As I mentioned in the
first section, over the past years, the number of patients affected by heart
valve diseases has been dramatically increased and as a result researchers have
put a lot of effort to find a solution. Tissue engineering is the most
promising approach for a potential treatment and this can be observed to a
certain degree through the following publications.   

To begin with, Kidane et
al. (2009) illustrate that the most commonly preferred methods for heart valve
replacement are the mechanical and biological prosthetic ones. However, over
the past years a significant focus has been demonstrated on the negative
consequences, like thrombosis, that either the mechanical or the biological
prosthetic heart valves have postoperatively on young and elder patients. To
handle this situation, the writers depict the use of polymeric materials which
on the one side have the ability to be resistant, flexible with good
haemodynamic properties and on the other side they have limitations such as the
degradation. In conclusion, the properties of polymeric materials make them
interesting for clinical and industrial use and with some further research in
future we can overcome their drawbacks in order to use them in surgeries.

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Moreover, Cheung et al.
(2015) review new, developing strategies to face heart valve disease based on
the technology of tissue engineering and evaluate their clinical application.
They emphasize that prosthetic have not proved to be capable of replacing human
heart valves, as they lack the ability of growing and resizing based on the
environmental requirements. They covered and reviewed a broad range of methods
and some of them were the decellularisation, electrospinning and 3D
bio-printing. In their conclusions, it is clearly stated that although it has
been recorded a significant progress with tissue engineered heart valves, a
deeper understanding in their structure and function needs to be performed.

In an earlier research, Rippel
et al. (2012) seek to identify a new and promising solution to the problems
that heart valve disease causes. They argue that although the mechanical and
biological prosthetic valves are used a lot in cardiovascular surgery, they
lead to many complications and are not able to grow or repair like the native
heart valves. Solution to these problems can emerge through tissue engineered
heart valves which are a new alternative method. They are produced by culturing
stem cells on suitable scaffolds, such as synthetic, in an environment that
mimics the one where the native heart valves are or by implanting scaffolds in
vivo that are being seeded on their own by the patient’s blood cells. The
authors conclude that tissue engineered heart valves is the most promising
approach in replacing the human native ones, as they are more sustainable with
less unwanted effects on the human organism than the other artificial heart
valves.

From a different
perspective, Hasan et al. (2014) present the concepts that explain the science
behind the mechanical properties of both human and animal heart valves. They
also show that there is a great need for tissue engineered heart valves due to
the disease that affects the native ones and for that reason it is crucial to
design and manufacture such artificial valves that have many similarities to
the function and mechanics of the native aortic and pulmonary roots. In their
article it is clearly stated that human heart valves are known for their
viscoelasticity, long fatigue and flexure behaviour, so these are the
properties that tissue engineered heart valves need to obtain in order to face
this serious problem. They conclude that despite the small availability of
native human heart valves a further investigation should be performed on the
mechanical properties of the tissue engineered ones and they suggest that by
utilizing tools like computational modelling we can solve the issue of lacking
big amounts of human heart valves.

Vafaee et al. (2017) seek
to investigate how the decellularisation process affect the properties of a
heart valve that is obtained by a donor. They compared cryopreserved heart
valves with decellularised ones, which have not been cryopreserved, by
histological, collagen, glycosaminoglycan quantification and some other
techniques. The decellularisation process was performed by sodium dodecyl
sulfate in low concentration and the conclusions depict that this method can
create biocompatible tissue engineered heart valves with no DNA on their
extracellular matrix but with the desired biomechanics on their bulk. Finally,
they suggest that further research should be applied to the application on
younger patients.

In addition, Desai et al.
(2018) investigate how the decellularisation process that Vafaee et al. (2017)
introduced, affects the in vitro biomechanics and hydrodynamics of human aortic
and pulmonary roots which were cryopreserved. They compared decellularised
cryopreserved biological aortic and pulmonary roots, which have their cells
being removed from their extracellular matrix using this procedure, with
cellular native ones. Based on the outcomes of their experiments, they
concluded that the biomechanics and hydrodynamics of both decellularised aortic
and pulmonary roots are showing similarities to the cellular ones and can
potentially be used clinically to replace human heart valves.

            Konig
et al. (2012) depict that current artificial valve replacements do not have the
desired results in facing heart valve disease. They also agree that research
should be more focused on tissue engineering heart valves and they suggest that
bioreactors could lead to better results. These constructs assess the tested
valve to open and close properly by regulating the flow rate. In this article,
a pulsatile bioreactor was constructed in order to modify the polyurethane
heart valve to shear stress and enhance both its biocompatibility and ability
to self-repair. They conclude that bioreactors are tools which can lead tissue
engineering heart valves to a closer level in solving heart valve disease
through a simpler and more accurate way.

Finally, Ramaswamy et al. (2017) express their
concern on the limitations and drawbacks of the current artificial heart valves
which are being used to face heart valve lesions at children. Based on their
article, the most promising solution is tissue engineered heart valves as they are
capable of growing, self-repairing and have long fatigue life. They conducted
their experiments by using as a scaffold porcine small intestinal submucosa and
after implanting them in 4 infants, the postoperative results seem to be very
promising.

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