A high-fidelity 3D S-FEM stress analysis of a highly heterogeneous swine skull

A statistical analysis of human talar shape and bone density distribution

The shape of the talus, its internal structure, and its mechanical properties are important in determining talar behavior during loading, which may be significant for the design of surgical tools and implants. Although recent studies using statistical shape modeling have described quantitative talar external shape variation, no similar quantitative study exists to describe the density distribution of internal talar structure. The goal of this study is to quantify statistical variation in talar shape and density to benefit the design of talar implants. To this end, weight-bearing computed tomography (CT) scans of the ankle were collected in neutral, bilateral standing posture, and three-dimensional models were generated for each talus. Local density derived from the Hounsfield unit of each CT voxel was extracted. A weighted spherical harmonic analysis was performed to quantify the talar external shape. One hundred and seventy-nine volumes of interest were placed in the same relative position within each talus to quantify the talar density. Additionally, a finite element analysis (FEA) was conducted on a talus with both heterogeneous and homogeneous material properties to observe the effect of these properties on the stress and strain response. Significant differences were found in the talar density in sex and age, as well as in the stress and strain response between homogeneous and heterogeneous FEA. These differences show the importance of considering heterogeneity when examining the load response of tarsal bones.

Boundary conditions investigation to improve computer simulation of cerebrospinal fluid dynamics in hydrocephalus patients

Three-D head geometrical models of eight healthy subjects and 11 hydrocephalus patients were built using their CINE phase-contrast MRI data and used for computer simulations under three different inlet/outlet boundary conditions (BCs). The maximum cerebrospinal fluid (CSF) pressure and the ventricular system volume were more effective and accurate than the other parameters in evaluating the patients' conditions. In constant CSF pressure, the computational patient models were 18.5% more sensitive to CSF volume changes in the ventricular system under BC "C". Pulsatile CSF flow rate diagrams were used for inlet and outlet BCs of BC "C". BC "C" was suggested to evaluate the intracranial compliance of the hydrocephalus patients. The results suggested using the computational fluid dynamic (CFD) method and the fully coupled fluid-structure interaction (FSI) method for the CSF dynamic analysis in patients with external and internal hydrocephalus, respectively.

Bone remodeling analysis for a swine skull at continuous scale based on the smoothed finite element method

In order to study bone response during chewing, bone remodeling analysis at a continuous scale is performed to a swine skull obtained using μCT. The smoothed finite element method (S-FEM) is utilized to replace the finite element method (FEM) in bone remodeling as it is solving the "overly-stiff" problem in FEM by introducing strain smoothing technology to soften the stiffness matrix. Three S-FEM models with different levels of softening effects are developed, including node-based, edge-based, and face-based, which leads to various bone remodeling results for a better understanding of the remodeling process. During the remodeling process, the strain energy density is used as the mechanical stimulus, and the surface elements or smoothing domains are regarded as cortical bone. Under the action of mechanical stimuli, cortical bone and cancellous bone have been remodeled. In remodeling progress, ES-FEM shows close results as compared with the experimental μCT in nodal bone density distribution, FEM and FS-FEM are close to the μCT experimental model in average nodal density. In summary, the combined use of several methods provides more angles for the description of bone remodeling.