Stretchable Traces For Flexible Circuits

Electronic components are getting smaller and smaller, but the printed circuit boards we usually mount them on haven’t changed much. Stiff glass-epoxy boards can be a limiting factor in designing for environments where flexibility is a requirement, but a new elastic substrate with stretchable conductive traces might be a game changer for wearable and even implantable circuits.

qxMo1DResearchers at the Center for Neuroprosthetics at the École Polytechnique Fédérale de Lausanne are in the business of engineering the interface between electronics and the human nervous system, and so have to overcome the mismatch between the hardware and wetware. To that end, [Prof. Dr. Stéphanie P. Lacour]’s lab has developed a way to apply a liquid metal to polymer substrates, with the resulting traces capable of stretching up to four times in length without cracking or breaking. They describe the metal as a partially liquid and partially solid alloy of gallium, with a gold added to prevent the alloy from beading up on the substrate. The applications are endless – wearable circuits, sensors, implantable electrostimulation, even microactuators.

Looks like progress with flexibles is starting to pick up, what with the conductive silicone and flexible phototransistors we’ve covered recently. We’re excited to see where work like this leads.

40 thoughts on “Stretchable Traces For Flexible Circuits

  1. Im curious how robust this material is. Does it still work at high/low temps? They suggest it as useable to create smart skins, but I would want to be sure it is still flexible at least at the temperatures a person would encounter. Very cool though. Opens lots of interesting doors

      1. PDMS is just silicone. Not only contact lenses, but very many things are made of this stuff. From cookie formers over diving masks to artificial boobs. So biocompatibility is already proven in a long term test. And also flexibility over a wide temperature range.

    1. Doesn’t matter. The resistance of the wires is negligible compared to the resistance of the electrode site. Capacity is also no issue since they are looking at very low frequency signals.

    1. If you aren’t mainlining or smoking nano sized particulates I don’t think bringing up a informal fallacy question is considered real.

      rotometals MSDS_GALLIUM.pdf

      I wouldn’t expect this to replace human organs at any time that said joints AKA the class 1 class 2 class 3 external levers that wear out or lose form to amputees prosthetic usage would greatly benefit for this. Read again please; the gallium and gold is between contact lens “plastic”.

      If you happen to have any questions about the toxicity of gold or titanium please let us know if you have stopped beating your wife?

          1. yeah, sorry last verse needs some work… Maybe retired old diabetes can pay for… or Your abused choir is dead, Or the the science you’ve HaD.

          1. >All compounds are quite toxic as you said Danny. As are most heavy metal salts.

            Well Said Niko, Good thing this article IS NOT ABOUT INTERNAL IMPLANTS…

        1. It’s really sad when children, with no technical background whatsoever, try to use Google to pretend they have the knowledge, background, and intelligence required to converse with an intelligent person. It is instantly obvious that JohnScnow has no idea what he is talking about.

      1. Gold is not used for implantable devices due to the risk of eliciting an inflammatory response in some patients. It’s use in dental situations has a low probability of immune response.
        Platinum-Iridium alloys or Titanium are preferred for implantation applications.

        1. Yo, Bro, No… If you imagine you are referring to this?

          Raw Platiunum IS toxic and consider heavy metal. Iridium much the same DEPENDING ON What tissue you are attempting to integrate with. It is a Simple Squalamous Tissue Layer? Columnar Layer? or Cubic type? AND What of the 11 systems are you attempting to interface, interact or apply to. (Platinum) Aside from Dental applications it has no immune response… Now GOLD, you could have a clean 99.99999% bar replaced with your GD spleen and it won’t kill you, ZERO immune response. Aside from site inflammation and negative feedback as to the organism attempting to reconnect parasympathetic nerve channels. Why no impurities ALL studies you are ATTEMPTING to mention indicate some sort of adulteration process be it lead, copper or nickle or a degraded radioactive isotope.

          You are more likely to die from Hypochondria and fixation of “this foreign thing”, But Please go on… we are interested how far the rabbit hole you want to go with this.

        2. Lemme just kill your defense, before you hatch it AND headshot it, before the the pre-nup that you want to marry… “that makes no sense.” Come mad strong or don’t even speak at all.

          1. Dave, yes. & no! It is dependent on the surface chemistry and location. A Platinum-Iridium alloy is toxic an Iridium-Platinum would not be. Dave? Dave. What are you doing Dave. Are you siding with a majority due to fallicies or looking to find loop holes in defense of others. Most importantly “WHAT IS THE APPLICATION OF: ‘Stretchable Traces for Flexible Circuits'” Internal or External? If you happen to say ‘internal’ most if all heavy metals are toxic with the exception of titanium and pure gold. If you happen to say “externally” then you’ve already proven the validity of claims and usage. So, where do you think this is going?

            Shall we control group and test group different alloys? We are hackers that expound on usability NOT “OMG Research Bio-hackers Toxicity Material gets approved” This isn’t Buzzfeed or some Kossack circle jerk group.

          2. We use an FDA approved 90/10 Platinum-Iridium alloy in the cochlear implants we produce. The mechanical and electrical properties are perfect for the application. And because it’s safety is backed by 30 years of efficacy studies, all we had to do was find a previously approved supplier. We originally designed the device with a Platinum-Tungsten alloy that had prior FDA approval, but found it too brittle and fractured too easily during mechanical testing.

          3. Sara plz.

            Those electrodes aren’t intended for permanent implantation.

            Tin = intramyelin oedema induced by triethyltin, and neuronal necrosis caused by trimethyltin.
            Platinum = vestibular ototoxicity

            And the above tech isn’t intended for implantation either. Sounds like we are starting to get medical manufacturing shills pissed off at material prices.

        3. As I am sure Sarah, Dave, and Niko have noticed, JohnScnow does not appear to have any background in medicine or biochemistry. The proficient use of Google does not counteract a lack of background knowledge or intelligence. And I am sure they would also agree, it is a waste of our time to attempt to converse with such a person.

  2. I’m from the field and develope similar interfaces. I don’t quite know why one needs stretchable traces. I wouldn’t want to use them due to reliability issues. As long as the substrate is soft, the traces don’t have to necessarily stretch. Typically they are so thin, that it’s no problem in terms of stiffness. 30 electrodes per mm² are no problem whatsoever. One of the points might be that they want to use silicone as substrate as it has an FDA approval. But even there, so far people just used meandering traces (google Cortech Neuro). Same effect without the reliablity issues. Gallium isn’t very inert, it quickly oxidizes. And since the plastic or silicone will always be permeated by small amounts of water, they might be running into degrading quite easily. Currently people use Platinum and Gold for the traces, which are obviously much more stable in wet environments.

  3. It would be interesting to know the smallest pitch surface mount package which could be used with this without having problems. Without the ability to connect real ICs to this, it is just another flexible circuit board that has the same problems as every other FCB – It still requires a packaged microcontroller on a rigid PCB somewhere to be useful. Still very cool though.

    1. the flex is just for the cables between the elctrodes and the amplifier / plug. Somewhere they will become rigid. Nobody needs to mount any components on the flex-part, let alone packaged ICs.

  4. This would be an excellent “bearing” or “bushing” fitting material for an amputee with a custom prosthetic. Don’t need re-machining redesigning contact surfaces just replace the connector fitting without having to re-tune re-calibrate or re-program the external device.

    1. @[JohnScnow]


      Wall warts convert from AC to DC first by routing the AC through a transformer and then through a rectifier. If you try to back feed DC or even AC into a wall wart, you wouldn’t get anything, because transformers need AC to function, and the rectifier would ensure that only DC reaches the transformer. If you are only using the transformer from a wall wart, you still need AC, but then you are just using a transformer. I was not able to understand the rest of your comment.

      1. take 2 wires solder them to the AC plug or wrap some wire to them…. ensure you make skin contact…. now strip end connector feeding DC and apply the contacts to a common 9v battery. Enjoy that “I didn’t feel anything”.

      2. It is clear from reading through JohnScnow’s posts he lacks the background or intelligence required to comment in a useful way. As Brett said, This guy isn’t too bright. It is really sad when someone attempts to follow and contradict an intelligent persons statements purely to get the last word. JohnScnow can’t form a cogent argument with his lack of knowledge, and attempts to fill in his lack of knowledge by spewing Googled papers and terms he really has no understanding of.

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