## 2 Results and Discussion
### Boosting Antifouling Action by Incorporation of Zosteric Acid or Zosteric Salt  
Having assessed the baseline antibacterial activity of simple surfaces from acrylate oligomers **(1)**, the synthesis of films containing the NR oligomers and zosteric acid (ZA) or zosteric acid salt (ZAS) was performed for the first time. ZA, a sufoxy ester of coumaric acid, is a natural product extracted from the eelgrass _Zostera marina_; it is water soluble, completely biodegradable and it non-toxic towards larval fish. When embedded in silicone and successively released, it was found ([PERSON] [26]) that in presence of \(\sim\)2 um ZA, barnacle larvae did not attach to surfaces and were not killed. It appears that ZA does not inhibit the  
Figure 5: Dynamic tests in flow cells: comparison of _Pseudomonas aeruginosa_ attachment on acrylate **(1)** surfaces made by spin coating on borosilicate glass coupons (thin = 45 nm polymer thickness, thick = 0.1 mm) with other non coated materials (polycarbonate, bare glass coupon and titanium). growth of fouling bacteria, but it blocks attachment on surfaces and it blocks adhesion of a diversity of fungal and algal spores, and quagga mussels as well [27]. The preliminary results presented in this research work concern the approach of mixing the ZA or ZAS powders with the liquid oligomers and the photoinitiator, in order to obtain antifouling coatings by photopolymerization. The synthesis of both the acid and the salt forms has been carried out because they have a different solubility in water. As in this study, the objective was to incorporate the solid powder and to observe if it was released by the hydrophobic polyisoprene matrix; it was judged useful to start from the two forms, as in the other published studies it was not specified which compound was used. The synthesis of ZA has been realized to overcome the long procedure of its extraction and purification from the marine plants. The one involving the reaction of _para_-coumaric acid with a complex formed by sulfur trioxide and pyridine in dimethylformamide (DMF) was chosen [28] (Scheme S3). The product was obtained as a white powder, constituted by the disodium salt of the zosteric acid, with 98% yield, and it structure has been confirmed by \({}^{1}\)H and \({}^{13}\)C-NMR, FTIR and high resolution mass spectroscopy (Figure S8). The zosteric acid was obtained as a white solid by acidification of a ZAS solution to pH 2 with HCl 2N. The \({}^{1}\)H-NMR spectrum showed that a mixture of \(\sim\)95% zosteric acid and \(\sim\)5% \(p\)-coumaric acid was obtained (Figure S8). Both the zosteric acid and the salt forms were used in the film formulations. The idea of incorporating ZA into a polymer and to study the effect of its release was inspired by previous studies [29], in which ZA was incorporated into silicone. The authors measured the minimum amount of ZA that had to be charged and successively released to reduce the attachment of a Lake Erie bacterial consortium and _Pseudomonas putida_ by more than 90% in comparison to the untreated silicone. For our series of experiments, the silicone was replaced by the NR-based films formed by acrylate **(1)**, in which the ZA or ZAS were incorporated as powders, and the pathogenic bacteria PA, SE, and SA were used instead of the freshwater ones. The polymer films were obtained on the bottom of the wells of a 24-well cell culture plate and the attachment experiments were carried out in the same static conditions described in Section 2.1. It was found that PA and SA (Figure 4) adhesion was significantly reduced by the presence of ZA and ZAS in comparison to the control and to the acrylate **(1)**, while for SE the effect was more mitigated. These data indicated that ZA and ZAS were partially released from the polymeric substrate because, in absence of any leaching, the same activity of empty acrylate surfaces should have been obtained. Moreover the relative amounts were sufficient to exert a significant effect on the bacteria.