On the design and development of a thermoplastic polyurethane-cotton-lycra fiber-based wearable sensor using 3D printing

Abstract

Over the past two decades, significant work has been reported on fused filament fabrication (FFF) of thermoplastic polyurethane (TPU). But hitherto little has been reported on TPU printed on cotton-lycra fiber for shape-memory applications (under tensile loading) as a wearable sensor. This study highlights the design and development of tensile coupons (per ASTM-D638-Type-V) of TPU on 75% cotton-25% lycra fabric, using a design of experiments (DOE) approach to establish the FFF process for monitoring of shape memory (muscle movement) under tensile loading conditions. The result based on the general linear model (GLM) approach suggested that the sample fabricated at the stretched-cotton-lycra (SL) of 20 mm, printing orientation towards the weft (stretchable) side (POTWS) of cotton-lycra of 0°, and infill density (ID) of 100% observed the peak stress (PS) of 14.37 MPa, stiffness of 25.50 N/mm, total energy (TE) of 2863.39 N.mm, and Young's modulus (E) of 26 MPa. The wearable sensor was designed and simulated in the high-frequency structure simulator (HFSS). After the simulation, the sensor was fabricated as a microstrip patch antenna (MPA) at the suggested settings and tested on a vector network analyzer (VNA), yielding a resonance frequency (R_f) of 2.47 GHz and a return loss (S₁₁) of −20.03 dB. Also, the dielectric properties of the selected sample were 2.63 with a simulated specific absorption rate (SAR) of 0.22 W/kg, indicating it may store electrical energy, enabling consistent, efficient signal transfer with minimal energy loss, making it a more preferable choice for real-time monitoring in muscle memory applications.