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remain in the solution for 2.5-3.0 h for the formation and hardening of spherical
beads.
As mentioned earlier about the variation of the CA entrapment procedure, the
chemical concentrations, centrifugation speed, dropping rate of the cell-alginate
mixture, and hardening time may be modified for enhancing the bead durability
and/or convenience of bead preparation. For instance, the hardening time of the CA
gel beads normally ranges from 0.5 to 3.0 h; however, it has been shown that more
durable beads can be obtained by increasing the hardening times to overnight [20].
The CA entrapped cells can be de-entrapped by vigorous vertical shaking in a 0.3 M
sodium citrate solution at pH 5 [20, 46] or 50 mM phosphate buffer at pH 7 [40].
7.2.2.2 Carrageenan
Carrageenan Chemistry and Gelation
Carrageenan is another common matrix for cell entrapment. It is produced from red
seaweed [38, 43, 47]. Its structure contains 1,3-linked
β
-D-galactose and 1,4-linked
3,6-anhydro-
-D-galactose. There are three types of CN based on the number and
position of sulfonation: kappa (
α
) (Fig. 7.4). Lambda-CN is
water soluble; therefore, it is not suitable for cell entrapment. Between
κ
), lambda (
λ
), and iota (
ι
κ
and
ι
-CN,
κ
-CN is a better cell entrapment matrix since it has a stronger gel network.
The CN gelation process can be either ionictropic or temperature-induced (cool-
ing) gelations. Similar to CA gel,
κ
-CN gel can be formed with different ions, such
Fig. 7.4 Chemical structure
of carrageenan [47]
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