Flexible magnetic small-scale robots use patterned magnetization to achieve fast transformation into complex three-dimensional (3D) shapes and thereby achieve locomotion capabilities and functions. These capabilities address current challenges for microrobots in drug delivery, object manipulation, and minimally invasive procedures. However, possible microrobot designs are limited by the existing methods for patterning magnetic particles in flexible materials. Here, we report a method for patterning hard magnetic microparticles in an elastomer matrix. This method, based on ultraviolet (UV) lithography, uses controlled reorientation of magnetic particles and selective exposure to UV light to encode magnetic particles in planar materials with arbitrary 3D orientation with a geometrical feature size as small as 100 micrometers. Multiple planar microrobots with various sizes, different geometries, and arbitrary magnetization profiles can be fabricated from a single precursor in one process. Moreover, a 3D magnetization profile allows higher-order and multi-axis bending, large-angle bending, and combined bending and torsion in one sheet of polymer, creating previously unachievable shape changes and microrobotic locomotion mechanisms such as multi-arm power grasping and multi-legged paddle crawling. A physics-based model is also presented as a design tool to predict the shape changes under magnetic actuation.
Despite increasing interest in minimally invasive surgical techniques and related developments in flexible endoscopes and catheters, follow-the-leader motion remains elusive. Following the path of least resistance through a tortuous and potentially delicate environment without relying on interaction with the surrounding anatomy requires the control of many degrees of freedom. This typically results in large-diameter instruments. One viable solution to obtain dexterity without increasing size is via multiple-point magnetic actuation over the length of the catheter. The main challenge of this approach is planning magnetic interaction to allow the catheter to adapt to the surrounding anatomy during navigation. We design and manufacture a fully shape-forming, soft magnetic catheter of 80 mm length and 2 mm diameter, capable of navigating a human anatomy in a follow-the-leader fashion. Although this system could be exploited for a range of endoscopic or intravascular applications, here we demonstrate its efficacy for navigational bronchoscopy. From a patient-specific preoperative scan, we optimize the catheters’ magnetization profiles and the shape-forming actuating field. To generate the required transient magnetic fields, a dual-robot arm system is employed. We fabricate three separate prototypes to demonstrate minimal contact navigation through a three-dimensional bronchial tree phantom under precomputed robotic control. We also compare a further four separate optimally designed catheters against mechanically equivalent designs with axial magnetization profiles along their length and only at the tip. Using our follow-the-leader approach, we demonstrate up to 50% more accurate tracking, 50% reduction in obstacle contact time during navigation over the state of the art, and an improvement in targeting error of 90%.
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