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Many bodily functions in humans are manifested by mechanical deformations to the skin—from the stretching, bending and movement of muscles and joints to the flutter of a pulse at the wrist. These mechanical changes can be detected and monitored by measuring different levels of strain at various points throughout the body.

In recent years, much attention has been focused on wearable sensors to measure these strains for use in personal health monitoring. Some of these sensors can detect high-level (40-100%) strains, such as those associated with the movements of fingers and limb joints, others detect mid-level (10-40%) strains, as found in swallowing and facial movements and still others are sensitive to low-level (<1%-10%) strains observed in wrist pulses and vocal cord vibrations.

Due to its highest levels of conductivity and stability, a highly-favored material for these types of sensors is PEDOT:PSS, or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Previously, very sensitive PEDOT:PSS strain sensors have been developed that can detect strain from very minute movements (<1%), but the inherently poor stretchiness of PEDOT:PSS films result in deteriorating levels of performance and function when used to measure larger strains (>20%). Attempts to solve this problem by adding stretchy polymers, or elastomers, have resulted in increased stretchiness but decreased sensitivity in detecting small strains.

A collaborative team from the Terasaki Institute for Biomedical Innovation has addressed these challenges by designing a wearable strain sensing device that can effectively detect a wide range of strains. In order to maximize the stretchiness of this sensor, the TIBI researchers 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 snake skin, the researchers observed that snake skin 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.