Biomedical Engineering Reference
In-Depth Information
Figure 10.5.
Organ-tissue-length scale model of the rat ulna. The model relates solid and fluid mechanical behavior of bone to
transport within bone, based on a loading scenario after the ulna compression model of Lanyon and colleagues [13]. (A) The human
radius and ulna is a length scale larger than that of the rat (B-D). (B) Finite element model depicting strain in the radius, R and
ulna, U, etc. Reprinted from
, Volume 40, A. E. Tami, M. B. Schaffler, and M.L. Knothe Tate, “Probing the tissue to subcel-
lular level structure underlying bone's molecular sieving function,” pp. 583, 584, 586, 2003, with permission from IOS Press.
Biorheology
embedded in the gauge, which can be mea-
sured, and with the aid of circuit theory, the
strain is calculated. In this way, one can check
whether the strains predicted by the fi nite
element model are appropriate for the model at
hand. It would of course be cumbersome to
glue thousands of gauges to the surface of the
bone to obtain values for the actual strains at
every point for every loading condition. Instead,
this information is provided by the predictive
model, which also predicts the strain within
the bone interior.
It is possible to observe the displacement or
fl ow of fl uid in bone by using visualization
methods, as in a fl uid mechanics experiment in
which dye is added to the fl ow stream to visual-
ize streamlines and/or turbulence. In a living
being an intravital fl uorescent tracer (of a spe-
cifi c molecular size and shape) is injected into
the blood stream prior to the application of
loads. After the ulna has been loaded, the bone
can be examined histologically and the tracer
distribution in the loaded ulna can be com-
pared to that in the contralateral, unloaded
control (Fig.
D-G).
Observations of histological cross sections
taken from the mid-diaphysis show that
mechanical loading pushes the tracer fl uid out
of the medullary cavity, through the cortex,
and toward the periosteum (Fig.
10
.
5
10
.
5
D and E).
