a range of different chemical compositions and several methods were compared for preparing membranes with different porosities and pore sizes [16e18].
Extensive characterization of the materials led to the selection of the most suitable formulation/structure to be used in the further stages of the development of these skin tissue equivalents. Neodermal tissue synthesis occurred in these membranes seeded with autologous cells and there was no evidence of conventional scar formation. New and apparently normal functional skin was generated in less than 4 weeks. It was demonstrated that, although the acel-lular membranes can also be used to regenerate skin defects, the cell-seeded membranes provide a means for closing the largest full-thickness skin wounds in a shorter period of time [15]. This system, mainly based on a 3D polymeric matrix obtained from two natural origin polymers (collagen and GAG), also resulted in the first tissue-engineered product to be approved by FDA (1996), and clearly opened the way to the concept of tissue engineering, i.e., to the regeneration of tissues using cells seeded onto a 3D matrix made from the natural-origin polymers.