M. Sendoh

Swimming micro-machine driven by magnetic torque

Abstract Magnetic micro-machines capable of swimming through liquid or gel were fabricated. The micro-machines were driven by an external rotating magnetic field and featured a screw-shaped structure and permanent magnet. The machines could swim under condition of a Reynolds number ( Re ) of 10 −7 , and were able to run through agar or a bovine tissue sample using the same principle. Their running behavior was dependent on the frequency and strength of the external field, and on the surrounding media. These machines have great potential for medical applications in the human body.

Spiral-type micro-machine for medical applications

The spiral-type magnetic micro-machine, which is driven by a rotating magnetic field, is characterized by wireless operation for swimming. The machine has to swim under a lower Reynolds number environment, when the machine is downsized and working inside the human body. In this study, using various silicone oils whose kinematic viscosity ranged from 1 to 5/spl times/10/sup 5/ mm/sup 2//s, the swimming performance of the machine at low Reynolds number was examined. The machine composed of a cylindrical NdFeB magnet could swim in oils under condition of Re=10/sup -7/. This Reynolds number is the same as that of a micro-machine with micron size swimming in water. In addition, the machine could turn by controlling the external rotational magnetic field, and therefore the swimming direction of the machine could be controlled. Using these principles, a magnetic micromachine, which can run in a gel, was also fabricated.

Magnetic micromachines for medical applications

The spiral-type magnetic micromachine can swim in a liquid and in a gel. In addition, this machine has a function of heating. This machine is suitable for local heat treatment in the body. The active bending is obtained by attached tiny magnet at the tip of the guide-wire. This is simple and useful for inserting the catheter to the lung or to the blood tube.

Direction and individual control of magnetic micro-machine

Motion control of magnetic micromachines driven by magnetic fields was examined. To control the motion of the machines individually, the shape of each machine was controlled. Even if the applied field was uniform, one working machine could be selected by choosing the frequency of the field. Furthermore, the moving direction control was studied experimentally and theoretically. The radius of the turn of the machine was minimum at the applied field angle of 60/spl deg/ if the field was strong enough.

Effect of machine shape on swimming properties of the spiral-type magnetic micro-machine

The effect of machine shape on the swimming properties of a spiral-type magnetic micro-machine was examined by using a finite volume method. The optimum design of the blade shape was obtained by using the results of the simulation. According to the optimum design, the micro-machine was fabricated by stereolithography. The swimming properties of the machine agreed well with the analyzed results.

Magnetic Actuator for a Capsule Endoscope Navigation System

A gastrointestinal (GI) endoscopy is widely carried out in order to find diseases at their early stages. A capsule endoscope is proposed for inspection by swallowing. The capsule moves passively through GI tract with the aid of peristalsis. In previous studies, the effect of GI tracts spiral structure on moving properties of a capsule-type magnetic actuator has been reported. In addition, it was reported that the actuator can pass though an intestine extracted from a pig. In this study, the effect of the spiral structure on the velocity and on the thrust force properties of the actuators were examined using silicone tube as a phantom. If a spiral angle and number of spirals are different, the velocity and the thrust force are varied. Results show that when the spiral angle is 45 degree, the number of spirals is 4, and the spiral height is 1-mm/spl phi/, the velocity and the thrust force had maximum value. A moving test for a capsule-type magnetic actuator was also examined in the pigs large intestine on the slope. It took 300 seconds for the large intestine to pass through to the other end. In addition, the actuator could pass on the slope of 30 degree without a hitch. These results shows that the magnetic actuator has great potential for a navigation system of a capsule endoscope.

Spiral type magnetic micro actuators for medical applications

Magnetic micro actuators are characterized by their wireless operation. In this study, 3 types of magnetic micro actuators are fabricated. First, swimming micro actuator is described. The actuator could swim in the silicone oil. Second, on the basis of swimming actuator, a magnetic actuator running in a pigs liver was fabricated. Third, magnetic actuator for colonoscope navigation was fabricated. A motion test of the actuator was examined in a large intestine of living dog. All actuators indicate good performances and they have great potential for medical applications.

Three-dimensional analysis of swimming properties of a spiral-type magnetic micro-machine

The swimming properties of a spiral-type magnetic micro-machine were analyzed theoretically using 3D finite volume method. The basic equations of incompressible viscous fluid flow were integrated. The flow field around the micro-machine was calculated to estimate the swimming velocity, thrust, drag, and load torque of a spiral-type magnetic micro-machine. Good agreement was obtained between the experimental and theoretical results in a low Reynolds number. Therefore, the 3D analysis method without any fitting parameters was judged to be established.

Swimming of magnetic micro-machines under a very wide-range of Reynolds number conditions

A magnetic micro-machine, a minuscule device composed of a cylindrical body with a magnet and spiral blade, swims in liquid under the force of a rotational magnetic field. To obtain a machine capable of swimming through organs and blood vessels for medical applications, it must be designed on a scale below the mm order and retain its swimming capability under highly varied conditions. The swimming properties of a spiral-type magnetic micro-machine were examined under various Reynolds number conditions by altering the kinematic viscosity of the liquid. The machine could swim in liquids with kinematic viscosities ranging from 1.37 to 5/spl times/10/sup 5/ mm/sup 2//s, which translates into a Reynolds number from 430 to 6/spl times/10/sup -7/. The Reynolds number of blood flow is within this range. In addition, the load torque for swimming was studied theoretically and experimentally. The results obtained suggested great promise for the development of a micro-machine that can be put to work inside the human body.

Fabrication of magnetic actuator for use in colon endoscope

Magnetic actuator for colonoscope navigation is fabricated. The actuator composed of tube-shape permanent magnet and spiral structure that made by rubber. The magnet is magnetized to the direction of its diameter. By applying the rotational magnetic field the machine rotate and moved in an intestine. The actuator is attached on an end of simulated endoscope. The actuator with flexible air tubes can move in small and large intestines of pig. This result suggests that the actuator have great possibility for colonoscope navigation.