Print my leg (english doc)

 
Tutoriel
Create its own leg prosthesis, low-cost with 3D printing and new technologies.
  • Difficulty : Abordable
  • Duration : 2 days
  • Budget : <100 euros
 

Foreword

The Print my leg project is led by Christophe Debard.
The goal is to create aesthetic leg prosthesis.

This documentation was written by Floss Manuals (Elisa de Castro Guerra and Joyce Markoll) during the Fabrikarium 2016

The team from Fabrikarium was composed of various skills : mecanical engineer, Fablab manager, 3D printer, executive assistant, makers, doc writers, Airbus college, designer, graphic designer, optimisation engineer, prosthetist and fashion designer :
Adamou Adamou, Amandine Labbé, Simon Colin, Stéphanie Rochereau, David ripol, Jérôme Colmagro, Marine Gimenez, Didier Castel, Vincent Loubière, Christophe Debard, Guillem Colombiès, Yeoil Song, Rémi Lansiaux, David Mazo, Thomas Grougon, Fouad zarour, Aurélie Brachet

 

Presentation of Print My Leg

The problematic of Christophe today is to get an aesthetic leg both functionnal and aesthetical. In general, leg prosthesis should compensate the lack of volume in the calf area. The proposed solution is to sculpt or design an artificial leg taking as reference the valid leg and paint it. In any case, it remains a plastic leg that tries to imitate the other valid leg, but not so good.

And if the solution was to inverse this trend and to make visible the prosthesis? How would it look like? And if the shell were interchangeable, like a garment, in an easy and fast way in order to satisfy the need of different aesthetics? What could be the means of anchorage to adress this issue? Could the principle be universal and adapt itself to both prosthesis and orthoses?
Could this innovation be reproducible and cost less than 100 euro?

Usual aesthetic of prosthesis

Here is an example of prosthesis on which a yoke comes over to adress the missing part. The result is unsightly.

 

Other aesthetic solutions

Nowadays some companies offer more interesting and innovating designs. The problem is their cost, around 6000 euros. Hulls are not interchangeable. Then it's difficult to get one, so let's not speak about getting more than one ...

 

Understand the technical challenge

Depending of the amputation and of the target activities, the prosthesis are differents. The issue is to understand what is the most universal in order to give the benefit to the maximum of persons.
After the amputatio, the length of the stump is variable. The stump could be long or short. The fixation should be considered for both cases.
The prosthesis could be composed of one tube or one blade. The foot could be either dynamic to facilitate the walking and sportive activities, or at the contrary passive.

 

To summarize, the challenge is to find how to fix these hulls to the prosthesis in a way that they could be removable, and does not exceed the cost of 100 euros.

During the Fabrikarium hackathon, two solutions were created and tested by the team.

  • One hull prosthesis interface solution based on inflatable seal (Pump solution)
  • One hull prosthesis interface solution based on a boa system (Boa solution)
 

Designed hull

The creation of a double hull is intended to envelop a leg prosthesis. Then , it can be decorate to customize it in a personal way to give to the person the will to assume it and to get rid of the fear of the eyes of the others. Good design for prosthesis exists but it's almost always a tailored solution, hence it's very expensive. The research around prosthesis with digital fabrication has for goal to liberate disability from the financial weight. It also opens new possibilities facilitating the custumization as it's done for garnment.
The work around customized design is strongly depending of the finished hull prototype. The design can then be created through 3D printing, lasercut which can be used with many various material or only cutter or scissors. Hulls could be prepared with an sublayers of paint spray or tinfoil.

The following creations were experimentals for testing purpose. If the covering is interchangeable on the hull, it needs an easy to use attachment system. (Example: laces, buttons, flat elastics fixed from below in the upper and lower part, magnetic system ...)

The process of design creation is different for each person, each one could print his leg depending of its tastes, materials and tools he has.

 

From design to lasercut

When the above patterns were created, they were drawn with a pen, and after few operations taking a bit of time, the magic has operated: a pre-cut leather sheet with little leaves. Another pattern was also created. How to proceed?

First, we take an existing drawing or we create a new one. Then we scan it in order to import it in a software like Inkscape which is open source ans available for Windows, MAC, and Linux. Then we vectorize it ( Menu>Path>Vectorize the bitmap). Tick the preview box to adjust your settings. You can then export it in the SVG format to backup the file we just created.

We then export the file under DXF format : Menu File>Save under >Choose .dxf extension.
The result recorded with the option "visible only" can now be read by the laser cutter, depending of the model you use. On a Epilog one it will work directly with SVG format.

On other ones JPG could work, but globally DXF is the most used.
Now you get the dxf, open it in Inkscape: if the drawing was full of color you should now see only the outlines.
Check up the software of the lasercut to see if you need to give a particular color to these outlines. Indeed, on some lasercut the color and thickness of the line will give the parameters for the lasercut.

 

Example to extract a pattern with Inkscape

We take a drawing at SVG format, created in Inkscape. For this example , we extracted the bamboo part to use it as a pattern to repeat it and decorate a support.

 

Good to know for preview files that should be cut on the laser cutter machine

There is also an open source software named Visicut. It's delivered with LibLaserCut, an independant library for lasercut machines (supported by Epilog ZING, MINI? HELIX and thoses which use LAOS open source card. Other drivers will be developped in the future. It allows to use various format : SVG, EPS, PLF VisiCut  (Portable Laser Format), to preview your drawing applied to the material and as well to prepare you cuts at home.

This software makes it possible to use format such as SVG, EPS, DXF et le PLF VisiCut (Portable Laser Format), and to preview your drawing once it will be applied to the material. You can then prepare you lasercut files at home, and avoid bad surprise when you will import your files in a Fablab.  (Translated approximately from the official website).

In order to save material when using lasercut and to get the biggest surface on the cutting support here is the link of svgnest with documentation.

 

Print My Leg : Pump solution

The goal is to link decorated hulls to an upper muff prosthesis covering part or totally the prosthesis to the feet. The hulls are decorated, so it's imperative that the attachments are not visible or at least that they impact as less as possible the appearence of the hulls.

This document presents the attachment prototype. The whole design is still work in progress and will be released in the future by the team of this project.

Principal of this solution

This solution proposes an interface based on inflatable seal. It Its benefit is to be resistant to water, cheap, and to support different hull sizes (depending of the person morphology, hull design, and the form of socket prosthesis) and of course to not damage or modify the prosthesis.

Depending on the length of the socket and the shells, it may be envisaged to provide two fasteners in order to solidify the shells. In cases where two fasteners are required, the upper part will be attached to the socket and the lower part to the prosthesis via its blade or tube.
The shells will have to integrate a fastening system between them of type clips and in their internal face a profile to accomodate the inner tube: a maintenance groove.

 

Junction of half-hulls

The inflated seal should be placed between the hull and the prosthesis and be in contact avec the whole diameter of the socket prosthesis. In this area, the two hulls should be closed, rigidified, resistant against the joint pressure. It is therefore necessary to ensure that the hull integrates two stiffeners to rigidify (in stiffness and holding) locally the two half-hulls. In there, the two half hulls must be solidarized.

This prototype was made with ABS plastic thanks to 3D printing. The thickness is 2mm and represents a hull part of 50mm.
The locking between the two half-hulls is achieved by a system of clips and the pressure of the inflatable seal on the other.

The clips have the advantage of being flat, space-saving and offering a flat surface (the design of the shells) as well as proposing a constraint on a line and not on a point. This reinforces the hulls.

 

Schema of clip system

 

Inflated seal

Once the hull have been st up around the socket prosthesis, a simple bycicle air pump must be used to fix the hull on the socket prosthesis.

Inflatable profiles are commercially available. We opted for a hijacked and accessible system, easy to find and cheap. As an inflatable seal, a simple inner tube for racing bicycle 700x19 does the job.

In order that the tube does not slide off the hull, a groove must be integrated in the in order to maintain the tube when it's inflated.

 

It's possible to glue the tube in the groove with double face tape for example.

In the lower part, in the case of a short prosthesis, the clearance is greater between the tube or the blade and the shells. It may be necessary to create an adapter piece so that the clearance at the joint is adapted and more regular. In the case of a dynamic foot, the lower part of the shell moves of several millimeters. It will then be necessary for the inflatable seal to be enough flexible, but nevertheless solid. It is also possible to adapt the clearance shell joint for better flexibility front / rear or lateral. A solution of elastomer or foam should be considered as an alternative solution.

 

Production

Necessary material

- Tube from bicycle
- Socket prosthesis
- Hulls
- Bicycle pump compatible with the valve of the inner tube

 

Produce two hulls with the personalisation and the cut of your choice (S form, straight ...) integrating a hinge system, a groove for inserting the inner tube and a clip system.

The hulls must not be too thin (the prototype was too thin with only 2 mm) in the joint section because forces will be involved and they should not deform or break them. In some areas, depending of the choosen design and its material, it could be necessary to reinforce the hulls. It is preferable to predict this when modeling the shells and before printing.

On the other side of the connection between the two shells it is recommended to use a hinge or other system of clips, according to your shells.

The holding of the printed parts is not the same in all directions, so the printing will preferably be done in the direction of the axis of the shell which is generally more resistant.

The connection between the two shells can be over the entire length or only partial depending on the aesthetics and their size. The hull is in fact open-ended outside the fixing zones.

You should now remove the construction mesh (supports) and lightly sand to prepare the insertion of the inner tube.

 

Step 2 : Prepare the inner tube

The inner tube must be cut to the shell diameter. To do this, wrap the inner tube around the two shells and cut. Think of integrating the valve into the conserved space.

 

Keep the valve open or bore the hulls to allow the valve to pass. Choose a long, smooth valve, in case it is necessary to cut it. It will thus be easier to deport it by cutting it and sticking it to a plastic tube. If you need to tinker with this, use epoxy glue or silicone glue.

 

Step 3: Setting up the hulls around the prosthesis socket

Surround and clip the shells around the socket.

 

Step 4 : Fixing hulls to the socket

Inflate the tube slowly so that the pressure keeps the shells through the counter-force. The air cushion must resist 1.5 bar or 2 bar. This pressure is sufficient to maintain the shell. The choice of the diameter is according to the groove to be compensated between the shell and the socket or the prosthesis.

 

Print My Leg : Boa Solution

The goal is to link decorated hulls to an upper prosthesis sleeve covering part or totally the prosthesis to the feet.

Principal of this solution

This solution proposes a collar in contact with the socket in order to fix the half-shells therein. This collar is ideally placed between the socket and the shells. It will have the role of lengthening the flat surface for a good tightening of the hulls. The shells will be fixed with wires that will interlace the whole and will tighten the shells very well to the socket (the clamping system is of the boa type for example).

 

Production

Necessary Material

- 3D printer to print the collar
- A boa type clamping system
- Clamping fanges
- A 3D scan of the socket prosthesis

 

Step 1 : Scan 3D

It will be necessary to make a 3D scan of the socket. If the fablab does not get one, you can make it with an iPad and a 3D scan device to put over the camera . You will find one under the name « structure sensor ».

Placez l'emboîture sur un tabouret et scannez tout autour.

 

The photogrammetry software create meshes : a 3D object. This devices allows to easily capture an object and create its 3D object The result is not really clean but enough to be used. The delivered file is under STl format.

Open then the mesh, for example in Blender to create "slices" used for 3D printing.

 

Step 2 : Create the object to be printed

When opening the stl file with Blender, you will see the socket. Select only faces of one ring around the socket in orthogonal view.

 

In orthogonal view, cut the rings in two parts :

  •  Use the knife tool and cut the whole with constraing angle (K+C+Z).
  • Select the faces of ine half and separate it with P key.
  • realise some changes on mesh if needed.
  • export in STL format. Check that holes are closed.
 

Step 3 : print the STL object

Find a 3D printer (in a Fablab for example) and print the object.

 

Step 4 : Integrate the boa system

The clamping system used was the boa system, which contains a wire reel that points with the hand and wires that hold the hull. This technology has been used early in the world of snowboarding and was expanded to other sports sliding, bike sports and a version is also planned to the medical world.

 

Step 5 : Setting up of parts

Group the socket, the boa clamping system, the printed part and the hulls.

Place the printed part in front of the socket. If necessary, add a piece of rubber or foam to prevent it from slipping. Place the shells in front of all this and tighten it with the boa system.

We have noticed that it is particularly difficult to place everything correctly. We think it would be preferable for the shells to incorporate the boa system and / or wires for tightening as well as grommets to hold the wires in their alignment. Our various tests have not been conclusive despite the screws inserted in the shells to hang the clamping wires.

 

Conclusion

This system is not satisfying as is.

It is necessary that the printing of the shells integrates eyelets to hold the wires of the clamping system of the boa type. It is also necessary to provide a female slot to accommodate the wires of the boa system and integrates part or all of the clamping disk of the boa system.

The production of the collar part is also complex. It needs a 3D scan of the socket, which is not always obvious and also needs to model on this collar a male location that goes well with the fixation of the boa clamp disk placed on the shells ...

In conclusion, this system is not adapted for a plug and play use mentionned in the specification of the project.