Improving Implants: Orthopedic Research Benefits Animals and Eventually, Humans
Engineering Review
Susan James may be in just her third year at Colorado State, but already her presence is being felt. James is responsible for starting three separate, but related, projects aimed at making joint surgery in humans more reliable.
“The main goal is to make total hip and knee replacements last longer,” says James, an assistant professor in Mechanical Engineering, working in conjunction with colleagues in the College of Veterinary Medicine and Biomedical Sciences, retrieve hip replacements from canine autopsies and study those replacements in an effort to understand how they perform in service. Veterinary surgeons at CSU have been doing hip replacements in mechanical engineering. “Right now they fail in about ten years.”
The first project is the Orthopedic Implant Retrieval Program (OIRP), which James created. Over 350,000 human total joint replacements are performed each year in the United States, most commonly with the hip or knee, using artificial materials. OIRP researchers from the Department of Mechanical Engineering, working in conjunction with colleagues in the College of Veterinary Medicine and Biomedical Sciences, retrieve hip replacements from canine autopsies and study those replacements in an effort to understand how they perform in service. Veterinary surgeons at CSU have been doing hip replacements in canines for almost a decade, but this is the first major effort to recover and examine the canine hips.
“It seemed like a great opportunity to retrieve hip replacements from canines, and if I can do that in conjunction with getting implants from humans through other contacts, not only will we be able to help canines,” James says, “but we would be able to compare the results of that research to humans.”
The second avenue of research for James has been the development of a new polymer. A polymer is a chemical compound or mixture of compounds made up of very large molecules (macromolecules) which consist of many repeating units. “A polymer is any material composed of macromolecules,” James says. Some common examples are DNA, silk, synthetic plastics, and cotton.
The goal of the research is to develop a new polymer that will utilize the lubricant that the human body already contains, and in the process improve total joint replacements. One of the major failure modes of joint replacements occurs when the artificial polymer currently used in the joint articulation wears away. The wear debris or particles released from the polymer in this process cause negative immune responses in the body which result in bone loss.
“What we are trying to do is make the polymer look more like cartilage to the body,” says James. “Cartilage is a very well-lubricated material. In fact, it has a lower coefficient of friction than virtually all synthetic materials and lubricants. Our new polymer should be as well lubricated as cartilage, unlike the current material, and thus should wear significantly less than the current material.” This research, James feels, has great potential.
“I think if we could make this idea work, it will have a huge impact on the life of total joint replacements,” she says. “However, right now, we are still in the beginning stages, and the chemistry challenges we’re facing are quite demanding.” Guy Beauregard, a graduate student in mechanical engineering, is currently working on the chemistry.
The third area of research for James is the development of a hip simulator, which will apply forces and motions to a hip implant in the same way the human body would. It will be used to test the new polymer described above.
Mary O’Connell, a graduate student in mechanical engineering, has been working on the design of the model for about a year. She hopes the simulator will be completed and operational by May. The idea of a hip simulator is not new, but in the past these devices have had only a single axis of force. The simulator being designed by James and O’Connell will have more axes of force, and a patent will be pursued on the model. O’Connell says she likes the fact that she can finally take ideas from paper and build a model from them. “I put a lot of creativity into it,” says O’Connell. “I think one of the most valuable things I get out of it is the application of real-world mechanical design to a biomedical engineering problem.”
James’ unique background has benefitted students, both in the laboratory and the classroom. After earning her bachelor’s degree in metallurgical engineering and materials science from Carnegie Mellon, she continued her studies at Massachusetts Institute of Technology, receiving a Ph.D. in polymers. Before joining the faculty at CSU, James worked as an engineering consultant for Failure Analysis Associates in Calif., where she consulted on a variety of cases involving the analysis and prevention of failures of polymeric materials for clients in both industry and the litigation business.
James’ research at CSU was recently enhanced by a three-year NSF equipment grant. Among other things, the grant provides James with the resources to obtain equipment for the multidisciplinary Orthopedic Biomechanics Lab, and to develop the hip simulator. “It has meant a great deal to both colleges,” James says. This year she was awarded a four-year career grant from NSF and a three-year Whittaker Foundation grant, both of which will fund her current research projects. James also has a three-year NSF Research Experiences for Undergraduates grant which provides funds for hiring undergraduate researchers in several mechanical engineering labs during the summers.