Soft artificial heart completes initial trials in Swiss project

Researchers from the Functional Materials Laboratory at ETH Zurich have developed an artificial heart that closely imitates a human heart.

The heart, which is made from silicone and resembles a human heart in size and shape, gave mixed results in its laboratory trials: while it pumps fluid effectively and moves like a natural heart, the material from which it was made could not stand up to the strain of operation for a long period.

The heart is the result of a project led by Prof Wendelin Stark of the Swiss Federal Institute of Technology in Zurich (ETH Zurich). While mechanical hearts and cardiac assistance device have existed for some time, and are used as a stopgap while the patients waits for a heart transplant, currently in around 5000 people every year, they can cause problems such as blood cell damage leading to clotting; their components are vulnerable to failure; and they leave the user without a physiological pulse, which may have health consequences. The team hopes that a soft heart, which more closely mimics the function of the natural organ, will be a better option.

Graduate student Nicholas Cohrs has developed the heart under test, which was cast in silicone using a lost-wax technique where the wax model was made by 3D printing. Weighing 390g and with a volume of 679 cm³, “it is a silicone monoblock with complex inner structure," said Cohrs. It has a left and right ventricle, separated by an additional chamber which is inflated and deflated by an external supply of compressed air, providing the pumping action delivered by muscle contraction in a living heart.

A team from ETH Zürich’s Product Development Group tested the heart on a rig that simulates the human circulatory system, including a working fluid with the same viscosity and flow characteristics of blood. "Currently, our system is probably one of the best in the world," claimed testing team member Anastasios Petrou. In a paper in the journal Artificial Organs, Cohrs, Petrou and colleagues reveal that the heart achieved a flow rate of 2.2litre/min when beating at 80bpm, and gave “physiologically shaped signals of blood flow.” However, it only lasted for 3000 beats — 30 to 45 min operation — before the silicone material gave way under the strain.

Cohrs is not discouraged. “This was simply a feasibility test,” he said. “Our goal was not to present a heart ready for implantation, but to think about a new direction for the development of artificial hearts.” With the concept now demonstrating its potential, the team is turning its attention to investigating materials with better tensile strength than the original silicone, while other parts of the team look at ways of reducing blood damage from mechanical pumping.

Both Cohrs and Petrou hope to continue with this research. "As a mechanical engineer, I would never have thought that I would ever hold a soft heart in my hands. I'm now so fascinated by this research that I would very much like to continue working on the development of artificial hearts," said Petrou.