The rise of "soft robotics"

Today, my first publication on soft robots appears in the journal "Bioinspiration and Biomimetics". It is indeed very difficult to publish both in biology and robotics at the same time. Please check out the supplemental videos going along with my paper first. For more stories about the development of my other robots, feel free to browse some older posts.

Almost 5 years ago, I finished my B.A. in a hurry to plunge myself into the research of animal locomotion. As I accepted Tufts' Ph.D student position, I knew that I was caught in a wave of modern robotics innovation. Five years ago, "soft robotics" is a funny term. Even today, roboticists still debate what soft robots really are. In any case, "soft robotics" has transformed from a crazy talk to becoming an active field of research in the past few years. You will hear a lot more about soft robotics this year from me and from many other research teams around the world.

What really triggered this movement is not really clear. But I would venture to say that the DARPA ChemBot project certainly motivated and cultivated the first generation of soft roboticists in the United States. Many Ph.D students PostDocs alike were supported by this program to pursue soft robotics in many aspects. I was one of them.

Although I have received my Ph.D at Tufts and am now working as a postdoc at Harvard, I will continue to blog about caterpillars and soft robots as long as I am still publishing my thesis work throughout the summer. Beyond that point I will probably have to decide where to begin telling a new series of stories about my new pursuit in animal flight.

It's just the beginning!

Caterpillar acoustics

I have been trying to write a new post with real scientific materials in the past two weeks. Frankly, it was very difficult to decide where to start after such a long break. In any case, I finally decided to start with a literature review about acoustics in caterpillars.

Yes, some caterpillars do make sounds and use acoustics for communications. Sounds are essentially mechanical vibrations transmitted via some medium. Any organism capable of creating vibration has the potential to transmit information acoustically. In recent years, acoustic communication has become one of the hot topics among the caterpillar biologists. We know that soft tissues are extremely good at absorbing vibrations. How do caterpillars make a sound with such soft bodies?

Well, there are a number of rigid parts in caterpillars where significant vibration can be generated. For example, the mandibles (the mouthparts) are made of tanned cuticle (chitin composite). They can be as hard as some aluminum or carbon-fiber reinforced polymers (Vincent 2004). To signal territory, cherry leaf roller caterpillars (Caloptilia serotinella) scrap their mandibles across the leaf surface to create vibrations on the leaf. Sometimes, plucking the leaf would be sufficient to generate the vibration. These behaviors are observed more frequently when a conspecific (another caterpillar) stumbles onto the leaf roll (Fletcher et al 2006). Some direct body vibration was observed in these caterpillars but with much rare occurrence. Most acoustic signals are still generated by working the hard mandibles against the substrate.

Alternatively, caterpillars can drag their rear ends across the leaf to produce vibrations. Yes, “anal scraping ” is the technical term used in the original literature that reports this behavior (Yack et al 2001). As much as it sounds indignant for the caterpillars, the methodology is quite effective. Larvae of the hook-tip moth (Drepana arcuata) develop a pair of modified oar-like setae instead on their anal segments (they do not have terminal prolegs). These stiff “anal oars” are less than half a millimeter and bit into the leaf as the animal drag the anal segment across the leaf surface to produce relatively long and audible noise (Bowen et al 2008). Such adaptation has been observed exclusively in the family Drepanae, and it can be shown that the anal oars are derived morphologies in these small leaf-rollers as a special adaptation (Scott et al 2010).

The acoustics in caterpillars continue to make headlines. In February, the Journal of Experimental Biology features a research article reporting whistling behaviors in caterpillars. Again this is not a metaphoric description but an illustrative one. Caterpillars of the North American walnut sphinx (Amorpha juglandis) can produce sounds by expiring forcefully through the spiracles (caterpillar’s air valves) (Bura et al 2011). When a caterpillar contracts forcefully, the body compression can squeeze air out of the tracheal system. I reported this phenomenon in one of my earlier posts as I put crawling caterpillars under water. In the walnut sphinx, however, the spiracles of the anal segment are elongated to produce wider lips for whistling. The caterpillar produces three types of audible acoustic signals in response to simulated predation and effectively startles an attacking bird.

The diverse morphologies and behaviors of caterpillars continue to amaze biologists in different contexts. For caterpillars that are vocal, they certainly have expanded their abilities to relay signals important for survival.

Caterpillars, make some noise!!

References

Bowen, J. L., Mahony, S. J., Mason, A. C. and Yack, J. E. (2008). Vibration‐mediated Territoriality in the Warty Birch Caterpillar Drepana Bilineata. Physiol. Entomol. 33, 238-250.

Bura, V. L., Rohwer, V. G., Martin, P. R. and Yack, J. E. (2011). Whistling in Caterpillars (Amorpha Juglandis, Bombycoidea): Sound-Producing Mechanism and Function. J. Exp. Biol. 214, 30-37.

Fletcher, L. E., Yack, J. E., Fitzgerald, T. D. and Hoy, R. R. (2006). Vibrational Communication in the Cherry Leaf Roller Caterpillar Caloptilia Serotinella (Gracillarioidea: Gracillariidae). J. Insect Behav. 19, 1-18.

Scott, J. L., Kawahara, A. Y., Skevington, J. H., Yen, S. H., Sami, A., Smith, M. L. and Yack, J. E. (2010). The Evolutionary Origins of Ritualized Acoustic Signals in Caterpillars. Nature Communications 1, 1-9.

Vincent, J. F. V. and Wegst,U.G.K. (2004). Design and Mechanical Properties of Insect Cuticle. Arthropod Struct.Dev. 33, 187-199.

Yack, J. E., Smith, M. L. and Weatherhead, P. J. (2001). Caterpillar Talk: Acoustically Mediated Territoriality in Larval Lepidoptera. Proc. Natl. Acad. Sci. U. S. A. 98, 11371.

Huai-Ti's Ph.D and beyond

Dear friends,

I apologize for the lack of update for such a long time. In the past 5 months, I've been busy with publications, thesis and postdoc interviews. I have successfully defended my thesis on January 26th and am now starting my first postdoctoral research at Harvard University. Many colleagues inquire whether I would keep on blogging. The answer is yes, as this is my major contribution in science outreach. However, given the among of sleep I've been missing and the number of duties I have, I could probably only update once a month.

In the world of scientific research, the researchers are "the projects". There is no way to separate "work" from what people call "life" because research is part of a scientist's life. In fact, it is what makes a scientist "a scientist".

Sincerely
HTL