## 4 Discussion  
Traditionally, studies on plasma polymerization of PEO-like coatings were focused on LP PE-CVD because they provide excellent control over the gas chemistry, and allow use of high energetic reactive species like positive ions bombarding the surface of substrates [11; 15]. At present, though, following the development of processes and equipment for AP PE-CVD, many research groups are developing non-thermal equilibrium (cold) plasma processes for plasma deposition of PEO-like coatings in AP conditions [16]. Engineering coatings for biomedical applications implies, more stringently than for other applications, that controlled composition and adequate stability of the coating on the substrate are granted for the whole time of application in biological media like, for example, cell culture media. Delamination of the coating, changes in chemical composition, and uncontrolled cell adhesion can occur if the process is not properly optimized, and the final function of the plasma modified surface could be compromised. The plasma is characterized by different active species with energies up to tens of electron volts (eV), which provide sufficient energy to break most of the chemical bonds of the organic precursor monomer employed in this technology. The plasma polymeric films obtained are usually highly cross-linked, thermally stable, pinhole-free, highly conformal, and strongly bound to most substrates [11; 33]. LP and AP plasma deposition processes, though, have different features, that need to be addressed for properly optimizing the properties of the treated surfaces. As an example, LP deposition of soft organic coatings on inorganic substrata could produce unstable films due to slight ion bombardment of the underlying substrate, while in the case of using thick plastic substrates in AP we could promote some electrical instabilities that are reflected in the coating composition if the substrate is included in the electric circuit [1]. In this paper, we have shown two different approaches to deposit PEO-like coatings with chemical characteristics able to discourage (non-fouling) or promote (cell-adhesive) cell adhesion. Monomers with high boiling points have been used to produce, in LP, cell-repulsive or cell-adhesive coatings that were stable both in water and in cell culture medium during cell culture experiments. Following strategy 1 of Figure 1, PEO-like coatings from DEGDME vapors were deposited at different input power values of the process, resulting in a PEO-character that decreases as the input power increases. To add and modulate cell-adhesive character in the coatings, DEDGME vapors were mixed with VAc ones following strategy 2 of Figure 1: in this way, COOH groups were included during the growth of PEO-like coatings. The use of VAc as the monomer is nearly absent in literature; indeed, it offers the advantage of a double bond in its structure, that allows easier polymerization through the conventional mechanism, and ester/carboxyl groups (-COOR (H)) useful to promote cell-adhesion [20]. In Figure 2, it is demonstrated that the chemical composition of coatings deposited in LP PE-CVD can be tuned by using VAc/DEGDME feed mixture with DEGDME flow lower than 0.5 sccm, low input power, without Ar as a buffer gas. In this way stable coatings are produced, that resist to water immersion, useful for biomedical applications. Sticky oily coatings may result when high boiling point monomers are used in high fraction (i.e., \(\phi\)DEGDME > 0.5 sccm) if the experimental conditionsare not properly selected and controlled (i.e., low input power and absence of a carrier gas), due to low fragmentation and condensation of the monomer and oligomer molecules on the substrates.