Monitoring The Heart

Balloon catheters outfitted with a stretchable electronic sensor can provide new and better data about the heart during clinical procedures, researchers report (Nat. Mater., DOI: 10.1038/nmat2971). The sensor—which so far has been used only in animal studies—is fashioned from otherwise hard and rigid material that can bend and stretch when the catheters are inflated.

The researchers, led by John A. Rogers, a materials scientist at the University of Illinois, Urbana-Champaign, constructed the new sensor devices by embedding semiconductor electronics on a soft substrate compatible with soft tissue. The sensor-bearing material is then attached to the surfaces of commercially available balloon catheters.

Rogers' collaborator Marvin J. Slepian, a cardiologist at the Sarver Heart Center at the University of Arizona, has used the sensors to measure the electrical activity of rabbit hearts by pressing one of the electrode-bearing catheters against the outside of the heart. For the much-larger human heart, such measurements would be carried out by threading the catheter through blood vessels into the heart.

The challenges for integrating a sensor on a catheter were "daunting," Rogers says, because the electronics are made from rigid semiconductors that must bend and stretch without adversely affecting the sensor or substrate.

"We had to figure out how to integrate hard materials with soft, stretchable ones in a way that preserved the mechanical properties of the elastic material and essentially masked the fact that the devices are hard and rigid," Rogers says.

They got around these problems in two ways, Rogers says. First, they made the semiconductors thin enough that they become flexible. Then, they patterned that flexible material in stretchable serpentine curves. This design enables a catheter balloon to blow up "just like it would if the circuits weren't there," Rogers says.

In future versions, the catheter with circuits on it will be encapsulated with an elastomer, Rogers says. "That way, we can isolate even more effectively the devices from the tissue, the blood, and surrounding biofluids."

The work is a "nice demonstration of flexible electronics for biomedical applications," says Zhenan Bao, a chemical engineer at Stanford University who is also developing flexible electronics. "It will inspire the chemistry community to develop new materials."