Magnetic Actuation Device Enhances Laparoscopic Surgery

Two new studies describe a local magnetic actuation (LMA) approach using coaxial gears to ease tissue manipulation during minimally invasive surgery (MIS) procedures.

Researchers at Vanderbilt University (Nashville, TN, USA) developed An LMA actuation unit that consists of a pair of diametrically magnetized single-dipole cylindrical magnets, working as a gear system that crosses the abdominal wall. In principal, one unit is external, placed on a patient’s abdomen; the second is an internal unit small enough to fit through the access ports used in MIS. During operation, the internal unit is magnetically anchored to the inside of the abdominal wall, while the other unit provides the mechanical force that powers the device.

The magnet in the external unit is attached to the shaft of a powerful electric motor that causes it to spin. The magnet in the internal unit is also attached to a shaft, but one that drives a two-inch lever. When the electric motor on the external unit twirls its magnet, it generates a rotating magnetic field that forces the magnet on the shaft in the inner unit to spin at the same speed. When it spins in one direction, the lever opens up, and when it spins in the opposite direction, the lever closes.

To retract an organ, the surgeon inserts the internal unit with a laparoscopic grasper and inserts it through the port into the body. When the internal unit is close enough to the external unit, it snaps into position against the inner surface of the abdominal wall. The motor on the external unit is then engaged, lowering the lever. Using standard laparoscopic instruments, the surgeon attaches one end of a line to the tip of the lever and the other end to a clip or suction cup fastened to the organ that must be moved. The electric motor is run in reverse and the lever retracts, pulling the organ into the desired position.

The first LMA device the researchers built as proof of principle was used during liver resection in vivo on an anesthetized porcine model. The researchers found that when abdominal wall thickness is 2 cm, the retractor is able to lift more than ten times its own weight. The researchers concluded that LMA can enable the transfer of a larger amount of mechanical power than that possible by using motors on the laparoscopic instrument itself. The studies were published in the February 2015 issue of IEEE Transactions on Robotics and the March 2015 issue of ASME Journal of Medical Devices.

“This device demonstrates for the first time that controllable mechanical power can be transferred across the abdominal wall via an intelligent magnetic link to power a robotic instrument,” said lead author Assistant Professor of Mechanical Engineering Pietro Valdastri, MSc, PhD. “Besides the ability to deliver a lot of power, the magnetic actuation approach has some other important advantages; the internal units do not contain any expensive and delicate electronics, so they can be easily sterilized and, if manufactured in bulk, could be made inexpensively enough to be disposable.”

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