Rib and costal cartilage fractures are the most common injuries resulting from blunt thoracic loading scenarios, including motor vehicle collisions. The costal cartilage is a cylindrical hyaline cartilage composed of two layers: a core interstitial matrix enveloped by the perichondrium. The perichondrium itself has an inner chondrogenic layer and an outer fibrous layer. The objective of this study was to evaluate the tensile material properties of human costal cartilage perichondrium at two loading rates for a range of subject demographics. Fifty-six (n=56) samples containing the fibrous layer and chondrogenic layer (i.e., two-layered samples) were fabricated from thirty-three (n=33) donors aged from 11 to 69 years of age (19 M, 14 F). Thirteen (n=13) samples without the fibrous layer (i.e., one-layered samples) were fabricated from eight (n=8) donors aged from 11 to 54 years of age (5 M, 3 F). The perichondrium was isolated from the interstitial matrix for all samples and the fibrous layer was removed for one-layered samples to assess the effect of the absence of the fibrous layer. The tissue was then stamped into a dog bone-shaped coupon and sanded down to a uniform thickness of ~1.3 mm for two-layered samples and ~1 mm for one-layered samples. The gage length of the completed coupons was marked with a black ink dot pattern to facilitate strain calculations via video tracking. The coupons were loaded axially in tension to failure at either a slow (0.005 s⁻¹) or fast (0.5 s⁻¹) target loading rate using a material testing system. The elastic modulus, ultimate stress, ultimate strain, failure stress, failure strain, and strain energy density (SED) were then calculated for each test. Material property data were compared by sample type and loading rate. Since there was no significant influence of sex on any material properties, the data were grouped together for the analysis. Modulus, ultimate stress, failure stress, and SED were found to significantly decrease with donor age at both loading rates and ultimate and failure strain also significantly decreased with donor age at the 0.5 s⁻¹ target loading rate. Failure stress in the two-layered samples was found to be greater than that of the one-layered samples at both loading rates. One-layered samples had a greater failure strain than two-layered samples at both loading rates. Perichondrium data were compared to interstitial matrix data from a previous study to further investigate the role of cartilage layer on material properties. The modulus, ultimate stress, and failure stress of costal cartilage decreased moving radially inward (greatest in two-layered perichondrium samples, least in interstitial matrix samples). The opposite was true for ultimate and failure strain, with the greatest failure strain values occurring in the interstitial matrix and the least in the two-layered perichondrium samples. The sample size of one-layered samples was too small to draw any substantial conclusions regarding age trends. This was the first study to analyze the material property trends in costal cartilage perichondrium. The results of this study can be incorporated into virtual human body models to improve the accuracy of thoracic injury prediction in the context of motor vehicle safety. / Master of Science / Motor vehicle collisions are the second leading cause of death due to unintentional injury in the United States, with rib and costal cartilage fractures being the most commonly observed injuries. The cylindrical costal cartilage connects the front of the ribs to the sternum and is composed of two layers: a core interstitial matrix enveloped by the perichondrium. The perichondrium itself has an inner chondrogenic layer and an outer fibrous layer. Virtual human body models incorporate material property data to improve their ability to predict injury risk and are frequently used among vehicle manufacturers to evaluate safety during vehicle development. Currently, models have to make simplifications and assumptions regarding the perichondrium properties, since there are no material property studies on the isolated perichondrium to date. Therefore, the purpose of this study was to quantify the tensile material properties of human costal cartilage perichondrium at two loading rates for a range of subject demographics. Dog-bone shaped coupons with either both perichondrium layers (i.e., two-layered samples) or just the chondrogenic layer (i.e., one-layered samples) were loaded to failure under tension at either a slow (0.005 s⁻¹) or fast (0.5 s⁻¹) target loading rate using a material testing system. Data were obtained for fifty-six (n=56) two-layered samples from thirty-three (n=33) donors aged from 11 to 69 years old. Data were collected for thirteen (n=13) one-layered samples from eight (n=8) donors aged from 11 to 54 years old. The elastic modulus, ultimate stress, ultimate strain, failure stress, failure strain, and strain energy density (SED) were quantified for each test. Material properties of two-layered samples decreased with increasing donor age. No trends were found with regard to donor sex. Only ultimate and failure stress of two-layered samples were significantly affected by loading rate. Perichondrium material property data were compared to interstitial matrix data from a previous study to investigate the effect of cartilage layer on costal cartilage material properties. Elastic modulus, ultimate stress, and failure stress decreased when moving inward in cartilage layers, while ultimate and failure strain increased. Overall, this is the first study to evaluate the material properties of the perichondrium and the change in material properties with cartilage layer. These data can be used to improve the accuracy of human tolerance to thoracic injury in human body models.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/119199 |
| Date | 31 May 2024 |
| Creators | Damron, Julia Anne |
| Contributors | Department of Biomedical Engineering and Mechanics, Albert, Devon Lee, Hardy, Warren Nelson, Kemper, Andrew R., Agnew, Amanda M. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nc-nd/4.0/ |
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