**3. Decellularization of tissues**

The concept of decellularization is referred as the extraction of cellular components from natural tissues of human or animal origin. Different approaches have been reported as effective procedures to remove cells from xenogeneic and allogeneic collagenous tissue with the aim of removing cellular antigens and procalcifying remnants while the extracellular matrix (ECM) integrity is preserved as much as possible (Schmidt & Baier, 2000). The combination of chemical, physical and enzymatic methods destroys the cell membrane and removes nuclear and cellular material (Gilbert et al., 2006). The remaining acellular ECM will be a complex mixture of structural and functional proteins, glycoproteins and glycosaminoglycans arranged in a three-dimensional architecture. However, some mechanical and structural alterations on the ECM can be induced during the decellularization process.
