P16084: Lung Model
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Systems Design

Table of Contents

Team Vision for System-Level Design Phase

Goals:

Completed:

Not Completed:

Functional Decomposition

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Benchmarking

Current lung model (click image for demonstration)

Current lung model (click image for demonstration)

[1]Homemade lung model. [2]University of Wisconsin lung model

[1]Homemade lung model. [2]University of Wisconsin lung model

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An up to date Benchmarking document can be found here.

Source [1]

Source[2]

Concept Development & Selection

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Morphological Chart

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System Design

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Systems Architecture

System Architecture

An up to date System Architecture document can be found here.

Feasibility

Overview:

Creation of an anatomically accurate rib cage is one of the most critical aspects of the new lung model. The rib cage also had the most unknowns in terms of feasibility and how much it will cost. Evaluation of manufacturing the rib cage through 3D printing was done in detail. Several other options were eliminated due to our budget constraints ($250) and the lower expected cost of 3D printing. 3D printing will be executed in the NextPrint lab (Booth A620) on a Makerbot Replicator 2X. This printer was chosen due to its availability and Dakota’s familiarity with the machine and software.

Prototyping:

A 3D model (.stl) of a rib cage was downloaded off Thingiverse.com and cut in strategic locations to allow for hinge points and print files small enough to be printed on the Makerbot (25x16x20cm). This was executed in Rhinoceros 5 with several orthogonal cut planes and the use of the “MeshSplit” command. This resulted in 21 unique print files that range in print time of ~12 hours to ~1 hour depending on geometry and size. Print times can be cut by ~2/3 by decreasing the resolution/quality of the print.

The most complex file is “BC 2” which represents the center region of the thoracic spine and 4 pairs of ribs. This file has a very complex geometry with large “overhang” areas and other challenging aspects that must be considered for 3D printing. The prints of "BC 2" show the progression of finding the best print orientation and use of novel unique printing practices to achieve a print with the best resolution.

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Analysis and Simulation:

Dakota experimented with 5 practices and techniques to effectively evaluate the feasibility of 3D printing a full sized rib cage.

Print orientation:

This effects which region of the print will have the best resolution. Determination of higher resolution desired on the ribs rather than the vertebrae resulted in a print orientation with the short side of the ribs on the build plate. Prints 1 and 2 were printed with the largest vertebrae on the build plate, prints 3,4,5 were printed with the shorter ribs on the build plate.

Fusion of prints with an acetone solution:

A sample of fused cylinders demonstrates the success of this technique, further testing will be executed to determine the strength of this fusion.

"Assist Plate”:

Allows better resolution on overhang areas where support structures are used. The increased resolution can be seen while comparing print 3 and 5 on the short side of the ribs and underside of the vertebrae.

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“Repair” process with Makerbot software:

This consisted of adding customized shapes to fill in areas of the print file that were not recognized as a solid. This was a side effect of cutting the original complete rib cage file into 21 sections. The cross sectional cut area in the “B Center 2” file was repaired with an oblong cylinder designed in SolidWorks that was later imported into the Makerbot software. Prints 3 and 5 show the addition of the cylinder and the increased area of the vertebrae that can now be used for fusion to neighboring regions of the spine.

Cold acetone vapor bath:

Executed on prints 2 and 4 to smooth the surface of the print. Due to the complex geometry and overhangs seen in these files the bath damaged the prints and caused considerable distortion. This process will not be used on any prints for the rib cage.

Conclusion and Future Plans:

This feasibility analysis shows that a high quality print of the most complex region of the rib cage can be 3D printed. Thusly, solidifying 3D printing as a viable manufacturing method for the rib cage. Application of the techniques tested on the remaining files will be used to create 21 “ideal” print files for full size printing.

Risk Assessment

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Plans for next phase

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