Computational simulation of the mechanical response of brain tissue under blast loading.

In the present study, numerical simulations of nonlinear wave propagation and shock formation in brain tissue have been presented and a new mechanism of injury for blast-induced neurotrauma (BINT) is proposed. A quasilinear viscoelastic (QLV) constitutive material model was used that encompasses the nonlinearity as well as the rate dependence of the tissue relevant to BINT modeling. A one-dimensional model was implemented using the discontinuous Galerkin finite element method and studied with displacement- and pressure-input boundary conditions. The model was validated against LS-DYNA finite element code and theoretical results for specific conditions that resulted in shock wave formation. It was shown that a continuous wave can become a shock wave as it propagates in the QLV brain tissue when the initial changes in acceleration are beyond a certain limit. The high spatial gradient of stress and strain at the shock front cause large relative motions at the cellular scale at high temporal rates even when the maximum stresses and strains are relatively low. This gradient-induced local deformation may occur away from the boundary and is proposed as a contributing factor to the diffuse nature of BINT.

Effect of posterolateral disc replacement on kinematics and stress distribution in the lumbar spine: a finite element study.

The current study aimed to compare the biomechanics of the L3-S1 spine segment treated either by fusion or total disc replacement (TDR) using the TRIUMPH(®) Lumbar Disc (Globus Medical, Audubon, PA). A validated three-dimensional, nonlinear finite element model (FEM) of L3-S1 was altered at L4/L5 by fusion and implantation of the TRIUMPH(®) Lumbar Disc. Under a hybrid testing protocol, the resultant range of motion (ROM), nucleus pressure at the adjacent levels, facet joint force, and anterior longitudinal ligament (ALL) force were analyzed. FEM predicted several changes in biomechanics when compared to the intact segment. The analyses suggest that posterolateral lumbar disc arthroplasty with the TRIUMPH(®) Lumbar Disc can preserve the mobility of the surgical level while not allowing excessive ROM and reducing segmental motion at the adjacent levels when compared to fusion. The current finite element model could be valuable for engineers and surgeons seeking to optimize TDR designs.

Finite element analysis of the effect of an interphase on toughening of a particle reinforced polymer composite.

A numerical method was used to study the interaction between a crack and the filler phase in a particle-reinforced polymer composite. The simulation was achieved by implementing a progressive damage-and-failure material model and element-removal technique through finite element analysis, providing a framework for the quantitative prediction of the deformation and fracture response of the composite. The effect of an interphase on composite toughness was also studied. Results show that a thin and high strength interphase results in efficient stress transfer between particle and matrix and causes the crack to deflect and propagate within the matrix. Alternatively, a thick and low strength interphase results in crack propagation within the interphase layer, and crack blunting. Further analysis of the effect of volume fraction and particle-particle interactions on fracture toughness as well as prediction of the fracture toughness can also be achieved within this framework.