Advances in additive manufacturing for flexible sensors: bespoke conductive TPU for multianalyte detection in biomedical applications

Abstract

• Conductive filament for additive manufacturing is made with 40 wt% carbon black CB) in TPU. • Optimised loading of CB achieved an ideal balance between flexibility, printability, conductivity and electrochemical performance. • The correct use of additive manufacturing technology is critical to avoid print failure. • Additively manufactured electrodes are shown that the connection stem bent at five different angles, showing no deterioration of their electrochemical performance. • Electrodes are applied to the simultaneous multianalyte detection of dopamine, uric acid and nitrite within urine. Additive manufacturing electrochemistry has the potential to revolutionise the wearable sensors industry through the rapid and customisable production of sensors; however, the currently available conductive filaments are not fit for purpose due to issues with their base polymers and filler loadings. In this work, we present the development of a highly flexible and conductive filament for additive manufacturing made with 40 wt% carbon black (CB) in thermoplastic poly(urethane) (TPU). This optimised loading of CB achieved an ideal balance between flexibility, printability, conductivity, and electrochemical performance, as demonstrated by bulk resistance measurements, TGA, SEM, XPS, Raman and through electrochemical scan rate studies, where a heterogeneous electron transfer rate constant ( k 0 ) of 2.69 (± 0.10) x 10 –3 cm s -1 was obtained. Importantly, the electrodes exhibited great stability over 100 scans and excellent reproducibility after cleaning and re-use. Moreover, the additively manufactured electrodes were tested with the connection stem bent at five different angles, showing no deterioration of their electrochemical performance. Furthermore, we show that within the use of additive manufacturing technology, the choice of printer is key to avoid print failure; using a distance from extruder gears to nozzle, namely the filament path, as short as possible results in more reproducible additive manufacturing. Finally, the electrodes bent to the highest angle were applied to the simultaneous multianalyte detection of dopamine, uric acid and nitrite within urine demonstrating an excellent electroanalytical performance with a clear separation of the three peaks. This highly flexible and conductive material holds the potential to elevate additive manufacturing within the fields of flexible electronics and wearable electrochemical sensors.

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