There are so many interesting and wild creatures to study, each exhibiting unique characteristics. Research in my group tends to focus on the the biomechanical, material, archtectural and kinematic aspects of animal biology. I will cover a few highlights from over the years below.

Tree climbing fish

I had to start with these guys since they're essentially, multi-talented movers with the ability to climb vertical and over vertical surfaces such as mangorve trees and rock faces, are able to walk and jump on land, can dive, swim, build burrows and... wait for it... waterhop! We've spent some time characterising the tree-climbing abilities of this fish and identified the important role of pelvic fin flexibility in enabling adhesion to surfaces (cf. Zoology 119(6):511-517). They do antaogonistically move their pelvic and pectoral fins, which you would expect to some extent, however in another study we noted that this is at least partly enabled by a simplistic, yet ingenious mechanical piston-like system inside their bodies (cf. JMBA 98(8):2121-2131). It doesn't stop there though... these fish are wonderfully versatile on the water surface, being able to hop repeatedly, change direction, and indeed launch from, and land on both substrates even when vertical. Our work on characterising their kinematics and kinetics can be found here (Zoology 139:125750). Morphology obviously has a role to play in all of this, and you can find some of our morphological work in this paper (Proc Zool Soc 75:83-93).

Figure above: Periophthalmus variabilis, a tree climbing water hopping fish

A 'snip'pet on crabs

We've had our fair share of fun researching crabs, predominantly with my students in Indonesia. If you've heard of Majoidae, then you know this is a superfamily that has the ability to camouflage to not only hide from predators, but also, to improve prey capture. Amongst the many decorator crabs in this suerpfamily, we chose to try and understand how Tiarinia cornigera manages to passively decroate itself. Curiously, we found our specimens in Java, which was the first time that this species had been found there. But more importantly, using a variety of characterisation, experimental and modelling techniques, we discovered that these crabs grow flowery chitin rich structures on their carapaces. These flowery structures are arranged in such a way, that water flows stagnates on the carapace surface, allowing sticky biopolymer secreting microorganisms to attach, which in turn enable the attachment of macroalgaes Acta Biomaterialia 41:52-59. But that's not the only thing that's special about crab carapaces... the effectiveness of every carapace as a protective shell, is also partly enabled by the geometry of the shell. This is something we discuss in Materials13(18):3994.

Figures above: (Top) Decorator crab T. cornigera and its passive decoration strategies (Bottom) Examples of different Brachiuran crabs with different carapace geometries

Shrimps with guns!

Now, a not too distant cousin of the crab is the shrimp (at least in the sense of the subphylum or arthropods: crustacea). Most people I speak to do not belive that shrimps carry guns. I probably wouldn't either except that I've been shot by a shrimp and let me tell you... it is a cutely painful sting that leaves you wondering, "how?"... The shrimps I'm talking about are snapping shrimps, also known as pistol shrimps as one of their chelids is in fact an oversized gun that shoots high pressure air at curious bipedals (and also to stun prey, ward off predators, and generally flex a bit during mating season). Anyhow, their guns are plunger-socket systems and naturally, a specialised set up like that will have a specialised material make up, which was the topic of conversation in our paper in Zoology 126:1-10, where we discuss the layered sandwich composite structure of the plunger. Well worth a read for those who are interested in multifunctional sandwich structures.

Figure above: Our front cover image of a snapping shrimp (or pistol shrimp)

Why dragonfly wings don't 'snap'...?

Yes, it's true... I'm milking the whole snip-snap side of these stories. Why not? Anyways, this is a fair question... why don't insect wings, like dragflies, snap during flight? They are very thin, very brittle, generally what I would consider weak relative to the varied environmental conditions they face. But importantly, they also flap - fast! Dragonflies flap at around 30-40 times per second. So why don't their wings fracture or tear? Well, their wings are pretty cleverly structured composites. Between many of their stiff chitin joints, they have a rubbery material known as resilin, which fills space between the joint. This rubbery resilin basically absorbs dynamic mechanical energy during flight, decreasing stress concentrations in the wing itself, and thus conserving the wing continuum. Ingenious. We published a couple of papers on this subject, one in Arthropod structure and Development 43 (5):415-422, and the other in Composites Part B 87:274-280. 

Figure above: Examples of the resilin inset located at the nodus of a Libellulid dragonfly wing

'Caught up' in a spider's web

A long while back, I heard a rumour. "A group of mothers in Kenya were making things out of spider silks." Now, to those who know, this is pretty tricky, since spiders are cannibalistic so it's hard to farm them, they also not exactly the quickest for silk reeling... they're not really farmable. So how is it then I thought, are these Kenyan mothers making anything out of spider silk? Naturally, the next obvious move was to hop into a car with a couple of locals who knew their way around Kenya, after which we started chasing this rumour. Sadly, it turned out to be just that. A rumour, however, the journey led me to a few insect farmers in Kisumu and we started searching for different spider species to 'find out' if there were any special ones over there. After over two years and a very large number of spider species, we found one, Nephilengys cruentata, spinning an egg case that I found unbelievably difficult to break through. So naturally being scientists, we researched this for a while, from both mechanical and architectural perspectives, and it turned out that this spider species spins the toughest recorded tubuliform (egg case) silk thread recorded to date. You can read about our findings in a letter we sent to Materials Science and Engineering C 69:195-199. 

Figure above: Nephilengys cruentata, the spider that spins the worlds toughest tubuliform (egg case) silk

While this research was conducted at a fibre length scale, we've also had a healthy interest in developing a molecular level understanding of spider silks. Speciifc areas of interest to us have been in the formation of semi-crystalline regions between crystalline and amorphous material in spider silks as published in the following two places: Materials Science and Engineering: C 58:366-371 and International Journal of Biological Macromolecules 92:1006-1011. I have also had an interest in the unfolding vs separation mechanics in spider silk nanocrystals, which I modelled here: Advances in Natural Sciences: Nanoscience and Nanotechnology 5(1):015015.

Figure above: Examples of semi-crystalline regions forming in oversheared silk nanocrystals

Moth cocoons

'Sticking' to the subject of silk - moth cocoons are also silk based, and this has been an area of interest in recent work where we have investigated the tear strength of specifically Bombyx mori silk cocoons. Our work was published in ACS Materials Au 4(4):403–412 and as you can see in the image below, these cocoons are complex, architected laminates with a balanced trade off between tear energy and density.

Figure above: Bombyx mori cocoons are architected layered materials with a balanced trade off between tear energy and density

Whales

It was 2013 when I realised that I didn't know enough about dinosaurs. Thus, I took some time out to work with Prof. Anusuya Chinsamy Turan at the University of Cape Town, who introduced me to the wonderful world of whales. Big extant animals - as close to dinosaurs that I was likely to get (excluding chickens of course...!). A few years of work on the bones of these animals resulted in a paper published in Zoology 119(1):42-51, where we describe the structure, properties and function of the sperm whale skull amphitheatre. I still have some whale bones to finish writing about when I have the time. They're all very different in terms of structure. It is figuring out why that structure exists as it does, that is the tricky part.

Figure above: Histology (left) and simulation (right) of the sperm whale skull amphitheatre

Tree climbing lizards

Since this page begins with a discussion on tree climbing fish, I could as well finish discussing some of our work on tree climbing lizards. This was a fun project that started with a trip to meet Dr. Christofer Clemente in Australia who does a lot of work on varanids. To put it simply, some varanids use their claws to help them climb trees (i.e. they are arboreal), while others use their claws to burrow into the ground. The varanids we researched exhibited clear distinctions in claw morphology, with the arboreal varanids having tighter claw curvatures. To characterise their claw grip strengths, we designed and made a special piece of equipment and found that the arboreal lizard claws had a superior gripping efficiency when compared against the burrowers. There's so much more to research with these guys but you can read more about this specific study in Biology Open 12 (5): bio059874.

Figure above: Lizard claws are an amazing example of morpho-functional diversity