Engineered antifouling microtopographies - effect of feature size, geometry, and roughness on settlement of zoospores of the green alga Ulva.

The effect of feature size, geometry, and roughness on the settlement of zoospores of the ship fouling alga Ulva was evaluated using engineered microtopographies in polydimethylsiloxane elastomer. The topographies studied were designed at a feature spacing of 2 microm and all significantly reduced spore settlement compared to a smooth surface. An indirect correlation between spore settlement and a newly described engineered roughness index (ERI) was identified. ERI is a dimensionless ratio based on Wenzel's roughness factor, depressed surface fraction, and the degree of freedom of spore movement. Uniform surfaces of either 2 mum diameter circular pillars (ERI=5.0) or 2 microm wide ridges (ERI=6.1) reduced settlement by 36% and 31%, respectively. A novel multi-feature topography consisting of 2 mum diameter circular pillars and 10 microm equilateral triangles (ERI=8.7) reduced spore settlement by 58%. The largest reduction in spore settlement, 77%, was obtained with the Sharklet AF topography (ERI=9.5).

Engineered antifouling microtopographies--correlating wettability with cell attachment.

Bioadhesion and surface wettability are influenced by microscale topography. In the present study, engineered pillars, ridges and biomimetic topography inspired by the skin of fast moving sharks (Sharklet AF) were replicated in polydimethylsiloxane elastomer. Sessile drop contact angle changes on the surfaces correlated well (R2 = 0.89) with Wenzel and Cassie and Baxter's relationships for wettability. Two separate biological responses, i.e. settlement of Ulva linza zoospores and alignment of porcine cardiovascular endothelial cells, were inversely proportional to the width (between 5 and 20 microm) of the engineered channels. Zoospore settlement was reduced by approximately 85% on the finer (ca 2 microm) and more complex Sharklet AF topographies. The response of both cell types suggests their responses are governed by the same underlying thermodynamic principles as wettability.

Antifouling potential of lubricious, micro-engineered, PDMS elastomers against zoospores of the green fouling alga Ulva (Enteromorpha).

The settlement and release of Ulva spores from chemically modified, micro-engineered surface topographies have been investigated using poly(dimethyl siloxane) elastomers (PDMSe) with varying additions of non-network forming poly(dimethyl siloxane) based oils. The topographic features were based on 5 microns wide pillars or ridges separated by 5, 10, or 20 microns wide channels. Pattern depths were 5 or 1.5 microns. Swimming spores showed no marked difference in settlement on smooth surfaces covered with excess PDMS oils. However, incorporation of oils significantly reduced settlement density on many of the surfaces with topographic features, in particular, the 5 microns wide and deep channels. Previous results, confirmed here, demonstrate preferences by the spores to settle in channels and against pillars with spatial dimensions of 5 microns, 10 microns and 20 microns. The combination of lubricity and pillars significantly reduced the number of attached spores compared to the control, smooth, unmodified PDMSe surfaces when exposed to turbulent flow in a flow channel. The results are discussed in relation to the energy needs for spores to adhere to various surface features and the concepts of ultrahydrophobic surfaces. A factorial, multi-level experimental design was analyzed and a 2nd order polynomial model was regressed for statistically significant effects and interactions to determine the magnitude and direction of influence on the spore density measurements between factor levels.