Textile sensor geometries for wearable respiration systems incorporated carbon nanotube-based conductive inks

Respiratory illnesses, particularly in densely populated and rapidly industrializing regions, have become a leading cause of death, placing a growing burden on healthcare systems. Traditional medical devices for monitoring breathing signals often require complex setups, both in and outside of hospitals, leading to patient discomfort and increased operational costs. As a result, there is a pressing need for innovative, affordable, and comfortable on-body sensing solutions for continuous, patient-centric monitoring. This study proposes a metal-free, water-based, sustainable, and cost-effective conductive ink formulation incorporating carbon nanotubes and plant-based cellulose nanocrystals for scalable textile printing. Through rheological analysis, ink stability, and surface coverage, the optimal ink composition was investigated by changing the relative composition of these two ink components. A systematic study was then conducted on the piezoresistive sensitivity of different sensor patterns, tested under cyclic loading that mimics human chest movement. Textile sensors printed with the optimal CNT/CNC-1:1 ink composition, featuring line, strain gauge, and star geometries, demonstrated sensitivity values of 46.34 and 71.91 at 5 % and 10 % strain for line pattern; 20.97 and 27.93 for the strain gauge pattern; and 34.11 and 40.47 for the star pattern, respectively. The on-body performance of these sensors, when placed on a humanoid mannequin, showed reliable and consistent breathing profiles, enabling remote communication for health data transmission. The proposed approach offers a scalable, versatile, accessible, and polymer- and metal-free solution for creating wearable sensors that are responsive to strain values up to 10 %. This work paves the way for material-led sensing technologies in future patient-centric healthcare systems.