Remote controllability, real-time response, and small size are critically requirement of medical devices operated in blind, unstructured, and fluidic environments of biomedical regions. Untethered swimming soft milli-robots have been developed to fulfill treatment and therapy in such that region under magnetic navigation. The soft robot's motor-less mechanism with a high-DOF utilizes magnetic compliance of the deformable structure with a minimal control of oscillating magnetic field. Theoretically, magnetic property of the robots is defined by magnetic moments consisting of orientation and strength. Orientation can be programmed by magnetizing technique, and strength is defined by quantity of magnetic moments in the structure. Herein, this work investigates how orientation and quantity of magnetic moments affect swimming behavior and performance of the robots. The soft robots are designed into three distinguish types of magnetic property embedded in the deformable structure; the I-robot has non-uniform magnetic orientation and uniform magnetic strength, the II-robot has uniform magnetic orientation and non-uniform magnetic strength, and the III-robot has non-uniform magnetic orientation and non-uniform magnetic strength. The results interestingly report that each type of robot's property functions mechanism and benefits swimming performance differently under the same control parameters. The I-robot does not have any exceptional potential, but the II-robot can be operated at the higher control frequency even reaching the step-out point. The III-robot shows the greatest performance in swimming and maneuverability. These results are useful to design a swimming soft-robot capable of applying for various purposes, especially when the demand concerns non-harm, small-scale, soft-interface, and remote controllability.

Among the development of technology, a large number of medical devices have been designed, improved, and implemented in various forms and functions to facilitate therapy and treatment (e.g., medical guidewires, catheters, implants). Remote controllability, real-time response, size, and non-toxicity of the devices are all critically required to operate in the blind, unstructured, and fluidic environments of biomedical regions. Herein, an untethered soft swimming milli-robot has been developed to fulfill the remote operation in such regions. The robot employs magnetic property as a motor-less mechanism powered by the dynamic magnetic field. Non-uniform magnetization embedded in the soft structure allows the robot to propagate the body-wave deformation utilizing a high degree of freedom provided by magnetic compliance for swimming in the fluid. The robot is experimentally investigated in the swimming performance under the different control parameters. The results report that the swimming velocity is directly proportional to the strength and frequency of the actuating magnetic field. It swims with the fastest velocity about 5.5 mm/s, under 15 mT and 13 Hz of the oscillating magnetic field. On the other hand, swimming velocity is dramatically dropped since the frequency is over 13 Hz. The magnetically controllable robot is capable of applying for various purposes, especially where the demand concerns small size, soft interface, and remote controllability.