If your looking for a hard challenge, then take a look a how to build Body powered or Electronic powered finger prosthetics. I would think with the ability to do 3D printing, it should not be possible.
As a disabled veteran and four finger amputee I have more than a couple challenges in life, and one of the biggest has been what I call work shop prosthetics. The VA Hospital provided me with prosthetic fingers (a couple grand per finger) but they are for looks only, and because they are silicon they have no support. what is needed is something a bit more complex, but more heavy duty than the Xfingers on the market, but zero need to look like real fingers. it's about function and not looks, that provides a bit more dexterity and grip then what we currently have. something to strap to the wrist so it stays on, and allow the use of holding a tool. not being able to work with tools much at all has been one of the hardest things to get used to for the last 7 years. originally I was a gunsmith, and intended to teach myself engraving, but holding a small tool in my left hand and a hammer in the right, seems to get in the way. in fact anything as simple as trying to carry a clothes basket, or bags after shopping with the left hand can be troublesome, especially because i have to hold a cane in the right. for the longest time i tried to build something that I could just slip a glove over that would add length, and the ability to hold something as simple as a can (holding a small tool like a punch would be the ultimate goal in time) but just being able to slip something on and be able to lift or grab tools or everyday items like a fry pan to cook would be the goal. I'm not talking about bionics or top of the line prosthetic design. just something for the purpose of working around the house, that's 100% usability and zero % looks is what is needed. something thats more TOOL than the current line of prosthetics on the market. that have arms, hands, legs feet, but when it comes to fingers (especially multi fingers) the only thing available is a fake finger for looks and not for use. and that is what needs to change. it just needs someone to look outside the box for once.
how is that for an extreme challenge
