and degrade whichcan lead to loosening of the implant, inflammation, etc.A common example ofthis is seen in galvanic corrosion where two metals of different compositions areelectrically coupled while exposed to an electrolyte solution.The metal thatreacts more will corrode as the more inert metal is protected.Since the humanbody a highly oxygenated, electrolytic, and slightly basic, warm environment it’snot surprising that the reactivity of a metal in this given environment can greatlyimpact how it corrodes as an implant over time.Specifically, the passivation layer of the metal’s surface is a layer of metaloxide that acts as a shield to protect the material from corrosion.It does this bycreating a relatively inert layer on the metals surface.By placing a material underpassivation the oxide layer is grown quicker and thicker than it would be undernaturally occurring conditions.1This results in a film layer that reduces the metalssurface reactivity (and reducing the migration of ions/electronics) therebyincreasing its corrosion resistance.This being said, flaws in the passivation layer can lead to localized corrosion attacks which, after breaking down the passivating oxide film, can create small pitted holes.This, along with other forms ofcorrosion, can weaken the metal’s structural integrity.