Strain-Insensitive Heater on Wrinkled Surface Integrated with Carbon Nanotube Bundles for Wearable Thermal Therapy and Multimodal Tactile Displays

Flexible or stretchable heaters can generate heat despite their deformation, making them suitable for various applications such as wearable devices and human-machine interfaces. This study presents the development and characterization of a highly stretchable heater integrating vertically aligned carbon nanotubes (VACNTs) on a wrinkled elastomer substrate designed to maintain consistent heating performance under mechanical strain. Through a synergistic design considering both material and mechanical structure, the strain-insensitive heater achieves minimal temperature variation (less than 5%) across a tensile strain range of 0-350%. This stable heating performance is attributed to the entangled VACNT strands within a wrinkled structure, which facilitates continuous contact between the nanotubes even under significant strain. Additionally, the heater exhibits high durability, enduring 10,000 cycles at 200% strain, with a heating variation of less than 5%. Furthermore, practical applications of the strain-insensitive heater are demonstrated as a thermal treatment device for finger joints and as a multimodal tactile display capable of transmitting both thermal and pressure sensations. This study represents a significant advancement in the field of flexible and stretchable electronics, offering promising opportunities for wearable thermotherapy and haptic interfaces.