Marine biofouling — the steady accumulation of microorganisms, algae and larger organisms on surfaces exposed to water — is among the most stubborn and expensive problems in shipping, industry and aquaculture. Researchers at Sultan Qaboos University have now reported a materials strategy that combines microscopic surface patterns with nanoscale zinc oxide structures to make it harder for bacteria and microalgae to settle. The findings appear in the journal PLOS One.
The study, authored by Al-Busaidi, Dobretsov, Kyaw and Myint, fabricated zinc oxide nanorod coatings on three differently patterned polymer surfaces, labelled D1, D2 and D3. The resulting materials layered microscale topography beneath nanoscale zinc oxide structures, and the team then measured how well each combination resisted colonisation under laboratory flow conditions.
Why biofouling is a persistent engineering problem
When microorganisms and larger marine organisms accumulate on submerged surfaces, the consequences ripple through entire operations. A fouled hull drags more water, which reduces vessel performance and increases fuel consumption. Corrosion accelerates. Water intakes and heat exchangers can become blocked. Aquaculture equipment is likewise affected, with the same process threatening the hardware that fish farms depend on.
These costs have long driven the search for antifouling materials. Older approaches have proven effective but often at an environmental price, and the field has increasingly focused on durable coatings that limit attachment while reducing environmental toxicity. The Sultan Qaboos University team positions its nanostructured approach within that effort.
How the engineered surfaces were built
The researchers produced zinc oxide nanorod coatings on top of polymer substrates carrying three distinct micropatterns. Scanning electron microscope images documented the geometry of the uncoated micropatterned polymers, along with cross sections for each of the three designs, providing a structural baseline before the ZnO layer was applied.
The design logic rests on combining two length scales. The microscale patterns alter how water and organisms interact with the surface, while the nanoscale zinc oxide rods add chemistry and texture at a much finer resolution. Together, the two levels of structure produced materials that behaved quite differently from plain polymer.
Testing under flow conditions
Rather than relying on static immersion, the team tested the engineered surfaces under laboratory flow conditions. Two organisms served as the primary biological probes: the bacterium Escherichia coli and the marine diatom Amphora sp. Choosing both a bacterium and a diatom allowed the researchers to examine two distinct stages of the fouling process — initial bacterial attachment and the settlement of single-celled algae that help form biofilm communities.
The team also assessed possible acute toxicity using larvae of the whiteleg shrimp Litopenaeus vannamei, a step that speaks to the wider question of whether antifouling chemistry harms non-target marine life.
Wettability shifted dramatically
Applying the zinc oxide coating transformed the wetting behaviour of the patterned polymers. Uncoated surfaces showed water contact angles in the region of 80 to 90 degrees. After coating, contact angles climbed to approximately 150 to 165 degrees, making the surfaces highly water-repellent.
That shift matters because reduced wettability can limit how quickly a liquid film spreads and how firmly organisms can establish contact with a surface. In this study, wettability is treated as one contributor among several rather than the sole explanation for the observed antifouling performance.
Attachment results differed by pattern and organism
The biological results revealed a clearly pattern-dependent effect. Bacterial attachment fell by 60.3%, 48.8% and 5.8% on the coated D1, D2 and D3 surfaces respectively. Diatom coverage, meanwhile, dropped by 9.9%, 72.9% and 71.8% on the same three surfaces.
- D1: strongest reduction in bacterial attachment at 60.3%, but only a 9.9% decrease in diatom coverage.
- D2: moderate bacterial reduction of 48.8% combined with a large 72.9% drop in diatom coverage.
- D3: the weakest bacterial result at 5.8%, yet still cut diatom coverage by 71.8%.
The spread of these numbers is notable. No single micropattern dominated across both organism types: the geometry that best deterred bacteria performed poorly against diatoms, and vice versa. That divergence suggests the two organisms respond to different surface cues, and that pattern geometry is a tunable variable rather than a solved problem.
What is driving the antifouling effect
The authors attribute the performance to a combination of mechanisms rather than one dominant factor. Their explanation includes the release of zinc ions, the generation of reactive oxygen species, the wettability of the surface, and the interaction between the microscale and nanoscale structures.
Zinc ion release and reactive oxygen species are chemical routes that can interfere with attached organisms, while wettability and micro-nanoscale topography represent physical routes that influence whether organisms can anchor in the first place. Presenting these as a combined effect is consistent with the observed variation across patterns — surfaces sharing the same zinc oxide chemistry but differing in micropattern geometry produced substantially different biological outcomes.
Environmental questions remain open
Zinc is not a neutral additive in marine settings, and coatings that rely on ion release raise legitimate questions about long-term exposure in the water column. Including whiteleg shrimp larvae in the testing programme acknowledges that tension directly. What the work does not establish is a complete environmental profile; acute toxicity testing is an early step, not a full assessment of ecosystem effects.
The broader goal, however, is clear: antifouling materials that perform without the drawbacks associated with older chemistries. A coating that pairs physical topography with a controlled chemical component may offer ways to tune performance while limiting the amount of active material required.
What comes next for micro- and nanostructured antifouling
Several questions follow from these results. Real marine environments present far more complex fouling communities than a single bacterium and a single diatom, and fouling develops over months rather than the timeframe of a laboratory flow test. Durability under abrasion, sunlight and repeated immersion will determine whether patterned zinc oxide coatings can survive in service.
Still, the study adds a useful data point to the antifouling literature. It shows that microscale patterning and nanoscale zinc oxide can be combined on polymer substrates, that the resulting surfaces become strongly water-repellent, and that attachment by bacteria and diatoms can be reduced substantially — with the size of the reduction depending heavily on which pattern is used.
For engineers working on hull coatings, intake protection and aquaculture hardware, that pattern-dependent behaviour is the most actionable finding: the design of the surface texture may matter as much as the chemistry applied to it.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
