The enduring children's toy known as Silly Putty has long amazed kids and scientists alike with its strange properties. Also known as polysilicone, the putty acts like a liquid over long periods of time, but behaves like a solid otherwise. Depending on the force applied, it might bend, or bounce or break.
Researchers in Ireland announced this week that they've discovered still more profound weirdness in polysilicone putty. When infused with graphene - a form of carbon with some very strange qualities of its own - the putty conducted electricity and transformed into a super-sensitive sensing device.
In fact, according to the research team, polysilicone could potentially power whole new categories of medical sensors that monitor vital signs.
The researchers found that electrical resistance in the graphene-infused putty, dubbed G-putty for now, is extremely sensitive to the slightest physical pressure, deformation or impact. When applied to skin on the head or neck, the G-putty can be used to measure breathing, pulse and even blood pressure at levels "hundreds of times more sensitive" than traditional medical sensors, according to the research team.
Lead researcher Jonathan Coleman, professor in the School of Physics at Trinity College Dublin, said that the main applications for the technology will be in health monitoring and diagnostics. For instance, a permanent G-putty sensor on the skin could continuously monitor blood pressure and trigger early warnings for patients and doctors.
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"There is no current tech to do this. G-putty is the only mechanical sensor sensitive enough," Coleman said. "Basically, the electrical resistance of G-putty changes measurably in response to even the slightest pressure. Pressing against the skin at an artery, the pulsing of the blood can be turned into electrical signals."
Those signals could be fed into a lightweight device worn on the wrist, Coleman said, which would then translate the electrical resistance changes into diagnostic information, instantly and continuously. The key to the technology is the putty's high sensitivity, which can detect blood pressure levels without the squeezing of a traditional blood pressure monitor cuff.
"[The device] would send the data by Bluetooth to a smart phone where an app would do data processing, outputting heart rate and importantly blood pressure," Coleman said. "Current sensors can measure pulse but not blood pressure, at least not continuously. It takes a doctor or nurse a minute or two to do it."
In other tests unrelated to medical applications, the G-putty was found to be sensitive enough to register the individual footfall of a spider. All eight of them, presumably. This suggests that G-putty could have potential applications in other fields as well, although Coleman and the research team haven't mapped out any specific scenarios as of yet.
"The behavior we found with G-putty has not been found in any other composite material," Coleman said. "This unique discovery will open up major possibilities in sensor manufacturing worldwide."
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The discovery of G-putty's electrical properties came after a postdoctoral researcher suggested mixing graphene and Silly Putty. It was essentially an accident, Coleman said, albeit the kinda-sorta deliberate accident that scientists like to encourage when mucking about in the lab.
"The inspiration was a playful one, as part of our 'kitchen physics' approach," Coleman said. "The student, Conor Boland, thought it might be fun and I agreed, thinking it might be useful for outreach. However, it quickly became clear that the composites had very interesting properties of their own."
That's Coleman in the image up top, along with his son Oisín.
"We do this stuff a lot for fun and to show that science doesn't always have to be complicated," he said.
Coleman's research, published in collaboration with Robert Young of the University of Manchester, appears this week in the journal Science.
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