Byungkyu Kim

Design and fabrication of a locomotive mechanism for capsule-type endoscopes using shape memory alloys (SMAs)

Endoscopes are medical devices to diagnose various kinds of diseases throughout the whole gastrointestinal tracks. Generally, they are divided into conventional push-type endoscopes and more recently developed wireless capsule-type endoscopes. The conventional endoscopes cannot reach the small intestines and generate pain and discomfort to patients due to the stiffness of their body. Such disadvantages do not exist in wireless capsule-type endoscopes. However, commercialized capsule-type endoscopes move passively by peristaltic waves (and the gravity), which makes it impossible for doctors to diagnose the areas of his or her interest more thoroughly and actively. To address this problem of passivity, a locomotive mechanism is proposed for wireless capsule-type endoscopes. Prototypes with micro brushless dc motors, ionic polymer metal composite actuator, and shape memory alloy (SMA) wires are designed and fabricated for preliminary tests. Based on the tests, spring-type SMA actuators are selected to be microactuators for capsule endoscopes. Thus, two-way linear actuators using a pair of SMA springs are developed based on a static analysis on them. Moreover, a simple and effective clamping device is developed based on biomimetic approach. A prototype endoscope with four pairs of SMA springs and four clampers was developed. It has 13 mm in diameter and 33 mm in total length, with a hollow space of 7.6 mm in diameter to house other parts that are needed for endoscopy such as a camera, an RF module, sensors, e.g., for endoscopic ultrasound, and a battery. A sequential control of the four actuators improves the efficiency of locomotion up to four times. To validate the performance of the proposed locomotive mechanism, a series of experiments were carried out including in-vitro tests. The results of the experiments indicate that the proposed locomotion mechanism is effective to be used for micro capsule-type endoscopes.

A biomimetic undulatory tadpole robot using ionic polymer–metal composite actuators

The development of a wireless undulatory tadpole robot using ionic polymer–metal composite (IPMC) actuators is presented. In order to improve the thrust of the tadpole robot, a biomimetic undulatory motion of the fin tail is implemented. The overall size of the underwater microrobot prototype, shaped as a tadpole, is 96 mm in length, 24 mm in width, and 25 mm in thickness. It has one polymer fin tail driven by the cast IPMC actuator, an internal (wireless) power source, and an embedded controller. The motion of the tadpole microrobot is controlled by changing the frequency and duty ratio of the input voltage. Experimental results show that this technique can accurately control the steering and swimming speed of the proposed underwater tadpole robot.

Fabrication of nanostructures of polyethylene glycol for applications to protein adsorption and cell adhesion

A simple method was developed to fabricate polyethylene glycol (PEG) nanostructures using capillary lithography mediated by ultraviolet (UV) exposure. Acrylate-containing PEG monomers, such as PEG dimethacrylate (PEG-DMA, MW = 330), were photo-cross-linked under UV exposure to generate patterned structures. In comparison to unpatterned PEG films, hydrophobicity of PEG nanostructure modified surfaces was significantly enhanced. This could be attributed to trapped air in the nanostructures as supported by water contact angle measurements. Proteins (fibronectin, immunoglobulin, and albumin) and cells (fibroblasts and P19 EC cells) were examined on the modified surfaces to test for the level of protein adsorption and cell adhesion. It was found that proteins and cells preferred to adhere on nanostructured PEG surfaces in comparison to unpatterned PEG films; however, this level of adhesion was significantly lower than that of glass controls. These results suggest that capillary lithography can be used to fabricate PEG nanostructures capable of modifying protein and cell adhesive properties of surfaces.

A superelastic alloy microgripper with embedded electromagnetic actuators and piezoelectric force sensors: a numerical and experimental study

This paper presents the analysis, design, and characterization of a superelastic alloy (NiTi) microgripper with integrated electromagnetic actuators and piezoelectric force sensors. The microgripper, fabricated by electro-discharge machining, features force sensing capability, large force output, and large displacements to accommodate objects of various sizes. The design parameters for the embedded electromagnetic actuators were selected on the basis of finite element sensitivity analysis. In order to make the microgripper capable of resolving gripping forces, piezoelectric force sensors were fabricated and integrated into the microgripper. The performance of the microgripper, the integrated force sensors, and the electromagnetic actuators was experimentally evaluated. A satisfactory match between experimental results and finite element simulations was obtained. Furthermore, comparison studies demonstrated that the superelastic alloy (NiTi) microgripper was capable of producing larger displacement than a stainless steel microgripper. Finally, experimental results of optical fiber alignment and the manipulation of tiny biological tissues with the superelastic microgripper were presented.

Development of a piezoelectric polymer-based sensorized microgripper for microassembly and micromanipulation

This paper presents the design, fabrication, and calibration of a piezoelectric polymer-based sensorized microgripper. Electro discharge machining technology is employed to fabricate the superelastic alloy-based microgripper. It was experimentally tested to show the improvement of mechanical performance. For integration of force sensor in the microgripper, the sensor design based on the piezoelectric polymer polyvinylidene fluoride (PVDF) film and fabrication process are presented. The calibration and performance test of the force sensor-integrated microgripper are experimentally carried out. The force sensor-integrated microgripper is applied to fine alignment tasks of micro opto-electrical components. Experimental results show that it can successfully provide force feedback to the operator through the haptic device and play a main role in preventing damage of assembly parts by adjusting the teaching command.

Modeling and Experimental Validation of the Locomotion of Endoscopic Robots in the Colon

In this paper we present a biomechanical study to evaluate the efficiency of the motion of endoscopic robots in the colon, with a special focus on “inchworm” locomotion. A quasi-linear viscoelastic model for soft tissues has been introduced in order to find the mechanical behavior of colon and mesenteries. A study of efficiency of the motion phases, through biomechanical and geometrical factors, allowed us to calculate the “critical stroke” to perform motion inside intestinal walls. This study has provided the guidelines to design a high-stroke pneumatic robotic prototype for colonoscopy. Phantom and in vivo tests have been extensively performed and have shown high efficiency of the robot in navigating inside a pig’s intestine; the performance of the semi-autonomous robot has achieved that of traditional colonoscopes in terms of traveled colon length.

A ciliary motion based 8-legged walking micro robot using cast IPMC actuators

In this paper, we present a micro robot using IPMC (Ionic Polymer Metal Composite) actuators. The IPMC actuator usually has been fabricated with commercially available ion-exchange polymer with the typical thickness of 100-300 /spl mu/m. By the casting of liquid ion-exchange polymer solution, the thickness of the IPMC actuator could increase up to a few millimeters. Based on the casting method, we could achieve the IPMC actuator that has larger stiffness and produces more generative tip force than the IPMC actuator fabricated with the commercially available solid ion-exchange polymer. A ciliary type 8-legged micro robot using the casting based IPMC actuators is constructed. The ciliary type 8-legged micro robot is 6.5 cm in length and 4.2 cm in width, and 1.5 cm in height and the total weight is 4.4 g with the actuators installed. The IPMC actuators used in this robot have a dimension of 20 mm in length, 4 mm in width and 1.15 mm in thickness. The input voltage to the IPMC actuator is set to /spl plusmn/4 V and the frequencies to the IPMC actuator is varying from 0.2 Hz to 1.0 Hz; with the increment of 0.2 Hz. The walking speed of the micro robot is changed from 3 mm/min to 17 mm/min with the variation of the frequencies.

Paddling based Microrobot for Capsule Endoscopes

Recently, the capsule endoscope can be widely used for the diagnosis of digestive organs. It is passively moved by the peristaltic waves of gastro-intestinal tract and thus has some limitations for doctor to get the image of the organ and to diagnose more thoroughly. As a solution of these problems, therefore, a locomotive mechanism of capsule endoscopes has being developed. Our proposed capsule-type microrobot has synchronized multiple legs that are actuated by a linear actuator and two mobile cylinders inside of the capsule. By the novel kinematic relation between the legs and the mobile cylinders, the microrobot can easily move forward in the gastro-intestine. For the feasibility test of the proposed locomotive mechanism, a series of experiments were carried out including in-vitro and in-vivo tests. Based on the experimental results, we conclude that the proposed locomotive mechanism is not only easy to be used for micro capsule endoscopes but also effective to move inside of intestinal tract.

An earthworm-like locomotive mechanism for capsule endoscopes

A wireless capsule endoscope, M2A, has been developed to replace the conventional endoscope. However, the commercialized capsule endoscope moves passively by peristaltic waves and gravity, which has some limitations for doctors to diagnose more thoroughly and actively. In order to solve this problem, a locomotive mechanism is proposed for a wireless capsule endoscope. Based on the tests of various actuators, a piezoactuator is selected as a microactuator for the capsule endoscope. Piezoactuators are known to have limited displacement with high voltage supply. In order to overcome the limitation of common piezoactuator, the impact based piezoactuator is developed to realize long stroke up to 11 mm. Moreover, clampers mimicked the claw of insects are employed. A prototype of the earthworm-like locomotive mechanism integrated with an impact based piezoactuator and engraved clampers is developed. It has 15 mm in diameter and 30 mm under retraction stage and 41 mm under elongation stage in total length. Hollow space is allocated to comprise essential endoscope components such as a camera, communication module, battery, and biosensors. For the feasibility test of proposed locomotive mechanism, a series of experiments was carried out including in-vitro tests. Based on results of the experiments, we conclude that the proposed locomotive mechanism is effective to be used for microcapsule endoscopes.

Locomotion of a legged capsule in the gastrointestinal tract: theoretical study and preliminary technological results

This work illustrates the analysis of locomotion in the gastrointestinal tract obtainable by a legged capsule for diagnostic and therapeutic purposes. A preliminary simulation of the legged locomotion onto slippery and deformable substrates has been performed and -simultaneously- mechanisms for on board actuation of the legs have been developed and tested. Moreover, an engineering translation of medical needs in endoscopy is presented, with some ad hoc solutions for improving diagnostic capabilities.