Biomedical Engineering Reference
In-Depth Information
are contractile; these filaments actively generate mechanical tension through a
filament-filament sliding mechanism similar to that used in muscle (35,39).
Thus, the entire cytoskeleton and cell exists in a state of isometric tension. In
essence, by organizing this multimolecular network, the cell translates a struc-
tureless chemistry into a physical entity with well-defined mechanical proper-
ties. For example, this tensed intracellular scaffold is largely responsible for the
viscoelastic properties of the cell. It also generates the tractional forces that
drive cell movement as well as changes in cell shape.
4.1.2. Cellular Tensegrity
Past work on cell shape and mechanics ignored the cytoskeleton and as-
sumed that the cell is essentially an elastic membrane surrounding a viscous or
viscoelastic cytosol (16,17,22). In contrast, over the past twenty years, we and
others have been able to show that the cytoskeleton is the major determinant of
cell shape and mechanics, and that cells may use a particular form of architec-
ture known as "tensegrity" to organize and stabilize this molecular network (re-
viewed in (39)).
Tensegrity was defined by Buckminster Fuller as a building principle in
which structural shape of a network of structural members is guaranteed by con-
tinuous tensional behaviors of the system and not by local compressional mem-
ber behaviors (21). The purest representation of the tensegrity principle is found
in the creations of the sculptor, Kenneth Snelson, which are composed of a con-
tinuous network of high-tension cables and a discontinuous (isolated) set of
compression struts (Figure 2). However, the tensegrity principle also applies to
Figure 2
.
Tensegrity model
. A prestressed tensegrity structure composed of 6 compression-resistant
struts (white struts) interconnected by 24 tension cables (black lines) on its periphery; this model also
contains radial cables connecting the ends of the struts to the cell center (red lines). The theoretical
tensegrity model of the cell is based on this architecture. In the cell model, the black lines correspond
to viscoelastic actin cables, the red lines to viscoelastic intermediate filaments (of different time
constants), and the white struts to rigid microtubules.
