W M Mihalko — Page 2 | PubMed Health

PubMed1991

Finite element modelling of polymethylmethacrylate flow through cancellous bone.

A mathematical model based on the Finite Element Method is developed to simulate the non-linear flow of acrylic bone cement through cancellous bone. The cancellous bone bed is modelled as a bed of parallel capillaries filled with equal spaced toroidal trabeculae. By manipulating the relative size of the torus and the capillary, the flow within bone of varying porosity is simulated. An apparent permeability based on the volume weighted average viscosity and Darcy's law is developed to describe the flow of the acrylic through the cancellous bone bed. The model predicts a cancellous bone permeability of 5.6 x 10(-9)-8.3 x 10(-9) m2 for linear flow. The non-linear behavior of the acrylic cement results in an increase of apparent permeability when compared to the permeability computed for linear flow. Estimates of penetration are achieved by running the model in a quasi-steady state fashion with pressure applied over a fixed time increment. Close agreement is shown between model predictions of penetration depth and experimental results available in the literature.

Biocompatible Materials↗

PubMed1989

Mechanical properties and material characteristics of orthopaedic casting material.

In this study, two types of orthopaedic casting materials were evaluated: the Johnson & Johnson Specialist plaster bandage and the 3M Scotch-cast Plus fiber glass bandage. The materials were evaluated using tensile tests to determine the elastic modulus, yield strength, and ultimate tensile strength. To determine the structural characteristics and stiffness of a cylindrical cast, each material was formed around a foam cylinder core and tested in a four-point bend jig. A computer-based model using the finite element method (FEM) was developed for a cylindrical cast of both types and compared with the experimental findings. A second FEM model with loads applied at the periphery was performed to simulate the clinical observations of plaster bandage breakdown at the ends of a cast. It is with these tests that the two bandage materials were compared and evaluated. It was concluded that the plaster bandage, while initially stiffer than the fiber glass bandage, had much lower yield stress. This implies that the plaster cast may break down under loads that would leave the fiber glass cast intact. It was also determined that the plaster bandage load displacement curve is bilinear. The bilinear characteristic of the plaster bandage explains its breakdown at the ends of a cast.

Biomechanical Phenomena↗