Hips don't lie

Jan 20, 2010

An interdisciplinary research project at Kettering University that examines hip replacement components could aid manufacturers in producing longer lasting artificial hip joints.

It might start with a subtle lower back ache.

Usually the spot just above the hip starts to chirp, perhaps a small reminder of an old sports injury or accident. Over time, the leg might begin to over-compensate and pain develops in the knee or upper thigh. Eventually, one gains a few extra pounds, thus causing a bit more stress on the hip joint, which may one day require replacement if too much bone degradation has occurred.

Unfortunately, artificial hip replacement components don’t last very long. According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health, wearing of the artificial joint surface becomes an issue after 15 to 20 years. But an interdisciplinary research project at Kettering University in Flint, Mich., that draws on the combined expertise of Chemistry/Biochemistry, Industrial Engineering (IE), Mechanical Engineering (ME) and Physics faculty, staff and students is working to help prolong the lifespan of artificial hip components so that patients may never have to go through revision surgery again.

Dr. Ali Zand of Kettering’s Chemistry/Biochemistry Dept. is leading the wear testing project on high density polyethylene used in hip replacement components. The project has received important support from McLaren Regional Medical Center of $80,000 in the past two years, which has helped support a Kettering co-op student working on her senior thesis. But the impact of this effort extends far beyond the classroom and lab.

The goal of this project is to create a sample polyethylene placard that shows dramatically less wear mass (or degradation) in extreme scenarios. Additionally, Zand and his team hope to provide data to manufacturers of hip components regarding the use of biopolymers and their ability to extend the life of hip replacement components, thus increasing the quality of life for patients who have hip replacement surgery.

Dr. Matthew Sanders, a professor of Industrial and Manufacturing Engineering who assists the project with logistics and technical support, continues to assign several students from his IE Capstone class to conduct research, collect date and ensure proper operation of the robot used during experiments. Sanders said that this project is important for a number of reasons, one of which is the “cross-disciplinary approach of the team. This is truly what makes the project work.”

To gain a better understanding of the importance of this project, one must look closely at hip replacements. Typical hip replacement components often consist of metal and plastics. The hip joint is located where the upper end of the femur (thigh bone) meets the acetabulum. The femur resembles a long rod with a ball on the end and the acetabulum is similar to a cup-like structure in the pelvis.

This ball and socket orientation allows a range of movement, like sitting, standing and walking. During hip replacement surgery, the surgeon removes the diseased bone tissue and cartilage from the hip joint, leaving the healthy areas intact. The surgeon then replaces the head of the femur and acetabulum with the artificial hip components.

Unfortunately, when the replacement hip components begin to wear and break down, wear debris particles break off and float around in the joint capsule. These particles induce an immune response and inflammation, which leads to the release of proteolytic enzymes and other inflammation markers near the prosthesis. These enzymes are non-specific and begin to break down the healthy bone tissue in the area surrounding the hip. As a result, the bone becomes weaker and prone to secondary breakage.  

The project examines the potential of using surface modified ultra high molecular polyethylene material in joint replacements to reduce this scenario. The bearing surface of the polymer within the joint is modified through the introduction of hydrophilic, water loving groups, which allow the biological solutions found within the body and the joint to act as lubricants for this surface and lead to reduction of wear. The Kettering team utilizes two methods to accomplish this surface modification.

The first method is a chemical modification; the second procedure grafts a biocompatible polymer onto the surcae of UHMWPE. The chemical modification employs the Beholztech Process, created by Dr. Lars Beholz, who serves as the Kettering laboratory manager for the Chemistry/Biochemistry Dept. This process is the only means by which surfaces of inexpensive and inert polymers are chemically modified in a 100 percent water-borne media without the use of flames or chemicals. Atoms and functional groups are chemically attached to the polymers on an object’s surface. These atoms and functional groups greatly increase the polarity of the surface or its “stickiness,” Beholz explained. 

“The idea,” Zand said, “is to make cups more molecularly robust and durable. But just as important is the need to make them bio-compatible, similar to contact lenses, so no immune response is induced. Polymer grafting can create a molecular cushioning effect and the use of biocompatible polymers on the surface lead to wear particles that are biologically inert and can avoid an auto immune response. If we can do this, we could prolong the life of these replacement components, which would mean less revision surgery and a higher quality of life for patients.”

The team also utilizes a pin and plate wear testing robot that was designed and built at Kettering. Sanders consulted initially with Dan VanCura, a senior academic lab coordinator for Industrial and Manufacturing Engineering, and Dr. Henry Kowalski, professor of Mechanical Engineering, on an enhancement to this robot to meet the current needs of the project. The current device collects debris during the ongoing testing. According to VanCura, design and production of this device took about a month. It uses a speed variable electric motor and utilizes a ball with weight that does not move. In addition, the slide mechanism—lifted from the concept of a drawer design with a sliding mechanism—glides back and forth fluidly and is adjustable in height.

VanCura said that once the specifications for the device received approval, it took only days to make, since everything he and Kowalski needed was available in Kettering laboratories. “The opportunity to make this device in-house saved the institution several thousand dollars,” VanCura said, adding that the device also helped make the development work on Ketterer’s thesis go more smoothly. The wear testing device produced by VanCura and Kowalski followed an exceptional first effort of a version by Dr. Doug Melton of Kettering’s Electrical and Computer Engineering Dept.

“The first device was extremely helpful in terms of refining the equipment as it evolved into this latest version,” Kowalski explained, adding that without Melton’s assistance, the current device would not be as successful as it is

Testing for this research effort takes places on two sets of placards: those that are surfaced modified and those that are left untreated as a control set (virgin sample). Wear testing is then performed to simulate accelerated wear within artificial joints to determine which surface treatment is more resilient to frictional wear, which causes less mass loss. The primary idea is to treat the surface of the placards with liquid to change their molecular structures as a means of perhaps eliminating the wear debris and avoid the body’s attacks, thereby eliminating further bone degradation.

The team is working to determine which specific modified polymer surface leads to less wear on the cup. Zand co-authored a paper titled “Preparation of Hydroxylated Polyethylene Surfaces,” which appeared in the Oct. 24, 2007 issue of the Journal of Biomaterials Science, Polymer Edition (http://www.brill.nl/jbs). The other authors of this work include Dr. Norm Walter of McLaren Regional Medical Center, Dr. Maher Bahu of Orthopedic Specialists of Oakland County (formerly of McLaren) Kettering Senior Sara Ketterer, Sanders, Kettering Associate Physics Professor Yuri Sikorski, Robert Cunningham, lab coordinator for Physics, and Beholz. In addition, collaborations with Dr. Walter at McLaren and Dr. Casey Baran, a resident at this hospital, continue to yield important information on how to prevent what are called secondary fractures of the hip structure through the wear testing project.

“McLaren has been very generous with financial support and through the help of their experts like Dr. Walter and Dr. Baran,” Zand said. “This has also been a tremendous opportunity for Kettering co-ops to engage in a complex, important research project that impacts many people throughout the world. The multidisciplinary approach, which blends materials science, chemistry and engineering, is perfect for providing students a real-world application of what they can expect in their careers,” he added.

Another critical aspect of this research is the work conducted by Sikorski. He designed the experiment and procedure to measure the degree of hydrophilicity—or the degree to which a molecule is solvated by water—of surfaces before and after various chemical and mechanical treatments. Additionally, he designed the procedure for the institution’s environmental scanning electron microscope (ESEM)—a device that combines high vacuum, low vacuum and gaseous environment operations to support a range of applications—for analysis purposes of surfaces before and after these treatments.

The results thus far are very promising. By using the ESEM, researchers are able to closely examine samples before and after they’re treated with the specific fluids. With the wear testing robot working on three to nine-hour increments, Zand said that the virgin samples gain mass. After nine hours, the treated samples show less wear, which bodes well for future manufacturing of these components.

Chemistry Senior Sara Ketterer from Flint, who is engaged in her thesis project involving this effort, runs the devices and compiles all data. Her work on this effort exceeds two years and has provided her an opportunity to utilize her Chemistry background and interact with the different Kettering departments.

“It’s just been a great undergraduate research experience,” she said. Ultimately, she hopes to use this opportunity to help gain entrance into graduate school at Michigan State University or the University of South Carolina.

To learn more about this project, contact Dr. Ali Zand at (810)762-7971 or via email at azand@kettering.edu.

Written by Gary J. Erwin