Adhesion and motility of fouling diatoms on a silicone elastomer

Abstract

Recent demands for non-toxic antifouling technologies have led to increased interest in coatings based on silicone elastomers that 'release' macrofouling organisms when hydrodynamic conditions are sufficiently robust. However, these types of coatings accumulate diatom slimes, which are not released even from vessels operating at high speeds (>30 knots). In this study, adhesion strength and motility of three common fouling diatoms (Amphora coffeaeformis var. perpusilla (Grunow) Cleve, Craspedostauros australis Cox and Navicula perminuta Grunow) were measured on a poly-dimethylsiloxane elastomer (PDMSE) and acid-washed glass. Adhesion of the three species was stronger to PDMSE than to glass but the adhesion strengths varied. The wall shear stress required to remove 50% of cells from PDMSE was 17 Pa for Craspedostauros, 24 Pa for Amphora and >>53 Pa for Navicula; the corresponding values for glass were 3, 10 and 25 Pa. In contrast, the motility of the three species showed little or no correlation between the two surfaces. Craspedostauros moved equally well on glass and PDMSE, Amphora moved more on glass initially before movement ceased and Navicula moved more on PDMSE before movement ceased. The results show that fouling diatoms adhere more strongly to a hydrophobic PDMSE surface, and this feature may contribute to their successful colonization of low surface energy, foul-release coatings. The results also indicate that diatom motility is not related to adhesion strength, and motility does not appear to be a useful indicator of surface preference by diatoms.

Progress of marine biofouling and antifouling technologies

“…For instance, non-stick fouling-release compounds (such as silicone coatings) have been trialed for antifouling through release of macrofouling organisms when hydrodynamic conditions are sufficiently robust [1,37]. In this case, it appears that fluoropolymers and silicones possess the necessary properties for antifouling by release [1].…”

“…Some low surface energy coatings have also been prepared with modified acrylic resin and nano-SiO 2 [89]. However, accumulated fouling organisms are not as easily released as anticipated [37,90,91]. In addition, this method has many deficiencies, such as high cost, poor mechanical properties, [23].…”

“…Many scientists have focused on diatom gliding in the belief that this would help to understand the adhesion mechanism. However, Holland et al [37] found no relation between adhesion and locomotion of diatoms. It is generally acknowledged that diatom gliding is the result of an actin-myosin motility system meditated by extracellular proteoglycans.…”

“…Study has shown that fouling diatoms [37] adhere more strongly to a hydrophobic polydimethylsiloxane (PDMSE) surface than to glass. For other fouling organisms such as bacteria and Ulva spores, if the surface contact angle is greater than the adhesion is stronger [121][122][123][124].…”

Designing biomimetic antifouling surfaces

“…coatings based on silicone elastomers with low surface free energies, are generally only successful for fast-moving vessels, as the decrease in adhesion strength facilitates removal at speeds greater than 20 knots (Brady 2001). However, diatoms have higher attachment strength on hydrophobic surfaces (Holland et al 2004 (a combination of micrometre-scale and nanometre-scale roughness, along with a low surface free energy, resulting in high water contact angles greater than 150 • ) have been studied for their AF performance (Zhang et al 2005;Scardino et al 2009a,b) and are known to exhibit reduced viscous drag due to slip associated with a layer of air trapped at the liquid-solid interface. However, loss of superhydrophobicity is due to the so-called Cassie-Wenzel transition, where it has been shown that both Cassie (air trapped) and Wenzel (surface roughness) regimes can coexist on the same surface.…”