Encapsulated Zosteric Acid Embedded in Poly[3-hydroxyalkanoate] Coatings—Protection against Biofouling

The natural, non-toxic antifouling compound zosteric acid (ZA, p-coumaric acid sulfate) was encapsulated in polystyrene (PS) microcapsules (30 mg ZA/1 g PS) with an efficiency of 30 % via an in-liquid drying process. Electron micrographs showed microcapsules with smooth surfaces and a mean diameter of 200 μm. The FIB method was used to cross-section a microcapsule in order to visualize the inner capsule structure and to localize ZA via element analysis. Coatings of a biocompatible polyester, poly[3-hydroxyalkanoate-co-3-hydroxyalkenoate] (PHAE), were prepared on microscopic slides. These coatings contained dispersed ZA (PHAE/ZA) or ZA-loaded PS microcapsules (PHAE/PS(ZA)). The release of ZA was monitored via conductivy measurements in water and was 4 μgcm -2 d -1 for PHAE/ZA and 0.9 μgcm -2 d -1 for PHAE/PS(ZA) coatings. To follow the initial steps of biofilm formation, coated slides were exposed to activated sludge and analyzed for cell adhesion with ESEM. ZA was effective during the burst release time of the PHAE/ZA coating, but no significant differences in biofouling were observed after 48 h. This was attributed to the minimal effective release rate of ZA, which is approximately 10 μgcm -2 d -1 .