Page 222 - Biodegradable Polyesters

200 8 Systematic Development of Electrospun PLA/PCL Fiber Hybrid Mats

1600 1000
Fibre diameter of PLA/15% HMW PCL
1400 Fibre diameter of PLA/15% LMW PCL 900
Solution viscosity of PLA/15% HMW PCL
Solution viscosity of PLA/15% LMW PCL 800
1200 700
Solution viscosity (cP) 800 600 Fibra diameter (nm)
1000

500
400
600

400 300
200
200
100
0 0
(1/0) (3/1) (1/1) (1/3) (0/1)
PLA/PCL blend ratio
Figure 8.4 Solution viscosity and resulting fiber diameters of PLA/15% HMW PCL and
PLA/15% LMW PCL solutions dissolved in DCM/DMF with different blend ratios.

8.3.3
Effect of Solvents

The appropriate selection of solvents is one of important steps to fabricate
electrospun polymer fibers incorporated with drugs for effective release [68,
69]. Pristine PLA microfibers have an average diameter of 510 ± 15 nm using
chloroform/methanol and 570 ± 15 nm with chloroform/acetone (Figure 8.5).
Increasing the amount of LMW PCL to PLA with a blend ratio of 1/3 generates
disordered fiber-bead structures with average nanofiber diameters of 325 ± 25 nm
and 375 ± 30 nm accordingly. When further increasing blend ratio up to 1/1,
nonfibrous structures occur, as indicated in Figures 8.6c,f.
Increasing the amount of LMW PCL considerably reduced the solution viscos-
ity (Figure 8.5). However, the viscosity values are quite close irrespective of the
solvent systems used in either chloroform/methanol or chloroform/acetone. The
fibers manufactured from DCM/DMF have smaller fiber diameters with better
fiber uniformity as opposed to those achieved from chloroform/methanol and
chloroform/acetone (Figure 8.5). In fact, the electrical conductivity of DCM/DMF
in terms of dielectric constants is higher than that of chloroform/methanol, which
is in turn higher than chloroform/acetone (Table 8.1). As a consequence, higher
conductivity can facilitate a greater charge density on the surface of the electro-
spinning jet [70], resulting in the fabrication of smaller fibers.