Multi-material Direct Ink Writing and Embroidery for Stretchable Wearable Sensors

Abstract

The development of wearable sensing systems for sports performance tracking, rehabilitation, and injury prevention has driven growing demand for smart garments that combine comfort, durability, and accurate motion detection. This paper presents a textile-compatible fabrication workflow that integrates multi-material direct ink writing with automated embroidery to create stretchable strain sensors directly embedded into garments. The process combines sequential multi-material printing of a silicone-carbon grease-silicone stack with automated embroidery that provides both mechanical fixation and electrical interfacing in a single step. The resulting hybrid sensor demonstrates stretchability up to 120% strain while maintaining electrical continuity, with approximately linear behaviour up to 60% strain (R^2 = 0.99), a gauge factor of 31.4, and hysteresis of 22.9%. Repeated loading-unloading tests over 80 cycles show baseline and peak drift of 0.135% and 0.236% per cycle, respectively, indicating moderate cycle-to-cycle stability. Mechanical testing further confirms that the silicone-fabric interface remains intact under large deformation, with failure occurring in the textile rather than at the stitched boundary. As a preliminary proof of concept, the sensor was integrated into wearable elbow and knee sleeves for joint angle monitoring, showing a clear correlation between normalised resistance change and bending angle. By addressing both mechanical fixation and electrical interfacing through embroidery-based integration, this approach provides a reproducible and scalable pathway for incorporating printed stretchable electronics into textile systems for motion capture and soft robotic applications.

Figures (8)

• Figure 1: (1) Multi-material direct ink writing of silicone and conductive ink to form a soft, stretchable strain sensor. (2) Automated embroidery mechanically anchors the printed sensor to a textile substrate while simultaneously creating electrical interconnects. (3) The integrated system enables wearable motion sensing applications.
• Figure 2: Fabrication and integration of the printed strain sensor. (a) Direct ink writing process of the sensor (b) Embroidery step used to stitch and mechanically anchor the printed sensor to the fabric. (c) Front view of the integrated strain sensor showing the printed and stitched structure. (d) Back view illustrating the embroidered conductive interconnects.
• Figure 3: Custom multimaterial 3D printing system. (a) Overview of the modified printer structure based on an Ender 5 Plus platform. (b) Syringe-pushing assembly for silicone mixing. (c) Dual printhead rack featuring separate printheads for silicone and conductive ink.
• Figure 4: Characterisation and demonstration of the printed strain sensor. (a) Tensile testing setup showing the sensor mounted on the universal testing machine. (b) Sensor condition after mechanical failure during the stretch-to-failure test. (c) Integration of the printed and embroidered sensor onto an elbow sleeve for wearable motion sensing.
• Figure 5: Cyclic strain characterisation of the printed strain sensor. The black curve represents the mean of the load and unloading sections, while the grey shaded region indicates ±1 standard deviation. The green dashed line shows the average midpoint between loading and unloading for each cycle, and the red line is the linear regression of this midpoint curve, used to evaluate sensor linearity and sensitivity.