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Biology

New technology inspired from ancient art

Teoh, Z.E., Phillips, B.T., Becker, K.P., Whittredge, G., Weaver, J.C., Hoberman, C., Gruber, D.F. and Wood, R.J., 2018. Rotary-actuated folding polyhedrons for midwater investigation of delicate marine organisms. Science Robotics, 3(20), p.eaat5276.

At mid-depths, the ocean is diverse, expansive, and varies in space and time.  Scientists explore these harder to reach places of the ocean with underwater vehicles. However, their ability to sample organisms is a limitation to their ability to classify the deep ocean communities, especially in the pelagic (mid-depth, open-ocean) part.  Sampling limitations are further compounded by the delicate nature of some of the animals sampled (like jellyfish).

Traditional methods used to sample organisms from mid-depths include net tows and trawls, suction samplers, and detritus samplers.  They each have their own limitations, including the common inability to catch delicate organisms.  Net tows and trawls carry the risk of crushing the delicate organisms in their heterogeneous collection, suction samplers can destroy organisms in their plumbing, and the detritus samplers (which looks like a can with top and bottom lids that capture specimen inside the cylinder section) requires very precise positioning.

Figure of a 12-sided polygon. Source: https://commons.wikimedia.org/wiki/File:Chambers_1908_Dodecahedron.png
By Rev. Thomas Davidson 1856-1923 (ed.) [Public domain], via Wikimedia Commons

Studying organisms at mid-depths became potentially easier with the introduction of rotary-actuated folding polyhedrons, whose 2D to 3D transformations are inspired by origami. The best polyhedron design was one with 12 sides, called the ‘Rotary-Actuated Dodecahedron’ or simply, ‘RAD’. It functions via a single-axis rotational mechanism which runs a mechanical link system to transform the RAD from a 2D to 3D object. The usual way to operate mechanical link systems is to use an actuator for every link pair. The reduction in parts from the use of a single actuator is advantageous to Teoh et al.’s (2018) design.

Figure similar to 2D view of RAD. Source: http://www.texample.net/tikz/examples/foldable-dodecahedron-with-calendar/

By itself, the RAD structure has a lot of flexibility, has low friction, and low mass, much attributed to the axisymmetric (symmetrical about the axis) design that enables the load to be distributed evenly.  The friction and weight are reduced with 3-D printing and using fluoropolymer (a type of synthetic material) bearings.  The RAD works faster in water than on land because the mass is offset by its buoyant design.  The soft edges in the design are meant to protect the organisms, enable a tight enclosure, and reduce the risk of over driving when closing.

The RAD size is limited by the available space on the underwater submersibles and by the size of the 3D printers.  However, organism size and shape was a consideration in the design of RAD.  The sampling size (~3 liters) is comparable to the available sampling devices (3-10 liters).

A key feature of the RAD design is that it is useful at the entire depth range of the ocean. There are no sealed voids and it is made with an non-compressible material so it can theoretically be used at the deepest ocean depths (11 km), although it was only tested to 700m in the field.  I imagine the device is limited by the speed at which the ROV is able to move.

At its current design state, the RAD enables catch-and-release of organisms in the open-ocean.  The hope is that in the future, 3D imaging cameras will be used to document the organism while it is captured, in situ DNA and RNA sampling will be possible, and sensors to determine water conditions like temperature and salinity will be added to the design.

As Teoh et al., 2018 describe, designs like the RAD, although fascinating for their explicit application, have great potential for roles in other science and industry, such as folding solar panels that can be attached satellites or used in the medical field.

The project was particularly interesting because Teoh et al. (2018) are applying an ancient and beautiful art to modern technological exploration.  Also cool is that they are an interdisciplinary team made up of biologists, engineers, underwater vehicle operators, and oceanographers from Massachusetts, Rhode Island, New York, and California. 

 

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