A Multi-Line Refreshable Braille Device Using a Variable Stiffness Polymer and Stretchable Joule Heating Electrodes

This work demonstrates a multi-line refreshable Braille device (RBD) employing a hybrid actuation system composed of a variable stiffness polymer (VSP) substrate integrated with stretchable Joule heating electrodes (JHE) and a micropump. The electrodes feature a multilayer structure comprising carbon nanotubes (CNT) and silver nanowires (AgNW), optimized for electrical conductivity, mechanical resilience, and thermal uniformity. The multilayer is laser-patterned into individual serpentine traces to enable localized and efficient Joule heating to soften the VSP membrane above its glass transition temperature (∼50 °C) within 2 seconds, thus allowing pneumatic pressure to raise tactile pins by >0.5 mm for Braille reading. The Joule-heating electrodes require ∼0.027 W per dot, corresponding to a total energy of ∼0.04 J per dot per actuation, including the micropump, which is low compared to existing technologies. Comprehensive electrode characterization identifies an optimal resistance range (5.5 to 6.9 kΩ) for uniform and stable heating. Thermal analysis reveals a critical upper power limit (∼0.04 W), beyond which the AgNW structure undergoes degradation. A fully integrated 4 × 10 cell prototype demonstrates robust mechanical performance and reliable multi-line refresh capabilities over hundreds of cycles. These findings provide a promising foundation for combining deformable polymers and stretchable conductive electrodes in advanced tactile interfaces, advancing compact, energy-efficient multi-line Braille displays. Areas for future refinement are discussed to enhance the practical usability and reliably of the RBD devices.