# Functionalization Strategies and Fabrication of Solvent-Cast PLLA for Bioresorbable Stents
## 3 Results and Discussion
### Degradation of PLLA Films  
BRS stents are expected to maintain their radial strength at least during the 6 months post-implantation, the stent material should degrade without losing mechanical properties during this period of time [60; 61]. The high M\({}_{\rm w}\) PLLA are expected to have a slow degradation rate compared to the low M\({}_{\rm w}\) polyester [62]. An accelerated degradation assay was conducted in conditions similar to the previous works [28; 44; 45; 63]. The films were immersed in a 0.1 M NaOH solution during 10 days in order to evaluate the effect of solvent-casting, thermal, and activation treatments on the degradation of high M\({}_{\rm w}\) PLLA by measuring the percentage of mass loss (Figure 4). Moreover, SEM images of the surface and  
Figure 3: High-resolution spectra of C 1s obtained by XPS for: (**a**) TT; (**b**) OP; (**c**) SH; and (**d**) ET surfaces. Dashed lines represent the fitting components and the solid line represents the sum of these components. **TT**: Thermally treated films; **OP**: Oxygen plasma TT films; **SH**: Sodium hydroxide etched TT films; **ET**: Enzyme treated TT films. roughness measurement by WLI of the studied surfaces before and after the degradation assay are shown in Figure 5.  
As expected, all the samples presented a quasi-linear decrease in the percentage of mass loss with time. This behavior, was already described by [PERSON] et al. [44] in an alkaline solution and is completely different from the sigmoidal degradation pattern observed for PLLA in saline and buffered solutions or in body conditions related to [PERSON] et al. [61]. SC films clearly presented statistically significant faster degradation rates compared to the other surfaces. For example, the SC mass loss after 10 days was higher than 45%, whereas, all the other films had a mass loss lower than 30%. According to the literature [44], as  
Figure 4: Percentage of mass loss evolution during the alkaline accelerated degradation assay on the REMEDY stent and all solvent-cast PLLA films. The assay was done in a 0.1 M NaOH solution during 10 days. **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. Figure 5: SEM images and roughness ratio Raf/Rai of the REMEDY stent and all solvent-cast PLLA films before and after the alkaline accelerated degradation assay. The assay was done in a 0.1 M NaOH solution during 10 days. Scale bar = 50 \(\upmu\)m. Roughness was obtained from WLI. The REMEDY stent roughness could not be characterized for geometrical reasons. **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. degradation occurs first in the amorphous parts of the polymer, the faster degradation on SC can be explained by the lower crystallinity of this film. In addition, on the one hand, OP and ET films presented the same mass loss as the TT films at each time point, suggesting that the studied activation treatments do not affect the PLLA degradation since they act at the outermost layers of the surface. On the other hand, SH films presented a slightly faster degradation rate than the TT films resulting probably from the greater surface in contact with the NaOH solution, due to its higher roughness. Finally, TT, OP, and ET films showed a degradation rate statistically similar to the REMEDY stent degradation rate. Associating this result with the high mechanical properties of TT films and the unaltered crystallinity and Mw after plasma and enzyme hydrolysis, it can be concluded that the TT, OP, and ET films are suitable for stent fabrication. According to the SEM images, a clear degradation of the surface and an increased roughness can be observed for all the samples, except for the REMEDY stent surface.