A biological assay for detection of heterogeneities in the surface hydrophobicity of polymer coatings exposed to the marine environment

Minimally adhesive polymers are being developed as potential coatings for use in the marine environment. A 'bioprobe', the bacterium Psychrobacter sp. strain SW5, was employed to detect heterogeneities in substratum hydrophobicity at a micrometer level, rather than the millimeter level detected by traditional contact angle measurements. This novel assay was based on substratum-induced shifts in bacterial morphology and was used to demonstrate that characteristics of these surfaces can be evaluated for maintenance of parameters such as low surface free energy as well as temporal stability when immersed in water. Immersion of developmental substrata in artificial seawater for up to 90 d prior to testing with the bioprobe potentially affects the stability of the designed characteristics of the polymers. It is proposed that the shifts in cell and biofilm morphology results from changes influencing the surface hydrophobicity of the polymers. An unpredicted outcome of this testing was the detection of modifications td coatings inferred by the addition of filler particles. Exposure of coatings to the natural microbial community of seawater revealed colonization characteristics that substantiate the results obtained by using the bioindicator.