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PAPERS: Novel Applications of Design for AM

Design for Additive Manufacture of Fine Medical Instrumentation—DragonFlex Case Study

[+] Author and Article Information
Filip Jelínek

Austrian Center for Medical
Innovation and Technology,
Viktor-Kaplan-Straße 2/1, Building A,
Wiener Neustadt 2700, Austria
e-mail: filip.jelinek@acmit.at

Paul Breedveld

Department of BioMechanical Engineering,
Faculty Mechanical, Maritime and
Materials Engineering,
Delft University of Technology,
Mekelweg 2,
Delft 2628 CD, The Netherlands
e-mail: p.breedveld@tudelft.nl

Contributed by the Design for Manufacturing Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received February 21, 2015; final manuscript received April 21, 2015; published online October 12, 2015. Assoc. Editor: Timothy W. Simpson.

J. Mech. Des 137(11), 111416 (Oct 12, 2015) (7 pages) Paper No: MD-15-1158; doi: 10.1115/1.4030997 History: Received February 21, 2015; Revised April 21, 2015

The recently popularized domain of additive manufacturing (AM) has much to offer to medical device development, especially to the growing field of minimally invasive surgery (MIS). With the advancements in AM materials, one could soon envision materializing not only the proofs of concept but also the final clinically approved instruments. DragonFlex—the world's first AM steerable MIS instrument prototype—was recently devised with the aim to follow this vision. Apart from the medical device design restrictions, several limitations of AM materials and processes had to be considered. The aim of this paper is to present these insights to those opting for this means of manufacture, serving as a helpful design and material guide. Over the course of its development, DragonFlex has gone through four design generations so far, each differing in the AM material and process used. Due to being a prototype of a MIS instrument of miniature dimensions, the printing processes were limited to stereolithography (SLA), as to achieve the best possible precision and accuracy. Each SLA process and material brought along specific advantages and disadvantages affecting the final printout quality, which needed to be compensated for either at the design stage, during, or after printing itself. The four DragonFlex generations were printed using the following SLA techniques and materials in this order: polymer jetting from Objet VeroBlue™; SLA Digital Light Processing™ (DLP) method from EnvisionTEC® NanoCure RCP30 and R5; conventional SLA from 3D Systems Accura® 60; and DLP based SLA process from a ceramic composite. The material choice and the printing orientation were found to influence the final printout accuracy and integrity of thin features, as well as material's postproduction behavior. The polymeric VeroBlue™ proved structurally sound, although suffering from undermined accuracy and requiring postprocessing, hence recommended for prototyping of upscaled designs of looser manufacturing tolerances or overdimensioned experimental setups. The NanoCure materials are capable of reaching the best accuracy requiring almost no postprocessing, thus ideal for prototyping small intricate features. Yet their mechanical functionality is undermined due to the high brittleness of RCP30 and high flexibility of R5. The transparent Accura® 60 was found to lose its strength and appeal due to high photosensitivity. Finally, the ceramic composite shows the best potential for medical use due to its biocompatibility and superior mechanical properties, yet one has to compensate for the material shrinkage already at the design stage.

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Figures

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Fig. 1

(a) Rigid [6] and steerable [7] laparoscopic instruments; (b) rigid instrument DOF [8]; and (c) additional steerable tip DOF [9]

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Fig. 2

(a) Real-scale 5 mm wide DragonFlex prototype tip. (b) Combined with the cable guiding profiles of radius R, the rolling joint equalizes the cable moment arms A. (c) Section through the basic modular parallelogram construction of DragonFlex joints (bent 90 deg). Adapted from Ref. [9].

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Fig. 3

(a) Upscaled Objet VeroBlue™ DragonFlex I prototype demonstrating tip opening and pivoting in 2DOF. (b) Close-up picture highlighting the striking size difference between the 5 mm and 15 mm wide prototype tips. Adapted from Ref. [9].

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Fig. 9

(a) Comparison of DragonFlex II and III grasper printouts showing the effect of material choice and printing orientation on the warpage of grasper flaps (curved dashed lines). (b) Old and new Accura® 60 grasper halves showing the impact of material's photosensitivity on its appearance (the new darker grasper on top gained a yellow hue) and increased brittleness (missing broken flap marked by a dashed contour).

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Fig. 8

(a) Real-scale DragonFlex III prototype made from 3D Systems Accura® 60 and featuring (b) an innovative solution for cable-slack reduction and (c) a bolt-and-wheel mechanism for easy cable tensioning and fixation. (Reproduced with permission from Jelínek et al. [11]. Copyright 2015 by Informa Healthcare).

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Fig. 7

(a) Replacement of several NanoCure RCP30 DragonFlex II components by the more flexible and creep-resistant NanoCure R5 alternative. (b) The location of the loosened cable-fixing bolt, originally having an interference fit with the handle, due to permanent radial expansion of the hole.

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Fig. 6

(a) Inner rod and slot in DragonFlex II accommodating a compression spring for cable tensioning. (Reproduced with permission from Jelínek et al. [11]. Copyright 2015 by Informa Healthcare). (b) Breakage of the inner rod due to force F applied along the printed layers, demonstrating the importance of choosing an optimal printing orientation.

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Fig. 5

(a) Real-scale DragonFlex II prototype made from EnvisionTEC® NanoCure RCP30. (b) Close-up on the tip showing cable-driven joints and grasper. Adapted from Ref. [9].

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Fig. 4

Upscaled DragonFlex I joint component made from Objet VeroBlue™ showing the wear of the outermost sticky coating and some sign of oxidization

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Fig. 10

(a) Comparison of DragonFlex II and IV grasper printouts demonstrating the shrinkage of solid long and thin features (grasper flaps) made from the alumina–zirconia composite. (b) The effect of sintering on hollow long and thin features (cable holes) shrinking to 0.36, 0.39, and 0.58 mm in diameter from the designed 0.5, 0.6, and 0.7 mm, respectively.

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