Mechanical Properties Of Brain Tissue

Mechanical property of biological soft tissue is one of the research topics in the areas of mechanics, medicine, materials, etc. The brain is the most amazing organ in human body, and it is also the softest and the most vulnerable organ. Traumatic brain injury resulting from an impact in daily fall, sports, and car accident, is one of the leading causes of death and severe disability. In the process of impact, compression, tension and shear deformation may occur in the brain tissue, causing brain damage. In order to develop effective protective precautions and a reliable prediction method for the possible brain damage, we need to accurately understand the mechanical properties of brain tissue and, establish a suitable analysis model. In addition, with the development of automation and virtual reality technologies in the medical field, we also need a theoretical model to precisely predict the stress-strain relationship when brain tissue is subjected to an impact.Based on literature survey, we here investigated the mechanical properties of brain tissue. Since the mixture specimen of brain white matter and grey matter cannot reflect the mechanical properties of brain tissue accurately, pure white matter and grey matter specimen are prepared using a house-developed cutting device to explore the differences in mechanical properties of white matter and grey matter. The main contents of this thesis are as follows: through a set of tension, compression and tension-relaxation experiments of brain white matter and grey matter, it is found that the stress-strain relationship of white matter and grey matter in the tension and compression experiment depends on strain rate, and the elastic modulus of white matter is higher than the grey matter's (strain rate> 0.025/s). In tension-relaxation test, white matter's relaxation time is longer than the grey matter's at the same initial strain level. In order to study those differences in mechanical properties between white matter and grey matter, we have also discussed the mechanical mechanism of brain tissue. Through testing white matter and grey matter specimen by differential scanning calorimetry (DSC) and calculating enthalpy change, it is found that grey matter may dissipate more energy than white matter in the process of phase transformation. By Fourier infrared spectroscopy (FTIR), the results indicate that the existence of strong polar groups and the hydrogen bonds in the white matter can improve the interaction between biological molecules, reducing the compliance. This explains why the energy dissipation capacity of white matter is lower than grey matter structures. Finally, by fitting the tension experimental data of brain tissue under different strain rates, a hyperelastic constitutive model is obtained. Meanwhile, by fitting the tension-relaxation experimental data, a viscoelastic mechanical constitutive model is obtained.