Biomedical Engineering Reference
In-Depth Information
In another study, Min et al. reported the infl uence of solvent system on the fi ber
diameter of electrospun PLGA nanofi bers. Electrospinning of PLGA in polar
HFP led to a smaller average fi ber diameter (310 nm) as compared to fi bers pro-
duced in the same concentration of a non-polar chloroform (760 nm) [161].
Similar results were reported by You et al. while studying the role of solvent
polarity in infl uencing fi ber diameter of PLGA, PLA and PGA [163]. They dem-
onstrated that electrospun PLGA fi bers using less polar chloroform as a solvent
system had a average fi ber diameter of 760 nm, whereas PGA and PLA fi bers
electrospun using polar HFP had average fi ber diameter of 310 nm and 290 nm,
respectively. In another study, Bashur et al. studied the infl uence of polymer
solution concentration on the diameter of electrospun PLGA fi bers [163] . They
demonstrated an increase in fi ber diameter with increase in polymer solu-
tion concentration with least average fi ber diameter of 140 nm at 5% polymer
concentration.
The degradation products of PLGA are LA and GA. The acidic end products
decrease the pH of the microenvironment and this can adversely affect growth
factor delivery in tissue engineering due to acid catalyzed degradation of the
encapsulated/released protein [164]. Thus, there is a need to blend PLGA with
other polymers to enable the use of PLGA nanofi bers as protein delivery vehicles
in tissue engineering applications.
13.4.2.2 Polycaprolactone (PCL).
PCL is a semicrystalline polymer that is
synthesized by ring-opening polymerization of its monomer
- caprolactone [165] .
Apart from possessing excellent biocompatibility, it is a slow-degrading polymer
with high mechanical strength and has been widely explored in the area of tissue
engineering [166]. Lee et al. reported the synthesis of PCL nanofi bers and studied
the infl uence of solvent system on the morphology and diameter of electrospun
PCL nanofi bers [81]. The solvent systems studied were: methylene chloride
(DCM), mixture of DCM and N, N-DMF, mixture of DCM and toluene. It was
observed that with an increase in the content of DMF in the solvent system,
surface tension and viscosity decreased while conductivity and dielectric constant
increased, thereby leading to a decrease in the fi ber diameter. Another group
reported the synthesis of electrospun PCL nanofi bers in DCM/methanol (7 : 3)
solvent system [167]. Methanol was primarily used to increase the conductivity of
the solution, which was further increased by addition of heparin to the spinning
solution. The average fi ber diameter decreased from 360 nm (without heparin) to
260 nm (with heparin).
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13.4.2.3 Polyurethanes (PU).
Polyurethanes form a class of elastomeric
polymers that have been explored for the synthesis of long-term implants with
stable mechanical properties [168]. They have found applications in cardiac pace
makers and vascular grafts since they possess excellent biocompatibility [168,169].
Electrospun PU nanofi bers have been demonstrated to have potential for wound-
dressing based applications. Khil et al. studied mixture of THF and DMF as the
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