The material of choice for longer-lasting orthopedic implants--such as joint replacements for hips and knees--is ultrahigh molecular weight polyethylene paired with an alloy of cobalt and chromium, a combination that has proven to be durable and compatible with the human body. But even joints made from these components last only about a decade, prompting industry to search for better materials.
Innovative devices have been needed desperately to speed up the screening of new materials for orthopedic implants; it takes about six months for conventional equipment to simulate the natural wear of artificial hips. Such a long testing period results in higher research and development costs for companies trying to bring better products to market.
So, NIST and four companies teamed under cooperative research and development agreements to design and construct a new apparatus to do the job. The resulting machine can evaluate a diverse combination of materials, produces debris and changes in surface texture resembling the wear that implants get in the body, and can complete a screening in about one week.
Now that the device has been tested successfully, the next step in the industry/government collaborative effort (the CRADAs soon will be extended for two years) will be to use it to study how potential, alternative implant materials hold up under the effects of motion, environment and a variety of stress-loading cycles that represent the physical routines of different people).
The four companies that supported the development of the accelerated wear device and intend to extend their CRADAs with NIST as part of the Orthopedic Accelerated Wear Resistance Consortium are Biomet Inc., and Zimmer Inc., both in Warsaw, Ind.; Johnson & Johnson Professional Inc., Raynham, Mass.; and Osteonics Corp., Allendale, N.J. NIST researchers involved in the development of the new machine are John A. Tesk, Ming Shen and Steve Hsu.
Contact: Emil Venere
National Institute of Standards and Technology (NIST)