September 2015 – Bio-Imitation of Seahorse Tail Inspires Innovative Robotic Machinery
By Kaamna C. Mirchandani
If imitation is truly the sincerest form of flattery, we should find seahorses overjoyed, along with spiders, snakes and sea cucumbers; other participants of the biomimicry effort. Known as the unique equine bony fish of the sea, seahorses possess several distinctive qualities from other creatures, particularly in that the males endure impregnation and labor. They are not known for their motility, in fact, they are poor swimmers. However, seahorses can significantly aid in the creation of flexible robotic arms. The key lies in their prehensile tail. The tail has the ability to grasp and support the seahorse; as well as protect the seahorse from crushing forces. Mechanical engineer, Michael M. Porter is one of the leading authorities studying seahorses and is now translating their astounding abilities into the generation of robotic arms, and additional forms of biomimicry.
What started as a side-project during his doctorate, has transformed into an imaginative and fascinating topic in science engineering. Dr. Michael Porter currently teaches a class on biomimicry at Clemson University, and leads the novel “Natural Engineering” lab. While working towards his PhD at University of California San Diego, Dr. Porter studied magnetic freeze casting, where he used ice and magnetic fields to make ceramic materials that mimic different biological structures. Intrigued by the bio-design aspect of his dissertation, and at the recommendation of his mentor, Dr. Porter began observing seahorses at UC San Diego. Prior to seahorses, Dr. Porter had worked on material composition of drifting surfboards; as well as bioplastics utilizing bacteria to generate bio-derived and biodegradable plastic structures. While studying these plastics made from bacteria, Dr. Porter noticed that their mechanical properties failed to meet the expectations desired. It was then that he hypothesized the advantage in imitating nature with synthetic materials, rather than utilizing nature-derived materials. Dr. Porter continues to study the seahorse tail structure, and various other biological structures at Clemson University alongside a team of graduate and undergraduate students. The amalgamation of biology and engineering is essential to his studies, “My research and teaching interests lie at the intersection of three areas; biology, material science and mechanical engineering”.
So how do seahorse tails lead us to robotic arms? Surprisingly, the seahorse does not utilize its tail for swimming. Rather, the tail is used as a grasping accessory for nearby coral, seagrasses and mangrove roots. The gripping function of the tail allows the seahorse to feed and elude attack. Computer software helped convert Micro CT images of the seahorse tail into 3D printed structures. This helped Dr. Porter understand the complex geometry behind the plates of the seahorse tail. Hand assembly revealed the bendable structure and function comprising the chain of plates. Dr. Porter also created a similar 3D structure of circular plates, representing the typical cylindrical tail. “The square structure had more mechanical advantages than the circular cross-sectional structure. Tests in bending, twisting and compression revealed that the square structure is better at gripping, better as armor, and has the ability to bend and twist. The flat profile allows it to grasp objects with more control.” As a protective armor for the seahorse, the tail compresses rather than crushes, when under attack or pressure. This is allowed by the four L-shaped plates encompassing a central vertebra. When under force, the plates can glide over and produce a compact stiff resilient configuration.
With almost 50 different species, seahorses range in size from half an inch to about twelve inches. “[Micro Photonics] is a great service because, although we have access to a Micro CT [at Clemson], the one we have, the resolution does not go down to what we needed for the particularly small seahorses.” It is plausible that smaller scans may divulge changes in tails of smaller species that may present additional functions.
The initial seahorse observation suggested by Dr. Porter’s mentor was but an idea. Dr. Porter’s keen eye for structure and mechanics lead him to concentrate on the prehensile seahorse tail; an ingenious structure with promising innovations. “You can take an idea and run with it, you can convince people it’s worth studying, and you can turn it into something one day.” Some of the future applications for this tail could be robotic arms for surgery, use in industry, search-and-rescue type robots, ocean-assisted armors, human exoskeletons and various other applications. Dr. Porter focuses his work towards dissecting the structure of the seahorse tail, hoping to reveal new applications. “Informing ourselves about the biology allows us to better fine-tune what we should focus our efforts on in the long term for the application”.
Works Cited
1. Porter, Michael M., et al. “Highly deformable bones: unusual deformation mechanisms of seahorse armor.” Acta biomaterialia 9.6 (2013): 6763-6770.
2. Porter, Michael M., et al. “Why the seahorse tail is square.” Science 349.6243 (2015): aaa6683.