Creating bioproof, flexible wiring for the body



  • talking bout coating and stuff. there seems to be a supplier of medical-grade silicones suited for long-term implantation. smallest quantity is 1kg which sells for bout 350 dollar. added the link to the wikipage
  • While a bioproof hose would be convenient if it worked, it just seems a little too risky.  Would make it convenient to route new wires/ switch out things, though.

    Nice find!  Is there a reliable way of applying bioproofing at home?  I imagine pulling wire through a bucket of it would not be sufficient.
  • that silicone is less for bioproofing wires (you'd buy bioproof wires in first place). it was more intended for constructing the plugs and coating of the actual implant.
    but from what i know, that's 2 component silicone. you can build a mold, put in your implant, mix the silicone, pour it in, and bake it according to the specsheet. that's all i guess. so it could be done at home.
  • This is a very interesting discussion.
    I guess a slight introduction is in place as it's my first post.
    I'm a medical student, soon to be a medical doctor, so I'll try to chip in with my knowledge from the medical field.

    The idea of running wires under skin or in general inside body isn't new as there are already various implants either using wires (pacemakers for example) or tubes (brain implants used to release too high brain fluid pressure) across the body.

    Usually no special mechanism is needed, the wires and tubes if they're not supposed to grow in and allow mobility across joints (the brain implant tube has to go from through skull and then down the neck, on chest and into abdominal cavity most commonly - so neck flexibility, abdomen flexibility, chest movements) are made simply by using tube/wire with bioproof coating of PTFE or other material that doesn't form connection with the tissues (sometimes in a few places with inserts of coating that does grow in - to fix it in a few places while allowing mobility in other ones) and leaving additional length by placing it under skin in a 'snakelike' wavy shape, so that it can allow full mobility.

    It's worth to note that our own blood vessels don't like stretching really (even if they can stretch a little) and they achieve their mobility in body by the same method - forming a wavy line which stretches to a straight line when the joint stretches.

    The materials like PTFE which don't allow cells to bind with them, will cause the channel made during implantation to be left in there - if the person with implant isn't immobilized during 2-4 weeks after surgery a connective tissue channel should start forming around that implanted wire, creating sort of a tube inside which the wire will be able to move.
    The person can't be immobilized - because by moving around she'll stretch the wire not allowing the tissues to grow in a way that'd hamper wire's mobility.
    It might be a good idea to perform once or twice a day during first month after implantation some sort of set of exercises to fully stretch the joint(s) through which the wire goes.

    Also, in medicine usually such wires/tubes are implanted subdermally - it's quite easy to do with proper tools, you cut skin (small 1-2cm cuts) at the beginning and at the ending points, and if the wire has to go further also a few midsteps with similar cuts, and then with a metal probe one does detach the skin from connective tissue underneath. Skin except for a few places on body usually comes off quite easily in fact.
    By this method of pushing through with a dull probe (not sharp, not to pierce the skin or tissues under it) a channel is formed through which the wire/tube is then pushed or dragged by that probe or thicker leading wire.

    So neither any special coatings or mechanisms are needed, neither is needed cutting deeply to place the wires along the bones - which would indeed require quite a big surgery with proper operating room and aftercare, with possibility of high bloodloss...
  • now that's fairly detailed information :) fantastic to see someone from a medical field joining in.

    from a DIY approach i read this as:
    1. get ptfe coated wires. (or a ptfe-tubing in case of multiple wires to put in at the same time)
    2. lift up a bit of skin and do 2 small cuts.
    3. use a non-sharp stainless steel/ptfe rod/probe to form a channel under the skin (and preferably pull the wire in right behind it. man that'd look crazy)
    4. connect the wires to the implant and be done with it.
    5. after the surgery, go practice yoga one or twice a day.

    my questions would be: do you get that wiggly line? just adding some extra wire into the straight tunnel you push in below the skin and let the body do the rest?
    2.are there any known connection-systems that allow you to connect wires and implants during the surgery?
    3. what diameters are acceptable for the probe? the wires don't need much but having a few mm extra for the connector would sure help. would 5 to 8mm still be ok?
  • Indeed ;)
    It's normally done under general or at least regional anesthesia - I'm not sure how doable it is in home conditions, but I guess it's still better than cutting the skin all the way to insert the wires.
    One can also try cutting in places which aren't well visible or where skin already bends and forms wrinkles by itself, so that scars aren't that visible...

    1. Pretty much yes, simply adding needed extra length - make sure you measure the length with the joint fully stretched to get longest needed length... Then when pulling/pushing wire into the channel under skin make sure it doesn't coil up in one place - it usually doesn't and if it would it probably would get stretched once you stretch the joint after implantation, but it's better to check it so that it doesn't entangle on itself or you'd need to open sutures/cut again to make it straight again.

    2. Well, there are, but I'm pretty sure they're all branded and patent protected as companies making such implants need to spend a lot to test them to be bioproof and then get major profits from selling those. I don't know any specifics unfortunately. For home-made purposes I guess it'd be needed to make it as watertight as possible, maybe gluing it somehow together after connecting the wires with the implant...

    Dunno, maybe people who know electrics/electronics better than me know some connectors that are used in damp or otherwise electronics-hostile environment?

    3. Diameters of the probe are the diameters you need ;P Just don't get too pointy one... For inserting a thicker cable you'd certainly need bigger probe to make wider channel to fit the wire into and to give it some wriggle space, while for thin single wires you could use a thin one. It's determined pretty much only by how wide the channel is supposed to be.
    The larger diameter probes usually are flat in cross-section to allow lifting the skin without pulling too hard on surrounding tissues.
  • so.. except for the connector part, this sounds rather straight forward.

    the body is a lot less hostile towards the electronics than the other way round. but that should be no problem as i planned to cast the electronics into dow-corning implant-grade silicone. and the wires would probably go into ptfe shrinking tube from BOLA.

    so all that's left to do is to create a good, easy to manufacture, robust and during-surgery-pluggable connector system. sounds like a good weekend project to me.

    oh and thanks again for sharing your medical expertise. much appreciated.
  • edited September 2012
    Well, the implants are hostile towards body for sure with all those compounds that could leak into body and potentially poison you (sure as hell if I'd be implanting anything myself I'd try to keep toxic compounds away from the implant - no leaded soldering, and even lead-free solders I'd check what exactly is added into them, as not all elements in those are neutral to health either... No copper wires, only silver/gold plated silver... and such <_< )...

    But also the body can be really hostile towards the implants - that's one of biggest problems in medical implantology - creating alloys and compounds which at the same time are safe for the body and won't get dissolved by the body. Our bodies react to foreign objects among other things by trying to oxidize everything. With time it can chew through really though alloys and coatings, so if one plans having an implant for years - it'd be good to choose materials for implants well both for own safety and for safety of the implant ;P
    And it's my pleasure to chip in with my knowledge, I'm fascinated by whole field of implantology and cybernetics ;)
  • rdbrdb
    edited September 2012
    Sure, but PTFE and medical grade silicone have been used for many years in implants without risk of degradation, so as long as the coating is done properly, it doesn't matter if what's in it is pure poison.  Whether it's the lead in solder or just some PVC wire isolation, as soon as the coating breaches, then you're at risk of death, so let's make sure it doesn't get to that point.
  • I personally would try to get sure that I have as good bioproofing as possible to prevent contact of implant insides with the tissues, as well as try to make as sure as possible with stuff I can access that the insides of the implant are quite bioproof and nontoxic either. You never know when you might hit something, or get hit with something and the casing will get cracked/torn.
    Lets be honest - it's experimental, meaning those implants weren't tested to see how they'll withstand potential abuse. Nor their casings are made in medical industry high quality control environment which makes them be really, really as safe as possible.

    But that might be the matter of preference simply - I'd like to make my future implants as 'clean' from toxic and in general unfriendly stuff, as possible - just in case. Especially that I don't plan to cut myself to put inside something that I'll have to take out a few years later. I'm young and plan to live long *hums 'Who wants to live forever' from Highlander* if science will allow.

    Plus actually I'm more concerned of results of lead poisoning (brain damage) than dying.

    I don't see why even in home conditions we shouldn't try to make it as safe as possible ;P
    Even if we're just theoretically talking about it not encouraging anyone to get such implants ;P ;P
  • "I don't see why even in home conditions we shouldn't try to make it as safe as possible"

    that's exactly what we are trying to do. since there is absolutely no chance to build the implant bioproof from ground up, we have to rely on the coating. ←from my shopping list.
    the implant will be molded into several mm of that silicone.
    the only other thing that's exposed to the body are the PTFE parts, and the electrode wires which will be lab-grade platin-iridium.

    so by a risk factor.. i'm fine with keeping the risk of implanting something into my body lower than the risk of getting hit by a car while crossing a street. and from what i see, we are on a good track to reach that risk-level.
  • Fair enough ;)
    Maybe I'm simply paranoid - still I'll watch closely what I'm soldering with when doing something I'll insert into myself ;)
  • I've been experimenting for the last couple months using titanium and implant grade stainless steel gauges sufficiently narrow to allow great flexibility, and they've seemed promising...  The main problem being that while titanium is the superior metal, it also is a bitch to solder to (any solder, as well as components, should obviously be encased in silicone).  I do know that in medical applications tungsten wires going from the chest to the head are used, despite all of the muscles and joints involved around the neck and shoulders.  Honestly, I don't think a lack of elasticity is a huge issue...  You're limited in where you can run wires, everything past the elbow is tricky, and you don't want to go along the hamstring or the knee, but other than that, there don't seem to be major issue.

    Connections are a hard part, I've looked at medical connectors and automotive connectors (which are agressively anti-corrosion and waterproof, which actually compares well with biocomptibility needs), for inspiration, but the best I've been able to come up with is actually tying knots.  Ideally the rejection of a single component would not mean rejection of the entire array of implants, so connectors would break away easily when needed, but remain stable when not...  This is hard to achieve.

    Regardless, I'm glad to see more people talking about more modular, wire-linked implants here.  Last time I was around there wasn't much interest in them.  A crucial component here, in my mind, is the microdermal, which could allow transdermal connections with much lower risks, and allow offloading of power and data processing to devices with fewer size and safety constraints.

    As for conductive tattoos, has anyone ever practically produced one that worked, ever?...  I considered experimenting with this, but put it off due to lack of funds.  It would require making a friend with a tattoo gun, a trip to the pet store for a rat, a variety of potential inks, and some electro-acupuncture needles...  Anyway, I have my doubts as to viability, no matter what you try.  As tattoos heal, tiny globs of pigment are individually encased in dermal fibroblasts.  There is no contact between the individual bits of pigment, and thus any current must be transmitted from ink-droplet to ink-droplet through what is probably one of the more resistive part of the human body (there is loads of collagen in the dermis, which is not particularly helpful).  It is much less likely that certain that this will work acceptably to transmit current, and it seems like sustained use of it to do so could cause damage to living cells that would not be desirable...  Conductive (more importantly, EM-reflective) tattoo inks can be used for a certain type of RFID (which is basically just regular tattoo available for sensors in a non-visible spectrum.), which is still cool.
  • I was actually planning on induction rather than a microdermal, mostly because I want this thing entirely under my skin.  I'm glad that you don't think elasticity will be needed. Have you tried implanting any wire yet?
  • edited September 2012
    Use a very thin silicone tubing similar to those in IVs, fill it with a saline solution which has a very low electrical resistance. Not only would this be flexible, but should the coating fail, it won't have an adverse reaction to the body. There is a slight resistance of 0.2089 ohms/m on the saltwater so keep that in mind.
  • @geckogut, you also get the metal-saline contacts which might cause unwanted chemical reactions.

    last night i was brainstorming a bit more and ended up with a comparebly complex system, which is easy to build and handle.
    it consists of fully ptfe-enclosed electronics, which form an magnetic loop. power is transmitted via inductive charging, which works well because the coupling factor is pretty high. there's also an option to add led and phototransistor based communication into the same connector , which allows highspeed data transmittion in both directions.
    the whole plug would be bout 5mm wide. maybe 20mm long and maybe 3 to 4mm high. it'll be fully enclosed in a ptfe shrinktube with a wall thickness of about 300μm.
    the plugs snap into place using small magnets. so even if you pull on the wire too hard, nothing will break. it also allows to easily plug stuff in and out. so you can have the battery on a separate module, and should it ever need replacement you don't have to rip out the entire implant. but only make a small incision and pull one module out.

    it's not the most efficient method. but it should be good enough in terms of performance. and it is easy to build yourself with all materials are available for purchase online.

    currently i'm still busy finishing another project. once i am done with that i'll try to make some drawings of the new connector, aswell as trying to calculate the efficiency.
  • I really like that approach.  That should work for my build.  You just trumped all my thinking on the subject.
  • @ThomasEgi What about gold connectors that are commonly found in electronics? It's very corrosion resistant and also bioproof. Using small gold plated plugs to cap off the tubing should work in theory, you could also gold plate some small magnets like you said so you've got the best of both worlds.
  • @geckogut gold coatings have proven to be faulty in the past, especially in combination with magnets. regular electronic gold plating is everything but long-term-bioproof and also wears off due to mechanical motion. gold is very expensive too.
  • there wouldn't be very much mechanical motion, would there?
    since the wearing off occures mainly during the plugging process cold coating might still be an option for some connector designs
  • there is a chance that it will move, and if there is the chance then there's a chance of failure.
    gold contacts are not that out of question. but a thin coating itself is not a very safe option. and if you rely on electronic-grade coating you won't get any purity at all.

    no matter how i look at it, gold plated plugs look neither qualify for safety nor function given our requirements. i see no reason why we should pick them over a safer lab-grade alternative.
  • I'm pretty sure there are other metals that can be used like that, though.  I know at least one magnetic implant has had a metal coating.
  • One generation of magnets used gold coating, followed by a silicone coating.  The silicone coating is essential, the gold coating is just for some temporary protection when the silicone coating is breached, until the magnet is removed.
  • Found it: this article mentions a custom magnet with a titanium coating.
  • tell me if its its already been suggested but to create tunnels under the skin for wire to run through why not get some standard silicone subdermal rod implants wherever you want to run the wire, wait for them to heal so that the pockets there then get the ends scalpelled open and put thick teflon tubing in there to run the wires through. it'd be much easier to heal two minor wounds than a long fistula. saves spending years trying to heal something that big and it doesnt really require major surgery. going round joints would still be a problem. you could go out one tube and into another but im sure it wouldnt be nice when you catch the exposed piece of wire on something aha. but yeah that procedure allows people to heal things like this so it might be useful at some point, unless you want it to be completely subdermal
  • edited October 2012
    Alright. This is an interesting thread so far. I haven't been around a while and was very happy to see this since i've been thinking about it.
    I assume the squiggly wire is pretty much agreed upon as being a method of great potential, diy-wise.

    My humble input consists of this; as someone already mentioned tattoos are not a whole "flake" of pigment in the skin. It's pretty much a powder healed into place. If you were gonna make it usable as a conductor you would need to figure out a way to make it pretty much solid and return to the problem of elasticity/stretchiness.

    What I guess you could do would be to tatto in a conductive ink as tightly as possible, and then feed it a constant current. The state of your skin (dryness, heat etc) as well as the difficulty in guessing what resistance you might get would screw up any attempts at a "real" data connection as well as using it as a stabile power conduit. What you could do is send data as simple spikes in the electical current. Highspeed morse-code. Extremely basic.

    This would probably not scale up beyond a certain length of the tattoo without requiring too strong a current, but it might work if you just wanted to connect say a pulse sensor to a tiny led. This would assume that the power source was built-in to either just the sensor or both the sensor and the led (preferably both since that would ensure operation of the led upon receiving data without having to rely on the crappy current).

    Of course, I don't know enough about electronics to prove any of this. It's just some thoughts.

    That being said- if anyone had a solid idea for a conductive ink as well as a way to test it without any major procedures and a good plan to ensure accurate results-  I would be willing to do the tattoo myself.
    I assume a simple stick/poke tattoo should work as long as you do it really dense.
  • Well, there is a company that makes paint I've seen tattooed(bare conductive), though it isn't technically skin-safe.  It is conductive, though, so it would be more than enough to prove the point if used on some dead meat.  It was proposed to use a magnet to stretch droplets into longer strands, though that still doesn't solve the issue of each droplet getting coated.  If you wanted to test it, you could do it all pretty easily.  But at this point it doesn't seem worth it.  Best case, we have a metal strand in the body exposed to the flesh, which will seep current and could be interesting feeling.
  • edited October 2012
    I want to throw an industrial process into this thread that I have found useful in some medical apps.  It is vapor deposition.  You can do this with many metals (inc titanium, platinum, palladium and gold) and with gold I would expect that it would be superior to simply plating with gold in terms of bond strength, micro pores, etc.

    One non-metallic conductive coating that may be useful here is Titanium Nitride (used in medical as well as for machine tools).  Decent electrical conductivity and excellent hardness and inertness.  May pair well with tubular saline conductors.  As a ceramic, it will have some brittleness to it that will need to be considered and it definitely won't solder.  Along with this, there are many non-conductive ceramic coatings that are also very inert.  With some creative masking/processing, you could get solder-able gold on one part of the part and TiN on the the other.

    There are also diamond coatings that can be doped to make them either conductors or semi conductors.  As a semi conductor, it could be made to give off heat if given some voltage.  Again, very biocompatible and durable given the usage.

    None of this is cheap to do (compared to plating), but if you get some people together to do a run, it might not be too bad.

    Alas, this stuff won't work with magnets as the processing temp are quite high.  Maybe there are ways to re-induce magnetism?  Thinking of electrical connections for the most part.
  • having a ceramic or PTFE pin with a compatible coating vapored onto it might be an option. but it would still lack the elastic-counterpart that presses against it to make the actual connection. however i don't see how we could get hands on one for testing tho. got a small VD-apparatus at home? if so, i'd have a list of other items i'd like to try coating.

    diamonds are out of question for many reasons. too expensive, too hard to get and very very hard to process.

    i'd like to welcome more possible solutions that are based on materials easily available at reasonable costs.
  • I THINIK he meant diamond coating as in "built up from carbon" which can be done via vapor related treatments, so you wouldn't have to pay for diamonds per se, but for the building process.
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