## Results
### LP Plasma Deposition of Differently Cell-Repulsive Coatings
The C1s best fitting data of Figure 8 show a slight decrease in the PEO-character from 70% to 67% for the PEOA coatings as the soaking time increases, while a constant value of 55% was measured for the PEOB coatings. The XPS results are in good agreement with the morphological characterizations reported in Figure 7, both indicating good stability of the coatings in water media, as well as a stable adhesion to the polymer substrate underneath. Figure 7: Optical microscopy pictures acquired on untreated PC (**a**) and PEOA coated one (3.15 slm He/TEGDME aerosol flow, 4.85 slm He carrier flow, 8.5 kV\({}_{\text{p-p}}\), f 26 kHz, 5 min) before (**b**) and after 5 min (**c**) and 3 days (**d**) of soaking in double-distilled water. Pictures in the same rectangle report images acquired at different magnitudes. Differently from the data reported above, after water soaking, when PEOA and PEOB single-layer coatings were used in cell growth experiments, clear delamination of the coating from the substrates was observed after 4-5 h of culture in DMEM at 37 \({}^{\circ}\)C, as clearly visible in Figure 9. This phenomenon occurs whatever the chemical composition of the PEO-like coating is investigated. To improve the interface stability of PEO-like coatings deposited in AP plasma conditions in cell-culture experiments, a multi-step deposition process was carried out to obtain a vertical chemical gradient from the bottom, at the substrate and film interface, to the top side of the film, at the film and air or liquid interface. The LP plasma deposition of coatings characterized by a vertical chemical gradient has been recently reported [31], to improve the adhesion of the coatings to a substrate. We show the AP PE-CVD synthesis of a vertical gradient through 3-layer deposition approach, starting from a process fed with only C\({}_{2}\)H\({}_{4}\), followed by deposition with a mixture of C\({}_{2}\)H\({}_{4}\) and TEGDME, and topped with deposition of only TEGDME. The three processes are run in continuo in the DBD reactor. We believe that this approach can be used in many cases to improve the adhesion between a coating and a substrate or to gradually increase the content of certain functionalities going towards its topmost layer, as shown by other authors with LP PE-CVD processes [32]. Figure 10 describes how thickness and WCA develop for two different PEOA coatings deposited at two different frequencies (see Table 1) on PC substrates with similar trends. After step 1, a cross-linked  
Figure 2:0 C1s best fitting data for PEOA (**a–c**) and PEOB (**d–f**) single-layer coatings as-deposited (**a,d**), after 5 min (**b,e**) and after 3 days (**c,f**) in double-distilled water. The percentage contribution II (PEO-character) remain almost unchanged for PEOA (around 70% PEO-character) and PEOB (55% PEO-character) even after 3 days of water soaking. Figure 2:1 Delamination of PEOA (**a**) and PEOB (**b**) from the PC substrate (black arrows) under cell-growth conditions. PEOA (3.15 slm He/TEGDME aerosol flow, 4.85 slm He carrier flow, 8.5 kV\({}_{\text{p}-\text{p}}\), f 26 kHz, 5 min); PEOB (3.15 slm He/TEGDME aerosol flow, 6.85 slm He carrier flow, 8.5 kV\({}_{\text{p}-\text{p}}\), f 26 kHz, 5 min). polyethylene-like (PE-like) hydrocarbon layer is deposited from the C\({}_{2}\)H\({}_{4}\)/He feeds, resulting in a 60 nm thick hydrophobic coating (WCA: \(81\pm 2^{\circ}\)). Step 2 from TEGDME, C\({}_{2}\)H\({}_{4}\), and He resulting in a 20 nm thick coating characterized by WCA of \(68\pm 2^{\circ}\). Step 3, finally, leads to the deposition of the PEOA film 180 nm thick showing a WCA value of \(53\pm 3^{\circ}\). The WCA values are the same at the two frequencies used. The AP deposition of PEO-like films has been performed by implementing the three steps described above. The effect of the frequency and the applied voltage was evaluated on the uppermost PEO-like layer, using in step 3 a carrier flow rate (\(\phi\)He-carrier) of 4.85 slm (PEOB) coatings or 6.85 slm (PEOA coatings).