Powering Devices within the Body

I'm new, so if this is already here, my bad.

Even simple devices within the body seem hard to power. Is there anything that is simple to implant that is easy to recharge and replace (pace-maker batteries are neither)? I'm thinking: EM induction, piezoelectric materials, blood sugar (or other chemicals).


  • Induction is currently the favoured method. GHWW is working on making it practical. Piezos have a pretty crappy current return, and you have to put them in spots that move around (not good for implants at all) but they don't need charging, which is cool.

    We've been bitching about the blood-sugar thing for ages now but nobody has put much effort into it. (as far as I know). From the papers I've read about it it uses either nanotubes or modified bacteria, both of which are outside our tech level.

    You might be able to make a lower tech copy that's slightly less efficient, but still good enough to use. If you want to try... well, I'll happily buy a few off you, and you get to be a cyborg. :P
  • How much wiring is need for inductive charging?
  • If you want a transdermal jack for charging, I figured out how to do that a while ago, but nobody seemed to care.

    (Not that I can blame them. It could get nasty quite easily. But the volume it occupies is a tiny fraction of what an induction charger would, and if you keep it flat it shouldn't suffer any accident).
  • @SixEcho: I figured that out too, but have no results, cause I haven't implanted it yet. My mind is stuck on the issue of the thing hanging out, how would you fixate it? Would that not be too limitating in terms of sports etc...?

    If you have a good way, I'll give it a try, could also implant a usb storage like that... Thought's?

  • edited August 2012
    You'd have to keep it very flat to the surface, for example like those plugs in the matrix. Almost nothing should be above the skin surface besides the rim of the jack. Maybe use a TRS jack, or something home-made with fine pins if you need more than three connections.
    My design was based on the ITAP implant. (http://bit.ly/P9s1S4) I gave up on hydroxyapatite, though, and used a textured PTFE (medical gore-tex) collar to allow the skin to form a seal. I'd also recommend a flange underneath the skin to keep strain off the bond and stop it moving about, although my test did not have that, to its detriment.
    The seal should be perpendicular to the skin surface, although the actual jack doesn't have to be.

    I'm not a super-active person, so I haven't worried about it too much. If you are, maybe cut a section of compressive material tube, like sweatbands or those arm-sock things, and put it over the jacks so they can't get in the way.
    They would be pretty vulnerable while plugged in, though. Secondary support, like having an adhesive patch on the cable to take strain, would be good.

    USB storage is a great idea. It shouldn't be hard to do either, and has an immediate practical use. It could be later expanded to a personal network, I guess if the conductive tattoos work.

    In regards to the inductive chargers, the grindhouse fellows (hope they don't mind me sharing this) seem to like this product: http://www.diybin.com/products/DIYbin-Wireless-Power-Supply.html
    Seems a bit large, but a lot of it could be casing, and it could be cut down.
    It's worth linking this, too. https://www.sparkfun.com/products/674
    Of course, the blood-sugar thing is still preferable above either method, because it would allow implants to self-charge.
  • edited August 2012
    For a transdermal charger, what are the specifics angles and locations for attachment?

    For a long bone, like the femur or humerus, would you attach the receiving end of the TRS jack perpendicular to the bone with something similar to normal ITAPs? Or would it be better to attach pins to the bone, still sub-dermal and mount the receiving end slightly parallel to the bone, but with enough angle to be exposed on the outside?

    I'm thinking of a way to minimize the amount of muscle interrupted.
  • I wouldn't bother attaching it to the bone at all. That would hurt a lot. We probably won't get to that for a while, until we need load-bearing joins for prostheses and stuff. The important part of that ITAP link was how they constructed the transdermal section.
    The whole assembly would be quite happy sitting on top of the fascia and not interrupting muscles at all. (I'm sure you'd be happier that way too).

    I would suggest putting it somewhere that is not directly over a bone so it would be more resilient, really in any low-impact area. Mine was on the inner side of my lower leg, in the soft part between the bone and calf muscle. (Also, using a jack that doesn't take much pressure to get in and out).
    But yeah, putting the jack on an angle is a good idea, especially if you're thin, because there isn't much depth to work with otherwise.
    I don't have specifics, unfortunately. Maybe 30 degrees relative to the rest of the assembly. Any more seems like it would stick out too much.

    A TRS jack might not be the way to go. I'm beginning to think my suggestion of some very fine pins and sockets would be a better idea- you could have more connections, and it might be flat enough that you could ignore the angle.

    Off the topic of transdermals, do either of you think it would be possible to replicate the glucose cell without using nanotubes? Maybe other species of carbon would work, or other kinds of fibrous material. Really all it does is ion transfer, the important part seems to be the catalyst.
  • I admit, I missed the importance of the transdermal section construction. I was thinking something like the titanium with microscopic pores that
    dentists use for dental implants, though much shorter, and narrower,
    just a mount for an angled jack.
    Your right about the jack, too. It would have to be rather dainty in order to remain painless.

    On the topic of glucose cells, I have not seen one yet. Could you point me in the right direction?
  • edited August 2012

    Haven't read much about dental implants, but they seem to work very well, especially given the load that teeth have to put up with.

    We should 'recruit' some dentists.
  •  If you're looking for bone-conduction of sound, dental implants are pretty much THE way to go, given the fairly straightforward linkage to the ear.
  • edited August 2012
    That glucose fuel-cell seems problematic though, as it would only really function in the clear, sparsely celled, glucose-rich spinal fluid. Anywhere else blood would gunk it up, or there wouldn't be enough glucose.

    The dental implant only appealed to me because of the titanium/bone fusion; could you implant a device into the mandible and still have audible vibrations that aren't interrupted?

    A bit off topic, but does anyone know any place that does parylene coating?
  • a quick search for parylene coating on google brought up like dozens of companies that do that. many that have medical-equipment-grade coating offers, some have request forms for coating prototypes too. so i guess it is a matter of how deep your pockets are.
  • @SixEcho: "The important part of that ITAP link was how they constructed the transdermal section."  Can you elaborate on this please? I took a quick look at the paper, but it seemed that this can not be done at home. Did you try to get your hands on one of those PTFE transdermals? That small bit is enclosed by tissue right? I can't see how this wouldn't get rejected on let's say, my forearm...


  • edited August 2012
    Naw, I didn't. The structure seems to be more important than the materials used. (Don't quote me on that... I did this once, I can't be called an expert).
    Anyway, the transdermal section basically has something for the skin to bond to, and a flange underneath it to stop things moving around. The flange also stops the skin growing any lower than a certain point.

    Mine was a carbon fibre rod coated in PTFE cloth. (the carbon was scrap and I got the PTFE off the internet). I gave up on the HA after I realised how hard it was to make a coating without the proper equipment.
    I mean, HA would be way better if we could manage the coating. 
    There was no flange, it was just a straight peg, but I think the flange would help a lot.

    Although, it was only in for a couple weeks. This really needs some more testing before we start using it.
  • Damn! That ITAP document doesen't focus on the rubber piece... I need the to know what shape makes the skin not reject a bigger then 2mm transdermal implant. If we know details about it we can get a quote on printing prices and this experiment can start... Thoughts?
  • just out of curiosity, what sort of power requirements do most of these things have??
    i havnt been able to find much about what sort of ranges you would be looking at, but i assume its pretty small??

  • I don't reckon PFTE would reject if you keep it really clean. The texture is pretty much integral here though. I think non-rejection was the point of the HA coat. You know, I still have a jar of that stuff, if you want to try anything with it.

    I wish there was a place to test this that doesn't hurt. What do we need to get printed?

    Yeah, pretty tiny power consumption. It's worth pointing out that fuck-all complex mods have been constructed yet so it's kind of hard to tell. Generally though when we are designing them we use the lowest power options available.
  • I was thinking some kind of kinetic power would be the most logical for many applications, like:

    Or like the batteries used in kinetic powered watches. I presume this is just electromagnetic induction brought on by movement like those wavesnakes on a smaller scale? How small could you make them? I like the idea that this would mean your own body was powering the device too.

    I wish there was a place to test this that doesn't hurt. 

    Do you own a cat? :-P (Jokes!)
  • How the hell did we not think of that already? That actually sounds promising. I will put that on the experiment checklist too. You could easily make them small enough to implant. Don't know how the efficiency scales down, seems like heavier/longer ones would work better, but hey.

    As a cat owner... too far. Not even joke material. The neighbour's dog, however, is a different matter.
  • Glad to have contributed something useful :-D

    And lol no I understand, I had written dog originally but as an ex-dog owner I felt guilty and had to delete. That said, having a postdog for a pet would rock ...
  • Hamsters or rats are far cheaper, and less controversial. ;-)
  • i want to throw in some numbers at this point of the discussion:

    a regular wristwatch battery holds about 0.1 to 0.2 Wh worth of energy, and it usualy runs years on that.

    a very low power implant with a microcontroller, some sensors and input/output to some nerves would run between a couple of days and maybe 2 weeks on  the same battery.

    as people bring up implants with stuff like vibration motors up every now and then, such a thing would last only a few hours on the same battery.

    kinetic charging works well, but the output is very minimal and, in best case, could only keep the lowest-power implants running at all. ( such as a pacemaker). everything that's smarter , requires more power.

    as for inductive charging: pretty straight forward. low complexity, cheap, robust, well known and delivers a good amount of energy, enough to recharge a battery in a few hours. all you need to do is roughly align the 2 transmitter coils. the rotation against each other is not that critical. if you can keep it within +-45 degrees you are perfectly good. distance mainly depends on the coils but even with the most simple equipment i was able to get over 4 or 5cm without trouble.
    charging a battery within a few hours, and running 1 to 2 weeks on it is pretty decent.

    transdermal is a lot harder to pull off. and the only advantage is that you could deliver more power over it than with inductive charging.

    we already covered kinetic powering, which might be an option for implants that go into the lower leg, but they have their issues too.

    another low-power option is solar charging, but i haven't looked to much into that. it's more like a trickle charge.

    for now. best way we have at hands is inductive charging,
  • SixEcho: I don't think that PTFE prevent's rejection, the factor is size. The beigger, the faster and worse the rejection. I think that what makes it not reject is the texture and shape(edit:and material of course). I don't see HA coating to be much use with this either, HA bonds well to bone, don't know about skin, maybe I just have to try... With printing I meant to get the transdermal part 3D-printed. And keeping it clean might be too much work, near impossible. Take an earplug(tribal body-mod) for example, you have to take it out and clean it thoroughly every two days, otherwise it stinks like hell and the skin around it rots and dies.. That's a problem...
  • Well then, how big is too big for implants?  I've got a couple ideas that are on the 1.5-2 inch scale.
  • ptfe is bioinert. it will neither bond nor will it be rejected. it simply doesn't interact with the body in any way. size hardly matters unless it is SO big that you disturb the supply of body cells with nutritions/blood etc.
  • The issue isn't the inertness or not of the PTFE, it's the interestingness of whatever colonizes it - a transdermal is a potential Royal Road through the first and best part of our immune system; MRSA and necrotizing fasciitis (flesh-eating bacteria to you and me) both live harmlessly on the skin, but when they get through it... So the skin needs to bond to it pretty well, and/or  it needs to be kept clean.
    The problem is the tendency of the skin to retreat from a transdermal, which is what the ITAP geometry is supposed to overcome, no? I've come across a paper trying to solve that problem with a transdermal geometry based on deer antlers, I'll see if I can dig it up.
  • hm. may i ask why transdermals are getting back into discussion over and over again when they are clearly the worst possible choice?
  • Yeah, I'm with TE here, transdermals are not particularly viable with our current technology level. They might be in the future, but not now, and not for power when inductive charging would work so well!
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