Research Output
1 - 3 of 3
Publication
Experimental Characterisation of Neural Tissue at Collision Speeds
2012, Rashid, Badar, Destrade, Michel, Gilchrist, M. D.
Mechanical characterization of brain tissue at high loading velocities is particularly important for modelling Traumatic Brain Injury (TBI). During severe impact conditions, brain tissue experiences a mixture of compression, tension and shear. Diffuse axonal injury (DAI) occurs in animals and humans when both the strains and strain rates exceed 10% and 10/s, respectively. Knowing the mechanical properties of brain tissue at these strains and strain rates is of particular importance, as they can be used in finite element simulations to predict the occurrence of brain injuries under different impact conditions. In this research, we describe the design and operation of a High Rate Tension Device (HRTD) that has been used for tensile tests on freshly harvested
specimens of porcine neural tissue at speeds corresponding to a maximum strain rate of 90/s. We investigate the effects of inhomogeneous deformation of the tissue during tension by quasi‐static tests (strain rate 0.01/s) and dynamic tests (strain rate 90/s) using different thickness specimens (4.0, 7.0, 10.0 and 13.0 mm) of the same diameter (15.0 mm). Based on a combined experimental and computational analysis, brain specimens of aspect ratio (diameter/thickness) S = 10/10 or lower (10/12, 10/13) are considered suitable for minimizing the effects of inhomogeneous deformation during tension tests. The Ogden material parameters were derived from the experimental data both at quasi‐static conditions (µ = 440 Pa and α = ‐4.8 at 0.01/s strain rate) and
dynamic conditions (µ = 4238 Pa and α = 2.8 at 90/s strain rate) by performing an inverse finite element analysis to model all experimental data. These material parameters will prove useful for the nonlinear hyperelastic analysis of brain tissue.
Publication
Linear Viscoelastic Properties of Cerbral Cortex at Thresholds for Axonal Damage
2010, Rashid, Badar, Gilchrist, M. D., Destrade, Michel
Traumatic brain injury (TBI) is caused by rapid deformation of the brain that
leads to shearing of axons. While deformation below the limits of ultimate
failure can activate pathophysiological cascades that cause
neurodegeneration [1], bleeding does not always occur even after tearing of
axons. Traditional imaging studies such as CT and MRI are designed to
detect areas of bleeding but these can fail to detect the presence of multiple,
widespread, microscopic axonal injuries that can result in devastating
neurological deficits. A large knowledge gap still exists defining the
relationship between axonal injury at a microscopic level (morphological
injury) and the material properties of the corpus callosum, hippocampus and
cerebral cortex on the macroscopic level, but at identical strain levels. This
research investigates the linear viscoelastic properties of the cerebral cortex
at known thresholds of axonal injury (0.14 - 0.34 strains [2]). During quasi
static loading of tissue in creep tests, instantaneous strains were generated
corresponding to axonal thresholds. A linear viscoelastic constitutive model
was used to determine six Prony parameters suitable for finite element
simulation in ABAQUS and ANSYS. Use of such properties at the levels of
axonal damage will help to accurately predict injuries during numerical
simulations, to design safety helmets and air bags, and also to refine
existing injury criteria and to improve the precision in surgical procedures.
Publication
Mechanical Properties of Excised Human Skin
2010, Ní Annaidh, Aisling, Ottenio, Melanie, Destrade, Michel, et al.