Research Papers

A Magnetically Actuated Drug Delivery System for Robotic Endoscopic Capsules

[+] Author and Article Information
Fredy Munoz

School of Mechanical, Materials and
Mechatronic Engineering,
University of Wollongong,
Wollongong, NSW 2522, Australia
e-mail: ffm517@uowmail.edu.au

Gursel Alici

ARC Center of Excellence for
Electromaterials Science,
School of Mechanical, Materials and
Mechatronic Engineering,
University of Wollongong,
Wollongong, NSW 2522, Australia
e-mail: gursel@uow.edu.au

Weihua Li

School of Mechanical, Materials and
Mechatronic Engineering,
University of Wollongong,
Wollongong, NSW 2522, Australia
e-mail: weihuali@uow.edu.au

1Corresponding author.

Manuscript received June 20, 2015; final manuscript received September 30, 2015; published online November 16, 2015. Editor: Rupak K. Banerjee.

J. Med. Devices 10(1), 011004 (Nov 16, 2015) (11 pages) Paper No: MED-15-1203; doi: 10.1115/1.4031811 History: Received June 20, 2015; Revised September 30, 2015

There is an increasing need to incorporate an actively controlled drug delivery system (DDS) into the next generation of capsule endoscopy in order to treat diseases in the gastrointestinal tract in a noninvasive way. Despite a number of attempts to magnetically actuate drug delivery mechanisms embedded in endoscopic capsules, longer operating distances and further miniaturization of on-board components are still drawbacks of such systems. In this paper, we propose an innovative magnetic system that consists of an array of magnets, which activates a DDS, based on an overly miniaturized slider–crank mechanism. We use analytical models to compare the magnetic fields generated by cylindrical and arc-shaped magnets. Our experimental results, which are in agreement with the analytical results, show that an optimally configured array of the magnets enhances the magnetic field and also the driving magnetic torque and subsequently, it imposes a high enough force on the piston of the DDS to expel a required dose of a drug out of a reservoir. We conclude that the proposed magnetic field optimization method is effective in establishing an active DDS that is designed to deliver drug profiles with accurate control of the release rate, release amount, and number of doses.

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Fig. 1

The main components of the proposed DDS for WCE. A: ring-shaped external magnetic system, B: drug release module, C: the robotic capsule, D: complementary modules within the capsule (anchoring mechanism, active locomotion system, and localization and orientation detection module), E: patient bed, F: clinician, G: joystick, and H: human capsule interface. Point P represents the origin of the general coordinate system XYZ, θ is taken with respect to the x-axis, and φ is taken with respect to the z-axis.

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Fig. 2

The components of the slider crank mechanism. A: IPM, B: disk-shaped piston, C: connecting rod, D: disk, and E: robotic capsule. The coordinate system XcYcZc of the IPM with respect to the general reference system XYZ is shown in Fig. 1.

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Fig. 3

(a) A diametrically magnetized cylindrical magnet with radius R, length L1 = z2 − z1, and magnetization grade M, (b) arc-shaped permanent magnet, and (c) top view of different types of arc-shaped permanent magnets (i.e., A1, A2, A3, and A4) used in this work

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Fig. 4

(a) Single cylindrical EPM, (b) top view of the position and orientation of the EPM with respect to general reference system, (c) EPM′s volume that produces 103 mT from a distance d = 240 mm, magnetization M = 1.32 T, and (d) contour line for Bx = 103 mT (Vmin occurs at L = 425 mm)

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Fig. 5

(a) Array of four diametrically magnetized cylindrical magnets Ci (i = 1, 2, 3, and 4) around a small permanent magnet (IPM) whose center is located at point P and (b) four arc-shaped permanent magnets, Ai (i = 1, 2, 3, and 4), radially and tangentially magnetized. Distance d2 is determined from point P to the center of any Ai. P is located at the center of a circle with a radius d1.

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Fig. 6

Comparison of the flux density along the x-axis produced by an optimized cylindrical EPM, four cylindrical EPMs, and four arc-shaped magnets. Operating distance d of 240 mm.

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Fig. 7

Comparison of Bx produced by a single cylindrical EPM, structure C1234, and structure A1234

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Fig. 8

Vector field of the magnetic flux density norm on the plane z = 0 generated by the structure A1234, when the operating distance d is 30 mm. Scale on the right-hand side is given in Tesla.

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Fig. 9

(a) Scaled-up magnetic system (dimensions in millimeter). Left: a single custom arc-shaped permanent magnet and right: assembly with smaller arc-shaped magnets. (b) Comparison of Bx produced by the array of cylindrical magnets (denoted as C1234) and the array of arc-shaped magnets (denoted as A1234) when the operating distance d is 240 mm.

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Fig. 10

(a) EPMs fixed on the aluminum case and rotated by θa  = 30 deg and (b) experimental setup consisting of the measurement instruments and the array of arc-shaped permanent magnets

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Fig. 11

Bx produced by arc-shaped magnets: (a) radially magnetized (A1 and A12), (b) tangentially magnetized (A3 and A34), and (c) the array A1234

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Fig. 12

τz produced by single and multiple permanent magnets on the cubic IPM

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Fig. 13

(a) The cubic IPM case connected to a disk through the crankshaft. (b) Components of the slider–crank mechanism. A: Platform, B: connecting rod, C: piston, D: the reflective surface for laser-based displacement measurements, E: spring holder, F: IPM case, G: platform support. β is the angle formed by the external magnetic system and the x-axis (i.e., β=180 deg−θa and θa is shown in Fig. 10(a)).

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Fig. 14

Slider–crank mechanism for the drug delivery. The z-axis is positive into the page.

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Fig. 15

Components of the slider–crank mechanism and the mechanical spring to measure the piston force

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Fig. 16

(a) External magnetic system powering the slider–crank mechanism and rotated by β  = 180 deg. (b) Thelaser was used to measure the piston displacement along the x-axis.

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Fig. 17

Piston force response with a variety of cubic IPMs. It shows the compression and extension of the spring in the entire cycle.

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Fig. 18

Crankshaft torque response with a variety of cube IPMs. It shows the compression and extension of the spring in the entire cycle.

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Fig. 19

Vector representation when the EPMs are oriented at β = 60 deg. This vector representation is a top view of the coordinate system defined in Fig. 13(b).




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