Confocal microscopy-based goniometry of barnacle cyprid permanent adhesive

Abstract

SUMMARYBiological adhesives are materials of particular interest in the fields of bio-inspired technology and antifouling research. The adhesive of adult barnacles has received much attention over the years; however, the permanent adhesive of the cyprid -the colonisation stage of barnacles -is a material about which very little is presently known. We applied confocal laser-scanning microscopy to the measurement of contact angles between the permanent adhesive of barnacle cyprid larvae and self-assembled monolayers of OH-and CH 3 -terminated thiols. Measurement of contact angles between actual bioadhesives and surfaces has never previously been achieved and the data may provide insight into the physicochemical properties and mechanism of action of these functional materials. The adhesive is a dual-phase system post-secretion, with the behaviour of the components governed separately by the surface chemistry. The findings imply that the cyprid permanent adhesion process is more complex than previously thought, necessitating broad re-evaluation of the system. Improved understanding will have significant implications for the production of barnacle-resistant coatings as well as development of bio-inspired glues for niche applications.

Barnacle biology before, during and after settlement and metamorphosis: a study of the interface

“…The localization of bacteria around the adhesive plaque suggests that bacteria may be attracted to the plaque location via positive chemotaxis. Bacteria surrounding the cyprid adhesive plaque were observed previously (Aldred et al, 2013), which led to the discovery of a lipidaceous barrier to the plaque, covering and perhaps protecting the proteinaceous portion of the adhesive (Gohad et al, 2014), a potential nutrient-rich material for bacteria. By stage 6, the newly metamorphosed juvenile, bacteria were abundant and showed two patterns of viability.…”

“…Confocal laser scanning microscopy was performed as described previously (Gohad et al, 2009(Gohad et al, , 2012(Gohad et al, , 2014Aldred et al, 2013). Most images were taken using the Zeiss LSM 780 inverted confocal laser scanning microscope at Duke University equipped with laser lines of 405, 458, 488, 514, 561 and 633 nm.…”

“…In terms of direct interaction between barnacle adhesives and bacteria on a surface, previous work observed bacteria surrounding the adhesive plaque, which forms during the initial stage of settlement (Aldred et al, 2013), suggesting that bacteria may be attracted to and excluded from the adhesive material. Additionally, it was found that partially metamorphosed juveniles adhere more strongly on biofilm-coated surfaces than on clean ones, but found no difference in adhesion strength for completely metamorphosed juveniles (Zardus et al, 2008), suggesting there may be something important about the interaction with biofilms at specific stages of settlement and metamorphosis for adhesion.…”

“…Mechanisms of barnacle attachment via fluids that undergo curing have garnered scientific interest for applications to control biofouling in industrial (Callow and Callow, 2002;Holm, 2012) and medical contexts (Shivapooja et al, 2013) and bioinspired glues that cure in aqueous environments (Joseph et al, 2011;Kamino, 2013). First, the barnacle cyprid attaches to the substratum via a permanent adhesive, released from cement glands through the two walking appendages, a pair of antennules, embedding them completely, creating an adhesive plaque that anchors them in place (Knight-Jones and Crisp, 1953;Crisp, 1960;Walker, 1971Walker, , 1973Yule and Walker, 1985;Mullineaux and Butman, 1991;Matsumura et al, 1998;Phang et al, 2008;Gohad et al, 2012Gohad et al, , 2014Aldred et al, 2013). The subsequent phases of settlement and metamorphosis for acorn (balanomorph) barnacles involve major changes to the body plan and shape, resulting in a disk-shaped basis parallel to the substratum as a juvenile.…”

Modulation of gregarious settlement of the stalked barnacle, <em>Pollicipes pollicipes</em>: a laboratory study

“…Once the attachment site has been selected, the cyprid secretes a second adhesive that permanently fixes it to the substratum (e.g. Nott and Foster 1969, Walker 1971, Aldred et al 2013. Immediately after attachment, the cyprid begins metamorphosis into the juvenile barnacle.…”