A chemistry professor at Case Western Reserve University is trying to find out why some of the world’s toughest plastics wear out as fast as they do when used in hip and knee implants. Ultra-high molecular weight polyethylene can be tougher to scratch than carbon steel—so why does it wear out so rapidly in hips and knees?
Researcher Works to Toughen Implant Plastic
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Anna C. Samia, Ph.D., an assistant professor specializing in metallic nanostructures has received a five-year $600, 000 National Science Foundation career grant to create new materials and equipment to test ultra-high molecular weight polyethylene. This is the substance used to make artificial joints. Samia points out that, “Studies that have been done don’t identify the mechanisms in situ. We will mimic how the implants age in the body and test how the microstructure of the polymer affects its wear properties while being simultaneously subjected to chemical stress.”
Samia has already discovered that too many nanoparticles weaken the properties of the implant plastic. So, she is changing the nanoparticle structure in order to create strongly magnetic polymer composite materials. These will enable her team to mix fewer particles in the plastic and still get a magnetic signal strong enough to show what’s happening to it. Samia’s team plans to bathe the polyethylene in biological fluids, hydrogen peroxide and strong acids and invent techniques to take images while the imbedded plastic is in the baths.
They also plan to devise equipment to mimic the mechanical stresses of walking and running. Samia says that her ultimate goal is to make the material used for implants so resistant to the environment inside the body that joint implants will last a lifetime.
Samia will be working with Case Western Reserve’s Robert W. Brown, Distinguished University Professor in the department of physics, and Mark A. Griswold, director of MRI Research and professor of radiology at the School of Medicine. Their collaborative research team has been recently awarded an Imaging Guided Biomaterials Development pilot grant by the Institute for Advanced Materials (IAM) at the university.
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This is a fascinating development. In my practice we've seen similar outcomes with the revised protocol. The key differentiator seems to be patient selection criteria. Has anyone else noticed the correlation with BMI thresholds?
Great point. I'd push back slightly on the conclusion, the sample size in the cited study is too small to draw population-level inferences. That said, the directional signal is compelling and worth a larger RCT.
We implemented a similar approach last year. Early results are promising but we're still gathering 12-month follow-up data. Happy to share our protocol if anyone is interested.
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