How to Design Custom, 3D Printable Braces for Arm Injury

Cross-posted on my website at piper3dp.com.

Traditionally, casts for broken bones are made from heavy, solid, non-breathable plaster. This can create discomfort and skin problems for the patient during the healing process, like itchiness, rashes and skin infections. Custom 3D printed casts made with a breathable, voronoi pattern are a potential DIY solution. This method is obviously not medically approved (as yet) and shouldn’t be used in place of seeing your doctor. However, if you normally wear a wrist split/other brace for injury you could create your own custom version of this with approval from your occupational therapist or specialist.

While this is a great potential solution, 3D modelling and 3D printing a custom cast or brace is time consuming. A standard 3D print of a wrist cast takes about 3 hours to print on a 3D printer, where plaster tends to take about half an hour to fit to a patient and is very cost effective. This method is a DIY solution for experimentation only. I’ve previously blogged on how to create Wrist Braces using Meshmixer, this method is more complex but has a better result and a better fit.
To make one of these, you’ll need a 3D scanner and a copy of Meshmixer and Rhino 3D software, with Grasshopper, the algorithmic modeling plugin installed.

Here's a video with a walkthrough of the Rhino steps:

https://youtu.be/Goci-HOPpvo

Step 1: 3D Scanning

First, you’ll need to take a good scan of the area you’d like to make a brace for. I recommend asking ‘patient’ to hold their arm out and resting the fingertips on something to stop the arm from involuntarily shaking. Import the 3D scan into Meshmixer, and use the Plane Cut function to cut away the areas you do not want, i.e. the fingers, thumb and arm. You may also want to do some cleaning with the brush tools depending on the quality of your 3D scanner.

Step 2: Rhino 3D

Next, import your trimmed arm model into Rhino 3D. Use the function MeshtoNURBS to convert the .stl into a polysurface. Create an array of roughly spaced surface planes to fit the length of your scanned model, like the images below.

Step 3:

Next, use the function IntersectTwoSets and highlight first your surface planes, and then the arm model. You will create a series of ‘plane cut’ style curves like the image below.

Step 4:

Sometimes these curves will come out a bit irregular. Use the function _Rebuild on the curves to fix this. Next, use the Loft function to create a new surface using the arm curves. You’ll need to select the curves in order for this to work correctly.

Step 5:

Next, use the function OffsetSurf to create a surface 2mm above the existing surface. This will make sure the brace will sit nicely on top of the skin. You can also cut the brace in half by using the Boolean split tool. Launch Grasshopper for the next step. You’ll need to download this Voronoi algorithm and open it in Grasshopper.

For this algorithm to work as intended, you'll also need the Weaverbird plugin. You can get it here:

http://www.giuliopiacentino.com/weaverbird/

Right click the first Brep input component of the algorithm and select Set one Brep and click on the first half of the brace when prompted.

Step 6:

This will now map a voronoi pattern to the offset arm scan. You can go through the algorithm and tweak different aspects, including the hole size and more.

Step 7:

After you’re happy with the outcome, highlight the last section of the algorithm, right click and choose Bake.

Step 8:

Repeat the process on the other half of the brace. You now have a voronoi brace! You should be able to print this standing upright without any supports. You can use ribbon and beads to act as a hinge, or 3D model on a hinge of your own design. Xkelet has some great designs for inspiration. Enjoy!

Comments

[Careers4kids]

Do you accept partnership proposals for product design? I'm an entrepreneur capable of raising all the necessary capital to launch and market my product but I need help with professional design so I can patent and also try to cover any simple alternatives a competitor would use to copy. Thank you!

[sjpiper145]

Hi, Thanks for your interest. You are welcome to use this as you please, but I intend to keep this method as open source. I am working on other projects and am unable to partner, but happy to help with questions. I'm not sure how useful a patent would be with other companies like Exovite and Xkelet working on this too. Good luck if you end up working on this, it's an exciting space. Looking forward to see how you go!

[samc227]

Hello steph,
I'm Roni Geva 7th grader student in high school SULAM TZOR in ISRAEL.
my Entrepreneurship teacher Challenge me in project, to make your idea (to make 3D printer hand holder).
can you send me the file?
PLEASE

Excuse me if I didn't write true

I don't know English very well.

thank you roni

[pititaff]

how did you scan your arm ?

[sjpiper145]

Hi Ptitaff, I've got a (now discontinued) Primesense Carmine 1.09 used with Skanect. You could use something like the Structure Sensor with similar results. Doesn't need to be super accurate.

[Captain_Nemo]

As someone who has had an arm injury, I can say I've seen no 3D printer filament that is strong enough to cope with that injury. I've also never seen a cast made from plaster; The cast I had was fiberglass, which was more than strong enough, along with being small and lightweight. 3D printing a brace is a step backwards, you now need a cad operator just to use it; Firberglass can be applied by a nurse.

[JonathanB147]

The cool thing about a 3D Printed on would be that you can shower with it and scratch yourself ;)

All the Casts that I got were plaster bandages. never got a fiberglass one. (austria)

[Captain_Nemo]

It's barely more waterproof than fiberglass, the tiny valleys you get with
3d printing will support bacteria colonies.

[lobo13]

if you concern is bacteria you know you can always print one every week if you like and trow away the old one with "bacteria" also diffrent colors.

[DaveL142]

Would have LOVED this if it was done in something that most of us can get access to (Fusion 360, TinkerCAD, GrabCAD etc) but Rhino is WAY too expensive for the typical Instructables user and Meshmixer has a learning curve as steep as they come There is no discussion about how to obtain the 3D scanned image in terms of equipment etc

I have seen USED scanners in the $3K range so how do we take this tutorial and make it work for the typical reader/maker?

Dr D

[maave]

I've been working on the same idea but with free software. A Kinect ($15 on ebay) with Skanect (free) for scanning, and Blender (free, open source) for editing. I've been depressed and haven't finished it yet. Here are my instructions so far. I hope this helps.

https://blog.silocitylabs.com/post/2018/08/30/3d-p...

[sjpiper145]

Wow nice work Maave! Great to see different ways to do this.

[sjpiper145]

Great questions! Would have really loved to do this in some of the maker friendly softwares, but I believe you can get a 30 day free trial of Rhino if you'd like to have a play. 3D scanning wise, you'll need a handheld scanner for this. To do this for free or cheaply, there's a few options:

- Xbox Kinect scanner using the Kinect SDK

- Autodesk Remake scanning using photogrammetry

- Budget 3D scanner like the Structure Sensor or XYZPrinter scanner

I suspect that smart phone apps will also be able to 3D scan soon too. 123D catch used to be great for this before it was removed. Hopefully another great app will spring up for this purpose.

[DaveL142]

How about showing us how to do it with Kinect in detail

I have one but haven't been able to set it up to scan as so many others claim they can.

[HelenaTroy]

This might also do for superhero/warrior costume arm guards …

[Omnivent]

Hi,

Probably the best use of a 3D-printer I have seen in a long time - Too bad I don't have one - I'm sure you could make good "sleeping braces" to counter carpal tunnel syndrome better than my idea of 2 pieces of plywood bound with string as a sandwich (but I'm afraid to karate-chop something in my sleep, so it only exists on paper and probably hard to tie the second hand as well ;)

Nice, very nice job.

Have a nice day :)

[DIY Hacks and How Tos]

Looks way better than any commercial arm brace that I have ever seen.