Conversion of eggshell wastes to multifunctional sensing layer for wearable health monitoring

Abstract

Temperature and strain sensing are two essential parameters for long-term healthcare monitoring systems, such as fever detection and rehabilitation training. A biocompatible, flexible sensor is presented to enable multifunctional monitoring (e.g., temperature and strain), fabricated using a simple and rapid drop-casting technique that challenges conventional, complex fabrication methods. Specifically, the inner eggshell membrane with its porous structure, fibrous networks, and chemical absorption capacity is employed as both structural support and a conductive polymer capture agent, offering mechanical flexibility, electromechanical stability, and strong interfacial adhesion. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), blended with polyvinyl alcohol (PVA) and pullulan, was employed as the conductive coating material and uniformly deposited onto the inner eggshell membrane to form the sensing layer. The performance of the fabricated sensor is based on resistive-type temperature detection. It exhibits a linear temperature dependence of resistance in a temperature range of 20–40 °C with the correlation coefficient of R² = 0.9606 for the line fitted to the experimental data. The mentioned temperature sensor displays a negative temperature coefficient of resistivity (TCR) of −1.89 %/°C., which is comparable with the conventional metal temperature sensors. In addition to serving as a reliable temperature sensor, the device can also operate as a strain sensor, capable of real-time detection of human motions such as knee and finger bending. This biocompatible, organic, and multifunctional wearable sensor exhibits strong potential for physiological signal monitoring. To the best of our knowledge, this is the first report of an inner eggshell membrane-based multifunctional sensor that incorporates reduced e-waste components for sustainable medical applications.