  Brain tissue is a heterogeneous material, constituted by a soft matrix filled
with cerebrospinal fluid. The interactions between, and the complexity of each
of these components are responsible for the non-linear rate-dependent behaviour
that characterizes what is one of the most complex tissue in nature. Here, we
investigate the influence of the cutting rate on the fracture properties of
brain, through wire cutting experiments. We also present a model for the
rate-dependent behaviour of fracture propagation in soft materials, which
comprises the effects of fluid interaction through a poro-hyperelastic
formulation. The method is developed in the framework of finite strain
continuum mechanics, implemented in a commercial finite element code, and
applied to the case of an edge-crack remotely loaded by a controlled
displacement. Experimental and numerical results both show a toughening effect
with increasing rates, which is linked to the energy dissipated by the
fluid-solid interactions in the process zone ahead of the crack.
