Biomedical Engineering Reference
In-Depth Information
different solvents or solvent mixtures and stirred for 8 h at room temperature. Specifi c amounts of
BSA, previously dissolved in 0.5 mL of distilled water, were mixed with the PLA solutions and
emulsifi ed by sonication for 10 min. The emulsion was drawn into a syringe with an 18-gauge
metal needle, which was applied at a voltage in a range of 0-30 kV. Different solvents had different
effects on the morphology of particles when the voltage and fl ow rate were fi xed at 12.5 kV and
1.0 mL/h, respectively. The experimental results showed that BSA-loaded PLA particles prepared
with dichloromethane solvent were spherical with smooth surfaces and had an average diameter of
4.68
1.35 μm. The BSA-loaded particles using 1,2-DCE solvent were also spherical with smooth
surfaces and had an average diameter of 4.77
±
1.97 μm. The average diameter of the electro-
sprayed particles using 1,2-DCE/acetone solvents was 1.64
±
0.51 μm, signifi cantly smaller than
that using 1,2-DCE. However, the PLA particles were no longer spherical. The results revealed that
the spherical particles cannot be achieved from a concentration of 1% PLA, but spherical particles
were formed from 2% emulsion. Fully spherical particles were produced at a concentration of 3%
emulsion. Further increasing the concentration to 4% resulted in the formation of a mixture of beads
and fi bers. The experiment also showed that the average diameter of the particles decreased as the
applied voltage was increased from 10 to 15 kV, but increased as the fl ow rate was increased from
0.5 to 3 mL/h.
±
11.2.8.4.2
Cell-Encapsulated Biomaterials
Electrospraying technique was employed by Zhou et al. to achieve a scalable encapsulation of
hepatocytes in the microcapsules formed by complex coacervation between the cationic methyl-
ated collagen and the anionic terpolymer of hydroxylethyl methacrylate, methyl methacrylate, and
methylacrylic acid (HEMA-MMA-MAA) [102]. Figure 11.46 shows a schematic illustration of the
setup for hepatocyte microencapsulation. The system consisted of a syringe pump equipped with
a syringe, a rotator, and a high-voltage power supply. For generating encapsulated microbeads, a
cell-collagen suspension was electrosprayed into a terpolymer solution (5% w/v) through a syringe
fi xed on the rotator. This rotator was used to prevent the hepatocyte sedimentation in the colla-
gen solution. It consisted of a shaft with a bearing and an impulse-generator motor, which moved
clockwise and counterclockwise repeatedly. The cell-collagen suspension was electrosprayed into
tiny droplets using the processing parameters: a high voltage of 5-15 kV between the nozzle and
grounded collecting plate and a spraying distance of 3.7 cm between the tip of the nozzle and the col-
lection plate. The microcapsules were exchanged in PBS solution by sedimentation for cell culture
and the subsequent characterizations. The encapsulated particles prepared using electrospraying
had a diameter in the range of 200-800 μm with a narrow size distribution (standard deviation of
5-28%). The experimental results proved that the microcapsule sizes were dependent on several
Syringe pump
Syringe
High-voltage
generator
Syringe
needle
Rotator
FIGURE 11.46
A schematic diagram of electrospraying for microencapsulation. (Reprinted from Zhou, Y.
et al.,
J. Biotechnol.
, 117, 99, 2005. © Elsevier Science. With permission.)
