Brain Tissue Biomechanics: new tissue phantoms, mechanical characterisation and modelling strategies for enhanced surgical procedure

Abstract

This thesis aims to clarify some standing issues in the available mechanical knowledge of the human brain. An extensive experimental campaign has been carried out aiming at unravelling the mechanical properties of brain tissue. The outcomes include stiffness, relaxation, permeability and storage and loss moduli measurements. The effect of temperature and humidity is also reported, highlighting the importance of monitoring the environmental conditions when testing this complex organic tissue. The work includes testing of surrogate materials and the design of a new composite hydrogel tailored to reproduce the mechanical behaviour of the tissue. The making of a dynamic life-sized phantom is also achieved and described in detail. This overcomes the rare availability of brain shift intra-operative data and enables the possibility to develop reliable models for pre-surgical planning and surgical training. A series of modelling examples are also reported, using several material formulations and boundary conditions, in order to investigate different modelling approaches, the importance of each material parameter in the analysis, the effect of the presence of the liquid phase on the results etc. Finally, a full 3D model of the human brain is presented. The model is evaluated comparing the deformation field measured in the life-sized phantom against the computed deformation fields obtained by using three different material formulations. The model is described in detail and the results demonstrate that the poro-hyper-viscoelastic material formulation exhibits the smallest deviations in comparison with the experimental apparatus.