Cardiovascular diseases are the most frequent causes of death, at least in people living in the industrialised world. Circulatory disorders of the cardiac muscle due to the narrowing of the blood vessels (stenosis) that occurs as a result of arteriosclerosis because of deposits in the arteries play the most important role here. The consequence of narrowed or clogged arteries is that the heart, which is by nature a muscle, does not receive sufficient oxygen, which can lead in the course of time to death of the muscle tissue and thus of the patient.
Second on the list of causes of death due to the heart is the heart attack, which is triggered, for example, by a blood clot that clogs the blood vessel and stops the blood flowing completely. In third place is heart failure, which can be congenital and is associated with insufficient heart pumping capacity.
The heart is a hollow muscle that operates like a pump. It keeps the blood circulation system going with its contractions, as a result of which all body tissues are supplied with oxygen and necessary nutrients. During the pumping process, blood is forced out of the heart into the vascular system. When the heart muscle relaxes, new blood flows in. A septum divides the heart up into a left half and a right half, which consist in turn of a left and right atrium and a left and right ventricle. The atriums and the ventricles are connected by heart valves. The purpose of the heart valves is to make sure that no blood flows in the wrong direction, which can have dramatic consequences. The blood flows into the ventricles from the atriums and then flows on via heart valves into the blood vessels that take it away.
On closer examination, it becomes clear that the four heart valves really do act as valves; they regulate the direction of blood flow. Congenital heart defects, degenerative changes as one gets older or inflammation can, however, have an impact on the heart valves and stop them working properly. It is not unusual for functional disorders to lead to heart failure or other serious heart diseases.
Heart valve disorders can occur at any age and an operation is frequently the only cure. Whereas it is possible to eliminate the heart valve problem suffered by some patients without replacing the natural heart valve, most patients require the heart valve to be removed and replaced by a different one. Thousands of people all over the world now live with redesigned, implanted human, animal or artificial heart valves.
Children can have heart valve defects too. Due to the growth process that young people go through, several operations are normally needed in order to adapt the size of the implant to the size of the heart. Every operation proves to be a burden on and risk for the patient, however.
Svenja Hinderer reports that she included proteoglycanes – which, among other things, determine the water storage capacity of the heart valve tissue – in the spinning process, in order to make the properties of the material even more similar to those of natural heart valves. The scientist explains that it was important to make sure that the sensitive proteins, which settle on the transplant, do not lose their function. At the end of her tests, Svenja Hinderer succeeded in producing a structure that was very similar in its morphology to the natural, extra-cellular matrix of the heart valve.
In a bioreactor, which pumps water through the valves – like the heart pumps blood – the chemist simulated the physiological pressure exerted by the heart – with satisfactory results: the material passed the test. The bioreactor simulation apparently documented in an impressive way how the material took over the opening and closing function as a heart valve substitute.
A next test was carried out in a bioreactor developed by an engineering student in her team, in which she managed to cultivate the electrospun material together with human cells. Svenja Hinderer: “Due to the mechanical stimulation in the reactor – which was modelled on the situation in the human organism – the cells started to form elastic fibres after only six days.” The tissue created in the bioreactor had the same structures as an embryonal heart valve that develops naturally.
Elastic fibres give tissues like skin, blood vessels or – in this case – heart valves their resistance and elasticity. Once they are destroyed, the human organism is not able to regenerate or replace them itself. They are only formed during the embyonal development phase and in the first years after birth. The artificial heart valve based on the way nature works that has been developed by Dr Svenja Hinderer can help to eliminate irreversible damage effectively:
The polymer-based substrate, which is stable and at the same time elastic, is biocompatible and sterilisable – and is therefore eminently suitable for medical applications. The aim is now “to develop a cell-free medical product that is not settled by cells until after it has been implanted in the patient”. To achieve this aim, Hinderer – who has headed the “biomaterials, bioreactors and bioimaging” group at the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) since July 2015 – is researching how the substrates can be modified with further specific proteins, in order to attract stem cells specifically.
Further plan: while the cells settle on the material and form a new heart valve with their own matrix, the basic polymer structure is supposed to degrade later on in the body. As a result, it has the potential to grow as the child’s heart grows. However, until this stage has been reached, the artificial heart valve will have to prove its effectiveness initially at the animal level in pigs.