Making a 'glove' type hand support

[WindyMiller 2]

Hi all

 

I am trying to help a lady with a severe skin disease (epidermolisi bollosa).  What is required is a support that can enclose her hand and fingers to prevent the fingers touching each other.  If the fingers touch, the skin fuses together joining the fingers.  This is a truly awful disease.  

 

I have been provided with an STL file of her hand that was produced by a medical CT scan.  Ideally I need to generate a two piece 'glove' that could encase the hand and fingers from the front (palm) side and the back (dorsal) side.  I am imagining something about 1mm thick maximum.

 

I have tried to make the pieces by printing out flat templates and thermoforming them to the hand model that I have printed, but this has not been successful due to the complex geometry.  I can imagine that it is possible to create the necessary shapes and then print them, but I don't see how with the limited resources that I have available (e.g. tinkercad).  Have I missed an easy solution?

 

A photo of the hand stl file is below (hopefully 🙂 )

[nallath 1,124]

Have you considered something like vacuum forming? You can get a lot more complicated shapes that way.

[geert_2 558]

What about "painting" a glove onto her hands?

 

The first idea is of course latex, but that might *not* be a good choice because it could cause allergies, due to the enzymes it contains. And latex is said to shrink upon drying, so it might cause discomfort. I would not recommend this.

 

Maybe painting liquid and reasonable fast curing silicone onto her hands might work? Silicone is relatively inert chemically, and it is also used in dentistry, and in arts: most soft masks and fake wounds are made from silicone. Be sure to use platinum-cured silicone (=addition cured), not tin-cured because that is not stable and only suitable for single use. Be sure to check they are approved for use on the skin. And even then of course do a test on a very small spot to make sure it doesn't hurt.

 

You can find such silicones in special effects shops for film and artist accessories.

 

But silicones can be hard to remove from any model, due to their accuracy in duplicating shapes: they go into the finest pores, forming an airtight seal. So you might want to lubricate her hands with vaseline or another separator first. Try beforehand if the separator is compatible with the silicone: some products do inhibit the curing.

 

If the scan is accurate enough, you could try painting the silicone (or whatever else product you find) on the scan also.

 

If it has to be a two-piece glove, maybe you could mould-in some sort of clips or locks, to keep both parts together? Apply the first layers, let them half-cure (not liquid anymore, but still tacky), apply the clips or locks, and then apply more silicone until they are fully embedded.

 

Silicone comes in various hardnesses: from very soft like skin, medium like rubber bands, and harder like car tires. Some very elastic, some not. You can often combine them: soft where necessary, and harder where more support is required.

 

On Youtube, search for: body casting and mould making, or: creating silicone masks, or similar terms. There are lots of excellent tutorials. These are in the field of arts and dentistry, but the techniques may be usefull.

 

Of course, only use skin-approved non-stick silicone for mould-making and mask-making. Never use sanitary silicone, which is sticky, and is often quite agressive as it might contain vinegar acid: this could cause severy chemical burns.

 

[gr5 2,224]

Why can't you just buy ordinary gloves at any clothing store?  They come in many sizes and many materials such as cotton, wool, leather, etc.

[WindyMiller 2]

Thank you for your replies.

 

The moulding ideas are interesting.  I think that nothing can be moulded directly onto the skin because of the damage that the process would cause.  I like the idea of moulding 'hard' silicone onto the printed hand.  That could provide parts that would to some extent be self-supporting.  It might even be possible then to get those parts scanned and print them in PLA.

 

Actual gloves are not possible because sliding them over the fingers would remove the epidermis (the outer layer of the skin).  It has to a a two-part solution that can be brought together from the front / back of the hand and then joined.

[geert_2 558]

56 minutes ago, WindyMiller said:

...

The moulding ideas are interesting.  I think that nothing can be moulded directly onto the skin because of the damage that the process would cause.  I like the idea of moulding 'hard' silicone onto the printed hand.  That could provide parts that would to some extent be self-supporting.  It might even be possible then to get those parts scanned and print them in PLA.

...

 

Yes, you should start moulding on a printed model or on a testpiece anyway, until you have the procedure in your fingers. Don't experiment on sensitive persons. The application of liquid silicone itself on the hand would probably cause no problems, it is just a thick liquid. But the removal of the cured silicone might: you would have to pull and slide that cured silicone off, or cut it off by going under it with scissors. Both will require some force and shear action: in a normal person this is no problem, but on a very sensitive or weak skin it could do mechanical damage.

 

I would suggest you make a silicone impression of one of your fingers: fill a tiny cup with fast curing liquid silicone, put your finger in it, let it cure, and then try to slide it off. This will give you a good subjective feel of it.

 

If you do the moulding on a 3D-printed plastic model, you can cut the silicone in two pieces with a sharp knife (scalpel), or with fine scissors.

 

But I still don't get the purpose of printing a PLA glove? PLA is very hard, and due to the layer lines, and it being biodegradable (=eaten up and broken down by bacteria), bacteria can get a good grab onto it. This might cause health risks. Also, you can't desinfect PLA-prints very well: the desinfectant may not get into the tiny openings. And PLA softens from 55...60°C on, and melts from about 80°C. (I heard from doctors that sometimes PLA supports are used internally in the body during surgery, when putting bones back together, because they gradually dissolve and get replaced by the own body cells.)

 

You might consider moulding the whole glove from silicone: start with soft and comfortable inner layers, where they will touch the skin. Then gradually add layers of stiffer silicone on the outside. If more stability is needed, you could add stiffeners/thickeners into the outer layers of the silicone, which would make it stiff like a car tire. Or add a hard outer shell on top of the soft silicone. Then you have both the comfort of the soft inner layers, and the stability of the hard outer layers.

 

The biggest advantages of silicone are: it can be from skin-soft rubber up to stiff rubber (depending on version), it is chemically almost inert (can be chemically desinfected), and it is temperature resistant to 150...200°C (can be autoclaved). Solvents like alcohol do get into the silicone, since it is a little bit porous to oils and solvents (not to water: it repels water), but they do not destroy it.

 

Maybe you might want to contact a special effects shop, or people in the special effects branche (film studio, art school), and ask how they would do it. They use these things daily and have much more experience than I have. And they will know all the risks and caveats. I only use silicones occasionally, and then only a few dental versions.

 

[WindyMiller 2]

On 9/16/2019 at 5:44 PM, geert_2 said:

But I still don't get the purpose of printing a PLA glove? PLA is very hard, and due to the layer lines, and it being biodegradable (=eaten up and broken down by bacteria), bacteria can get a good grab onto it. This might cause health risks. Also, you can't desinfect PLA-prints very well: the desinfectant may not get into the tiny openings. And PLA softens from 55...60°C on, and melts from about 80°C. (I heard from doctors that sometimes PLA supports are used internally in the body during surgery, when putting bones back together, because they gradually dissolve and get replaced by the own body cells.)

 

Hi, and thank you for your further help.

 

The original concept (from the lady's radiologist, who is in Italy, which introduces a further 'remoteness' problem) was that 3D printing would be a readily available way to produce a relatively complex geometry 'glove' (actually 'shell' might be a better word) which would provide separation, support and protection for the hand/fingers without being too bulky.  I can still see the logic in that.  A multi-layered silicone item would have the hygienic and fabrication advantages that you describe, but I imagine that it would be significantly more cumbersome than the 1mm thick hard plastic shell that I was imagining.  To provide context, the lady's fingers are only a few centimetres long, similar to a young child, although she is an adult.

 

(Incidentally, I am a huge fan of your salt water adhesion procedure.  It has never let me down.)

 

[geert_2 558]

47 minutes ago, WindyMiller said:

The original concept (from the lady's radiologist, who is in Italy, which introduces a further 'remoteness' problem) was that 3D printing would be a readily available way to produce a relatively complex geometry 'glove' (actually 'shell' might be a better word) which would provide separation, support and protection for the hand/fingers without being too bulky.  I can still see the logic in that.  A multi-layered silicone item would have the hygienic and fabrication advantages that you describe, but I imagine that it would be significantly more cumbersome than the 1mm thick hard plastic shell that I was imagining.  To provide context, the lady's fingers are only a few centimetres long, similar to a young child, although she is an adult.

 

Yes, I can also see the reasoning from the radiologist. However, I am not sure that he is fully aware of the porosities, layer lines, PLA-degradation, and occasional blobs and strings in FDM 3D-prints, which could cause discomfort and health risks, and which require post-processing. Most collegues who ask me to 3D-print something, aren't aware of these, so I have several test pieces sitting around to show the typical limitations.

 

Maybe the best is to just try all options, and see what works best?

 

- a hard 3D-printed shell

- a soft silicone liner (for comfort), inside of a hard shell (for stability)

- a multipl-layer silicone shell, soft inside, harder outside

 

What I just come to think about: as I said, most 3D-printing materials, especially PLA, are not heat resistant. However, two-component epoxies like those used in dentistry for dental retainers, are more heat resistant. And they are strong. They are skin-safe (after curing) and they can be polished to a high gloss, eliminating all porosities and irregularities. Maybe that might be another option? You could mould such a hard shell on the 3D-printed replica, with or without soft silicone inner liner? Be sure to use a good separator, so the methylmetacrylate plastic does not stick to the model.

 

Have a look at these Youtube-videos to get an idea of the concept. This guy used the "salt and pepper method" to make the shells, but you could also mix both products beforehand to a honey-like liquid, and pour that over a model. But it is a bit messy.

 

https://www.youtube.com/watch?v=Mn9QbX-jID4

https://www.youtube.com/watch?v=APRw1wgvwy8

https://www.youtube.com/watch?v=QvhWSiXUtzU

 

Quote

(Incidentally, I am a huge fan of your salt water adhesion procedure.  It has never let me down.)

 

 

Glad to hear that.

 

[NBull 14]

Sorry if i misread it wrong but is it something like a cast, then you might get some idea her.

https://www.sculpteo.com/blog/2019/04/29/can-additive-manufacturing-heal-bones-with-a-3d-printed-cast/

 

 

[nallath 1,124]

You might also want to have a look at the e-nable project. They make prosthetic hands for kids. The use case is not as extreme as this, but it has some of the same problems (Fit, comfort, sturdyness) that you face.

[WindyMiller 2]

Well the problem has been solved, but not by me.  A company that specialises in printing plastic orthoses has produced exactly what was required free of charge.  Photo attached.  The hand model is in the middle with an orthosis to either side.  The one on the left is a mesh to allow for some air circulation, the one on the right is 'solid'.

 

Thanks to all for your ideas.

[Smithy 1,145]

Thanks for the update and great that it could be solved!