Researchers have developed an ultrathin pressure sensor that can be attached directly to the skin to measure how fingers interact with objects to produce useful data for medical and technological applications. The sensor has minimal effect on the users’ sensitivity and ability to grip objects and it is resistant to disruption from rubbing.
There are many reasons why researchers wish to record motion and other physical details associated with hands and fingers. The hands are the primary tools for directly interacting with and manipulating materials and environments. By recording the way in which hands perform various tasks, it could help researchers in fields such as sports and medical science as well as neuroengineering.
Fingertips are extremely sensitive — so much so that a superthin plastic foil just a few millionths of a meter thick is enough to affect somebody’s sensations. A wearable sensor for the fingers has to be extremely thin, which also makes it very fragile and susceptible to damage from rubbing or repeated physical actions. In order to overcome this, the team created a special functional material that is thin and porous called a nanomesh sensor.
Two kinds of layers were made for the sensors. Both layers were made by a process called electrospinning, which resembles a spider spinning its web. One is an insulating polyurethane mesh with fibers about 200 nanometers to 400 nanometers thick. The second layer is a stencil-like network of lines that forms the functional electronic component of the sensor. This is made from gold and uses a supporting frame of polyvinyl alcohol, often found in contact lenses, which after manufacture, is washed away to leave only the gold traces it was supporting. Multiple layers combine to form a functional pressure and movement sensor.
The sensor maintained its performance as a pressure sensor even after being rubbed against a surface with a force of 100 kilopascals (roughly equivalent to atmospheric pressure) 300 times without breaking.