In a new study, researchers at the University of Minnesota have 3D printed a functioning centimetre-scale human heart pump that could have major implications in the fight against heart disease.
In previous studies, researchers have tried to 3D print heart muscle cells, cardiomyocytes, using pluripotent human stem cells – cells with the potential to develop into any type of cell in the body. They would reprogram these stem cells to form heart muscle cells and then use specialised 3D printers to print them within a three-dimensional structure, called an extracellular matrix. Though promising, this method never produced cells dense enough for the heart muscle to function.
To get around this issue, the University of Minnesota researchers flipped the process around.
“The stem cells were expanded to high cell densities in the structure first, and then we differentiated them to the heart muscle cells,” said Prof Brenda Ogle, the lead researcher and head of the Department of Biomedical Engineering in the University of Minnesota College of Science and Engineering.
Using this method, they found that they could reach high enough cell density within less than a month to allow the cells to beat together, just like a human heart.
“I couldn’t believe it when we looked at the dish in the lab and saw the whole thing contracting spontaneously and synchronously and able to move fluid,” said Prof Ogle.
The heart muscle model is about 1.5 centimetres long and was specifically designed to fit into the abdominal cavity of a mouse for further study. It is like a closed sac with a fluid inlet and outlet, allowing researchers to measure how a heart moves blood within the body.
“We now have a model to track and trace what is happening at the cell and molecular level in pump structure that begins to approximate the human heart. We can introduce disease and damage into the model and then study the effects of medicines and other therapeutics,” said Prof Ogle.
“All of this seems like a simple concept, but how you achieve this is quite complex. We see the potential and think that our new discovery could have a transformative effect on heart research.”
Reader Q&A: Does a human heart have a finite number of beats?
Asked by: Tony Ferrer, High Wycombe
Yes. At an average of 80 beats per minute, most of us will manage less than four billion beats in our lives. But you don’t die because you run out of heartbeats – you run out of heartbeats because you die.
Among mammals, the number of heartbeats over the lifespan of different species is fairly constant. So hamsters’ hearts beat 400 times a minute and they live for about four years, which is 840 million beats, and an elephant manages 35bpm for 35 years, or about 640 million beats total.
Those numbers are similar, but that’s just because animals with faster heart rates are also smaller and more at risk from predation and starvation. Their lifespans have evolved to compensate for this by reproducing early and often – they ‘live fast, die young’. Heart muscle can only repair itself very slowly, so eventually every heart will wear out but not after a specific number of beats.