Printable Prosthetics R&D Q&A FAQ: Part 1 – The Questioning

Top down view, extension view, and flexion view

Top down view, extension view, and flexion view

Marc Petrykowski of Creighton University was kind enough to provide some additional practical experience and information about the university’s research study into printable prosthetics.  For anyone looking to dive into this project, I’m cross-posting the information from the e-NABLE Google Plus group here.1 I’ve adjusted the formatting slightly, but otherwise everything below are Marc’s words.

  1. What exact measurements do you need (e.g., hand-length from where to where?) 
    1. Below are photos of all of the measurements I use for designing a hand.2 Yes it does seem like a lot, but all of them are needed to ensure the best custom fit for the hand we make for the user. When making a custom hand, it is important to make the 3D printed hand as similar to the non effect hand (fingers, width, length, etc). Each hand also has to be custom because of the size (length, width, height) or the stump. Some are very tiny and some are much bigger, so that also plays a big role when you have to design a hand. There are two photos that are measuring angle of flexion and extension. Those are important to see how tight or how loose the hand has to be for the power and strength of the individual and to make the hand as functional as possible.
  2. How do you get them from scans etc.
    1. Scans from our 3D scanner are in the format .STL which can be imported into programs such as blender (Shown below). Then I can lay it into the preexisting hand design and see an image of how it will fit, including the gauntlet size. If there are further changes to be made, I can do it all in blender before the print.
  3. How do you apply those measurements to your model
    1. As stated above, the measurements matter for the size of the hand. You can’t have a hand that is much smaller then the opposite hand, but you also can’t have a hand that is too small or large for the stump. Everything has to be customize depending on each case. This is where the designing takes the longest. My goal as the designer and printer is to make the hand as near perfect as the other hand so it feels the same to the body and brain, thus they will respond with the effected hand like it was their real non effected hand. Also as stated above, the degrees of flexion and extension and the size/length of the fingers are all incorporated into the final design before the printing the hand.
    2. And if, as +Jorge Zuniga suggests, ALL parts can be pre-printed, I’m hoping you guys will take the lead in helping us make it easy.  (As easy as buying shoes at a shoe store)
    3. This is possible because all of the redesigning and redoing of the measurements are all done in blender. Remember, if you resize a finger to a certain percentage, then you have to do the same for the rest of the fingers, thumb, phalanges, palm, and the gauntlet. That is how you can print everything off as one complete print.
  4. What are the pre-printed unit descriptors and dimensions small medium large XL? Narrow/wide?
    1. Pre Print units are based off of the measurements and how you converted them in blender. Instead of having small, medium, large, XL, etc. I have converted that into being resizing percentages. I use makerware since we use makerbots (2x and 2) so for a hand such as below picture measurements, I would classify that as a small or (110-130%), an extra small would be closer to 100-110% (which is super small like a 4 year old or so), a medium hand will be around 130-150%, a large will be around 150-170%, and an extra large is around 170%-190%+. Again, the percentage matters from the sizes that correspond the non effected hand as you want to make it as close to the other hand as possible.
  5. Does a Medium finger always go with a Medium hand?  If not, what’s the deal?
    1. Yes, whenever you print a certain size of one finger, you do that same size for the rest of the print. For example, if I printed a palm at 110%, I would have to make the fingers, phalanges, thumb, thumb phalanger, and the gauntlet all at 110%.
  6. Where are  the models for printing S M L XL hands or fingers, etc..
    1. The problem is that there are no models. Each hand is supposed to be custom depending on each case scenario.

I have several follow up questions, but I’ll leave those for the next post.

  1. The Google Plus group is private and you have to request an invitation, freely given, to be included.  While discussing discrete issues is easy enough, without the ability to quote original text, a detailed multi-issue open design discussion is very difficult. []
  2. Note:  I’ve removed the photographs.  I am not sure I have permission to post these pictures publicly. []
April 6, 2014 | Comments Closed

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