# Functionalization Strategies and Fabrication of Solvent-Cast PLLA for Bioresorbable Stents
## 3 Results and Discussion
### Surface Characterization
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Elemental Composition (Atomic \%)**} & \multicolumn{3}{c}{**Relative Chemical Carbon**} & **Bonds (\%)** \\ \cline{2-7}  & **O 1s** & **C 1s** & **N 1s** & **Na 1s** & **O/C** & **284.7 eV** & **286.6 eV** & **288.8 eV** \\  & & & & & & **C-C, C-H** & **C-O** & **O=C-O** \\ \hline TT & 37.7 \(\pm\) 0.5 & 62.3 \(\pm\) 0.5 & 0.0 \(\pm\) 0.0 & 0.0 \(\pm\) 0.0 & 0.61 & 42.1 \(\pm\) 0.9 & 28.7 \(\pm\) 0.7 & 29.2 \(\pm\) 0.6 \\ OP & 42.3 \(\pm\) 0.3 & 56.8 \(\pm\) 0.4 & 0.8 \(\pm\) 0.1 & 0.0 \(\pm\) 0.0 & 0.75 & 30.4 \(\pm\) 0.2 & 32.8 \(\pm\) 0.1 & 36.9 \(\pm\) 0.1 \\ SH & 39.0 \(\pm\) 0.3 & 60.9 \(\pm\) 0.2 & 0.0 \(\pm\) 0.0 & 0.2 \(\pm\) 0.0 & 0.64 & 34.6 \(\pm\) 0.9 & 34.7 \(\pm\) 1.4 & 30.7 \(\pm\) 1.0 \\ ET & 49.0 \(\pm\) 0.2 & 50.4 \(\pm\) 0.2 & 0.5 \(\pm\) 0.1 & 0.0 \(\pm\) 0.0 & 0.97 & 31.1 \(\pm\) 0.4 & 32.4 \(\pm\) 0.6 & 36.6 \(\pm\) 0.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Analysis of the atomic composition percentage at the TT, OP, SH, and ET surfaces by XPS. The elemental composition of O 1s, C 1s, N 1s, Na 1s, and the ratio between O/C were obtained from the XPS survey spectra. Values of the relative chemical carbon bonds were obtained from the deconvolution of C 1s peaks. **TT**: Thermally treated films; **OP**: Oxygen plasma TT films; **SH**: Sodium hydroxide etched TT films; **ET**: Enzyme treated TT films. Figure 2: Surface properties of the solvent-cast PLLA films submitted to different treatments: (**a**) Roughness Ra (arithmetic roughness average) calculated from white light interferometry (WLI) images; (**b**) water contact angle on the different PLLA films. Columns marked with different letters belong to statistically different groups (_p_-value < 0.05). **SC**: Solvent casting PLLA films; **TT**: Thermally treated SC films; **OP**: Oxygen plasma TT films; **SH**: Sodium hydroxide etched TT films; **ET**: Enzyme treated TT films. on these surfaces than on the alkaline surface (\(30.7\pm 1.0\%\)). When hydrolyzing an ester bond, a single-COOH and a single -OH group are created [59]. As the NaOH solution and enzyme act on PLLA only by ester bond hydrolysis, on the SH and ET surfaces the increase of hydroxyl groups is proportional to the increase of the carboxyl groups. The plasma treatment does not act only by hydrolysis; there is also a grafting of new functional groups in the surface with the oxygen-excited species present in the plasma. The fact that the O/C ratio was inferior on OP compared to ET and that OP and ET presented a similar percentage of carboxyl groups suggested that OP had fewer hydroxyl groups than ET. The higher density of functional groups on OP and ET compared to the SH samples is coherent with the higher decrease of wettability observed after the plasma or enzyme hydrolysis compared to the alkaline hydrolysis, suggesting that the plasma and enzyme hydrolysis presented the best efficiency to create functional groups to the subsequently biofunctionalized surface or to improve the implant biological response.