Stretchable All‑Rubber Thread‑Shaped Triboelectric Nanogenerators for Self‑Powered Wearable Energy Harvesting and Biomechanical Tracking

Introduction

Wearable electronics that are comfortable, soft, and breathable are becoming integral to biomedical monitoring, robotics, human‑computer interfaces, military applications, and consumer devices. However, conventional batteries and supercapacitors struggle to meet the demands of these systems because of their rigidity, limited lifespan, added weight, and environmental impact. A sustainable alternative is to harvest the abundant mechanical energy produced by human motion. Triboelectric nanogenerators (TENGs), which convert mechanical deformation into electrical energy via triboelectrification and electrostatic induction, are lightweight, inexpensive, and versatile, making them ideal for self‑powered wearables.

Thread‑shaped TENGs have shown promise for monitoring physiological signals such as joint movement, tactile sensing, and pulse detection. Yet their stretchability—a critical requirement for complex limb motions—has remained a challenge. Existing smart textiles often rely on serpentine metal foils, pre‑strained substrates, or metal nanowires, limiting large‑scale production and durability.

To overcome these limitations, we introduce a double‑helix, all‑rubber SATT that combines silver‑coated glass microspheres dispersed in silicone rubber (SCT) with a silicone‑rubber‑coated version (SSCT). This design achieves >100 % stretchability, high electrical output, and mechanical robustness, enabling both energy harvesting and self‑powered sensing in a single, flexible thread.

Methods

Fabrication of the SCT

Silver‑coated glass microspheres (Shenzhen Xiate Science and Technology Co. Ltd., China) were blended with solid silicone rubber (TN‑920) at a weight ratio of 3:1 for 1.5 h. The mixture was extruded and vulcanized at 110 °C using a screw extrusion machine, producing a 1 mm‑diameter conductive thread. Five such threads were coiled together, and their ends were coated with a silicone‑rubber mixture (Ecoflex 00‑30 and curing agent, 1:1) and cured under vacuum (20 min) and 80 °C (2 h). The resulting SCT exhibited excellent stretchability and conductivity.

Fabrication of the SSCT

The SCT was placed into a 4 mm‑diameter mold, and a silicone‑rubber mixture (Ecoflex 00‑30 + curing agent) was injected. After evacuation and heating, the SSCT was demoulded, yielding a fully encapsulated triboelectric partner.

Measurement System

Scanning electron microscopy (SEM) was performed with a ZEISS EVO18 (Carl Zeiss Jena, Germany). Electrical outputs were recorded using a KEITHLEY 2611B electrometer.

Results and Discussion

The SATT integrates two double‑helix all‑rubber threads: the SCT, containing uniformly dispersed silver‑coated glass microspheres, and the SSCT, a silicone‑rubber‑coated SCT. Fabrication details are shown in Fig. 1a. The high‑load silicone matrix ensures excellent mechanical compatibility, while the embedded microspheres form a 3‑D conductive network, granting the SCT high conductivity and stretchability. SEM images (Fig. 1b–f) confirm the absence of gaps between the conductive core and silicone coating, and the overall structure (Fig. 1g) can be stretched to ~100 % strain—well beyond previously reported thread‑shaped TENGs.

Electrically, the SATT behaves like a series of capacitors in parallel. When stretched, the silicone surface and the conductive core separate, creating a potential difference that drives electrons through the external circuit. Releasing the strain reverses the flow, completing a full cycle of charge transfer.

Finite‑element analysis using COMSOL (Fig. 2b) validates this mechanism: the potential difference increases linearly with applied tensile force. The SCT’s resistance remains stable up to 50 % strain but rises modestly at higher strains; incorporating five intertwined conductive threads mitigates this effect (Fig. 2c‑d). Tensile durability tests show that the SCT maintains performance over 10 000 cycles at 100 % strain (Fig. 2e). The electrical output scales with the number of conductive threads: a 5 cm SATT reaches 3.82 V (open‑circuit) and 65.8 nA (short‑circuit) at 100 % strain (Fig. 2f‑g). Response and recovery times at 1 Hz are 48 ms and 220 ms, respectively, indicating suitability as a self‑powered motion sensor.

To translate this capability into a textile, we wove SCT and SSCT units into a plain‑weave self‑powered smart textile (SPST, 5 × 7 cm²) (Fig. 3a‑b). When stretched to 100 % strain, the SPST generates 8.1 V and 0.42 µA (Fig. 3d‑e). During contact‑separation with cotton, the SPST produces up to 150 V and 2.45 µA at 100 N (Fig. 4c‑d). Power output peaks at 163.3 µW under a 120 MΩ load (Fig. 4e). Stability tests over 10 000 cycles show no voltage degradation (Fig. S2). Capacitor charging experiments demonstrate that a 0.47 µF capacitor reaches 14 V in 150 s, enabling the SPST to power LEDs and a commercial watch (Fig. 4f).

Functional testing confirms the SATT’s ability to act as a self‑powered active sensor. When attached to a finger, the device produces distinct voltage peaks corresponding to bending states (Fig. 5a). The SPST, when affixed to elbow and knee joints, delivers 105 V–116.9 V and 0.73 µA–0.89 µA during flexion/extension, illustrating its potential for rehabilitation monitoring and activity tracking (Fig. 5b‑c).

Conclusion

We have developed a fully rubber‑based, double‑helix thread‑shaped TENG that achieves 100 % strain, converts mechanical energy into electrical power, and serves as a self‑powered sensor for finger and joint motion. Woven into a plain‑weave textile, the device delivers 8.1 V/0.42 µA under stretch and 150 V/2.45 µA during contact‑separation, with a maximum power of 163.3 µW. These robust outputs enable the SPST to power commercial electronics, harvest biomechanical energy, and support future medical and smart‑tracking applications.