Flexible Textile-Based Hybrid Piezoresistive Sensors for Human-Motion Monitoring

Textile-based sensors offer a promising platform for human-motion monitoring because of their flexibility, comfort, and ease of integration into clothing. The objective of this study was to develop a textile-based hybrid piezoresistive sensor by combining carbon black (CB) and carbon nanofibers (CNFs) with different filler geometries within a flexible poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) matrix. The novelty of the proposed approach lies in incorporating CB and CNFs into the same elastomeric sensing layer directly deposited onto an elastic knitted textile substrate and systematically comparing its sensing behavior with the corresponding single-filler CB/SEBS and CNF/SEBS systems. Three sensing coatings, CB/SEBS, CNF/SEBS, and hybrid CB+CNF/SEBS, were deposited onto textile substrates by blade coating. All formulations exhibited uniform coating and good adhesion to the fabric. Coating uniformity and adhesion were assessed through visual inspection, electron microscopy, and mechanical cycling by monitoring peeling, cracking, and delamination. Dynamic piezoresistive tests demonstrated that all sensors were capable of strain monitoring, while the 2 wt% CB+ 2 wt% CNF hybrid formulation exhibited the highest sensitivity among the investigated systems. The resistance response was dependent on both the magnitude and rate of strain deformation. The hybrid sensor was further successfully applied to monitor knee, wrist, and elbow movements during physical exercise. These findings demonstrate that the combination of CB and CNF fillers within a flexible SEBS matrix provides a promising route toward highly strain-sensitive textile sensors for wearable human-motion monitoring.