New octopus-inspired smart adhesive sensors developed

Researchers have developed sensors that mimick the suction cups on octopus's tentacles, an advance that may lead to the development of wearable health sensors.
With increased study of bio-adhesives, a significant effort has been made in search for novel adhesives that will combine reversibility, repeated usage, stronger bonds and faster bonding time, non-toxic, and more importantly be effective in wet and other extreme conditions, researchers said.
Scientists from Korea Institute of Science and Technology and Ulsan National Institute of Science and Technology in South Korea studied the structure and adhesive mechanism of octopus suckers and then used what they learned to develop a new type of suction based adhesive material.

"Although flexible pressure sensors might give future prosthetics and robots a better sense of touch, building them requires a lot of laborious transferring of nano- and microribbons of inorganic semiconductor materials onto polymer sheets," researchers said.
In search of an easier way to process this transfer printing, they turned to the octopus suction cups for inspiration.
An octopus uses its tentacles to move to a new location and uses suction cups underneath each tentacle to grab onto something. Each suction cup contains a cavity whose pressure is controlled by surrounding muscles, researchers said.

These can be made thinner or thicker on demand, increasing or decreasing air pressure inside the cup, allowing for sucking and releasing as desired, they said.

By mimicking muscle actuation to control cavity-pressure-induced adhesion of octopus suckers, researchers engineered octopus-inspired smart adhesive pads.
They used the rubbery material polydimethylsiloxane (PDMS) to create an array of microscale suckers, which included pores that are coated with a thermally responsive polymer to create sucker-like walls.
Researchers discovered that the best way to replicate organic nature of muscle contractions would be through applied heat.
At room temperature, the walls of each pit sit in an 'open' state, but when the mat is heated to 32 degrees celsius, the walls contract, creating suction, therby allowing the entire mate to adhere to a material (mimicking the suction function of an octopus), researchers said.

The adhesive strength also increased at high temperature, they said.
Researchers also found that the mat worked as envisioned - they made some indium gallium arsenide transistors that sat on a flexible substrate and also used it to move some nanomaterials to a different type of flexible material.
They expect that their smart adhesive pads can be used as the substrate for wearable health sensors, such as Band-Aids or sensors that stick to the skin at normal body temperatures but fall off when rinsed under cold water.
The findings were published in the journal Advanced Materials.