3D‐Printed Flexible Multimaterial Wearable System Based on Auxetic Strain Sensors and Dry Electrodes for Cardiorespiratory Monitoring

ABSTRACT

Wearable sensors play a key role in the continuous monitoring of physiological parameters for healthcare and well‐being applications. However, many existing systems still suffer from limitations related to cost, complexity, and limited mechanical compliance. In this scenario, fused deposition modeling (FDM) technique has emerged as an enabling technology for the development of low‐cost and customizable wearable sensing platforms, while fully 3D‐printed multimodal systems remain largely unexplored. This work presents a fully 3D‐printed flexible wearable system that integrates, for the first time, both a strain sensor and dry ECG electrodes made of carbon‐black‐loaded thermoplastic polyurethane (CB‐TPU) within a single flexible device for simultaneous respiratory and cardiac monitoring. The strain sensor features a re‐entrant hexagonal auxetic geometry and was fabricated in three configurations and two lengths. All designs exhibited excellent linearity in the physiologically relevant 0–5% strain range, Gauge Factors up to 3.2, low hysteresis (<10%), and stable performance over 1000 cycles. Dry electrodes with different geometries were characterized in terms of electrode‐skin impedance and signal‐to‐noise ratio, achieving performance comparable to commercial Ag/AgCl electrodes. Preliminary tests demonstrated accurate and stable estimation of respiratory and heart rates, confirming the effectiveness of the proposed fully 3D‐printed CB‐TPU wearable platform for multimodal physiological monitoring.