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The Warsaw Voice » The Polish Science Voice » November 28, 2013
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Biological Heart Valves
November 28, 2013   
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Researchers from the Foundation for Cardiac Surgery Development in the southern city of Zabrze have used tissue engineering technology to develop a new type of biological heart valve. The valves are called biological because the patients themselves are the source of cell material used in them.

In simple terms, heart valves are a kind of door in blood vessels. They ensure that blood in different parts of the heart is flowing in the right direction. People with defective heart valves—either as the result of a congenital condition or of disease—cannot function normally. They need a transplant. Unfortunately, the number of valve donors is—and will always be—smaller than the number of those who need them. Sometimes mechanical valves are used, but these damage the patient’s blood. In turn, animal-derived valves do not last long. So scientists have come up with the idea of producing heart valves from the patient’s own cells and they are also looking for ways to make these valves last longer.

The scientists at the Foundation for Cardiac Surgery Development have received a zl.1.5 million grant from the National Center for Research and Development for their project. Now they are continuing their work as part of two other projects managed by Dr. Piotr Wilczek, head of the Foundation’s Bioengineering Laboratory.

The biggest problem with biological valves is that they wear out relatively quickly. “Human valves, taken from deceased persons, have an average life span of about 15 years,” says Wilczek. “They come from humans, but it’s someone else. The recipient’s body will reject them unless special technical procedures are used prior to implantation.”

These procedures, however, cause the valve tissue to die slowly. After 15 years, it becomes calcified and undergoes other damage, as a result of which it ceases to function properly.

Valves derived from animals, usually pigs, cause similar problems. And although access to these organs in this case is much easier, it must be remembered that this is material from another species. As a result, an implantation attempt produces a violent reaction in the human body, which tries to reject the foreign material.

“We need to prepare such a valve in the right way first, and also reduce the rejection reaction by using various chemical substances,” says Wilczek. These substances are effective in that the immune response is low. But unfortunately, they are also aggressive, resulting in the slow death of the tissue and ruling out any repair processes in it. Moreover, such a valve becomes calcified after some time, and the younger the recipient, the faster these adverse changes are. In children the valve needs to be replaced after about 10 years, sometimes even sooner than that, according to Wilczek.

Sometimes doctors decide to use durable mechanical valves for implantation, Wilczek says. But these too have their drawbacks—they damage different components of the patient’s blood, such as platelets and red blood cells. A patient with mechanical heart valves needs to take anticoagulants continuously. Not everyone can be provided with such a valve. Contraindications include pregnancy, because such medication could cause bleeding and serious complications during labor.

The imperfections of valves available on the medical market have prompted researchers to search for an optimal biological valve. In recent years, research in this area has been related to tissue engineering. Such a natural valve can work for much longer than other types of grafts. The Zabrze researchers have additionally tried to increase the durability of such biological heart valves. As part of their “New methods for the development of biological valves” project, the researchers have created a prototype of a valve using tissue engineering technology. The acellular or biodegradable scaffolding of the valve will be covered with cells derived from the patient’s bone marrow.

“Each tissue, including those of the valves, consists of two components: an extracellular matrix, i.e. proteins that form a kind of sponge-like scaffolding, and cells embedded in it,” says Wilczek. “We came to the conclusion that the cell is the element that can the most severely limit the durability of the valve. The idea of creating the new valves is based on culturing the patient’s own cells on a protein—animal-derived—scaffold. We call that an autologous valve.”

The scientists thus create a living structure. In order to leave the protein scaffold intact, they use special scissors. They cut out the cells using a variety of enzymatic and chemical methods. They culture the recipient’s cells on the scaffold prepared in such a way. In such a living tissue, cell replacement, repair and remodeling processes keep taking place. There is consequently a chance that such a valve will grow with age, like a normal valve in our body, Wilczek says. Its durability should be much greater than that of previously used valves, he adds.

The Zabrze scientists have created a prototype of their biological valve. They have subjected it to a battery of tests. Histological studies have made it possible to assess to what extent the tissue modification connected with the enzymatic method for removing cells may affect their structure. Biomechanical and hemodynamic studies were conducted to determine whether and to what extent the tissue fulfills its mechanical function after modification. An important role was also played by tests designed to determine the culturing conditions after the isolation of the cells as well as the parameters enabling the differentiation of cells isolated from the bone marrow and identification of their functional features.

The researchers have reserved the rights to a specialist tool for studying tissues. A key element of the functioning of the valve are cusps—delicate structures that the researchers need to examine to test their mechanical properties. “In order to obtain highly accurate results, we have developed a special tool for these studies,” says Wilczek.

The researchers have also applied for a patent for their method of cross-linking tissue using special substances that are not toxic to the body and cells. Thanks to them, the cells can grow freely on the scaffold. The new tissue maintenance methods are based on the use of chemical compounds such as flavonoids, which do not exhibit cytotoxicity.

Another outcome of the researchers’ work is a bioreactor for culturing cells where the valve “scaffolding” is assembled. The cells are cultured in the device, which performs four revolutions per minute. The rotating motion gives them a chance to attach to the substrate and become deposited on the entire surface of the cusp. “If we stopped at this stage and tried to implant such a structure in the body, the cells would be so weakly connected with each other that the flow of blood would cause it to be washed away immediately,” says Wilczek. “Therefore, in the bioreactor, we are trying to recreate the actual conditions under which the valve operates. We program a certain flow and pulsation, similar to the pulsating manner in which the heart works.”

From the start of the project, the researchers from the Foundation for Cardiac Surgery Development have collaborated with the Silesian Center for Heart Diseases in Zabrze, headed by Prof. Marian Zembala. This is a leading center in the modern treatment of cardiovascular diseases. Wilczek’s team has also been supported by the Ship Design and Research Center (CTO) in the coastal city of Gdańsk, which works with the Foundation for Cardiac Surgery Development on other projects, including work on an artificial heart.

During their work on biological heart valves, the Zabrze researchers have also collaborated with the Institute of Animal Production in Balice near Cracow and with the Institute of Human Genetics in Poznań, which provided genetically modified pigs for the project.

When will the heart valves developed by the Zabrze researchers be used in medical practice? Wilczek says his team is ready for tests on animals. At the moment, the researchers are looking for funds for further stages of research so as to move beyond the prototype stage.
Karolina Olszewska


The Foundation for Cardiac Surgery Development in Zabrze was set up in 1991 as an initiative by a pioneering Polish heart transplant surgeon Prof. Zbigniew Religa. It aims to support the development of Polish cardiac surgery and bring modern techniques and technologies to clinical practice in heart disease treatment.
Over the years, the foundation has grown into an innovative hi-tech center that conducts various research programs, including research into a new type of biological heart valve, an artificial heart, and surgical robots. The research and design work is conducted in four laboratories: the Artificial Heart Laboratory, Biological Heart Laboratory, Biocybernetics Laboratory, and the Bioengineering Laboratory. The foundation uses subsidies, research grants and donations from private individuals, firms and institutions interested in the development of Polish cardiac surgery.
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