Biomedical Engineering Reference
In-Depth Information
minimize the expel force during the meta stable stage. The latter
effort on methodology alteration will be discussed in the next sec-
tion.
The addition of an extra ingredient having an intermediate
property from these extremes is a possible approach to increase
the physical compatibility between ingredients. For instance, in
the study carried out, the addition of polyvinyl alcohol (PVA)
has found to increase the encapsulation e
ciency of H
2
O
2
in
PLGA microspheres. PVA acts as a surfactant that stabilizes H
2
O
2
emulsion within the organic PLGA phase, creating a hydrophilic
microenvironment within the hydrophobic polymer phase dur-
ing the meta stable stage. Thus this reduces the expel force and
promotes effective encapsulation. However, in this case, further
increment in the hydrophilicity of PLGA by blending in methoxy
polyethylene glycol (m-PEG) shows no significant improvement
on the encapsulation e
ciency, although such an approach is
being reported suitable for the encapsulation of several other
compounds.
54
,
55
PEG is the hydrophilic segment widely used to
change the physicochemical properties of PLGA in achieving bet-
ter encapsulation for these highly hydrophilic compounds.
56
,
57
The failure may be due to the small size of H
2
O
2
that can
diffuse out quickly from a more hydrophilic shell consisting of the
blended matrices during the meta stable stage. The observation has
demonstrated the importance of first understanding the nature of
the ingredients chosen and the whole working mechanism involved
beforetryingtotuneitsphysicalcompatibilitytotheoptimumusing
a secondary addictive.
The design of an elegant ORM sometimes requires the combina-
tion of various working mechanisms that operate in a chronologi-
cal manner. Each working step is interrelated, and the sequence of
the processes must be followed, such as the rate of release for the
oxygen source matches the decomposition rate and the flow of the
source is from the reservoir to the activation region, not the oppo-
site direction. It is also important for the source to stay stable at the
reservoir and only get decomposed when required. Under consid-
erations based on the differences in role and activation time, inte-
gration of these functionalities within one same segment of matrix
withouttheminteractingbeforerequired isoftendi
cult.Thus,the
option of using a combination of different matrices each having the
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