Micro-Mechanosensory insights from Nature’s Mimosa leaves to shape memory adaptive robotics

Abstract

• Investigate the micro-mechanosensory properties of Mimosa Pudica pinnule and pulvinule using manual and nanoindentation methods. • Pulvinules demonstrated ∼ 2.3, 1.7, and 2.9 times greater response times, trigger and reactive forces, respectively, than pinnules. • A bioinspired soft robotic device, mimicking Mimosa leaves, was developed using graphene-enhanced shape memory polyurethane. • Bioinspired "Mimosa" device exhibited 3.63-fold faster shape transformation than pure polyurethane, due to enhanced thermal conductivity. This study is focused on the micromechanics of the Mimosa Pudica plant to develop an adaptive robot that is 3D-printed using shape memory polymer-graphene composite . Traditionally, leaf-folding responses of Mimosa are examined at the pinna (leaflet) level due to the difficulty of applying small, localized forces without causing damage. Here, we use both hand touch and nanoindentation to analyze the micro-mechanosensory properties of the smaller leaf structures, pinnule and pulvinule. We found that pulvinules respond 1.5 times faster than pinnules when touched by hand due to faster osmotic processes. When using a nanoindenter, the pulvinules showed response times, trigger forces, and reactive forces that were approximately 2.3, 1.7, and 2.9 times faster, respectively, compared to pinnules. Nanoindentation also proved to be more effective than touch, with response times 1.4 times faster and displacement magnitudes 1.2–5.1 times greater. Inspired by these findings, we developed a bioinspired, 3D-printed soft robotic “MIMOSA” device using shape memory polyurethane (SMPU) with graphene nanoplatelets (GNP). This device exhibited shape changes 3.63 times faster than pure SMPU due to the high thermal conductivity of GNP. Our research demonstrates how biomimicry can lead to the development of adaptive robotic systems with potential applications in wearable technology and electronics.