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BATON ROUGE -- Not all mechanical engineers design for industry. Some, like LSU's Michael Murphy, design for the human body.
Murphy and his graduate students, Vinod Palikala and Frederik Majkut, are working on two devices that will help doctors make diagnoses. One is a tiny sensor, like an array of pinhead-sized drums, that will help doctors decide when to remove the stainless-steel plate that helps stabilize two parts of a broken bone. Another is a device to test the health of the articular cartilage in a joint.
The first device, a sensor which Murphy describes as "a bunch of rectangular drums covered with a thin titanium skin," is being developed with physicist Werner Schomburg of IMT-FzK in Germany.
The sensor is fastened to a stainless-steel "fracture fixation" plate doctors screw into a bone to fasten the two broken ends together. When a pulse of ultrasound is sent through the flesh, the "drumheads" on the sensor absorb some of the energy and return the rest of it.
"As the fracture heals, the load on the plate changes, and you can detect when you want to take the plate out by a change in the drum frequency," Murphy said.
Removing the metal plate as soon as possible is especially important in children because their bones are still growing. Bones receive nourishment through their surfaces, and bone under a metal plate can die if the plate is left on too long. Current methods of determining when the bone is healed depend on a "calcium signature," which doesn't show up until well past the time the bone is healed, Murphy said.
AO/ASIF, which is a major manufacturer of fracture fixation plates, has provided a $61,500 grant for the research, and the National Science Foundation has given $135,000 for this and the other project, because both are minimally invasive procedures.
The other project Murphy is working on is a device that will help doctors diagnose joint diseases. Using a special tool on the end of an arthroscope -- a thin tube often used for knee surgery and video examination of the joint -- he intends to test the mechanical properties of cartilage.
Cartilage is a tough, fibrous material filled with a network of tiny cavities that hold synovial fluid, Murphy said. It is this synovial fluid that gives cartilage its cushioning properties -- the fluid bears 80 percent of the load in a healthy joint. But if resistance to the movement of fluid in the cartilage breaks down, the tissue itself bears more and more of the weight. This can lead to arthritis and other joint problems, he said.
Using facilities at LSU's Center for Advanced Microstructures and Devices, Murphy, along with graduate student Kevin Zanca and undergraduate Lyle Breaux, is devising a tool for the end of an arthroscope that will put a small indentation in the cartilage. A tiny ultrasound transducer, also on the tip of the arthroscope, will establish how fast the indentation fills up. This will give doctors a practical way to diagnose the health of the tissue, Murphy said.
Murphy got involved with knee research because of an athletic injury he received playing lacrosse in college. "I got involved in knee research when I was doing my doctorate. I didn't like the answers I was getting from the surgeons, so I thought I would look for my own," he said.
Murphy said he hopes to have a prototype ready by spring.
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