These ‘mini hearts’ are only as big as a sesame seed, beating to the beat. This is the first time that a mini human heart has been created in the laboratory that has a clear beat.
A heart cell organ that can beat like a real heart. Photo: livescience According to sciencemag.org, this mini organ (cell organelle) mimics the real heart of a 25-day-old human embryo and could help solve many mysteries, such as why children’s hearts don’t have scars. after having a heart attack. Not involved in the new study, but Zhen Ma, a cardiac organelle development bioengineer at Syracuse University, says it’s a great study, and the experiment is important in understanding Congenital heart defects and human heart formation. This process has so far relied solely on animal models. Although other mini-organs such as the brain, intestines, and liver have been grown in the lab for more than a decade, the heart cell organ presents a more challenging challenge for scientists.
The first cardiac organoids were created from mouse heart cells. They may beat on a lab plate, but they look like a bunch of heart cells, not a real heart. According to Aitor Aguirre, a stem cell biologist at Michigan State University, the cardiac organelle needs to function. With the heart, one wants the heart cell organ to have chambers and function to beat in rhythm. Watch a video of a mini heart beating in the lab (source: Sciencemag.org): To create an embryonic-like self-organizing heart cell organelle, the authors of the new study programmed human pluripotent stem cells (cells that have the ability to develop into any type of tissue). which) for this cell to turn into other types of heart cells. They wanted to create three layers of cells in the wall of the chambers of the heart, one of the first developing parts of the heart. Next, they embedded these stem cells in different concentrations of growth-promoting nutrients. They tried until they found a recipe to get these stem cells to form tissue in the correct order and shape in the embryo. After a week of development, the cardiac organelle was structurally equivalent to the heart of a 25-day-old embryo. At this stage, the heart has only one chamber, which will later be the left ventricle of the mature heart. Cardiac organelles are only about 2mm in diameter and have the typical major cell types in this stage of development: myocytes, epithelial cells, fibroblasts, and the epicardium. They also have a clear chamber that beats at a rate of 60-100 beats per minute, similar to the heart rate of embryos of the same age. Lead study author Sasha Mendjan, a stem cell biologist at the Institute of Molecular Biotechnology of the Austrian Academy of Sciences, said: “When I first saw it, I was surprised that these chambers had self-forming. What’s amazing is that you see right away whether this experiment works and if this organelle is working, because it has a pulse.” 
Scientists were able to study heart formation in unprecedented detail. Photo: livescience The mini-heart has so far been more than three months old in the lab and will help scientists monitor the heart’s development in unprecedented detail. They can know the source of heart diseases such as congenital heart defects in children and heart cell death after a heart attack. Mendjan and his colleagues also frozen organelles to test their response to injury. They found that cardiac fibroblasts, a type of cell responsible for maintaining tissue structure, travel to the site of damage to repair dead cells, as happens in children who have had heart attacks. Scientists have long wondered why children’s hearts can regenerate after being damaged without scarring, unlike adults. Mr. Aguirre said the next step would be to connect this organ of beating heart cells to a network of blood vessels and test its ability to pump blood. Mendjan’s team intends to find a way to modify the nutrient solution to produce a four-chambered heart cell organ. With this innovative heart cell organ, researchers were able to learn more about heart problems that can arise when the walls of the heart’s chambers begin to form. Meanwhile, Mr. Ma said that growing a more mature heart cell organ with all four chambers and structure is a matter of the future. He thinks this will take a decade to materialize.
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