A Sprayable Electrically Conductive Edible Coating for Piezoresistive Strain Sensing

Edible electronics leverages the electronic properties of food-derived materials to deliver safer technologies that can be degraded (or digested) in the environment (or body) at the end-of-life. Sensors will be central to future smart edible robots, and edible strain sensors are particularly interesting as they can transduce deformation, providing real time feedback of the movement. Yet, to date edible strain sensors have been limited to the use of ionic conductive hydrogels, resulting in sensors not directly suitable for direct current operation and therefore not compatible with existing edible batteries. Here, the first edible strain sensor based on electronic conduction made of a novel conductive ink sprayed over an edible substrate is presented. The ink formulation consists of activated carbon (conductor), Haribo gummy bears (binder), and water−ethanol mixture (dispersant). The ink, deposited on multiple substrates by spray deposition, produces edible electrically conductive composite coatings with resistivity of ≈50 Ω cm. The coatings were used as a piezoresistive layer to fabricate strain sensors with gauge factors of 19−92 suitable for direct current operation. As a proof-of-concept of future edible systems, the sensor is validated by integrating it within a gelatin actuator to produce a sensorized gripper powered by an edible battery.