Biomedical Engineering Reference
In-Depth Information
cytometry [11], three-dimensional measurement of membrane thermal fluctuations
[12, 13], and observations of RBCs immersed in both shear and in pressure-driven
flows [14, 15, 16, 17, 18]. Micropipette aspiration and optical tweezers techniques
tend to deform the whole RBC membrane directly, while optical magnetic twisting
cytometry and measurements of membrane thermal fluctuations probe the membrane
properties locally. The macroscopic shear modulus of healthy cells is reported in the
range of 2-12
N/m from the two former techniques, while the two latter ones allow
measurements of local rheological properties (e.g., the complex modulus).
These experiments provide sufficient evidence for a complex membrane mechan-
ical response including its unique viscoelastic properties. In addition, Li et al. [19]
suggest that metabolic activity or large strains may induce a continuous rearrange-
ment of the erythrocyte cytoskeleton. Consequently, in their numerical model the
RBC membrane may exhibit strain hardening or softening depending on certain con-
ditions. Moreover, the cytoskeleton attachments can diffuse within the lipid bilayer,
but such behaviour can be neglected at short time scales. Gov [20] proposed an ac-
tive elastic network model, where the metabolic activity may affect the stiffness
of the cell through the consumption of ATP. The activity induced by ATP would
also greatly affect membrane undulations [2, 21] resulting in fluctuations compara-
ble to an effective temperature increase by a factor of three. For parasitic infectious
diseases, powerful imaging techniques have been developed in recent years, which
allow to observe details of parasite development inside the RBC and also to gain
information about the properties of the cell components [12, 22]. Fig. 10.1(a) shows
the parasite
P. falciparum
inside an infected RBC during the ring stage of parasite
development, which was obtained using soft x-ray imaging technique. The parasite
and some elaborate structure, which extends from the parasite into the cell cytosol,
can be clearly seen in the image.
μ
(a)
(b)
Fig. 10.1.
(a) Soft x-ray micrograph of intra-erythrocytic ring stage
P. falciparum
malaria parasite
imaged in RBC (Reproduced from [22]). (b) The computational RBC model consists of particles
connected with links. The model is immersed into DPD fluid and fully interacts with it through
pairwise forces. The internal DPD fluid has a higher viscosity to match the viscosity of RBC cytosol.
The
P. falciparum parasite
is modelled as a rigid sphere of two microns in diameter
