World's first 'mini-heart' formed by a team of German scientists

A team of German scientists has found a way to develop the first-ever 0.5-millimetre-sized heart in a petri dish. The new discovery will pave the way for future research on the developments of the human heart, as well as facilitate research on different types of diseases.

The researchers from the Technical University of Munich (TUM) in Germany created the "mini-heart" using 35,000 pluripotent stem cells, which were then spun into a sphere using a laboratory centrifuge. The resulting organoid contains both heart muscle cells and cells of the outer layer of the heart wall.

Throughout the young history of heart organoids, starting from the year 2021, scientists had only thought of creating these simplified organ structures by using cardiomyocytes, otherwise known as heart muscle cells, and cells from the inner layer of the heart wall.

Organoids are "a self-organised 3D tissue that is typically derived from stem cells (pluripotent, fetal or adult), and which mimics the key functional, structural and biological complexity of an organ," according to Nature Reviews. Though the "mini-heart" cannot pump blood, it can be stimulated electrically and is capable of contracting, just like actual human heart chambers.

The team was headed by Dr Alessandra Moretti, a Professor of Regenerative Medicine in Cardiovascular Disease, at the TUM. They published their work in the journal Nature Biotechnology, with an accompanying study that was published in Nature Communications.

Under a set protocol, various signalling molecules were added to the cell culture over a period of several weeks. "In this way, we mimic the signalling pathways in the body that control the developmental program for the heart," Moretti stated.

Through the analysis of individual cells, the team determined that stem cells that have developed to the stage wherein they are committed to forming a particular type of new blood cell, only recently discovered in mice, are formed around the seventh day of the development of the organoid.

The epicardium, the innermost layer of the pericardium, is formed from these types of stem cells. "We assume that these cells also exist in the human body, if only for a few days," said Moretti.

Study author Dr Anna Meier also stated: "To understand how the heart is formed, epicardium cells are decisive. Other cell types in the heart - for example in connecting tissues and blood vessels - are formed from these cells. The epicardium also plays a very important role in forming the heart chambers."

These new insights may also lead to discoveries of why fetal hearts have the capability to repair themselves while adult human hearts generally cannot. This knowledge could also aid in research pertaining to new treatments for heart attacks and other types of conditions, as well as investigations on the different illnesses of individual patients.

Human hearts generally develop three weeks into the pregnancy, even before the mother is aware that she is bearing a child. The muscular organ, usually sized as big as a large fist, has the responsibility of pumping blood throughout the whole body "via the vessels of the circulatory system, supplying oxygen and nutrients to the tissues and removing carbon dioxide and other wastes," Live Science reports.

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, other types of drugs could also be tested directly on them in the future, furthering disease prevention and treatment. "It is conceivable that such tests could reduce the need for animal experiments when developing drugs," Moretti added.

In other related news, a 31-year-old woman who had been suffering from a congenital heart defect finally got her pig and cow heart valves replaced with human ones. Vaccines for cancer and heart diseases could also be available by 2030, according to America-based pharmaceutical company Moderna.