| The biomechanics of the brain in reaction to injury, surgery, or disease is dependent on bulk mechanical properties of central nervous system tissues. Accurately measured mechanical properties can be used to predict structural changes and determine internal stresses within brain tissues subjected to various environmental forces. Previous studies have characterized mechanical behavior of brain tissues over large brain regions or have classified tissue properties for either gray or white matter regions only. Therefore, they are limited in their ability to explain complex deformations due to interactions between different anatomical regions. Moreover, loss of cell viability and morphological change of tissue which could potentially affect the changes of mechanical properties were not critically considered. This study provides a fundamental methodology for characterizing local mechanical properties of ex vivo, thin brain tissue slices and soft, hydrated biomaterials.;Firstly, two different microindentation systems, Hysitron nanoindentation and optically-based indentation systems, were introduced to measure mechanical behaviors in local regions of thin brain tissue slices and soft hydrated biomaterials. The Hysitron nanoindentation system allowed measurement of local mechanical behavior with various testing modes and an optically-based micro indentation system was introduced for mechanical testing of even softer materials over long time periods. Secondly, FE models were developed to estimate accurate mechanical properties, while considering a finite thickness effect, large deformation and complex geometry. Biphasic FE models were introduced to estimate mechanical and transport properties, hyperviscoelastic FE models were used to estimate viscoelastic parameters and equilibrium modulus over long time periods. Finally, histology methods were developed to detect a loss of cell viability and changes of tissue integrity.;Overall, a methodology for indentation tests was developed to improve mechanical properties measurements of acute brain tissue slices and soft hydrated biomaterials. With the combination of developed methodologies, this study provides more accurately measured mechanical properties in brain tissue and takes into consideration 1) spatial changes in different anatomical regions, 2) temporal changes during the loading period and 3) biological changes due to tissue degradation. Additionally, this technique may be used to characterize the mechanical behavior of other thin tissue slices and biomaterials. |
