This finding confirmed that concentration of the natural bioactive compounds and treatment time influence on antimicrobial effects. Phenolics in PE breakdown plasma membrane integrated proteins and inhibit enzymes (glycosyltransferases), leading to cell death (Mohammed, Hassanien, El, Afify, & Mohammed, 2016) depicting it as a broad spectrum antibiotic.
2.4. Characterization of electrospinning polymer blends
Viscosity and electrical conductivity of different electrospun blending solutions of CS/PEO/PE are shown in Table 1.
Chitosan alone cannot be electrospun due to strong hydrogen bond between NH2 and OH making them rigid and highly viscous (Yuan, Jenkins, DiGeorge Foushee, Jockheck-Clark, & Stahl, 2016).
As shown in the Table 1 a pure chitosan solution showed higher viscosity (731.4 ±2.2, mPas) than blend with PEO. Addition of PEO favored the electrospinning process by reducing the viscosity (Yuan et al., 2016; Safi, Morshed, Hosseini Ravandi, & Ghiaci, 2007) which is attributed to the change in inter and intramolecular interactions of chitosan chains. PEO molecules bound onto chitosan backbone disrupt the self-association of chitosan chains forming additional hydrogen bonds between its hydroxyl groups and water molecules.
However, when reducing PEO as 60/40/PE, 70/30/PE and 80/20/PE in blends, it resulted in increased viscosity as 572.1±1.3, 601.3±2.1 and 644.0±2.6 (mPas) respectively, which corroborated with report by Safi et al. (2007). Polymers with very less viscosity are not entangled, easily drop out of needle and shun formation of jets occur, while high viscosity hinders the spinning ability of polymers producing beads (Amariei et al., 2017).
In addition, electrical conductivity during electrospinning is crucial which controls the tendency to form nanofibers by increasing the elongation capacity of the blends and does not produce sprayed nanodrops. The blends devoid of conductivity cannot be electrospun (Amariei et al., 2017). The maximum electrical conductivity of blends was recorded as 4.8±0.1 mS/cm for pure chitosan since it was cationic and lowest conductivity was observed for pure PEO with 1.2 ±0.2 mS/cm followed by 50/50/00 (CS/PEO/PE) with 2.7 ±0.1 mS/cm. Electrical conductivity of blending solutions was decreased by increasing PEO ratio as reported by Saquing et al. (2013). Moreover, higher conductivity leads to more electrostatic repulsive force, which could hinder electrospinning process and inhibit the fiber formation (Lin et al., 2018a; Saquing et al., 2013).
2.5. SEM analysis of nanofiber
The morphology of fabricated nanofibers is represented in Fig.2. Pure PEO nanofiber was prepared as control and compared with fibers produced from CS/PEO/PE blends. As shown in Fig.2A, the PEO nanofibers appeared as thin and uniform thread like fibers without any beads with size distribution of 100-400nm and mean diameter as 227±16 nm (Fig.2a). However, the diameter of nanofibers was slightly increased by adding chitosan and PE (50/50 and 50/50/PE) (Fig.2B, C), with average diameters of 253±23 and 306±21 nm respectively (Fig.2b,c). The increase in fiber diameter after encapsulation of natural antimicrobial agents within electrospun fibers had been documented earlier (Lin et al., 2018b; Mendes, Gorzelanny, Halter, Schneider, & Chronakis, 2016). Average diameter was found to be increased (347±23 nm) (Fig.2D,d) for 60/40/PE blend. However, when CS was increased to 70/30/PE and 80/20/PE, uneven beaded nanofibers were obtained (Fig.2 E,F), due to increase in viscosity. This finding was in agreement with Safi et al. (2007), who obtained uniform fibers with no beads by increasing the content of synthetic polymer PVA to sodium alginate. Hence, it is studied that reduced chitosan content yielded uniform beads electrospun nanofibers with average diameter. Also FDA approved surfactants could be used for creating smooth nanofibers. Pluronic F-127, is one such choice due to its non-toxic nature unlike Triton-X 100 (Bonino et al., 2011). As shown in SEM images, Fig.2G,H, addition of Pluronic F-127 (1 v%) effectively reduced the beads in the nanofibers from blends of 70/30/PE and 80/20/PE (CS/PEO/PE) with average diameter of 370±26 nm (Fig.2g) and 406±15 nm respectively (Fig.2h). Uniform and unbeaded nanofibers were due to decrease in viscosity and surface tension after adding Pluronic F-127 (Bonino et al., 2011).