A Magnetically Transformable Twisting Millirobot for Cargo Delivery at Low Reynolds Number.

Inspired by bacteria flagella, miniature robots often use a helical shape to propel themselves in fluids at low Reynolds numbers. The helical microstructures in the robots are often rigid and are made by advanced 3D micro-/nanofabrication techniques. However, it remains challenging to fabricate these 3D helical structures without complicated machinery. Herein, for the first time, a magnetically transformable millirobot-TwistBot-with a flexible body that can transform from a simple flat ribbon to a helical shape under an applied magnetic field is reported, enabling its propulsion in viscous fluids. The robot's twisting is modeled using numerical simulation and its geometry is optimized to maximize the twist angle. The unique shape transformation not only allows the propulsion through narrow lumens but also facilitates TwistBot in carrying and delivering solid cargo successfully to the target. The concept of the TwistBot opens new opportunities in designing soft transformable minirobots for targeted cargo delivery.