For heart valve replacement, at present mechanical and biological prostheses are used. These function well but consist of material that is foreign to the body and have the disadvantage that they cannot grow in size. In children and teenagers this is a serious disadvantage as they “grow out of” the replacement valve and need several corrective operations. A potential solution to this problem may lie in the tissue engineering of replacement cardiovascular tissue. The principle of tissue engineering is to use autologous cells (cells from the patient’s own body) to produce viable, functioning replacement tissue that would become integrated into the surrounding tissue, grow with it and form highly durable valves (Fig. 1).

The constructed valve fabricated from human cells and scaffold material, for example a biodegradable polymer, must be produced under optimal in vitro conditions so that it can be later be transplanted into the heart of the patient from whom the cells were taken.

A particular focus of research of the DHZB laboratory is the identification of a source of suitable cells. Since it is not possible to use cells from heart valves themselves, cells must be utilized that are as similar as possible to heart valve cells. In the past few years human vascular umbilical cord cells have been evaluated as a source of autologous cells for cardiovascular tissue engineering. The umbilical cord is normally discarded as superfluous tissue after birth. It has several long blood vessels and can be used to harvest a very large number of vascular cells without the patient undergoing any harvesting procedure. These cells can be stored in liquid nitrogen until required (Fig. 2).

In our laboratory the vascular umbilical cord cells are characterized using immunohistological and molecular biological methods (e.g. FACS analysis, transmission electron microscopy). The main target group for the possible use of these cells is newborn children with congenital heart valve defects. In older children and teenagers other suitable cells (mesenchymal precursor cells) are to be isolated from the patients’ own bone marrow and used to engineer heart valves.

A further focus of our research laboratory is the development of cell culture systems and “bioreactors” in which the heart valve construct is conditioned by mechanical means. By rotating the reactor, for example, it is possible for the cells to be evenly distributed on the scaffold material (Fig. 3).

These are the preconditions for the formation of tissue-like united cell structures on a complex three-dimensional scaffold like that for a heart valve. Influenced by pressure and flow in the bioreactor, the cells align in a particular direction. Thus the formation of extracellular matrix proteins is encouraged, which is very important for the development of cell tissue (Fig. 4).