If you’re unlucky enough to need a heart valve replacement, a pacemaker or an internal defibrillator, there’s a new invention that could soon smooth the way.
Researchers led by Ellen Roche at the Massachusetts Institute of Technology in Cambridge, US, have made a “soft” robotic heart by encasing the innards of a pig heart in a pneumatic silicone shell, moulded to be a perfect replica of the original.
The result is a melding of pig and polymer the team calls a “biorobotic hybrid heart”. It can pump at different rates and strengths, mimicking a range of human conditions all the way from healthy exercise to heart failure.
With development, the device could mean patients waiting for heart procedures get their ticker modelled in the lab beforehand, allowing surgeons to tailor-make interventions such as valve replacements.
Down the track, even people on the list for a heart transplant could benefit.
“[W]ith further tissue engineering, we could potentially see the biorobotic hybrid heart be used as an artificial heart,” says co-lead author Christopher Nguyen, from Harvard Medical School in the US.
To manufacture their robo-heart, the team carefully dissected out the lining of a pig’s heart.
This bit has a precise anatomy that is hard to imitate synthetically. There are the valves that stop blood flowing backwards, the slender fibrils that guide the valve leaflets to open and close, and the gullies or “trabeculae” that corrugate the lining of each chamber.
The researchers then took the outer, muscular layer of the heart, “unwrapped” it and laid it out flat to be scanned with a high-resolution version of MRI called diffusion tensor imaging (DTI).
DTI is often used to map, with incredible refinement, the messaging pathways of the brain. Here the team used it to record the complex criss-crossing of the heart’s muscle fibres.
They now had the blueprint for a new, bespoke muscle layer.
It came in the form of a series of bubble wrap-sized air pockets called “pneumatic artificial muscles” that could be programmed to inflate and deflate, copying the squeezing of real heart muscle.
The pig lining and pneumatic muscle layers were then bonded with a new adhesive called TissueSil, custom-made by the team to overcome existing difficulties joining flesh and silicone.
Finally, those two inner layers were sheathed in a form-fitting silicone mould taken from the pig’s heart, a step that might be duplicated in people using DTI scanning.
For technical nerds, the device, which was limited to the heart’s main pumping chamber the left ventricle, squeezed out 68% of its contents. That matches the blood pumping strength of a real heart.
The robo-heart addresses a number of problems with existing heart models, which are used to develop and test devices such as pacemakers and valves, and train doctors to implant them.
You can take out beating pig hearts but they only last 24 hours before getting stiff and decaying. Using live anaesthetised animals is costly and time-consuming.
“Regulatory testing of cardiac devices requires many fatigue tests and animal tests,” says Roche.
“[The new device] could realistically represent what happens in a real heart, to reduce the amount of animal testing or iterate the design more quickly.”
The study appears in the journal Science Robotics.
The motion of the biorobotic hybrid heart under MRI.
CREDIT: Park et al., Sci Robot. 5, eaay9106 (2020)
Paul Biegler is a philosopher, physician and Adjunct Research Fellow in Bioethics at Monash University. He received the 2012 Australasian Association of Philosophy Media Prize and his book The Ethical Treatment of Depression (MIT Press 2011) won the Australian Museum Eureka Prize for Research in Ethics.
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