Catalytic Synthesis and Characterization of Biodegradable ...

Chapter 1
The introduction of polyelectrolytes led to the materials being hydrophilic enough to swell
in water, which allows the easy diffusion of entrapped protein. When the PPy was reduced by
negative potential, the anions were quickly expulsed in less than one minute. The in vitro test
demonstrated that the released NGF still retained activity. Generally the polymeric carriers
will affect the entrapped protein’s folding and activity due to the strong hydrophobic nature
of the polymer. However, this approach employed polyelectrolytes to increase the
hydrophilicity of the materials, which had solved this problem in some extent.
In another investigation, authors incorporated streptavidin into the PPy films doped with
both biotin and dodecylbenzenesulfonate. Then the biotinylated NGF was immobilized to this
film. When the film was electrically stimulated, NGF was exclusively released. The activity
of the released protein was also confirmed in vitro. This method can be expanded to most of
drugs that could be delivered through biotin-streptavidin strategy.
Hydrogels have been studied for a long time as drug carrier. The release behaviors of
“smart” hydrogels can be controlled by many stimuli, including pH, temperature,
biomacromolecues and electrical stimulation. For example, PVA hydrogels were covalently
immobilized onto aldehyde groups modified PPy films (Figure. 1.5.16). The heparin was
loaded into the hydrogels and could be released through the diffusion without electrically
stimulation. 165 When PPy was electrically stimulated, the release of heparin from the
hydrogel was accelerated. Many factors were considered by the authors that could affect the
results, such as changes in temperature, electrophoresis, changes in pH as a result of
electrolysis, and the polyanionic nature of heparin.
Besides the film, electroactive polymers can be fabricated into other shapes for drug
delivery. For example, PEDOT nanotubes were synthesized on the electrospun PLGA fibers
(~100 nm diameter) template (Figure. 1.5.17). 164 Then the PLGA loaded with dexamethasone
was removed to produce PEDOT nanotubes encapsulating small molecules. The drug release
of PEDOT nanotubes drug delivery system can be controlled by the electrical stimulation,
probably as a consequence of expansion/reduction of polymer cavities induced by the
expulsion of anions.
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