Viscoelastic behavior of human tracheal cartilage

The respiratory function of trachea depends on its mechanical performance, being most affected by the mechanical properties of tracheal cartilage, as a rigid tissue which prevents the tracheal collapse in response to negative respiratory pressures. Determining the mechanical properties of trachea and therefore tracheal cartilage would be of great significance for future attempts to fabricate tracheal implants or tissue engineering scaffolds. Unlike the equilibrium mechanical properties of tracheal cartilage which have been well investigated, its viscoelastic behavior has not been previously examined. In this study, after harvesting human tracheal samples from brain-dead patients and subsequent preparation of cartilaginous specimens, the viscoelastic behavior of tracheal cartilage was assessed based on stress relaxation tests at two strain levels of 5% and 10%. Assuming the viscoelastic linearity for tracheal cartilage, 2-, 3- and 4-term Prony series were used to fit the average relaxation data. We also compared the results according to the age and gender of the patients. The 4-term Prony series was selected to describe the relaxation behavior of tracheal cartilage. According to the results, cartilage samples of old patients were stiffer than those of the young cases, however we observed no significant effect of gender of the patients on the stress relaxation behavior of tracheal cartilage. The results of this study can be useful in better understanding the mechanical properties of human trachea and developing treatments for tracheal defects, such as tissue engineering.