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Sound Engineering: Improving the catheter

Catheters are relatively simple in the grand scheme of medical tools, but they make a host of advanced treatments possible, including complex procedures that take place within the chambers of the heart. Michael Zinn, an assistant professor of mechanical engineering at UW-Madison, says medicine can greater realize the benefits of catheters if we improve their construction and control. In this edition of the Sound Engineering podcast, Zinn describes his proposal for a new type of catheter that combines safety with precision.

Scott Gordon: Some clinicians spend years mastering the use of catheters, those small medical tubes that aid in everything from cardiac procedures to brain surgery. Some catheters are very flexible, which means they’re soft and present less danger to the patient, but are harder to control. Some are more rigid, making for greater precision but sacrificing those safety benefits. Michael Zinn, an assistant professor of mechanical engineering at UW-Madison, is developing catheters that combine the best of both.

Michael Zinn: The new and the crucial development is this idea of what we call interleaved manipulation, which is trying to marry the advantages of a flexible catheter, with its inherent safety, by interleaving very small, what we call rigid-link joints, more traditional types of joints that are actuated in a more traditional way, but that are potentially much more precise than the flexing. So you have this redundant, this doubling of the degrees of freedom that you normally would need, the flexible segments providing, say, larger motions, and the rigid links being able to correct the errors that come from those flexible segments. 

Scott Gordon: By using flexible and rigid sections in different configurations, this approach will offer catheters better suited to specific procedures. It is also requiring Zinn and his research group to take a hard look into controlling and predicting the movements of catheters. It’s relatively easy to steer through the blood vessels, where the anatomy essentially helps to guide the catheter. But control systems need to be more sophisticated when you’re working in the chambers of the heart, for example, to deliver ablation to treat an irregular heartbeat.

Michael Zinn: So when you’re working in a small volume of the heart—an atrium is not much bigger than a plum, actually considerably the smaller, more the size of a pit of a peach—and you’re trying to navigate around there and lay down, in the case of atrial fibrillation, trying to isolate the pulmonary vein, openings that come into the atrium, and you’ve got to precisely march around these openings and what we call the osteum and ablate the tissue, and it requires dexterity in addition to precision.

Scott Gordon: Through years of research and conversations with clinicians, Zinn has learned a lot about the possibilities that improved catheters can open up in health care.

Michael Zinn: I’m working with a collaborator, Amish Raval, over in cardiology, and he is interest in delivering stem cells as a possible stem cells as a possible treatment for post-heart attacks. So you have this infarcted region, this potentially scarred region of the heart, and the theory is that by introducing stem cells around the periphery of this infarcted region, you can encourage blood vessel growth, and resuscitate the tissue to some degree and try to restore some cardiac function that was lost because of the heart attack the patient suffered. But in that regard, you have to relatively precisely position the needle when you’re injecting the stem cells. You also need to be able to control the orientation of the needle, because that’s important in controlling the ultimate depth of the needle. So it’s not just where in the tissue they inject the stem cells, but they want to control the depth into the heart muscle.

Scott Gordon: Zinn and his collaborators have managed to build prototypes that do offer greater control, flexibility, and precision. Their next challenge is to make their design small enough to actually be used inside patients.

Michael Zinn: The biggest challenge is the miniaturization of the rigid-link joints, the structure itself, as well as the method of actuation and sensing used for the rigid-link joints. 

Scott Gordon: By reinventing thise relatively inexpensive and mundane device, Zinn hopes to impact many areas of medicine.

Michael Zinn: It offers potentially big benefit in terms of not just stem-cell injection, but any kind of therapeutic procedure that requires any kind of either accurate placement of a device or some kind of therapeutic treatment within the chambers of the heart, for instance. They’re also used in the brain and in other applications, G.I. applications, urology and such. All of these things can benefit from what we’re proposing here.

Scott Gordon: For more information on Zinn’s work, look up his faculty page at engr.wisc.edu. 

Scott Gordon
2/12/2014