Research Papers

Shape Deposition Manufacturing of a Soft, Atraumatic, and Deployable Surgical Grasper

[+] Author and Article Information
Joshua Gafford, Ye Ding, Andrew Harris, Terrence McKenna, Panagiotis Polygerinos, Dónal Holland

School of Engineering and Applied Sciences,
Harvard University,
Cambridge, MA 02138

Conor Walsh

School of Engineering and Applied Sciences,
Harvard University,
Cambridge, MA 02138;
Wyss Institute for Biologically Inspired Engineering,
Harvard University,
Cambridge, MA 02138
e-mail: walsh@seas.harvard.edu

Arthur Moser

Department of Surgery,
Beth Israel Deaconess Medical Center,
330 Brookline Avenue,
Boston, MA 02215

This mechanical model is a linear simplification used to quickly compare different finger geometries and their resulting deformed shape under loading. Ei is an “effective modulus,” that was obtained by comparing the model to empirical behavior of the urethane-based rubber joints. The accuracy of this linear model compared to hyperelastic models (such as Ref. [24]) warrants further investigation and analysis.

The cable actuation force is treated as a point load on the distal-most segment.

1Corresponding author.

Manuscript received August 15, 2014; final manuscript received December 23, 2014; published online February 27, 2015. Assoc. Editor: Aaron M. Dollar.

J. Mechanisms Robotics 7(2), 021006 (May 01, 2015) (11 pages) Paper No: JMR-14-1215; doi: 10.1115/1.4029493 History: Received August 15, 2014; Revised December 23, 2014; Online February 27, 2015

This paper details the design, analysis, fabrication, and validation of a deployable, atraumatic grasper intended for retraction and manipulation tasks in manual and robotic minimally invasive surgical (MIS) procedures. Fabricated using a combination of shape deposition manufacturing (SDM) and 3D printing, the device (which acts as a deployable end-effector for robotic platforms) has the potential to reduce the risk of intraoperative hemorrhage by providing a soft, compliant interface between delicate tissue structures and the metal laparoscopic forceps and graspers that are currently used to manipulate and retract these structures on an ad hoc basis. This paper introduces a general analytical framework for designing SDM fingers where the desire is to predict the shape and the transmission ratio, and this framework was used to design a multijointed grasper that relies on geometric trapping to manipulate tissue, rather than friction or pinching, to provide a safe, stable, adaptive, and conformable means for manipulation. Passive structural compliance, coupled with active grip force monitoring enabled by embedded pressure sensors, helps to reduce the cognitive load on the surgeon. Initial manipulation tasks in a simulated environment have demonstrated that the device can be deployed though a 15 mm trocar and develop a stable grasp using Intuitive Surgical's daVinci robotic platform to deftly manipulate a tissue analog.

Copyright © 2015 by ASME
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Fig. 1

Deployable manipulator prototype, with daVinci ProGrasp forceps for scale. When closed, the device has a diameter of 14 mm and a length of 96 mm. When open, the diameter of the finger tips is 86 mm, resulting in an encompassed volume of 116 cm3.

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Fig. 2

Left: artist's rendition of robotic pancreaticoduodenectomy, where the pancreas, SMV, and SMA are shown, and right: port placement. (Reprinted with permission from Zeh et al. [1]. Copyright 2011 by Elsevier).

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Fig. 3

Procedural workflow of deployable atraumatic grasper, where two forceps are used to position and actuate the device. After the device has been deployed, only one forcep is required for additional retraction tasks (deploy through 15 mm trocar, retrieve with laparoscopic forceps, and tighten around tissue until LED turns red).

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Fig. 4

Grasper prototype mapped against a rendering of an insufflated abdomen (daVinci tools provide reference)

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Fig. 5

Shape deposition process used in the fabrication of empirical finger models, consisting of a series of subtractive, additive, and pick-and-placement steps: (1) mill initial pockets for stiff polymer, (2) place components, (3) fill stiff polymer, (4) mill flexible pockets for flexible polymer, (5) fill flexible polymer, and (6) release finger

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Fig. 6

Geometric and material parameters of a single segment consisting of a flexible joint (i − 1) and stiff segment (i)

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Fig. 7

Cable orientation schemes and their resultant transmission ratio, cable configuration 1: direct-through and cable configuration 2: top-mounted

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Fig. 8

Parasitic cable friction effects as the finger assumes a curved or actuated profile

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Fig. 9

Empirical finger models with varying configurations

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Fig. 10

Comparison of analytical versus experimental SDM finger showing agreement

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Fig. 11

Left: experimental setup for measuring the transmission ratio, and right: comparison of analytical versus experimental SDM finger showing agreement

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Fig. 12

Torsional stiffness enhancement analysis. For a steel flexure thickness of 50 μm, the bending stiffness of the joint remains unchanged, whereas the torsional stiffness is improved by 50%.

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Fig. 13

Calibration curve for the embedded barometric pressure sensors

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Fig. 14

Closed-top mold design (U.S. quarter for scale): (1) countersunk holes for fasteners, (2) inflow and outflow sprues/risers for polymer injection, (3) overflow basin to isolate screws from elastomer, (4) outlet for cable sheath, (5) stiff segment pocket, (6) press-fit feature for pressure sensor, (7) overflow drain, (8) alignment holes (mate with pin on underside of top mold, not shown), (9) release pin through-hole, (10) inlet for cable sheath and wiring, and (11) press-fit pocket for steel-reinforced flexible segments.

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Fig. 15

Closed-top SDM: (1) open-top molding of flexure hinges with embedded steel flexures, (2) pick-and-placement of flexures, sensors, and cabling in master mold, (3) mold closure, (4) injection of task-9 polyurethane, and (5) release fingers after sufficient curing

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Fig. 16

Handle operation (cross-sectional isometric view), showing (1) initial state (no tension), (2) tensioned state, engaging ratchet pin with pawl, (3) relieved state, disengaging ratchet and pawl, and (4) spring return to initial state

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Fig. 17

Sectional view of grasper modules with callouts to important features

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Fig. 18

Creep test (displacement versus time) with a 1.5 N load applied to the end of the joint in cantilever fashion (inset shows the testing setup)

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Fig. 19

Top: benchtop simulation showing the grasper prototype manipulating a porcine pancreas (weight: 80 g), and bottom: representative pressure profile captured during simulation

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Fig. 20

daVinci simulation storyboard as seen through stereoscope (inset is external view): (1) device retrieval, (2) device positioning around pancreas analog, cable tensioning, and (3) cephalad retraction




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