A new concept for artificial hearts

Materials World magazine
,
1 Sep 2017

Ellis Davies reports on a soft artificial heart that functions similarly to the real thing, and could provide an alternative to heart transplants. 

An artificial heart that beats in a similar fashion to a human’s has been developed at the Functional Materials Laboratory at ETH Zurich, Switzerland. Closely resembling a human heart, it is the first entirely soft artificial heart, which could remove complications associated with the mechanical parts of blood pumps. 

26 million people worldwide suffer from heart failure, and artificial blood pumps are used to help bridge the waiting time until a patient receives a donor heart or their own recovers. The researchers hope that the artificial heart could eventually be used as a destination therapy – a long-term support in lieu of a transplant. 

The body of the heart is made of silicone elastomer, uses mechanical heart valves that are used in heart surgery, and weighs 390 grammes, with a volume of 679cm3. The researchers use pressurised air to drive the heart, and a mobile compressor would therefore be required when implanted in the body.

Nicholas Cohrs, Doctorate at the Department of Chemistry and Applied Biosciences at ETH Zurich, explained the manufacturing process to Materials World. ‘We designed the artificial heart in close resemblance to the real human heart using a 3D printer [using a lost-wax casting technique] to quickly manufacture a mould. This way, we got a heart that is made of one monoblock,’ he said. Through the use of medical imaging techniques and 3D printing, the team aims to supply personalised artificial hearts for patients.

‘As the artificial heart is a machine, it does not perfectly replicate the motion of the human heart,’ said Cohrs. However, it does behave in a qualitatively similar manner to the human original – measurements of the aortic pressure curve of the soft heart show a close similarity. ‘The soft artificial heart is more physiological than existing systems, especially ventricular assist devices, which give a continuous blood flow rather than a pulsatile one,’ Cohrs explained. 

Like a real human heart, the silicone alternative has a right and left ventricle. However, these are not separated by a septum, but by an additional chamber that inflates and deflates. This pumps fluid from blood chambers, and mimics the muscle contraction of the human heart. 

In testing, the heart achieved a blood flow of 2.2L/min against a systemic vascular resistance of 1.11mm mercury (Hg) second/millilitre (afterload), when operated at 80bpm. The mean pulmonary venous pressure (preload) was fixed at 10mm Hg and aortic pulse pressure of 35mm Hg was measured, with a mean aortic pressure of 48mm Hg. The results showed physiologically shaped signals of blood flow and pressures by mimicking the movement of a real heart. 

The main issue with the prototype is its lifespan. Currently, the heart can function for around 3,000 beats, which only amounts to 30–45 minutes of use. ‘We are working on another prototype, which is made of another elastomeric material that is more robust. We are confident that we can improve the lifetime significantly,’ said Cohrs. Silicone elastomers are widely available in medical grades.

Moving forward, the team will address the issue of lifetime and tensile strength of the materials used – the current prototype is for the purpose of feasibility tests – optimising design and materials to move beyond the proof-of-concept stage. Developing a more robust heart will benefit those that are not eligible for heart transplants. ‘The goal is to have an implant that does not cause problems or adverse events,’ said Cohrs.