XXI ICTAM, 15-21 August 2004, Warsaw, Poland MEASURING THE MECHANICAL PROPERTIES OF SOFT BIOLOGICAL TISSUES

INTRODUCTION The mechanical characterization of soft biological tissues is essential to a number of medical applications, such as surgery planning, surgical training deploying virtual reality based simulators, or diagnosis. Quantitative data sets are available on the in-vivo mechanical properties of soft tissues in animal organs, but very limited data are available on the behavior of soft tissues associated with human organs. This deficiency is primarily due to the severe technical and ethical problems related to the experiments. In this work two new techniques are presented for soft tissue’s mechanical testing, that were designed to fulfill the requirements for in-vivo measurements on human organs during open surgery: the aspiration test and the dynamic torsion test. In the aspiration test relatively large local tissue deformations are imposed and the time dependent behavior of the tissue can be observed. The experiment is characterized by well defined kinematic and static boundary conditions and the time required for each measurement is very short (of the order of 20 seconds). This device has been used already for the in-vivo characterization of the mechanical behavior of human organs during open surgery. In the dynamic torsion test the soft tissue is made part of a vibrating system. The complex shear modulus of the soft tissue is determined from the transfer function of the system. Measurements are performed at frequencies ranging from 1 to 10 kHz. This non-destructive technique can be applied for in-vivo measurements. The goal of the quasi-static and dynamic experiments is to derive a constitutive model of the soft tissue. Typically a large number of material constants need to be determined for model formulations that account for viscoelastic or viscoplastic behavior at large deformations. Numerical methods are used for the solution of the inverse problem. From the quasi-static and the dynamic experiments different types of constitutive model are evaluated in their capability of describing the soft tissue response.