by Katie Galloway
Geckos and Mussels Inspire New Wet/Dry Adhesive
The Bible declares that nature reveals God’s workmanship from the beasts of the fields to the stars of the sky. Job implores, “But ask the animals, and they will teach you, or the birds of the air, and they will tell you; or speak to the earth, and it will teach you, or let the fish of the sea inform you. Which of all these does not know that the hand of the LORD has done this?” (Job 12:7-9). Scientists have begun to draw from this well of knowledge by studying designs in nature to inspire solutions to engineering challenges.
Recently, scientists set out to design an improved reversible wet/dry adhesive inspired by mussels and geckos.
Geckos adhere to surfaces with footpads made of foot-hairs called setae that are subdivided into nanoscale spatulae (hair tips). Adhesion is promoted through weak secondary bond forces such as van der Waals interactions and capillary forces.
Previous work on gecko-foot mimetic nanoadhesives demonstrated that the number of reversible cycles that retained adhesion were limited. Wet conditions nearly obliterated adhesion.
In nature mussels readily solve the wet adhesion problem by secretion of specialized proteins containing a high amount of 3,4-dihydroxy-L-phenylalanine (DOPA). DOPA is known to impart increased interfacial adhesion strength when added to natural and synthetic adhesives and to remain reversibly adhesive after many cycles.
Researchers speculated that combining the two naturally derived designs could lead to a reversible wet/dry adhesive with increased strength and longevity. Gecko-mimetic nanoscale pillar arrays were cast from polydimethylsiloxane (PDMS). The pillars were coated with a thin layer of poly(dopamine methacrylamide-co-methoxyethyl acrylate) (p(DMA-co-MEA)), a polymer designed for low-water solubility and high DOPA content. These properties are thought to be important in the adhesive mussel proteins.
The combination of these two adhesive technologies—to create an adhesive termed ‘geckel’—increased the wet adhesion strength per pillar fifteen times over previous gecko-mimetic designs. Geckel also maintained reversibility over many adhesion cycles. Compared to flat designs coated with p(DMA-co-MEA) alone, geckel demonstrated robust performance.
Success that results from the reverse-engineering of natural designs demonstrates that natural systems are endowed with specialized knowledge from which even the most intelligent biological designers can benefit. The engineering solutions found in nature reveal a highly creative and intelligent Designer who endowed his creation with unique properties to function in diverse environments.
The Creator instilled a natural curiosity within humans to explore creation and has commissioned humanity to seek knowledge through understanding nature. Not only does this search bring innovative technologies to society, but it also brings us closer to realizing what the animals already know: “…that the hand of the LORD has done this.”