What is a water flow sensing system inspired by the spines of a sea urchin?
A research team, noticing the unique movement of sea urchin spines, has developed an artificial structure that mimics them. It is said to be able to monitor water flow in real time without using batteries.
Echinoderm stereom gradient structures enable mechanoelectrical perception | Nature
Sea urchin spines inspire self-powered underwater sensors
Inspired by the growing focus on developing machines based on natural structures, Anan Chen and his colleagues at City University of Hong Kong focused on the spines of sea urchins and studied their structure.
Since sea urchins are not thought to have organs specifically for sensory perception, Chen and his colleagues suspected that their spines might be acting as sensory tools. They dropped a single drop of seawater onto the spines of live sea urchins in the laboratory and used a high-speed camera to measure how quickly the spines moved. The results showed that the spines rotated about 10 degrees within one second of the water droplet touching them.
To verify the details, Chen and his colleagues attached electrodes to two different locations on the spine and measured the potential difference. They confirmed that the spine exhibited a potential difference of up to approximately 116 mV when seawater touched or flowed over its tip. Both spines from living and dead sea urchins were tested, and since both generated electrical signals, Chen and his colleagues concluded that 'this electricity is generated not by biological tissue or nerves, but by the physical structure of the spine.'
The key was a porous structure called a 'stereotom.' This structure consists of countless tiny holes in bone-like parts inside the spine. These holes are larger at the base and gradually become smaller and more densely packed towards the tip. This unevenness alters the flow of water, causing an uneven distribution of electric charge on the surface of the spine, which leads to an electrical potential difference.
To investigate the possibility that these structures help sense water movement, Chen and his colleagues 3D printed artificial spines out of plastic and ceramic. When water was passed over these spines, they generated electricity in the same way as sea urchin spines. For comparison, they created artificial spines with a smooth structure and showed that the stereotactic spines produced three times the voltage output and eight times the amplitude difference.
Chen and his colleagues stated, 'Artificial spines that utilize the mechanisms of sea urchins have the potential to be used in a wide range of applications, from underwater robots to marine environment monitoring and water resource management.'
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