Page 214 - Biodegradable Polyesters

192 8 Systematic Development of Electrospun PLA/PCL Fiber Hybrid Mats

field to produce the electrostatic repulsive force for overcoming the surface
tension of solution droplets from the spinneret, thus further elongating the
droplets into fibrous structures [25]. Besides, the mixed solvents in the solution
either act as the enhancer of electrical conductivity or the polymer-dissolving
agent, which gradually evaporate in the jet flow during the electrospinning
process to produce nonwoven fibrous mats [26, 27].
Poly(lactic acid) (PLA) is a biodegradable polymer manufactured from sustain-
able substances [28, 29] such as starch, sugarcanes, wheat, and sugar beets [30].
It is a biodegradable polyester, originating from α-hydroxy acids with acceptable
mechanical properties and numerous potential usages [31, 32]. PLA is extensively
utilized for medical purposes because of its biocompatibility and easy degradation
to form nontoxic monomers. It undergoes the separation to monomeric units of
lactic acid in the body, which certainly appear in the carbohydrate metabolism
[33, 34]. Nevertheless, using PLA in this way is not helpful because it creates
an elementary drug burst release at the beginning of curing [34], apart from
possessed fragility and relaxed crystallization [30, 35]. Moreover, the degradation
of PLA is harmful to local body tissues [36] owing to its low pH value [37]. On
the other hand, poly(ε-caprolactone) (PCL) polymer is typically employed for
promoting elasticity [38] owing to its hydrophobic and semicrystalline charac-
teristics [39]. PCL is well recognized as having satisfactory drug permeability
and good biocompatibility [40], whose degradation does not generate local acidic
environment. Moreover, PCL is a slowly degraded biopolymer relative to PLA in
view of its semicrystalline nature [40]. When accompanied by simultaneous drug
release, PCL chains break up to low-molecular-weight nontoxic components for
consumption with little damage to local body tissues [41]. However, the drawback
of PCL in biomedical applications lies in the limited functional usage [42, 43],
arising from its hydrophobicity and semicrystalline behavior. In particular, the
imperfect mechanical properties and poor porosity of PCL hinder its potentials
to be used in tissue engineering and drug delivery system, respectively. The
tailored properties of electrospun nanofiber mats such as swelling, hydropho-
bicity, and mechanical strength [44], to a greater extent, rely on the control of
material compositions in solutions. Polymer blending appears to be an effective
processing approach to improve or modify the physicochemical properties of
polymers [45]. Consequently, several polymer blends can be formed with unique
properties, making them considerably diverse from individual polymers. In the
electrospinning process, the processing parameter and solution characteristics
are key aspects to influence the morphology and properties of fiber mats [46, 47].
Solution parameters such as solution concentration, solution viscosity, solution
surface tension [48, 49], and polymer molecular weight normally can affect
polymeric chain entanglements [50]. Furthermore, solvent properties such as
dielectric properties, solubility, boiling point, and solvent volatility also take an
important part in the electrospinning technique. The examination for the effects
of parameters on electrospun fiber mats are quite challenging owing to their
interactions [51].