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On-X Pyrolytic Carbon

On-X carbon differs from the carbon used in other valves in that it is not alloyed with silicon carbide. It is 100% pure carbon. The silicon alloying in other valves is a means of providing consistent wear resistance required by heart valves.

A processing breakthrough by the Bokros team in 1992, however, provides needed wear resistance without the silicon. In addition, this form of pure carbon is actually tougher and stronger than the alloyed carbons.

Because On-X carbon is less brittle, valve design options were broadened to include flow-friendly features like the near-natural length and inlet flare. The pure surfaces provide a smoother surface finish and greater biocompatibility than alloyed carbons.


In addition, patented process technologies allow very precise dimensional control of the carbon coating process. This eliminates the need for machine grinding in the critical leaflet pivot areas, leaving smoothly blended, highly polished contours that wash freely.

On-X Carbon Overview

  • On-X carbon is a pure form of isotropic pyrolytic carbon utilizing patented processes
    • It does not require silicon alloying to ensure wear resistance found in most other available forms of pyrolytic carbon
  • It is a structural carbon coating that is most often deposited on a high density, high purity graphite pre-form
    • Other substrate pre-forms can be used
    • Components of solid On-X carbon can be produced
  • Thickness of the deposited carbon depends on the design requirements of the product
  • The surface can be polished to a high gloss where articulation or thromboresistance is required
    • Alternatively, the surface can also be left in an as deposited state providing some surface topography for bone and or tissue on-growth

What is Pyrolytic Carbon (PyC)?

  • Pyrolytic carbon is an isotropic turbostratic form of carbon.
    • The crystalline structure of pyrolytic carbon has a distorted lattice structure with random unassociated carbon atoms (ref. a) unlike, as an example, graphite (ref. b).
    • This structure provides it with isotropic properties (similar in all directions)
  • It is formed by pyrolysis of a hydrocarbon gas creating random crystallization
  • It exhibits excellent stability, strength, wear resistance, fatigue resistance and biocompatibility

How is Pyrolytic Carbon (PyC) Produced?

  • PyC is generally deposited as a structural coating over a substrate pre-form
    • Alternately, for some geometries solid PyC can be generated
  • It is usually formed in a fluidized bed furnace
    • The bed consists of small ceramic particles and parts to be coated
    • A levitating gas creates required random motion of parts within the bed
    • Heating elements raise furnace temperature to 1200° -1400°C
    • An introduced hydrocarbon gas undergoes decomposition at these temperatures creating free carbon that recrystallizes on whatever surface it comes in contact with first