So there's a reason we aren't doing this... Right?

TLDR: If we can vapor-deposit parlyene, gold, and photoresist we should be able to make extremely thin flexible implantable electronic devices.

So rather than creating PCBs for all our implantable electronics needs, why not start off with the biocompatible coating as the substrate? In the paper I posted below the authors created an electrode array by using a 2-micron sheet of parlyene as the substrate (which I assume was vacuum deposited), onto which the gold circuit was additively photolithographically patterned (photoresist deposition -> gold deposition -> exposure). The main thrust of the paper was the use of organic transistors to record brain activity, so I'm not sure whether it would be difficult to integrate traditional CMOS components (microcontrollers, LEDs, other SMD components) onto a gold circuit on parlyene, seeing as how I've got no clue how to deal with making PEDOT::PSS semiconductor components much less the board itself.  But at least making the circuit board doesn't sound impossible. I'm guessing the hardest part involves the vacuum deposition of each of the materials. @chironex on a scale of 1 to difficult how difficult would it be?


  • edited November 2015
    19. lol

    If you had the equipment to do it it wouldn't be that bad but some of those steps are a bitch to do. Also remember that paraleyne cracks easily so it wont be all that flexible. What'd be far better is to use pdms as the base. It's flexible, biocompatible and better still you can mould it into incredible thin layers. It's the stuff the gecko adhesive is made of because of how well you can shape it at a microscopic scale. If you start with that you're already better off. Easiest way i can think of to do to electronics themselves is a pedot:pss ink and then inkjet print out the patterns onto the pdms. once you've got the electronics down do a second layer of pdms to seal it and keep it safe.

    edit: as to the organic transistors and stuff, not as hard as you think and i'm working on paint on transistors anyway. But that's like a year off.
  • I like the idea of flexible pcb.  Also taking inkjet a step sideways, is it possible to 3d print a blank layer, then print gold traces, then another blank layer, so on and so forth.  you could even print short wave antennas and inductive charging circuits.  As long as the layer is flexible, biosafe, and nonconductive.  I think HDPE may be all of those things, PEEK may exibit flexibility in thin layers, ive only worked with machining stock
  • I saw this on my fb feed.  its an adjustable z-axis pcb printer.  So I thought pour the base, set, touch-off z-axis, print, set resistors and chips and the like, pour layer, set, touch-off, print, repeat...

    I'm not sure atm how one could make the conduit material elastic, and even more, without changing the resistance in the circuit and similar problems.

  • I super like this idea. I feel like putting down (thick) traces in a serpentine pattern may be a workaround for flexibility? (think how pipelines have U shaped zigs every so often to allow for thermal expansion)...
    Possibly even using something like conductive thread could work, if only as a prototype.
    I know I've looked quite a bit into flexible/diffuse conductors for tattoos and it's quite the puzzle...
  • Why not use flexible PVC then do thin biocoating
  • I'd like to step in to fork the ideas into two streams of ideas here:
    1. thin flexible biocompatible circcuits
    2. 3d, rigid circuits.

    Thick and flexible won't mix well. Gives you a lot of trouble, spots with high mechanical stress,  cracked traces etc. You can build full 3D circuits with all parts embedded into a solid structure with metal traces running through it. Very few companies offer to build such things. Needless to say it's expensive as hell. The really hard point is building them in a way they remain reliable.

    As for both, flexible thin, and 3d rigid circuits. Elastic conductive glue could be an interesting choice. I read a paper about those once, no clue if it was any good tho. It does come with interesting aspects. There's no need to reflow solder glue so you can use temperature sensitive (and thus maybe more biocompatible) substrates.

    Btw how's kapton in terms of biocompatibility? Any data on that?
  • Could they possibly be drawn on with a pin filled with conductive ink, they used to sell them at radio shack. Or what about a P2P soldered circuit in cases in silicon.
  • @JohnDoe, I feel like the conductive ink wouldn't be very robust. It's good for prototyping but I doubt it will hold up over the years of flexing it will face.

    What comes to mind for me is Pyralux. It's 9 bucks for a 6in square of it on Adafruit. That's a brand name of course, but apparently you can etch it with ferric chloride just like a normal pcb.
  • edited March 2016
    Do you think that it would be a issue even if the whole thing is encased in silicon? So me it seems like it would have no ware to go. I will look into Pyralux some more maybe see about a cheaper (non branded) substitute.
  • You could totally vacuum deposit aluminum or copper traces onto a sheet of acetate for flexible circuits. Or better still, get a sander and some graphite. Instead of a sanding disk attach a soft cloth. Then buff the graphite onto the acetate for about an hour slowly adding more graphite. you'll end up with a mirror shiny layer of highly conductive graphene. Then you can use a simlpe eraser to remove material to form your circuit. The real problem is the IC's/componants . I know surface mount stuff can be tiny but you'd really need to keep it small. And there's plenty of risk that during bending whatever is holding it on could fail. Honestly I'd be more worried about componentscoming off vs the traces themselves. So you need a good conductive epoxy/glue (working on it). Or you get a series of semiconductor paints and paint the IC's/resistors/capacitos/etc on too. But that's exponentially harder. 
  • What about vacuum deposition of a higher resistance material for the resistors. You would know more about caps than me.
  • What I'm thinking isnt really in regards to the components themselves, but I like where Chironex is going with the expoy/glue idea.

    You can get really really tiny SMD components, like you could inhale them and not even realize it. If you could secure those to a flexible pcb using some sort of flexible and conductive glue, then there would be less mechanical stress on the circuit.

    That way we wouldn't have to redevelop the components themselves.
  • What kind of hardware would you need to solder/glue parts that small?
  • Very expensive hardware. High magnification lenses, like what surgeons wear, at least.
  • I've solder 1206 components on a regular basis, but haven't really needed to go much smaller than that. I've never tried it before, but I could probably handle size 603. Anything smaller than that, and you will probably need to ask your best friend with a pick - n - place machine to do you a solid. 

    Do you really need to go much smaller than 603? Any EEs in the house? Thomas? ElectricFeel?
  • 0603 can still be dealt with using tweezers and a good soldering iron, no problem. 0402 is quite a pain to process manually. Even if you have it pick'n placed you have to be careful with the thermal design and a lot of soldering process parameters. Otherwise you can get tombstones all over. No reason to think about parts smaller than that.
  • I handle 0402s without much trouble; gel flux and hot air are your friends. They make 0201s, which I haven't played with yet. They shouldn't be too much harder than 0402s since the pads are on the long edges for most of them. I have a stereo microscope and a reflow setup, which makes it simple. I wouldn't want to do smaller than 0603 by hand regularly.

    There's not much reason to get insanely tiny unless you have a really complex circuit; the effort isn't worth it when you have a large battery and other irreducible constraints like coating thickness. It depends on how small you're trying to get, but I would say that in nearly all cases going smaller would be better achieved by using a thinner PCB fab, optimizing placement and design before shrinking components.
  • edited March 2016
    In my mind I am picturing some sort of glue that is a paste/putty at room temperature. Then once it takes a trip through the reflow oven with all the necessary components, it will come out no longer be a paste. Instead it would then have melted/formed/solidified(?) as a conductive elastic glue that can reliably hold your components in place while still being able to flex with the presumably flexible circuit board. Whether that be a vacuum deposited board of acetate, or Pyralux, or some other comparable solution. 

    Personally, I am a big fan of the vacuum deposited or graphene boards to mix things up a little bit, but that starts to exit the realm of home production. 

    @Chironex, have you ever experimented with a graphene circuit board? It just sounds cool. Also, I am no chemist, would such a glue/epoxy/gel be within the realm of feasibility, or even reality for that matter? 
  • Have I, yes. Can I make such a glue, yes. Am I already working on it, also yes. Gimme time. Wanna mess around with the decellularized organs for a couple more days then i'll get back to supercaps and conductive stuff.
  • @chironex,  you are really a powerhouse, it seems like there simply aren't enough hours in the day for a man like you! Look forward to seeing the results of the decelluarization
  • Ya pretty much. The decell is going really well, especially considering i've got no pump and the starting organ was meh at best. Hoping it's totally white by tomorrow, but due to soak times it may need an extra day. I'll try the conductive glue this weekend
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