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the joint. (Reviewed by Vonk et al . [381]) The use of allogeneic MSCs gives the opportunity to generate “prefabricated” cell populations. Distinct isolation and co-culture protocols, as well as the effect of allogeneic MSCs on several scaffold materials, needs to be further elucidated for their possible future clinical use in cell-based cartilage repair in the head and neck area. In conclusion, the combination of chondrocytes and MSCs holds great promise for cell- based cartilage repair in the head and neck area. Location and type-specific chondrocytes in combination with generally available MSCs are specifically recommended in this thesis. Scaffolds Currently, several 3D scaffolds have been developed and investigated for their use in cell- based cartilage repair. [83] They can be roughly classified into synthetic and natural scaffolds, and numerous of them have been introduced in the field of cartilage tissue engineering. [83] In this thesis, we have focussed on natural scaffolds only. In particular, the quality and suitability of alginate, bacterial nanocellulose and decellularized ECM were studied for tissue engineering purposes in the head and neck area. Q3 Which natural scaffolds (i.e. alginate, bacterial nanocellulose, decellularized ECM) are a suitable candidate for future cell-based cartilage repair in the head and neck area? Matrix-derived scaffolds Scaffold selection have been an important pillar of the tissue engineering process. The contemporary concept of scaffold engineering is to mimic the natural micro-architecture of the 3D ECM of the targeted tissue itself. Scaffold design should thereby substitute for the cell natural environment providing instantaneous cell support and guiding tissue development and remodelling. Intuitively, native ECM has the potential to be the most ideal scaffold for tissue engineering and regenerative therapies. Preservation of native ECM is best retained through the process of decellularization. [93] Decellularized ECM-derived scaffolds demonstrate immediate functional support [382] without evoking an adaptive immune response upon implantation due to absence of donor cellular and nuclear antigens [94]. Moreover, ECM-derived scaffolds provide specific structural, mechanical and biological cues to cells guiding tissue regeneration and remodeling. [82] The preparation as well as the biocompatibility of a decellularized cartilaginous ECM was extensively studied in chapter seven . In fact, we were the first to evaluate structural and functional properties of decellularized full-thickness ear cartilage scaffolds. Ear cartilage was decellularized utilizing the protocol of Kheir et al. [101] and modified by the incorporation of a 24 hour course of elastase (0.03 U/mL). The mechanism by which elastase contributed decellularization is unfortunately unknown. Elastin is however, one of the main ingredients of the pericellular matrix surrounding chondrocytes in elastic cartilage. [383] Degradation of this matrix protein would logically disintegrate the pericellular matrix facilitating the outflow of cellular material. Moreover, elastase does not only hydrolyse elastin proteins, but is also involved in the cleavage of other matrix components such as proteoglycans, collagens and fibronectin. [384-386] Breaking down these matrix components will further weaken the tightly interconnected ECM and will likely enhance decellularization. The decellularization protocol 183 DISCUSSION AND FUTURE PERSPECTIVES 9