Biomedical Engineering Reference
In-Depth Information
In such a system, the decomposition of H
2
O
2
only occurs once
it is released from the PLGA segment and enters the alginate layer.
The decomposition rate depends on the controlled release rate of
theH
2
O
2
fromthePLGAandtheconcentrationofcatalasegraftedon
thealginate.TheuseoftwolayersavoidsseriouslossesofH
2
O
2
dur-
ing the ORM production as H
2
O
2
does not have direct contact with
catalase.
32.3.3
Techniques for Producing ORMs
32.3.3.1 Double-emulsion and solvent evaporation technique
The solvent evaporation method has been used extensively to pro-
duce microspheres encapsulated with various compounds such as
drugs,
60
-
62
peptides,
63
andbioreagents.
64
,
65
PLGAisoneofthemost
frequently used materials in this technique. Microencapsulation by
thesolventevaporationtechniquecanbedoneviavariousprotocols,
and the selection for the best option readily depends on the prop-
erty of the compounds used.
11
Therefore, this technique is also a
suitable alternative in producing ORMs to encapsulate the oxygen-
releasing source into a polymeric matrix with a micrometer-ranged
capsule. As the oxygen sources often consist of water-soluble com-
pounds, the double-emulsion-type option made up of a few major
steps can be employed.
9
-
11
First is the dispersion of the oxygen-
generatingsourceintoanorganicsolventthatisapredissolvedpoly-
meric matrix. The state of the art falls on the unique interphase
formation between immiscible aqueous and organic layers, turn-
ing the aqueous phase into fine emulsion droplets. This emulsion
mixture is then dispersed into an aqueous solution forming a sec-
ondary emulsion, which is commonly known as a water-oil-water
(W
1
/O/W
2
) double emulsion. Under such a process, the first aque-
ous droplets will be entrapped in the core of the polymer, while
physically the polymer is shaped into small, fine spheres due to the
secondarydispersion.Themicrospheresareusuallystabilizedusing
a suitable surfactant. The organic solvent will be extracted from the
dispersed phase by a continuous phase, transforming the droplets
into solid microspheres that are free from the toxic organic solvent.
Finally is the harvesting and drying of the microspheres from the
continuous phase. In real practice, all these process-engineering
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