The first medical implant to make that discovery was a thin foil that electrically jerked injured tissue. kick-start nerve regeneration, which the team tested on rats. Rogers then teamed up with cardiologists, including Arora, who saw an opportunity to give up traditional temporary pacemakers used to treat slowed heart rhythms. Rogers compares this soluble device to an internal wound healer, an “electronic drug” in which all components are soluble.
At first glance, a device half an inch wide and half an inch long can look like a thin plastic strip. In fact, it is a dynamic array of surfaces and carefully selected elements. Electrical contacts are a mixture of tungsten and magnesium. Wireless power enters these contacts using a flat helical antenna made of the same materials. Energy comes from near-field communication or an NFC-enabled antenna that can sit on a hospital bed or on a wearable patch. (Unfortunately, the NFC phone you pay for by touch is not yet efficient enough to break your heart.)
Having a stable electrical contact is crucial for any cardiac device, as each blood pumping contraction depends heart cells fire fast pulses. But the device must also be dynamic. When a wet heart is filled and emptied, its curved surface tenses and strains. The challenge is to make something that is stable at the same time i Flexibility has been an open issue for this area for some time, ”Rogers says. “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, but also attaches chemical. The hydrogel forms covalent bonds with the tissue surface. Loose molecular threads on the hydrogel and heart are woven chemically. Nitrogen atoms merge with carbon atoms in the other, and vice versa, to form strong protein-like bonds. “It provides a mechanically soft, intimate electrical connector,” Rogers says.
Each layer can begin to dissolve as soon as it gets wet, and it is important that the device does not decompose too soon after implantation. So the pacemaker sits inside a melting polymer shell that acts as a buffer over time – the hardware has two weeks to do its job while its shell dissolves. The rest begins to disintegrate after that, but until then the patient no longer needs a pacemaker. In cases where a longer-lasting device is needed, the team could make a version with a thicker capsule.
The team tested the device on animals with small hearts (rats and mice), medium hearts (rabbits) and those with hearts of almost human size (dogs). In all cases, their device could control the heart rate of the animal. (They also tested tissue isolated from human donors and found the same success.)
The Rogers and Arora team also tested how pacemakers disappear in rats. They showed that the devices remained intact for one week, were mostly dissolved in three weeks, and stopped working in four weeks. By 12 weeks they were completely gone.
“Achieving that functionality, but also removing the whole thing without any potentially dangerous or toxic by-products – it’s a huge challenge,” he says. Ellen Roche, a biomedical engineer at MIT who develops cardiac devices, and who was not involved in this business. “Independent of any of that is possible,” Roche continues. “But to do them both together, I think is a great achievement.”
“It’s really great to see simple materials; we already know about their burden of toxicity, ”says Chris Bettinger, a biomedical engineer at Carnegie Mellon. “I think simplicity is often underestimated.”
But an invasive device like a pacemaker will require much more testing to prove safety and effectiveness in humans. Another challenge could be the landscape of the surface of the heart, which would be much more damaged among cardiac patients than among laboratory animals. Raman, a cardiologist who is not part of Arora’s team, notes that some of the people who might need this type of device already have scarring on the tissues caused by heart disease and blockages, making it difficult to make electrical connections. “But based on the design, it could be assumed that it will probably succeed,” says Raman.