Soft Micromotors with Switchable Motion Enabled by 3D-to-3D Shape Reconfiguration

Soft self-propelled motors have attracted great attention due to their potential applications for mixing, sorting, and transportation. However, it is still a challenge to have fast yet dynamically controllable motion, especially when reducing the dimension to the microscale level. Here, responsive hydrogel-based, microscale motors capable of dynamic switchable motion are constructed, propelled by the recoiling of bubble expelling. The motors indicate full reversible and tunable moving performance, including switchable trajectory from straight line to spiral path, and rapid velocity increase over 1 order of magnitude. A maximum velocity reaching up to 1000 μm/s, more than 20 body lengths per second, is obtained. This in situ motion modulation is achieved by autonomous 3D-to-3D shape reconfiguration of the micromotors under an external temperature stimulus. The shape morphing endows control of the bubble ejection frequency and the thrust force direction to consequently switch the motion. Based on this strategy, diverse movements can be obtained by rational design of the morphology transformation based on responsive polymeric materials instead of an external field such as a magnetic field. The micromotors indicate the merits of microscale level, soft body, fast velocity, dynamically tunable trajectory, and ability to accelerate fluid mixtures in microfluidic devices, which could boost the applications in miniaturized robotics, biomimetic devices, and transportation/fluid mixture.