Stretchable Electronics Flex Their Circuits

Many medical device applications are relying increasingly on complex electronics to perform an array of functions, such as sensing, ablating, monitoring, and analyzing. But as long as electronics are fabricated on inflexible semiconductor substrates, they will be ill suited for accommodating curvilinear device surfaces. Addressing this limitation, John Rogers and his team of scientists at the University of Illinois at Urbana-Champaign (U of I) have developed flexible, stretchable electronics that are now being incorporated into balloon catheters for performing an assortment of diagnostic and surgical functions.

Conventional electronics are built on rigid, planar semiconductor wafers, according to Rogers, the Lee J. Flory-Founder chair in engineering at U of I. "What we were interested in is building circuits with the kinds of performance capabilities associated with state-of-the-art silicon-type devices, but in formats that can be bent, stretched, folded, and even manipulated like a rubber band or a balloon."

Flexible electronics can be achieved relatively easily by using a sheet of silicon that is perhaps a thousand or ten thousand times thinner than a silicon wafer, Rogers explains. But going beyond flexibility, the U of I team has achieved stretchable electronics by configuring circuits into open-mesh designs consisting of springy wire interconnects bonded to an underlying rubber sheet. "We've exploited these two ideas--thinness and mesh geometry--to integrate a range of sensor and electronic functionalities onto the surface of an otherwise conventional balloon catheter," Rogers says.

Designed for treating certain classes of arrhythmias, the balloon catheter features stretchable electronics that perform an array of functions. For example, the circuit can map the electrophysiology of the beating heart to identify regions of the tissue that are behaving in an aberrant or abnormal fashion. Then, it can ablate damaged tissue using dedicated sensors and electrodes. "First you map, and then you zap using the same catheter in the same position, and then you're out," Rogers remarks. In contrast, such discrete procedures traditionally require the use of two different catheters.

"We can incorporate just about any kind of semiconductor device technology into this platform," Rogers comments. Thus, in addition to developing mapping and zapping sensors and electrodes, the U of I scientists have fitted the balloon catheter with temperature, flow, and tactile sensors for performing a variety of tasks. For instance, while temperature sensing enables doctors to monitor the effects of the ablation electrodes on body tissue, flow sensing is important for monitoring blood flow, which can impede the rate of cooling and the contact of the electronics to the tissue. Furthermore, tactile sensing, according to Rogers, is important for measuring how hard the balloon presses against the tissue.

"I think that stretchable electronics are suitable for a whole host of different application areas," Rogers notes. "We're pushing in a variety of directions and trying to do as much as we can in close collaboration with surgeons so that we can direct our technologies to the things that are most important."