The materials science of the strong protein composite threads by which mussels attach themselves to rocks and ships hulls is well known but not yet fully understood. Nevertheless research published in the journal Matter is taking inspiration from these mollusks and looking at how biomimetic materials might be used in cleaning up oil spills or treating contaminated water.
The strength of mussel threads, which can withstand powerful ocean currents and dramatic waves is due in part to the presence of the amino acid, dihydroxyphenylalanine (DOPA). DOPA is very sticky, it can bond tightly to a huge range of materials. Similarly, its chemical cousin dopamine, can bind well to substrates. Indeed, research that showed how dopamine could form a coating on a wide range of substrates has spurred interest in mussel biomimetics.
"Mussels are broadly regarded as a nuisance in marine industries because they will colonize submerged surfaces," explains Hao-Cheng Yang of Sun Yat-sen University, China. "But from another point of view, the robust attachment of mussels on substrates under water has inspired a biomimetic strategy to realize strong adhesion between materials in water." [Wang, Z et al, Matter; DOI: 10.1016/j.matt.2019.05.002]
Research has already shown that materials for separating oil and water can be developed based on this chemistry and might be used in mitigating the environmental damage of an oil spill in a way that was not possible before. Importantly, the researchers suggest that the new generation of biomimetics could be suitable for industrial scale-up a limiting factor with earlier laboratory efforts. Mussels have already inspired advancement in water purification technology to remove heavy metal contaminants, organic pollutants, and even pathogens from wastewater. The focus in this context has been on polymerized dopamine. This material readily bonds to a wide range of contaminants to form aggregated solids that can be filtered out of the water.
There remain challenges to be overcome, however. The nature of the structure-property relationships in the mussel biomimetics, including polydopamine, is not yet fully understood. "Despite simplicity and effectiveness, there are still some inherent limitations," explains Yang. "Alkaline conditions are usually needed to realize the polymerization of dopamine, so it cannot be applied to materials that are unstable under alkaline conditions. Moreover, the deposition of PDA is a time-consuming process - it takes tens of hours to form a uniform coating on most material surfaces."
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase. His popular science book Deceived Wisdom is now available.