US scientists have created sensors that rival a fish's ability to detect underwater flow. The sensors could provide an alternative to sonar for underwater research, they claim.

Vladimir Tsukruk, at the Georgia Institute of Technology, Atlanta, and colleagues coated man-made flow sensors with a hydrogel to mimic the flow sensing hair system on blind cave fish.

The hydrogel-capped sensors rival the sensitivity of fish flow receptors

Cave fish rely on their natural flow sensors rather than eyesight for 'seeing' nearby obstacles. Their flow sensors consist of a variety of specialised structures, including long, bendy structures known as cupulae, that transmit flow information to bundles of hair cells. As the fish glide past objects, they can detect movement in the surrounding water and avoid collisions.

Tsukruk built up droplets of a polymer onto a man-made flow sensor. When the droplets dried, they formed a tall hydrogel structure that mimicked the structure of a cupula. He compared the water flow sensitivity of bare sensors with the hydrogel-capped versions and found that the capped sensors were significantly better and rivalled the sensitivity of fish flow receptors.

Tsukruk explains that sonar detection of underwater objects can harm the surrounding environment. The hydrogel-capped sensor could provide an alternative to sonar in underwater applications, such as port security and tsunami detectors, as well as marine research, he claims. 'It's a simple but robust demonstration of the potential of bio-inspired design in solving difficult engineering problems,' he says.

Igor Luzinov, an expert in polymer films at Clemson University, US, was impressed with the approach. 'What's most amazing is that this man-made version is working pretty well,' he says.

Tsukruk says the challenge for the future is obtaining sufficient computing power to interpret the significant amount of information that an array of the sensors would produce.

Fay Riordan

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