Local Magnetic Actuation
Laparoscopic surgery is widely applied to treat diseases in a less invasive manner than open surgery, with a total of 2,103,544 procedures performed annually in the United States. This technique requires at least three dedicated incisions distributed over the abdomen. Each incision is traumatic for the patient and is a potential infection site, with U.S. costs associated with surgical site infections estimated at more than $100 million per year. The next frontier for surgical instrument science is to further reduce invasiveness, while continuing to improve efficacy through enhanced surgical dexterity and access.
Magnetic coupling is one of the few known natural phenomena that can be harnessed to transmit motions across a physical barrier, and thereby eliminate many incisions. This approach enables multiple fully insertable surgical instruments deployed through a single tiny incision, which move around inside the abdomen without access-point constraints. However, reliable and precise control of magnetic surgical tools is challenging due to the rapid decay of magnetic field strength with distance (which is particularly significant for obese patients) and to the challenge of modeling interaction with human tissues.
At the STORM Lab we are harnessing magnetic fields using novel actuation strategies and models to create a new generation of intelligent surgical-assist devices capable of improving patient quality of life. We propose local magnetic actuation as a novel approach to transfer controlled mechanical power across a physical barrier to multiple miniature devices, operating in the confined space of the abdomen. Our strategy consists of an external driving system controlling the pose of a set of permanent magnets outside the patient, causing controlled motion of magnetically coupled surgical tools inside the patient, without direct penetrations through the abdominal wall. Currently we are characterizing the interaction between two rotating magnets (magnetic spur gears) and developing a dynamic model that will pave the way for precise control methods. In the video below, we show the coupling between the External Driving
and an Internal Driven Magnet (EDM and IDM, respectively) of an LMA-based link. The EDM is axially rotated by a motor, thus causing the rotation of the IDM. The mechanical power – in terms of rotational speed and load torque – transferred to the IDM can then be used to actuate a mechanism instead of an embedded motor.
In designing robotic instrument for laparoscopic surgery, Local Magnetic Actuation can enable the transfer of a larger amount of mechanical power than what is possible to achieve by embedding actuators on board. This has the concrete potential to enhance both the dexterity and the miniaturization of the robotic surgical instrument. The feasibility of this approach was demonstrated by the LMA-based tissue retractor represented in the two videos below. In this device, magnetic gears were used to transmit mechanical power from the external motor to the mechanism inside the retractor. The spinning motion of the IDM is fed to a custom mechanical train, which was designed to maximize the lifting force at the grasper and to fit the size constraints of a 12-mm surgical port. The device is 154 mm long, 12.5 mm in diameter, and weights 39.16 g.
When abdominal wall thickness is 2 cm, the retractor is able to lift more than ten times its own weight. The model is able to predict the performance with a relative error of 9.06±0.52%. Liver retraction trials demonstrates that the device can be inserted via laparoscopic access, does not require a dedicated port, and can perform organ retraction.
Additional information in the press release from ResearchNews@Vanderbilt.
C. Di Natali, J. Buzzi, N. Garbin, M. Beccani, P. Valdastri, “Closed-Loop Control of Local Magnetic Actuation for Robotic Surgical Instruments”, IEEE Transactions on Robotics, 2015, Vol. 31, N. 1, pp. 143-156. [ PDF]
N. Garbin, C. Di Natali, J. Buzzi, E. De Momi, P. Valdastri, “Laparoscopic Tissue Retractor Based on Local Magnetic Actuation”, ASME Journal of Medical Devices, 2015, Vol. 9, 011005-1-10. [ PDF] [AWARD]
M. Simi, R. Pickens, A. Menciassi, S. D. Herrell, P. Valdastri, “Fine tilt tuning of a laparoscopic camera by local magnetic actuation: Two-Port Nephrectomy Experience on Human Cadavers”, Surgical Innovation, 2013, Vol. 20, N. 4, pp. 385-394. [ PDF]
C. Di Natali, T. Ranzani, M. Simi, A. Menciassi, P. Valdastri “Trans-abdominal Active Magnetic Linkage for Robotic Surgery: Concept Definition and Model Assessment”, in Proc. of IEEE International Conference on Robotics and Automation (ICRA) 2012, St Paul, MN, USA, May 2012, pp. 695-700. [ PDF ]
C. Di Natali, P. Valdastri “Remote active magnetic actuation for a single-access surgical robotic manipulator”, in Proc. of the XVI Annual Conference of the International Society for Computer Aided Surgery (ISCAS) 2012, Pisa, Italy, June 2012, International Journal of Computer Assisted Radiology and Surgery, 2012, Vol. 7, Suppl. 1, pp. S169-S170. [ PDF] [ AWARD ]