Biomedical Engineering Reference
In-Depth Information
Agarose Microcapsules
Agarose is a natural polysaccharide extracted from the cellular walls of agarophyte
seaweed and exhibits temperature-sensitive water solubility. Agarose hydrogel has been
widely studied for biomedical applications for use in transplantation with cells, such as tissue
scaffolds [41-44] and cell encapsulation vehicles [45-47] due to a high biocompatibility.
Agarose gel is formed by cooling aqueous agarose solution, which is obtained by heating an
aqueous suspension of agarose powder until a clear solution is formed. Using agarose with a
low gelling temperature (26-30°C at 1.5%), mammalian cells can be suspended in the solution
at 38°C and kept viable. Cell-enclosing agarose microcapsules of about 100 μm in diameter
can be obtained by extruding a cell-suspending agarose solution from a needle with an inner
diameter of 300 μm into the ambient liquid paraffin stream with laminar flow at 38°C, and
subsequently cooling the resultant emulsion system in an ice bath. The gelated microcapsules
are collected via centrifugation after adding biological buffer into the emulsion system. The
feline kidney cells enclosed in the agarose microcapsules with a diameter of 79 μm had a
89.2% viability [35]. In addition, these cells survived for more than 2 months
in vitro
. These
results indicate that use of the thermal gelation process for agarose is effective for obtaining
cell-enclosing microcapsules of less than 100 μm in diameter.
Figure 6. Photograph of CYP2B1-expressing cells-enclosing agarose microcapsules after 1 day of
culture
in vitro
(Reproduced with permission, from Sakai S et al. Mol. Cancer Ther. [48] @ 2005
American Association for Cancer Research).
In order to demonstrate a potential application of the agarose microcapsules of less than
100 μm in diameter, we enclosed cells genetically modified to express the cytochrome P450
2B1 enzyme (CYP2B1) in the agarose microcapsules of about 90 μm in diameter (Figure 6).
