To restore blood flow in a narrowed or blocked artery, doctors can implant a metal stent to hold open the vessel. But over time, stents can cause inflammation and turbulent blood flow that lead to new blockages. Now, researchers have designed a stent carrying a suite of onboard electronic sensors, drug delivery particles, data storage, and communication capabilities to detect and overcome these problems. The entire device should dissolve as the artery heals (ACS Nano 2015, DOI: 10.1021/acsnano.5b00651).
Traditionally, stents have been small mesh tubes made from stainless steel. Newer stents made from polymers or magnesium can release drugs to prevent inflammation and renarrowing of the blood vessels, and over time they break down and are harmlessly absorbed by the body. Such bioresorbable devices should pose less risk of long-term problems. Some biodegradable and drug-eluting stents are now approved by the Food & Drug Administration.
Dae-Hyeong Kim, a chemical engineer at Seoul National University, wants to take these stents to the next level. He’s one of a handful of researchers who have been developing flexible, resorbable electronics for smart medical devices.
Kim’s group started by making a bioresorbable magnesium stent. On the stent, they integrated temperature and blood-flow sensors to collect data, along with electronic memory to store it. These electronics are made out of nanomembranes of silicon and magnesium, which dissolve into harmless components in the body. They must be flexible so that doctors can insert the stent into occluded vessels in a collapsed state and then expand it against the walls of the vessel. What’s more, the magnesium stent itself acts as an antenna that can both broadcast data, like a radio-frequency identification chip, and wirelessly power the electronics.
The electronic stent also delivers therapeutics. Ceria nanoparticles embedded in a film of polylactic acid reduce inflammation by scavenging reactive oxygen species. And gold and silica nanoparticles release the drug rapamycin when heated with infrared light, opening narrowed blood vessels.
Kim has done extensive testing of the electronic stent in animals, including implanting the devices in the carotid artery of dogs. So far all the components function while inside the body, dissolve, and do not trigger any adverse side effects.
“This massive amount of integration is a great technical achievement,” says Christopher J. Bettinger, a biomedical engineer at Carnegie Mellon University. None of the individual components are in themselves new, he says, but they have never been put on a stent before. The sheer number of parts and functions Kim’s group has integrated and tested is “an amazing demonstration,” he says. Bettinger says medical device companies and cardiologists might look at this electronic stent as a kind of menu from which they can pick whatever components are most promising for treating certain kinds of cardiovascular disease.
The next step, says Kim, is tuning the materials. He wants to strengthen the magnesium stents and tailor the components so that they dissolve on a predetermined schedule. Also, all of the new parts on board the stent will have to be approved by FDA before such a device can be adopted in the clinic.