FDM-based fabrication of flexible CNT/TPU strain sensors with optimized infill patterns and ultrasonication CNT coating for wearable health monitoring

Siriporn WU; Nutthapong  POOMPIEW; Pranut POTIYARAJ; Chuanchom AUMNATE; Patrapee  KUNGSADALPIPOB

doi:10.55713/jmmm.v36i4.2690

Authors

Siriporn WU Department of Materials Science, Faculty of Science, Chulalongkorn University, Phayathai road, Bangkok, 10300, Thailand
Nutthapong POOMPIEW Department of Materials Science, Faculty of Science, Chulalongkorn University, Phayathai road, Bangkok, 10300, Thailand https://orcid.org/0000-0002-8740-1303
Pranut POTIYARAJ Department of Materials Science, Faculty of Science, Chulalongkorn University, Phayathai road, Bangkok, 10300, Thailand ; Center of Excellence in Responsive Wearable Materials, Faculty of Science, Chulalongkorn University, Bangkok 10330 Thailand https://orcid.org/0000-0002-9114-9155
Chuanchom AUMNATE Center of Excellence in Responsive Wearable Materials, Faculty of Science, Chulalongkorn University, Bangkok 10330 Thailand ; The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330 Thailand https://orcid.org/0000-0003-4377-333X
Patrapee KUNGSADALPIPOB Department of Materials Science, Faculty of Science, Chulalongkorn University, Phayathai road, Bangkok, 10300, Thailand ; Center of Excellence in Upcycled Materials from Industrial and Agricultural Wastes, Faculty of Science Chulalongkorn University, Bangkok 10330 Thailand https://orcid.org/0009-0001-1215-052X

DOI:

https://doi.org/10.55713/jmmm.v36i4.2690

Keywords:

Strain sensor, 3D printing, Carbon nanotubes (CNTs), Wearable electronics, Motion detection

Abstract

Wearable motion sensors have become essential tools for monitoring human movement across a broad range of health applications. In this study, flexible strain sensors were developed using 3D-printed thermoplastic polyurethane (TPU) substrates combined with carbon nanotubes (CNTs). Three internal architectures: triangle (TR), grid (GD), and honeycomb (HN) with infill densities ranging from 10% to 20% were fabricated using fused deposition modeling (FDM) to investigate the influence of structural design on mechanical and sensing performance. Conductivity was achieved by an ultrasonication cavitation-assisted CNT deposition followed by thermal treatment, enabling CNT attachment on TPU surfaces and partial penetration into interlayer gaps. SEM analysis confirmed the formation of a rough CNT-coated surface providing conductive pathways for strain sensing. Mechanical testing showed that infill pattern strongly influenced deformation behavior, with the honeycomb structure demonstrating greater structural compliance and elongation than other patterns. Among all configurations, the C-HN10 sample (honeycomb infill with 10% density) demonstrated the best sensing performance, achieving a gauge factor of 9.283 in the low-strain region while exhibiting stable cyclic responses. The optimized sensor maintained repeatable electrical signals under bending deformation and when integrated into body-motion monitoring wearable bands. These results demonstrate that pattern control of FDM-printed structures provides an effective strategy for tuning the mechanical flexibility and sensitivity of CNT-coated TPU strain sensors, offering a scalable method for developing wearable motion-tracking devices.

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