Three-dimensional printed thermoplastic polyurethane on fabric as wearable smart sensors

Abstract

The microstrip patch antenna (MPA) with a thermoplastic substrate has been widely used in wearable sensors primarily due to its lightweight, flexibility, strength, and compactness. But up till now, little has been conveyed on the use of three-dimensional (3D) printed thermoplastic polyurethane (TPU) on cotton-lycra woven (CLW) fabric-based substrate as a wearable sensor. This study presents a novel and scalable approach for characterizing, simulating, and fabricating the substrate for wearable sensor applications. In this study 3D printing of TPU on CLW fabric (70% cotton (on the warp side)-30% lycra (on the weft side) using fused filament fabrication (FFF) process) has been reported with a tradeoff between flexibility and strength (of a substrate for wearable sensor applications). The rheological, mechanical, morphological, four-dimensional (4D), and resonance frequency (RF) characterization of the substrate has been established. As regards rheological properties, the melt flow index (MFI) of primary (1°) recycled TPU was observed as 29.758 g/(10min). Further, the optimized 3D printing settings of TPU were obtained based on the mechanical testing (minimum stiffness, maximum peak strength (PS), maximum Young's modulus (E), and maximum strain energy (SE)) which comes out to be 225°C nozzle temperature, 18 mm/s printing speed and 60% infill density with a stiffness of 3.311 N/mm and PS of 9.628 MPa. The mechanical properties of TPU printed on stretched and unstretched CLW fabric were tested for lower stiffness (more flexibility). To ascertain the mechanical properties, porosity analyses of samples printed on CLW fabric have been performed based on scanning electron microscopy (SEM). For dielectric properties, and RF characterization, the ring resonator (RR) test was performed based on a Vector network analyzer (VNA). Finally, 4D characterization of the substrate was performed by applying a load from 0 to 25 N, resulting in programable RF output (in the industry scientific and medicine (ISM) band).

Preparation and electromagnetic performance of a light-weight, thin, and high-gain three-dimensional woven hollow structure microstrip antenna

“…The overall performance of the 3D woven hollow structure microstrip antenna was good during the compression process without apparent delamination. 32

Figure 13.Process diagram of three point bending experiment.

Figure 14.Mechanical performance analysis of 3D woven hollow structure microstrip antenna (a) Load displacement curve (b) Compression failure process (c) Three-point bending failure process.

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“…The overall performance of the 3D woven hollow structure microstrip antenna was good during the compression process without apparent delamination. 32 As shown in Figure 14(a), the maximum load of the 3D woven hollow structure microstrip antenna was 364 N, and it could be seen from the curve that brittle damage occurred in the sample bending. The curve changed into three stages.…”

On comparison of sensing capabilities of three-dimensional printed wearable sensors

“…The 3D printing of TPU substrates (60 × 54 × 0.65 mm) was performed at 225 °C nozzle temperature, 60 °C bed temperature, 18 mm/s printing speed, and an infill density of 60% on the CLWF with FFF set up (Make: Creality Ender 3 Pro 3D Printer, open source). 14 After this, the silver ink was screen printed for a ring, feed lines, and ground plane of the ring resonator. The silver ink (Make: Electra Polymers ED3000) was directly printed on the TPU substrate using a screen printer (Make: TWS SR 2700 semi-automatic) through a screen with 61/64 polyester mesh and then was cured in an oven for 15 min at 100 ± 5 °C, and no effect on TPU or cloth was noticed.…”

“…13 In one of the recent studies, 3D printing of recycled thermoplastic polyurethane (TPU) on the cotton (80%)-lycra (20%) woven fabric (CLWF) was explored for dielectric properties and four-dimensional (4D) characteristics by using conductive copper as a patch and ground plane for the sensor. 14 Typically, textiles bonded to thick woven materials for conductivity are not suitable for 3D printing owing to their roughness, for textile-based sensors. The previously published literature outlines that in the past two decades, significant studies have been reported on fabricating conducting parts of wearable sensors with silver ink screen printing and copper tape on fabrics.…”

“…This study is the extension to previously reported work where TPU was printed on CLWF (cotton 80%-lycra 20%) and the copper tape was used as conducting patch/ ground plane for the sensor. 14 It may be noted that changing the composition/ proportion of cotton-lycra will change the dielectric property of the substrate material. This combination of cotton-lycra was selected based on commercially available composition/proportion.…”