Surface-grafted, environmentally sensitive polymers for biofilm release

Controlling bacterial biofouling is desirable for almost every human enterp rise in which solid surfaces are introduced into nonsterile aqueous environ ments. One approach that is used to decrease contamination of manufactured devices by microorganisms is using materials that easily slough off accumul ated material (i.e., fouling release surfaces). The compounds currently use d for this purpose rely on low surface energy to inhibit strong attachment of organisms. In this study, we examined the possible use of environmentall y responsive (or "smart") polymers as a new class of fouling release agents ; a surface-grafted thermally responsive polymer, poly(N-isopropylacrylamid e) (PNIPAAM), was used as a model compound. PNIPAAM is known to have a lowe r critical solubility temperature of similar to 32 degrees C (i.e., it is i nsoluble in water at temperatures above 32 degrees C acid is soluble at tem peratures below 32 degrees C), Under experimental conditions, >90% of cultu red microorganisms (Staphylococcus epidermidis, Halomonas marina) and natur ally occurring marine microorganisms that attached to grafted PNIPAAM surfa ces during 2-, 18-, 36-, and 72-h incubations were removed when the hydrati on stale of the polymer was changed from a wettability that was favorable f or attachment to a wettability that was less favorable, Of particular signi ficance is the observation that an organism known to attach in the greatest numbers to hydrophobic substrata (i.e., H. marina) was removed when transi tion of PNIPAAM to a more hydrated state occurred, whereas an organism that attaches in the greatest numbers to hydrophilic substrata (i.e., S. epider midis) was removed when the opposite transition occurred. Neither solvated nor desolvated PNIPAAM exhibited intrinsic fouling release properties, indi cating that the phase transition was the important factor in removal of org anisms. Based on our observations of the behavior of this model system, we suggest that environmentally responsive polymers represent a new approach f or controlling biofouling release.