Discovery new materials hip implants

Discovery of new materials for hip implants

3:02 AM, 26th December 2011
Discovery of new materials for hip implants
X-ray of the hip region with a metal-on-metal implant superimposed, and a schematic illustrating graphitic material on the surface of the implant. The red spheres represent the positions of the carbon atoms in a single layer of graphite.

EVANSTON, US: A team of engineers and physicians have made a surprising discovery that offers a target for designing new materials for hip implants that are less susceptible to the joint’s normal wear and tear. Researchers from Northwestern University, Rush University Medical Center, and the University of Duisburg-Essen found that graphitic carbon is a key element in a lubricating layer that forms on metal-on-metal hip implants. The lubricant is more similar to the lubrication of a combustion engine than that of a natural joint.

Prosthetic materials for hips, which include metals, polymers and ceramics, have a lifetime typically exceeding ten years, however, beyond that the failure rate generally increases. The ability to extend the life of implants would have enormous benefits, in terms of both cost and quality of life. “Metal-on-metal implants can vastly improve people’s lives, but it’s an imperfect technology. We have a target for how to make the devices better,” said Laurence D. Marks, Professor of Materials Science and Engineering, Northwestern’s McCormick School of Engineering and Applied Science.

“Hip replacement surgery is the greatest advancement in the treatment of end-stage arthritis in the last century. By the time patients get to me, most of them are disabled. Our findings will help push the field forward by providing a target to improve the performance of hip replacements,” said Dr. Joshua J. Jacobs, M.D., Professor of Orthopedic Surgery and Professor, Department of Orthopedic Surgery, Rush University Medical Center, and the Principal Investigator of the study.

Earlier research by team members Alfons Fischer, the University of Duisburg-Essen and Markus Wimmer, Rush University Medical Center discovered that a lubricating layer forms on metallic joints as a result of friction. Once formed, the layer reduces friction as well as wear and corrosion. This layer is called a tribological layer and is where the sliding takes place. But, until now, researchers did not know what the layer was, the layers were assumed to be made of proteins.

The electron-energy loss spectra, a method of examining how the atoms are bonded, showed a well-known fingerprint of graphitic carbon. This, together with other evidence, led the researchers to conclude that the layer actually consists primarily of graphitic carbon, a well-established solid lubricant, not the proteins of natural joints.

“Metal-on-metal implants are a lower wear alternative to metal-on-polymer devices, and allow for larger femoral heads, which can reduce the risk of hip dislocation. It is also the only current option for a hip resurfacing procedure, a bone-conserving surgical alternative to total hip replacement. The next phase is to examine the surfaces of retrieved devices and correlate the researchers’ observations of the graphitic layer with the reason for removal and the overall performance of the metal surfaces,” said Jacobs.

“Knowing that the structure is graphitic carbon really opens up the possibility that we may be able to manipulate the system in a way to produce graphitic surfaces. We now have a target for how we can improve the performance of these devices,” said Fischer.

© Northwestern University News

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