Hydrogel-Based Microﬂuidic Cell Culture 95
Figure 5.5. Alginate microcapsules. (A) Schematic model of alginate microcapsules:
the ”egg-box” model. G-units (black arrows) are linked by cations, forming the porous
network that surrounds the producer cells (white arrow). (B) Light microscopic image
of a homogeneous alginate bead and producer cells (650 μm in diameter). (C) Schematic
model of an inhomogeneous alginate bead comprising an outer rim of alginate and an
inner cell compartment. (D) Light microscopic image of an inhomogeneous bead. Original
on the alginate chain can include addition of RGD peptides to encourage cell
Cell viability can be increased by decreasing the molecular weight
of the alginate, which decreases the low shear viscosity of pre-gelled solutions.
High viscosity of the pre-gel solution may cause higher shear forces during cell
suspension. The molecular weight of the gels can be decreased by irradiation.
Agar gels are also polysaccharides derived from seaweed or algae. Agar gels have
been used as food thickeners and as a vegetarian gelatin substitute. Agar gels have
been used to coat petri dishes in bacterial cell culture.
Agarose is one of the main polysaccharide components of agar. Agarose gels
have been used in electrophoresis for DNA separation.
Dilute solutions of agarose
form gels which permit the separation of large DNA molecules through the pores
of the gel under an applied electric ﬁeld.
Agarose is a copolymer consisting of (1,3)-linked β-
D-galactose and (1,4)-
L-galactose. Agarose forms a thermally reversible gel in
a range of temperatures depending on the molecular weight and concentration of
the polymer. Agarose melts around 85
C and solidiﬁes around 35
C, although a
low gel temperature agarose will melt at 70
C. Agarose can also be formed into
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