Biomedical Engineering Reference
In-Depth Information
distance) becomes an important parameter for estimating
the adhesion formation on the injured flexor tendon that cannot withstand the
reciprocating motions of a pendulum test [17].
The work (force
×
5.4
Theoretical Analysis for Tribological Issues
Theoretical analyses of the tribology of natural and artificial joints can be classified
as either an estimation of theoretical film thickness between two bearing surfaces
[31] or a calculation of contact pressure distributions in the bearing material [32].
The elastohydrodynamic lubrication analysis, where the governing equations
consist of Reynolds and elasticity equations, is used for an estimate of the film
thickness, and the lubricant representing the synovial fluid is assumed to be
Newtonian, isoviscous, and incompressible. However, the main component of
synovial fluid is the polysaccharide HA, which is non-Newtonian (Figure 5.10).
Issues concerning the viscosity of the lubricant will inevitably arise in more precise
analyses [33].
The contact pressure distribution in the bearing material is generally computed
by means of a three-dimensional finite element method (FEM). The FEM is a
revolutionary technology that is widely used in industry; however, it cannot be
overemphasized that the precision of the analysis is dependent upon its boundary
conditions. Neither the influence of friction at the contact point between two objects
nor the influence of wear or wear debris on FEM analysis has yet to be established.
100
Mw
0.9 million
Mw
=
2.7 million
=
10
1
0.1
1
10
100
1000
Shear rate (1 s)
−
1
Figure 5.10
Non-Newtonian liquid of water solution of hyaluronic acid (HA).
