Hygroscopic braille surface enabled by hydrogel swelling

Tactile displays provide critical access to information for individuals with visual impairments, yet most current systems remain limited in functionality and accessibility in healthcare applications. Here, we present a hydrogel-based tactile display system that utilizes hygroscopic swelling to generate tactile Braille patterns through deformation of an overlying elastic film. The system integrates polyacrylamide hydrogels embedded in PDMS microchannels and enables localized, touch‑perceivable protrusions upon moisture absorption. Our experiments show that the extrusion height of Braille dots increases with hydrogel sizes and decreases with film thickness. A theoretical model is developed to capture the mechanical interplay between hydrogel swelling and film elasticity, showing agreement with experimental data. Furthermore, we demonstrate functional extensions of the hydrogel Braille systems, including a sweat-capturing patch and a flow pressure sensor based on capillary bursting valves, both designed to provide non-visual feedback.