A new study suggests that natural proteins can be used to test replacement hip and knee joints in the laboratory effectively. The work could help improve design in order to reduce wear and tear and increase the lifespan of prosthetics.
Belinda Pingguan-Murphy and Subir Ghosh of the University of Malaya, Malaysia, and Dipankar Choudhury of Brno University of Technology, Czech Republic, explain that albumin and globulin proteins are the predominant protein components of the synovial fluid that surrounds healthy joints. Albumin is also the main protein component of egg white and blood plasma. The proteins are also found within the fluid held around our joints by the synovial membrane. They play important roles in the lubrication mechanism of our joints.
The selection of materials for the prosthesis head and cup of a replacement joint relies on the mechanical and surface properties of the materials chosen and how well they take aboard the natural lubricating proteins. Advanced joints use ultra-high molecular weight polyethylene (UHMWPE) because it’s not only flexible but also resistant to wear. UHMWPE also repels water. It is hydrophobic. This is usually coupled with a ceramic component which is the opposite, hydrophilic, and so makes a perfect sliding partner for least friction.
However, there is always room for improvement in terms of lowering friction, making a prosthetic joint move more smoothly, and extending the lifespan of a joint. Such improvements would give patients a better quality of life as well as extending the time between prosthetic surgery.
"Our work seeks to better understand the use of natural lubricant selection in the in vitro [laboratory] testing of potential joints," explains Pingguan-Murphy. "Many joints which do well in tests fail in practice; and one of the reasons may be the failure to use these natural lubricants in testing, and so failure to mimic the actual tribology in vivo [in a patient]," she explains.