Biomedical Engineering Reference
In-Depth Information
compute the deformed profile in a self-consistent manner and thus the
constitutive relation.
4.
Adhesion of Cells and Tissues
The many faceted cell adhesion has from time to time serious
consequences in biomedical manifestations and applications. On the
negative side, life threatening diseases develop due to inability to express
cell adhesion such as leukocyte adhesion deficiency-I (LAD-I), or
excessive adhesion such as atherosclerosis. Conversely, formation of
natural-prosthetic tissues-organs, morphogenesis and developmental
embryology also depends on adhesion of apposing cells. In fact, there are
situations when the mechanical properties of macroscopic tissues depend
on the hierarchical constitutive components. The multi-scale behavior of
the nano-scale lipid bilayer membrane (~100 Å), the micro-scale cell
with an encapsulated viscoelastic cytoplasm (~10
m), meso-scale multi-
cell aggregates (~100 μm), and macro-scale biomembranes and organs
(>1 mm) can be expressed by a simple phenomenological equation for
elastic modulus,
μ
E
macro
meso
m
n
×Θ ×Θ×
E
+
C
+
C
+
C
micro j
,
nano i
,
nano i
,
nano i
,
micro j
,
meso
j
=
1
i
=
1
micro j
,
meso
(10-23)
where
is the structural factor governing the geometrical arrangement,
and C is the mechanical properties of the interconnecting or interlocking
mechanism ( e.g. surface forces, extra-cellular matrix).
Cell adhesion and detachment are apparently complex interplay of
biochemistry and mechanical properties of the cell membrane and
substrate. Rather than tackling the comprehensive cell adhesion theory
and phenomena, we focus only on the mechanical aspects of intersurface
physical and chemical forces that lead to adhesion interfaces. The origin
of surface forces can be roughly divided into two main categories. The
non-specific forces arise from electrostatics, van der Waals interaction,
configurational forces ( e.g. intercalating adsorption layers at the adhesion
Θ
 
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