Multiscale Modeling of Primary Cilia - Multiscale Modeling in Biomechanics and Mechanobiology - page 99

Fig. 5.12 Effects of oscillatory fluid flow (1 Pa for 1 h) in microtubule morphology for IMCD-
SSTR3 cells. Both images were taken with the same intensity. Images are produced from experiments
in [ 81 ]
filaments into a two-dimensional box. Since the position and orientation of filaments
are uniformly distributed over the allowed ranges, the networks are isotropic and
homogeneous on sufficiently large scales. Each intersection between filaments is a
cross link. The elastic moduli can be computed from the discrete Hamiltonian that
consists of both the discrete bending energy and compression/extensional energy
[ 89 - 91 ].
5.6 Conclusions and Open Questions
The mechanics of the primary cilium has been extensively investigated experimen-
tally. Several attempts have been made to theoretically model its bending mechanics.
From our modeling approaches we find that it is essential to capture the fluid-structure
interaction between fluid flow and the elastic ciliary axoneme. The slender-body
theory is modified to incorporate the basal body anchorage, which behaves like a
nonlinear rotational spring. With such rotational stiffness at the cilium base, the
slender-body model reproduces the experimentally observed bending dynamics, and
sheds light on the repetitive bending of primary cilia.
The primary cilium has been known to play an important mechanosensory role
in numerous tissues across many species and organisms [ 92 ]. The cilium's ability
to do so depends on its adaptation to different situations. For example, the primary
cilium is able to dynamically modulate its length, and thus, fine tune its sensitiv-
ity to the extracellular environment. By blocking calcium ion entry and increasing
intracellular cAMP (cyclic adenosine monophosphate), Besschetnova et al. recently
demonstrated that the length of the primary cilium (in a mammalian epithelia and