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In vivo indenter experiments on soft biological tissues for identification of material models and corresponding parameters

Petekkaya, Ali Tolga
Soft biological tissues, being live and due to their physiological structures, display considerably complex mechanical behaviors. For a better understanding and use in various applications, first study to be carried out is the tests made particularly as in vivo. An indenter test device developed for this purpose in the METU, Department of Mechanical Engineering, Biomechanics Laboratory is operational. In this study, in order to carry out precise and dependable tests, initially, various tests and improvements were conducted on the device and the software controlling the device. At the end of this study, displacement and load measurement accuracies and precisions were improved. Better algorithms for filtering the noisy data were prepared. Some test protocols within the software were improved and new protocols were annexed. To be able to conduct more dependable tests a new connection system was attached to the device. In order to study the anisotropic behavior of soft tissues ellipsoid tips were designed and produced. In the second phase of the study, tests on medial forearm were carried out. In these tests, hysteresis, relaxation and creep behaviors displaying the viscoelastic v properties of the soft biological tissues were observed. In addition to viscoelastic behaviors, preconditioning (Mullin’s) effect and anisotropic response were examined. By using the results of the relaxation and creep tests, parameters of the Prony series capable of modelling these data were determined. With this study, some important conclusions regarding the soft biological tissues were drawn and thus the behaviors of the soft biological tissues were better understood. Besides, the difficulties inherent to in-vivo tests were recognized and actions to reduce these difficulties were explained. Finally, clean experimental data, to be used in the computer simulations, were obtained.