In early 2014, two research groups showed off a soft, stretchy sheet of electronics that could wrap snugly around an entire heart. Led by biomedical engineer Igor Efimov at Washington University in St. Louis and materials scientist John Rogers at the University of Illinois at Urbana-Champaign, the team shaped the sheet on a 3D-printed copy of a rabbit heart, then fitted it to real rabbit hearts in the laboratory. Dozens of tiny sensors and electrodes mapped the heart’s electrical activity, temperature, chemistry and movement, and the electrodes could also deliver pulses to correct an abnormal rhythm.
The short answer to the obvious question: this was a research prototype, tested on isolated animal hearts, not a device that keeps a human heart beating “forever”. It remains one of the clearest early demonstrations of where heart devices might be heading.
What the team actually built
The researchers called their creation a 3D multifunctional integumentary membrane. “Integumentary” simply means a covering, like skin. Instead of a box with a wire or two touching the heart, it is an ultrathin elastic sleeve that hugs the whole outer surface of both ventricles.
The work appeared in Nature Communications on 25 February 2014, with Lizhi Xu and Sarah Gutbrod as joint first authors. Washington University’s announcement described the sleeve as soft silicone moulded to match the epicardium, the thin layer that forms the heart’s outer wall.
Rogers compared the idea to an artificial pericardium. The real pericardium is the fluid-filled sac that surrounds the heart, holds it in place and cushions it. The engineered sleeve adds something the natural one lacks: a dense network of measuring and stimulating electronics.
How a 3D printer gave the membrane its shape
Every heart has a slightly different shape, which is why the team began with imaging. The workflow shown below has four steps.
- Capture the geometry. The heart is scanned with medical imaging such as CT or MRI, and the scan becomes a digital 3D model.
- Print a replica. An inexpensive 3D printer turns that model into a solid copy of the heart.
- Mould the sleeve. The printed copy serves as a mould for a thin elastic membrane, onto which the sensors are transferred using a printing technique developed in Rogers’s lab.
- Fit it to the heart. The finished membrane is slipped over the organ, where its natural elasticity keeps it in gentle contact with the surface.
The sensors themselves are built from semiconductor materials such as silicon and gallium arsenide, together with metals and polymers, patterned so thin that they bend and stretch with each heartbeat.
What the sensors measured in the rabbit hearts
According to the published paper, the experiments used rabbit hearts removed from the animals and kept alive with a Langendorff setup, a long-established laboratory method that pumps an oxygenated nutrient solution through the heart’s own arteries. That detail matters: the heart kept beating because of that perfusion, not because the membrane powered it.
The prototype carried an impressive mix of hardware:
- 68 gold electrodes to record the heart’s electrical activity across its front and back surfaces and to deliver pacing pulses.
- pH sensors made of iridium oxide, which tracked the drop in acidity when blood flow was cut off, then its recovery when flow returned.
- 16 temperature sensors that followed the heart as it was cooled by about 7 °C and picked up local heating during a simulated ablation.
- Strain sensors that registered each contraction and showed a chaotic pattern during ventricular fibrillation.
- Nine micro-LEDs used to excite light-sensitive dyes for optical mapping.
The electrical maps from the membrane closely matched those from optical mapping, a standard laboratory technique, which was the main proof that the sleeve was reading the heart accurately. Modelling also suggested that the pressure the sleeve placed on the heart was similar to the normal pressure from the pericardium.
Why cover the whole heart instead of one spot?
Conventional pacemakers and implantable defibrillators use leads that touch the heart at only a few points. Efimov put the limitation plainly in the university’s release: “Contact with the tissue is only at one or two points, and it is at a very low resolution.”
A sleeve covering the whole surface could, in principle, spot where a dangerous rhythm starts and treat it with smaller, better-targeted pulses delivered from the right location. The researchers pointed to ventricular arrhythmias and to atrial fibrillation, which the university said affects 3 to 5 million people in the United States. They also suggested such membranes might one day carry a sensor for troponin, a protein released when heart muscle is damaged, to give early warning of a heart attack.
Efimov was careful to describe the project as an early step, calling it “just the beginning”. The team’s stated next goal was to combine the technology with ventricular assist devices, the pumps used to support failing hearts.
The video above accompanied the original 2014 coverage of the experimental membrane.
Common misunderstandings about the membrane
“It keeps a heart beating forever.” No device does that, and this one was never tested for long-term use. The experiments lasted hours on isolated hearts.
“The membrane brought a removed heart back to life.” The perfusion system kept the organ alive; the membrane recorded and stimulated it.
“It will be in human patients within 10 to 15 years.” Some 2014 coverage gave that kind of estimate, but the university release set no date. As far as published reports show, a full-heart sensing sleeve of this kind has not entered routine clinical use.
“It is just a fancy pacemaker.” Pacing is only one function. The main advance was high-resolution, whole-surface measurement of several properties at once.
What came next for soft heart electronics
The same two scientists continued working together. In 2021, teams led by Rogers, by then at Northwestern University, and Efimov, by then at George Washington University, reported in Nature Biotechnology a wireless, battery-free temporary pacemaker that weighs less than half a gram and dissolves in the body over roughly five to seven weeks. It was tested in a range of animal models and is aimed at patients who need pacing only for a short time, for example after heart surgery, so that a second operation to remove leads is not needed.
That later device shows the direction of travel: thinner, softer electronics that fit the body rather than forcing the body to fit the hardware.
What this means for people with heart rhythm problems
For anyone living with an arrhythmia today, the 2014 membrane is a glimpse of possible future tools, not a treatment option. Approved pacemakers and defibrillators are well established and save many lives each year. If you have palpitations, fainting spells or a diagnosed rhythm disorder, talk to a doctor about what is right for you.
The lasting lesson of the rabbit-heart experiment is less about a single gadget and more about a design idea: medical electronics that are custom-shaped to an individual organ, gentle on tissue and able to see the whole picture at once.
Sources: Washington University in St. Louis news release (February 2014); Xu, Gutbrod et al., Nature Communications 5, 3329 (2014); GW Today: wireless, battery-free pacemaker dissolves in the body (2021); Wikipedia: Pericardium. Originally reported by Gizmodo via Endo Riot; see also St. Louis Public Radio.
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