Y. Li et al., 2023
The human fingertip is a highly sensitive instrument for perceiving objects in the environment through touch. According to a recent paper published in the journal Cell Reports Physical Science, a team of Chinese scientists mimicked the underlying sensory mechanisms to create a bionic finger with an integrated tactile feedback system. .
“We were inspired by the human finger, which has the most sensitive sense of touch we know.” The contours of the underlying bone can also be felt.This haptic technology opens up a non-optical method for non-destructive inspection of the human body and flexible electronics.”
According to the authors, the artificial tactile sensors developed so far were only able to recognize and distinguish shapes, surface textures, and hardness. However, we cannot perceive subterranean information about these substances. This typically requires optical techniques such as CT scans, PET scans, ultrasound tomography (which scans the exterior of the material to reconstruct an image of its internal structure), or MRI. But they all have drawbacks as well. Similarly, optical profilometry is often used to measure surface profiles and finishes, but it works only on transparent materials.
When a finger touches something, the skin experiences mechanical deformations such as compression and stretching, causing mechanoreceptors to send out electrical impulses. These impulses travel through the central nervous system to the somatosensory cortex of the brain. The brain integrates these electrical impulses to discern the characteristics of the objects we touch. This tactile feedback allows us to perceive material shape, surface texture, hardness and softness.
A bionic finger inspired by a hard letter A coated with soft silicone. Credit: Y. Li et al., 2023
A smart bionic finger mimics this feedback system. A metal cylinder attached to the top of the finger acts as a contact tip, and a carbon fiber beam acts as a tactile mechanoreceptor (sensing unit). These are connected to the signal processing module. A finger “scans” the surface of an object by applying periodic pressure in a stabbing fashion. This compresses the carbon fibers and, depending on how much the material is compressed, conveys information about its relative stiffness or softness. That information, along with the recorded ground locations, is sent to a computer, which transforms the data into a 3D map.
The authors tested bionic fingers using a variety of complex objects. For example, we tested the finger’s ability to detect and map the hard letter “A” (see video above) and other abstract shapes just beneath the soft silicone layer. I could even tell with my fingers if the inner material was hard or soft, and if the outer silicone coating was soft.
They also created a 3D printed physical model of human tissue from three layers of rigid polymer (“skeleton”) and a soft silicone outer layer (“muscle”). The bionic finger was scanned and successfully reproduced his 3D profile of the structure of the model tissue, including the location of the ‘vessels’ underneath the ‘muscle’ layer.
Finally, the authors tested the bionic finger on a defective electronic device and successfully created a map of the internal components. Fingers were able to pinpoint where the circuit was severed and pinpoint improperly drilled holes without breaking through the surrounding outer layer. “Next, we want to develop the ability of bionic fingers to do omnidirectional detection using different surface materials,” he said.
DOI: Cell Reports Physical Science, 2023. 10.1016/j.xcrp.2023.101257 (About DOI).
