15502-m-pleumeekers

DISCUSSION There has been a long and ongoing wish to cultivate human cartilage in a shape or manner that can be used in reconstructive and plastic surgery. Autologous material is preferred for grafting, and cartilage donations come from the nasal septum, auricle and rib. Surgically, clinicians or surgeons are looking for a material where the decision whether the graft qualifies for implant is usually made by palpation; i.e. compressive stiffness. Bending and tensile properties would be more reflective of functional material properties, but also require large sample dimensions. With growing interest in TE materials, the primary interest was to obtain a benchmark of mechanical performance against which to evaluate TE strategies, and therefore, a stress-relaxation indentation and biochemical map of human native ear cartilage is presented. Ear cartilage has significantly lower strength, stiffness and sGAG content; and significantly higher relaxation time and DNA content compared to nasoseptal cartilage. Ear cartilage also contains >15% elastin content per sample wet mass; and significant differences between age groups were observed for thickness and matrix components (sGAG and hydroxyproline), and significant regional variations were observed for all mechanical parameters, DNA and sGAG content. Relatively large Eeq values (10–15 MPa) were measured for nasoseptal cartilage compared to typical values reported in literature for articular cartilage (1–2 MPa). [158] Although articular and nasoseptal cartilage are classified as hyaline, they present different architectures (no Benninghoff arcade in nasoseptal cartilage) and functions (articular provides joint lubrication and stress distribution, while nasoseptal cartilage provides mechanical support), which could explain the different moduli. Stress-relaxation indentation is able to capture both instantaneous (Ein) and equilibrium behavior (Eeq) of cartilage. [159] In literature, reports of quantitative mechanics for TE constructs are given for confined compression [148, 160], unconfined compression [150] and tension [149, 161]. While no comparison can be made with tension, the indentation results in this study Eeq compare well with compressive equilibrium or apparent modulus in literature. TE constructs are inferior to native tissue, where all values are less than 1 MPa [146, 148, 150, 160] compared to 2.2 ± 1.2 MPa in the softest region (HE) up to 7.2 ± 4.7 MPa in the stiffest region (AT) in this work. Chondrocytes from ear and nasoseptal cartilage have different proliferations rates and gene expression profiles. [40, 56] In this work, higher DNA and lower sGAG contents were observed in ear cartilage. Higher DNA content is likely a direct consequence of high cellularity [143], confirmed by histology. Hydroxyproline content, an indicator for collagen content, was not significantly different between ear (60.0 ± 25.7 nmol/mg) and nasoseptal cartilage (53.5 ± 19.0 nmol/mg), but nasoseptal cartilage displayed an almost two times higher sGAG content. The effect of this was observed mechanically; i.e. significantly higher Ein, σ max , and Eeq in NC. Indeed sGAG side-chains are negatively charged, which generates an osmotic swelling pressure that attracts interstitial fluid. Under compression, load applied on hyaline cartilage is carried simultaneously by the solid matrix (collagen network with its fixed charge density) and resistance to fluid flow induced by compression. [162] Higher sGAG content observed in nasoseptal cartilage was consistent with higher mechanical properties. Ear cartilage, on the 38 CHAPTER 2