A paper recently published in Nature Materials by Kim and colleagues highlights exciting work in materials science to improve the mechanical balloon catheter, that staple of cardiology used to open stenotic arteries, insert and expand stents, and find and ablate tissues in the heart that are the source of dangerous arrhythmias.
In this study, the researchers designed a “smart” balloon catheter specifically for cardiac ablation therapy, a technique that is used to treat sustained arrhythmias such as atrial fibrillation (A-fib). Time is often an important factor in treating such conditions, and using conventional mechanical catheters to find the malfunctioning heart tissue then inserting a second catheter to perform the ablation is a time-consuming process that takes a great deal of art and skill on the part of the practitioner. New catheters are improving some of the mechanics, but they still do not provide important sensory information to the physician such as local blood flow, temperature, pressure, etc.
Here the researchers sought to integrate semiconductor devices and sensor technologies directly into the membranes of balloon catheters. The catheters that they tested included micro-tactile sensors that help the surgeon to guide the catheter safely in the heart without damaging healthy tissues. One of the challenges is designing sensors that are highly sensitive to interactions between the catheter and the heart tissue, but not sensitive to the inflation/deflation or change in shape of the balloon. They accomplished this by using ultra thin layers of the silicone rubber that will stretch (not break) with the balloon and return to the original shape.
For the temperature sensor, a similar design strategy was applied to uncouple the stimulus of inflating the balloon from actual sensory input of temperature changes of the heart tissue. A thin string of platinum was used as a resistance-based detector for temperature. Temperature provides a way for estimating the size and depth of a lesion created by ablation. To measure blood flow near the surface of a tissue, they used changes in resistance of a thin metal film. For electrophysiological measurements (like EKG), they used uniform metal pads distributed within the silicon mesh.
The authors tested their “smart” catheter in laser ablation in rabbits in which electrophysiological, temperature and tactile data were gathered. They also tested the electrophysiological sensors in a smart surgical glove to observe the changes in heart beat and rhythm as a result of an occluded coronary artery in rabbit heart. In both instances, the smart materials were able to provide meaningful sensory data about the tissues with which either the catheter or the surgical glove was in contact.
Such technology is not just useful for cardiac catheter procedures, but might also have application in other diseases such as those of the GI or urinary tracts. And once this technology becomes standard in the medical world, it will probably migrate to the home front as well. Imagine the day when gloves routinely have temperature sensors integrated into the finger tips. Moms everywhere will don a finger-tip glove when they touch the forehead of an ailing child to check for fever, and data will be returned alongside a mother’s comforting touch.
Kim, D., Lu, N., Ghaffari, R., Kim, Y., Lee, S., Xu, L., Wu, J., Kim, R., Song, J., Liu, Z., Viventi, J., de Graff, B., Elolampi, B., Mansour, M., Slepian, M., Hwang, S., Moss, J., Won, S., Huang, Y., Litt, B., & Rogers, J. (2011). Materials for multifunctional balloon catheters with capabilities in cardiac electrophysiological mapping and ablation therapy Nature Materials, 10 (4), 316-323 DOI: 10.1038/NMAT2971