Biomedical Engineering Reference
In-Depth Information
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Figure 10.6
Magnetically responsive alginate beads containing entrapped Sacchar-
omyces cerevisiae cells and magnetite microparticles. Millimeter-sized
beads (left) and microbeads (right). The scale bar corresponds to 50 mm.
Reproduced, with permission, from Ref. 25.
particles and polymer in a hydrophobic phase under stirring and sub-
sequently inducing gel formation.
- Bead formation of ionotropic polymers after dripping the mixture of
cells, magnetic particles and polymer into a medium containing an
appropriate hardening ion.
.
Such a procedure can be very mild, enabling magnetic modification of
living cells and subsequently employing their biological activities. One of the
major drawbacks of the entrapment technique is the possible diffusional
limitation as well as the steric hindrance, especially when the macro-
molecular compounds have to be treated with immobilized cells.
3
In a
typical example, magnetically responsive alginate beads containing en-
trapped Saccharomyces cerevisiae cells and magnetite microparticles were
prepared. Larger beads (2-3 mm in diameter) were prepared by dropping the
mixture into a calcium chloride solution, while microbeads (the diameter of
majority of particles ranged between 50 and 100 mm) were prepared using
the water in oil emulsification process. The immobilized cells were used as
whole-cell biocatalysts for hydrogen-peroxide degradation and sucrose hy-
drolysis (Figure 10.6).
25,55
10.2.4 Crosslinking of Cells or Cell Walls
Microbial cell walls contain free amino and/or carboxyl groups, which can
easily be crosslinked by a bi- or multifunctional reagents such as glutar-
aldehyde or toluene diisocyanate. The cells are usually crosslinked in the
presence of an inert protein like gelatine, albumin, raw hen egg white and
collagen. Microbial cells can also be immobilized by ionic crosslinking
through a flocculation mechanism by addition of polyelectrolytes.
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