ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Stress [Pa]
4
3
2
1
0
Mean stress
Adhesion cell-bead = 20e-6 J/m 2
Number of cells
1
0 20 40 60 80 100 120 140
0
Time [h]
Figure 2: Average mechanical stress and total cell number vs time. Red: mean stress level ± 1 standard
deviation. Black: Number of cells on microcarrier.
4.2 Influence of microcarrier properties
Commercial suppliers of microcarriers apply coatings to the beads in order to increase cellsubstrate
adhesion, resulting in a higher cell yield after cell expansion cultures. We simulated
cell expansion on spherical microbeads for five different values of cell-substrate adhesion Ka,cb in
order to investigate their effect on the mechanical microenvironment. In Figure 3, the positions
and stresses of the cells are shown for cell-bead adhesion values. Not only the spatial distribution
and geometry of the cells, but also the magnitude of the compressive stress changes with Ka,cb.
It should be pointed out that in the cases of very small Ka,cb, the cells won’t attach properly to
the bead and will die or wash off in in vitro experiments. Both the mean compressive stress and
spreading of stresses increase when Ka,cb becomes large (Figure 4a).
(a) (b) (c) (d) (e)
Figure 3: Simulated microcarrier cell expansion on microbeads with different cell-substrate adhesion values.
(a): Ka,cb = 2.5e-6 J/m 2 , (b): Ka,cb = 5e-6 J/m 2 , (c): Ka,cb = 10e-6 J/m 2 , (d): Ka,cb = 20e-6
J/m 2 , (e): Ka,cb = 40e-6 J/m 2
Additionally, we performed simulations of cell expansion on microbeads for different Young’s
moduli of the beads. The distribution of mechanical stresses on the cells is not as heavily influenced
by the young’s modulus of the bead than its surface adhesion properties (Figure 4b).
300
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50
Number of cells