Research Papers

Magnetic Torsion Spring Mechanism for a Wireless Biopsy Capsule

[+] Author and Article Information
Massimiliano Simi

The BioRobotics Institute,
Polo Sant'Anna Valdera,
Pisa 56025, Italy
Department of Mechanical Engineering,
Vanderbilt University,
Nashville, TN 37212
e-mail: m.simi@sssup.it

Giada Gerboni

e-mail: g.gerboni@sssup.it

Arianna Menciassi

e-mail: a.menciassi@sssup.it
The BioRobotics Institute,
Polo Sant'Anna Valdera,
Pisa 56025, Italy

Pietro Valdastri

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

Manuscript received October 2, 2012; final manuscript received July 16, 2013; published online September 24, 2013. Assoc. Editor: William K. Durfee.

J. Med. Devices 7(4), 041009 (Sep 24, 2013) (9 pages) Paper No: MED-12-1122; doi: 10.1115/1.4025185 History: Received October 02, 2012; Revised July 16, 2013

The authors present a novel magnetomechanical elastic element that can be loaded remotely by varying the magnetic field surrounding it and that is able to store and release mechanical energy upon external triggering. The magnetic torsion spring (MTS) is used as the core component of a self-contained miniature biopsy capsule (9 mm in diameter and 24 mm long) for random tissue sampling in the small bowel. Thanks to the MTS concept, the biopsy mechanism can be loaded wirelessly by a magnetic field applied from outside the body of the patient. At the same time, magnetic coupling guarantees stabilization against the small bowel tissue during sampling. Extreme miniaturization is possible with the proposed approach since no electronics and no power supply are required onboard.

Copyright © 2013 by ASME
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Fig. 1

The basic components of an MTS

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Fig. 2

(a) The MTS torque versus angular displacement of the rotating magnet. (b) The MTS potential energy as a function of the angular displacement of the rotating magnet.

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Fig. 3

(a) Wireless biopsy capsule design embedding two MTSs to actuate a cylindrical blade. (b) The application of an external magnetic field loads the MTSs and opens the lateral hole.

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Fig. 4

Section view of the biopsy capsule operation principle. (a) Applying an external magnetic field the capsule is attracted toward the lumen wall, the lateral hole is open, and the MTSs are loaded. (b) Removing the external magnetic field triggers the MTSs and the blade rotation cuts and stores a tissue sample. (c) Without any external magnetic field, the biopsy capsule is closed and travels along the GI tract under the effect of peristalsis.

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Fig. 5

(a) The MTS maximum magnetic torque (θ = ±π/2) as a function of MTS magnet distance obtained by finite element simulation. Scheme of the (b) magnetic configuration and (c) simulation screenshot. Magnet properties, such as shape, dimension, magnetization direction, remanence, and magnetic permeability (μ0 = 1.05) were set into the simulation. The selected mesh consisted of approximately 150,000 elements with a maximum element size set at 1/50 of the maximum geometric feature in the scenario.

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Fig. 6

(a) Screenshot for the finite element simulation for θ = 0. The selected mesh consisted of approximately 250,000 elements with a maximum element size set at 1/50 of the maximum geometric feature in the scenario. (b) Sketch of the experimental bench test used to assess Tm2(θ).

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Fig. 7

Simulated and experimental trends for Tm2(θ)

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Fig. 10

Plot of the magnetic attraction force between the external permanent magnet and the biopsy capsule embedding two MTSs as a function of de. Simulation results for θ = 0 and θ = π superimposed to experimental data.

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Fig. 8

Finite element simulation screenshot for estimating the torque exerted by the external permanent magnet on two MTSs located de = 27 mm away on the vertical axis. The two MTSs were spaced ds = 7 mm each other and θ = 0 was assumed. The mesh consisted of approximately 380,000 elements with a maximum element size set at 1/50 of the maximum geometric feature in the scenario.

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Fig. 9

Sketch of the experimental setup to measure the magnetic attraction force between a capsule embedding two MTSs and the chosen external permanent magnet

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Fig. 11

(a) Sketch of the experimental setup to estimate the typical volume of the tissue penetrating the lateral hole as a function of the hole diameter. Image of a capsule mock-up, with a 5 mm hole, pressed against an excised porcine small intestine sample.

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Fig. 12

Top view of (a) the lateral hole and (b) central cross section of the biopsy capsule

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Fig. 13

Plot of the theoretical pressure exerted by the blade on the tissue during cutting for the selected design parameters

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Fig. 14

Capsule components: (a, b) the shaft and (c) the blade (d) assembled together. (e) The ruby bushings and (f) the metallic layer assembled in (g) the prototype.

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Fig. 15

Assembled biopsy capsule prototype laying on graph paper for reference

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Fig. 16

Ex vivo trials. (a) The capsule is lifted against the tissue by magnetic interaction with the external magnet, while the MTSs are loaded. (b) Removing the external magnet the MTSs turn the blade, cutting a sample. (c) The lumen wall region where the sample has been removed. (d) The biopsy sample retrieved from the capsule.



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