15502-m-pleumeekers

Cartilage tissue engineering can offer promising solutions for restoring cartilage defects in the head and neck area and has the potential to overcome limitations of current treatments, reestablishing unique biological and functional properties of the tissue. This thesis focuses on the requirements that are necessary for future cell-based cartilage repair in the head and neck area. Specifically, the suitability of cells or combination of cells on natural scaffolds were evaluated. Cartilage is a highly complex avascular tissue comprising chondrocytes surrounded by a dense extracellular matrix that contains various macromolecules such as proteoglycans, collagens and elastin. Due to its avascular nature, cartilage has a very limited capacity for self- repair once damaged. Tissue engineering is a promising potential treatment modality for the reconstruction of such defects. Cartilage morphology and molecular composition as well as the fundamentals of tissue engineering are introduced in chapter one . Chapter two and three established a precise biomechanical and biochemical characterization of native human ear and nasal cartilages (i.e. nasoseptal and alar cartilages) in order to set a benchmark against which to evaluate cartilage tissue engineering attempts. In general, indentation Eeq of human adult facial cartilages ranged from approximately 1-15 MPa. Ear cartilage had significantly lower stiffness compared to nasal cartilage, although regional variations were observed. Ear cartilage biomechanical properties are most likely related to the presence of elastin in the extracellular matrix. Defining an appropriate cell source for successful cell-based cartilage repair in the head and neck area is crucial. Currently, cell-based cartilage repair is predominantly based on two distinct cell types: chondrocytes and mesenchymal stem cells. However, their individual use is associated with specific disadvantages. First, chondrocyte-based cartilage repair is limited by the ability to obtain sufficient numbers of chondrocytes, necessitating the use of culture- expansion. During culture expansion, chondrocytes change phenotypically to a fibroblast morphology and lose their chondrogenic potential; they dedifferentiate. Second, mesenchymal-stem-cell-based cartilage repair is hampered by the phenomenon of chondrocyte hypertrophy. During chondrogenic differentiation, they undergo terminal differentiation through the process of endochondral ossification and produce cartilage that is unstable and predisposed to mineralization and ossification in vivo . In chapter four , the cartilage-forming capacity of cells from several anatomical locations were studied. Independent on their origin (i.e. articular joint, ear, and nose), culture-expanded chondrocytes dedifferentiated. After chondrogenic stimulation, ear and nasal chondrocytes were most potent for cartilage regeneration in vivo . Moreover, location and type-specific chondrocytes resulted in cartilage regeneration of their original molecular nature. Currently, the combination of chondrocytes and mesenchymal stem cells holds great promise for cell-based cartilage repair as it reduces the required number of chondrocytes and diminishes many disadvantages of the individual cell types. Co-cultures of primary chondrocytes (i.e. articular, ear, and nasal chondrocytes) and mesenchymal stem cells (i.e. adipose-tissue-derived and bone-marrow-derived mesenchymal stem cells) were further elucidated in chapter five and six . Eighty percent of the chondrocytes could be replaced by mesenchymal stem cells without influencing cartilage matrix production nor stability. Clear location and type-specific differences were observed in co-cultures containing articular, ear 193 SUMMARY 10