Biomedical Engineering Reference
In-Depth Information
and 44 μm in diameter [defined as the viability of cells enclosed in the droplet]/[viability of
the cells before extruding in co-flowing liquid paraffin × 100] were more than 95% (Figure
5a). In addition, cells retrieved from these droplets showed almost the same growth profiles in
cell culture dishes with those seeded using a normal subculture protocol (Figure 5b). It is well
known that mammalian cells are easily damaged by the forces exerted by the external
environment, such as shear stress. In the droplet breakup process in co-flowing immiscible
liquid, drag force is the most influential force to affect the viability of cells suspended in the
polymer solution. However, the results for viability and growth profiles of the cells exposed
to the droplet breakup process (Figure 5) demonstrate that the drag force necessary for droplet
breakup in water-immiscible liquid resulting in droplets of less than 100 μm in diameter from
the needle of several hundred micrometers in diameter is insufficient to damage cell viability
and growth activity.
Figure 5. (a) Percentages of undamaged human tongue squamous carcinoma cells enclosed in droplets
obtained from an aqueous solution with different viscosities: (white) 1, (diagonal line) 36, and (black)
194 mPa⋅s. (b) Proliferation profiles of the cells cultured in tissue culture dishes (white) before and after
being retrieved from droplets obtained from aqueous solutions of (diagonal line) 36 and (black) 194
mPa⋅s. Droplets were prepared by extruding cell suspensions from a needle with a 300 μm i.d. at 1.2
cm/sec into an ambient co-flowing liquid paraffin stream of 23.5 cm/sec (Reproduced with permission,
from Sakai S et al. Biotechnol Prog. [34] @ 2005 American Institute of Chemical Engineers).
Cell Encapsulation in Microcapsules
As described above, the method using liquid paraffin as an ambient co-flowing fluid is
effective for obtaining droplets of polymer solution with a diameter of less than 100 μm while
scarcely damaging the cells. The resultant droplets exist in a water-immiscible fluid; thus a
smart approach to obtain gelated capsules is to carry out gelation of the droplets.
Thermosensitive and photo-curable polymers are good candidates for this process. We
prepared capsules based on two types of gelation processes, thermal gelation using
unmodified agarose [35,36] and agarose-based materials [37,38], and enzymatic gelation
using polymers incorporating phenolic hydroxyl groups [39,40].
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