from spiny-headed worms to swellable microneedle adhesive

     My post on Velcro featured a plant inspired attachment discovery, and so it is only fair to counter that with a discovery of animal inspired attachment.

“There are several unmet clinical needs for adhesives to affix connective tissues including tendons and ligaments, to improve contact between tissues to reduce motion of tissue grafts, and to seal tissues for prevention of fluid (intestine) or air (lung) leaks.” (Yun Yang et al. 2013)

     In other words, society is in need of some better glue to secure different types of tissues in place after surgery. I am going to go out on a limb and speculate that surgical adhesive tape is not something many of us think about or use on a regular basis. I would also venture to guess that if one of us were scheduled for surgery, we would hope our surgeon had access to the best of the best when it came time to put us back together. Introducing Pomphorhynchus laevis, a spiny-headed worm that makes it’s living as an intestinal parasite of fish. The common name of this parasite, the spiny-headed worm, starts telling the story all on its own. To attach to a host, the worm embeds its spiny head into the intestinal lining of the fish. The head then starts to swell, preventing it from going backward, and the worm is anchored in place. Herein lies the story of an unknown fish parasite and its rise to fame as it walks the red carpet with swellable microneedle adhesives, sort of.

Image credit: Verweyen et al. (2011), Figure caption: (E) Habitus of Pomphorhynchus laevis from Platichthys flesus (Baltic Sea) shows [m]any trunk hooks on bulb, neck and trunk. Scale bar = 100 µm.

      I wanted to start our story with the original species description of Pomphorhynchus laevis (which can be abbreviated P. laevis from now on). A species description is a published narrative describing how one species is morphologically distinct from close relatives. The purpose of a species description is to anchor a name, an actual specimen of that species (known as the type specimen), and its morphological characteristics all in one publication. For example, if we think of our own species, Homo sapiens (genus Homo, species sapiens), the existence of a species description helps us classify newly discovered Homo skeletons. Are they members of our own species, Homo sapiens? Do they belong to an already described species such as the extinct Homo habilis? Or, is it a new species that has yet to be described? In fact, just last year scientists described a new species of Homo, Homo naledi, discovered near Johannesburg, South Africa. In order to identify what species the new skeleton was, scientists had to make comparisons with other Homo species using their species descriptions, and then make a case for why it was different. This can be controversial. We had enough controversy after last week though, back to parasites. In order for parasites to inspire, they first need to be discovered, named, and described; and then pursued with further investigation to see how they attach to their hosts.

     In the original publication introducing the efficacy of the swellable microneedle adhesive, the authors cited P. laevis as the inspiration for their swellable adhesive (often referred to as a biphasic adhesive, which just means two phases. Unswelled, or flaccid. And swelled). This was based on scanning electron micrographs they found when searching for parasite inspiration on the Google. But, the paper they actually reference for the worm attachment mechanism was for a different species, Acanthocephalus ranae. I emailed Jeff Karp, the corresponding author of the paper, to ask about this and he said they were inspired by the idea of swelling as a way to establish an anchor, which is used by many of these species (both are close relatives in a more inclusive group of organisms, the Acanthocephala). And, like me, they found an intriguing image of P. laevis but probably could not a find a citation for it’s attachment mechanism, and thus cited the mechanistic description of A. ranae instead.

     That may be more straightforward for our story too. In my investigation of P. laevis I found a discrepancy as to who originally described the species. Some papers cite Müller 1776 but the ITIS (an authoritative reference) lists Zoega 1776. All right already, I know I am getting very detailed about names, but this will be important and interesting as we march though a variety of discoveries so I am not editing it out. Names are important, they are the only way we can track things through time. An unnamed species is an unstudied species. At this point though, I am thinking our swellable needle story might need to be told in two parts, because you are probably losing your attention span for parasites at this point.

     Stick with me just a little longer. Acanthocephalus ranae was described by Schrank in 1788. After a little digging online I am very curious about what kind of person Schrank was. What was his life like? Why was he describing parasite species? (And not just one, it looks like there were many.) His full name was Franz von Paula Schrank (1747-1835). (Just to reinforce the importance of names, try typing Schrank into Google. Now try typing Franz von Paula Schrank. Much better.) Schrank was a German multi-tasker and is classified as a priest, zoologist, and botanist. He authored many books, all of which are old, and in German, so I am a little stumped on their content, but I did translate the titles using Google translate. Most are natural history accounts with beautiful illustrations focusing on insects, plants, and parasites. It looks like there is just one book on parasites: Verzeichniss der bisher hinlänglich bekannted Eingeweidewürmer, nebst einer Abhandlung über ihre Anverwandtschaften (Google translate: Directory of previously well bekannted intestinal worms, together with a discussion of their Anverwandtschaften), and there are only three copies worldwide. Might be a little difficult to get my hands on one. However, in 1981, Annette Zimmerman wrote a dissertation on Schrank, “Franz von Paula Schrank (1747-1835): Naturforscher zwischen Aufklärung und romantic” (Google translate: Naturalist between Enlightenment and Romanticism) that I would love to see. It is actually at the Stanford Library (QH31.S34 Z55), and I will be close to Stanford in March so I am going to try and get a look at it. We are going to learn about Schrank. But everything is in German. So it may not be soon.

Image credit

      Okay, done for today. Next week we are going to delve into the world of R.A. Hammond, the scientist who performed detailed studies on A. ranae to figure out how it attached to it’s host intestinal lining. After some searching I have not been able to find out much about him, including first name. That’s okay though, because what I would really like to do is spend some time exploring how he studied the attachment mechanism of parasitic worms, and how his studies relate to the discovery of microneedles. And there is actually a lot more to talk about with regard to the actual microneedles themselves, and the variety of tasks they have been able to accomplish since their invention.