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.

Steering microswimmers toward 3-D autonomous manipulation tasks has received extensive attention. Our previous works have accomplished autonomously manipulating microswimmers in the 2-D space. This article aims to extend the 2-D autonomous manipulation to 3-D autonomous manipulation. Specifically, this article addresses the problem of an autonomous system that consists of 3-D path planning and 3-D path following for magnetically driven helical microswimmers. The path-planning algorithm called optimal Bidirectional RRT* is formulated to explore the shortest route in the confined 3-D space. A proxy-based sliding mode control (PSMC) approach is developed to design stable controllers based on the error model in the Serret–Frenet frame. We transport the swimming model trained by a kind of neural network to another new helical microswimmer according to an online updating scheme. The updating scheme can identify and refine compensating angles between the swimming direction of the microswimmer and the magnetic direction in the 3-D space facing the weight disturbances of the swimmer and lateral disturbances. The experiments are conducted to quantitatively validate the 3-D autonomous manipulation system. Experimental results show the effectiveness of path planning and path following with submillimeter accuracy in a 3-D space. Future works will focus on autonomous manipulations in dynamic environments.Note to Practitioners—This article is motivated by the issue of 3-D autonomous manipulation tasks for magnetically driven helical microswimmers. The formulated path planning is responsible for finding the shortest route in the 3-D confined space. The closed-loop controller is charge of steering the helical microswimmers on a reference path based on an online updating model trained by neural networks. It is demonstrated that the helical microswimmer can find the shortest path and follow it in a 3-D space with submillimeter accuracy.

Untethered and wirelessly-controlled microrobots have many applications in the field of biomedicine. Therefore, many laboratories and scientists have invested more scientific research into magnetic microrobots which can make more contributions to medical care. Many magnetic field devices and microrobots are manufactured. In the development of micro-robots, helical microrobots have been well developed. Rigid-body robots account for the majority of these, but they may cause damage to human organs during treatment. However, soft and deformable robots can relieve more medical restrictions. In general, helical microrobots are driven by uniform fields which have their own limitations while the gradient magnetic field can relieve more restrictions and have more functions. This paper presents a flexible deformable helical swimmer controlled in a rotating gradient magnetic field. Helical swimmers are covered with magnetic nano-particles and the helical structure is derived from the inner fiber structure of the lotus root. The soft helical swimmers are controlled to swim several special trajectories in the rotating gradient magnetic field and we analyze the frequency and other factors for velocity or other effects.

Microrobots show great potential to realize a wide range of medical applications especially in a hard-to-reach region within human body. Among a diversity of medical applications, the microrobots are expected to efficiently perform tasks within the human body, but the existing electromagnetic coil systems such as Helmholtz coil, Maxwell coil, etc. do not compromise on the insertion of such a large volume of human parts. We aim to magnetically manipulate diverse microrobots in medical applications with respect to surgical or biopsy tasks within insiders of the human head such as to perform brachytherapy with the helical microswimmer, etc. For this reason, we proposed a novel, a magnetically actuated system called the HyBrid system with the conceptual design in capability of generating both uniform and gradient magnetic fields. The system consists of three different coil setups orthogonally arranged over a large workspace which is available to let the human head inserted into. The simulation results of the magnetic field generation expressed that its performance is suitable and feasible towards magnetically manipulation within the human head, and more efficient than 3D-Helmholtz coil system under the same conditions.