Hacking Prosthetics: Bionic Hand Modifications

This project is about exploring modifications to prosthetics, which may inspire future designs...

I worked with Nigel Ackland, a 'Prosthetic Pioneer', after we met at Future Fest 2016 (and check out his amazing talk at Wired, at the last step). We had been discussing how Nigel's bionic arm was a marvel of engineering - but like many things in life, from car tyres to batteries - things wear out and need replacing.

Nigel's fingertips had 'worn out' after some months or normal use, and he was left with the frustrating choice of either having a defective grip (the rubber tips were flapping about - and gave a less reassuring grip), or sending it back for repair - but then being without his arm for up to a few weeks!

It was all the more frustrating, as one might suppose the fingertips (like car tyres) should be designed to be changed without sending back the whole thing! At the time, I happened to work at Sugru as Head of R&D - I saw a great application for this mouldable silicone glue, which sets to a hard rubber overnight. I suggested he try to re-make his fingertips himself. Shown is his first attempt, with some 'texture' I suggested he add for grip.

This later inspired me to consider what other 'functional additives' (Glow in the Dark, or Colour Changing With Heat (ThermoChromic), as well as different Hardness/Softness in tips.) could be incorporated into the fingers and fingertips. Naturally, I didn't want to do anything irreversible to his original fingers, so I found a way to cast them, and have written this up in a separate Instructable which details how to cast copies of small parts. (LINK). Interestingly, these too can be made to glow, etc.!

This particular Instructable is about how to 'hack' or shall we say, 'customise' prosthetic fingers/tips to have other functionality, but is also useful for other applications which call for rubbery grips!

Disclaimer: It is likely prosthetics companies don't encourage this. This Instructable was created in my own time, and is not endorsed by Sugru. It is shared in good faith as an inspirational project, but no liability or responsibility can be accepted for this process, or what you ultimately use it for, be it in prosthetics or otherwise.

You will need, Sugru in colours of your choice (the colours can be mixed like paint), scalpel, wire mesh (and other textured items to make grippy surfaces).

1. Open Sugru, knead like dough between finger and thumb, and separate into 5 balls. I have in fact combined 2x Red 5g packs here to make 5 balls for one hand.

2. After removing the damaged grips on the fingertips, take Sugru and at first smudge/work/press it into every available space in the mould.

3. Once a small amount has been worked in, like a 'primer', then add a cosmetic layer - and then smooth out to the right profile.

4. If you want it smooth in places, wet your finger/tool slightly and 'burnish' to a smooth finish. Use some lightly soapy water (or spit!) for a smoother finish.

5. Apply to other digits.

6. It helps to have pre-made some drying rig to keep tips from sticking to things, while it drys for 24 hours for every 3mm thickness (ideally in a warm place like an airing cupboard).

NOTE: I'm proud to say that although Sugru has since become Family/Kid Safe (see www.sugru.com), it is not food safe, so don't use this hand for cooking just yet, or if you do, perhaps put a glove on!

You may well be wondering why Nigel needed Glow in the Dark fingertips - it's an interesting story - so watch the video if you are curious. For making Sugru Glow, read on...

1. I suggest using scales that measure to 0.1g (LINK), but you are weighing out about 2.5g of Glow in the Dark powder, available from hobby shops and Amazon (LINK).

2. You may not need to mix in all 2.5g of powder to 4g of Sugru (keep 1/5 back), but this will do fine. One simply kneeds in the powder slowly, ensuring the Sugru is still sticky in texture. I suggest using some paper to do this to keep it going everywhere!

3. Using the 1/5 (1g) of Sugru you didn't mix with powder, use this to smear into the finger tips (having cleaned out all the old rubber, or cast your own blue ones like this shown).

4. Now take your glowing Sugru mix, and stick this over the tips (this will bond to the Sugru better than if you do this with the powder, as of course the powder reduces the Sugru's sticking properties, but this makes a comparable bond).

5. I find it can be done with 1x 5g Pack of Sugru, but it's better to do it with 2x 5g packs if you can spare it. Or make two batches in the same ratio.

6. Add texture while still uncured/set. Leave to dry like last time for 24hrs.

And of course if you liked this - please vote for it in the Glow Contest - thanks =)

So this is very much getting into some hacking territory, and explains why I cast copies of Nigel's fingers, as I cut out large sections to allow me to create a different experience.

Sugru can also be made softer, as shown here in this cool modification for Olympic fencing supplier, Leon Paul. (LINK). Essentially, this is adding light 'fillers' to the Sugru to make it more squishy.*

1. I mentioned in the previous Instructables, that hollow forms can be cast as solids. So, I did this with these fingertips. I then cut out a section of the resin copy of the fingers to make room for larger chunks of Sugru & Softener.

2. I drilled out some holes, to allow the Sugru to 'key' into the resin copy better.

3. I then smeared in some normal Sugru into the holes, as an anchoring compound for the following mixed blend of Sugru & Softener (applied to this within 15-30 mins).

4. I then took 1:1 mixture of Sugru (black) : Softener (white), and kneded them together. This takes the Shore-A Hardness down from about 70 to 45. I then applied this mix over the blue (normal Sugru) and shaped to the profile I wanted.

5. Add texture as before.

A little info on Hardness of Rubbers here. (LINK).

*You can experiment with a variety of things (perhaps before applying to the final article!!) one can even mix it with Blutack, cork, rubber shavings, graphite, chalk...!

I incorporated ThermoChromic pigments/powders with Sugru (in ratios of 0.1-0.25g pigment to 4g Sugru). It's readily available in places like Amazon and craft shops (LINK). Similar process to Softener - use the normal Sugru as an anchor for the following blend.

For reference, I added Red pigment to Yellow Sugru, but any combination works if the Sugru is light and the Pigment is darker - essentially pigments go transparent with heat. This one 'activated' at 38C (body temp). But they come in different temperature ranges.

However, I also added <0.1% by weight to casting resin process in the previous Instructable. Again, this was a yellow pigmented resin, with red thermochromic powder.

I'm sure you get the idea, but post if unsure =)

Currently, Nigel is sporting the Glow In The Dark fingertips, with textured grip!

I'm very pleased with how this compliments his new colour finish on his latest arm.

Do post if this inspires any other modifications with colour-changing effects, grips, or other interesting ideas about how me might modify our selves and our lives for the better.

More at judepullen.com

Thanks =D

I wanted to share the amazing talk Nigel gave at Wired UK. I hope his talk (and perhaps this Instructables) helps inspire you to reconsider the marvel of human/robotic synergies, be it for a prosthetic or reconsidering how we can augment our lives with technology for the better.