Effects of Sex, Strain Rate, and Age on the Compressive and Tensile Material Properties of Human Costal Cartilage

The objective of this study was to evaluate the effects of sex, loading rate, and age on the compressive and tensile material properties of human costal cartilage over a wide range of subject ages and sexes. Cylindrical compression samples and dog-bone shaped tension samples were tested to failure on a material testing system using target strain rates of 0.005 strain/s and 0.5 strain/s. Compression data were obtained from forty (n = 40) subjects (M = 26, F = 14) ranging in age from 11 – 69 years (Avg. = 39.1 ± 18.2 yrs.), and matched loading rate data were obtained for thirty-four (n = 34) samples. Tension data were obtained from forty-one (n = 41) subjects (M = 30, F = 11) ranging in age from 10 – 59 years (Avg. = 32.9 ± 14.9 yrs.), and matched loading rate data were obtained for seventeen (n = 17) samples. For both compression and tension, load and sample deflection data were collected and used to calculate stress and strain. For the compression data, the toe region was fit using a second-order polynomial, and the toe transition stress, toe transition strain, second-order polynomial coefficient A, and second-order polynomial coefficient B were calculated. In addition, the elastic modulus, ultimate stress, ultimate strain, and strain energy density (SED) were also calculated for each test. For the tension data, only the elastic modulus, ultimate stress, ultimate strain, and SED were calculated for each test. There were no effects of sex on the material properties for either method of loading or strain rate. Therefore, male and female data were combined for the age and loading rate analyses. For compression, toe transition stress, toe transition strain, A, elastic modulus, ultimate stress, and SED were all found to be significantly higher at 0.5 strain/s compared to 0.005 strain/s. For tension, no material properties were found to differ with respect to loading rate. Regarding the effects of age, toe transition stress, toe transition strain, A, B, ultimate stress, ultimate strain and SED were found to significantly decrease with advancing age for the 0.005 strain/s compression data. At 0.5 strain/s, toe transition stress, toe transition strain, elastic modulus, ultimate stress, ultimate strain, and SED all significantly decreased with advancing age. For tension, ultimate stress, ultimate strain, and SED were found to significantly decrease with advancing age at 0.005 strain/s and 0.5 strain/s. Comparing the two loading modes, the ultimate stress, elastic modulus, and SED were significantly higher in compression than in tension. For the compression samples, sample density and percent calcification were also obtained for each sample using physical measurements and micro-CT scans, respectively. However, since there were only a few samples with large calcifications, no meaningful trends were found. This is the first study of its kind to analyze the effects of sex, loading rate, and age on both the compressive and tensile material properties on human costal cartilage from such a wide range of subject ages. The results from this study can be used to develop more accurate finite element models of the human body, which will allow researchers to better evaluate human occupant response and injury risk in motor vehicle collisions for both young and old individuals.