Post Fabrication Processes
After fabrication, the surfaces of some implants can be treated or coated with additional materials to help improve their physical characteristics or function. Some of these techniques actually change the material while others simply add a coating to the surface of the material to enhance a certain function.
Nitriding
Nitriding is a process where an implant surface is infused with gaseous nitrogen to create a substance called titanium nitride on the surface to increase its hardness. This process is sometimes performed on titanium alloy implants to make them more resistant to wear.
Ion Implantation
Ion implantation is a process where a metal implant surface is bombarded with nitrogen ions. The nitrogen ions actually penetrate the surface, changing the surface characteristics of the metal, and making it more resistant to wear.
Precoating
Some implants are designed to be cemented into place using a special bone cement. Although this cement is not a glue, it is important that it has close contact with the surface of the implant. Precoating is a process where the implant surface is coated with a thin layer of bone cement when it is manufactured. Then, when more bone cement is used during the surgical procedure, a bond can be achieved between the precoated implant and the bone cement.
Porous Coatings
Porous coatings, which may consist of small metal beads or fibers, are applied to some implant surfaces to help hold the implant in place. Imagine a jar full of marbles that are all glued together. The small spaces between the marbles are known as pores. When an implant is coated with metal beads or fibers, bone cement can flow into the pores to get a better grip.
For an implant that is used without bone cement, bone can grow into these pores to get a better grip on the implant. Some porous-coated implants may also be coated with a second material that is intended to help the bone grow into the pores. This material is made from a substance called hydroxyapatite/tricalcium phosphate, which is absorbed as new bone grows into the porous surface.
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