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Research Papers

Laparoscopic Tissue Retractor Based on Local Magnetic Actuation

[+] Author and Article Information
Nicolò Garbin

STORM Lab,
Department of Mechanical Engineering,
Vanderbilt University,
Nashville, TN 37212
Department of Electronic, Information
and Biomedical Engineering,
Politecnico di Milano,
Milano 20133, Italy
e-mail: nicolo.garbin.1@vanderbilt.edu

Christian Di Natali

STORM Lab,
Department of Mechanical Engineering,
Vanderbilt University,
Nashville, TN 37212

Jacopo Buzzi, Elena De Momi

Department of Electronic, Information
and Biomedical Engineering,
Politecnico di Milano,
Milano 20133, Italy

Pietro Valdastri

STORM Lab,
Department of Mechanical Engineering,
Vanderbilt University,
Nashville, TN 37212
e-mail: p.valdastri@vanderbilt.edu

1Corresponding author.

Manuscript received May 14, 2014; final manuscript received September 15, 2014; published online November 14, 2014. Assoc. Editor: Carl Nelson.

J. Med. Devices 9(1), 011005 (Mar 01, 2015) (10 pages) Paper No: MED-14-1177; doi: 10.1115/1.4028658 History: Received May 14, 2014; Revised September 15, 2014; Online November 14, 2014

Magnetic instruments for laparoscopic surgery have the potential to enhance triangulation and reduce invasiveness, as they can be rearranged inside the abdominal cavity and do not need a dedicated port during the procedure. Onboard actuators can be used to achieve a controlled and repeatable motion at the interface with the tissue. However, actuators that can fit through a single laparoscopic incision are very limited in power and do not allow performance of surgical tasks such as lifting an organ. In this study, we present a tissue retractor based on local magnetic actuation (LMA). This approach combines two pairs of magnets, one providing anchoring and the other transferring motion to an internal mechanism connected to a retracting lever. Design requirements were derived from clinical considerations, while finite element simulations and static modeling were used to select the permanent magnets, set the mechanism parameters, and predict the lifting and supporting capabilities of the tissue retractor. A three-tier validation was performed to assess the functionality of the device. First, the retracting performance was investigated via a benchtop experiment, by connecting an increasing load to the lever until failure occurred, and repeating this test for different intermagnetic distances. Then, the feasibility of liver resection was studied with an ex vivo experiment, using porcine hepatic tissue. Finally, the usability and the safety of the device were tested in vivo on an anesthetized porcine model. The developed retractor 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 demonstrate that the device can be inserted via laparoscopic access, does not require a dedicated port, and can perform organ retraction. The main limitation is the reduced mobility due to the length of the device. In designing robotic instrument for laparoscopic surgery, LMA can enable the transfer of a larger amount of mechanical power than what is possible to achieve by embedding actuators on board. This study shows the feasibility of implementing a tissue retractor based on this approach and provides an illustration of the main steps that should be followed in designing a LMA laparoscopic instrument.

Copyright © 2015 by ASME
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Figures

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Fig. 1

An external controller is required to anchor and actuate an LMA-based surgical instrument. The anchoring unit supports the device because of the attraction force that the EAM generates on the IAM. The magnetic coupling between the EDM and the IDM provides actuation. A mechanism connected to the IDM controls a DoF of the end effector.

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Fig. 2

Schematic representation of the LapR-LMA and the external controller components

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Fig. 3

FEA simulation and two term exponential fit for the magnetic attraction force at increasing intermagnetic separation distance

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Fig. 4

(a) Schematic cross section of the EDM and IDM composing the actuation unit. (b) Torque transferred from the EDM to the IDM as a function of the angular displacement between EDM and IDM. The cross section view of the actuation unit is reported below the plot. (c) Vertical attraction force generated by the actuation unit as the magnets rotate. This plot assumes Δθ = 0. The cross section view of the actuation unit is reported below the plot.

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Fig. 5

(a) Tmax and its exponential regression at different separation distances, the solid horizontal line represents the average nominal torque for commercially available EM motors that would fit a volume similar to the IDM [26-28]. (b) Fv and Fh and their exponential regressions at different separation distances, assuming Δθ = 0.

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Fig. 6

(a) Three-stage PG components fabricated by spark erosion. (b) One of the three stages assembled.

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Fig. 7

Experimental setup used to test the efficiency of the PG

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Fig. 8

Schematic representation of the OCM. The slider is placed with an offset (BC¯) with respect to the hinge point of the crank (O). Thanks to the connecting rod (AB¯), the nut linear motion is converted in a crank angular displacement γ.

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Fig. 9

Mechanical pseudo-advantage Γ (mNm/N) of the OCM and its polynomial regression as a function of the lever angle γ (rad). A maximum value of 9.63 mNm/N is obtained for γ = 2π/17, while a 4.67 mNm/N minimum occurs for the fully open configuration (i.e., γ = π/2).

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Fig. 10

Perspective rendering of the assembled LapR-LMA in the closed (γ = 0) configuration (a) and in the open (γ = π/2) configuration (b). (c) The LapR-LMA prototype, where part of the outer shell was removed to shows the internal components.

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Fig. 11

Maximum weight that can be lifted by operating the LapR-LMA (dashed line), and maximum weight that can be statically supported by the LapR-LMA (solid line). Both weight limitations are plotted as functions of the intermagnetic distance and the opening angle of the retracting lever. The measurements obtained during benchtop experiments are presented as single data points.

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Fig. 12

Structural model used to predict the weight that the LapR-LMA can statically support. (a) Cross section of the LapR-LMA with the points of application of the different forces. (b) Free body diagram of the LapR-LMA. A is the extremity of the device at the side of the IAM, B is the point of application of Fanc, C is the point where the hinge of the lever is located, D is the point of application of Fact, X is the LapR-LMA center of mass.

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Fig. 13

Perspective rendering of the external controller

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Fig. 14

Experimental setup during the benchtop experiments

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Fig. 15

Sequence showing a single trial with a weight of 500 g at d = 2 cm. Lifting up the weight required 21 s, as indicated by the stopwatch in the lower right corner.

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Fig. 16

Ex vivo liver retraction using the LapR-LMA. In the sequence presented in (a), the intermagnetic distance is 2 cm, while in the sequence in (b) is 4 cm.

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Fig. 17

LapR-LMA performing liver retraction during the in vivo trials

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