The first medical implant to come from that breakthrough was a thin foil that electrically shakes injured tissue to start nerve regeneration, which the team tested in rats. Rogers then partnered with cardiologists, including Arora, who saw an opportunity to forgo the traditional temporary pacemakers used to treat slow heart rhythms. Rogers compares this soluble device to an internal healing agent, an “electronic medicine” in which all the components are soluble.
At first glance, the device that is half an inch wide and half an inch long may look like a strip of flimsy plastic. But, in reality, it is a dynamic stacking of carefully selected surfaces and elements. The electrical contacts are a mixture of tungsten and magnesium. Wireless power feeds these contacts through a flat coil antenna made of the same materials. The energy comes from a near-field communication, or NFC-compatible, antenna that could sit on a hospital bed or portable patch. (Sorry, your phone’s tap-to-pay NFC is not yet good enough not to break hearts.)
Having stable electrical contact is essential for any heart device, as every blood pumping contraction depends on heart cells emitting rapid pulses. But a device must also be dynamic. When a wet heart fills and empties, its curved surface contracts and deforms. The challenge of doing something that is both stable and flexible has been “kind of an open question for this area for a while,” says Rogers. “Bioelectronics is great, but then how do you maintain robust interfaces over time? “
The team solved this problem with an adhesive hydrogel, which not only mechanically sticks to the heart, it clings. chemically. The hydrogel forms covalent bonds with the surface of the tissue. Loose molecular threads on the hydrogel and the heart are chemically woven. Nitrogen atoms in one merge with carbon atoms in the other, and vice versa, to form strong, protein-like connections. “It provides a mechanically smooth and intimate electrical coupling,” says Rogers.
Each layer can begin to dissolve as soon as it gets wet, and it is important that the device does not degrade too soon after implantation. So the pacemaker sits inside a soluble polymer shell that acts as a buffer against time – the hardware has two weeks to do its job while its shell dissolves. The rest starts to break down after that, but by then the patient should no longer need the pacemaker. In cases where a more durable device is needed, the team could build a version with a thicker capsule.
The team tested the device on animals with small hearts (rats and mice), medium hearts (rabbits), and animals with almost human-sized hearts (dogs). Either way, their device could monitor an animal’s heart rate. (They also tested tissue isolated from human donors and found the same success.)
Rogers and Arora’s team also tested how pacemakers faded in rats. They showed the devices remained intact for a week, were mostly dissolved at three weeks, and stopped working at four weeks. At 12 weeks, they were completely gone.
“Realizing that functionality, but also making it all disappear without having potentially dangerous or toxic byproducts, is a huge challenge,” says Ellen Roche, a biomedical engineer at MIT who develops cardiac devices, which has not been involved in this work. “Regardless, one or the other is doable,” continues Roche. “But doing them both together, I think, is a great accomplishment.”
“It’s really cool to see simple materials; we already know their toxicity load, ”says Chris Bettinger, biomedical engineer at Carnegie Mellon. “I think simplicity is often underestimated.”
But an invasive device like a pacemaker will require a lot more testing to prove safety and effectiveness in humans. Another challenge could be the landscape of the heart’s surface, which is said to be much more damaged in heart patients than in laboratory animals. Raman, the cardiologist who is not on Arora’s team, notes that some of the people who might need this type of device already have tissue scars from heart disease and blockages, which would make the formation of electrical connections more difficult. “But based on the design, you could assume it will work,” says Raman.