Biomedical Engineering Reference
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cross-linking agent between amine-amine groups.
71
,
72
However, in
this study, the covalent immobilization was performed using the
well-established carbodiimide chemistry. In this approach, carbodi-
imide is used to activate carboxylic from a matrix and the activated
terminalwillformacovalentbondinthepresenceofanaminegroup
from the catalase. N-hydroxysuccinimide is added to stabilize the
activated species for better covalent bond formation. Alginate will
beagoodcandidatefortheimmobilizationasthebackbonecontains
a carboxylic group for the grafting to take place. After the immobi-
lization, the alginate solution was formed into a hydrogel using cal-
cium(II)ions,andPLGAmicrosphereswereincorporatedwithinthe
alginate. Observation shows that the catalase retains its activity in
decomposing H
2
O
2
after immobilization and also after being trans-
formed into the hydrogel format, although the decomposition rate
was slightly slowercompared with the free catalase.
32.3.3.3 Instrumentations for the preparation of microspheres
The involvement of some simple instrumentation for the produc-
tion of ORMs can ensure the batches obtained in a more standard
fashion and repeatable manner. Besides reducing the deviation in
the microspheres' physical properties, the involvement of instru-
mentation also opens a possible step in mass production and com-
mercialization. In the first stage of H
2
O
2
encapsulation, involve-
ment of instrumentations is not required as the double-emulsion
andsolventevaporationmethodissimpleandreproducibleandcan
be scaled up easily for mass production. However, there are other
options of microsphere production that involve instrumentations,
such as thespray-drying technique.
73
In the study of producing ORMs, the later stage of alginate bead
productionhavingPLGAmicrospheresimbeddedcanemployinstru-
mentationtoobtainbetterandstandardbeads.Forinstance,theuse
of a syringe injected by hand produces uneven-sized alginate beads
ranging from 2 to 6 mm. When a microinjector was attached to the
syringe for a fixed injection rate, beads having an evenly distrib-
uted size of around 2 mm were obtained. In an effort of reducing
the size into the micrometer range, further improvement was made
by applying high voltage on the needle head having the setup as
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