Keratin eutectogel as a strain sensor: Towards environmentally friendly technologies

Flexible strain sensors have gained a lot of interest in the last decade in response to the increasing demand for wearable and flexible electronic devices for medical applications and soft robotics. In this work, a simple economic strategy is proposed to fabricate a protein-based strain sensor from bovine horns. The keratinous material undergoes a mild alkaline hydrolysis at low temperatures in the presence of a deep eutectic solvent (DES) to obtain a keratin eutectogel. These novel materials showed great stretchability (similar to 90 %) and excellent sensing capabilities (gauge factor = 3.7), while being biocompatible and biodegradable. Furthermore, the materials were used for more than 600 operating cycles without any significant signal loss and with excellent linearity of the electrical response. Due to the ionic nature of the DES, the keratin eutectogel showed high ionic conductivity and anti-drying properties, allowing their use for extended periods of time without a significant loss of signal stability. As a result, the proposed strain sensor was successfully used for the sensing of human motions. This work can lead to a paradigm shift in the construction of flexible sensing devices by envisioning environmentally friendly materials with excellent properties to replace synthetic ones, thereby helping to reduce the negative impact of technological developments on nature.