Biomedical Engineering Reference
In-Depth Information
steps may vary from case to case, depending on the ingredients
involved. Therefore, optimization is needed for different systems,
andstepscanbemodifiedinparticulartoachievetheencapsulation
e
ciency required.
In encapsulating H
2
O
2
, a series of modifications and improve-
ments on the standard technique are required. Although microen-
capsulation of water-soluble compounds is not something new and
has been commonly reported, to our best knowledge, no studies
have pursued a similar thought on molecules having a weight less
than 100 g mol
-
1
. Theoretically, the idea seems to give no signif-
icant variations in achieving the final encapsulation e
ciency as
those reported for larger compounds; however, a practical study
using H
2
O
2
reviews that the outcome was not even near to the
expectation. No significant existence of H
2
O
2
was observed from
the PLGA microspheres prepared using the conventional standard
method. The major reason is related to the high diffusion coe
-
cient of H
2
O
2
due to its small size, leading to failure of encapsu-
lation as leaching occurs seriously into the continuous phase. In
order to avoid the leaching, a thermodynamic factor was consid-
ered to create a condition where the diffusion will occur back to the
microspheresinsteadofoutorbeatleaststabilizedduringthemeta
stable stage. One of the possible approaches is via inducing a
back-
ward concentration gradient
, where H
2
O
2
is added into the continu-
ous phase and the concentration is controlled above or is the same
as the one added in the microspheres. Under such circumstances,
H
2
O
2
diffuses from the high-concentration region of the continu-
ous phase toward the low-concentration region of the microsphere
core. Effective encapsulation can be achieved after the hardening
of the microspheres (Fig. 32.2). As far as cost, safety, and handling
precautions are concerned, the volume of the continuous phase
needs to be reduced as a counterbalance of the high concentra-
tion of H
2
O
2
used. Having reduced volume, the stirring time for sol-
vent evaporation is extended for complete organic solvent removal,
while increasing the concentration of the surfactant to stabilize
emulsion droplets to avoid coalescence.
66
No obvious differences
in size and shape were observed from the batch of microspheres
prepared from the modified method compared with the standard
protocol.
Search WWH ::
Custom Search