Development and validation of a constitutive growth model for brain tissue characterising brain alterations in space and time

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The brain, as a part of the central nervous system is probably the most complex biological system, which undergoes significant changes, especially during its growth phase. Because of these complexities, both, at the macroscopic and microscopic level, and the associated difficulties in experimental sampling, there are insufficient experimental investigations. In addition, age-related, mechanical investigations on brain tissue, which were also carried out spatially resolved, are extremely rare. However, such experiments are essential in order to better understand the mechanical properties and functions of the brain during growth and to be able to develop and validate numerical models. The performance of such models in terms of predictive accuracy depends particularly on the quality of the identified material parameters.The objective of this research project is the development and validation of a constitutive growth model for brain tissue that characterises alterations of the mammalian brain both, in space and time. This goal will be achieved in four steps through a close interplay of experiment, modelling, and simulation. Experiments will be performed on porcine brain tissue, displaying similar microstructural and mechanical properties as the human brain. An essential requirement for the modelling is the method development (I) to perform appropriate tissue-level experiments. Since grey and white matter tissue will be sampled individually, the tissue specimens are relatively small. This implies that for the axial, biaxial, and triaxial experiments planned within this project, micromechanical measurement setups under a microscope have to be developed, constructed, and verified. These measurements will allow us to accurately characterise the axial, biaxial, and triaxial behaviour of brain tissue (II). To examine the influence of neurodevelopment on the mechanical properties, brain samples will be collected at different ages. In a third step, the microstructure as well as the macroscopic geometry of the brain will be determined by means of immunohistological investigations (III). The resulting cell density, myelin content, and tissue microstructure will directly inform the model development and validation (IV).