Measurement of viscoelastic properties in multiple anatomical regions of acute rat brain tissue slices

Mechanical property data for brain tissue are needed to understand the biomechanics of neurological disorders and response of the brain to different mechanical and surgical forces. Most studies have characterized mechanical behavior of brain tissues over large regions or classified tissue properties for either gray or white matter regions only. In this study, spatially heterogeneous viscoelastic properties of ex vivo rat brain tissue slices were measured in different anatomical regions including the cerebral cortex, caudate/putamen, and hippocampus using an optical coherence tomography (OCT) indentation system. Cell viability was also tested to observe neuronal degeneration and morphological changes in tissue slices and provide a proper timeline for mechanical tests. Shear modulus was estimated by fitting normalized deformation data (D/ti), which was defined as the ratio of deformation depth (D) to initial thickness of the tissue slice (ti), to a viscoelastic finite element model. The estimated shear modulus decayed nonlinearly over 10 min in each anatomical region, and the range of instantaneous to equilibrium shear modulus was 3.8-0.54 kPa in the cerebral cortex, 1.4-0.27 kPa in the hippocampus and 1.0-0.17 kPa in the caudate/putamen. Although these regions are all gray matter structures, their measured mechanical properties were significantly different. Accurate measurement of inter-regional variations in mechanical properties will contribute to improved understanding organ-level structural parameters and regional differential susceptibility to deformation injury within CNS tissues.