15502-m-pleumeekers

other hand, presents a significantly higher t 1/2 , again indicating that different mechanisms are at play in these cartilage subtypes; ear cartilage has a more elastic behavior, i.e. lower viscous dissipation of strain energy, and differences in architecture and composition. [143] The presence of elastin is most likely responsible for these differences. Differences in post-maturity growth rate of the auricle between male and female donors have been reported in literature [163], however this was not reflected in the parameters measured here, where no significant differences were observed. For the purpose of establishing a benchmark for TE ear cartilage, a distinction between male and female is considered unnecessary. Within ear cartilage samples, significant age-related differences were identified. Increasing h with age was observed while sGAG and hydroxyproline contents decreased. Age- related augmentation of tissue thickness is consistent with previous reports of continued growth of the auricle during adult life. [163-165] This is likely due to altered quality of the fiber network, specifically elastic fibers become increasingly fragmented and heterogeneous with age. [164] Additionally, cleavage of collagen fibers has been linked in articular cartilage to increased thickness [166], and a similar mechanism could exist in ear cartilage. Age-related decreases in sGAG and hydroxyproline content were not reflected in mechanical properties. While sGAG and collagen fiber network are known to govern mechanical behavior in articular cartilage [162], it is hypothesized that in ear cartilage the contribution of sGAG and collagen to mechanical properties is reduced due to the elastin network. A large contribution would likely come from this extensive network, since it is mechanically critical in other tissues. [144, 145] Elastin is responsible for elasticity in human skin [144], elastic recoil of lung tissue [167], and reversible extensibility in large elastic arteries [168]. Measured parameters were observed to vary significantly between different regions of the ear; where AT was stiffest and HE was softest. DNA and sGAG content displayed similar variations, with correlative trends to mechanical parameters. No regional variations were observed for hydroxyproline and elastin content. This suggests that unlike hyaline cartilage, an altered mechanical–chemical–architectural relationship exists in elastic cartilage, and tissue composition alone cannot fully explain local mechanics. Literature on hyaline cartilage [158, 159, 162, 169-175] supports the idea that ear cartilage mechanics are linked to architecture and composition. Functionally, specific local mechanical properties are necessary for three dimensional structure. The human auricle has large vestigial musculature anchoring the head (extrinsic) and connecting regions of the auricle (intrinsic). [122] Local variation highlights the need for TE strategies aimed at producing scaffolds and grafts with spatially tunable mechanics. [155] However since these differences are quite small it may also be worth investigating whether thickness variation is sufficient to provide the necessary mechanical integrity in TE constructs. Significant correlations, despite weak Pearson coefficients, were observed between biochemical and mechanical parameters. sGAG content has been linked to mechanical behavior in articular cartilage [162], while DNA content does not. Nonetheless, higher cell density implies that extracellular matrix occupies a lower volume fraction, and assuming that chondrocytes present lower mechanical properties than the matrix [176], increased cell density would result in lower mechanics and explain the negative correlations. 39 EAR CARTILAGE CHARACTERISTICS 2