3D-printed flexible strain FDM sensor for monitoring finger joint movement

Journal Article

2026

Published in: https://link.springer.com/article/10.1007/s10854-026-17057-7

Wearable sensors have recently become essential tools in both preventive and corrective healthcare. Fused deposition modeling (FDM) is one of the rapidly evolving 3D-printing fields with considerable potential for building and improving wearable sensors. In general, FDM filaments consist of thermoplastics that are considered electrical insulators. However, manufacturers start to add carbon-based composites to some of these FDM filaments to create electrically conductive filaments. These conductive filaments open the door for building functional sensors. The authors of this paper designed and 3D-printed two thermoplastic polyurethane (TPU) resistive-based flexible strain sensors (two different conductive tracks: a strain gauge and an open oval) that are capable of measuring finger flexion. These sensors are tested and compared using four different finger movement protocols and a three-point bending flexural test. Results of the three-point bending flexural test demonstrate that the strain gauge design achieves a superior negative gauge factor of − 12.1, while the open oval sensor realizes a negative gauge factor of − 10.65. However, both sensors exhibited pronounced hysteresis (41.7% for the strain gauge and 71.6% for the open oval). The comparative study revealed that a conductive track with a strain gauge is as effective as, or even better than, an open oval, except for repeatability error (8.02% for the open oval and 13.00% for the strain gauge). These findings are significant as they pave the way for creating 3D-printed wearable strain sensors. This study aims to promote the use of commercially available FDM conductive filaments in the design and manufacture of wearable flexible sensors for monitoring human joint movements.

• Publisher Name: Journal of Materials Science: Materials in Electronics