polymery 2010 - Institute of Macromolecular Chemistry - Akademie ...

L-12
EXTERNAL AND INTERNAL GELLING METHOD FOR PREPARATION OF
PLANAR ALGINATE HYDROGELS
E. Papajová a , M. Danko a , D. Chorvát Jr. a,b , Z. Kroneková a , I. Lacík a
a Polymer Institute of the Slovak Academy of Sciences, Dúbravská cesta 9, 845 41
Bratislava 45, Slovak Republic
b
International Laser Centre, Ilkovičova 3, 841 04 Bratislava 4, Slovak Republic
e-mail: eva.papajova@savba.sk, igor.lacik@savba.sk
Sodium alginate (SA) is a linear polysaccharide extracted from brown algae or bacteria. SA is
composed of mannuronic (M) and guluronic (G) monomeric units arranged in homopolymer
blocks or blocks of alternating M and G units. The structure of SA depends on the type of
source and tissue, age and growth conditions.
Three-dimensional hydrogel networks are formed from SA in the presence of divalent cations
(e.g. Ca 2+ or Ba 2+ ) [1]. The mild conditions of gelling process are advantageous for using SA
hydrogels in the biology-oriented applications. Although vast information about the SA
hydrogel formation for various applications exists, a further work is needed toward the
flexibility in shape variability (beads, thin layers, thicker slabs, fibres, rods etc).
Nowadays, two basic principles are known for SA hydrogel preparation, i.e. internal [2] and
external [1] gelling methods. Internal gelation is based on dissolving of CaCO3 particles (as a
source of Ca 2+ ions) dispersed in SA solution upon lowering the pH value. This type of
gelation is most often used for preparation of SA hydrogels of planar, cylindrical and
spherical geometries. An external gelling is based on diffusion of dissociated divalent cations
from external environment into the SA solution. The gelling process begins immediately after
the mutual exposure of these two phases. In this case, a bead is the most typical geometry.
The external gelling is not common for formation of SA hydrogels of planar geometry due to
the fact that fast exposure of SA solution by solution of divalent cations results in an
uncontrolled shape distortion.
This contribution deals with preparation of planar hydrogels by external gelling method. The
external gelling in formation of planar SA hydrogels introduces advantages over the internal
gelling process represented by physiological pH and the absence of CaCO3 particles not
always completely disappearing after the gelling. The main idea of planar hydrogel
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