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The force is gradually increased, and a plot of F/A (A = cross sectional area of
the gel) versus relative compression (
Δ
L/L) may look something like in Fig. 26
(right).
Young’s modulus is defined as the slope of the initial tangent
(d(F/A)/d(
Δ
L/L)
Δ
L/L
→
0
. It depends not only on the type of alginate, but also the
molecular weight, the type of gelling ion (Ba > Sr > Ca >> Mg).
Young’s modulus is well correlated to the G-content of the alginate (Figure 25
above). However, alginates rich in alternating (..MGMGMG..) sequences are
poorly gelling because they lack G-blocks which are required for the formation
of cross-links.
1.2.19. Cell
immobilization and
encapsulation
Mammalian cells, microorganisms and in principle
nearly any particle can easily be immobilized in an
alginate gel or capsule as illustrated below:
Figure 25. Compression of a gel: The basis for determining Young’s
modulus (’gel strength’)
Figure 26. Human cells (insulin
producing) immobilized in an alginate
bead