Matthew J. Vucko

Using textured PDMS to prevent settlement and enhance release of marine fouling organisms

The antifouling efficacy of a series of 18 textured (0.2–1000 μm) and non-textured (0 μm) polydimethylsiloxane surfaces with the profiles of round- and square-wave linear grating was tested by recording the settlement of fouling organisms in the laboratory and in the field by monitoring the recruitment of a multi-species fouling community. In laboratory assays, the diatoms Nitzschia closterium and Amphora sp. were deterred by all surface topographies regardless of texture type. Settlement of propagules of Ulva sp. was lower on texture sizes less than the propagule size, and settlement of larvae of Saccostrea glomerata and Bugula neritina was lower on texture sizes closest to, but less than, the sizes of larvae. After a six month field trial, all textured surfaces lost their deterrent effect; however, the foul-release capabilities of textures were still present. High initial attachment was correlated with most fouling remaining after removal trials, indicating that fouling organisms recruited in higher numbers to surfaces upon which they attached most strongly.

Enhancing the settlement and attachment strength of pediveligers of Mytilus galloprovincialis bychanging surface wettability and microtopography

Surface wettability and microtopography can either enhance or deter larval settlement of many sessile marine organisms. This study quantifies the effect of these surface properties on the settlement of pediveligers of Mytilus galloprovincialis, using polymers spanning a range of wettability and microtextured polydimethylsiloxane (PDMS). Furthermore, the adhesion strength of settled pediveligers on microtextured PDMS surfaces was quantified using a flow chamber. Settlement was enhanced at the hydrophilic end of the wettability spectrum, where mean settlement on nylon reached 33.5 ± 13.1%. In contrast, mean settlement on the most hydrophobic polymer (PDMS) was 4.2 ± 3.2%. Microtopography had a much stronger effect compared to wettability, where 400 μm textured PDMS enhanced settlement above 90%. Settlement preferences were also positively correlated to adhesion strength at flow rates of 4 knots, with all initially settled pediveligers on smooth PDMS detaching, while 79.9 ± 5.7% of pediveligers remained on the 400 μm texture.

Enhancing the efficacy of fouling-release coatings against fouling by Mytilus galloprovincialis using nanofillers.

Fouling-release (FR) coatings minimise the adhesion strength of fouling organisms. This study describes improved technologies to control the settlement and adhesion of the important fouling organism Mytilus galloprovincialis by incorporating the nanofillers titanium dioxide (TiO2) and carbon nanotubes (CNTs) in polydimethylsiloxane (PDMS) matrices. The incorporation of TiO2 prevented larval settlement when photoactivated with UV light, even at the lowest concentration of the nanofiller (3.75 wt%). Notably, there was 100% mortality of pediveligers exposed to photoactivated TiO2. However, plantigrades initially settled to photoactivated TiO2, but their adhesion strength was significantly reduced on these surfaces in comparison to blank PDMS. In addition, plantigrades had high mortality after 6 h. In contrast to the enhanced antifouling and FR properties of PDMS incorporating TiO2, the incorporation of CNTs had no effect on the settlement and adhesion of M. galloprovincialis.

Cold spray metal embedment: an innovative antifouling technology

The study demonstrates that embedment of copper particles into thermoplastic polymers (polymers) using cold spray technology is an effective deterrent against fouling organisms. Two polymers, high-density polyethylene (HDPE) and nylon were metallised with copper powder using cold spray technology. After 250 days in the field, Cu-embedded HDPE and copper plate controls were completely free of hard foulers compared to Cu-embedded nylon and polymer controls which were heavily fouled with both soft and hard fouling. Antifouling (AF) success is related to the interaction between the properties of the polymers (elastic modulus and hardness) and the cold spray process which affect particle embedment depth, and subsequently, the release of copper ions as determined by analytical techniques. Embedding metal using cold spray equipment is shown to be an effective AF technology for polymers, in particular those that are difficult to treat with standard AF coatings, with efficacy being a function of the interaction between the cold spray metal and the polymer recipient.

Optimising settlement assays of pediveligers and plantigrades of Mytilus galloprovincialis

The mussel Mytilus galloprovincialis is a common aquaculture species, and also a major fouling organism that has negative economic impacts. There are no standard assay conditions for this important species and therefore, this study quantified the effect of key factors on the settlement of pediveligers and plantigrades. Density dependent settlement did not occur for either pediveligers or plantigrades. Settlement increased in drop assays in a 12 h light:12 h dark cycle, while bottom shade had no effect of any magnitude. In addition, settlement was significantly enhanced by storing pediveligers for between 4 and 24 days at 4°C. Overall, these data provide the template to optimise and standardise static laboratory settlement assays for mussels in order to develop materials that either enhance settlement for the aquaculture industry, or deter settlement for antifouling applications. Furthermore, simple mechanisms such as storage at 4°C can enhance settlement beyond current methods used in aquaculture hatcheries.

Marine antifouling from thin air.

The dynamic relationship between the settlement behaviour of marine biota (cells, spores, larvae) and the longevity of an entrapped air layer (plastron) on submersed superhydrophobic surfaces was systematically investigated. Plastron lifetime decreased with increasing hydrophobic polymer loadings, and was correlated with the settlement rate of a range of fouling species of varying length scale, motility and hydrophobic/hydrophilic surface preference. The results show that the level of fouling on immersed superhydrophobic surfaces was greater when plastron lifetimes were minimal, regardless of the length scale, motility and the surface preference of the organisms. This is the first direct demonstration of the broad-spectrum attachment-inhibiting properties of a plastron on an immersed superhydrophobic surface.

Combining a photocatalyst with microtopography to develop effective antifouling materials

Polydimethylsiloxane surfaces textured with a square-wave linear grating profile (0, 20, 200, 300 and 600 μm), and embedded with a range of photocatalytic titanium dioxide (TiO2) nanoparticle loadings (3.75, 7.5, 11.25 and 15 wt.%), were used to test the combined efficacy of these technologies as antifouling materials. Settlement of the fouling bryozoan species Bugula neritina was quantified in the laboratory under two intensities of UV light. The lowest settlement rates were observed on 20 μm surfaces. However, texture effects were not as critical to larval settlement as the presence of TiO2. In conjunction with UV light, TiO2 completely inhibited larval metamorphosis even at the lowest loading (3.75 wt.%) and the lowest intensity of UV light (24 W m−2). Recruitment of B. neritina was also quantified in field trials and showed similar results to laboratory assays. The lowest recruitment was observed on 20 and 200 μm surfaces, with recruitment being significantly lower on all surfaces containing TiO2. Therefore for B. neritina, although all TiO2 loadings were effective, 3.75 wt.% can be used as a minimum inhibitory concentration to deter larval settlement and the addition of a 20 μm texture further increases the deterrent effect.

Polyurethane seismic streamer skins: an application of cold spray metal embedment

Cold spray metal embedment is an innovative antifouling (AF) technology that delivers metal particles with AF properties into many thermoplastic polymers. AF efficacy was quantified for low (22.1 ± 4.8 g m−2) and high (101.1 ± 10.8 g m−2) densities of copper particles embedded into polyurethane (PU) seismic streamer skins, which are used in geophysical exploration. Failure of each Cu-embedded treatment was defined as settlement of hard foulers. Low-density streamers failed after 42 days while high-density streamers failed after 210 days. Most importantly, the high-density streamers were completely free of hard foulers including the barnacle Amphibalanus reticulatus during this time period. In conclusion, cold-spray metal embedment is an effective AF technology for PU seismic streamer skins, under intense fouling conditions. Higher copper particle densities enhance AF longevity and the effect of density provides a tool to extend efficacy and enhance AF performance for specific polymers.

The red macroalgae Asparagopsis taxiformis is a potent natural antimethanogenic that reduces methane production during in vitro fermentation with rumen fluid

Livestock feed modification is a viable method for reducing methane emissions from ruminant livestock. Ruminant enteric methane is responsible approximately to 10% of greenhouse gas emissions in Australia. Some species of macroalgae have antimethanogenic activity on in vitro fermentation. This study used in vitro fermentation with rumen inoculum to characterise increasing inclusion rates of the red macroalga Asparagopsis taxiformis on enteric methane production and digestive efficiency throughout 72-h fermentations. At dose levels ≤1% of substrate organic matter there was minimal effect on gas and methane production. However, inclusion ≥2% reduced gas and eliminated methane production in the fermentations indicating a minimum inhibitory dose level. There was no negative impact on substrate digestibility for macroalgae inclusion ≤5%, however, a significant reduction was observed with 10% inclusion. Total volatile fatty acids were not significantly affected with 2% inclusion and the acetate levels were reduced in favour of increased propionate and, to a lesser extent, butyrate which increased linearly with increasing dose levels. A barrier to commercialisation of Asparagopsis is the mass production of this specific macroalgal biomass at a scale to provide supplementation to livestock. Another area requiring characterisation is the most appropriate method for processing (dehydration) and feeding to livestock in systems with variable feed quality and content. The in vitro assessment method used here clearly demonstrated that Asparagopsis can inhibit methanogenesis at very low inclusion levels whereas the effect in vivo has yet to be confirmed.

Assessing the antifouling properties of cold-spray metal embedment using loading density gradients of metal particles

Particles of copper, bronze and zinc were embedded into a polymer using cold-spray technology to produce loading density gradients of metal particles. The gradients were used to identify the species with the highest tolerance to the release of copper and zinc ions. The gradients also established the minimum effective release rates (MERRs) of copper and zinc ions needed to prevent the recruitment of fouling under field conditions. Watersipora sp. and Simplaria pseudomilitaris had the highest tolerances to the release of metal ions. Copper and bronze gradient tubes were similar in their MERRs of copper ions against Watersipora sp. (0.058 g m−2 h−1 and 0.054 g m−2 h−1, respectively) and against S. pseudomilitaris (0.030 g m−2 h−1 and 0.025 g m−2 h−1, respectively). Zinc was not an effective antifoulant, with failure within two weeks. In conclusion, cold-spray gradients were effective in determining MERRs and these outcomes provide the basis for the development of cold-spray surfaces with pre-determined life-spans using controlled MERRs.