A team of German scientists has developed a 'mini-heart' that is just 0.5 millimetres in size to study the earliest development phase of the human heart and facilitate research on diseases.

The team from the Technical University of Munich (TUM) are the first researchers in the world to successfully create the 'mini-heart' known as organoid -- containing both heart muscle cells (cardiomyocytes) and cells of the outer layer of the heart wall (epicardium).

Although these do not pump blood, they can be stimulated electrically and are capable of contracting like human heart chambers.

In the young history of heart organoids -- the first were described in 2021 -- researchers had previously created only organoids with cardiomyocytes and cells from the inner layer of the heart wall (endocardium).

Led by Alessandra Moretti, Professor of Regenerative Medicine in Cardiovascular Disease, the team developed a method for making a sort of 'mini-heart' using pluripotent stem cells. Around 35,000 cells are spun into a sphere in a centrifuge.

Over a period of several weeks, different signalling molecules are added to the cell culture under a fixed protocol.

"In this way, we mimic the signalling pathways in the body that control the developmental programme for the heart," said Moretti.

The team published their work in the journal Nature Biotechnology with an accompanying study published in Nature Communications.

Through the analysis of individual cells the team determined that precursor cells of a type only recently discovered in mice are formed around the seventh day of the development of the organoid.

"We assume that these cells also exist in the human body -- if only for a few days," said Moretti.

These insights may also offer clues as to why the foetal heart can repair itself, a capability almost entirely absent in the heart of an adult human.

This knowledge could help to find new treatment methods for heart attacks and other conditions.

Further, the team also showed that the organoids can be used to investigate the illnesses of individual patients.

Using pluripotent stem cells from a patient suffering from Noonan syndrome -- a genetic disorder that prevents normal development in various parts of the body, the researchers produced organoids that emulated characteristics of the condition in a Petri dish.

Over the coming months the team plans to use comparable personalised organoids to investigate other congenital heart defects.

With the possibility of emulating heart conditions in organoids, drugs could be tested directly on them in the future.

"It is conceivable that such tests could reduce the need for animal experiments when developing drugs," Moretti said.