To incorporate capsaicin and zosteric acid into silicone by (a) chemical bonding or physical adsorbing to the surface and (b) physical entrapping into the silicone matrix. To examine the possible bonding formation between NPA molecules and silicone coating during surface immobilization. Completion of these tasks will enable the PIs to ascertain the optimal approach for NPA incorporation that yields an effective product with an extended service life.
To verify and develop antifouling mechanisms of coatings incorporated with NPAs by (a) evaluating the effects of NPA incorporation on coating properties, surface energy, surface roughness and coating modulus, related to fouling and anti-fouling performance of the coating, and (b) examining NPA depletion and antibacterial performance of the NPA incorporated silicone coating. These tasks will corroborate antifouling mechanisms for NPA-incorporated silicone coatings. The result of objective 2 will also be used to optimize the parameters for the 'final' AF/FR coating (i.e., NPA concentrations, NPA incorporation method, etc.).
To evaluate the release mechanism of the NPA physically entrapped inside silicone coatings, and how leaching of NPA affecting the properties of the coatings.

Two representing NPAs, capsaicin and zosteric acid, were sought as potential less toxic antifoulants to be incorporated into foul-released silicones. First, the toxicity of these two compounded were evaluated, and it was found that both compounds were substantially less toxic as compared to the currently used antifoulants such as such as TBT or SeaNine 211. The EC50 value of capsaicin for various fresh water and marine bacteria ranged from 3 to 23 mg/L, and it was around 10 to 440 mg/L for zosteric acid. When these compounded were simply dispersed in water containing the bacteria, as the antifoulant concentration increased, a significant inhibition of bacteria attachment and prevention of biofilm formation were achieved.

Simultaneously, various methods were sought to incorporate the compound into two silicone coatings, and the NPA incorporated silicone coatings showed enhancement in antibacterial attachment, range from ~ 50 % to ~ 80% reduction in bacterial coverage with only 1 wt.% of the compound in the coating. The leaching of the entrapped compound from the coating was exclusively examined to optimize the adequate release of the compound in preventing fouling while providing the long term (> 10 years) service of the coating.

Fouling by marine organisms has consistently been a major problem for maritime industries. It increases not only the drag and fuel consumption of marine vessels, but also the costs of vessel maintenance. For instance, reducing drag related biofouling by only 1% would reduce the U.S. Navy's fuel penalties $5 million/yr. Because traditional anti-fouling (AF) coatings release environmentally toxic materials, alternative non-toxic AF coatings need to be sought. One of the alternatives is to incorporate non-toxic natural product antifoulants (NPAs) into foul-released (FR) coatings. The NPA's would eliminate the potential transfer of marine community(s) from one location to another, thereby maintaining the natural ecosystem. The new AF coating could be introduced for marine infrastructure materials such as loading docks, fish hatcheries, etc. In Ohio alone there are over 88,000 docks, 125 fish hatcheries, and 829 marinas, therefore there is a potentially large market in the private.

In the proposed research, two representing NPAs, capsaicin and zosteric acid, will be incorporated into foul-released silicones, and the effects of NPA incorporation on AF and FR performances will be examined. Both surface (energy and roughness) and bulk (modulus) properties will be determined as functions of incorporated NPA concentrations, incorporation method, as well as water immersion time. The adhesion between the NPA incorporated silicone coating and an epoxy adhesive will be measured to mimic the fouling strength of marine organisms and our coatings. In order to correlate adhesion data to the coatings, anti-fouling performances and bacteria attachment using model freshwater and marine bacteria will be conducted to evaluate biofilm formation. Optimistically, the experiment data can be used to develop and verify antifouling mechanism of silicones incorporated with NPAs.

Toxicity studies of two natural product antifoulants (NPAs): capsaicin and zosteric acid, were evaluated using both a standard Microtox assay and a static toxicity test. The EC50 values of various fresh water bacteria: P. putida and enriched bacteria isolated from the Lake Erie water, and marine bacteria: V. natriegens and V. parahaermolyticus, were found to the in the range of 3 to 23 mg/L for capsaicin, and 10 to 440 mg/L for zosteric acid. These values are substantially higher, meaning less toxic, than the currently used antifoulants, such as TBT (EC50 < 0.01 ppb). The bacteria attachment studies were also performed to evaluate how these NPAs affect attachment and biofilm formation on silicone coatings when the NPAs are present in water as a free suspension. The reduction on biofilm formation was observed to increase as the NPA concentration in water increased. The NPA concentration to achieve a 90% reduction in bacterial attachment was found to be ~ 20 mg/L and ~ 50 mg/L for capsaicin and zosteric acid, respectively. The properties of the coatings immersed in water were also evaluated, and the results indicated that the variation on coating properties have little effect on bacterial adhesion. The antifouling ability of capsaicin and zosteric acid incorporated inside silicone coatings was evaluated using attachment studies of fresh water bacteria. Various methods were sought for incorporating the compound into silicone to prolong the release of the compound. The NPA entrapped coatings exhibited enhanced antibacterial attachments. However, the release of capsaicin from the incorporated coatings was found to be too fast, due to the formation of capsaicin crystal, to have a long service life (i.e. six months for a coating with a 1 wt.% capsaicin incorporated). Zosteric acid, on the other hand, could be distributed uniformly inside the coating with small aggragate size (1 ¨C 4 microns), and the leaching rate of zosteric acid from these resulting coatings was orders of magnitude slower (~ 0.02 µg/day-cm²) than those of previous reports (~ 1 mg/ day-cm²). The release results indicate that the service life of our coatings could be extended to 10 or 20 years even with a small amount (i.e. 1 wt.%) of zosteric acid incorporated.