The sensitivity of artists, craftsmen and surgeons could now be digitized: Researchers have developed a measuring sensor that can convert movements and pressure when using the fingertips into data for technological applications. The special thing about it is that the resistant nano-mesh material is so thin that it covers the fingertip like a second skin and does not impair the wearer’s natural sensitivity.
In addition to seeing and hearing, the sense of touch usually receives little attention – but one thing is clear: The sensitivity of our fingers and the associated ability to use the hand in complex ways is a key element of human success. The concept is based on ingenious systems of perception which, in cooperation with the brain, result in our amazingly fine motor tools. Researchers have been on the trail of the secrets of the sense of touch and the sensitive behavior of the fingers for some time. The results are important for various areas: Neuroscience, medicine and technology can benefit from insights into the fundamentals of the biological system.
In order to track down the sensitivity, attempts have already been made to obtain information through sensors that record data on the movement and pressure behavior of the fingertips. But there has been a problem so far, which in turn is related to the very aspect that you want to research: the high level of sensitivity. It is well known that a person’s fingertips already react to tiny sources of interference, which irritates them in their work. This can strongly falsify measurement results when examining natural behavior.
Filigree layer system with golden lines
In contrast to previous concepts, an optimal fingertip sensor would have to have characteristics that are difficult to reconcile: the material capable of measuring would have to be extremely thin and flexible on the one hand, but also be able to withstand frictional loads and other physical stresses on the other. A Japanese-German research team has now faced this technological challenge. As a solution, they present what is known as a nanomesh sensor. It consists of four ultra-thin, nano-structured layers that can be applied to the skin of the fingertips in order to record human tactile behavior there without interference.
“The Nanomesh layers are produced using the so-called electro-spinning process,” says co-author Takao Someya from the University of Tokyo. As he explains, a layer of polyurethane nanofibers serves as the system’s carrier layer on the skin. “The polyurethane nanofibers are between 200 and 400 nanometers thin, two hundred times thinner than a human hair,” says Someya. On top of this material is a very thin layer of gold. Above this there is again an intermediate layer made of parylene-coated polyurethane nanofibers and then another layer of gold follows.
The precious metal structures form a kind of line matrix that forms the functional electronic component of the sensor, the scientists explain. To make them, gold was applied to a substrate made of polyvinyl alcohol – a plastic that is also used for contact lenses. This substance is rinsed out after the layer has been produced so that only the gold structures remain. The four layers of the sensor are then sealed with another thin layer of polyurethane and polyvinyl alcohol nanofibers, which protects the system from mechanical stress.
Manual dexterity can be grasped without interference
To test the extent to which the concept delivers what it promises, the researchers carried out tests with 18 test subjects. “It showed that the sensors were imperceptible and did not affect the ability to grasp objects or the perceived sensitivity compared to performing the same task without the sensors attached. This is exactly the result we were hoping for, ”says co-author Sunghoon Lee from the University of Tokyo.
It was also shown that the sensor is very stable despite its filigree structure: In abrasion tests with a pressure of one kilogram per square centimeter, its capabilities were not lost even after 300 repetitions. “This shows that we can measure the manipulation of any kind of object – that was not possible before,” says co-car David Franklin from the Technical University of Munich. “In the past, we only had comparatively coarse and stiff measuring instruments that seriously impaired the feeling of the finger,” emphasizes the scientist.
As the researchers explain, this first finger sensor, which can take measurements without the loss of human sensitivity, offers interesting application possibilities. An example would be the digital archiving of the sensitive working methods of craftsmen or surgeons. “Let’s take the fine motor skills of a watchmaker. With the help of the Nanomesh sensor, we could archive for posterity the pressure with which it grips the small individual parts of a watch and how it moves them, ”explains Franklin. If such processes can be recorded digitally, it could also be possible to equip robots with comparable capabilities, say the scientists.
Source: University of Tokyo, Technical University of Munich, specialist article: Science, doi: 10.1126 / science.abc9735