Putting a spring in your step

30 September 2014 - By: Cornelia Eisanach

Putting a spring in your step 

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Self-sealing foam in action. The fissure in the membrane is visible while the foam has closed its fissure and so seals the membrane. Photo: Plant Biomechanics Group Freiburg

By Cornelia Eisanach

Aristotle was probably one of the first who recorded thoughts on how animals move and Leonardo Da Vinci famously envisioned a flying machine based on his study of a bat’s wing. Since the works of these pioneers our understanding of the mechanics of biological systems has come a long way. Thanks to this research we can now apply the mechanical principles used in animals and plants to engineering problems.

To advance and communicate this understanding the SEB holds a General Biomechanics session every year at their annual meeting. Speaking to Biomechanics group convenor Peter Aerts at this year’s SEB meeting in Manchester, he explains: “Our topics range from plant biomechanics to locomotion, from feeding mechanics to cellular mechanics. This makes our sessions very fruitful and inspiring. But as is typical for the SEB, the science always has a biological question as its starting point.”

“One such question, for example, is plant morphogenesis during growth and development”, says Bruno Moulia, group leader at INRA, Clermont-Ferrand in France. “When I was studying plant growth for my degree, I realised that the research was really limited if you didn’t consider the mechanics.” He explains that while biomechanics can be seen as a tool to better understand plant function by applying the laws of Newtonian physics to it, there is also a second aspect to the field that deals with the question of how mechanical forces such as wind, water currents, gravity or injury affect the shape, morphology and ultimately the function of plants.
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Design for a flying machine by Leonardo Da Vinci, ca. 1488.Photo: Public Domain

Both Peter and Bruno believe that biomechanics as a methodology itself is very powerful in understanding complex, biological systems. One classic example to illustrate this is the process of running or walking. Peter explains that a lot of muscles, limbs, tendons and skeletal elements are involved in these actions, but for walking, for instance, the movement itself can be described as that of an inverted pendulum. “This model can explain how we can walk economically and recover energy, but not how the transitions from one step to the next are achieved. Abstraction to a mechanical model was able to show us we were missing something - a spring; tendons can act as springs.” As soon as springs were theorised to act in the step-to-step transition, the mechanism of walking could be explained by a simple mechanical model. This model is known as the ‘Spring-Loaded Inverted Pendulum’ model. “And the beauty of this abstraction”, says Peter, “is that it also describes the mechanism of running and it applies to all animals. No matter if it is humans, other mammals, reptiles, insects, birds - all use that same basic principle.”

Of course, as is often the case in biology, once a principle is understood it can be applied to other systems, for example in engineering, prosthetics or biomimetics. Olga Speck, who manages the Competence Network Biomimetics at the University of Freiburg, has already successfully navigated this road. “We studied the biomechanics of ‘self-sealing’ in the winding plant, Dutchman’s Pipe, which has led to the discovery of a self-sealing foam for pneumatic systems”, says Olga. “Imagine a normal rubber boat filled with air being pierced by a 2.5 mm hole - in about 20 minutes, you run out of air. In stems of Dutchman’s Pipe, when the peripheral ring of strengthening tissue is injured, surrounding parenchyma cells expand rapidly and so seal the fissure.” In collaboration with engineers and an industrial partner, Olga’s team have translated this discovery into a polymer foam that seals pneumatic systems rapidly. “In the case of the rubber boat the self-sealing foam might be a great advantage”.

The study has led to engineering solutions, but Olga highlights that this has an added benefit. “I think biomimetics is also a good reason to speak about biodiversity”, she says. “Nature holds so many solutions to common problems and this should provide additional motivation to protect and conserve our planet’s richness of plant and animal species”.

Category: Plant Biology
Cornelia Eisenach-RS

Cornelia Eisanach

Originally from Berlin, Cornelia completed her PhD research in Plant Cell and Molecular Biology at Glasgow University. Apart from researching plant ion channels she also helped to establish and contributed to the GIST, a Glasgow-based popular science magazine, worked at science outreach events with kids and gathered work experience at the BBC. Since 2013 she has been a post-doctoral research fellow at the University of Zürich, Switzerland, and works as a science writer for the SEB, the Neue Zürcher Zeitung and SciViews.