Page 308 - Biodegradable Polyesters

286 11 Electrospun Biopolymer Nanofibers and Their Composites for Drug Delivery Applications

drug in pH = 7 simulated gastric fluid, indicating that the nonmetallic concentric
spinneret could be exploited to conduct coaxial electrospinning and facilitate the
smooth and continuous preparation of electrospun core–sheath nanofibers for
providing biphasic drug release profiles [65].

11.3.2
Emulsion Electrospun Drug/Biopolymer Nanofibers

While coaxial electrospinning predominately relies on the complexity in designing
and controlling of the electrohydrodynamic process for production of biodegrad-
able core–shell structures, an alternative process based on the emulsion electro-
spinning technique can produce distinct kind of scaffold in order to promote a
better control of release kinetics. In emulsion electrospinning, the drug or aque-
ous protein solution is emulsified within a polymer solution referred to as the oil
phase, which can be produced into nanofibers containing uniformly distributed
low-molecular-weight drugs or with core–shell fibrous structures [66–68].
RHB and BSA were successfully incorporated into nanofibers by means of
emulsion electrospinning to form composite nanofibrous mats [69]. In vitro dual
drug release behaviors indicated that the incorporated drug and/or proteins in
composite fibrous mats made from electrospinning could be controllably released
by adjusting the processes of emulsion preparation. Xu et al. investigated the
release behavior of a water-soluble anticancer agent, DOX, from the drug-loaded
nanofibers prepared by emulsion electrospinning [70]. The laser scanning
confocal microscopic images indicated that the drug was well incorporated into
amphiphilic PEG–PLLA diblock copolymer nanofibers, forming core–sheath
structured drug-loaded nanofibers. The drug release behavior showed a three-
stage diffusion-controlled mechanism, in which the release rate of the first stage
was slower than that of the second stage, but both obeyed Fick’s second law. On
the basis of these results, it is concluded that DOX-loaded fibers prepared by
emulsion electrospinning represent a reservoir-type delivery system in which
DOX release rate decreases with increasing DOX content in the fibers.
In drug therapy, most therapeutic drugs are of low molecular weight and could
freely diffuse in biological environment depending on the applied administration
route. The main reason for the development of polymeric drug carriers is to
obtain desired effects such as sustained therapy, local and controlled release,
prolonged activity, and reduction of side effects. Alternatively, polymeric carriers
can be made biodegradable in order to be eliminated by natural ways after a
certain time of therapy. Core–shell fibers from coaxial spinneret or emulsion
electrospinning are good candidates for the development of such devices.
However, difficulties remain especially in controlling the release over a sustained
period.
A novel technique combining coaxial and emulsion electrospinning was pre-
sented to produce microstructured core–shell fibers. The design of micro drug
reservoirs of variable size within the bulk of fibers combined with a tailored dif-
fusive barrier allows modulating the release kinetics of these novel carriers. A