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or nasal chondrocytes. Meanwhile, large differences between adipose-tissue-derived and bone-marrow-derived mesenchymal stem cells in co-culture were hard to expose. In co- culture, we found no evidence that cartilage formation was the consequence of chondrogenic lineage differentiation of mesenchymal stem cells. In contrast, the cartilage matrix that was formed, clearly originated from chondrocytes, which suggested a predominantly trophic role for mesenchymal stem cells. The trophic and paracrine function of mesenchymal stem cells herein appeared essential rather than mesenchymal stem cells actively undergoing chondrogenic differentiation. We showed that stem cell trophic function is a general feature that applies to both adipose-tissue-derived and bone-marrow-derived mesenchymal stem cells. Co-culture supports the application of a one-stage cell-based cartilage repair procedure for cartilage defects in the head and neck area. Ear and nasal chondrocytes in combination with generally available mesenchymal stem cells are specifically recommend for the reconstruction of ear and nasal cartilage defects respectively. For successful cartilage regeneration, the properties of the three dimensional scaffold are of equivalent importance. The contemporary concept of scaffold engineering is to - at least partially - mimic the natural micro-architecture of the three dimensional extracellular matrix of the targeted tissue itself. Intuitively, native extracellular matrix has the potential to be the most ideal scaffold for tissue engineering and regenerative therapies. Preservation of native extracellular matrix is best retained through the process of decellularization. The decellularization protocol described in chapter seven preserved native collagen and elastin contents of full-thickness ear cartilage tissue, as well as cartilage major architecture and shape. Moreover, decellularized scaffolds were non-cytotoxic and supported chondrogenic differentiation of mesenchymal stem cells in vitro . Thereby, we have introduced a decellularized matrix-derived scaffold with potential therapeutic benefits. However, at this stage, the shortage of donors and the inability to accurately match cartilage shape of donor facial cartilages, impedes its translation towards a clinical therapy for cartilage defect in the head and neck area. Therefore, natural scaffolds, in particular alginate and bacterial nanocellulose have been further characterized for their use in cartilage tissue engineering. Both alginate and bacterial nanocellulose scaffolds support cartilage tissue regeneration and homeostasis. Besides, bacterial nanocellulose has biomechanical properties that reaches values analogous to facial cartilages. Alginate, on the other hand, has poor biomechanical properties and is typically used as a cell-laden hydrogel, created to encapsulate cells. In chapter eight bacterial nanocellulose scaffolds were infused with cells encapsulated in alginate. These hybrid scaffolds were biocompatible and supported neocartilage formation both in vitro and in vivo . Therefore, the combination of alginate and bacterial nanocellulose could provide a potential therapy for the reconstruction of cartilage defect in the head and neck area. Our research has identified potential for future translational research in the head and neck area. Tissue engineering strategies could technically simplify and thereby improve the surgical treatment of cartilage defect in the head and neck area. 194 CHAPTER 10