## 2 Results and Discussion
### Possible Mechanism of Action for the Anti-Adhesion Effect  
The data obtained so far confirmed that the surfaces obtained from NR-derived oligomers containing only the polyisoprene backbone have a weak but noticeable activity _per se_, independently from the oligoisoprene chain length. This inhibition of the bacteria attachment was consistently enhanced if a known biocide group was inserted, such as a quaternary ammonium with at least one long carbon chain on the nitrogen atom. A possible explanation for the basic activity might be found looking at the function, if any, of the latex produced by the _Hevea_ rubber trees. The rubber particles suspended in the aqueous latex are a secondary metabolite and the polyisoprene chains are their main constituent. The liquid latex, which is often mistaken for the tree sap, is produced by a system of laticifers, which are chains of contiguous cells connected by anastomoses, and arranged in rings in the secondary phloem. The cells are differentiated from the vascular cambium, and the most important laticifers are in the bark. When the bark is carved, the latex flows out and it rapidly coagulates to generate a solid natural rubber film on the scar. The reason why the tree produces the latex containing the rubber particles is still not clear, however it appears that it has a role of defense from pathogens  
Figure 6: Comparison of basic activity of acrylate **(1)** surfaces using different marine bacteria: _Flavobacterium_ II2003, _Alternomonas_ IVA014, _Bacillus_ IV3004, _Shewanella_ IV3014, _Bacillus_ IVA016, _Vibrio splendidus_. (**a**) = bacteria suspended in the supernatant media; (**b**) = bacteria attached to the control (polystyrene) or polymer surface. *, difference in values significant at \(p\leq 0.05\), ** difference in values significant at \(p\leq 0.01\).  
and herbivorous insects [49]. More generally, latexes can be produced by different plants; they are sticky and viscous liquids, deterrent for insects that try to bite because they are immobilized when they touch the plant surface. Studies have shown that hundreds of proteins are present in the latex, mainly hydrolytic enzymes, and defense or stress-related genes are abundantly expressed during rubber production [50]. Among all these compounds, some latexes contain molecules which are toxic for animals and in some cases they are monoterenes or diterpenes [51]. Because of the structural resemblance of the polyisoprene backbone with terpen having a natural antimicrobial activity, we formulated the initial hypothesis [18] that this similarity was the reason for the natural rubber-based surfaces antibacterial effect. With the aim of testing this hypothesis, the sequence of the carbon-carbon double bonds in the NR-based oligomers was modified by hydrogenation or epoxidation, expecting a reduction in the antifouling action of the resulting polymeric films. The results have shown that the suppression of some double bonds can have a small positive influence, but not negative in any case as expected. By partial hydrogenation or epoxidation of the NR oligomers, a modification of the terpenic structure was realized but, at the same time, the polarity of the surface was also changed. It appears that, in our case, the polarity is the key parameter to determine repulsion or attraction, more than the resemblance to natural terpen. It has been shown [52], however, that it is quite complicated to draw definitive conclusions, because the number of colonies formed on a surface depends not only on the hydrophobicity or the chemical composition, but also on the nutrient level, the age of the microbial culture, the nutrient ability to adsorb on the examined polymeric surface, the ionic strength of the medium, and the static or dynamic conditions in which the attachment experiment is carried out.