# Optimizing CNT Loading in Antimicrobial Composites for Urinary Tract Application
## 3 Results and Discussion
### CNT/PDMS Characterization  
The characterization of CNT/PDMS composites was initially performed through contact angle measurements and the calculation of the respective \(\Delta G_{ini}\) (Table 2). This last parameter is an indicator of the hydrophobicity of the sample, as previously explained (Section 2.3.2). From the final results, it is possible to observe that all the tested surfaces were hydrophobic, contrarily to _E. coli_ CECT 434 GFP that demonstrated a hydrophilic character, similarly to previous studies with the same bacterial species [42]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **S\({}_{\mathrm{BET}}\) (m\({}^{2}\) g\({}^{-1}\))** & **V\({}_{\mathrm{p}}\)** **p/p0 = 0.99 (cm\({}^{3}\) g\({}^{-1}\))** \\ \hline CNT-O & 197 & 1.917 \\ CNT-BM 1 h & 215 & 1.119 \\ CNT-BM 2 h & 219 & 0.825 \\ CNT-BM 3 h & 226 & 0.799 \\ CNT-BM 4 h & 227 & 0.661 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Textural properties of pristine and modified CNTs. Looking a little closer, it is not possible to observe a linear trend in the evolution of hydrophobicity either with the incorporation of increasing CNT-O concentrations or with the use of ball-milled composites. Although only slight differences were obtained concerning the hydrophobicity of PDMS, it is interesting to note the lower hydrophobic character of 3 wt% CNT-O/PDMS and 3 wt% CNT-BM 4 h/PDMS surfaces. These surfaces presented, together with 3 wt% CNT-BM 1 h/PDMS and 5 wt% CNT-O/PDMS, lower values for the contact angle with water (with significant differences comparatively with PDMS and 1 wt% CNT-O/PDMS, \(p<0.01\)). As the free energy of adhesion (Table 3) is higher than 0 mJ m\({}^{-2}\), from a thermodynamic point of view, _E. coli_ adhesion to PDMS and CNT/PDMS surfaces was not expected to occur. Following the same line of interpretation, it is also possible to state that 3 wt% CNT-O/PDMS, 3 wt% CNT-BM 4 h/PDMS and 5 wt% CNT-O/PDMS surfaces are less prone to microbial adhesion from a purely thermodynamic standpoint. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Contact Angle (\({}^{\circ}\))**} & \multicolumn{2}{c}{**Hydrophobicity (m) m\({}^{-2}\))**} \\ \cline{2-5}  & \(\theta_{w}\) & \(\theta_{F}\) & \(\theta_{B}\) & \(\Delta G_{irui}\) \\ \hline \multicolumn{5}{c}{_Surface_} \\ \multicolumn{5}{c}{PDMS} \\ \multicolumn{5}{c}{PDMS} \\ \multicolumn{5}{c}{0.1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{2 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{3 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{3 wt\% CNT-BM 1 h/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-BM 2 h/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-BM 3 h/PDMS} \\ \multicolumn{5}{c}{3 wt\% CNT-BM 4 h/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{1 wt\% CNT-O/PDMS} \\ \multicolumn{5}{c}{_Bacteria_} \\ \multicolumn{5}{c}{_E. coli_ CECT 434 GFP} \\ \multicolumn{5}{c}{19.4 \(\pm\) 5.0} \\ \multicolumn{5}{c}{78.1 \(\pm\) 5.5} \\ \multicolumn{5}{c}{62.2 \(\pm\) 4.9} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Contact angles with water (\(\theta_{w}\)), formamide (\(\theta_{F}\)) and \(\alpha\)-bromonaphthalene (\(\theta_{B}\)), and free energy of interaction (\(\Delta G_{irui}\)) between two entities of a given material (_i_) (surface or bacteria) when immersed in water (\(w\)). Values are means \(\pm\) standard deviations (SDs) of three independent experiments. Figure 2: Pore size distributions obtained by Non-Linear Density Function Theory. Surface characterization of selected CNT-filled composites was complemented by SEM analysis (Figure 3).