Page 300 - Biodegradable Polyesters

278 11 Electrospun Biopolymer Nanofibers and Their Composites for Drug Delivery Applications

a result of pH-dependent solubility of CAP, the addition of small amounts of
human semen (pH between 7.4 and 8.4) immediately dissolves the fibers, thus
resulting in the release of encapsulated antiviral drugs, together with CAP which
has been reported to have intrinsic antimicrobial activity, to efficiently neutralize
HIV in vitro [18].
As FDA-approved biodegradable polymers, alicyclic polymers such as PCL,
PLA, and poly(lactic-co-glycolic acid) (PLGA), have gained increasing attention
for their excellent biocompatibility and mechanical properties [19, 20]. The
release profiles of drugs with different hydrophilic properties from electrospun
poly(L-lactic acid) (PLLA) fibers have already been reported in early studies. The
influence of surfactants on the diameter size and uniformity of PLLA fibers were
carefully studied by adding various surfactants (cationic, anionic, and nonionic)
into PLLA solution, with which significant diameter reduction and uniformity
improvement have been observed [21]. The same research group further studied
the influence of solubility and compatibility of drugs in the drug/polymer/solvent
system on encapsulation of drug inside electrospun PLLA fibers. Burst release
of drugs was avoided by using compatible drugs with polymers, which followed
nearly zero-order kinetics due to the degradation of PLLA fibers in the presence
of proteinase K [12]. Similarly, Kim et al. realized the successful incorporation and
sustained release of a hydrophilic antibiotic drug (MefoxinR, cefoxitin sodium)
from electrospun PLGA-based nanofibrous scaffolds without loss of structure
and bioactivity. The morphology and density of the electrospun scaffold were
found to be dependent on the drug concentration, which could be attributed
to the effect of ionic salt on the electrospinning process [22]. Chew et al. [23]
examined the release of b-nerve growth factor (NGF) stabilized in bovine serum
albumin (BSA) from a copolymer consisting of ε-caprolactone and ethyl ethylene
phosphate (PCLEEP). Owing to its relatively hydrophobic backbone, PCLEEP
exhibited a slow degradation rate with a mass loss of approximately 7% over a
3-month period. Thus, they inferred that NGF release was primarily occurring
via diffusion, demonstrating that a biodegradable system can be used to obtain a
desirable release profile while still eliminating the need for a second surgery for
implant removal.
Fabrication of drug-loaded ultrafine natural biopolymer or polyester fibers
usually involves the use of organic solvents, which is difficult to be completely
removed and may bring about toxicity issues. Therefore, much attention has
been focused on biomedical applications of poly(vinyl alcohol) (PVA) hydrogel
including contact lenses, artificial organs, and drug delivery systems because of
its biocompatibility and nontoxicity [24, 25]. Aspirin- and BSA-embedded water-
soluble PVA nanofibers were produced by aqueous solution electrospinning [26].
Li et al. even developed fast-dissolving drug delivery systems by electrospinning
using PVA as the filament-forming polymer and drug carrier, with caffeine and
riboflavin as the model drugs. Pharmacotechnical tests showed that PVA/caffeine
and PVA/riboflavin nanofibrous membranes had almost the same dissolution
time (about 1.5 s) and wetting time (about 4.5 s). The release measurements
indicated that drugs can be released in a burst manner (caffeine to an extent