Sehyuk Yim

Design and Rolling Locomotion of a Magnetically Actuated Soft Capsule Endoscope

This paper proposes a magnetically actuated soft capsule endoscope (MASCE) as a tetherless miniature mobile robot platform for diagnostic and therapeutic medical applications inside the stomach. Two embedded internal permanent magnets and a large external magnet are used to actuate the robot remotely. The proposed MASCE has three novel features. First, its outside body is made of soft elastomer-based compliant structures. Such compliant structures can deform passively during the robot-tissue contact interactions, which makes the device safer and less invasive. Next, it can be actively deformed in the axial direction by using external magnetic actuation, which provides an extra degree of freedom that enables various advanced functions such as axial position control, drug releasing, drug injection, or biopsy. Finally, it navigates in three dimensions by rolling on the stomach surface as a new surface locomotion method inside the stomach. Here, the external attractive magnetic force is used to anchor the robot on a desired location, and the external magnetic torque is used to roll it to another location, which provides a stable, continuous, and controllable motion. The paper presents design and fabrication methods for the compliant structures of the robot with its axial deformation and position control capability. Rolling-based surface locomotion of the robot using external magnetic torques is modeled, and its feasibility is tested and verified on a synthetic stomach surface by using a magnetically actuated capsule endoscope prototype.

Biomedical Applications of Untethered Mobile Milli/Microrobots

Untethered robots miniaturized to the length scale of millimeter and below attract growing attention for the prospect of transforming many aspects of health care and bioengineering. As the robot size goes down to the order of a single cell, previously inaccessible body sites would become available for high-resolution in situ and in vivo manipulations. This unprecedented direct access would enable an extensive range of minimally invasive medical operations. Here, we provide a comprehensive review of the current advances in biomedical untethered mobile milli/microrobots. We put a special emphasis on the potential impacts of biomedical microrobots in the near future. Finally, we discuss the existing challenges and emerging concepts associated with designing such a miniaturized robot for operation inside a biological environment for biomedical applications.

Biopsy using a Magnetic Capsule Endoscope Carrying, Releasing, and Retrieving Untethered Microgrippers

This paper proposes a new wireless biopsy method where a magnetically actuated untethered soft capsule endoscope carries and releases a large number of thermo-sensitive, untethered microgrippers (μ-grippers) at a desired location inside the stomach and retrieves them after they self-fold and grab tissue samples. We describe the working principles and analytical models for the μ-gripper release and retrieval mechanisms, and evaluate the proposed biopsy method in ex vivo experiments. This hierarchical approach combining the advanced navigation skills of centimeter-scaled untethered magnetic capsule endoscopes with highly parallel, autonomous, submillimeter scale tissue sampling μ-grippers offers a multifunctional strategy for gastrointestinal capsule biopsy.

Shape-Programmable Soft Capsule Robots for Semi-Implantable Drug Delivery

In this paper, we present a shape-programmable magnetically actuated soft capsule robot for semi-implantable drug delivery applications. The shape of the proposed soft capsule is changed by an external magnetic field. To change the robot shape by an external permanent magnet, the relevant soft robot design features and required conditions are investigated using simulations and experiments. If the magnetic field is increased above a critical value, the capsule collapses to a sphere-like stable shape, which keeps the capsule inside the stomach all the time, and it cannot move to the duodenum by gastric peristalsis. We conducted experiments inside a synthetic stomach-like membrane to investigate how much tissue stress is induced by the soft capsule under emulated gastric peristalsis to show that the capsule induces no pain in the stomach and can sustain its spherical shape against external forces. Such a soft capsule can be used to release drugs, which can be contained on its body parts or inside a reservoir, while staying in the stomach. After depletion of the drug, a controlled rolling motion using the external magnetic field is proposed to recover the initial cylindrical shape. Then, the capsule can move into the duodenum by peristalsis and is discharged through the anus.

Magnetically Actuated Soft Capsule With the Multimodal Drug Release Function

In this paper, we present a magnetically actuated multimodal drug release mechanism using a tetherless soft capsule endoscope for the treatment of gastric disease. Because the designed capsule has a drug chamber between both magnetic heads, if it is compressed by the external magnetic field, the capsule could release a drug in a specific position locally. The capsule is designed to release a drug in two modes according to the situation. In the first mode, a small amount of drug is continuously released by a series of pulse type magnetic field (0.01-0.03 T). The experimental results show that the drug release can be controlled by the frequency of the external magnetic pulse. In the second mode, about 800 mm3 of drug is released by the external magnetic field of 0.07 T, which induces a stronger magnetic attraction than the critical force for capsules collapsing. As a result, a polymeric coating is formed around the capsule. The coated area is dependent on the drug viscosity. This paper presents simulations and various experiments to evaluate the magnetically actuated multimodal drug release capability. The proposed soft capsules could be used as minimally invasive tetherless medical devices with therapeutic capability for the next generation capsule endoscopy.

3-D Localization Method for a Magnetically Actuated Soft Capsule Endoscope and Its Applications

In this paper, we present a 3-D localization method for a magnetically actuated soft capsule endoscope (MASCE). The proposed localization scheme consists of three steps. First, MASCE is oriented to be coaxially aligned with an external permanent magnet (EPM). Second, MASCE is axially contracted by the enhanced magnetic attraction of the approaching EPM. Third, MASCE recovers its initial shape by the retracting EPM as the magnetic attraction weakens. The combination of the estimated direction in the coaxial alignment step and the estimated distance in the shape deformation (recovery) step provides the position of MASCE in 3-D. It is experimentally shown that the proposed localization method could provide 2.0-3.7 mm of distance error in 3-D. This study also introduces two new applications of the proposed localization method. First, based on the trace of contact points between the MASCE and the surface of the stomach, the 3-D geometrical model of a synthetic stomach was reconstructed. Next, the relative tissue compliance at each local contact point in the stomach was characterized by measuring the local tissue deformation at each point due to the preloading force. Finally, the characterized relative tissue compliance parameter was mapped onto the geometrical model of the stomach toward future use in disease diagnosis.

A Robotic Biopsy Device for Capsule Endoscopy

This paper introduces a robotic biopsy device for capsule endoscopes. The proposed device consists of three modules for the complete process of biopsy, which includes monitoring the intestinal wall by a tissue monitoring module (TMM), aligning onto a polyp by an anchor module (AM), and sampling of the polyp tissue by a biopsy module (BM). The TMM utilizes a trigonal mirror as well as an on-board camera; since the TMM continuously takes images through lateral apertures, an operator such as a medical doctor is able to anchor the capsule endoscope onto the polyp and biopsy it with the visual feedback in real-time. When the operator finds a polyp using the TMM and the frontal camera of a capsule endoscope, then the AM is used to approach the polyp for biopsy. When the AM is in use, outriggers are extruded by shape-memory-alloy (SMA) springs, which results in the swelling of capsule endoscope body. In addition, an alignment module, which is a part of the AM, rotates the body of the capsule endoscope such that the biopsy razor can be aligned onto the polyp. Then, the BM excises a part of the polyp and seals the aperture, and the capsule endoscope continues exploring the intestine. The concept and working principles of the proposed device are introduced in this paper and are verified by a prototype that successfully integrates the three modules.

A 5-D Localization Method for a Magnetically Manipulated Untethered Robot Using a 2-D Array of Hall-Effect Sensors

This paper introduces a new 5-D localization method for an untethered meso-scale magnetic robot, which is manipulated by a computer-controlled electromagnetic system. The developed magnetic localization setup is a 2D array (8 × 8) of mono-axial Hall-effect sensors, which measure the perpendicular magnetic fields at their given positions. We introduce two steps for localizing a magnetic robot more accurately. First, the dipole-modeled magnetic field of the electromagnet is subtracted from the measured data in order to determine the robots magnetic field. Second, the subtracted magnetic field is twice differentiated in the perpendicular direction of the array, so that the effect of the electromagnetic field in the localization process is minimized. Five variables regarding the position and orientation of the robot are determined by minimizing the error between the measured magnetic field and the modeled magnetic field in an optimization method. The resulting position error is 2.1 ± 0.8 mm and angular error is 6.7 ± 4.3° within the applicable range (5 cm) of magnetic field sensors at 200 Hz. The proposed localization method would be used for the position feedback control of untethered magnetic devices or robots for medical applications in the future.

Design and analysis of a magnetically actuated and compliant capsule endoscopic robot

In this paper, we propose a compliant and tetherless magnetic capsule endoscopic robot. The proposed capsule robot has two key features. First, it has one extra degree of freedom axial contraction capability to perform additional tasks such as a drug releasing, a drug injection, or a biopsy. Also, design features of the magnetically deformed capsule robot are introduced. Its characteristic deformation curve, which was measured using an indentation setup, presents not only the deformation behavior of the magnetic capsule robot but also considerations in the capsule design process. Next, by implementing a magnetically actuated rolling locomotion scheme, the capsule can be controlled externally using a permanent magnet. The proposed magnetic capsule robot is anchored on a tissue wall by the magnetic attraction and rotated by a magnetic torque. This behavior allows a stable locomotion of the magnetic capsule robot and its orientation is controllable during locomotion. To verify the feasibility of proposed locomotion method and the compliant capsules shape deformation, the magnetic capsule robot was actuated in a synthetic stomach model. The experimental results show that locomotion behavior of the capsule is stable and a successful tracking performance of the proposed magnetic actuation method; average distance gap between the capsule and the external magnet was only 20% of the capsules body length. Such a soft and tetherless capsule robot can potentially enable minimally invasive diagnostic and treatment applications for stomach diseases.

SoftCubes: Stretchable and self-assembling three-dimensional soft modular matter

This paper proposes a self-assembling soft modular matter, called SoftCubes, where soft-bodied modules are disassembled into a flexible string by an external tension and self-assemble into the preprogrammed three-dimensional (3D) shape. The developed soft modular matter has three main design features. Firstly, entire modules of the 3D shape are serially connected. Such a structure allows all the modules to be disassembled by external tension. Secondly, the outer body of the modules and the connecting parts are made of soft stretchable elastomer. Due to the soft body of the modules, after disassembling, the serially connected modules become a highly flexible and soft string, and have an extreme shape adaptation capability. Also, if the external tension is removed, the preprogrammed 3D shape is recovered by the elastic restoring force of soft-bodied modules. Finally, embedded small permanent magnets induce magnetic self-assembling forces and maintain a mechanical robustness of the 3D shape of module assembly. Due to the magnetic self-assembly, the soft modules are precisely aligned with neighboring modules in a lattice structure. The paper also presents an algorithm to generate the serial connection path of modules for creating a given 3D shape. Various physical interactions between self-assembling module prototypes are visualized in two-dimensional motion tracking experiments. Finally, the shape reconfiguration ability of soft modular matter is demonstrated. SoftCubes is a new class of programmable modular matter where shape memory ability is embedded in the structure, and shows a physical implementation of various 3D shapes with a high resolution and a high scalability.