*3.7. Antibacterial Activity*

Due to the significant toxicity and minimal cell proliferation, the sample with 7% TiO2 was eliminated as a candidate from further studies. Amongst the remaining samples, annealed sample with no coating was taken as the control. The electrospun PCL fiber mat shows a relative increase in the bacterial count compared to the control (Figure 7). This is attributed to the fibrous nature of the interface which provides ample opportunities for cellular attachment. This attachment promoting behaviour is also seen in previous studies where the increased surface area contributes to the increase in hFOB proliferation and attachment to electrospun PCL mat and PCL mat containing 2% TiO2. This factor proves to be advantageous for bone growth and repair as observed from the study with mammalian cells. However, it may also cause problems due to increased adhesion of bacterial cells. So, it is advisable to use an antimicrobial agent blended with PCL to retard and offset the bacterial growth. TiO2 has proven to be such an agent. The antimicrobial properties of TiO2 are well known.

**Figure 7.** Antibacterial activity on different substrates against *S.aureus*.

As presented in Figure 8, several fundamental mechanisms for cell killing and bacterial growth inhibition by the TiO2 photocatalytic processes were presented in the literature [45,46]. As a result the blend of PCL and 2% TiO2 was initially tested against *S.aureus*. However, there is no significant difference between the PCL fiber mat and the PCL fibers containing 2% TiO2. This implies that this concentration of TiO2 is not enough to bring about a photocatalytic effect that reduces the bacterial count. On increasing the TiO2 concentration to 5%, significant reduction is seen in the bacterial colony count compared to plain annealed sample (control). Thus 5% TiO2 also seems to be the minimal

concentration necessary to be incorporated with PCL to achieve antibacterial activity. It also appears to be the optimal concentration of TiO2 necessary for to give an antibacterial action without significant toxicity. This nanocomposite thus proves to be an efficient approach to achieving bioactivity and improving integration of the titanium implants.

**Figure 8.** Schematic illustration for the mechanism of degradation bacteria by TiO2 nanoparticles under UV radiation and cellular activity of PCL/TiO2 nanocomposites.
