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October 15, 2008

Pill-size to bacteria sized robots for surgery and in-body therapies




In 2001, the FDA approved the use of capsule endoscopy, which uses a capsule size camera [1.2 inches long by 0.4 inches in diameter]. These are passive systems. There is work to make smaller robotic systems and systems that can perform more of the capabilities of regular endoscopes. These capabilities include therapeutic and diagnostic operations such as ultrasound, electrocautery, biopsy, laser, and heat with a retractable arm.

1. Scientists at the Technion University, teamed with a researcher from the College of Judea and Samaria, have developed a miniature robot that can move within the bloodstream.



The miniature robot has been planned and constructed (2007), that has the unique ability to crawl within the human body's veins and arteries," said Dr. Nir Shvalb of the College of Judea and Samaria. The Israeli robot's diameter is one millimeter.

The researchers stress that the project is an "interesting development, but it has a long way to go before it is used in medicine." Solomon says that the tiny robot could be controlled for an unlimited amount of time to carry out any necessary medical procedure. The power source is an external magnetic field created near the patient that does not cause any harm to humans but supplies an endless supply of power for it to function. The robot's special structure enables it to move while being controlled by the operator using the magnetic field.







2. Sylvain Martel, Montreal, Canada, has made great progress towards micro-robots and nanorobots in the body.

A research team led by Prof. Sylvain Martel of Ecole Polytechnique de Montreal (EPM) in Canada demonstrated for the first time the feasibility of automatically navigate an untethered object in the blood vessels of a living animal. During the experiment, a 1.5 mm ferromagnetic bead was navigated without human intervention at an average speed of 10 cm/s in the carotid artery of a 25 kg living swine placed in a 1.5 T magnetic resonance imaging (MRI) system. (Journal Applied Physics Letters, March 12, 2007).

Dr Martel and his colleagues are also working with "magnetotactic" bacteria, which orient themselves with magnetic fields.


Magnetic bacteria drive micromotors and other devices

Because they are so tiny (only about two micrometres across), they are not strong enough to swim against the blood flow of larger vessels, though they are able to swim through vessels as little as four micrometres in diameter. Dr Martel's idea is to use the larger magnetic beads to transport the bacteria close to a tumour, and then release them and coax them, using applied magnetic fields, to swim to the tumour and deliver a therapeutic payload. Preliminary experiments in rats suggest that the bacteria can be steered toward tumours using specially designed magnetic coils.



Bacterial reservoirs acting as bacterial engines are 90 μm × 54 μm, and 90 μm × 186 μm (length × width). Silicon MEMS microrobots consist of a die containing micro-reservoirs that shelter magnetotactic bacteria to form a bacterial propulsion system.

Sylvain Martel, Computer Engineering & Software Engineering, École Polytechnique Montréal: "Towards Intelligent Bacterial Nanorobots Capable of Communicating with the Macro-World


3. Paolo Dario is making a pill-cam with legs and is working on assembling a mini-operating room inside the body.


Researchers on an ambitious project called ARES (short for Assembling Reconfigurable Endoluminal Surgical system). Its objective is to design a modular gastrointestinal robot made up of individual pieces that are small enough to be swallowed, one at a time. Once inside the stomach, the idea is that these pieces will assemble themselves into a larger robotic device. The aim is to build an "operating room" inside a patient that can be controlled from the outside by a doctor, says Dr Dario, who is co-ordinating the project.


4. Scientists from the Institute of Robotics and Intelligent Systems at the Swiss Federal Institute of Technology (ETH) in Zurich plan to steer tiny robots inside the eye for sensing, drug delivery and surgery. Current retinal procedures to repair detachments or rips, for example, may involve several incisions in the eye and stitches to tie off the perforated areas.



The Institute of Robotics and Intelligent Systems also has extensive nanorobotics work.

5. James Friend, co-director of the Micro/Nanophysics Research Laboratory at Monash University near Melbourne, Australia, is building a flagella-inspired micro-motor he hopes will one day propel a micro-robot through an artery or vein. At the core of the motor are piezoelectric materials—special crystals or ceramics that change shape very slightly in the presence of an electric field. When such a material is placed in a rapidly alternating electric field, it starts to vibrate. That vibration can then be coupled to another structure to turn a rotor, which in turn operates a flagellum-like tail. In recent years Dr Friend has built successively smaller versions of his motor—the current version is 250 micrometres in diameter. Providing an on-board power supply is difficult, however, so he is investigating the use of external magnetic fields to power the device.


6. Metin Sitti, director of Carnegie Mellon University's (CMU) NanoRobotics Lab in Pittsburgh, Pennsylvania, is using bacteria as biological motors to propel small spheres through fluids. Instead of relying on an external system for controlling their movements, Dr Sitti and a colleague use chemical signals to tell the bacteria what to do. In recent experiments they proved that they could stop and start the bacteria's flagella simply by exposing them to two different kinds of substances.

CMU is working ona a truly microscale (characteristic length of the robot doesn't exceed 100 um) swimming robot


Current Status of the micro-swimmer:Bacteria, only 0.5 um in diameter and 2 um long, are propelled by rotating their corkscrew like tails known as flagella at very high speed (~ 300 Hz). These flagella are only 20 nm in diameter and are about 10 um long. Here, S. marcescens bacteria are attached to Polystyrene (PS) microspheres via electrostatic, van der waals and hydrophobic interactions. As the attached bacteria rotate their flagella they push the microsphere forward. The on/off motion of the microspheres is controlled by introducing different chemicals into the experimental environment. To stop the motion, copper ions are introduced. These ions bond to the rotor of the flagellar motor and prevent its motion. To resume the motion we introduce another chemical called ethylenediaminetetraacetic acid (EDTA), which traps the copper ions attached to the rotor of the flagellar motor, allowing it to resume its motion.


CMU is also working on magnetically actuated micro-robots.


FURTHER READING
Summary of small robots for in body medicine at the Economist magazine

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