Characterizing the Material Properties of Abdominal Organs

Abstract

Understanding the behavior of abdominal organs under load will greatly improve several fields involving injury biomechanics. In order to determine the behavior of abdominal organs under load and be able to predict the response, the mechanical properties need to be properly characterized. The characterization of these properties will provide researchers the ability to create finite element models that will provide a better understanding of the mechanism of injury resulting from traumatic events. Finite element models of today, that simulate traumatic injuries, lack properly characterized material properties. The current body of literature contains a large range of material property values which could be the result of the wide range of testing methodologies used. Because of this lack of consistency among research, several gaps in knowledge exist for many of the abdominal organs regarding material properties. The gaps in literature were found to be the feasibility of using porcine organ material properties instead of human, the quantification of the effect of strain rate, and the impact of using different testing methodologies on the same organ. Therefore this project quantified the relationship between the elastic modulus, failure stress, and failure strain and strain rate and determined the feasibility of using porcine instead of human organ material properties for the liver, kidney, spleen, prostate, bladder, gallbladder, and intestine. A comparison between the elastic modulus found using a probing protocol and using an unconfined compression protocol was also made for the liver, kidney, spleen, and prostate. These gaps in literature are addressed through four manuscripts: three regarding solid organs that were tested in compression, and one regarding fluid filled/pressurized organs that were tested in tension. The elastic modulus, failure stress, and failure strain was found for the prostate, liver, kidney, and spleen at rates ranging from 1%/s to 1000%/s using unconfined compression testing. A strain rate dependency was found for the elastic modulus of all tested solid organs. The failure stress was observed to be strain rate dependent for the liver, kidney, and spleen, while the failure strain was found to be strain rate dependent for only the liver. A numerical model was created to estimate the relationship between these material properties and strain rate. The elastic modulus was also measured using a probing protocol and the human liver, kidney, and spleen were found to be stiffer using the probing method versus unconfined compression testing. Porcine failure stress for the prostate, kidney, liver, and spleen were comparable to that of the human host. The elastic modulus of the porcine liver and spleen were found to be a feasible substitute for the respective organ from the human host. In tension, the elastic modulus, failure stress, and failure strain of the gallbladder, bladder, and intestines were measured at various rates. The elastic modulus and failure stress were found to be strain rate dependent for all organs measured in tension. A numerical model was created to quantify this strain rate dependency. Porcine tissue was determined to be a feasible substitute for the elastic modulus and failure stress for human intestines and gallbladder. In addition, the failure strain was comparable between human and porcine gallbladder. The knowledge gained from this research provides useful information that can lead to the improvement of finite element models. Creating models with higher fidelity will produce results with higher accuracy and greater applicability. Advancements in modeling from the current characterization of abdominal material properties will have a positive impact on such areas as forensics, diagnostics, injury prediction, personal protective equipment development, and many other fields.