Determination of linear viscoelastic behavior of abdominal aortic aneurysm thrombus.

The objective of this study is to determine whether the linear viscoelastic properties of an abdominal aortic aneurysm thrombus can be determined by rheometry. Although large strains occur in the in vivo situation, in this work only linear behavior is studied to show the applicability of the described methods. A thrombus exists of several layers that vary in composition, structure and mechanical properties. Two types of thrombus are described. In discrete transition thrombi the layers are not or at most weakly attached to each other and the structure of each layer is different. Continuous transition thrombi consist of strongly attached layers whose structure changes gradually throughout the thickness of the thrombus. Shear experiments are performed on samples from both types of thrombus on a rotational rheometer using a parallel plate geometry. In the discrete type the storage modulus G' cannot be assumed equal for the different layers. In the continuous thrombus, G', changes gradually throughout the layered structure. In both types the loss modulus, G'', does not vary throughout the thrombus. Furthermore, it was found that Time-Temperature Superposition is applicable to thrombus tissue. Since results were reproducible it can be concluded that the method we used to determine the viscoelastic properties is applicable to thrombus tissue.