Tissue instead of Titan

13. October 2008

One percent of the infants in the Western world are born with a valve vitium in the form of a stenosis or insufficiency. Since the frequently needed replacement valves do not grow with the child, they have to be replaced several times until the patient reaches adulthood. By means of tissue-engineering those surgeries might become superfluous.

The children are hit by a hard lot because all attempts to get a grip on the inherent defect with mechanic heart valves or the biological version from a pig are coupled with lifetime restrictions. Those patients depend on blood thinning drugs. There can be no question of a carefree childhood. In addition the artificial implants carry the risk of rejection respectively to calcify. Even more grave for children is the fact that the valves do not grow with them. That means that a young person has to expect four surgeries during his or her youth – for the most part on the open heart. A heart valve made of the child’s own body tissue growing with the little one would be the perfect solution. Scientists all over the world are hoping that tissue engineering will make that wish come true in a few years down the road. Germany is leading in this field and neck and neck with the US, reports Dr. Stefan Jockenhövel to DocCheck.

Heart valve made by injection molding

Dr. Stefan Jockenhövel, until 2005 heart surgeon at the university hospital Zurich/Switzerland and other, now works as the department manager of the working group “Cardiovascular Tissue Engineering” at the chair of Applied Medical Device Technology at the RWTH Aachen/Germany. He and his team have proof of initial achievements concerning the development of heart valve growing with the patient create by a special injection molding procedure. Normally, machine tool builders use this procedure to making moldings, for example of plastics, for industrial use.

Since engineers are part of the team as well, the transfer of the term to heart valves does not really come as a surprise. Because the be-all and end-all is the supporting structure respectively the mold which makes sure that cultivated cells condition to a natural valve structure. Cell donors could be veins, arteries or, during birth of a baby suffering from a cardiac disease, especially the umbilical cord. The first step would be the isolation followed by cultivation of a sufficient number of vascular cells. Parallel to that the people in Aachen prepare a fibrin gel-matrix made of the patient’s own blood. Together with the cultivated cells, the whole thing – in brief – is molded and then further bred in the bioreactor. After about three months the completely body own heart valve prothesis is ready for implantation. The procedure of Jockenhövel & Co. Already stood the test in animal experiments.

Heart valve research with diverse approaches

In Germany, the Deutsches Herzzentrum Berlin (DHZB, German Heart Center) and the Medizinische Hochschule Hannover (MHH, Medical University Hanover) are also working on the heart valve made of body own tissue. The basic principle of all three research groups, i. e. using body own respectively autologous cells, is comparable. Fundamental differences are the selection of the supporting structure respectively the carrier material.

The Berlin heart surgeons use biodegradable polymer populated with cells. They also use umbilical cord tissue for newborns with a cardiac defect. For teenagers, suitable cells are planned to be isolated from their own marrow. British physicians at the Imperial College London follow a similar approach. In Hanover, says Jockenhövel, decellularized pig valves are reprocessed as matrix and populated with cells extracted from the patient’s own blood. The Zurich University also reports successful research where heart valves are bred with stem cells extracted from human amniotic liquor. “however, our research project at the RWTH is the only one with the target to create a completely body own heart valve prothesis”, emphasizes Jockenhövel.

EU-Regulations – an obstacle

The Aachen researcher hopes that that children suffering from a cardiac disease will benefit from his heart valve in about five years. One obstacle could be the new EU regulation concerning quality standards. And everybody expects that the obstacles will be even set higher. Although this is considered understandable since security of the patient has utmost priority. But the regulation obsession of the EU commissions might go by reality – as it does so often, complains Jockenhövel. Also expected are bottle necks regarding EU funds. Although the EU is currently strengthening the researches in the field of tissue engineering, the Aachen researcher’s application for additional EU-funds will be one out of 200.

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