Strain Sensing Device Image
A wearable strain sensing device can effectively detect a wide range of strains. (Credit: Terasaki Institute)

Many bodily functions in humans are manifested by mechanical deformations to the skin, and these mechanical changes can be detected and monitored by measuring different levels of strain at various points throughout the body. Researchers have designed a wearable strain sensing device that can effectively detect a wide range of strains. To maximize the stretchiness of this sensor, they drew inspiration from an example found in nature.

Snakes are well known in having the ability to stretch to multiple times their normal body size when ingesting prey. Upon closer examination of snakeskin, the researchers observed that snakeskin is covered with overlapping scales; when strain is applied, these scales slide past each other and are displaced into separated scales with skin interspersed among them. This confers exceptional stretchiness to the skin.

The researchers used this design concept in fabricating their sensor. A thin layer of PEDOT:PSS was applied and baked onto an elastomer tape. This layer was then stretched to an experimentally optimized 50 percent strain level. This process resulted in cracks and the formation of microscale pieces, or “islands” in the layer’s surface, with interspersing areas of PEDOT:PSS. These exposed areas served as bonding sites for the application of a second thin layer of PEDOT:PSS. Once applied, the second layer was further stretched to a 100 percent strain level, resulting in the creation of additional islands and areas that naturally aligned with those of the first layer. When released from stretching, a structure was created with overlapping islands that mimicked the scaly structure of a snake.

The versatility of this wide-ranging wearable sensor can be applied to myriad biomedical needs, such as in monitoring cardiac or circulatory functions, aiding subjects with difficulties in vocalization or swallowing, or in the physical rehabilitation and evaluation of athletic performance. It can also be used in such creative applications as improving communication for those who work in noisy environments or in monitoring psychological conditions associated with facial expressions.