Magnetic Programming-Assisted Ultrasonic Printing for In Situ Fabrication of Untethered Robots

Magnetic soft robots offer significant potential for biomedical applications, as recent advances in magnetic programming and 3D printing technologies have enabled the fabrication of increasingly complex and multifunctional structures. However, current magnetic programming soft robots face limitations in injection and long-range manipulation. Here, we present a magnetic programming-assisted ultrasonic printing (MPUP) technique - a noncontact approach for the in situ fabrication of magnetically programmable soft robots within enclosed or hard-to-access spaces. We developed a magneto-responsive ultrasonic ink that can be selectively and rapidly cured by focused ultrasound. During printing, an externally applied magnetic field induces directional alignment of magnetic particles within the ink, enabling programmable magnetization profiles in the printed structures. The resulting soft robots exhibit diverse shape-morphing behaviors and programmable responses under external magnetic stimuli. In vitro through-tissue printing experiments demonstrate the feasibility of this method for clinical scenarios such as gastric perforation sealing and bleeding control. Overall, MPUP leverages the deep penetration and remote controllability of ultrasound to enable noninvasive, on-demand fabrication of untethered magnetic soft robots, offering a promising strategy for advancing their use in biomedical interventions.