## 4 Discussion  
The idea of building a bioartificial heart is not new. There has been a considerable amount of research in this field and yet many problems have remained unsolved. However, the current results are promising because the concept of whole-heart engineering is rapidly evolving [18; 30]. Heart tissue engineering requires a scaffold so the stem cells can rebuild the muscle and vascular structures. The role of the ECM has been proven to be more significant than previously thought [31]. Previous studies have shown that only the whole-organ decellularization process creates a 3D ECM that mimics nature's design perfectly [10]. This design cannot be reproduced by any synthetic material, even though important attempts were made in this field [32; 33]. This study presents an optimal decellularization protocol using sodium dodecyl sulfate (SDS) as a decellularization agent. This agent was chosen because important studies have shown its superiority when compared with other detergents such as Triton-X-100, PEG and trypsin [10; 34]. Decellularization was performed using a modified Langendorff experimental device created in our lab, as shown in previous works [26; 27]. This prototype provided efficient decellularization, taking about 14 h for the control rat hearts to become fully decellularized. Furthermore, we have demonstrated an alternative electric field system, apparatus and method of use for the preparation of decellularized rat hearts. The results supplied evidence that alternative electric decellularization was more efficient and time-saving, requiring about 8 h for the process to be completed. Every experiment was photographed for 16 h. As soon as the heart became completely translucent, the DNA and the total protein concentrations from the decellularization solution started to reach a plateau. The efficiency of the decellularization process was proven using optical and electronic microscopy. Thus, the generation of a decellularized rat heart with no residual nuclear material was possible. Another important component to check when performing a decellularization protocol is the integrity of the coronary vessel tree [21]. It was proved that the coronary vessel tree within the decellularized ECM was preserved after decellularization by injecting trypan blue solution through the connected cannula. The decellularized ECM present remains the best scaffold for tissue engineering but it has to deal with the difficult task of the complete removal of endogenous cellular components to avoid inflammatory events and immune rejection [35]. Most published studies have used histological characterization or quantitative techniques to analyze the DNA removal [12; 21]. Many decellularization protocols for hearts have been developed in recent years, with the most commonly applied technique being the Langendorff perfusion of decellularization agents via the ascending aorta [21; 36]. The ultimate goal of regenerative medicine is to create bioartificial hearts generated from patients' cells. Several considerable barriers remain before this technology can be scaled up to human size and be of clinical relevance. Our work represents an important milestone in the quest for organ bioengineering using decellularized scaffolds in small-animal models. The decellularization protocol using an electric field developed by our research team can be modified for human-sized hearts. The Langendorff device prototype can be improved to provide the optimal flow rate for the human heart after obtaining the ethical approval for human tissue research. The results of the decellularization protocol based on the application of an electric field were comparable to those of current gold-standard decellularization techniques. The first experimental prototype of a tissue-engineered human-sized porcine whole-heart was conducted by [PERSON] et al. in 2014. Researchers used pigs to obtain an ECM scaffold because porcine cardiac anatomy is similar to that of humans [16]. Other mammal-derived organs have also been studied for future in vivo implantation in humans.