Biomedical Engineering Reference
In-Depth Information
Figure 10.2.
The ecosystem of bone.
This concept is depicted at three length
scales, including systemic level (human
walking [m]), organ level (femur on thigh
overlay [m
−
1
]), tissue level (wedge of cor-
tical bone [m
−
2
]), and cell level (osteocyte
in lacunocanalicular system [m
−
6
to m
−
7
]).
Of particular note, the ecosystem includes
both the fluid environment of the vascu-
lar and pericellular space and the organic
and inorganic structural elements com-
prising the matrix, as well as the living
component of the tissue (i.e., the cells).
Reprinted with the permission of the
Cleveland Clinic Foundation.
10.3 Concept of Engineering
Bones at Multiple Time and
Length Scales
system of organs to move along the ground. The
system is composed of soft tissues, such as the
brain (central command system), heart (central
supply system), muscles (power for movement),
and digestive system (provides materials that
allow all organs to survive and maintain their
structure). Bones also provide protection from
impact. The ribs protect the heart and lungs,
and the cranium protects the brain. At the
tissue level, bone is a living electrophoretic and
ion-exchange column; in this role, bones
provide a reservoir and mobilization surface
for calcium, a key signaling molecule. In addi-
tion, bone provides an enclave for the bone
marrow, where hematopoiesis takes place.
Engineers create implants, artifi cial joints, pro-
tective plates, etc., that function for a defi ned
period of time, under static or dynamic loading
conditions. An example is the standard hip
replacement, which generally lasts
years.
The challenge to tissue engineering, however,
is that function varies with time and age. At
steady physiological state, a histological image
of bone at a given time, may, like a snapshot,
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