On the surface, human beings and barnacles don't really seem to have much in common. Sure, we share a kingdom with them, but they're crustaceans and we're homo sapiens. We've evolved to possess the beautiful gift and curse of consciousness and barnacles, well, they've really perfected the art of sticking to things.
The unexpected biological link between humans and barnacles becomes illuminated by answering a simple question of fluid properties. What fluids, besides barnacle cement, have the capacity to coagulate within a seawater composition? The list is short: blood and semen. Why is this significant to barnacle research? Human blood and barnacle cement don't seem to be related phenotypically (Brian's word), or aesthetically (my word), but genotypically, they are more similar than either of us imagined.
When we suffer an injury resulting in an open wound, whether a cut by knife or a simple knee scrape, we as a humans rely on Human Factor XIII to form a cross-linked meshwork of fibrin to coagulate the blood seeping from the wound. Human Factor XIII is an important element in the stablization of the meshwork of fibrin, which are agrigation of thrombin, the initial coagulate protein. Human Factor XIII increases the stability of the previously existing fibrin-thrombin matrix, connecting thrombin monomers to fibrin monomers across polymer chains, as the picture below illustrates.
Human Factor XIII stabilizing a protein chain (source: Wikipedia)
HFXIII is that thin blue line connecting the blue dots from one polymer chain (one of the linear chains running horizontally), to the little red dot situated diagonally below the big blue in a polymer chain running parallel to the one above it. The sequence of the coagulate proteins (i.e. the thrombin, fibrin polymer chains) allows for cross-linking to occur on a diagonal plane, creating a meshwork that reinforces the bonds existing vertically between the polymer chains.
Basically, HFXIII weaves the parallel polymer chains into a kind of protective biochemical fabric. And tada! human blood clots.
A hot new article in Science Daily, Super Sticky Barnacle Glue Cures Like Clots, suggests that the amino acid sequence making up the cross-linking protein, Human Factor XIII, is remarkably similar, and in some regions, identical, to the adhesive proteins present in barnacle cement. Fascinating stuff! For Rittschof, Dickinson, and Wahl, the researchers conducting the study, this means that barnacle adhesion could potentially be classified as a form of "wound healing."
The biological connection between the parasite plaguing our poor Scarlet and our own bodies really hit Brian and myself pretty hard. We began to re-evaluate the way we had been approaching barnacle-fouling possibilities. Our entire focus on anti-fouling prior had revolved around aggressive chemical compositions of surface coatings. Our main question had been: How could we alter the chemical composition of the surface of the glider? But Human Factor XIII introduced the delicacy of chemical composition into our discussion. If one of the most important factors of barnacle adhesion also exists in a similar biochemical system in our own bodies, chemical composition seems like a delicate thing to be toying with. The biological consequences are now prevalent in our minds...
That said, here's our list for possible chemical bio-fouling techniques as of the moment. They don't look promising:
- monochloroacetic acid
- trypsin-like serine protease inhibitor
Each of these possibilities is unsustainable for their own reasons. Obviously, we cannot coat the glider in urea and send it off into the ocean. Monochloroacetic acid is another liquid substance, and a halocarbon, which tends to be insoluable in water, but is also toxic. Polydimethylsiloxane used to be applied to boat bottom in oil form, but is also highly toxic to the marine environment. And a trypsin-like serine protease inhibitor would prevent the polymerization of fibrin into the first matrix of the diagram above, but couldn't possible be crafted into a material that could be coated on the glider to serve as a bio-fouling agent. So, chemically, we are at a standstill.
But, altering the topography of the surface of the glider itself, not the chemical composition of the coating necessarily, could be a viable bio-fouling option.
Development and Testing of Hierarchically Wrinkled Coatings for Marine Anti-Fouling
This study suggests that altering the topographical surface of a vessel (or vehicle) could be an effective way to prevent bio-fouling up to eighteen months. But, Brian and myself are uncertain as to whether or not this topographical manipulation would actually be something that could be applied to a glider, given the potential drag and piloting issues that could result from a topographically hierarchical surface.
Scott, Oscar, Josh, anyone?? We went on a feverish search for our mentors to ask them about the possible benefits/drawbacks to an option like this, but everyone had mysteriously vanished... very Nancy Drew mystery novel.
Until next time,
Amanda and Brian
[thanks to Kunal for sending me the Science Daily article!]