Additive Manufacturing of Customized Flexible Wearable Sensors for Sweat Analysis with Bespoke, Low-Cost Conductive TPU

The development of wearable technology that is non-invasive, customizable, comfortable for the user, and able to transmit data to healthcare providers from remote and rural locations has the potential to revolutionize the healthcare sector and aligns with key United Nations Sustainable Development Goals. In this work, bespoke conductive filaments based on thermoplastic polyurethane (TPU) incorporating different ratios of carbon black (CB) and graphite (GRT) were developed, for the first time, via melt extrusion for additive manufacturing of flexible, wearable electrochemical sensors. Eight formulations were systematically evaluated in terms of morphology, electrical resistance, wettability, and electrochemical behavior. The hybrid composition containing 20 wt% CB and 20 wt% GRT demonstrated the best balance between conductivity, mechanical flexibility, printability, and electrochemical activity, while producing a 45% saving in material cost. Surface activation through (electro)-chemical treatment and mechanical polishing significantly improved the electroactive surface area and heterogeneous electron transfer rate, especially for GRT-containing electrodes. The optimized electrode exhibited the highest <i>k</i> ₀ and <i>A</i> _e values and was integrated into a fully printed three-electrode wristband for non-invasive detection of uric acid (UA) in artificial sweat. Differential pulse voltammetry enabled reliable detection of UA in the 2.5-100.0 μmol L^-1 range with a limit of detection of 1.3 μmol L^-1 and recovery rates up to 99.7%. The sensor also demonstrated high selectivity against typical sweat interferents such as urea, glucose, and tyrosine. These findings support the potential of additively manufactured carbon-based TPU electrodes for application in wearable sensing platforms for real-time biomarker monitoring.