Biodegradable, renewable biopolymers for protective marine coatings

Marine biofouling is the undesirable accumulation of macromolecules, bacteria and organisms on the surfaces of submerged objects. Biofouling generates massive costs for maintenance and cleaning. In the case of ships, it also increases drag and thus fuel consumption and carbon dioxide emissions.

To combat the overgrowth, ship paints are loaded with biocides which inhibit attachment. To reduce the release of biocides into the ocean, new technologies are emerging which make ships easy to clean and allow ships to shed attached organisms by the shear created when moving through the water.

A new article reports on the anti-fouling and fouling-release properties of polyelectrolyte multilayers consisting of hyaluronic acid and chitosan, both of which are naturally occurring biopolymers. Hyaluronic acid fulfills multiple tasks in the human body, such as lubricating joints, keeping tissue elastic and hydrating the eyes. Chitosan is a natural constituent of crustaceans and known for its antimicrobial and fungicidal properties.

The two biopolymers carry opposite charges, which allowed the researchers to fabricate polyelectrolyte multilayers through a technique called layer-by-layer deposition. The results highlight the potential of these renewable, biocompatible and biodegradable biopolymers and suggest a suitable application as ingredients for protective marine coatings.

Both chemical and thermal crosslinking of the multilayers reinforced the coating against degradation in sea water, but the former technique led to hydrophilic multilayers with superior protein resistance. The protein-repelling properties were investigated by surface plasmon resonance spectroscopy, while the marine antifouling and fouling-release properties were tested against the settlement of zoospores of green algae. The results demonstrated that the multilayers are both effective against protein adsorption and able to counteract the attachment of green algae.

Source: “Layer-by-layer constructed hyaluronic acid/chitosan multilayers as antifouling and fouling-release coatings,” by Wenfa Yu, Julian Koc, John A. Finlay, Jessica L. Clarke, Anthony S. Clare, and Axel Rosenhahn, Biointerphases (2019). The article can be accessed at http://doi.org/10.1116/1.5110887 .