Plastic cuts artificial hip wear

One problem with artificial hip joints is that plastic particles are released as the metal ball portion of the joint wears down the polyethylene-lined socket. The body recognizes these particles as foreign matter and produces an inflammatory response that results in bone loss. Bone loss can cause the joint to loosen to the point where it must be replaced.

Researchers from the University of Tokyo, Japan Fine Ceramic Center, and Japan Medical Materials Corporation coated a polyethylene artificial hip socket with a biocompatible polymer molecule they had previously developed, and found that the joint produced fewer wear particles. The polymer, 2-methacryloyloxyethyl phosphorylcholine, or MPC, is used in stents, artificial lungs, and soft contact lenses.

A portion of the biocompatible polymer molecule resembles the phospholipids that make up biological membranes. The phosphorylcholine side chains produce a lubricating effect that results in fewer wear particles, making the joint more durable, according to the researchers.

At the same time, the wear particles are more compatible with the human body, according to the researchers. Because they are not recognized as foreign bodies by macrophages -- immune system cells that encapsulate foreign particles -- the material does not induce the inflammatory response, according to the researchers.

The researchers' study focused on artificial hip joints, which are the most prone to loosening. The material could be used in other joint prosthesis as well, according to the researchers.

The polymer could be used in practical applications within five years, according to the researchers. The work appeared in the October 24, 2004 issue of Nature Materials.