Viscoelastic properties of the P17 and adult rat brain from indentation in the coronal plane.

This technical brief serves as an update to our previous work characterizing the region-dependence of viscoelastic mechanical properties of the P17 and adult rat brain in the coronal plane (Elkin et al., 2011, "A Detailed Viscoelastic Characterization of the P17 and Adult Rat Brain," J. Neurotrauma, 28, pp. 2235-2244.). Here, modifications to the microindentation device provided for the reliable measurement of load during the ramp portion of load relaxation microindentation tests. In addition, a correction factor for finite sample thickness was incorporated to more accurately assess the intrinsic mechanical properties of the tissue.The shear relaxation modulus was significantly dependent on the anatomic region and developmental age, with a general increase in stiffness with age and increased stiffness in the hippocampal and cortical regions compared with the white matter and cerebellar regions of the brain. The shear modulus ranged from ∼0.2 kPa to ∼2.6 kPa depending on region, age, and time scale. Best-fit Prony series parameters from least squares fitting to the indentation data from each region are reported, which describe the shear relaxation behavior for each anatomic region within each age group at both short (<10 ms) and long (∼20 s) time scales. These data will be useful for improving the biofidelity of finite element models of rat brain deformation at short time scales, such as models of traumatic brain injury.