Biomedical Engineering Reference
In-Depth Information
the case. Rather, a lower pH shows greater decomposition, as evi-
denced from a scanning electron microscopy (SEM) micrograph. A
possible reason may be related to the presence of PVA in the con-
tinuous phase that undergoes de-protonation at high pH, leaving
the negatively charged terminal to form cheating complexes with
impurities. This avoids the decomposition of H
2
O
2
by these impu-
rities, which act as a catalyst. Oppositely, protonation of PVA occurs
at a lower pH and subsequently causes the dissociation of possible
present complexes of impurities. As this occurs, the impurities may
diffusethroughthepolymerlayeranddecomposetheH
2
O
2
,forming
a gas that will increase the porosity of the PLGA matrix. This indi-
cateslessH
2
O
2
ispresentinthefinalmicrospheresharvesteddueto
decomposition, which isnotpreferable.
The freeze-drying process is normally performed in many
microencapsulation works of drugs to remove excess water content
via low temperature and pressure. It is also been reported by Kim
and Park
56
as having a critical effect towards the sustained release
ofdrugs.Thefreezingprocesscancausemicrocracksonthepolymer
matrix, while the removal of water produces microchannels, both of
whichfavordrugrelease.However,inthisstudy,H
2
O
2
waschosenas
theencapsulationmolecule,whichhasalmostsimilarphysicalprop-
erties as water. Under such circumstances, H
2
O
2
will be removed
along with water molecules during the drying process. In the same
study by Kim and Park,
56
the freeze-drying process has reported to
remove almost 98% of the water content. Thus, it is not surprising
that PLGA microspheres show no evidence of the existence of H
2
O
2
afterbeingfreeze-driedforsixhours.Realizingthisfactor,theprepa-
ration process of consecutive batches of microspheres has skipped
the freeze-drying process, but they have instead just been dried
overnight under flowing air on a clean bench. The freezing process
was found to cause no significant effect towards the encapsulation
e
ciency of H
2
O
2
.
32.3.3.2 Functionalization of matrices selected as
building blocks
In tissue engineering, regenerative medicine, and other biomed-
ical fields, the modification of potential crude biomaterials is often
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