Biomedical Engineering Reference
In-Depth Information
important parameters, including the diameter of the nozzle, the fl ow rate, and the applied volt-
age. The parameters also infl uenced the hepatocyte viability and functions. By using appropriate
parameters, large quantities of microcapsules can be produced with a practical encapsulation rate
of up to 55 mL/h providing good support for hepatocyte viability and functions and maintaining
cell viability (
87%) and mechanical stability. The microcapsules formed by this method exhibited
good physical properties and hepatocyte biofunctions, which can meet the requirements in bioar-
tifi cial, liver-assisted device applications. A multiple electrospraying system can be developed for
mass production of microencapsulated hepatocytes or other sensitive cells for various cell-based
therapeutic applications. This system could represent a practical and scalable method of production
for the encapsulation of cell-containing microcapsules.
Al-Hajry et al. used electrospraying to encapsulate callus cells in alginate microparticles [103].
The encapsulation and growth of callus tissue in alginate particles prepared by electrospraying was
investigated, as was the mechanism of alginate-encapsulated droplet formation. The encapsulation
generation system, as shown in Figure 11.47, consisted of a syringe, a syringe pump, a needle, a
high-voltage power supply, and a collecting solution. The positive electrode wire was connected to
the needle, and the ground wire was attached to the CaCl 2 dehydrate collecting solution. When the
alginate solution was pumped through the needle by the syringe pump, the droplets were electro-
sprayed by the action of electric forces. In some experiments, the needle was removed and the posi-
tive electrode wire was inserted directly into the alginate solution. The sodium alginate solutions
were prepared fi rst by placing 300 mL of distilled water in a beaker in a boiling water bath, and
then alginate powder (3-18 g) was added to this beaker and stirred until the powder got dissolved.
After that, the alginate solution was placed in a sealed bottle and stored at 4°C. In the cell immobi-
lization studies, the alginate solutions were autoclaved at 120°C and 15 psi for 20 min before use.
For encapsulating the callus cells, the dissociated callus cells of 200 mg were added to a 5 mL of
sodium alginate solution with different concentrations of 2%, 4%, and 6% so that the cell loading
was approximately 20% (volume of cells/volume of alginate solution). The suspension was electro-
sprayed into the collecting solution to form encapsulated particles using the processing parameters:
an applied voltage of 5.0-10.0 kV, a spraying distance of 6-10 cm, and a fl ow rate of 36 mL/h. The
experiment revealed that callus cells were successfully immobilized by using electrospraying, and
the average size of alginate microbeads was as small as 500
>
50 µm in diameter. The callus cells
encapsulated in 2% sodium alginate and cultured on agar gel still retained viability over a 2-month
culture period. The encapsulation cell microbeads aided in the germination and growth of callus
tissue by enhancing higher cell densities and protecting cells from shear damage in culture media.
±
Pump
Alginate droplets
Syringe
+
Strobelight
Video camera
240 V AC
High-DC voltage
power supply
(0 30 kV)
Collecting solution
Microscope
Microbeads
PC
VCR
FIGURE 11.47 An electrospraying droplet generator and a video image analysis system. (Reprinted from
Al-Hajry, H.A. et al., Biotechnol. Progr. , 15, 768, 1999. © American Chemical Society. With permission.)
 
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