## 1 Introduction  
Plasma processes are well known as a powerful tool to deposit polymer-like thin coatings on materials surfaces, whose properties tightly depend on plasma experimental conditions. The process is known as PE-CVD, and is one of the most common plasma polymerization techniques, at LP as well as at AP [1]. One intrinsic advantage of PE-CVD is that the surface chemistry of the deposited film, in principle, only depends on plasma conditions regardless of the type of the substrates [2; 3]. In fact, after the initial deposition of the first atomic or molecular layer of material, the film growth is substrate-independent [2]. PE-CVD techniques are, nowadays, exploited in a wide range of applications in Materials Science and Technology, including many in the biomedical field [4]. Plasma deposited films are generally referred to as \"plasma polymers\" because of their structural analogy with such materials. However, while the atomic stoichiometry is often undefined, the retention of the starting monomer structure can be modulated to resemble the respective conventional polymer. The first degree of freedom when designing a plasma polymer is thus the monomer choice [5]. When the complexity of the monomer increases, careful tuning of the plasma conditions is needed to allow tailoring of the retention of the structure of the monomer in the coating, and the density of surface functionalities to suit any specific application [6]. In this way, it is possible to tune PE-CVD processes to improve film stability over time or upon soaking in liquids [7]. For most plasma polymers, chemical composition, the degree of retention of the monomer functionalities, and the final properties are highly dependent on the energy used to ignite the plasma. For instance, it is well accepted that high power inputs and low monomer-flow rates lead to stronger monomer fragmentation in the plasma and higher crosslinking of the resulting deposited coating. While this generally improves the stability of the coating, in contrast, its chemical composition can significantly deviate from that of the monomer. Carefully balancing the precursor flow rate and power allow, in principle, to achieve both stability and the desired chemical properties. Another way to adjust the chemical structure of a PE-CVD coating is to mix different precursors in the same discharge, to confer chemical features that belong to the used monomers [8]. To improve the fragmentation and activation of less reactive precursors, a carrier gas could be necessary [9]. Selecting the proper plasma regimes and source, at low or at atmospheric pressure, is also important for the final characteristic of the coating. Despite the possibility to finely tune the composition of the plasma deposited films, one of the most critical points of the process is the interaction of the film with the substrate. Even if the chemistry and the growth of the film are independent of the substrate, important features of the final coating, such as the depth profile, the aging or the mechanical stability, and others, strongly depend on the quality of the plasma and substrate interactions [5]. Films deposited by PE-CVD at LP and AP could exhibit poor adhesion to the substrate, delamination, and cracks when submitted to deformation, friction, or shear stress, such as those induced by cell adhesion in biomedical applications [10]. As plasma conditions are changed, processes need to be finely tailored to suit such specific applications and improve the interaction with substrates. In this context, LP plasma polymerization processes should induce better adhesion between the polymeric coating and the substrate due to the initial activation of the surface, through ion bombardment [11]. On the other hand, only a few strategies have been explored, and not completely, to improve the stability of the substrate-coating interface in AP plasma when chemical or physical characteristics of the substrate, and the PE-CVD film, are different [5].