Effect of Infill Density on Electrical Sensitivity of 3D-Printed Flexible Pressure Sensors Using Ultrasonication Cavitation-Enabled Treatment and Thermal-Assisted Method

The development of physiological detection is advancing rapidly, driven largely by the increase in the awareness of sport, healthcare, and biomedical knowledge. Wearable electronics have been integrated into real-world physiological sensing applications, with many recent studies aimed at enhancing their capabilities from both material selection and fabrication perspectives. To create the best fit for specific wearers, three-dimensional (3D) printing is an excellent candidate because of its potential to create structures ranging from simple to highly complex. This work investigates the effect of infill densities (20%, 40%, and 60%) on the electromechanical properties of 3D-printed thermoplastic polyurethane (TPU) using fused deposition modeling (FDM). The printing conditions were consistently controlled throughout the study, specifically using a honeycomb infill pattern. The flexible TPU substrates were successfully 3D-printed, and 1% w/v of multiwalled carbon nanotubes (MWCNTs) were embedded in the 3D-printed samples using an ultrasonic cavitation-enabled treatment and thermal-assisted method. This process aims to prevent CNT fallout while maintaining the compression load-bearing capacity. A compressive load of 10 kN was applied to the samples during electromechanical testing. The results show that a 20% infill density provides the optimum sensitivity of 11.32 MPa -1 at 2V applied voltage due to its appropriate current path, which is confirmed by scanning electron microscope (SEM). The dimension accuracy of the 3D-printed TPU samples tend to increase with higher infill densities and application of the double treatment.