An Intestine-Based Biocompatible Humidity Sensor for Environmental and Medical Measurements

The biocompatible devices suitable for recycling and biodegrading can be achieved with organic materials in nature. In this work, a biocompatible capacitive humidity sensor is presented to reduce the amount of electronic waste and contribute to the sustainability of natural resources and the future. The sensor consists of three layers. The first layer is the processed intestine layer of cattle. Biocompatibility is achieved with this layer. In addition to being a highly absorbing tissue, the intestine has been used for centuries for the long-term preservation of meat-based food. Correspondingly, the developed sensor is found to be more durable and long-lasting than other natural-material-based humidity sensors in the literature. The other layers of the sensor are interdigitated copper electrodes and a 0.2-mm-thick thin-film strip. A thin-film strip increases mechanical strength as well as flexibility. The developed sensor prototype was subjected to various tests in the humidity range of 20%–90%. In these tests, the hysteresis characteristic of the sensor, its response–recovery time, and its long-term stability and short-term step responses were examined. Moreover, as a possible application in medicine, the sensor can be used to detect breathing cycles. The sensor’s response and recovery times were measured as 8.72’ and 4.47’, respectively, possibly attributed to the stabilization of our test setup, while the sensor successfully detected deep, normal, and fast breathing. Despite being kept in an uncontrolled environment, the sensor continued to operate consistently for breath measurements after 56 weeks, which is more than a year.