## 2 Results and Discussion
### Influence of Partial Epoxidation or Hydrogenation of Acrylate Backbone  
In order to have insights about the reasons of the basic attachment inhibition exerted by the polyisoprene surfaces, it was decided to focus the attention on the polymer backbone constituted by the sequence of _cis_ carbon-carbon double bonds of the isoprene units, and to see if the suppression of some of them by hydrogenation or epoxidation could cause any change. Two different versions of the acrylate oligomers were synthesized: the epoxydated acrylates **(2)** (Figure 3), in which 30% or 55% of the double bonds were oxidized (transformed into epoxy groups), and the hydrogenated acrylates **(3)** (Figure 3), in which 33% or 67% of the double bonds were reduced by catalytic hydrogenation (see also Scheme S1). Cross-linked films were obtained in conditions similar to those described here in Section 2.1 through radical photopolymerization and tested with the same pathogenic bacteria. It appeared (Figure 3b,d,f) that the three bacteria tested did not attach to the surfaces obtained from the hydrogenated oligomers in comparison to the acrylate and the epoxidized ones, independently from the hydrogenation ratio, while the number of colonies remaining in suspension was not substantially different from the control one. The surfaces obtained from the epoxy oligomers with 30% of epoxy groups had no different behavior in comparison to the control polystyrene; the higher percentage of epoxidation provoked an improvement of activity in comparison to the simple acrylates only for SE.  
In conclusion, the hydrogenation or epoxidation ratio made a difference in the surface properties that affected the bacteria behavior. The surfaces from partially hydrogenated oligomers were the best in inhibiting bacteria attachment without any biocide action, as the number of colonies in suspension was similar to the control. The hydrogenated surfaces were the most hydrophobic and less polar of the three surfaces tested; the epoxidized surfaces were the most polar and hydrophilic, and also the least active (except for SA). As for the acrylate surfaces **(1)**, they were in between the two others, regarding the AF action and polarity. For instance, contact angle and surface energies had been previously measured and gave 7% polarity for acrylate **(1)**, as compared to 25% polarity for 30% epoxidized acrylate oligomers [20,21].  
Some samples presented values bigger than the control (see also Figure 2). Apart from possible pipetting errors (especially when the number of cells is twice that of the control), no satisfactory explanation can be provided. It is worth noting that for this series of experiments, overall, the total number of bacteria adhered to the surface accounted for _ca._ 3% (0.031 \(\pm\) 0.010, \(n\) = 20) of the total number of bacteria in suspension in the control (polystyrene) wells, a mean value twice higher than the percent of cells counted at the surface of the different polymers (_ca._\(0.015\pm 0.007\)). Although for these experimental conditions (set-up, species, duration), most of the bacteria stayed in suspension, with only a few percent of cells able to adhere to the surfaces, this general trend confirms that, whatever the strains and the polymers considered, the NR-based coatings do present an AF activity.