## 2 Results and Discussion
### Dynamic Tests and Modification of Surface Thickness by Spin Coating  
Different methods of performing the biological assays were used during the project. For the initial screening between the surfaces, the method of depositing polymer disks on an agar plate, covering with bacteria and observing the formation of an inhibition halo was adopted. In this quick and simple way, it was possible to see if bacteria had grown on the polymer surface and if there had been any leaching. However this technique is not quantitative and it was decided that more information could be obtained by counting the colonies formed on the surface after incubation and separation of the supernatant. Both techniques involved testing the polymers in static conditions, which is not characteristic of realistic environments. Therefore supplementary biological tests were performed in dynamic conditions. The available equipment was a flow cell with two lanes (BioSurface Technologies, Corp. (Bozeman, MT, USA), BST FC 271), which could hold two coupons in each lane, one was upstream from the other, not touching each other but with a space between. These coupons were round borosilicate disks (RD 128-GL), of 12 mm diameter and 5 mm height and they could fit into the flow cell only if the polymer film deposited on their surface was very thin. The form of the coupons as well as the necessity of having coatings with a low thickness required the deposit of the pre-polymerization mixture by spin coating. The acrylate **(1)** oligomers and the photoinitiator were dissolved in tetrahydrofuran (THF), the solutions were spread by spin coating on the glass disks, and they were photopolymerized after solvent evaporation. Parameters such as oligomer concentration, spinning time and rate were optimized to have thicknesses in the range 2-100 nm. For the dynamic test, the polymer called \"thin acrylate\" (Figure 5) was obtained with an oligomer concentration of 20 mg/mL, and a rate of 1000 rpm, while the \"thick acrylate\" was obtained by spreading the bulk pre-polymerization mixture at 3000 rpm for 30 s. The spin coated thin films were studied by X reflectivity (Figure S3, Table S1), prepared from two different oligomer chain lengths (1200 g\(\cdot\)mol\({}^{-1}\) for films A,B,C,D,F and 1700 g\({}^{-1}\cdot\)mol for films R,X,Y,Z,W). The electron density of spin-coated films was found to be around 0.38 electrons/A\({}^{3}\), in good agreement with the calculated one from the polymer formula and volume density. Spin-coated films divided into two classes: Thin films with 40-46 nm thickness, with a roughness around 5 nm and the presence of surface inhomogeneities in the form of surface domains (Figure S3a); and ultra thin films (2-3 nm, Figure S3b), more homogeneous laterally and with a low roughness comparable with the glass one. Atomic Force Microscopy (AFM) images were taken of the coupons bare glass surface and of a thick NR coating and they showed island domains (nanodroplets in pseudo-partial wetting), with thicknesses below 50 nm (Figure S4). A roughness of 1.6 nm was found for the uncoated coupon. The presence of polymer nanodroplets and reorganizations of the film during the UV-treatment is not excluded and we envisage for future development of thin films coatings to covalently graft the oligomers to the surface of the substrates during the thin film deposition, to reduce the surface inhomogeneities and prevent adhesion problems. The coupons covered by the polymer films were placed into the first lane of the flow cell and different control materials in the second one. A suspension of PA in 10% tryptic soy broth medium was introduced and left in static conditions, at 37 \({}^{\circ}\)C, for 1 h in order to allow the PA time to attach, and then the flow was started and left for 24 h, with a 3 mL/h flow rate. Polystyrene could not be introduced in the system as control as in the static tests, and it was replaced by polycarbonate, on which was found the highest number of attached bacteria.