3D Fabrication of Fully Iron Magnetic Microrobots.

Biocompatibility and high responsiveness to magnetic fields are fundamental requisites to translate magnetic small-scale robots into clinical applications. The magnetic element iron exhibits the highest saturation magnetization and magnetic susceptibility while exhibiting excellent biocompatibility characteristics. Here, a process to reliably fabricate iron microrobots by means of template-assisted electrodeposition in 3D-printed micromolds is presented. The 3D molds are fabricated using a modified two-photon absorption configuration, which overcomes previous limitations such as the use of transparent substrates, low writing speeds, and limited depth of field. By optimizing the geometrical parameters of the 3D molds, metallic structures with complex features can be fabricated. Fe microrollers and microswimmers are realized that demonstrate motion at ≈20 body lengths per second, perform 3D motion in viscous environments, and overcome higher flow velocities than those of "conventional 3D printed helical microswimmers." The cytotoxicity of these microrobots is assessed by culturing them with human colorectal cancer (HCT116) cells for four days, demonstrating their good biocompatibility characteristics. Finally, preliminary results regarding the degradation of iron structures in simulated gastric acid liquid are provided.

A Needle-Type Microrobot for Targeted Drug Delivery by Affixing to a Microtissue.

A needle-type microrobot (MR) for targeted drug delivery is developed to stably deliver drugs to a target microtissue (MT) for a given period time without the need for an external force after affixing. The MRs are fabricatedby 3D laser lithography and nickel (Ni)/titanium oxide (TiO2 ) layers are coated by physical vapor deposition. The translational velocity of the MR is 714 µm s-1 at 20 mT and affixed to the target MT under the control of a rotating magnetic field. The manipulability of the MR is shown by using both manual and automatic controls. Finally, drug release from the paclitaxel-loaded MR is characterized to determine the efficiency of targeted drug delivery. This study demonstrates the utility of the proposed needle-type MR for targeted drug delivery to MT with various flow rates in vitro physiological fluidic environments.

A Magnetically Controlled Soft Microrobot Steering a Guidewire in a Three-Dimensional Phantom Vascular Network.

Magnetically actuated soft robots may improve the treatment of disseminated intravascular coagulation. Significant progress has been made in the development of soft robotic systems that steer catheters. A more challenging task, however, is the development of systems that steer sub-millimeter-diameter guidewires during intravascular treatments; a novel microrobotic approach is required for steering. In this article, we develop a novel, magnetically actuated, soft microrobotic system, increasing the steerability of a conventional guidewire. The soft microrobot is attached to the tip of the guidewire, and it is magnetically steered by changing the direction and intensity of an external magnetic field. The microrobot is fabricated via replica molding and features a soft body made of polydimethylsiloxane, two permanent magnets, and a microspring. We developed a mathematical model mapping deformation of the soft microrobot using a feed-forward approach toward steering. Then, we used the model to steer a guidewire. The angulation of the microrobot can be controlled from 21.1° to 132.7° by using a magnetic field of an intensity of 15 mT. Steerability was confirmed by two-dimensional in vitro tracking. Finally, a guidewire with the soft microrobot was tested by using a three-dimensional (3D) phantom of the coronary artery to verify steerability in 3D space.

Fabrication and Characterization of a Magnetic Drilling Actuator for Navigation in a Three-dimensional Phantom Vascular Network.

Intravascular microrobots have emerged as a promising tool for vascular diseases. They can be wirelessly and precisely manipulated with a high degree of freedom. Previous studies have evaluated their drilling performance and locomotion, and showed the feasibility of using microrobots for biomedical applications in two-dimensional space. However, it is critical to validate micro-drillers in a three-dimensional (3D) environment because gravity plays an important role in a 3D environment and significantly affects the performance of the micro-drillers in vascular networks. In this work, we fabricated magnetic drilling actuators (MDAs) and characterized their locomotion and drilling performance in vascular network-mimicking fluidic channels. The MDAs were precisely manipulated in the fluidic channel network in both horizontal and vertical planes, selecting and moving through the desired path via the junctions of multiple channels. The MDAs also accurately navigated an artificial thrombosis in an artificial 3D vascular network and successfully drilled through it. The results obtained here confirmed the precise manipulation and drilling performance of the developed MDAs in 3D. We think that the MDAs presented in this paper have great potential as intravascular drillers for precise thrombus treatment.