*3.1. Surface Characterization*

SEM images of unmodified cpTi without any surface coating (Figure 1a) and PCL/TiO2 nanocomposites with and without TiO2 particulate additions were presented in Figure 1b–e respectively. Due to an exact balance between the solution viscosity and electrical conductivity, continuous uniformity of the fibrous structures without any beads were observed in all the samples. Figure 1b shows the pure PCL nanofibers (0 wt % TiO2) in uniform diameter with a smooth surface with an average diameter of 540 ± 40 nm. But, the morphology of the fibers was adversely affected by the addition of TiO2 nanoparticles. 8 wt % of PCL was used as the constant polymeric solution for electrospinning and a gradual growth in fiber diameter was observed when TiO2 content increased from 2 wt % (Figure 1c) to 5 wt % (Figure 1d) and to 7 wt % (Figure 1e). With the increase of TiO2 particle concentration, the size of nanofibers tends to become more significant and visible agglomeration to some extent were observed inside the fibers. For example, the average fiber diameter increases from 640 ± 60 nm to 710 ± 20 nm and 900 ± 89 nm for as-spun PCL/2TiO2, PCL/5TiO2 and PCL/7TiO2 composite nanofibers respectively. The results were in agreement with another study where the addition of nanoparticles increased the diameter of fiber [33].

**Figure 1.** SEM Images displaying (**a**) cpTi substrate; PCL mat containing (**b**) 0 wt % TiO2, (**c**) 3 wt % TiO2, (**d**) 5 wt % TiO2, and (**e**) 7 wt % TiO2.

Also, based on the SEM analysis of Figure 1c,d, the results also indicate that TiO2 nanoparticles are directly embedded inside the PCL nanofiber matrix rather than exposed on top of the fibers. The concentration of 7 wt % of ceramic TiO2 (Figure 1e) causes some of the nanoparticles surfaced on the as-spun nanofiber mats, indicating inhomogeneous mixing of the particles. In view of this, no further experiments above 7 wt % TiO2 have been conducted as it gives the notion that "*outer*" particles on fibers would be leached away easily as no chemical interaction with the PCL nanofibrous mat is made. Due to this, there may also be a negative effect on the mechanical properties (tensile strength and Young's modulus) of the composite. Also, the morphologies of fibers became more irregular when the increasing of TiO2 content which it might because of the influence of ceramic particles on the solution viscosity, surface tension, and concentration. So, optimization of nanoparticle concentration in connection to the mechanical properties of the nanocomposite is sometimes essential.
