## 1 Introduction  
Dental implants are a common solution to overcome the problem of tooth loss [1]. However, these implants can fail due to various factors, in which the lack of osseointegration--the growth of the implant into the bone structure--and implant-related infections are thought to play a key role [2, 3, 4, 5]. The lack of osseointegration can be explained by the implant's mobility, the surface properties of the implant, medical treatments applied to the patient (radiation therapy or pharmacological agents) and the patient's related factors, including osteoporosis, rheumatoid arthritis, renal insufficiency or smoking [6, 7, 8, 9]. Titanium is widely used to produce dental implants, mainly due to its biocompatibility, corrosion resistance, mechanical properties and low immunogenic potential [10]. Titanium is naturally covered by a titanium oxide layer that facilitates the adsorption of biomolecules, supporting cell adhesion and spreading [1]. Specific properties of the implant surface, such as chemistry and roughness, play a determining role to address specific cell responses (e.g., the adsorption of proteins, as well as the adhesion and differentiation of cells) suitable for biomaterial and tissue engineering. Therefore, various attempts have been made to increase the success rate of implants by tailoring the surface properties, including modification of the topography features [11], doping with inorganic antimicrobial agents [12; 13; 14; 15; 16; 17; 18], immobilizing bioactive molecules like antibiotics [19; 20] or peptides [21; 22; 23; 24; 25; 26; 27] and coating the titanium surface with polymers [28; 29; 30; 31]. Plasma polymerization has been widely used as a process for preparing biocompatible coatings, but until recently, the application was limited mostly to low-pressure plasma polymerization [32; 33; 34] or, alternatively, with atmospheric pressure plasma polymerization [35; 36; 37]. In the latter, either dielectric barrier discharges or plasma jets are employed, introducing monomers in the discharge by producing an aerosol which was led by the gas flow toward the surface of the material [38]. Lately, the interest in atmospheric pressure plasma jets has been growing, as they enable spatially resolved surface treatments, along with the creation of chemically heterogeneous surfaces to foster specific cell-surface interactions. Atmospheric pressure plasma jets (APPJs) have been used for the treatment of medical devices in order to produce chemically reactive surfaces with different functionalities [39], such as the preparation of carboxyl [39; 40] or amino rich surfaces [40], which can be further used for the immobilization of biomolecules like proteins or peptides. Those surfaces have been proven to increase the number of cells adhered on the plasma-treated material. APPJs have also been used to produce antifouling polyethyleneglycol (PEG) coatings by plasma polymerization in order to prepare antithrombogenic materials [41], or as a pretreatment of the substrate to immobilize cell adhesion peptides [42]. When focusing on the titanium dental implants, APPJs have been used as a methodology to render antibacterial surfaces [43] or to sterilize titanium implants [44]. A nanocomposite coating to be used as a drug delivery system, containing silica and poly(lactic-co-glycolide), has also been prepared using this technique, showing increased adhesion of osteoblasts and fibroblasts [45]. Besides that, for the improvement of biocompatibility, nitrogen- or oxygen-containing functional groups are known to support cell attachment and proliferation [46]. Recent developments are focused on the generation of oxygen-rich, hydrocarbon-based polymer coatings by using plasmas for the polymerization of polyethylene glycol, poly \(\varepsilon\)-caprolactone or acrylic acid to modify cell attachment on a variety of substrates, such as silicon [47; 48], polypropylene meshes [49], glass [50] or titanium [51].