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1.2.21. Alginate
foams: 3D
cell
cultures
A foamy material is often advantageous for growing mammalian cells in a
controlled manner. Cells can be added to the foam, whereby they distribute
evenly in the porous structure in 3 dimensions (3D). Foams seeded with
appropriate cell types (stem cells or differentiated cells) are promising
alternatives in tissue engineering.
Alginate foams may be obtained by freeze-drying alginate solutions, but
recently
14
a new method to prepare foams with better control over porosity
and mechanical properties was developed. In this case the CaCO
3
/GDL
gelation method is applied in a slightly modified way:
First, a suspension of Na-alginate containing CaCO
3
microparticles and GDL
in addition to plasticizers (glycerol, sorbitol) and HPMC
15
(foaming agent) is
prepared. The low rate of gelation allows the system to mix with air to form
stable bubbles.
As the alginate solution slowly forms a gel, the porous structure becomes
permanent as air bubbles are prevented from rising or coalescing. The porous
gel is the dried and stored (if necessary, sterilized) before use.
Figure 28. Preparation of alginate foams (Courtesy Therese Andersen, Ph.D.
thesis NTNU, 2013).
Cells are seeded into the foams simply by adding the cell suspension (in
appropriate buffer). The cell suspension fills the pores, and the cells thus
distribute evenly throughout the foam.
In order to ensure efficient seeding it is advantageous to use some Na-
alginate in the cell suspension. The added alginate will react with Ca
++
ions
(or alternatively Sr
++
) already present in the dry foam and form a gel inside the
pores. The final product is a homogeneous alginate gel (no longer a foam).
14 PhD thesis Therese Andersen, NTNU, 2013
15 HPMC: Hydroxypropyl cellulose