Flexible Biocoating?

Rytcd

Greetings,

So I have this implant which is still in the design phase. I'm pushing towards the goal of usable internal electronics which are as invisible as possible. To that effect, the plans right now give an idea of something which WITHOUT any coating is about a 4*3 cm rectangle in area, and about 2-3mm thick, and on top of that, will also be somewhat flexible, being made up of a circuit board laid on polyamide film and a 1s lipo (ever the one for the ambitious projects, me). I have a long way yet, but I think it could be something quite special. 

Anyway, my next question is probably obvious. I wish to maintain the ultra-low profile of this design, and also have it go from a circuit board to something that could be shoved into a forearm without the body getting angry with me. In addition, I would really like to see it retain some of its ability to flex. It would also obviously need to be durable enough to safely withstand being inside an active person's forearm. Budget is also a constraint, lending further to my problem of conflicting parameters.

As an aside, I'd also be eager to hear any inputs anyone has on any safety issues regarding to putting something with such surface area inside for long periods bordering on (ideally) indefinite; This would also extend to any thoughts if either inside the middle of the forearm, or the outside of the wrist would be a more risky procedure than the other.

Cheers,

Ryan

JohnDoe

You would most likely be needing to make them from titunium, the catch being that I am not sure it is biocompatible, you may want to look into making them from TiN.

Sincerely,
John Doe

AlexSmith

Rytcd please disregard what JohnDoe said. you are looking at silicone or parylene if you want to keep it flexible. or titanium if if you want to make it smaller, silicone needs a thicker coating.

Rytcd

Thanks for the response. It's my understanding that parylene and possibly the titanium would need to be vapor deposited, and silicone would need to be injection molded in order to be effective. Is this correct? I have not been able to even find parylene for purchase.  Any thoughts on just how thick the silicone coating would be on each side? There is a lipo involved, unfortunately (yet inevitably)..

I do have one concept in mind. It involves a custom-welded titanium casing/box with one open end, which would then have the electronics inserted in the open end. The case would then be both filled and partially encased with silicone. My thinking is that the silicone would then not need to be thick, since it would be supported by the casing, and if it were to break, the body would only see titanium underneath. It also would have the added benefit of eliminating some of the fear of the lipo rupturing or igniting internally. 

Low profile and a certainty that that lipo isn't going into my carotid definitely trumps my flexibility wish, If I had to pick. Course, it means I'd have to deal with welding Ti, which by all accounts is no picnic. 

Rytcd

Alright, Gents, I've put in many long nights, and have finally finished my implant, which I will call the Sepsisplinter I was gonna shove it in tonight, but I couldn't find a knife that was rusty enough, so I've put them all in a saltwater bath for a while. Just hafta wait. Backorders are piling up on me.

https://drive.google.com/open?id=1uFblDKeLmoT1ZacHbVqErvjADS0hUKX4ZPdrPVC0Gzw

https://drive.google.com/open?id=1uFblDKeLmoT1ZacHbVqErvjADS0hUKX4ZPdrPVC0Gzw

 Joking aside, made a wooden analogue to give my brain a better idea of whether I would end up with this big ugly lump on my arm or not (a semi-respectful wink to Grindhouse, who have helped inspire this project). Anyway, I am very pleased at the size. I have this perfect place for it where it seems to lay nice and flat. The plan is to go fairly boxy with the titanium for geometric easiness, then to use the silicone to smooth those sharp edges, thereby using it less as a coating, more as a.... gap filler? Anyway, still lots and lots to do, obviously.

AlexSmith

If you want a super thin form fitting metal layer coating, then yeah, vapor deposited TiN (titanium nitride) is an option, but it's pretty advanced, not something you can do cheaply, and it gets hot, so might damage the device. But if you are thinking a metal box like shell to go around the outside of the device, then a machined titanium (grade 5) case is probably easier. using silicone to seal such a box is possible, but not easy to do well, and does come with some risks. you probably want at least a 1mm layer of silicone. More if going its have force applied to it while implanted.

But ultimately, I can't endorse anything with a lipo battery, they simply don't meet my safety standards.

chironex

^seconded on the battery. I hate those things. Lithium to me is as archaic as lead. 

JohnDoe

Just wondering is there a preferred battery for implants.

Rytcd

@John. Just about every pacemaker uses a Lithium Iodide non-rechargeable, but these are not suitable for this task, and also I have not been able to find them available for purchase. If I'm not mistaken, the Grindhouse ones do use Lipos, however the one I have in mind is a particular 1s which is marketed to be somewhat safer.

 I don't believe having such a case machined could be done even slightly affordably, though I definitely stand to be corrected. With the wall thicknesses what they are, Welding a sheet would seem to me the way to go. I'll upload some better drawings later of what I'm describing.

Cheers

chironex

honestly? there's nothing I've seen on the market that's acceptable. Everything is lithium. SO people just spend extra effort adding in safety redundancies just because they're using a subpar battery. Supercaps and the like are our best bet for better batteries. Even if it's not mine, someone will make an acceptable one within a year I hope

JohnDoe

What about those generators that you create a temperature difference between the wires and it generates power? Won't leave toxins in to you blood with the bonus of never dieing.

chironex

I take it back. There are definitely clever ways to power a device. Currently non of them are feasible for the average person. But that could change soon. we'll see. 

JohnDoe

How much do you know about pizoelectotnics?
http://m.phys.org/news/2010-01-energy-harvesting-rubber-sheets-power-pacemakers.html
http://m.phys.org/news/2014-04-flexible-plastics-mechanical-vibrations-electrical.html

ElectricFeel

I don't follow your hatred of LiPos, handled properly they're the highest available energy density on the market. LiPos don't just go off on their own, they do that when they're mishandled.

JohnDoe

For me it is about there being a better way....

Rytcd

Heh, funny you should ask, John. Just yesterday I was designing a Coffee mug That would stir itself without batteries, based on a small Peltier or thermoelectric (same thing) generator. A thermoelectric generator, however, relies on one side of the element being hotter/colder than the other, and generates a voltage based on the difference. Trouble is, your skin is not much colder than the arm beneath it, and for an appreciable amount of energy, a large difference is typically needed. There's a couple other problems, but that's the main one.

 A Piezo element would also not work in this context. It requires a mechanical stimulus, such as a heartbeat, vibration, etc., and generates typically very small currents also. It would also likely need to have a small battery in it anyway for the times between heartbeats, and for general backup.

Supercapacitors are not a drop-in replacement for batteries, either, due to their much smaller ability to store energy. Contrary to optimistic media reports, I don't believe this are likely to change much in the near future.

I would be fairly confident in the ability of a properly protected, both mechanically and electrically, lipo to stay within the package. I've used them for years in model airplanes, which have crashed... well I don't want to say many times, but more than I'd like to admit, and have even had the leads be shorted and LEFT shorted and it did not ignite. 

I may look into LiFe batteries though. They're supposed to have their advantages.

chironex

it's not just them going off. If they leak, you're screwed. Or if one of the plates if damaged, which is easy to do to a foil cell in a flexible implant. I know that handled properly they're "ok", but that's not the point. I want something safe enough I can abuse the shit out of it and it not fail on me. And if it does, have it not spray carcinogens into my blood stream. Sure you can put your battery in a metal case and check your circuits a million times. You should probably do that anyway. But I'd rather something safer to start with. Add in that supercaps charge in a fraction of the amount of time and can withstand way more cycles without degradation.... it's just a matter of time before we make the switch.  Just need to increase the power denisty a bit further than what's around, which is difficult but far from impossible. 

JohnDoe

Could you possibly just make the power source transdermal or use a turbine to turn a generator at the hart beats though it? I think a tesla turbine would be best for for that....

chironex

LOL have fun with that. moving parts AND having blood through it? that's asking for trouble. connecting that would be a pain if not nearly impossible. if energy harvesting is your thing, you were better off with the piezo. thermal was even better. but not blood flow. 

JohnDoe

True but where I am about to be working won't allow me to have transdermals. Then again he did say "visible", humm.

Rytcd

@chironex. Personally I wouldn't be too afraid of asimple leak in the battery, whilst inside a titanium box and potted then encased in silicone. As for the super capacitors, don't get me wrong, I very much look forward to the day when they are a viable solution to the problems we currently turn to batteries for, but that day is not this year :). Again, no arguments here that a lithium battery is not optimal, but we work with what we have, correct? I think the battery will kill the flexing implant idea though.

Cheers.

Rytcd

Lol John, I love the blood generator idea. I mean, it would never work safely, but I love it all the same XD

chironex

@Rytcd heh gimme a few months.

ElectricFeel

It'll be interesting to see if what you can make can compete with commercialized and abundant hardware. We'll be watching.

JohnDoe

I do have to wonder if a magnet and and a wire coil could function like a guitar pickup and make a extremely low current, you would need a bunch of them, that must have put me into flow state because the ideas just keep coming.

chironex

commercialized and abundant hardware is crap. people get excited over a couple hundred farads. I'm aiming for megafarads. And it's not even that hard to do. The pitfall is that everyone uses acetylene black or activated carbon, which has no pseudocapacitance and isn't a great electrode material. 

chironex

also even minor additions of some forms of graphene increase capacitance by orders of magnitude. something no one does cause they think graphene is hard to make. sulfuric acid? lightscribe? pft screw that, use a blender. Takes 4 hours of you doing nothing and then showing up at the end going "oh look, a bucket of graphene". And hydrothermal lets you make way better carbons than acetylene black by a mile. And polymers are getting pretty good too. point is, the market is about to get a kick in the ass. 

Rytcd

Yeah, I've found that "the market" is a pretty poor representation of what's possible. The things I want like robots and freeze dryers are just incredibly expensive to buy. Tens of thousands and hard to find, but can be built for a few hundred. This case is not much different. All the parts are there(almost), just no one has done it yet.

By the way, LiFePO4 batteries are looking Really attractive. They are apparently not prone to the same problems with combustion or expansion. They are also available to buy and hold similar charges to same sized lipos. They also have a very amenable voltage per cell for the microcontroller im using. Now I just need to find one the right physical size, which may be tough.

I'll keep everyone posted.
Cheers

chironex

Nope. I looked into the chemistry of those batteries a while ago and theyre not better. They light up just the same. They may be slightly less likely to go off, but they suffer the same issues as the others. 

TheGreyKnight

While we're on the subject, @chironex , Are there any wet electrolytes in your super-caps? I think murray-smith had some with and without.

chironex

im exploring all my options. I'm looking at gels currently. since they solidify and can't leak after application. I'm looking at even dryer options as well and I'm staying away from submerging the plates. Everything is based on a series of paints, just let each layer dry before applying the next. It can never be totally dry but you can get it fairly dry all things considered. And it's all water based. I'm not touching hydrocarbons.