Researchers have developed magnetic hydrogel microrobots that can be precisely controlled using ultrasound, allowing them to change shape and locomotion mode adaptively in response to their environment. This breakthrough represents a significant step in the control of microrobots for biomedical applications, as the ability to adjust their movement and morphology in real-time is crucial for navigating complex and dynamic biological environments, such as the human body.

The system employs ultrasound-guided closed-loop control. Ultrasound not only serves for real-time monitoring of the microrobot's position and shape but also acts as the feedback mechanism to adjust the external magnetic field driving the robots. This integration enables highly precise manipulation, overcoming the limitations of open-loop control systems that cannot adapt to unexpected changes in the environment or the robot's properties.

The key to adaptability lies in the microrobots' ability to modify their "gait" or locomotion mode. For example, they can switch from crawling to swimming or rolling movements, optimizing their displacement according to fluid viscosity, the presence of obstacles, or surface topography. This versatility is achieved by altering the shape of the magnetic hydrogel, which deforms specifically under the influence of modulated magnetic fields, enabling different movement patterns.

This work opens new avenues for the development of microrobots with autonomous and adaptive navigation capabilities. The implications are broad, ranging from targeted drug delivery to specific body regions to performing microsurgeries or in-situ diagnostics. The robustness and biocompatibility of the hydrogel, combined with non-invasive ultrasound control, position these microrobots as promising candidates for future clinical applications, although further research is still required for their validation in complex biological environments.