In an important milestone, a tiny heart is made using human tissue.

Scientists used three-dimensional printing equipment to create a functional, vascularized human heart using human cells. However, the organ obtained is small. In fact, it is about the size of a rabbit's heart. Despite the size, what is impressive here is the technique used - and there is still a long way to go before we print a full-sized human heart andthat works.

This experiment, of the type known as a proof-of-concept experiment, may lead to organs or tissues with the patient's own genetic material, since this is important to avoid rejection of the organ in the recipient's organism. This according to the study that carried out the experiment and that was published in the scientific journal Advanced Science.

Until before the experiment was conducted, scientists in regenerative medicine, a field originating from the meeting between biology and technology, were able to print only simple tissues without blood vessels. In this study, to print the heart, researchers at Tel Aviv University (TAU) in Israel began by taking a small sample of a patient's adipose tissue.

Next, using genetic engineering, the scientists then tweaked the various component cells, reprogramming some of the cells to become heart muscle cells, or cardiomyocytes, and some to become blood vessel-generating cells, or pluripotent stem cells.

In the lab, the researchers separated the patient's adipose tissue into its component cells and the structure in which the cells lie, called the extracellular matrix. While the cells were reprogrammed to if, the extracellular matrix (ECM), a three-dimensional network of extracellular macromolecules such as collagen and glycoproteins, was processed into a custom hydrogel that servedas "ink."

"This is the first time anyone has succeeded in designing and printing an entire heart filled with cells, blood vessels, ventricles and chambers," Tal Dvir, a professor at Tel Aviv University, said in a statement.

"This heart is made of human cells and patient-specific biological materials. In our process, these materials serve as bio-inks, substances made of sugars and proteins that can be used to 3D print complex tissue models," Dvir explained. "Others have been able to 3D print the structure of a heart in the past, but those had no cells or vesselsOur results demonstrate the potential of our approach for individualized tissue engineering and organ replacement in the future."

Researcher Tal Dvir is a Professor at TAU's University of Molecular Biology and Biotechnology, Department of Materials Science and Engineering, Center for Nanoscience and Nanotechnology and Sagol Center for Regenerative Biotechnology and led the research.

The researchers then put that biotin into the 3D printer programmed to print a heart, based on CT scans taken of the patient. The printer took between three and four hours to print the small heart with basic blood vessels. The researchers then grew the printed heart by feeding it oxygen and nutrients. Within a few days, the cellsmuscles of the organ began to contract spontaneously and the heart pulsed.

But that beating of the organ was not exactly what a healthy human heart would do. "We need the cells to beat synchronously, not just individually," said study coauthor Assaf Shapira, lab manager at Tel Aviv University's Tissue Engineering and Regenerative Medicine Laboratory. A 3D printer builds a heart out of human tissue.

For the heart to efficiently pump blood through the body, its cells need to beat in unison, something the 3D printed heart has yet to do. "Right now we're working on maturing the tissue," Shapira said.

According to Prof. Dvir, the use of the patient's own native cells is crucial for the success of the tissue and organ engineering technique, as it provides biocompatibility (non-rejection).

"Biocompatibility of engineered materials is crucial to eliminate the risk of implant rejection, which compromises the success of such treatments," said Prof. Dvir. "Ideally, the biomaterial should possess the same biochemical, mechanical and topographical properties as the patient's own tissues. Here, we can report on a simple 3D printed approach for cardiac tissuesthick, vascularized, and perforatable tissues that completely match the immunological, cellular, biochemical, and anatomical properties of the patient."

According to The Washington Post, the Centers for Disease Control and Prevention ranks heart disease as the leading cause of death in the U.S. In 2019, 864 heart transplants were performed. More than 3,800 people are on the waiting list for a heart transplant in the country, according to data collected by the Department of Health and Human Services.A transplant isoften the last resort for patients in the late stages of congestive heart failure.

In Brazil, according to the Brazilian Organ Transplant Association - ABTO, the heart transplant is the fourth in the ranking of organ needs, behind the demand for cornea, kidney and liver. 353 heart transplants were performed last year, and 1661 transplants were needed to eliminate the waiting list for the organ.

The researchers now plan to grow the printed hearts in the lab and "teach them to behave" like hearts, says Professor Dvir. They then plan to transplant the 3D printed heart into animal models for further studies.

"We need to develop the imprinted heart further," he concludes. "The cells need to form a pumping capacity; currently, they can contract, but we need them to work together.Our hope is that we will succeed and prove the effectiveness and usefulness of our method."

"Perhaps, ten years from now, there will be organ printers in the best hospitals in the world, and these procedures will be routinely conducted."

But "there are a lot of technical issues and obstacles that need to be addressed," James Yoo, a professor at the Institute for Regenerative Medicine at Wake Forest School of Medicine in Winston-Salem, North Carolina, told Mach by email.

Yoo said it's unclear whether such a printed heart could withstand blood flow under high pressure or that the printed structures would remain stable after implantation in the body. And he expressed concern about the actual feasibility of the "complex" cell manipulation process used to create the biotin, though he called the first printed heart "a major breakthrough infield of bioprinting".

Doris Taylor, director of regenerative medicine research at the Heart Institute of Texas in Houston, told the same source that Israeli scientists had "gone where no one had gone before" in regenerative medicine, but did not call the 3D printed heart a major breakthrough.

"A successful bioartificial organ implanted in a human being will be an important medical breakthrough," she said in the email. "This is certainly a step that will lead to a breakthrough, but we are not there yet."