Living 'robofish' is built from human heart cells, swims just like a fish and could pave the way for artificial hearts, scientists say

 A living 'robofish' that's built from human cardiac cells and swims just like a fish could pave the way for artificial hearts, a new study reveals.

Created by researchers at Harvard University, the 'biohybrid' recreates muscle contractions of a pumping human heart to push its tail fin side to side.A living 'robofish' that's built from human cardiac cells and swims just like a fish could pave the way for artificial hearts, a new study reveals.

Created by researchers at Harvard University, the 'biohybrid' recreates muscle contractions of a pumping human heart to push its tail fin side to side.Under half an inch long, it's made of plastic fins and a paper spine, but on either side are two strips of living heart cardiac muscle cells that perform these contractions. 

The device, which could be mistaken for a real fish on casual viewing, was inspired by the shape and swimming motion of a zebrafish. 

Aside from its applications in the field of robotics, the scientists believe their creation marks a step toward building an artificial heart. 

Schematics of the autonomously swimming biohybrid fish, which swims by recreating the muscle contractions of a pumping heart. Under half an inch long, it's made of plastic fins and a paper spine, but on either side are two strips of living heart cardiac muscle cells

'Our ultimate goal is to build an artificial heart to replace a malformed heart in a child,' said study author Kit Parker at the Harvard John A. Paulson School of Engineering and Applied Sciences. 

'Most of the work in building heart tissue or hearts, including some work we have done, is focused on replicating the anatomical features or replicating the simple beating of the heart in the engineered tissues. 

'But here, we are drawing design inspiration from the biophysics of the heart, which is harder to do. 

'Now, rather than using heart imaging as a blueprint, we are identifying the key biophysical principles that make the heart work, using them as design criteria, and replicating them in a system, a living, swimming fish, where it is much easier to see if we are successful.'

The team built their biohybrid fish from cardiomyocytes – the cells responsible for generating contractile force in the heart – derived from human stem cells

HOW DOES THE 'ROBOFISH' SWIM?

Unlike previous devices, the biohybrid fish has two layers of muscle cells, one on each side of the tail fin.

When one side of muscle cells contract, it causes those on the other side to stretch. 

This stretch triggers a protein which prompts them to contract, which triggers another stretch, and so on.

Researchers describe it as the first fully autonomous biohybrid fish from human stem-cell derived cardiac muscle cells

WHAT ARE STEM CELLS? 

Stem cells are special human cells that have the ability to develop into many different cell types, from muscle cells to brain cells.

In some cases, they also have the ability to repair damaged tissues.

Stem cells are divided into two main forms – embryonic stem cells and adult stem cells. 

Embryonic stem cells can become all cell types of the body because they are pluripotent – they can give rise to many different cell types. 

Adult stem cells are found in most adult tissues, such as bone marrow or fat but have a more limited ability to give rise to various cells of the body. 

Meanwhile, induced pluripotent stem cells (iPSCs) are adult cells that have been genetically reprogrammed to be more like embryonic stem cells. Stem cells are special human cells that have the ability to develop into specialised cell types in the body, from muscle cells to brain cells. 

Unlike previous devices, the biohybrid fish has two layers of muscle cells, one on each side of the tail fin. 

When one side of muscle cells contract, it causes those on the other side to stretch. 

This stretch triggers a protein which prompts them to contract, which triggers another stretch, and so on. 

This 'closed loop system', which doesn't require human intervention, is able to propel the fish for more than 100 days, according to the researchers.      

Impressively, as the cardiomyocyte cells matured, the fish's muscle contraction amplitude, maximum swimming speed, and muscle coordination all increased for the first month. 

Eventually, the biohybrid fish reached speeds and swimming efficacy similar to zebrafish in the wild, the team report.  

An artificial heart grown from stem cells could help people with arrhythmias – an abnormality of the heart's rhythm that makes it beat too slowly, too quickly or in an otherwise irregular way. 

'By leveraging cardiac mechano-electrical signalling between two layers of muscle, we recreated the cycle where each contraction results automatically as a response to the stretching on the opposite side,' said co-author Keel Yong Lee at Harvard. 

'The results highlight the role of feedback mechanisms in muscular pumps such as the heart.'       

In future, the team aims to build even more complex biohybrid devices from human heart cells – ones that mimic the human heart more closely than ever. 

In the team's footage, the robotic fish, which is lined with human cardiac cells, can be seen swimming without human intervention 

The clever design is able to propel the fish for more than 100 days, according to the researchers

'I could build a model heart out of Play-Doh, it doesn't mean I can build a heart,' said Parker. 

'You can grow some random tumour cells in a dish until they curdle into a throbbing lump and call it a cardiac organoid. 

'Neither of those efforts is going to, by design, recapitulate the physics of a system that beats over a billion times during your lifetime while simultaneously rebuilding its cells on the fly. 

'That is the challenge. That is where we go to work.'    

In 2012, Parker's Disease Biophysics Group used cardiac muscle cells from rats to build a jellyfish-like biohybrid pump.  

Four years later, the researchers developed a swimming, artificial stingray also from rat heart muscle cells. 

This new study, performed in collaboration with colleagues from Emory University, has been published in the journal Science. 

STEM CELL ADVANCE COULD FIX A BROKEN HEART, SCIENTISTS SAY 

A breakthrough stem cell injection could one day help cure faulty hearts, according to scientists.

Previous attempts to regenerate hearts this way have faltered because the cells struggle to adapt to their new environment.

Researchers at University College London have figured out how to keep stem cells alive for longer in the heart by first growing them on to miniature spheres.

The size of the microspheres means they can be injected into heart muscle. The researchers say their method, which was tested in rats, could help cure heart failure.