We propose a novel closed-circuit magnetic navigation system (CMNS), which utilizes eight electromagnets connected by back yokes to maximize a magnetic field. We first show the effectiveness of a closed magnetic circuit (CMC) and conduct a parametric analysis to design a single CMC, which is utilized to construct the whole CMNS. A magnetic field mapping method is also developed utilizing the finite-element method and polynomial regression to evaluate and control the magnetic field over almost the whole workspace in real time. We investigated how the magnetic field changed based on the shape of core tips by comparing the isotropic magnetic field control authority, which is the ability to generate an equal magnetic field over the workspace regardless of the position and direction of the magnetic field. We experimentally verified the mathematical assumption that the magnetic field generated from the proposed CMNS can be linearly proportional to the applied current and that the magnetic field of the proposed CMNS can be expressed as a superposition of the magnetic fields generated by each electromagnet. Finally, we verified the effectiveness of the developed CMNS by performing experiments related to steering a commercial magnetic catheter.

A multifunctional magnetic catheter robot (MCR) is proposed in this paper to treat occlusive vascular disease by generating steering, tunneling, and stent delivery motions. Using external magnetic fields generated by a closed-loop magnetic navigation system, the MCR can be manipulated remotely and can generate each motion by magnetic manipulation methods. The MCR has novel structures with a magnetic joint and tension springs for selective stent delivery. Constraints and a dynamic model were derived to specify the manipulation conditions for the selective treatment motions and design parameters of the MCR. Then, the MCR was prototyped, and the steering, tunneling, and stent delivery motions were verified by several experiments. Finally, an in vitro experiment with a pseudo blood clot was conducted to demonstrate the effectiveness of the MCR and its motions for the treatment of occlusive vascular disease.

Objective: Non-invasive, pill-sized capsules can provide intestinal fluid sampling to easily retrieve site-specific gut microbiome samples for studies in nutrition and chronic diseases. However, capsules with both automatic sampling and active locomotion are uncommon due to limited onboard space. This paper presents a novel hybrid hydrogel-magnet actuated capsule featuring: i) pH-responsive hydrogels that will automatically trigger fluid sampling at an environmental pH of $>$ 6 and ii) active locomotion by an external rotating magnetic field. Method: Two capsule designs were fabricated (Design A: 31 $\mu$ L sampling volume with dimensions 8 mm × 19 mm, Design B: 41 $\mu$ L sampling volume with dimensions 8 mm × 21 mm). They were immersed in simulated gastric (pH = 1.2) and simulated intestinal fluid (pH = 6.8) to test for automatic intestinal fluid sampling. An external rotating magnetic field was applied to test for active locomotion. Finally, seal tests were performed to demonstrate sample contamination mitigation. Results: Preliminary experiments showed that sampling occurred quickly and automatically in simulated intestinal fluid at 6–15 hours, active locomotion via rotation, rolling, and tumbling were possible at magnetic field magnitudes $<$ 10 mT, oil piston seals were better at mitigating sample contamination than water piston seals, and minimum o-ring seal pressures limits of 1.95 and 1.69 kPa for Design A and B respectively were sufficient against intra-abdominal pressures. Significance: This work presents the ability to impart capsule multi-functionality in a compact manner without onboard electronics or external triggering for sampling.

Magnetic navigation systems (MNSs) have been developed to use in the diagnosis of gastrointestinal problems. However, most conventional magnetic navigation systems are expensive and have structural problems because of their large weights and volumes. Therefore, this paper proposes C-Mag, a novel compact MNS composed of two electromagnets and a robotic arm. The two electromagnets generate a planar magnetic field, and the robotic arm rotates and translates the electromagnets to manipulate the magnetic capsule in a large 3-dimensional (3-D) space. The C-Mag design considers the payload of the robotic arm and the capacity of the power supply unit. Under these limited conditions, the C-Mag was optimized to generate the maximum magnetic field considering several major factors. Finally, the C-Mag was constructed, and the maximum magnetic field that could be generated in one direction was 18.65 mT in the downward direction. Additionally, the maximum rotating magnetic field was 13.21 mT, which was used to manipulate the capsule. The performance was verified by measuring the generated magnetic field, and it matched well with the simulated result. Additionally, the path-following experiment of the magnetic capsule showed that the proposed C-Mag can effectively manipulate the magnetic capsule in 3-D space using the robotic arm. This study is expected to contribute to the further development of magnetic navigation systems to treat gastrointestinal problems.

We developed a crawling magnetic robot (CMR), which can stably navigate and perform biopsies remotely in tubular environments by controlling a magnetic field. The CMR is composed of a crawling part and a biopsy part. The crawling part allows the CMR to crawl forward and backward via an asymmetric friction force generated by an external precessional magnetic field. The biopsy part closes or opens the cover of a needle to use the biopsy needle selectively with the control of the external precessional magnetic field. The cover of the biopsy part prevents damage to the tubular environments because the biopsy needle is inside the cover while the CMR is navigating. We developed the design of the proposed CMR using magnetic torque constraints and a magnetic force constraint, and then we fabricated the CMR with three-dimensional printing technology. Finally, we conducted an experiment to measure the CMR’s puncturing force with a load cell and conducted an experiment in a Y-shaped watery glass tube with pseudo-tissue to verify the crawling motion, the uncovering and covering motion of the biopsy needle, and the CMR’s ability to extract tissue with the biopsy needle.

The magnetic navigation system (MNS) with gradient and uniform saddle coils is an effective system for manipulating various medical magnetic robots because of its compact structure and the uniformity of its magnetic field and field gradient. Since each coil of the MNS was geometrically optimized to generate strong uniform magnetic field or field gradient, it is considered that no special optimization is required for the MNS. However, its electrical characteristics can be still optimized to utilize the maximum power of a power supply unit with improved operating time and a stronger time-varying magnetic field. Furthermore, the conventional arrangement of the coils limits the maximum three-dimensional (3D) rotating magnetic field. In this paper, we propose an electrical optimization method based on a novel arrangement of the MNS. We introduce the objective functions, constraints, and design variables of the MNS considering electrical characteristics such as resistance, current density, and inductance. Then, we design an MNS using an optimization algorithm and compare it with the conventional MNS; the proposed MNS generates a magnetic field or field gradient 22% stronger on average than that of the conventional MNS with a sevenfold longer operating time limit, and the maximum three-dimensional rotating magnetic field is improved by 42%. We also demonstrate that the unclogging performance of the helical robot improves by 54% with the constructed MNS.