A team from the Terasaki Institute for Biomedical Innovation has developed a wearable device based on how the skin of a snake works.

Many functions of the human body are manifested in the form of mechanical deformation of the skin: it stretches, bends or moves muscles. These mechanical changes can be found and tracked by measuring stress levels at various points throughout the body.

In recent years, such movements have been monitored using wearable sensors, they can detect:

  • high level stress (40-100%): movement of fingers, joints and limbs
  • medium tension (10-40%): swallowing and face movement,
  • low voltage (<1% -10%): pulse and vocal cord vibrations.

In order to provide the highest level of conductivity and stability, it is best to use PEDOT: PSS is a polymer blend of two ionomers. One component in this mixture consists of sodium polystyrene sulfonate, which is sulfonated polystyrene. But the low elongation of PEDOT: PSS films leads to a decrease in the performance of wearable devices based on it.

The authors in a new work have developed a wearable device that effectively detects different levels of voltage. To maximize the extensibility of this sensor, the authors took snakeskin principles as a basis. Snakes can stretch several times over their normal body size because their skin is covered with overlapping scales. When tension is applied, these scales slide over each other and are easily displaced as needed. Therefore, the skin of snakes is extremely elastic.

The researchers used this design concept in their sensor. They applied a thin layer of PEDOT: PSS and baked it with elastomeric tape. Then this layer was stretched by 50%. This process led to the formation of cracks and microscopic pieces on the surface of the layer. These exposed areas served as bonding points for the application of a second thin layer of PEDOT: PSS. After application, the second layer was further stretched to 100%. As a result, new extensions and islands were formed, which naturally coincided with the regions of the first layer.

Based on the results of a number of experiments, the sensor produced well-defined signals with a sensitivity range of two orders of magnitude. The signals accurately reflected the degrees and angles of movement. In addition, the sensor has demonstrated excellent conductivity and durability.

The new development can be used to monitor cardiac or circulatory functions, to help people who have difficulty vocalizing or swallowing, as well as in physical rehabilitation or assessing athletic performance.