As I mentioned in thefirst section, over the past years, the number of patients affected by heartvalve diseases has been dramatically increased and as a result researchers haveput a lot of effort to find a solution. Tissue engineering is the mostpromising approach for a potential treatment and this can be observed to acertain degree through the following publications.   To begin with, Kidane etal. (2009) illustrate that the most commonly preferred methods for heart valvereplacement are the mechanical and biological prosthetic ones.

However, overthe past years a significant focus has been demonstrated on the negativeconsequences, like thrombosis, that either the mechanical or the biologicalprosthetic heart valves have postoperatively on young and elder patients. Tohandle this situation, the writers depict the use of polymeric materials whichon the one side have the ability to be resistant, flexible with goodhaemodynamic properties and on the other side they have limitations such as thedegradation. In conclusion, the properties of polymeric materials make theminteresting for clinical and industrial use and with some further research infuture we can overcome their drawbacks in order to use them in surgeries.Moreover, Cheung et al.(2015) review new, developing strategies to face heart valve disease based onthe technology of tissue engineering and evaluate their clinical application.They emphasize that prosthetic have not proved to be capable of replacing humanheart valves, as they lack the ability of growing and resizing based on theenvironmental requirements.

They covered and reviewed a broad range of methodsand some of them were the decellularisation, electrospinning and 3Dbio-printing. In their conclusions, it is clearly stated that although it hasbeen recorded a significant progress with tissue engineered heart valves, adeeper understanding in their structure and function needs to be performed.In an earlier research, Rippelet al. (2012) seek to identify a new and promising solution to the problemsthat heart valve disease causes. They argue that although the mechanical andbiological prosthetic valves are used a lot in cardiovascular surgery, theylead to many complications and are not able to grow or repair like the nativeheart valves. Solution to these problems can emerge through tissue engineeredheart valves which are a new alternative method. They are produced by culturingstem cells on suitable scaffolds, such as synthetic, in an environment thatmimics the one where the native heart valves are or by implanting scaffolds invivo that are being seeded on their own by the patient’s blood cells. Theauthors conclude that tissue engineered heart valves is the most promisingapproach in replacing the human native ones, as they are more sustainable withless unwanted effects on the human organism than the other artificial heartvalves.

From a differentperspective, Hasan et al. (2014) present the concepts that explain the sciencebehind the mechanical properties of both human and animal heart valves. Theyalso show that there is a great need for tissue engineered heart valves due tothe disease that affects the native ones and for that reason it is crucial todesign and manufacture such artificial valves that have many similarities tothe function and mechanics of the native aortic and pulmonary roots. In theirarticle it is clearly stated that human heart valves are known for theirviscoelasticity, long fatigue and flexure behaviour, so these are theproperties that tissue engineered heart valves need to obtain in order to facethis serious problem. They conclude that despite the small availability ofnative human heart valves a further investigation should be performed on themechanical properties of the tissue engineered ones and they suggest that byutilizing tools like computational modelling we can solve the issue of lackingbig amounts of human heart valves.Vafaee et al. (2017) seekto investigate how the decellularisation process affect the properties of aheart valve that is obtained by a donor. They compared cryopreserved heartvalves with decellularised ones, which have not been cryopreserved, byhistological, collagen, glycosaminoglycan quantification and some othertechniques.

The decellularisation process was performed by sodium dodecylsulfate in low concentration and the conclusions depict that this method cancreate biocompatible tissue engineered heart valves with no DNA on theirextracellular matrix but with the desired biomechanics on their bulk. Finally,they suggest that further research should be applied to the application onyounger 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 aorticand pulmonary roots which were cryopreserved. They compared decellularisedcryopreserved biological aortic and pulmonary roots, which have their cellsbeing removed from their extracellular matrix using this procedure, withcellular native ones. Based on the outcomes of their experiments, theyconcluded that the biomechanics and hydrodynamics of both decellularised aorticand pulmonary roots are showing similarities to the cellular ones and canpotentially be used clinically to replace human heart valves.            Koniget al.

(2012) depict that current artificial valve replacements do not have thedesired results in facing heart valve disease. They also agree that researchshould be more focused on tissue engineering heart valves and they suggest thatbioreactors could lead to better results. These constructs assess the testedvalve to open and close properly by regulating the flow rate. In this article,a pulsatile bioreactor was constructed in order to modify the polyurethaneheart valve to shear stress and enhance both its biocompatibility and abilityto self-repair.

They conclude that bioreactors are tools which can lead tissueengineering heart valves to a closer level in solving heart valve diseasethrough a simpler and more accurate way.Finally, Ramaswamy et al. (2017) express theirconcern on the limitations and drawbacks of the current artificial heart valveswhich are being used to face heart valve lesions at children.

Based on theirarticle, the most promising solution is tissue engineered heart valves as they arecapable of growing, self-repairing and have long fatigue life. They conductedtheir experiments by using as a scaffold porcine small intestinal submucosa andafter implanting them in 4 infants, the postoperative results seem to be verypromising.

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