Rice grains inspire new robots that adapt to speed and impact

Researchers have discovered that packed rice grains exhibit a unique mechanical property called rate softening, where the material’s strength decreases when compressed rapidly due to a sharp drop in friction between grains. Conversely, when compressed slowly, rice maintains its strength. By combining rice with other granular materials like sand that strengthen under rapid loads, scientists have engineered new metamaterials that autonomously change their stiffness and flexibility depending on the speed and nature of applied forces, without the need for electronics or sensors. This physics-driven approach allows these materials to automatically adapt their behavior—bending, buckling, or stiffening—in response to different stress rates. Such speed-sensitive metamaterials have promising applications in soft robotics, enabling the creation of lighter, safer, and more adaptable robots capable of assisting humans, navigating challenging environments, or performing delicate tasks like surgery. Additionally, the technology could improve wearable protective gear, such as helmets and pads, which would deform safely under sudden impacts to better absorb energy and prevent injury. Overall, this research highlights how