**7. Conclusion**

The complexity of the immune response poses a challenging environment for *in situ* tissue engineering of heart valves [46]. Clearly, a better understanding of the underlying pathways appears crucial for controlling the fate of implanted biomaterial scaffolds and modulating inflammatory reactions in such a way as to induce tissue regeneration and remodeling and prevent fibrosis and/or degeneration [12]. Remaining largely unknown are the specifications of the optimal components (i.e. cells, scaffold and potentially biological modulators) and process conditions (mechanical and metabolic) that will facilitate the formation of optimal substitute heart valve tissues, whose function best emulates the structure, function, and extended durability of a natural valve in vivo [5]. However, the prosperous results of synthetic and biological scaffolds so far demonstrate the ground-breaking potential of *in situ* tissue engineering for heart valves.

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