A new synthetic material that is both sensitive to touch and capable of healing itself at room temperature, could lead to smarter prosthetics or resilient electronics that repair themselves
Nobody knows the remarkable properties of human skin like the researchers struggling to emulate it. Not only is our skin sensitive – sending the brain precise data about pressure and temperature – but it also heals efficiently to preserve a protective barrier against the world. Combining these two features in a single synthetic material presented an exciting challenge for Stanford professor Zhenan Bao and her team.
Now, they have succeeded in making the first material that can both sense subtle pressure and heal itself when torn or cut. Their findings appear in the journal Nature Nanotechnology.
In the last decade, there have been major advances in synthetic skin, said Bao, the study’s principal investigator, but even the most effective self-healing materials was not a good bulk conductor of electricity, a crucial property.
“To interface this kind of material with the digital world, ideally you want it to be conductive,” said Benjamin Tee, a team member.
A NEW RECIPE
The researchers succeeded by combining two ingredients to get what Bao calls “the best of both worlds” – the self-healing ability of a plastic polymer and the conductivity of a metal.
They started with a plastic consisting of long chains of molecules joined by hydrogen bonds- the relatively weak attractions between the positively charged region of one atom and the negatively charged region of the next.
“These dynamic bonds allow the material to self-heal,” said Chao Wang, another member. The molecules easily break apart, but then when they reconnect, the bonds reorganize themselves and restore the structure of the material after it gets damaged, he said. The results is a bendable material, which even at room temperature feels a bit like saltwater taffy left in the fridge.
To this resilient polymer, the researchers added tiny particles of nickel, which increased its mechanical strength. The nanoscale surfaces of the nickel particles are rough, which proved important in making the material conductive. Tee compared these surface features to “mini-machetes,” with each jutting edge concentrating an electrical field and making it easier for current to flow from one particle to the next.
The result was a polymer conducted electricity. “Most plastics are good insulators, but this is an excellent conductor,” Bao said.
The next step was to see how well the material could restore both its mechanical strength and its electrical conductivity after damage.
The researchers took a thin strip of the material and cut it in half with a scalpel. After gently pressing the pieces together for a few seconds, the researchers found the material gained back 75 per cent of its original strength and electrical conductivity. The material was restored close to 100 per cent in about 30 minutes. “Even human skin takes days to heal. So I think this is quite cool,” Tee said. What’s more, the same sample could be cut repeatedly in the same place. After 50cuts and repairs, a sample withstood bending and stretching just like the original.
SENSITIVE TO TOUCH
The team also explored how to use the material as a sensor. Twisting or putting pressure on the synthetic skin changes the distance between the nickel particles and, therefore, the ease with which electrodes can move. These subtle changes in electrical resistance can be translated into pressure and tension data on the skin.
Tee said that the material is sensitive enough to detect the pressure of a handshake. It might, therefore, be ideal for prosthetics, Bao added. The material is sensitive not only to downward pressure but also to flexing, so a prosthetic limb might someday be able to register the degree of bend in a joint.
Tee pointed out other commercial possibilities. Electrical devices and wires coated in this material could repair themselves.
Next up, Bao said, is the team’s goal to make the material stretchy and transparent, so that it might be suitable for wrapping and overlaying electronic devices or display screens.
Nobody knows the remarkable properties of human skin like the researchers struggling to emulate it. Not only is our skin sensitive – sending the brain precise data about pressure and temperature – but it also heals efficiently to preserve a protective barrier against the world. Combining these two features in a single synthetic material presented an exciting challenge for Stanford professor Zhenan Bao and her team.
Now, they have succeeded in making the first material that can both sense subtle pressure and heal itself when torn or cut. Their findings appear in the journal Nature Nanotechnology.
In the last decade, there have been major advances in synthetic skin, said Bao, the study’s principal investigator, but even the most effective self-healing materials was not a good bulk conductor of electricity, a crucial property.
“To interface this kind of material with the digital world, ideally you want it to be conductive,” said Benjamin Tee, a team member.
A NEW RECIPE
The researchers succeeded by combining two ingredients to get what Bao calls “the best of both worlds” – the self-healing ability of a plastic polymer and the conductivity of a metal.
They started with a plastic consisting of long chains of molecules joined by hydrogen bonds- the relatively weak attractions between the positively charged region of one atom and the negatively charged region of the next.
“These dynamic bonds allow the material to self-heal,” said Chao Wang, another member. The molecules easily break apart, but then when they reconnect, the bonds reorganize themselves and restore the structure of the material after it gets damaged, he said. The results is a bendable material, which even at room temperature feels a bit like saltwater taffy left in the fridge.
To this resilient polymer, the researchers added tiny particles of nickel, which increased its mechanical strength. The nanoscale surfaces of the nickel particles are rough, which proved important in making the material conductive. Tee compared these surface features to “mini-machetes,” with each jutting edge concentrating an electrical field and making it easier for current to flow from one particle to the next.
The result was a polymer conducted electricity. “Most plastics are good insulators, but this is an excellent conductor,” Bao said.
The next step was to see how well the material could restore both its mechanical strength and its electrical conductivity after damage.
The researchers took a thin strip of the material and cut it in half with a scalpel. After gently pressing the pieces together for a few seconds, the researchers found the material gained back 75 per cent of its original strength and electrical conductivity. The material was restored close to 100 per cent in about 30 minutes. “Even human skin takes days to heal. So I think this is quite cool,” Tee said. What’s more, the same sample could be cut repeatedly in the same place. After 50cuts and repairs, a sample withstood bending and stretching just like the original.
SENSITIVE TO TOUCH
The team also explored how to use the material as a sensor. Twisting or putting pressure on the synthetic skin changes the distance between the nickel particles and, therefore, the ease with which electrodes can move. These subtle changes in electrical resistance can be translated into pressure and tension data on the skin.
Tee said that the material is sensitive enough to detect the pressure of a handshake. It might, therefore, be ideal for prosthetics, Bao added. The material is sensitive not only to downward pressure but also to flexing, so a prosthetic limb might someday be able to register the degree of bend in a joint.
Tee pointed out other commercial possibilities. Electrical devices and wires coated in this material could repair themselves.
Next up, Bao said, is the team’s goal to make the material stretchy and transparent, so that it might be suitable for wrapping and overlaying electronic devices or display screens.
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