# Modification of PLA Scaffold Surface for Medical Applications
## 3 Results and Discussion
### Effect of the Used Gas on the Surface Free Energy and Its Polar and Dispersion Components  
The effect of the gas composition on the SFE, polar and dispersion components, and the change of the polar component (\(\Delta\)p) of membranes MI and MII was investigated. The discharge power was 20 W, and the exposure time varied in the range of 15-60 s. It was expected that the radicals generated in the plasma by CO2 dissociation would react with the surfaces of the membranes. This may have raised the concentration of the carbonyl group on the scaffold surface. Moreover, excited argon etched the surface and may have also initiated CO2 dissociation. It was observed that extending the modification exposure time of membranes MI and MII in the plasma generated in argon increased the SFE and its polar component. The modification of the MI conducted for 60 s allowed for a 20% increase of the value of SFE compared with the unmodified sample to be obtained, while the polar component increased from 21.4 mJ/m2 to 36.3 mJ/m2. A similar effect was observed for MII. The SFE of the membrane modified for 60 s increased by 21% compared with the unmodified sample and reached 61.0 mJ/m2. The change in the polar component indicates that the introduction and formation of polar groups on the surface of the modified material improved the adhesive properties. The increase of the polar component, which was interrelated with the polar and induction effects, was a positive phenomenon. This effect will facilitate the wetting of the surface with polar liquids (e.g., water or its solutions) [27]. The dispersion component, responsible for London's interactions, decreased in value for both membranes. The polar component of MII after the modification in argon increased almost threefold, reaching 27.8 mJ/m2. The value of the dispersion component changed to a much lesser extent; it was 36.8 mJ/m2 and 32.9 mJ/m2 for exposure times of 15 s and 60 s (the dispersion component of the unmodified membrane was 38.6 mJ/m2). After the modification of MI in carbon dioxide, the best wettability was obtained after 15 s of exposure. The polar component value reached 34.0 mJ/m2, and the surface free energy was 66.1 mJ/m2. The increase of the exposure time to 30 s caused the decrease of the obtained values. A further extension of the exposure time to 60 s resulted in achieving similar SFE values to when the process was conducted for 15 s. The differences between the values achieved at 15 s and 60 s were approximately 0.7%. Similar relations were observed during the modification of MII. The most effective modification of PLA scaffolds obtained by the dry method was conducted for 15 s. The SFE value was 64.2 mJ/m2, and the polar  
Figure 3: The impact of the barrier discharge power generated in carbon dioxide on the change of the polar component (\(\Delta\)p). The exposure time was 15 s.  
component was 30.4 mJ/m\({}^{2}\), which was an almost threefold increase compared with the unmodified material. The effects of plasma modification of membranes MI and MII conducted for 30 s were weak. The membranes were less flexible and more fragile, which is very unfavorable from the application point of view. Membranes MI and MII after the treatment with DBD plasma generated in a 50%vol. Ar + 50%vol. air gas mixture had some of the highest SFE and polar components. All the MI samples exhibited a significant increase of the surface free energy after modification. The highest SFE value of 67.3 mJ/m\({}^{2}\) was obtained after 60 s of modification. The polar component obtained under these conditions was 34.4 mJ/m\({}^{2}\) and increased approximately 60% compared with the unmodified membrane. With an increasing exposure time, the SFE increased from 62.2 mJ/m\({}^{2}\) to 67.3 mJ/m\({}^{2}\), and the polar component increased from 30.6 mJ/m\({}^{2}\) to 34.4 mJ/m\({}^{2}\). Similar relations were observed for MII. It was found that the value of the SFE increased with an increasing exposure time.