The insect cuticle: (1) multi-functionality

This post is part of a series on the insect cuticle as a biological material that can inspire novel engineered materials. The characteristics of the cuticle, setting it apart from most synthetic/engineered materials, will be discussed in this series. The introduction to the series can be found here.

Cellular and acellular layers make up the insect cuticle. With the most interior layer being comprised of living epidermal cells that secret the outside layers, which then completely cover the insect – even some of the interior surfaces such as the trachea, foregut and hindgut – are lined with cuticle. (The hierarchical characteristics of these layers will be discussed in the next post.). One of the characteristics that makes the insect cuticle, an “inspirational” biological material is its multi-functionality – something that is rarely seen in engineered materials.

Living materials, including the insect cuticle, often exhibit novel properties that are difficult to incorporate (all at once) into engineered materials. Unique physical and chemical interactions of the biomolecules that make up the cuticle (building blocks) at the nanometer scale convey characteristics such as high strength, energy absorption, and flexibility. Currently multi-functionality in engineered materials is limited to different functions due to a hybrid of several distinct phases the material can attain.

Below I have sketched out some of the functions of the insect cuticle. (If I forgot some important functions please leave a comment below and I will add them to the diagram)

insect cuticle functions

Insect Cuticle Functions – probably not complete – click on diagram to enlarge.

Insect Cuticle Functions

Protective Barrier

The insect’s exoskeleton/cuticle/integument is doing the functions of both our skin and our bones. The cuticle completely covers the insect (~armored skin), while at the same time serving as a supportive skeleton (~bones).

The protective covering creates a barrier. Precious water and ions are prevented from freely moving outward, while pathogens, parasites and dangerous chemicals are prevented from moving inward. This function is not at all trivial for insects. Since insects are relatively small they present a large surface area to the outside environment so that loss of water is a greater problem than it is for larger animals such as mammals.

Structure and Form

The insect’s exoskeleton gives the insect structure and form. And over an individual’s lifetime that form can change. In the case of holometabolous insects, such as flies, wasps, bees, beetles, butterflies and moths, this form change is striking. As an immature caterpillar a moth has a cuticle that stretches and is relatively soft, as a pupa the same individual (using the same building blocks, or biomolecules) has a cuticle that is extremely tough and does not change shape easily. Then as an adult moth the cuticle, including the wings, has yet other features that make the insect successful.

The change in structure and form seen in holometabolous insects, and to some extend the growth strategies employed by ametabolous and hemimetabolous insects, enables the animal to exploit different habitats and diets – even during its lifetime.

This is one of the most striking things about the cuticle. During the separate life stages the cuticle has different functions, it therefore has distinct characteristics and appearance. Yet, the biomolecules that make up the cuticle are pretty much the same, and one individual can synthesize all these seemingly very different types of cuticle.

How different is the cuticle from life stage to life stage? I asked family, friends and colleagues to describe, in non-scientific terms, what the cuticle of each form of the hornworm (=moth) feels like. Here are their responses.

Caterpillar or Larva

CaterpillarDrawing

Caterpillar (Drawing by Marianne Alleyne)

Soft, rubbery, squishy, velvety, muscular, cold. Feels like pleather, like a writhing rubber pickle, like play dough that I rolled in my hands to make a snake.

Pupa

PupaDrawing

Pupa (Drawing by Marianne Alleyne)

Hard, smooth, leathery, acrylic, slick. Feels weird & dead.

Adult

Adult Moth (Drawing by Marianne Alleyne)

Adult Moth (Drawing by Marianne Alleyne)

Fuzzy, hairy, soft. Feels like perfumed talc from my grandmother’s vanity. Holding it will probably feel like a fluttering beakless bird but since I haven’t held a fluttering bird, with or without a beak, I can’t be sure.

Movement

The rigidity that the exoskeleton exhibits makes it possible that insects can make rather precise muscle movements since those are due to the insertion of muscles to the integument wall. It is often the cuticle that has important biomechanical features that enables an insect to run, jump, dig, fly or swim. These precise movements are also essential for respiration (creating flow of air in and out of the tracheal system), food manipulation, excretion and osmoregulation.

Sensing the Environment

Maybe surprisingly a rigid integument is not necessarily limiting awareness of the surroundings. The cuticle has been modified in many insects into structures that can sense most of the modalities that we can sense with our skin. Some examples are the trichoid sensilla, the campaniform sensilla and chordotonal organs. Note that all three of these sensors use the cuticle as an integral part of their structure.

The functionality of the trichoid sensilla - a mechanosensory hair - is dependent on the rigidity of the cuticle.

The functionality of the trichoid sensilla – mechanosensory hairs – is dependent on the rigidity of the cuticle. (Drawing by Marianne Alleyne)

The campaniform sensilla is a mechanoreceptor found in insects. When the exoskeleton bends the resulting strain stimulates the sensilla.

The campaniform sensilla are mechanoreceptors found in insects. When the exoskeleton bends the resulting strain stimulates the sensillum. (Drawing by Marianne Alleyne)

The chordotonal organ is a stretch receptor that senses to what degree the cuticle is being deformed. This deformation can then give information about movement of body parts, gravity (proprioception) and vibrations of the surrounding air (hearing).

The chordotonal organ is a stretch receptor that senses to what degree the cuticle is being deformed. This deformation can then give information about movement of body parts, gravity (proprioception) and vibrations of the surrounding air (hearing).

Energy Storage

For many insects the cuticle also represents a temporary food store. The basic building blocks, to some extend, can be withdrawn during times of nutritive stress. Having to molt to be able to grow in size is one of the drawbacks of having an exoskeleton. Molting consumes time, energy and metabolic resources, and makes the insect vulnerable against pathogens, predators and water loss.  Reabsorbing much of the cuticle during molting minimizes some of these costs. (The closed-loop cycle characteristics of the cuticle will be discussed in part 8 of this series.)

Behavior Modulation

The single layer of epidermal cells that secretes the cuticle also secretes and deposits within or on the cuticle hydrocarbons that are involved in behavioral sequences that are important in recognition and mating. Pheromones and pigments are also deposited. The cuticle may also have modified structures that are important in mating or other behavioral processes – such as bumps,  hairs, nano-scale structures that create structural colors.

By further studying the insect cuticle it is my hope that new materials can be created, using similar “manufacturing” steps as employed by insects, that can provide increased function through integrated or further-integrated systems. Insects do it, we should too.

Next: the structural hierarchy of the insect cuticle.

(My apologies to dumpy grey-brown moths everywhere. That is a terrible drawing of an adult moth. Oh, well)

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Insects have advanced degrees in Material Science and Manufacturing

There is much to learn from nature about biological materials – materials produced by a biological system. Just think about the materials in nature that you are most familiar with: wood, wool, cotton, shells, skin….consider:

  • Animals and plants are constructed from materials that are readily at hand – no dangerous mining endeavors in geo-politically sensitive areas. Sea shells are made from materials available in the sea water. Bone is made from components available in our (and our mother’s) diet. Insect cuticle is synthesized from maternal sources and from the individual’s diet.
  • The materials found in nature have many of the same attributes as engineered materials, yet avoid the heat-beat-and-treat manufacturing methods that are so costly to us and our environment. We manufacture materials by applying large amounts of energy so we can first homogenize materials, then add even more energy, and dangerous chemicals, to impose the structure that we want.
  • The periodic table categorizes more than 100 elements. Although around 25 types of elements can be found in biomolecules, only six elements are most common. These are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Few metals are used by nature, although iron, zinc, and manganese are essential in various ways.

PeriodicTable6If you create and then overlay* Ashby plots of biological and engineered materials you will learn that nature has many more tricks up its sleeve than we do. Insect cuticle is very similar to skin and bone, and some of the engineered materials, it is also ubiquitous, yet we know still so very little about it.

Collection of live and preserved insects hanging out in the Alleyne-lab. All insects have a cuticle with the same basic building blocks. But the cuticle of different species, or even different life stages, differ in hardness, flexibility. permeability, color, etc. (Photo: Marianne Alleyne)

At first glance the structure that is a characteristic of insects and other arthropods, the cuticular exoskeleton, seems such a simple yet sophisticated material. Upon closer inspection it is actually maddeningly complex and enigmatic, just ask any researcher working on it (needless to say, there aren’t too many). The chemical analysis of the insect cuticle is a frustrating undertaking.  Perform any manipulation to isolate it and “voila” the structure in which you were interested has been changed. The cuticle has been described by biochemists as “intractable.” It is possible to (partially) dissolve cuticle in various solvents and analyze the results, but the results are quantitative, both because it is not easy to break apart the assembled materials, but also because chemical transformations can occur during the process of dissolution. In the future multidisciplinary (including molecular) approaches may give us more insights into the exact composition of different types of cuticle. Maybe we will soon learn ‘why some bugs go “squish” when you step on them, but others go “crunch” even though they made out of same material’

As an old seasoned insect physiologist I am still amazed by the insect cuticle since it can have varied structure at the meso-level (allowing insects as a group to live out many life histories), yet the basic (nano-, micro-) structure and components of the cuticle are not numerous or terribly exotic. The insect cuticle is all around us, it is what makes the insects so successful.

The cuticle is produced at atmospheric pressure and at temperatures that are not extreme. Simple building blocks, mainly chitin, proteins and water, make up the insect cuticle. It can have many different features and characteristics just because the building blocks occur in different ratios or orientations. Large amounts of the cuticle are recycled by the individual insect itself, and the remainder can easily be broken down by other life forms.

Can we humans manufacture such an amazingly versatile material in a similar manner?

To manufacture anything close to the insect cuticle we need to understand the characteristics of the material. The characteristics of biological materials, that set them apart from most synthetic/engineered materials, were recently defined and listed by Meyers et al. (1). (The closed-loop cycle characteristic of the cuticle is rather unique to arthropod cuticle and should be added to the list when considering the insect cuticle).

  1. Multi-functionality
  2. Hierarchical structure
  3. Self-assembly
  4. Hydration
  5. Mild synthesis conditions
  6. Self-healing capabilities
  7. Closed-loop cycle
  8. Evolutionary and ecological constraints

Over the next few days/posts I will discuss each characteristic as it relates to the insect cuticle. At the conclusion of the series I will discuss how they all combine and result in the interesting mechanical properties of the insect cuticle, and how cuticle-inspired materials might become useful.

*Feel free to contact me for Bioinspiration learning module using Ashby plots.

References:

  1. Meyers, M. A., J. McKittrick & P-Y Chen (2013) Structural Biological Materials: Critical Mechanics-Materials. Science V339, pp 773-779. DOI: 10.1126/science.1220854

Next: the multi-functionality of the insect cuticle.

#EntSoc13 – One for the record books.

This post is not about Bioinspiration. Instead it is about the “service” part of my job. Read the post if you are interested in the Entomological Society of America, otherwise please stay tuned. Another bioinspiration-related post will be posted soon. There is a plea for symposia-ideas for the International Congress of Entomology in 2016 related to Insect Bioinspiration and Insect Biomechanics at end of this post.

I really love my primary professional society. I have been a member of the Entomological Society of America for almost 20 years now, and I have seen it go through changes – most of these changes resulting in a more inclusive and vibrant Society. Ever since my student-days I have tried to be involved within the leadership of the society; as Section leader of my section (first called Section B-> then the poorly named IPMIS-> and now PBT, Physiology, Biochemistry and Toxicology) and currently as a member of the Program Committee for the Annual Meetings.

How does one get to organize the arguably premier entomological conference? Hum, well, what happened was that my PhD advisor, Robert N. Wiedenmann, was elected president of the Society a few years back. I greatly admire Rob, he is one of my favorite people, so I may have, inadvertently, told him that I would do anything to help him make his term successful. Guess who called me back a few weeks later to ask me to serve as one of “his” Program Committee Co-Chairs for the Annual Meetings in Austin in 2013? Of course I said yes, also because the other co-chair Luis Cañas (the Ohio State University) has been a long-time friend. We were going to give the Society an international flair – with Central-American-Western-European-Midwestern sensibilities.

What does it mean to be on the Program Committee? Well, it is basically a 3-year commitment.

The first year you sit in on bi-weekly conference calls and you listen to the current Program co-chairs organize “their” meeting. You take LOTS of notes, and you try to ignore the increasing panic becoming obvious in their voices. During that first year you are also in charge of organizing the Student Competition, which means that at the summer meeting (held at the site for the Annual Meeting) you start badgering the Section Leadership (president and vice president) for names of moderators and judges, and try to figure out where the heck you are going to put all the sessions. No matter how organized you are, how supportive the ESA staff, the week before the Annual Meeting you are going to have missing judges – so this is where you start calling in favors and shaming people to “volunteer”. (This issue is worth a whole different post, and upon reflection this was my least favorite part of my term on the Program Committee). By the way this is where you sign up to volunteer for ESA.

The second year you get to put the program together.

  • Early on in the year you ask for Program symposium ideas. We had about 20-plus ideas to choose from, but we picked 6. The official theme for the meeting was “Entomology in a connected world” and so the topics for the Program symposia had to fit that theme. Our own motto was “inclusiveness and diversity”, we picked symposia that individually, and also as a group, reflected the motto. Diversity in topics, inclusiveness of sections, diversity of organizers and speakers, etc.. Then later in the Spring we picked Section and Member symposia, pretty much using the same criteria. We tried to have the conference as a whole reflect diversity and inclusiveness, it became more of a driving force, which meant that we were forced to turn some of the poorly developed proposals away. But that was a good problem to have.
  • The month before the summer meeting in July we had all the symposia picked and we knew how many posters and ten-minute papers (outside of the symposia) to expect. We started to divide up the symposia and assigned them to dates. we tried, as best we could, to incorporate peoples requests (for tech needs, for instance). We tried to have little overlap in topics. This can be difficult. For instance, the two most popular symposia topics across Sections were pollination and microbiomes. Both topics are relevant to multiple sections, meaning that members from one section do not want to miss symposia in another. Tricky stuff.
To organize all the symposia I went back to basics and used sticky notes. Top left shows me dividing up the P-IE, and bottom right shows my son entering info into ConFex.

To organize all the symposia I went back to basics and used sticky notes. Top left shows me dividing up the P-IE, and bottom right shows my son entering info into ConFex.

  • At the summer meeting we proposed our choices to the Section leadership. Mostly they were happy with the assignments and luckily pointed out a few conflicts which were then fixed. The most difficult part of the summer meeting can be the division of the available meeting rooms. It is Section Leadership who have to decide together in what part of the conference center a particular Section will hold most of its presentations. As you are probably well aware there are prime-areas in conference centers, and then there are not such great rooms. Luckily the Section Leadership worked together very well and and decided on a workable division quickly. Section leadership spent the remainder of the 2 days spell-checking submissions, finding moderators, and contacting potential judges and moderators for the student competitions.
The Program Committee hard at work during the Summer Meeting. Top left - assigning symposia to rooms. Top right - ESA staff entering choices into ConFex. Bottom - sifting through all the submissions looking for duplicate entries, spelling mistakes, etc.

The Program Committee hard at work during the Summer Meeting. Top left – assigning symposia to rooms. Top right – ESA staff entering choices into ConFex. Bottom – sifting through all the submissions looking for duplicate entries, spelling mistakes, etc.

Left: Program Committee of #EntSoc13 at Summer Meeting in Austin. Right: The people who make the meeting go smoothly Tori D. (ConFex), Cindy M. (ESA) & Rosina R. (ESA).

Left: Program Committee of #EntSoc13 at Summer Meeting in Austin. Right: The people who make the meeting go smoothly Tori D. (ConFex), Cindy M. (ESA) & Rosina R. (ESA).

  • The rest of the summer is a blur. This is when you have to field the complaints for assignments from members (1% of the membership takes up 90% of your time), and resolve timing/room conflicts. You have to double check that all the functions are accounted for. This is also when we distributed the Program Enhancement Funds, a difficult task because the need is great but there is never enough money. …..And….most of my twitter followers know what is coming….during the summer had to deal with the Common Names Index. Lets just say, people like to make sh*t up. Also, people have a difficult time spelling “Coleoptera”, even people who work on “Coleoptera” (See archived tweets in this section, and at the end of this post). I can proudly say that I saved a lot of trees because I spent most of my summer, while traveling by rail through Europe, to reduce an unedited 20+ page index to just over 3 pages. Surprisingly, I would rather create the many time tables in the front of the program book than do that task again. I will spend a lot of time over the next few months working with ConFex and the current Program co-chairs to make this onerous task more pleasant.
  • After much proof-reading (Honestly? not really, because at this point any spelling mistakes were in my opinion the responsibility of the submitter – I am looking at YOU, submitter) – the Program was finally done early on in the Fall and ready to be printed. This has to happen so early because type-setting, printing and shipping actually takes a long time. And then after all is finished, then the cancellations start pouring in. Of course. So here is a lesson for when attending an Annual Meeting, start relying on the mobile app more, that is where the changes are reflected in a more modern age fashion.
  • And then for 2 months or so you just wait, and wait, and wait, and you live with this feeling that you have forgotten to do something very important. But ESA staff is so incredibly competent, they seemed to have everything under control. So you wait for the shoe to drop.

And then, the meeting just starts, happens, and ends. And all the while you just bask in the glow, because the ESA staff has everything under control.

ESAstaff3

The awesome ESA staff. They make the meeting run smoothly.

The third year you that you serve on the Program committee you still attend the conference calls, the summer meeting, and you are in charge of the Poster sessions. But your primary purpose is to serve as a wise sage to the new Program Committee Chairs and Student Competition Chairs. A lot less work is involved, and you get to go more sessions, talks and posters at the Annual Meeting. Or at least that is what I think you do, guess I will find out next year.

As you might have heard by now the meetings were a big success. We had a record registration of almost 3500 entomologists, we had a record number of symposia and talks. Some of the things I am most proud of that we accomplished:

  • From the beginning of putting the Program together we had diversity and inclusiveness in mind. When soliticiting symposia ideas we included in the announcement that organizers should keep the same criteria in mind. Many symposia organizers (close to 50%) were female. I cannot think of one symposium that only had male speakers, which was a common occurrence when I was a graduate student.
  • President Wiedenmann included this mindset in his communications to the society. His “Ethics” essay for “Articulated Segments” was promted by another society’s study on inclusivness on women. I was only one of the people that pointed this issue out to him and asked him to address it from an ESA standpoint – it felt good to realize that those in power actually listen and appreciate input on challenging issues.

It is important that we “do the right thing,” looking out for each other and ourselves and, importantly, holding each other and ourselves accountable. As a professional society, we need to have clear policies, and we must be willing to act when ethical transgressions are found. Not necessarily to act swiftly, but to act fairly and boldly. –  R.N. Wiedenmann, President of the Entomological Society of America

  • Just prior to the Annual Meetings the other work-related community I care much about, the science communication community, just kinda seemed to implode. Much of the issues raised did not speak to me directly, but I did think that as organizers of a big meeting we could not ignore it. ESA was aware of the issues and agreed to take action promptly. Quickly they put up a no-harrassment policy onto the main page of the Annual Meeting website*, and the ethics and Governing Board considered a strongly stated ethics statement about harassment. This is no longer your good ol’ Entomological Society of America. Bravo!

Harassment of ESA participants of Entomology 2013 will not be tolerated in any form. Harassment includes offensive verbal comments related to ethnicity, religion, disability, physical appearance, gender, or sexual orientation in public spaces, deliberate intimidation, stalking, following, harassing photography or recording, sustained disruption of talks or other events, inappropriate physical contact, and unwelcome attention. Participants asked to stop any harassing behavior are expected to comply immediately. Retrieved from the http://entsoc.org/entomology2013 website.

Things I hope to help improve:

  • Incorporate non-standard symposia into the program. For instance, shorter traditional sessions, which then move into ten-minute papers and posters. Our new Society President – Frank Zalom has charged the new Program Committee to make this happen.
  • Child care at the meeting is important to many of our members. The Society has tried formal childcare, but it was far too expensive for the number of people using it. I think the society can be of assistance with informal childcare options that includes a virtual discussion board where people can set-up a childcare cooperative arrangement, as well as a parenting room where children can play and sleep.
  • I plan to encourage more people from under-represented groups to participate in serving the society at different levels. It can be very rewarding. My favorite part is that I get to spend more time with old friends but also make new ones, often people who are in completely different research areas as myself. It is key to find financial support for people in non-traditional academic or professional jobs to take on a committment to serve the society. In my case I do not have grant that can help me pay for registration, hotel and travel, and my Department has not given me financial support either (Granted, I have never asked). I can imagine that the very people that we want to attract to take increase diversity in leadership positions might have a difficult time to make such a financial commitment.

Serving on the Program Committee is a big commitment. It requires time away from your academic job, from family, and it costs money since you are committed to pay registration and travel and hotel to all three Annual Meetings. No, “I think I’ll skip this year and send my grad student”. (NB: travel to summer meetings and hotel are paid for by ESA)

I am glad that I was able to serve the Society as Program committee co-chair. I learned a lot, especially about the Society itself. The Entomological Society of America has many members, all from different backgrounds and with different reasons for why they are members and why they attend Annual Meetings. I myself often feel different from my entomology colleagues because of my non-traditional job description and my research & teaching interests, but being this involved in the ESA’s functioning always makes me realize that none of us really fits in a neat box – thank goodness! After almost 125 years the Society is strong and yet not content with the status quo. And because I am a glutton for punishment, I am also involved in the Program Committee for the 2016 International Congress of Entomology to be held in Orlando. (Please consider submitting symposia topics on Insect Bioinspiration and Insect Biomechanics – contact me!).

And then there were these reasons:

  1. Ten pounds of candy.
  2. Good friends.

As promised:

Below are my archived tweets from the Common Names & Program Book Index saga. I love how you can just see that I get pissier and pissier over the course of a few months.

So meta: A blog post about my poster about blogging.

Last week I attended the Annual Meetings of the (other) ESA in Austin, TX. Actually, I kinda helped organize that meeting. (More about that in my next post, which will focus on my time on the Program Committee.)

When I first submitted the title for the poster in June I had only just started this blog and I thought it would be a great idea to cover the numerous posts I would have written by November.

So, yeah, about that….

Still, it was a great exercise to go through and it helped keep me sane during the weeks leading up to the meeting.

ESA13PosterGrab

Click here for the pdf version of the poster

Below is a picture of what it looked like at the conference. I was unable to spend much time with it since the official social hour for the poster session was right at the time of various committee meetings (obviously poor planning on the part of the Program Committee). Judging by the bump in views at my blog some people did find it interesting.

As I mention on the poster, social media has enriched my scientific life. One of the best parts of the meeting was therefore to meet, or catch-up, with some of my ento-tweeps. (Bummed that I had to miss the “official” tweetup).

One of my major “accomplishments” as Program Co-Chair was to get ESA to provide these twitter stickers for name-badges:

Even people not at the conference were represented via a Twitter fall (The stream did not always work correctly, something to improve for next year.)

For more details on why twitter (and, in my opinion, other social media outlets) can be useful to entomologists please read @derekhennen‘s take at EntomologyToday.

To end this short post I’ll just include a tweet from @bug_girl because it reflects my sentiments exactly! Ento Bloggers Rule!

The termite mound: A not-quite-true popular bioinspiration story

The termite mound: A not-quite-true popular bioinspiration story

I traveled extensively over the summer; to Austin, TX, all through Western Europe and back to Illinois. All the while I was working on this blog post about bioinspired air-conditioning, which was appropriate because everywhere I went I seemed to have to suffer through heat-wave after heat-wave.

While wishing for Europe to have more air-conditioning units (especially in class-rooms and lecture halls), one of course wonders if that would only exacerbate the problem and make summers even hotter. Progress is constantly being made on making air-condition units more compact, more energy efficient, and thus more environmentally friendly. Inspiration on how to accomplish this has been already been found in natural systems.

Recently Brian Clark Howard wrote an interesting and popular article for National Geographic entitled: “5 Natural Air-Conditioning Designs Inspired by Nature”. Arthropods (termites & ticks) were prominently represented on this list. However, I would like to provide a little bit more detail and corrections to the NG’s list.

The insect examples touched upon in the NG article is that of the termite mound. The most famous architectural example of biomimicry or bioinspiration is the Eastgate Centre Building in Harare, Zimbabwe, which opened in 1996. Architect Mick Pearce and the firm Arup were supposedly partly inspired to build a building suitable for a tropical climate by considering the locally present termite mounds, and build their vision using locally available materials.

Eastgate Centre (with chimneys on roof) in Harare Zimbabwe. (Source: wikipedia.org. Unknown potographer)

Eastgate Centre (with chimneys on roof) in Harare Zimbabwe. (Source: wikipedia.org. Unknown photographer)

Anyone who is even the slightest bit interested in biomimicry knows of the Eastgate Centre, but since the political and economic situation in Zimbabwe has probably only deteriorated since 1996 I was wondering if it was actually still standing and still used as the commercial center it had been envisioned as.  So I took my questions to Twitter: [View the story “EastGate Building Harare, Zimbabwe” on Storify]. Turns out that the Eastgate building is still used and stands out prominently in the heart of Harare (and as @ardeans pointed out the building is located right on Robert Mugabe Road, sigh). One of the occupants is actually the United States Embassy.

It is just kind of too bad that the building is based on incorrect biology. Or is it?

First a little bit of background about the inspirational insect. Macrotermes termites (Macrotermitinae) occur over tropical Africa and Asia. There are about 330 species in this genus of relatively large termites. Most of the species build elaborate mounds. The tallest mounds occur in Africa (max of 30 feet, 9 meters). Macrotermes termites cultivate fungi, and spend most of their time, somewhere deep within the mound. The Macrotermes species that has been studied the most is the African species M. michaelseni.

Termite Mound

Flickr user Potjie uploaded this picture of a termite mound in Northern Namibia. (http://www.flickr.com/photos/potjie/3408013097/)

Popular wisdom says that in order to optimize fungus growth the interior of the mound needs to be maintained within the narrow range of 29-32°C. To keep keep within this narrow temperature range, despite of fluctuating temperatures during the day- and night time, the large mounds are not just heaps of dirt but in fact incorporate elaborate ventilation holes and air ducts and air pockets, which drive natural ventilation through convection. And remember, these structures are build by a million tiny insects that behave in an organized manner to come up with an architectural masterpiece, every time.

So no wonder that Mick Pearce, born and raised in Southern Africa, was inspired by the the termite mound to design a building in tropical Harare that would have similar features.

Up until recently two models for the termite mound function were proposed and commonly accepted. In case of mounds that were capped a “thermosiphon flow” was created – basically hot air created by the nest rises to the top of the mound where it gets refreshed and is supplied with water vapor through the porous mound walls. This denser air then is forced down below the nest, where the cycle is repeated.

2013-09-04 08.40.10

Thermosiphon flow model in which ventilation is driven by heat. (Drawing by Marianne Alleyne, based on Turner & Soar, 2008)

The second model applies to mounds that have a chimney at the top of the mound that opens to the outside. This arrangement creates induced flow, also called the stack effect. The chimney breaks the surface boundary layer and is exposed to higher wind speeds compared to inlets on the ground. The unidirectional flow draws fresh air from near the ground into the nest, where it passes on through the chimney and ultimately to the outside.

2013-09-04 08.40.20

Induced flow model in which ventilation is driven by wind. (Drawing by Marianne Alleyne, based on Turner & Soar, 2008)

The architects who designed the Eastgate Centre building tried to incorporate both the thermosiphon and induced flow principle into their design. The building has an extensive tube system within the walls and floors that move air trough the building. Heat generated within the building, along with stored heat within the structure, creates a thermosiphon-effect that draws air up and through the rooftops where large chimney stacks are located. These tall stacks are essential for creating an induced flow.

Detail of tube system within Eastgate Centre building.

Detail of tube system within Eastgate Centre building’s walls and floors (Original picture at http://harare.usembassy.gov).

When popular stories about the Eastgate Centre building say that the building works on the termite mound principle they ignore the fact that the building uses low capacity fans during the day, and high capacity fans during the night to keep the air from being too stagnant, effectively replacing the hot air that builds up during the day with cool air during the night. This works well, and avoids having to use expensive air-conditioning technology, but needless to say, no termite mound utilizes fans.

DayNight

The use of fans within the Eastgate Centre. Smaller fans run during the day-time hours (left). They keep the environment within the building comfortable while the walls store the heat from the outside. Larger fans run during the night-time (right), these fans pull the stored heat out of the walls and push the heat out through the ducting in the ceiling and walls. By the next morning the walls are ready to again store heat (Drawing by Marianne Alleyne).

Since 1996 the common assumptions about how termite mounds are ventilated has been refuted by researchers J. Scott Turner and Rupert C. Soar. And they do it (the disproving) in such a polite manner! (see Conference paper, Flash presentation, YouTube video).

Turner and Soar actually measured temperatures in and outside of the mound. It turns out that while termites may be able to dampen temperatures during the day the nest itself actually closely tracks the soil temperature, which ranges from 15 degrees C in the winter and 31 degrees C in the summer. Mounds have clearly a large thermal capacity, but their architecture, their infrastructure, and their ventilation have little to do with the internal temperature at any given time.

Nest temparature (blue) and ground temperature at 1m depth near nest (red)

Nest temparature (blue) and ground temperature at 1m depth near nest (red) Drawing by M. Alleyne based on Tune r& Soar, 2008))

In addition, whereas induced flow might work well in tall buildings because the likelihood of a boundary layer gradient between locations is pretty high, it has been shown that induced flow rarely operates in termite mounds, even open-chimney mounds, since they are commonly only about 6 ft tall. There is also no evidence that mound ventilation and nest ventilation are indeed linked. How respiratory gases are moved from the nest to the mound, and fresh air from the outside, through the mound, to the nest, is not well understood.

Now the Eastgate Centre, and other large buildings since then, accomplished what they set out to do – they saved in construction costs (HVAC systems are very, very expensive) and they save on operating costs, all while keeping the inhabitants comfortable. It probably does not matter that they were based on incorrect science, but it does matter that the misconception gets repeated over and over again. If biomimicry and/or bioinspiration want to be considered legitimate fields of study, and not just a feel-good endeavor, then the science that the field is based on has to be solid.

The termite mound should still inspire developers and architects because at it turns out, if we view the termite mound as the analogue of our own, respiratory system (lungs) then we still should be able to design “breathing” buildings that have that walls serve more as membranes rather than barriers.

Turner and Soar not only took relatively simple measurements of the temperatures, they also made plaster casts of the tunnel network of M. michaelseni mounds. They then created horizontal slices of the plaster filled mounds for easier recreation of future 3D models.

Based on these models, which showed actually very little continuous mixing between the air coming down from the above-ground structure and the air from the underground nest, they propose that the termite mound of M. michaelseni is in fact a functional analogue of a lung. And much like the lung the termite mound is far more complex than the simple models we have been using (for an excellent explanation comparing functional organization of both lungs and termite mounds please refer to Turner and Soar, 2008).

Comparison of the functional organization of mammalian lungs and the termite mound. There are areas of forced convection (large tidal flows) in red, areas where smaller tidal flows dominate creating mixing diffusion-convection, and then the areas where diffusion dominates.

Comparison of the functional organization of mammalian lungs and the termite mound. There are areas of forced convection (large tidal flows) (in red), areas where smaller tidal flows dominate creating a mix of diffusion-convection (in blue), and then the areas where diffusion dominates (in green). (Drawing by Marianne Alleyne, based on Turner & Soar, 2008)

This complexity opens up new avenues for bioinspired design based on the termite mound. Termites erect walls that are actually interface directly with the outside and indoor environments – the walls themselves let gases and energy through, it does not form an impenetrable barrier. Buildings that are designed based on correct termite mound architecture should incorporate porous walls and cladding (~skin) systems that incorporate tubes/tunnels through which air and energy can flow. Maybe we can design living buildings that are part of our extended physiology, as much as the termite mound is part of the living-system called the termite colony.

Resources:

I cannot recommend the Turner and Soar paper from 2008 enough. It is a wonderful read. The authors touch on more topics than I mention here (homeostasis, for instance). And again, their debunking of previously held beliefs is done in a way that should be emulated.

  • J. Scott Turner and Rupert C. Soar. 2008. Beyond biomimicry. What termites can tell us about realizing the living building.
  • The same authors also wrote a book chapter on a similar topic. But I have not yet been able to locate: Beyond biomimicry. What termites can tell us about realizing the living building. Chapter 15 in: Industrialised, Integrated, Intelligent Sustainable Construction. ISBN 978-0-86022-698-7. Ian Wallis, Lesya Bilan, Mike Smith & Abdul Samad Kazi (eds). I3CON/BSRIA. London. pp 233-248.

J. Scott Turner has also converted this work into very informative video lectures, such as:

  • Learning from nature: Termite mound lungs and the implications for breathing mines.

For great footage of how the termite mound models were created check out these videos.

I am not, by a long shot, the first to point out how the termite mound is NOT (yet) the perfect poster-child for bioinspiration and biomimicry. Here are two other blog-posts that discuss this very topic:

Additional pictures of the Eastgate Centre building in Harare Zimbabwe, click here.

Note: I would like to thank Adrian Smith who a few years ago made me aware of the work by Turner and Soar.

Insect Bits & Bytes (June 2013)

This month’s topics:

Silkworm pavilion

Another compound eye

Some of the stories behind insect-inspired robots

Anti-counterfeit money thanks to butterflies

How to defeat hackers

Miscellaneous – things I learned about social media while writing the blog-post.

Silkworm pavilion

I ended last month’s “Bits and Bytes” with a mention of a project that was making the rounds under the heading #biomimicry. I am still not sure if this really falls under biomimicry or bioinspiration, but during the month of June it kept popping up on Twitter, probably because it is just very, very cool. The project received extra attention because the project was on display in Boston, the city where the Biomimicry3.8 Education Summit and Global Conference was held during the month of June – so cross-pollination for all!

The Mediated Matter group, under the guidance of Professor Neri Oxman, studies additive fabrication techniques (such as 3D printing) and tries to scale some of them up to, for instance, building-size structures. One of the projects involves mobile swarm building where small robots could potentially build large structures. For this project, which is ongoing, they are currently studying how silkworms (the caterpillars of the moth Bombyx mori) can inform this type of building technique.

SILK PAVILION from Mediated Matter Group on Vimeo.

Reference:

Silk Pavilion information can be found on the Mediated Matter website here (tools: swarm printing), and here (environments: silk pavilion), and here (news: silk pavilion).

Coverage:

Another compound eye

Last month’s Bits and Bytes started off with the perfect insect-inspired story: an engineered compound eye from a University of Illinois lab. Great story to lead off the inaugural issue of a recurring blog feature – considering I cover insects, engineering and work at UIUC. Turns out that some of my ommatidia neglected to notice another story very similar to the one I covered. Last month the Laboratory of Intelligent Systems at EPF-Lausanne also created a miniature curved artificial compound eye.

Size comparison between CURVACE (Curved Artificial Compound Eye) and a dragonfly. Image: courtesy Dario Floreano / Swiss Federal Institute of Technology

Size comparison between CURVACE (Curved Artificial Compound Eye) and a dragonfly. Image: courtesy Dario Floreano / Swiss Federal Institute of Technology. http://curvace.org/

Maybe the manufacturing technique and the material used are not as cutting-edge as those used in the Rogers’ lab, but it seems to me that the final creation is a lot more like an insect compound eye.

The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager.

Illustration for the CURVACE assembly_method.

Illustration for the CURVACE assembly method. http://curvace.org/

Reference: Floreano, D., R. Pericet-Camara, S. Viollet, F. Ruffier, A. Brückner, R. Leitel, W. Buss, M. Menouni, F. Expert, R. Juston, M.K. Dobrzynski, G. L’Eplattenier, F. Recktenwald, H.A. Mallot & N. Franceschini. (2013) Miniature curved artificial compound eyes. PNAS V110 (230, pp 9267-9272. DOI: 10.1073/pnas.1219068110

Coverage:

Some of the stories behind insect-inspired robots

Robotic insects were again quite popular this month, or at least on Twitter they were. As I covered in an earlier post (The Dawn of the Artificial Coprophages) engineers have been interested in building robots that move and behave similar to insects for quite a while. It first started with terrestrial locomotion, but now we also see insect-inspired robots that can swim, walk on water, dig, jump and (The Holy Grail) fly.

Here are a few insect-inspired robots that came across my computer screen this week:

Flies

Nature Magazine’s News and Views section (=behind a pay-wall) published a great 2-page article by David Lentink (Dept. of Mechanical Engineering at Stanford University) covering the history of “robotic fly”.

Lentink reviews how the basic research on aerodynamics of insect flight inspired engineers to build robots using the data obtained by the biologists. And how this cross-pollination occurs at the same time as micro-manufacturing techniques are being developed. The article culminates with a recent publication from Rob Wood’s Harvard Microrobotics Laboratory.

Termites

This item does not need much introduction beyond this tweet:

Other

Some other popular science articles that came out this month but covered research that was made public earlier this year:

I also found the article by Emily Monosson for Aeon Magazine an interesting read.

Monosson does not mention insect or insect-inspired robots specifically but she does wonder if life/AI can evolve from wires and plastic. Considering all the work that is being done on insect-inspired robots I assume that we will soon find out.

Anti-counterfeit money thanks to butterflies

Another story that received a lot of twitter-buzz this month was the one about Morpho butterflies serving as inspiration for anti-counterfeit money. The fact that Morphos (and many other butterflies and moths) use structural colors has been known for some time. Engineers and Material Scientists have also been interested, for quite a while now, in manufacturing materials that incorporate nanostructures similar to those on the butterfly wing. So that begs the question, why is this big news now? Probably because of a strategically placed corporate press release. It is interesting to see that news can spread quickly via social media (see silkworm pavilion story, for instance) but also that the story never really goes away.

Reference: ??

Coverage:

How to defeat hackers

Another example of how not-really-news becomes (again) a relatively big story is the article by Rafe Sagerin on how biomimicry can help us stay ahead of hackers. This article was basically a synopsis of his 2012 book called “Learning from the Octopus” which was fun book to read – but did not feature near enough insect examples. This article mentions only one insect (the stingless bee, go figure) but sentences like;

“The best bet is to do what the most successful organisms on Earth do — accept the risk and adapt to the changes”

immediately makes me think of insects since they are so very very successful and ubiquitous.

That this particular article became so popular this month showed me that getting your core-message (look to nature to fight terrorists, diseases, hackers) into a magazine where the topic is not typically discussed (Harvard Business Review) will help reach a lot of new sets of eyes and will familiarize more people with the terms biomimicry and bioinspiration.

Miscellaneous

Lessons I learned from Twitter and this blog-post during the month of June:

  1. There is a lot of cool stuff out there about insect-inspired technology. I need to become better about cataloging all the awesomeness as it becomes available during the month. (Any tips?)
  2. There is so much cool stuff out there that sometimes I miss something, especially if the topics are similar to each other. Last month I assumed the engineered compound eye stories were one story, but it turns out that they are actually two different approaches.
  3. Some stories seem like new but they may actually be receiving a “second wind”, because a journalist/science writer revisits the story or because of a simple retweet. Some stories therefore never really disappear.
  4. Placing a story in a non-traditional media outlet will result in a whole bunch of new eyes seeing the work, and that is a good thing.

And after all these years I am still unsure if certain areas of research really fall under bioinspiration or biomimicry (for example, the silkworm story or biofuels). And that is OK. Not everything will fit neatly in a box, even though the scientist-side of me wishes it would.

Going Micro-Tubular

Going Micro-Tubular

The ability to manufacture devices at the very small, or micro, scale brings with it interesting applications possibilities and surprising challenges.  For instance, certain physical phenomena may not be generally encountered with doing macro scale experiments on the lab bench but are dominant when experiments are done with a micro scale “lab-on-a-chip.” The field of microfluidics deals with the behavior and manipulation of fluids, both liquids and gases, that are constraint to a small scale (1 to several hundred micrometer). The physical properties of fluids at this scale are particularly interesting and could possibly be exploited.  For instance, fluids at a certain scale are no longer practically compressible.  Also, it is difficult to maintain pressure or pressure-driven flow within a micro scale fluidic system. One example is the phenomenon of back-flow whereby fluid moves in one direction when pressure is applied only to have it reverse and flow back when the pressure is released.  Due to the physics of scaling laws, these various non-intuitive phenomena are less severe when transporting gasses than liquids in a micro scale device.  For instance, gravity has no influence on gasses and diffusion of gasses at the micro scale is VERY fast.  Therefore, gas species can mix through diffusion with simple laminar flows at low Reynolds numbers.

In nature microscale liquid and gas flow is quite common. Maybe engineers should look at insects to see how fluids can most effectively be moved around at the microscale. The insect’s respiratory system, for instance, uses microscale flow transport to achieve an absolutely essential physiological function.  The respiratory system at first glance seems so simple – just some gas-filled tubes. At the same time it seems so foreign – no breathing through mouth or nose, no lungs or blood or hemoglobin involved (at least not at first glance). The respiratory system is also elegant in its simplicity through ingenious feedback loops – fine-tuning through direct nervous innervation or by sensing chemical compositions of the blood (called hemolymph in insects).

This system that is key to maintaining homeostasis is also as varied as insects are varied. Ingenious adaptations are seen in insects that live in different habitats – within soil, in water, in arid climates, in cold climates, within a host, while pupating, while flying, while walking, etc.

In this post I’ll focus mostly on the “generalized” terrestrial insect.

The insect’s tracheal system

The insect’s respiratory system’s main functions are to carry oxygen and carbon dioxide to and from the tissues. The gas-filled tubes, called tracheae, start at the spiracles, which are paired openings in the cuticle that can occur in almost every or only a few segments (depending on the insect species). The spiracles are innervated by the nervous system and can be open and closed through muscular action.

Spiracles

Spiracles of a lepidopteran larva. Two are visible in this picture; they appear as black openings surrounded by yellow ring. (Picture by Geoff Gallice)

Inside the insect the tracheal systems starts out as two or more longitudinal trunks, which further into the insect branch into smaller and smaller channels. Tracheae range in diameter from a few mm to 1 μm. The smallest branches are called tracheoles, which range from 1 to 0.1 μm in diameter. The tracheoles’ tips are in contact with cells and are often fluid-filled. This means that at the tips of the tracheoles oxygen has to cross first a liquid, then the tracheolar walls, then cross the plasma membrane of the cell and finally move through the cytoplasm of the cells to reach the mitochondria. Carbon dioxide makes the same trek, but in the opposite direction.

Tracheal System

Tracheal System (Drawing by Marianne Alleyne)

TrachealSystem

Cross-section of the tracheal system of “general” insect. Other insects may have more than 2 longitudinal trunks and/or air sacs and/or no spiracle functional in a particular segment. (Drawing by Marianne Alleyne)

Cross section of tracheal tube. A tracheal tube is comprised of an epidermal outer layer which bathes in hymolymph, an inner intima layer, and taenidia which reinforce the intima layer much like a car's radiator hose is reinforced by coil of steel. (Drawing by Marianne Alleyne)

Cross-section of tracheal tube. Shown is an epidermal outer layer bathing in hemolymph, an inner intima layer, and taenidia, which reinforce the intima layer (much like a car’s radiator hose is reinforced by coil of steel). (Drawing by Marianne Alleyne)

In order to get oxygen to move into the cells and carbon dioxide to move out of the body, all while limiting energy use, insects rely on diffusion and convection.

  • Diffusion: passive movement of molecules down their concentration gradient.

Oxygen diffusion rate is more rapid in air than in liquid, and because the tracheal system consists mostly of air-filled tubes the gas-exchange by diffusion is extremely rapid and quite substantial.  While the cells use the oxygen, the partial pressure of oxygen decreases near the tips of the tracheoles, which then draws in more oxygen from the tracheae and the air outside of the insect. Diffusion is of critical importance at the tips of the tracheoles, but it can only work at micrometer distances since at this point the oxygen has to move through a liquid. This is why almost every cell in the insect is at close proximity to a tracheole tip. The cells that require high respiratory rates (flight muscle cells, for instance) may even have multiple tracheole tips invaginating the cell wall.

The prominent Danish physiologist August Krogh devised an early model (1920) of grasshopper respiration that was based on oxygen partial pressures and suggested that simple diffusion could provide adequate gas exchange in insects. This claim had a huge impact on the field early and quickly became dogma, despite some contemporary contrary evidence. In 1964 “a next-generation Dane” Torkel Weis-Fogh showed that in larger or more active insects the distance between the spiracles and the tips of the tracheoles was too great and that diffusion was insufficient if the insect was active. So what other mechanisms do insects use to move oxygen and carbon dioxide through the tracheae?

  • Convection: bulk movement of a gas or a liquid driven by differential pressures.

Compared to diffusion, convection can achieve greater gas exchange rates over longer distances. The trade-off is that it requires more work and thus more energy.

    • One type of convective air-movement seen in insects is, confusingly, termed suction ventilation. This movement of air is primarily achieved by opening and closing, or shielding differentially, a subset or all of spiracles at different parts of the body. This creates a pressure difference between the spiracles and the tracheal ends and thus creates passive airflow.
    • Autoventilation is achieved by using wings or legs to pump air through the body.
    • Abdominal pumping, using the muscles in the abdomen to pump air.
    • Another, more important, type of convective air movement is achieved by the tracheae (tracheal compression), and their associated air sacs (tracheal sections that are not reinforced by taenidia), collapsing and inflating.
Silkworm Bombyx Mori Spiracle and Trachea 100X mag

Digital image of silkworm Bombyx mori trachea with taenidea (100X mag) by Paul Joseph, Birmingham, UK.

With novel imaging and measurement techniques researchers have shown that rhythmic tracheal compression is quite common.  Synchrotron x-ray imaging has been used since 2003 to visualize tracheal structures in living insects. We can now see that muscles compress the exoskeleton of the insect, which results in air moving through the tracheae since the tracheae and air sacs are collapsing.  These studies, which are now linked with real-time flow-through respirometry, show that rapid cycles of collapse and re-inflation in a variety of insects’ tracheal systems – especially in the head and thorax regions – results in large changes in tracheal volume and are major components of ventilation in insects. Even the different ways the tracheal system can compress and re-inflate is probably as varied as insects themselves.

Must watch: Beetle Tracheae Collapsing (video 1, video 2, video 3). Supporting materials from Westneat, et al. (2003) Science V299 (5606), DOI: 10.1126/science.1078008

Using the insect’s tracheal system as inspiration for microscale flow devices

The impetus for this blog post was a recent paper I came across entitled: Selective pumping in a network: insect-style microscale flow transport, by Yasser Aboelkassem and Anne E. Staples.  The topic of microscale flow transport is of interest to engineers because there are many applications that need precise flow control of just microliters of gas or fluid. Microscale flow devices or microfluidic devices are already around us and are assumed to change research tools in the life sciences, aid drug discovery and chemical analyses, and revolutionize health diagnostics. Modern DNA sequencing systems (Fluidigm, Illumina, Roche (454), etc.) rely on microfluidics. “Droplet” analyses also rely on microfluidic technologies. Cheap paper-based microfluidic immunoassay tests will become important for healthcare in the developing world (Diagnostics for All). And those are just a few of the applications.

Insect tracheal systems have been of particular interest to engineers now that we are able to visualize this physiological process (moving fluid and air through tubes) in action.  Insects are able to move fluid and air with precision with minimal energy requirements and little input from outside of the body. All characteristics that would work well within a “lab-on-a-chip”.

Insects use contractions at very specific places along the tracheal system, which probably affords them more precise control than if just relying on the more crude pressure difference approach. Through these small, but targeted, compressions the airflow to specific areas of the body can be achieved. This is apparently not an easy task to achieve in small-scale devices, and one can appreciate that by imagining larger tubes.

even tho a mushroom didn't ask me to

Imagine a garden hose…(Image by zen Sutherland)

Imagine a garden hose. By stepping onto the hose at one point the fluid or air inside the hose will be displaced to either side. As soon as you step off the hose the fluid or air will rush back (=back-flow). How can one create directional flow of a particular speed or pressure? By stepping at multiple spots along the hose, sometimes closing the hose off completely and other times only partially. Stepping off of the hose according to a certain sequence will also result in a directional flow. Of course, this is just one hose. Now imagine doing this with hoses that are branching into thinner hoses, that have multiple openings, with many more feet that can step on and off of them…and then think of a miniaturized version of that and you will see the insect’s tracheal system.

This is what Aboelkassem and Staples tried to model in their paper. The fluid dynamics research group headed by Staples at Virginia Tech’s Department of Engineering Science and Mechanics is apparently closely aligned with the biomechanics research lab of Jake Socha at the same departments. The Socha lab is one of the labs that has used synchrotron x-ray imaging to study insect respiration. The theoretical and computational model proposed by Aboelkassem and Staples incorporates rhythmic wall contractions along a network of tubes (in this case an 8-armed network) without the need for valves. The model’s tubes/channels are squeezed at different places along the tube. The contractions were actuated to move with different time lags from each other. In this way the researchers showed that fluids can be transported and flow velocity, pressure and direction can be controlled.

Simplified insect physiological network modeled by Aboelkassem & Staples. The "trachea" can be collapsed at multiple points within the network (red arrows). The collapse motion protocol can be varied by including time phase lags. The result is precise movement of the liquid or gas.

Simplified insect tracheal network modeled by Aboelkassem & Staples. The “tracheae” can be collapsed at multiple points within the network (red arrows). The collapse motion protocol can be varied by including time phase lags. The result is precise movement of the liquid or gas (green arrows).

We have learned from insects that localized rhythmic tracheal contraction is an effective way to move gas through micro-tubes. Aboelkassem and Staples claim to have been inspired by the insect’s tracheal system to model “selective pumping in a network”. They show, by using theoretical (low Reynolds number) flow analyses and computation fluid dynamics, that the network might also enable fluids to be transported precisely into particular tubes without the use of mechanical valves – at least through an 8-armed tracheal system. It will be interesting to see if this research group will continue to follow the insects’ lead by adding more branches/channels, by adding air sacs (which seem to be very important in insects), by making the model 3D, by adding actively opening and closing ports/spiracles to the outside, and by incorporating the diversity of insect respiratory systems into different models. If done correctly, and by using microfabrication techniques that can make flexible micro- and nano-scale tubes, it is likely insects can make a contribution to the rapidly growing technological field of microfluidics.

Resources and References:

For a more detailed description of the insect’s respiratory system:

For description of how synchrotron x-ray imaging is used to study insect respiration:

  • Westneat, M. W., O. Betz, R. W. Blob, K. Fezzaa, W. J. Cooper and W. -K. Lee. (2003) Tracheal respiration in insects visualized with synchrotron x-ray imaging. Science V299, 5606, pp. 558-560. DOI: 10.1126/science.1078008
  • Westneat, M.W., J.J. Socha and W.-K. Lee. (2008) Advances in biological structure, function and physiology using synchrotron x-ray imaging. Annual Review of Physiology V70: 119-142. DOI: 10.1146/annurev.physiol.70.113006.100434
  • Socha, J.J., W.-K. Lee, J.F. Harrison, J.S. Waters*, Fezzaa, K. and M.W. Westneat. (2008) Correlated patterns of tracheal compression and convective gas exchange in a carabid beetle. Journal of Experimental Biology V211: 3409-3420. DOI: 10.1242/​jeb.019877
  • Socha, J.J., T. Förster and K.J. Greenlee. (2010) Issues of convection in insect respiration: Insights from synchrotron x-ray imaging and beyond. Respiratory Physiology and Neurobiology V173S S65–S73. DOI: 10.1016/j.resp.2010.03.013
  • Waters J.S.,W.-K. Lee, M.W. Westneat and J. J. Socha. (2013) Dynamics of tracheal compression in the horned passalus beetle. American Journal of Physiology:Regulatory, Integrative and Comparative Physiology V304(8) R621-7. DOI: 10.1152/ajpregu.00500.2012

Bioinspired microscale flow structures:

Special thanks to Dr. Paul Kenis for taking the time to discuss microscale flow transport with me. I appreciate his patience with me – clearly a novice. Bedankt!