Nano-Doped Matrices for Tissue Regeneration

Tissue engineering can be defined as an interdisciplinary field applying the principles of engineering and life sciences towards the development of biological substitutes that restore, maintain, or improve tissue function (Langer & Vacanti, 1993). To accomplish this aim, a balanced combination of cell culture growth with supporting biomaterials is required, as well as the introduction of bioactive agents able to enhance and direct cell and tissue aggregation. Regenerative medicine has been sometimes looked as an extension of tissue engineering, but it can be considered nowadays one of the major interdisciplinary scientific challenges, aiming at regenerating the soft and hard tissues, organs, and nerves damaged or responsible for main human disabilities. The definition given by Kaiser marks the difference of such field from others, and its specific link with pathologies care: “a new branch of medicine will develop that attempts to change the course of chronic disease and in many instances will regenerate tired and failing organ systems” (Kaiser, 1992). The central focus of regenerative medicine is represented by human cells. These may be somatic, adult or embryo-derived stem cells and, recently, induced-pluripotent stem cells. In both tissue engineering and regenerative medicine, the role of scaffolds is predominant, constituting the framework for cell attachment, proliferation, and differentiation. Biodegradable natural and synthetic polymers, as well as some non-biodegradable polymers have been extensively studied and used for the 2D and 3D reconstruction, as well as for the healing of different tissue typologies (Jagur-Grodzinski, 2006). Several requirements have been identified as crucial for the production of tissue engineering scaffolds: (1) the scaffold should possess interconnecting pores of appropriate scale to favour tissue integration and vascularisation; (2) it should be made from material with controlled biodegradability or bioresorbability, allowing the new forming tissue to replace the scaffold; (3) it should have appropriate surface chemistry to favour cellularattachment, proliferation and differentiation; (4) it should own adequate mechanical properties to match the intended site of implantation and handling; (5) it should not induce any adverse response; (6) it should be easy to fabricate into a variety of sizes and shapes (Hutmacher, 2001). Furthermore, it is known that the principal objective of a scaffold is to recapitulate extracellular matrix (ECM) function in a temporally coordinated and spatially organized structure, and a key issue is to encode required biological signals within the scaffold, in order to control the main cellular processes (Causa et al., 2007). In order to mimick the nanometric organization of biological structures, many attempts have been made in the latest years in order to obtain synthetic or natural scaffolds having